SYNTHESIS AND CHARACTERIZATION OF POTENTIALLY BIOLOGICALLY ACTIVE DERIVATIVES OF

POLYHYDROQUINOLINE AND QUINOLINE RING SYSTEMS

By Aisha Saddiqa

2003-GCUF-765-3

Thesis submitted in partial fulfillment of the requirements for the degree of

DOCTOR OF PHILOSOPHY IN

CHEMISTRY

DEPARTMENT OF CHEMISTRY GC UNIVERSITY, FAISALABAD.

September, 2014

iv

ABSTRACT

Multi-component reactions (MCRs) have emerged as an efficient and powerful tool in

modern synthetic organic chemistry allowing the facile creation of several new bonds in a

one-pot reaction. Clearly, for multi-step synthetic procedures, the number of reactions and

purification steps is among the most important criteria for the efficiency and practicability of

a process

The classical four-component Hantzsch condensation provides access to pharmaceutically

active polyhydroquinolines. We had carried out the reactions of cyclohexanone or

cyclohexane dione or dimedone with malononitrile or ethylacetoacetate and different

aliphatic and substituted aromatic aldehydes in the presence of ammonium acetate in ethanol.

These multicomponent reactions were carried out both by solvent free grinding and by

classical heating for comparison purposes. The catalytic activity of p-TSA (10 mol %) and

guainidine HCl (5 mol%) in these reactions was tested over a set of aldehydes. Through

catalytic screening, guainidine HCl (5mol%) at ambient temperature is proven to act as a very

active catalyst for multicomponent reactions (MCRs) of 2-amino-4-phenyl-3-cyano-5-oxo-

1,4,5,6,7,8-hexahydroquinoline derivatives and 2-methyl-4-phenyl-5-oxo-1,4,5,6, 7, 8-

hexahydroquinoline-3-carboxylate in excellent yield up to 96% from aldehydes, 1,3-

cyclohexadione, malanonitrile/ ethylacetoacetate and ammonium acetate.

we develop an expedient multi-component synthesis of 2-amino-5-oxo-4-substituted phenyl-

1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile 4-4f and 2-amino-5-oxo-4-substituted phenyl-

1,4,5,6,7,8-hexahydroquinoline-3-carboxylate 5-5l by using P-TSA under ultraviolet

irradiation. Chemical reactions were carried out by the absorption of long-wavelength

ultraviolet light by reactants to form product in a short period of time. We carried out the

synthesis of polyhydroquinoline via irradiating the cyclohexanone/ cyclohexane dione/

dimedone with malononitrile/ethylacetoacetate and different aliphatic and substituted

aromatic aldehydes in the prescence of ammonium acetate and P-TSA catalyst in ethanol

assisted with ultraviolet light. The absorption of ultraviolet radiation by substrate allows a

reaction to proceed by bringing the molecule to the activation energy, by changing the

symmetry of the molecule and by changing the configuration of molecules. The reaction time

is reduced from 1.5h to 4-5 min whereas % yield increased significantly by the ultraviolet

assisted reactions. Thus, the superiority of the ultraviolet assisted protocol for the synthesis of

polyhydroquinoline over thermal method had proved. Extensive biological studies on these

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polyhydroquinolines with a variety of substitution patterns exhibit that these compounds have

a mild potential of antimicrobial and antioxidant activities.

Chalcones are secondary metabolites of terrestrial plants, precursors for the

biosynthesis of flavonoids and exhibit various biological activities. A simple and

regioselective synthesis of substituted 2-chloro-3-formyl quinolines through Vilsmeier-Haack

cyclization of N-arylacetamide bearing an electron donating group at the meta position was

carried out. Yields with electron donating groups were good in all cases. First, the chalcones

were synthesized by direct Claisen-Schmidt condensation reactions between an equimolar

quantity of quinoline-3-formaldehyde and different heterocyclic/aromatic ketones (a-i) by a

base catalysed (40% NaOH solution) condensation. The 1H-NMR spectra of the synthesized

compounds were in good agreement with the structures of the synthesized compounds.

Extensive pharmaceutical studies in literature on various other quinolinyl chalcones indicate

that these compounds have a significant potential of biological activity.

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CHAPTER 1

INTRODUCTION

1.1 Heterocycles

Cyclic organic substances containing at least one atom other than carbon in the ring system

are known as heterocycles (Bellina & Rossi, 2004). The heterocycles has significance due to

the diversity of its synthetic procedures and continuous contribution to the development of

biological and industrial processes (Jacobi, 2002; Abadi et al., 2005). Nitrogen containing

heterocycles are widely known for their versatile biological activities.

1.2 Polyhydroquinolines

Polyhydroquinolines are structurally related to 1,4-dihydropyridine (DHP) which is a

pyridine molecule, semi-saturated with two substituents replace one double bond (Cindric et

al., 2010). DHPs can exist in 5 isomeric forms theoretically.

Figure 1.1: Resonance forms of 1,4-dihydropyridine (DHP)

Structures 1 and 2 are the most common isomeric forms of DHP. The lone pair of the

electrons on the nitrogen atom causes the delocalization of the π system which stabilizes the

structure. Substituent effects have been investigated on the stability of the DHP ring system.

Electron withdrawing groups (COR, CO2R, CN, NO2) which are capable of undergoing the

resonance interactions in the 3 and 5 positions are responsible for the stability of the

1,4DHP’s by extension of the conjugation. Otherwise, electron donating groups (OPh, SPh)

in the 3 and 5 positions destabilize the compound and 1,4 DHPs are also destabilized by the

alkyl amino substituents (Stout & Meyers, 1982).

2

Substituted 1,4-dihydropyridines (1,4-DHPs) are a most significant class of drugs and

analogues of nicotine adenine dinucleotide dehydrogenase (NADH) coenzymes (Zhang et al.,

2007). 1,4-dihydropyridine dicarboxylate also known as Hantzsch compound (Enders et al.,

1988). Initially, dihydropyridine is produced as a reaction product which can be oxidized to a

pyridine in a succeeding step. The second step of this reaction is aromatization. First of all, in

1881, Rudolf Hantzsch reported this reaction.

Figure 1.2: Hantzsch compound or 1, 4-DHP

A Hantzsch compound is the most significant antagonist of the calcium channel. The

aromatization of Hantzch ester has been found to proceed in water by potassium

permanganate or by ferric chloride (Xia & Wang, 2005). The 1, 4-DHPs such as 10 exhibit

moderate calcium channel blockade greater than nifedipine (Aydin et al., 2006).

Figure 1.3: Illustration of the variations in the 1,4-DHP core region of polyhydroquinolines

X-ray studies reveal that Hantzch esters adopts two conformations, if all the four positions

are unsubstituted it will adopt a planar conformation but if phenyl and pyridyl substituents at

3

the fourth position are present then it adopts a puckered ("flat boat") configuration as shown

below (Fossheim et al., 1982).

Figure 1.4: Configurations of 1,4- DHPs

Hexahydroquinoline and tetrahydroquinoline are polyhydroquinolines (Dodiya, 2011).

Figure 1.5: Structures 13 and 14 for polyhydroquinoline

These hexahydroquinolines, tetrahydroquinolines and dihydroquinolines are structural

subunits of quinoline scaffold. However, the 7,8-dihydroquinoline derivatives (Figure 1.5)

are polyfunctionalized 1,4-dihydropyridine (Chorvat & Rorig, 1988).

Figure 1.6: 7,8-Dihydro-7,7-dimethyl-2,4-disubstituted-quinoline-5(1H,4H,6H)-ones

By chemically modifying the 1,4-DHP ring system (Chorvat & Rorig, 1988) or by varying

the substituents, various extended structures found (Eisner and Kuthan, 1972). Among

various dihydroquinolines, biological and chemical profiles of 1,4-dihydroquinolines and 1,2-

dihydroquinolines is extensively studied. Some examples of the pharmaceutically active

derivatives of dihydroquinolines are shown in the following figure (Dodiya, 2011).

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Figure 1.7: Some biologically active polyhydroquinolines

1.3 Quinolines

Quinolines are a class of compounds characterized by the aromatic heterocyclic system

consisting of a fusion of pyridine and benzene rings. Both of which have two adjacent carbon

atoms (Sarade, 2011). Quinoline exists in following eight resonating structures with

structures 1-3 having major contribution

Figure 1.8: Resonance forms of quinoline

The pyridine nucleus in quinoline is reflected by the inclusion of doubly charged canonical

forms. However, resonance structures of (6) and (8) display the disruption of both

monocyclic π- systems simultaneously. It is found that these are of higher energy, and their

contribution is much less to the overall description of the molecule than (4) and (5) resonance

structures do that affect only the pyridine system (Sainsbury, 2001).

Quinoline exhibits reactions similar to those of the benzene and to the pyridine ring.

Benzo[b]-pyridine also displays electrophilic as well as nucleophilic subsitution reactions

(Khan, 2007). L-Azanaphthalene, 1-benzaine or benzo[b]-pyridine is the alternative name of

quinoline (Marella et al., 2013).

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Inspite of quinoline, isoquinoline is also called benzopyridine. Nicotinic acid, which prevents

pellagra, is principally manufactured from quinoline (Nagatsu, 1997). These are the structural

isomers of quinoline, depending upon the location of nitrogen atom in the ring (Bansal, 1999)

as shown below (Figure 1.9).

Figure 1.9: Structural isomers of quinoline

1.3.1 Natural sources of polyhydroquinoline and quinolines

Quinoline nucleus can be recognized in naturally occurring alkaloids, by interesting

pharmacological activities (Balasubramanian & Keay, 1996). Bone oil is a significant source

of quinoline (Clemo, 1973). A 0.2% component of the essential oil of Hibiscus syriacus is

quinoline (Bird et al., 1987), a 0.09 ppm component of spearmint oil is quinoline which is

extracted from Mentha gentilis f. Cardiaca. A 0.06 ppm peppermint oil extracted from

Mentha piperita (Ishihara et al., 1992), and it is a volatile constituent of carambola fruit

extract (Wilson et al. 1985) and 0.33 (±0.12) % of quinoline is obtained from the sclerotial

exudate of the pathogen plant Rhizoctonia solani (Aliferis & Jabaji, 2010).

1.4 Synthetic procedure of polyhdroquinoline

Synthetic procedures for tetrahydroquinoline derivatives have attracted considerable attention

due to the reported pharmaceutical profile. However, most of the literature describe the

synthesis of 1,2,3,4-tetrahydroquinoline nucleus and concise synthetic methods to access

functionalized 5,6,7,8-tetrahydroquinolinesare scarce in the literature (Skupinska et al.,

2002).

1.4.1 Synthesis of tetrahydroquinoline

Synthesis of novel 2-alkoxy-5,6,7,8-tetrahydroquinoline-3-carbonitriles afforded 95% yield

in a very short reaction time (Dodiya et al., 2012). The synthesis of tetrahydroquinoline is

carried out by the reactions of cyclohexanone and arylidene malononitriles in alcohol in the

presence of sodium under microwave irradiation at 300 W (Scheme1.1).

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Scheme 1.1: Synthesis of tetrahydroquinoline

1.4.1a Mechanism

Scheme 1.1a: Mechanism of the synthesis of tetrayhydroquinoline

The proposed mechanism for the synthesis of novel 2-alkoxy-5,6,7,8-tetrahydroquinoline-3-

carbonitriles involves Michael addition to generae intermediate A, followed by nucleophilic

alkoxide attack at one of the nitrile groups of A with dehydration and subsequent

dehydrogenation to afford the 5,6,7,8-tetrahydroquinoline (3) (Scheme 1.1a).

1.4.2 Synthesis of polyhydroquinoline

Among all reported methods for the synthesis of hexahydroquinoline, the classical method is

refluxing all components of the mixture in a solvent (Suárez et al., 1999). 2-Methyl-4-aryl-5-

oxo-1H,4H-5,6,7,8-tetrahydro-quinoline-3-carboxylate has been synthesized by the

condensation of aromatic aldehydes with 1,3-cyclohexanediones and β-aminocrotonate by

adopting the conventional heating method or by the use of ultrasound irradiation (Thirumalai

et al., 2006).

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Scheme 1.2: Conventional methods for the synthesis of polyhydroquinoline

1.4.2a Synthesis of polyhydroquinolines assisted by catalyst

Chemists have developed more efficient and alternate methodology for the synthesis of

polyhydroquinoline derivatives by using organic catalysts (Kumar & Maurya, 2007), metal

trifaletes (Wang et al., 2005), by microwave irradiation (Monts-Avila et al., 2012),

ultrasonications (Saurabh et al., 2011), grinding (Kumar et al., 2008), ionic liquids (Legeay et

al., 2006), HClO4 SiO2 (Maheswara et al., 2006), molecular iodine (Ko et al., 2005),

iodotrimethyl silane (TMSI) (Sabitha et al., 2003), organocatalysts (Karade et al., 2007),

HCM-41 (Nagarapuet al., 2007), montmorillonite K10 clay (Song et al., 2005), hafnium (IV)

bis(perfluorooctanesulfonyl) imide complex [Hf(NPf2)4] (Hong et al., 2010), scolecite

(Gadekir et al., 2009), ceric ammonium nitrate (CAN) (Ko& Yao, 2006), silica sulfuric acid

(Mobinikhaledi et al., 2009), HY-zeolite (Das et al., 2006), scandium triflate [Sc(oTf)3]

(Donelsonet al., 2006), K7[PW11CoO40] (Heravi et al., 2007), solar thermal energy

(Mekheimer et al., 2008), fluoro alcohols (TFE or HFIP) (Heydari et al., 2009), silica-gel

supported polyphosphoric acid (PPA-SiO2) (Khojastehnezhad et al., 2011), FeF3 (Surasani et

al., 2012), nickel nanoparticle (Sapkal et al., 2009) and aluminum phosphate (AlPO4)

(Purandar et al., 2012).

1.4.2b Synthesis of polyhydroquinolines assisted by ionic liquids as catalyst

The use of recyclable catalyst or solvent with best activity and selectivity is a rapidly growing

area of synthetic chemistry. In this context, ionic liquids have attracted a considerable

attention as environment friendly reaction media (Raghuvanshi & Krishna, 2013). A

proposed mechanism for the synthesis of polyhydroquinoline by using an ionic liquid (1-

vinyl-3-ethyl imidazolium iodide) as catalyst is described here. Where, ammonium acetate

has generated ammonia, which ultimately generates N-heterocyclic carbene (NHC) by acting

as base (Nair et al., 2008).

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1.4.2c Mechanism

Scheme 1.3: Synthesis of polyhydroquinoline assisted by ionic liquids as catalyst

1.4.3 Synthesis of polyhydroquinolines assisted by Brönsted ionic liquid catalyst

Synthesis of ethyl‐4‐aryl‐hexahydro-trimehtyl‐5‐oxoquinoline‐3‐carboxylate derivatives

assisted by binuclear Brönsted acidic ionic liquid, namely, 1,1'‐butylenebispyridinium

hydrogen sulfate (Bbpy)(HSO4)2 is presented here.

1.4.3a Mechanism

A tentative mechanism to rationalize the polyhydroquinoline formation is shown in (Scheme

1.4). Polyhydroquinolines 4 may be formed either through steps I-II or through steps III-IV.

Dimedone, ethylacetoacetate and substituted aldehyde was activated by the binuclear

Brönsted acidic ionic liquid catalyst. The (Bbpy)(HSO4)2 catalyst gave a proton to activate

carbonyl groups, where it catalyzes the Knoevenagel type coupling of aldehydes with active

methylene compounds and undergo the subsequent Michael addition of enamine II to

intermediate I or enamine IV to intermediate III followed by cyclization and dehydration

afforded the polyhydroquinoline product 4 (Nader,2014).

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Scheme 1.4: Mechanism of the synthesis of polyhydroquinoline

1.5 Most recent synthetic approaches to quinolines

The first formal synthesis of quinoline was published by Skraup (Caeiro et al., 2006a). This

synthesis is carried out by the treatment of aniline with acrolein and heated under sulfuric

acid but after some time several modifications to the original skraup method have been

reported (Heinrich & Steglich, 2003). There are conceptually only two synthetic approaches

towards quinoline. The first approach is due to the use of the aromatic primary amine the

nucleophilic component providing nitrogen whereas the second one relates to the o-

substituted aniline (Kouznetsov et al., 2005).

These are the synthetic approaches for quinoline synthesis

(I) From 1, 3-dicarbonyl compounds and arylamine

a. The Conard-Limpach-Knorr synthesis

b. The Combes synthesis

(II) From α, β-unsaturated carbonyl compounds and aryl amine

a. The Skraup synthesis

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(III) From carbonyl compounds and ortho-acylarylamines

a. The Friedländer synthesis

b. The Pfitzinger synthesis

(IV) Doebner reaction

(V) Vilsmeier-Haack synthesis

1.5.1 By aryl amine and 1,3-dicarbonyl compounds

Quinoline has been synthesized when anilines react with 1,3-dicarbonyl compounds to form

intermediates which undergo cyclization with an acid.

1.5.1a The Conard-Limpach-Knorr synthesis

The conard-Limpach-Knorr synthesis uses β-keto esters such as ethyl acetoacetate which

react with aromatic amine to give a quinoline (Heindel et al., 1966).

Scheme 1.5: Synthesis of quinoline by the Conard Limpach Knorr synthesis

1.5.1b The Combes synthesis

The combes synthesis closely resembles to the Conrad-Limpach Knorr synthesis.

Mechanistically, a ring closure step can be viewed as an electrophilic substitution, followed

by loss of water to give aromatic quinoline (Long & Schofield, 1953).

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Scheme 1.6: Synthesis of quinoline by the Combes method

1.5.2 By α, β-unsaturated carbonyl compounds and aryl amine

Aryl amines react with an α,β-unsaturated carbonyl compound in the presence of an oxidizing

agent to give quinolines.

1.5.2a The Skraup synthesis

The Skraup synthesis is the best for the synthesis of quinolines in which the hetero ring is

unsubstituted (Doebner, 1883; Kamiguchi et al., 2006).

Scheme 1.7: Skraup synthesis of quinoline

1.5.2b Substituted quinoline synthesis by Skraup method

Skraup-Doebner-Von Miller synthesis of substituted quinolines from anilines and α,β-

unsaturated ketones was proposed to involve a mechanism of fragmentation recombination

(Denmark & Venkatraman, 2006). The Skraup synthesis of quinolines can also be catalyzed

by a number of Lewis (Yb(OTf)3, SnCl4, ZnCl2, Sc-(OTf)3, InCl3) and Brönsted acids

(Amberlite, HClO4, TsOH) in addition to iodine (Badger et al., 1963).

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Scheme 1.8: Subsituted quinoline synthesis by the Skraup method

1.5.3 Quinoline synthesis from carbonyl compounds and ortho-acyl arylamines

1.5.3a. Friedländer Synthesis

Friedländer annulation is one of the simplest and most convenient protocols that were

originally designed by Friedländer (Friedländer, 1982). The Friedländer reaction was also

investigated by the use of various Lewis and protic acids such as ZnCl2 (McNaughton &

Miller, 2003), Bi(OTf)3 (Yadav et al., 2004a), FeCl3 and Mg(ClO4)2 (Wu et al., 2005), AcOH

under microwave irradiation (Perzyna et al., 2002), sodium fluoride (Mogilaiah and Reddy,

2003), HCl (Bailliez et al., 2004), silver tungstophosphate (Yadav et al., 2004b), ionic liquid

(Palimkar et al., 2003), sulfamic acid (Yadav et al., 2005) and NaAuCl4 (Arcadi et al., 2003).

Better yields of the product were achieved by the acid-catalyzed Friedländer reaction (Fehnel,

1966).

Scheme 1.9: Synthesis of quinoline by the Friedländer method

In the Friedländer synthesis, ortho-acyl aryl amines condense with a carbonyl (which must

containan α-methylene group) in the presence of an acidic or basic catalyst to build up

quinolines (Okabe & Sun, 1995). The advantage of the use of oxime ether is well known for

the α-methylene ketoneas synthon (Boger & Chen, 1995). Currently, Yao and co-workers

13

published an easy and efficient one-pot reaction for the synthesis of 3-nitroquinoline

derivatives (Yan et al., 2004).

Scheme 1.10: Synthesis of quinoline with a slight variation by the Friedländer method

1.5.3b The Pfitzinger synthesis

The Pfitzinger Borsche reaction is a formal extention of the known Friedländer protocol

reported in 1886 by Pfitzinger for the synthesis of quinolic acid (Calaway & Henze, 1939)

Scheme 1.11: Pfitzinger synthesis of quinoline

In this modification of the Pfitzinger synthesis, the o-aminoarylaldehydes are replaced by

isatin which hydrolyse the o-amino aryl glyoxalates, which finally react with the ketones to

produce the quinoline-4-carboxylic acids (Pfitzinger, 1886).

1.5.4. Doebner-von Miller synthesis

The Doebner synthesis is a modification of the Skraup synthesis of quinolines (Denmark &

Venkatraman, 2006; Eicher et al., 2013). In the Doebner synthesis glycerol is replaced by two

molecules of aldehydes (Eisch & Dluzniewski, 1989).

Scheme 1.12: Synthesis of quinoline by the Doebner-von Miller synthesis

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1.5.5 Vilsmeier-Haack synthesis

The Vilsmeier-Haack reaction is a mild and efficient method for the formylation of various

electron rich aliphatic, aromatic and heteroaromatic substrates (Marson, 1992; Meth-Cohn,

1993). However, the scope of the reaction is not limited to aromatic formylation. The

Vilsmeier- Haack reagent provides a convenient entry into a large number of heterocyclic

ystems (Meth-Cohn & Tarnowski, 1982). In 1978, a practically simple procedure of the

conversion of acetanilide into 2-chloro-3-quinoline carboxaldehyde with 68% yield (Meth-

Cohn & Narine, 1978) was performed by the group of Meth-Cohn. This quinoline synthesis

was termed as “Vilsmeier Approach” by Meth-Cohn (Meth-Cohn & Taylor, 1995).

Scheme 1.13: Synthesis of quinoline by Vilsmeier-Haack

1.5.5a Mechanism

Scheme 1.14: Mechanism for the synthesis of quinoline by the Vilsmeier-Haack method

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1.6 Biological profile of polyhydroquinoline and quinoline containing

compounds

Hantzsch described that dialkyl 1,4-dihydro-2,6-dimethylpyridine-3,5-dicarboxylates have

been significant drugs in the treatment of hypertension and angina (Lozytska et al., 2004).

Polyhydroquinoline decreases the passage of the calcium current across the membrane

because of binding itself to the calcium channels. Due to this calcium channels antagonists,

1,4-DHPs cause the reduction of the contraction of the cardiac muscle throughout the heart

and smooth muscles undergo the long lasting relaxation (Triggle, 2007). Moreover, 1,4-

dihydropyridine nucleus containing compounds exhibit several pharmaceutical applications

such as anti-aggregatory agents (Visentin et al., 1999), neuroprotectant (Schleifer & Tot,

2002) , cerebral and ischemic agents for curing the Alzheimer’s disease, and aschemo

sensitizer in cancer tumor therapy (Torchy et al., 2002).

Compounds of the quinoline family are broadely used as precursors to make drugs as

especially antimalarial medicines, biocides, dyes, fungicides, rubber, chemicals, flavoring

agents, alkaloids antiseptic and antipyretic. Quinaldine, 2-methylquinoline, has significant

importance for the ailment of malaria and for the preparation of other antimalarial drugs.

Carbolic acid is a substituted quinoline at the 2-position also known as quinaldic acid and it

acts as a catabolite of tryptophan (aromatic side chain amino acid). Prazosin and doxazosin

which are peripheral vasodilators act as antihypertensive agents consisting of quinaldic acid

nucleas (Muthumani et al., 2010). Among the pharmacologically active heterocyclic

compounds, quinoline and its derivatives have been acted as dehydrogenase (Shih-Fong et

al., 1990), leukotriene D4 receptor (Jones et al., 1989), antimalarial (Bray et al., 2005),

anticancer (Atwell et al., 1989), antihypertensive, anti-HIV(Ahmed et al., 2010), inhibitors

of gastric (H+/K+)–ATPase (Ife et al., 1992), antibiotic (Yan et al., 2004), antioxidant

(Hamdy et al., 2013), possess anti-proliferation (Chen et al., 2006a) and anti-inflammation

activities (Kuan et al., 2006), etc.

1.6.1 Anticancer activity

Cancer is a malignant growth of abnormal cells called tumors. It tends to spread indefinitely

over the body and can return even after removal which leads to the programmed cell death

(Vosooghi et al., 2010). A cell replicates by mitosis. When the normal processes of mitosis

such as initiation, control and termination cannot occur due to genetic mutations, cancer

16

occur (Gomes et al., 2011). Quinoline and polyhydroquinoline derivatives are very important

for their potential activity against cancer. The anticancer activity of these quinoline

derivatives depends not only on the bicyclic heteroaromatic pharmacophore but also on the

spatial geometry and nature of the peripheral substituents (Chen et al., 2006c). Certain 4-

anilino-2-phenylquinoline derivatives and their isomeric 4-anilino-2-(furan-2-yl) quinolines

were synthesized and underwent anticancer evaluation. Among them, 1-(3-phenyl)-ethanone,

its oxime and methyloxime exhibited cytotoxic activity with mean GI50 values of 10.5, 6.85,

and 20.6 M, respectively.

Figure 1.10: Quinoline exhibiting anticancer activity

1.6.2 Anti-inflammatory and analgesics activities

First response of the immune system to infection and the resistance of the system to foreign

substance is the inflammation (Thomas & Zachariah, 2011) and analgesic is any drug that

selectively relieves pain without affecting consciousness or blocking the conduction of nerve

impulses, but altering sensory perception (Keshri & Sharma, 2013). 4-Substituted-7-

trifluoromethyl quinolines have been found to possess an excellent analgesic activity (Abadi

et al., 2005). A quinoline based analgesic agent shows activity due to its antagonism at

Vanilloid receptors (Cui et al., 2006). A few quinoline derivatives can act as selective

agonists at Cannabinoid CB2 receptors and show analgesics activity (Manera et al., 2009).

17

Figure 1.11: Structures of quinolines with analgesic activities

1.6.3 Anti-tuberculosis activity

Mycobacterium tuberculosis is the main cause of the chronic infectious disease tuberculosis

(TB) (Zhang et al., 2006). This lung infection occurs via aerosol or by inhalation of drops

containing M. tuberculosis bacilli (Hasan et al., 2006). M. tuberculosis pathogenesis goes

through two stages: (1) an asymptomatic state, called latent TB, persist for many years (2) It

requires only few days for activation (Zhang, 2004). The replication of the bacteria begins

and causes symptoms such as chest pain, cough and weight loss. Effective TB treatment is

difficult because the mycobacterium cell wall has an unusual structure and chemical

composition which makes numerous antibiotics ineffective and develops a resistance against

these drugs (Chauhan et al., 2010). Although, many active antituberculosis agents have been

developed, a disturbing co-occurrence with the use of present drugs as single agents has

developed drug resistance (Patel et al., 2008). The development of this resistance can be

forestalled through the use of a combination of regimens. It is clear that the continuation of

drug resistance will be a problem (Lauinger et al., 2013). A quinoline ring is frequently used

in novel drug designing.

Figure 1.12: Structures of DCMQ and TMC 207

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The optimization of quinolines as anti-TB agents has been initiated by the identification of

novel quinolines as promising anti tubercular agents such as diarylquinoline (TMC 207) and

2,8-dicyclopentyl-4-methylquinoline (DCMQ) where diarylquinoline, is an adenosine ATP

synthase inhibitor. An antitubercular agent, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine

was found to act as a protein kinase inhibitor inhibiting the growth of two different

mycobacterial strains (Drews et al., 2001).

1.6.4 Anti-microbial activity

Quinoline and its derivatives play an important role in the design of therapeutically active

wide spectrum antibacterial drugs (El‐Sayed et al., 2002). South American Cinchona sp.,

Rubiaceae (cinchona alkaloids, quinine, etc.) consisted of natural quinoline products which

act as molecular models of quinoline alkaloids and bases for the motivation of the quinoline-

based antimicrobial drug development (Wang et al., 2006; Leemans et al., 2014). In chemical

laboratories, the first developed quaternary quinoline dyes, were nalixidic acids and oxolinic

acids (Bearden & Danziger, 2001; Anderson, 2008). In a small time period, the quinoline

derivatives which were used for the ailment of urinary tract infections, moved from a small

unimportant group of drugs to 6-fluoro-4-quinolone, such as norfloxacin, ciprofloxacin and

pefloxacin (Gómez and Kouznetsov, 2013). The huge number of newly synthesized

antibacterial agents is connected with the quinoline nucleus which acts as a DNA gyrase

inhibitor and promotes the cleavage of bacterial DNAs. As a result the rapid death of bacteria

occurred (Abdullah et al., 2014)

1.6.5 Anti-microbial activity of quinoline hybrid molecules and bisquinolines

Bisquinolines are found to possess an excellent degree of antimalarial potential not only

against the chloroquine resistant but also against chloroquine sensitive parasites (Raynes et

al., 1996). Design and synthesis of quinoline-based potentially antibacterial agents partially

possess the molecular hybridization approach due to the addition of two or more groups with

different biological properties (Prasath et al., 2013). Thus, the quinoline moiety could be a

hybrid with other heterocyclic molecules. This approach leads to the modification of the main

part of the quinoline based natural compounds and thus improves the biological activities by

forming the novel quinoline hybrid libraries (Gómez & Kouznetsov, 2013).

Polyhydrydroquinoline was synthesized and its antibacterial activity was determined against

gram positive bacteria bacillus subtilis, streptococcus pneumonia and clostrid tetani) and

gram negative bacteria (salmonella typhi vibrio cholera and escherichiacoli) and antifungal

19

activity against aspergillus fumigates and candida albicans. Some of the compounds were

evaluated as more or equal potent to the standard drugs. One compound showed a compelling

antituberculosis activity at concentrations of 6.25µg/ml with 90% inhibition (Shah et al.,

2012).

1.6.6 Antioxidant activity

Antioxidants have attracted a lot of attention because of their potential as therapeutics as

well as prophylactic agents in many diseases. Free radicals play an important role in various

biological problems such as the intracellular killing of pathogens by phagolytic cells (Valko

et al., 2006). An excessive amount of free radicals leads to the damage of biomolecules such

as proteins, lipids, DNA and enzymes in cells and tissues which may cause mutations and

malignancy (Hamdy et al., 2013). In carcinogens the most important step is the mutation of

DNA. The discovery of antioxidant minimizes the oxidative damage by inhibiting the

formation of free radicals or by terminating the chain reaction. Oxidative stress due to free

radicals is the main cause of cancer, autoimmune diseases, diabetes, neurodegenerative

disorders, cardiovascular diseases and aging (Ratnam et al., 2006). Minimizing oxidative

damage is necessary for the ailment and prevention of these cancer causing diseases.

Quinolines are significant pharmaceutical compounds. They exhibit a broad spectrum of

pharmaceutical activities such as anti proliferation, anticancer, antioxidant and anti-

inflammation. Polyhydroquinoline posseses a biologically active moiety i.e. 1,4-

dihydropyridines which are responsible for antioxidant activities (Yang et al., 2011).

Figure 1.13: Structures of antioxidant quinolines

1.6.7 Anti-malarial activity

Quinineis extracted from cinchona bark, and it is the basis for the formation of quinoline-

containing synthetic drugs (Foley & Tilley, 1998). After the isolation of quinine from the

20

cinchona bark, this compound has been used for curing the malaria (Foley & Tilley, 1998).

Since then chloroquine, other synthetic quinoline antimalarials AQ and mefloquine have been

used for the ailment of malaria in the past 50 years (Foley & Tilley, 1998; O'Neill et al.,

1998).

Figure 1.14: Quinoline: structures of chloroquine, amodiaquine and mefloquine

However, the scope of synthetic quinoline based antimalarials has been decreased in recent

years due to the development of parasitic resistance against malaria (Warhurst, 2001;

Winstanley et al., 2002). The mode of action of CQ is the binding of the drug to haematin

(ferri protoporphyrin IX, FP) that takes place in the digestive vacuole of the parasite

(Homewood et al., 1972; Fitch, 1973; Hawley et al., 1998).

1.6.8 Cardiovascular activity

Type and degree of substitution of quinoline has a significant effect on the biological activity

(Balasubramanian and Keay, 1996). Quinolines containing certain biaryl ether amide

moieties are useful in the treatment of dyslipidaemia (Bernotas et al., 2009).

Figure 1.15: Polyhydroquinoline: exhibiting cardiovascular activities

21

Polyhydroquinoline exhibit cardiogenic activity (Schade et al., 2012). Tetrahydroquinoline

has the ability to inhibit the platelet aggregation (Morales-Ramos et al., 2008). A goal of

regenerative medicine is the development of small molecules for the regeneration of damaged

tissues of the heart (Willems et al., 2011). However, a small number of chemical mediators of

cardiogenesis have been published, and most of them are not very potent in their action

(Willems et al., 2009). A class of condensed1,4-dihydropyridines (1,4-DHPs) (Willems et al.,

2012) forms the b-annulated 1,4-DHP cardiogenic compound which was among the most

effective candidates for cardiac activity (Rose, 1990).

Bossert et al. (1976) prepared an antihypertensive 1,4-dihydropyridines and a coronary

dilator containing a quinoline group at the C4 position. Ethyl 2-amino-4-(4-quinolyl)-

1,4,5,6,7,8-hexahydroquinoline-3-carboxylate have been prepared by the cyclization of 1,3-

cyclohexanedione with aldehyde and butyrimidamide.

Scheme 1.15: Bis quinoline or polyhydroquinoline compounds exhibiting cardiovascular

activity

1.6.9 Quinoline and polyhydroquinoline as CNS active agents

Quinoline based CNS active drugs act as NK3 receptor antagonists are the 15% of the total

therapeutic drugs (Smith et al., 2009).

Figure 1.16: Quinoline compounds as CNS active agents

22

1.6.10 Calcium channel antagonists activity of polyhydroquinoline

Derivatives of polyhydroquinoline are significant well known Ca2+ channel inhibitors and

constitute the main skeletons of drugs used in the treatment of cardiovascular diseases and

hypertension (Nishiya et al., 2002). Subsituted dihydropyridine (nifedipine, nitrodipine) are

calcium antagonists where calcium channels are voltage gated and play a significant role in

the entry of Ca2+ ions into excitable cells (Augustine et al., 1987; Miller, 1987). Long lasting

(L-type) calcium currents are due to the alpha-1C blocked by 1,4-dihydropyridines (DHPs)

such as phenylalkylamines, verapamil, nifedipine and benzothiazepines such as diltiazem

(Leuranguer et al., 2001)

Figure 1.17: Polyhydroquinolines acting as calcium channel antagonists

Kısmetli et al. (2004) investigated that compounds 33 and 34 act as calcium channel

antagonists. DHP is a heterocyclic ring with different substitutions at different positions

(Swarnalatha et al., 2011). The discovery that the 1,4-dihydropyridine class of calcium

channel blockers inhibits the Ca2+ influx into the heart muscle and thus this therapy reduces

the strength of contraction and it is an advance in the treatment of cardiovascular diseases

such as angina pectoris, hypertension and other spastic smooth muscle diseases (Fleckenstein,

1977). Calcium channel antagonist activity is due to the substitution at the 4-position

(Triggle, 2007). Various pharmacological activities such as anti-anginal (Breitenbucher and

Figliozzi, 2000), antihypertensive (Loev et al., 1974), antitumor (Boer et al., 1996), anti-

inflammatory (Schade et al., 2012), antitubercular activity (Wächter et al., 1998), analgesic

activity (Gullapalli and Ramarao, 2002) and antithrombotic (Sunkel et al., 1990; Cooper et

al., 1992) are commonly due to heterocyclic rings. They bind to both the L-type channel and

to the N-type channel with equal ease (Triggle, 1999).

23

1.6.11 Polyhydroquinoline as potential anti-osteoporotic activities

A progressive skeletal disorder called osteoporosisis known as unequal coupling between an

osteoblast mediated bone formation and an osteoclast mediated bone resorption (Shea et al.,

2000). It affects almost 50% of females and is usually spread in the old age population

(Alldredge et al., 2001). It is specified by a decrease of mineral density inside the bones and

ultimately increases bone fragility which causes a high risk of fractures (Johnell and Kanis,

2006; Kaufman et al., 2013). The main factors for osteoporosis are calcium deficiency, aging,

estrogen deficiency, vitamin D deficiency and fractures (Cummings et al., 1995). This has

been widely known as a ‘silent disease’ and at the evident of complication it becomes

clinically important (Ellis, 2004).

Figure 1.18: Polyhydroquinoline scaffolds showing anti-osteoporotic effects

Recently, it has been suggested that compounds in which the pyridine nuclease is present

may modulate anti-osteoporotic activity (Allen et al., 2010).

1.7 Industrial applications of polyhydroquinoline and quinoline derivatives

Dihydropyridine derivatives have applications in rocket fuel additives. They act as

antioxidants, and they are also used as photographic materials (Raftery, 1996).

Quinoline derivatives are significant compounds used for the preparation of nano-materials.

Moreover, quinoline derivatives are used in the synthesis of fungicides, biocides, virucides,

alkaloids, flavoring agents and rubber chemicals (Chung et al., 2001). Additionally,

quinolines are also used as polymers, preservatives, corrosion inhibitors, catalysts, and as

solvents for terpenes and resins. Furthermore, these compounds find applications in

luminescence chemistry and also in the chemistry of transition metal catalysts for

polymerization (Gondek et al., 2010). In refineries, quinoline derivatives, act as antifoaming

agents (Caeiro et al., 2006b).

24

The main objective of the current study i.e. “Synthesis and Characterization of Potentially

Biologically Active Derivatives of Polyhydroquinoline and Quinoline Ring Systems” was

started with the aim to develop new methodologies for the synthesis of novel and potentially

biological active molecules. The synthesized molecules were characterized by spectroscopy

as well as X-ray diffraction studies.

The following plan was devised:

To synthesize compounds containing polyhydroquinoline and quinoline ring systems.

Separation and isolation of the products.

To characterize the synthesized compounds by spectroscopic techniques.

X-ray diffraction studies.

To evaluate the biological potential of the synthesized compounds

25

CHAPTER 2

REVIEW OF LITERATURE

This review summarizes the synthetic methods, reactions and biological applications of

polyhydroquinolines (hexahydroquinoline, tetrahydroquinoline) and quinoline. Most reaction

types have been successfully applied and used in the production of biological active

compounds.

2.1 Synthesis of polyhydroquinoline viz tetrahydroquinoline

2.1.1 Hydrogenation of quinoline

Skupinska et al. (2002) have reported the synthesis of amino-5,6,7,8-tetrahydroquinolines

and amino-5,6,7,8-tetrahydroisoquinolines via catalytic hydrogenation of acetamido

quinolines and acetamido isoquinolines (Scheme 2.1)

N

NHCOCH3

(i) H2 (1 atm), 5% PtO2

TFA, 60ºC

(ii) 6% HCl, refluxN

NH2

Scheme 2.1: Synthesis of amino-5, 6, 7, 8-tetrahydroquinolines via catalytic hydrogenation

2.1.2 Synthesis of 5,6,7,8-tetrahydroquinoline-3-carbonitrile

Elkholy and Morsy (2006) and El-Salam et al. (2009) prepared 2-amino-5,6,7,8-

tetrahydroquinoline-3-carbonitriles by the reaction of arylidene malononitrile with

cyclohexanone and ammonium acetate (Scheme 2.2).

Scheme 2.2: Synthesis of 2-amino-5,6,7,8-tetrahydroquinoline-3-carbonitriles

Gholap et al. (2007) reported that the 2-amino-5,6,7,8-tetrahydroquinoline-3-carbonitriles

were obtained by the condensation of 3-amino-2-cyclohexen-1-one(enaminone) with

arylidene malononitriles in relatively better yields (Scheme 2.3).

26

Scheme 2.3: Synthesis of 2-amino-5,6,7,8-tetrahydroquinoline-3-carbonitriles by 3-amino-2-

cyclohexen-1-one

2.1.3 One pot synthesis of tetrahydroquinoline

Litvinov et al. (1985) reported the one pot synthesis of 4-alkyl/aryl-3-cyano-5,6,7,8-

tetrahydroquinoline-2(1H)-thiones by condensation of an enamine with aryl methylene

cyanothio acetamides (Scheme 2.4).

Scheme 2.4: Synthesis of 4-alkyl/aryl-3-cyano-5,6,7,8-tetrahydroquinoline-2(1H)-thiones

2.1.4 Synthesis of the racemic mixture of tetrahydroquinoline

Yao et al. (2006) reported the synthesis and structures of (S)- and (R)-2-[3-cyano-4-(2-

thienyl)-5,6,7,8-tetrahydroquinolin-2-ylsulfanyl]-3-methyl-N-phenylbutyramide by the

reaction of 4-(2-thienyl)-3-cyano-5,6,7,8-tetrahydroquinoline-2(1H)-thione with (R) and (S)

2-bromo-3-methyl-1-phenyl-butan-1-one (Scheme 2.5).

Scheme 2.5: Synthesis of (S) - and (R)-2-[3-cyano-4-(2-thienyl)-5,6,7,8-tetrahydroquinolin-

2-ylsulfanyl]-3-methyl-N-phenylbutyramide

27

2.1.5 Synthesis of tetrahydroquinoline by aza-Michael/aldol reaction

Sunden et al. (2007) reported highly enantioselective organocatalytic domino aza-

Michael/aldol reaction between 2-aminobenzaldehydes and α,β-unsaturated aldehydes for the

preparation of 1,2-dihydro quinolidines (scheme 2.6).

Scheme 2.6: Synthesis of 1,2-dihydro quinolidines by aza-Michael/Aldol reaction

2.1.6 Synthesis of tetrahydroquinoline by hetero aryl aldehydes

Savitha and Perumal (2006) published the synthesis of similar tetrahydroquinolines achieved

by reactions in a one-pot multi component manner between hetero arylaldehydes, anilines

and N-vinylpyrrolidin-2-one by using CAN, in H2O or aq. MeCN (Scheme 2.7).

R1-CHO + N O NH

N O

R

R1 N

R

R1

NH2

R

+

5mol %CAN

H2O or aq.MeCNr.t: 30-50min82-90%

2.5eq.CAN, N2

MeCN, 0°C,20min, 88-93%

R= H, Cl, Me, OMe: R1=C6H5, 2-Furyl. 2-Thienyl, 3-(2-quinolinyl)

3-(2-Cl- 6-Me-quinolinyl), 3-(2-Cl-6-OMe-quinolinyl)

Scheme 2.7: Synthesis of tetrahydroquinoline by heteroaryl aldehydes and conversion to

quinoline

2.1.7 Chiral synthesis of tetrahydroquinoline

Literature survey also revealed few reports on the synthesis of chiral 5,6,7,8-

tetrahydroquinolines.

28

Yan et al. (2008) reported a one pot approach using a modified two-step synthesis via a

Krohnke pyridine synthesis involving a three-component tandem reaction of N-phenacyl

pyridinium bromide, aromatic aldehydes and substituted cyclic ketones in ammonium

acetate-acetic acid under microwave irradiation (Scheme 2.8).

Scheme 2.8: Synthesis of tetrahydroquinoline via the Krohnke pyridine method

Brahmbhatt et al. (2005) reported the synthesis of 6-(4-aryl-8-aryledine-5,6,7,8-

tetrahydroquinolin-2-yl) coumarins from 3-phenyl-4-methyl-6-coumarinoyl methyl

pyridinium bromide and 2,6-dibenzylidene-cyclohexanone using Krohnke’s reaction

conditions under conventional heating (Scheme 2.9).

Scheme 2.9: Synthesis of 6-(4-aryl-8-aryledine-5,6,7,8-tetrahydroquinolin-2-yl) coumarins

Koyama et al. (1993) reported the synthesis of 5,6,7,8-tetrahydroquinolines by thermolysis of

oxime o-allyl ethers in the presence of boron trifluoride etherate (Scheme 2.10).

Scheme 2.10: Synthesis of 5,6,7,8-tetrahydroquinolines by thermolysis

Literature surveys revealed a very few strategies describing the synthesis of 7,8-

dihydroquinolines.

29

Rosen and Weber (1977) reported the synthesis of 7,8-dihydroquinolines based on the

condensation of a pyridine ring to specific partially reduced aromatic ring. The critical ring

closure reaction onto the pyridine nucleus was an electrocyclic reaction (Scheme 2.11).

Scheme 2.11: Synthesis of 7,8-dihydroquinolines

Yanai et al. (2007) reported an easy method for the synthesis of 2-polyfluoro methyl

quinolines by the reaction of 2-vinyl anilines and perfluorinated hemiacetals or aldehydes in

the presence of TMSCl in toluene. However, they observed that the 1,2-dihydroquinoline was

produced as the major product if the reaction was performed in pyridine (scheme 2.12).

Scheme 2.12: Synthesis of 2-polyfluoromethyl quinolines

Jacobs et al. (2000) prepared 6,7-dihydroquinolines and tested them as dual inhibitors of

thromboxane A2 synthase and aromatase (Scheme 2.13).

Scheme 2.13: Synthesis of 6,7-dihydroquinolines

Sakai et al. (2006) demonstrated the cyclization of an N-silyl enamine with 2-methylene-1,3-

cyclohexanedione in the presence of a Yb(OTf)3-catalyst to afford a 7,8-dihydroquinolin-

30

5(6H)-one derivative and its one-pot conversion to a 2,3,5- trisubstituted quinoline derivative

(Scheme 2.14).

Scheme 2.14: Synthesis of 7,8-dihydroquinolin-5(6H)-one derivatives

2.2 Synthesis of polyhydroquinoline-coumarine hybrids

Sashidhara et al. (2013) evaluated the anti-osteoporotic effects of the novel coumarin-

pyridine hybrids. They found that the production of alkaline phosphatase caused the

stimulation of osteoblast differentiation and mineralization. Hantzsch dihydropyridine

synthesis were carried out when coumarinic aldehyde undergo a multi-component reaction,

and lead to the production of the unsymmetrical Hantzsch polyhydroquinolines by the

reaction of active methylene compounds, coumarinic aldehydes and ammonium acetate as

nitrogen donor in the presence of glacial acetic acid.

OH

R1

CHO

CHOR1 O

CHO

R1O

R2O O

NH

O

R1

OR4

R5

R5

OR2

O O

OO

N

O

R1

OR4

R5

R5

OR2

O O

OO

OH

(i)

(ii)

(iii)

(iv)

(vi)

(vii)

Scheme 2.15: Synthesis of a coumarine-pyridine hybrid

Reagents and conditions: (i) HMTA, TFA, 4h,120˚C (ii) aq H2SO4, 2h, 100˚C (iii) diethyl

malonate, EtOH, piperidine, reflux, 30min (iv) glacial acetic acid, rt (v) ethyl acetoacetate,

NH4OAc, AcOH, EtOH, reflux, 5h (vii) DDQ, THF, rt, 1hr.

31

2.3 Synthesis of polyhydroquinoline-quinoline hybrids

Shah et al. (2012) synthesized the compounds of biquinoline in a one pot reaction using

catalytic amounts of sodium hydroxide by cyclocondensation of the pyridine moiety by active

methylene compounds, 2-chloro-3-formyl quinoline and 3-(pyridine-3-ylamino) cyclohex-2-

enone. By this protocol, a rapid synthesis of a new class of biquinoline pyridine hybrids was

carried out. They are active against microorganisms.

R1

NH

C

CH3

O N

CHO

Cl

R1

VHR

OO+

N

NH2

NH

N

O

N

R1 CHO

Cl

+ +

NH

N

O

EtOH, NaOH

reflux

CN

R2

N

N

R1

ClR2

NH2

N

O

R1= OCH3, R2= COOEt

Scheme 2.16: General synthetic rout for the synthesis of a biquinoline pyridine hybrid:

VHR= Vilsmeier Haack Reaction

2.4 Synthesis of biquinoline

Mahajan et al. (2006) obtained the 2'-chloro-2,3'-biquinolin-4 (1H)-one by one-pot

microwave-mediated multicomponent reactions of aldehyde, aryl methyl ketone, and

ammonium acetate using piperidine as a catalyst (Scheme 2.17).

Scheme 2.17: Synthesis of biquinoline by microwave-mediated method

32

More et al. (2006) synthesized biquinoline adducts in high yields by cyclization of [(2-

chloro-3-quinolyl)methylene]methane-1,1-dicarbonitriles, by the reaction between aldehyde,

malononitrile and 3-arylamino-5,5-dimethyl-cyclohex-2-en-1-ones under microwave

irradiation catalyzed by 4-(N,N-dimethylamino) pyridine (DMAP) (Scheme 2.18). The

synthesized compounds were screened for their antifungal and antibacterial activities.

Scheme 2.18: Synthesis of biquinoline under microwave-irradiation catalyzed by (DMAP)

2.5 Synthesis of quinoline

Hegedüs et al. (2007) synthesized 2,4-Diphenyl-2-methyl-1,2 dihydroquinoline by using

aniline and acetophenone in the presence of a small pore size E4 a zeolite catalyst.

Scheme 2.19: Synthesis of 2,4-diphenyl-2-methyl-1, 2 dihydroquinoline

Zhou et al. (2008a) developed a reaction of 2-amino substituted aromatic ketones carbonyl

compounds and a reactive methylene group in ethyl ammonium nitrate (EAN) to give 2,3,4-

trisubstituted quinolines .

33

Scheme 2.20: Synthesis of 2,3,4-trisubstituted quinolines

Ghassamipour and Sardarian (2009) synthesized aquinoline 3-carboxylate using 2-amino

substituted ketones by the reaction of poly-substituted quinolines in aqueous media under

solventless conditions in the presence of dodecylphosphonic acid (DPA) as catalyst.

Scheme 2.21: Synthesis of quinoline 3-carboxylate in the presence of a DPA catalyst

Zhou et al. (2009) developed a 3,4-dihydroquinolin-2-one synthesis by treating 2-

iodoanilines and ethyl acrylate with azo bis isobutyronitrile (AIBN) in the presence of

tributyl tin hydride (n-Bu3SnH).

Scheme 2.22: Synthesis of 3,4-dihydroquinolin-2-one in the presence of n-Bu3SnH

Wang et al. (2009b) synthesized 2-phenyl-4-alkoxy quinoline by condensation and

cyclization of 2-(2-trimethylsilyl) ethynyl) aniline with aryl aldehydes. The reaction is

promoted by sulfuric acid in the presence of methanol as solvent.

Scheme 2.23: Synthesis of 2-phenyl-4-alkoxy quinoline

Qi et al. (2009) synthesized certain halogen-substituted quinolines by condensation and

cyclization of two molecules of o-halo acetophenones with urea or primary amines.

34

Scheme 2.24: Synthesis of halogen-substituted quinolines

Kowsari and Mallakmohammadi (2011) reported the ultrasound promoted synthesis of

quinolines using basic ionic liquids (BIL) in aqueous media. The advantage of such a

procedure is the simplicity in operation and high yields. The reaction involves treating isatin

with aromatic methyl ketones at ultrasonic frequencies of 20–50 kHz.

Scheme 2.25: Synthesis of quinolines using basic ionic liquids (BIL)

Zografos et al., (1999) introduced a one-step methodology for the synthesis of quinoline

alkaloid analogues. The reaction is based on a modification of the Mukaiyama aldol

condensation, making use of the high reactivity of lactones or anhydrides.

Scheme 2.26: Synthesis of quinoline alkaloid analogues by Mukaiyama aldol condensation

Zhao et al. (2010) synthesized diversified 2-alkoxy- and 2-aroxy-3-substituted quinolines

from o-alkynyl aryl isocyanides alcohols and phenols promoted by 1,4-

diazabicyclo[2.2.2]octane (DABCO) .

35

R1

NHCHO

R2

CN

R2

N

R1 R2

OR3

POCl3, Pr2NEt

CH2Cl2, R.T

R3OH, DABCO

CH2Cl2

R1=H, Me

R2=R3= Aryl, Alkyl

R1

Scheme 2.27: Synthesis of 2-alkoxy- and 2-aroxy-3-substituted quinolines

Saqrma and Prajapati, (2008) synthesized 2,4-disubstituted quinolines according to a Meyer-

Schuster rearrangement. In this method 2-aminoaryl ketones and phenylacetylenes rearrange

in the presence of a catalytic amounts of zinc trifluoromethane sulfonate in the ionic liquid 1-

hexyl-3-methylilmidazolium hexafluorophosphate [hmim][PF6] resulting in 2,4-disubstituted

quinolines.

Lekhok et al. (2008) also obtained the same product in the presence of indium (III)

trifluoromethane sulfonate [In(CF3SO3)3] under microwave irradiation without any solvent.

R1

NH2R

O

+ Ph

NR Ph

R1

Zn(OTf)2

[hmim]PF6

85ºC, 2.25h

Scheme 2.28: Synthesis of quinoline catalyzed by indium (III) trifluoro methanesulfonate

Wang et al. (2011) proposed palladium-catalysed Wacker-type oxidative cyclization for the

synthesis of 2-methylquinolone with good yields under mild conditions.

R NH2

R2OH

R1

N

R1

R2

CH3R

Pd(OAc)2

1,10-phenanthroline

air,MeOH, 36h,25ºC or 40ºC

Scheme 2.29: Synthesis of 2-methyl quinoline with a palladium catalyst

Chen et al. (2006b) synthesized 2,4-disubstituted quinolines by cyclization of 2-iodoanilines

with alkynyl aryl ketones in the presence of a nickel catalyst.

36

R I

NH2 O

ArR1+

N

R1

R

Ar

NiBr2(dppe), Zn

CH3CN, 12h, 80ºC

Scheme 2.30: Synthesis of 2, 4-disubstituted quinolines

Gao et al. (2010) carried out the reaction to form quinoline derivatives via a palladium-

catalyzed Sonogashira coupling and subsequent cyclization.

Scheme 2.31: Synthesis of quinoline derivatives via palladium-catalysed Sonogashira

coupling

Musiol et al. (2007) published the synthesis of styryl quinolines via condensation of anilines

with croton aldehyde in the presence of HCl, the resulting quinaldine with aldehydes

subjected to microwave irradiation (Scheme 2.32).

NH2R1

N CH3R1N

R2R1

crotonaldehyde, HCl

aldehyde MW

R1= 2-CO2H, 3-CO2H, 4-CO2H, 5-CO2H, 3,5-(CO2H)2, 5-OH

R2= 3-Br, 4-Br, 2-Cl, 3-Cl, 4-Cl, 2-OH, 3-OH, 4-OH, 2-OMe,

Scheme 2.32: Synthesis of styryl quinolines

Desai and Dodiya (2014) demonstrated the synthesis of quinolone derivatives and utilized P-

TSA as catalyst under solvent-free conditions. They subjected their reaction under microwave

irradiation and conventional heating. The excellent yields of the products were observed

under both conditions. The reaction accomplished under microwave irradiation was

completed within a short time (Scheme 2.33).

37

NH2

R1

O+

R

R2

R3O

P-TSA (1eq)

N

R1

R2

R3R100ºC or

300W, 30-60sec87-96%

R= H, 2,4-(Br)2: R1= H, Me, 4-F-C6H4: R2=H , CO2Et, CO2Me, COMe

R3= Me, cy-Pr, i-Pr, C6H5, 4-Cl-C6H4: R2, R3=-(CH2)3-, -(CH2)4, -CO(CH2)3-

-COCH2Me2CH2-

Scheme 2.33: Synthesis of quinolone derivatives with the use of P-TSA as the catalyst

2.6 Synthesis of quinoline from chalcone

Kim et al. (2008) successfully transformed 2-nitrochalcones 2-aryl quinolines by a reductive

cyclization triggered by the reduction of a nitro group of o-nitrochalcone in the presence of

NH4Cl and produced the quinoline in good yields (Scheme 2.34).

Scheme 2.34: Synthesis of quinoline from chalcone

2.7 Quinoline carbaldehyde derivatives

Kalita et al. (2006) treated an aldehyde with allyl alcohol in the presence of sodium

hydroxide under phase transfer catalytic conditions to give allyl ether. Its oxime was prepared

from the reaction of the allyl ether with hydroxylamine hydrochloride in the presence of

aqueous sodium hydroxide. On treatment with NaOCl in the presence of Et3N at 0-20ºC

afforded dihydro-3H-[1,2]oxazolo[3',4':4,5]pyrano[2,3-b]quinoline in excellent yields via a

1,3-dipolar cycloaddition of the nitrile oxides (Scheme 2.35).

38

Scheme 2.35: Synthesis of dihydro-3H-[1,2]oxazolo[3',4':4,5]pyrano[2,3-b]quinoline

Singh et al. (2007) synthesized 3-formyl-2-mercapto quinolines in a one-pot reaction of an

aldehyde with sodium sulfide and hydrochloric acid in hot ethanol in good yields. The

reaction of hydroxylamine followed by cyclization with Ac2O causes the production of

isothiazolo[5,4-b]-quinolines. Subsequently, the compound was oxidized with H2O2 in acetic

acid to give 2H isothiazolo[5,4-b]quinoline 1,1-dioxides (Scheme 2.36).

Scheme 2.36: Synthesis of 3-Formyl-2-mercaptoquinolines

Basavaraju et al. (2006) prepared 2-(Naphthalen-2-ylthio) quinoline-3-carbaldehyde from

reaction between aldehyde and naphthalene-2-thiol in K2CO3/DMF (Scheme 2.37).

Scheme 2.37: Synthesis of 2-(Naphthalen-2-ylthio) quinoline-3-carbaldehyde

39

Fun et al. (2008) prepared a 2-(5-aryl-4H-1,2,4-triazol-3-ylthio)quinoline-3-carbaldehydes by

the reaction of an aldehyde with 5-aryl-4H-1,2,4-triazole-3-thiolin refluxing ethanol in the

presence of pyridine. The later compound on reaction with a substituted acetophenone gave

1-aryl-2-(2-aryl-9H-[1,2,4]triazolo[3,2-b][1,3]thiazino[6,5-b]quinolin-9-yl)ethanones

(Scheme 2.38).

N

R CHO

Cl

N

NH

N

R1

HS+

N S

N

NH

N

R1

R

R2COMe

EtOH, NaOH

EtOH, pyridine

reflux

N S

N

N

N

R2

R1

R

O

CHO

R= H, 6-Me, 8-Me: R1=Ph, 4-OHC6H4: R2=Ph, 4-ClC6H4

Scheme 2.38: Synthesis of 2-(5-Aryl-4H-1,2,4-triazol-3-ylthio) quinoline-3-carbaldehydes

Sonar et al. (2010) reported the synthesis of 2-azidoquinoline-3-carbaldehydes from reaction

of aldehydes with sodium azide in DMSO or DMF, and their ring-chain tautomerism

discussed (Scheme 2.39).

N

CHO

Cl

R1

R2

R3

N

N NN

R1

R2

R3

CHO

81-70%

N

R1

R2

R3N3

CHOAcOH, NaN3, DMSO

H2O,3h: rt, overnight

R1=H, Me, MeO,: R2= H, MeO,: R3=H, Me

Scheme 2.39: Synthesis of 2-azidoquinoline-3-carbaldehydes

Kidwai et al. (2000) synthesized 3-formyl-2-(3-hydroxy-1,4-naphthoquinon-2-yl)-quinoline

by the reaction of aldehydes with 2-hydroxy-1,4-naphthoquinone in basic alumina using

microwave irradiation (MWI) (Scheme 2.40). The synthesized compound showed promising

antibacterial activity.

40

Scheme 2.40: Synthesis of 3-formyl-2-(3-hydroxy-1,4-naphthoquinon-2-yl)-quinoline

Suman et al. (2014) synthesized (E)-ethyl 3-(2-chloroquinolin-3-yl) acrylate by aldol and

elimination reactions of aldehydes with ethyl trifluoro acetoacetate under basic conditions

which resulted in the generation of highly stereoselective product (Scheme 2.41).

Scheme 2.41: Synthesis of (E)-ethyl 3-(2-chloroquinolin-3-yl) acrylate

Shah et al. (2009) synthesized 12-(2-chloro-6-quinolin-3-yl)-2,3,4,12-tetrahydro-1H-

benzothiazolo[2,3-b]quinazolin-1-one in a one pot reaction by condensing aldehyde, 2-

amino-6-methoxy benzothiazole, and 5-dimethyl-1,3-cyclohexanedione in ethanol (Scheme

2.42 ).

Scheme 2.42: Synthesis of 12-(2-chloro-6-quinolin-3-yl)-2,3,4,12-tetrahydro-1H-

benzothiazolo [2,3-b]quinazolin-1-one

Gupta et al. (1998) carried out the reaction of 4-amino-5-aryl-4H-1,2,4-triazole-3-thiols with

quinolone without solvent using inorganic solid supports (e.g., silica or alumina) either in

microwave irradiation or in DMF containing potassium carbonate to give the triazolo

thiadiazole. The synthesized quinolone derivatives have been assessed for their anti-

inflammatory, antibacterial, and antifungal activities (Scheme 2.43).

41

Scheme 2.43: Synthesis of biologically active quinoline

Abdel-Wahab and Khidre (2013) reported that the oxidation of quinoline 3-carbaldehyde

with alkaline silver nitrate in ethanol gave the corresponding quinoline 3-carboxylic acid in

73–75% yields. 2-Chloroquinoline-3-carboxylicacids reacted with o-phenylenediamine or

4,5-dichloro o-phenylenediamine in xylene to afford [2,3-b][1,5]benzodiazepine-12-ones in

39–72% yield. In contrast, the reaction of quinoline 3-carboxylic acids with 4,5-dimethyl o-

phenylenediamine yielded benzimidazoles in 60–70% yield (Scheme 2.44).

N

R1

Cl

CHO

N

CO2HR1

Cl

73-75%

R2

R2

H2N

H2N

R2=H,Cl

Xylene

Me

Me

H2N

H2N

AgNO3/EtOH

N Cl

R1N

HN

Me

Me

R1=H, Me, OMe

N

R1

NH

NH

R2

R2

O

Scheme 2.44: Synthesis of quino[2,3-b][1,5]benzodiazepine-12-ones

2.8 Derivatization of quinoline to chalcones

Herencia et al. (1998) synthesized chalcones from the reaction of quinoline carbaldehyde and

aromatic or heterocyclic ketones. The synthesized chalcones were evaluated for their anti-

inflammatory activities (Scheme 2.45).

42

N

R1

R2 Cl

CHO

+Me R3

O

N

R3

O

Cl

R1

R2

56-85%

NaOH

EtOH

R1 = R2= OMe, H: R3= C6H5, 4-MeC6H4, 4-OMeC6H4, 4-FC6H4,

4-F3CC6H4, 2, 4-diOMeC6H3, 3-pyridinyl, 2, 2-dimethyl-3-furyl

Scheme 2.45: Synthesis of chalcones from quinoline

2.8.1 Cyclization of chalcones

Abdel-Wahab and Khidre, (2013) reported that the cyclization of chalcones carried out with

hydrazine, phenylhydrazine or thiourea yielded pyrazolylquinolines and

quinolinylpyrimidine-2-thiones. The anti-inflammatory activity of the prepared compounds

was studied (Scheme 2.46).

N

R1

R2 Cl

R3

O

N

N

R1

R2 Cl

N

R3

R4=H, Ph

R4NHNH2

R1

R2 Cl

NHN

R3

S

H2N NH2

S

R1= R2= H: R3=Ph, 4-OMeOC6H4, 4-MeC6H4, 4-ClC6H4, 4-BrC6H4

NR4

Scheme 2.46: Cyclization of chalcone synthesized from quinoline

43

CHAPTER 3

MATERIAL AND METHODS

3.1 General Methods

The reactions were carried out using standard laboratory equipment. Air and/or moisture

sensitive experiments were performed under an inert atmosphere of argon and with flame

dried glassware. All reactions were stirred by magnetic stirring and when needed warmed to

defined constant temperatures by hotplates with temperature probe control in dry heating

blocks or silicon oil baths. Reactions performed at low temperatures were stirred in reaction

vessels in ice/water (0°C). Rotary evaporators Büchi, B-461, B-481 or B-490, were used for

solvent evaporations (reduced pressure to 15 mbar); further drying was undertaken by the use

of a high vacuum apparatus. A Büchi GKR-50 Kugelrohr distillation apparatus was employed

for Kugelrohr distillations. For moisture sensitive reactions, freshly distilled solvents over

drying agents were used under inert atmosphere. Other chemicals were purchased from

Acros, Aldrich, Alfa Aesar or Fluka and were used without further purification, except if

indicated otherwise in the experimental procedure.

3.2 Chromatographic Methods

3.2.1 Thin Layer Chromatography

All reactions were monitored by thin-layer chromatography (TLC) which was performed on

precoated aluminium sheets of Merck silica gel 60 F 254 (0.20 mm) and visualized by UV

radiation with 254 nm and/or 366 nm without dipping reagent.

3.2.2 Column Chromatography

Column chromatography was performed with silica gel 60 (Merck, 230-400 mesh) under

increased pressure (Flash Chromatography) or as gravitational column chromatography. The

used eluting solvents are indicated in the text and these were distilled before use.

3.3 Physical Data

3.3.1 1H NMR Spectroscopy

The instruments Bruker DPX 500 (500 MHz), Bruker DPX 400 (400 MHz), Bruker DPX 250

(250 MHz) or Oxford 300 were used. The chemical shifts δ are given in ppm downfield of

tetramethylsilane (δ = 0 ppm). Compounds and crude reaction mixtures were dissolved in

44

either deuterated chloroform (CDCl3), deuterated acetone (acetone-d6) or deuterated

dimethylsulfoxide (DMSO-d6). Coupling constants (J) are given in Hertz. The multiplicity of

signals is designated as: s = singlet: d = doublet, t = triplet, q = quartet, quin = quintet, dt =

doublet of triplets, td = triplet of doublets, m = multiplet. Residual solvent peaks are assigned

as follows: 7.26 ppm for chloroform, 2.54 ppm for dimethylsulfoxide, 2.05 ppm for acetone.

3.3.2 13C NMR Spectroscopy

The instruments Bruker DPX 500 (125 MHz), Bruker DPX 400 (100 MHz), Bruker DPX 250

(62.5 MHz) were used. The chemical shifts δ are given in ppm downfield of tetramethylsilane

(δ = 0 ppm). Compounds and crude reaction mixtures were dissolved in either deuterated

chloroform, deuterated acetone or deuterated dimethylsulfoxide. Residual solvent signals are

assigned as follows: 77.4 ppm for chloroform, 40.5 ppm for dimethyl sulfoxide, 29.8 ppm

and 206.3 ppm for acetone.

3.3.3 Mass Spectrometry

Mass spectrometric measurements have been performed by R. Jenkins/R. Hick at Cardiff

University. Ions were generated by the atmospheric pressure ionisation techniques voltage

applied corona discharge pin (APCI), Electrospray (ES) or Electron Ionisation (EI). Mass

fragments usually are in atomic mass units per elementary charges (m/z) with relative

abundance of ion in percentage (%). The high resolution masss pectrometry (HRMS) for

most of the compounds was carried out by R. Jenkins/R. Hick at Cardiff University. The

molecular ion peak values quoted for molecular ion (M+) or the molecular ion plus hydrogen

(M+H+).

3.3.4 IR Spectroscopy

IR spectra were recorded on either a Perkin Elmer 1600 series FTIR or a PC supported

JASCO FT/IR 660 plus with “Spectra Manager for Windows 95/NT”, Version 1.53.01 from

JASCO Cooperation. Wavenumbers are quoted in cm–1. Crystalline compounds were

measured as KBr disk; non-crystalline samples were measured as neat films between NaCl

disks.

3.3.5 Melting Points

Melting Points were measured using a Gallenkamp variable heater with samples in open

capillary tubes. All melting points are uncorrected.

45

3.3.6 X-Ray Crystallography

A Bruker KAPPA Apex II CCD diffractometer was used with a thin glass pin supported by

copper rods. Data collection was performed at 296 K. SAINT was used for cell refinement as

well as data reduction while the structure solution and final refinement was achieved through

SHELXS-97. PLATON, in-built with Win GX18 was used for molecular graphics. All non-

hydrogen atoms were refined with anisotropic displacement parameters. X-Ray

crystallographic studies were carried out at the University of Sargodha, Pakistan.

3.4 Synthesis of polyhydroquinolines

3.4.1Synthesis of tetrahydroquinolines

3.4.1a. Synthesis of 2-amino-4-methyl-5,6,7,8-tetrahydroquinoline-3-carbonitrile

Scheme 3.1: Synthesis of 2-amino-4-methyl-5,6,7,8-tetrahydroquinoline-3-carbonitrile

Procedure:

A mixture of cyclohexanone (0.98 g, 0.01mol) with acetaldehyde (0.44 g, 0.01mol),

malononitrile (0.66g, 0.01mol) and ammonium acetate (1.15 g, 0.015mol) in ethanol (20 mL)

was refluxed for 1 h. The reaction mixture was then stirred overnight at room temperature

and the obtained solid was recrystallized from ethanol to obtain the pure product.

Yield: 40%

Appearance: yellow amorphous solid

m.p: 279ºC

IR (KBr): 3400, 3320, 2933, 2870, 2210 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 1.78 (d, J=2.8 Hz, 4H, 2CH2), 2.32 (s, 3H,

CH3), 2.50 (s, 2H, CH2), 2.74 (s, 2H, CH2), 5.16

(s, 2H, NH2)

46

MS m/z: 187(M+)

X-Ray Structure

Figure 3.1: ORTEP diagram of 1 drawn at 50% probability of thermal ellipsoids

3.4.1b Synthesis of 2-amino-4-methyl-5-oxo-5,6,7,8-tetrahydroquinoline-3-carbonitrile

(2)

Scheme 3.2: Synthesis of 2-amino-4-methyl-5-oxo-5,6,7,8-tetrahydroquinoline-3-carbonitrile

Procedure:

A mixture of 1,3-cyclohexandione (1.12 g, 0.01mol) with acetaldehyde (0.44g, 0.01

mol), malononitrile (0.66g, 0.01 mol) and ammonium acetate (1.15 g, 0.015 mol) in ethanol

(20 ml) was refluxed for 1 h. The reaction mixture was then stirred overnight at room

temperature and the obtained solid was recrystallized from ethanol to obtain the pure product.

Yield: 42%

Appearance: yellow amorphous solid

47

m.p: 207ºC

IR (KBr): 3315, 3216, 2960, 2878, 2180, 1683 cm-1

1H-NMR (DMSO-d6, 400 MHZ): δ: 1.08 (s, 3H, CH3), 1.90 (m, 2H, CH2), 2.41(t,

2H, CH2), 3.25 (m, 2H, CH2), 6.95 (s, 2H, NH2)

MS m/z: 201 (M+)

3.4.1c Synthesis of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene-1,3,3

tricarbonitrile (3)

Scheme 3.3: Synthesis of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene-1,3,3-

tricarbonitrile

Procedure:

A mixture of cyclohexanone (0.98 g, 0.01mol) with benzaldehyde (1.08 ml, 0.01mol),

malononitrile (0.66 g, 0.01mol) and ammonium acetate (1.15 g, 0.015mol) in ethanol (20 ml)

was refluxed for 1 h. The reaction mixture was then stirred overnight at room temperature

and the obtained solid was recrystallized from ethanol to obtain the pure product. However,

in an attempt to synthesize analogue of 1 by replacing benzaldehyde for acetaldehyde in the

same method, the unexpected formation of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-

naphthalene-1,3,3-tricarbonitrile takes place instead of 2-amino-4-phenyl-5,6,7,8-

tetrahydroquinoline-3-carbonitrile

48

X-Ray Structure

Figure 3.2: ORTEP diagram of 3 drawn at 50% probability of thermal ellipsoids

Yield: 62%

Appearance: yellow amorphous solid

m.p: 253ºC

1HNMR (CDCl3, 400MHz): δ: 1.39-1.80 (m, 4H, H5, H6), 2.25-2.34 (m, 2H,

H7), 2.92-2.95 (m, 1H, 4a-H), 4.02 (s, 1H, H8),

4.5 (d,3

J = 12.3 Hz, H4), 4.98 (s, 2H, NH2),

7.18-7.45 (m, 4H, ArH).

Ms m/z: 300(M+)

49

3.5 Synthesis of hexahydroquinoline-3-carbonitrile (4)

Scheme 3.4: Synthesis of 2-amino hexahydroquinoline-3-carbonitrile

Procedure

Method A: By conventional heating

To a stirred mixture of 1,3-cyclohexanedione (1mmol, 1.12g) and malononitrile (1 mmol,

0.66g) and p-TSA (10 mol%, 0.22g) in ethanol (20ml), benzaldehyde (1 mmol, 0.127ml) and

ammonium acetate (1.5 mmol, 0.077g) were added at room temperature. The reaction

mixture was heated at reflux temperature and by TLC monitoring the completion of the

reaction could be controlled. After 2-3 h the solid precipitate was collected, filtered and

recrystallized from ethanol. Column chromatography over silica gel using 30% EtOAc in

hexane as eluent gave the pure polyhydroquinoline.

Method B: By Ultraviolet radiation

A mixture of aryl aldehyde (1mmol), 1,3-cyclohexanedione (1mmol), malanonitrile (1mmol)

and ammonium acetate (1mmol) was added to p-TSA (10 mol%) and the reaction mixture

was stirred at room temperature and irradiated by ultraviolet light (λ = 254 nm) for 1–5min

(completion of the reactions was monitored by TLC). The ultraviolet radiation was operated

in one-second cycles. After the completion of reaction, the reaction mixture was diluted with

ethyl alcohol. The residue was filtered hot and kept at room temperature and the resulting

crystalline product was collected by filtration. The product formed was recrystallized from

ethanol.

50

3.5.1 Synthesis of 2-amino-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile

(4)

Yield: 95%

Appearance: white solid

m.p: 245˚C

IR (KBr): 3424, 3318, 3148, 2214, 1645, 1687 cm-1

1H-NMR (CD3OD, 400 MHz): δ: 2.10-2.20 (m, 2H, CH2), 2.40-2.48 (m, 2H,

CH2), 2.7 (m, 2H, CH2), 4.43 (s, 1H, CH), 6.97

(s, 2H, NH2), 7.10-7.20 (m, 4H, 3ArH, NH),

7.29 (t, J=7.0 Hz, 2H, 2ArH)

13C NMR: 22.3, 29.7, 36.7, 38.9, 58.5, 113.0, 120.0, 125.8,

127.6, 128.0, 144.0, 152.6, 165.0, 197.8

MS m/z: 266.08 [M+ H+]

3.5.2 Synthesis of 2-amino-5-oxo-4-p-tolyl-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile

(4a)

Yield: 89%

Appearance: yellow

m.p: 227˚C

51

IR (KBr): 3424, 3318, 3248, 2210, 1695, 1620, 1490 cm-1

1H-NMR (DMSO-d6, 400 MHz): δ: 1.90-2.00 (m, 2H, CH2), 2.10 (s, 3H, CH3),

2.30-2.35 (m, 2H, CH2 ), 2.7 (m, 2H, CH2), 4.10

(s, 1H, CH), 5.75 (s, 1H, NH), 6.90 (s, 2H,

NH2), 7.00 (m, 4H, 4ArH).

13C NMR (CDCl3, 100 MHz): 20.18, 26.80, 36.7, 39.43, 58.5, 113.0, 120.0,

114.2, 127.4, 129.2, 135.95, 143.0, 142.24,

158.77, 196.9

MS m/z: 280.12[M+ H+]

3.5.3 Synthesis of 2-amino-4-(4-chlorophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-

carbonitrile (4b)

Yield:

Appearance:

m.p:

IR (KBr):

91%

yellow

252˚C

3430, 3320, 3222, 2190, 1697, 1614, 1500 cm-1

1H-NMR (DMSO-d6, 400 MHZ): δ: 1.30-1.32 (t, J=7.0 Hz 2H, CH2 ), 2.0-2.2 (m,

2H, CH2), 2.40-2.42 (m, 2H, CH2), 4.30 (s, 1H,

CH), 5.8 (s, 1H, NH), 7.1 (s, 2H, NH2), 7.25 (d,

J=8.5Hz, 2H, ArH), 7.40 (d, J=8.5Hz, 2H, ArH)

MS m/z: 300.09 [M+ H+]

52

3.5.4 Synthesis of 2-amino-4-(4-hydroxyphenyl)-5-oxo-1,4,5,6,7,8- hexahydroquinoline-

3-carbonitrile (4c)

Yield: 92%

Appearance: light yellow

m.p: 265˚C

1H-NMR (DMSO-d6, 400 MHZ): δ: 1.90-2.40 (m, 6H, 3CH2), 4.10 (s, 1H, CH),

5.75 (s, 2H, NH2), 6.67 (d, J=8.5Hz, 2H, ArH),

6.97 (d, J= 8.5Hz, 2H, ArH), 9.43 (s, 1H, OH)

13C NMR (DMSO-d6, 100MHz): δ: 20.0, 27.8, 34.7, 38.43, 60.0, 113.0, 116.0,

118.0, 121.4, 128.2, 136.0, 155.0, 158.24, 165.0,

198.0

MS m/z: 282.10[M+ H+]

3.5.5 Synthesis of 2-amino-5-oxo-m-tolyl-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile

(4d)

Yield: 87%

Appearance: white

m.p: 245˚C

IR (KBr): 3420, 3300, 3250, 2200, 1700, 1628, 1480 cm-1

53

1H-NMR (DMS-d6, 400 MHz): δ: 0.9 (t, J=6.2Hz, 2H, CH2), 2.1 (s, 3H, CH3),

2.40 (m, 2H, CH2), 4.2 (t, J=6.2 Hz, 2H, CH2),

3.95 (s, 1H, CH), 6.70 (s, 2H, NH2), 6.80-7.00

(m, 4H, ArH)

13C NMR (DMSO-d6, 100 MHz): δ: 19.0, 26.8, 35.7, 47.0, 58.5, 71.0, 108.2,

115.0, 126.0, 128.0, 130.2, 137.95, 141.0, 158.0,

197.0

MS m/z: 280.12[M+ H+]

3.5.6 Synthesis of 2-amino-4-(3-chlorophenyl)-5-oxo-1,5,6,7,8-hexahydroquinoline-3-

carbonitrile (4e)

Yield: 90%

Appearance: Dull white amorphous solid

m.p: 251˚C

1H-NMR (DMSO-d6, 400 MHZ): δ: 1.00 (t, 2H, J=6.2Hz, CH2), 2.40 (m, 2H,

CH2), 2.52 (m, 2H, CH2), 4.10 (s, 1H, CH), 4.40

(s, 1H, NH), 7.00 (s, 2H, NH2), 7.20-7.35 (m,

4H, ArH)

MS m/z: 300.07[M+ H+]

54

3.5.7 Synthesis of 2-amino-4-(4-nitrophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-

carbonitrile (4f)

Yield: 96%

Appearance: yellow color

m.p: 241˚C

1H-NMR (DMSO-d6, 400 MHz): δ: 1.96- 2.00 (m, 2H, CH2), 2.30-2.42 (m, 2H,

CH2), 2.60-2.70 (m, 2H, CH2),4.42 (s, 1H, CH),

6.50 (s, 1H, NH), 7.30 (s, 2H, NH2), 7.5 (d, J=8.6

Hz, 2H, ArH), 8.20 (d, J=8.6Hz, 2H, ArH)

13C NMR: δ: 22.0, 24.8, 38.0, 39.3, 58.5, 110.5, 115.0,

124.0, 128.0, 137.9, 149.5, 150.0, 159.0, 198.9

MS m/z: 311.09[M+ H+]

3.6.1 Synthesis of hexahydroquinoline-3-carboxylate by solvent free grinding

Scheme 3.5: Synthesis of hexahydroquinoline 5 by solvent free grinding

Procedure: Method A: By Simple Grinding

A mixture of benzaldehyde (1 mmol, 0.127ml), 1, 3-cyclohexanedione (1mmol, 1.12g), ethyl

acetoacetate (1mmol, 0.127ml) and ammonium acetate (1.5 mmol, 0.077g) was thoroughly

55

mixed in a mortar and pestle followed by grinding until the reaction was completed as

monitored by TLC within 15-20 min. The product obtained was washed with water to remove

any unreacted ammonium acetate and then air dried. The product was re-crystallized from

ethyl alcohol. The product was purified by column chromatography.

3.6.2 Synthesis of hexahydroquinoline-3-carboxylate by using P-TSA as catalyst

Scheme 3.6: Synthesis of hexahydroquinoline-3-carboxylate by using p-TSA as catalyst

Method B: By using P-TSA as catalyst

To a stirred mixture of 1,3-cyclohexanedione (1mmol, 1.12g) and ethyl acetoacetate (1

mmol, 0.127ml) and p-TSA (10 mol%, 0.22g) in ethanol (20ml), benzaldehyde (1 mmol,

0.127ml) and ammonium acetate (1.5 mmol, 0.077g) were added at room temperature. The

reaction mixture was refluxed and the completion of the reaction was monitored by TLC and

then stirred at room temperature for 2-3 h. The resulting solid precipitate was filtered and

recrystallized with ethanol and then subjected to column chromatography over silica gel

using 30% EtOAc in hexane as eluent to obtain the pure polyhydroquinoline.

Method C: By using Ultraviolet radiation

A mixture of aryl aldehyde (1mmol), 1,3-cyclohexanedione (1mmol), ethyl acetoacetate

(1mmol) and ammonium acetate (1mmol) was added to P-TSA (10 mol%), and the reaction

mixture was stirred at room temperature and irradiated by ultraviolet light (λ = 254 nm ) for

1–5min (completion of the reactions was monitored by TLC). The ultraviolet radiation was

operated in one-second cycles. After the completion of reaction, the reaction mixture was

diluted with ethyl alcohol. The residue was filtered and kept at room temperature, and the

resulting crystalline product was collected by filtration. The product formed was

recrystallized from ethanol.

56

Scheme 3.7: Synthesis of hexahydroquinoline-3-carboxylate assisted by Ultraviolet radiation

3.6.2a Synthesis of ethyl 2-methyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-

carboxylate (5)

Yield: 80 %

Appearance: dull white colour

m.p: 241˚C

IR (KBr): 3292, 3210, 1700, 1628, 1602 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 1.12 (t, J=6.9 Hz, 3H, CH3), 1.70-2.00 (m,

2H, CH2), 2.10 (s, 3H,CH3 ), 2.30-2.40 (m, 4H,

2CH2), 4.00 (q, J=7.0 Hz, 2H, CH2), 5.00 (s,

1H, CH), 5.7 (s, 1H, NH), 7.00-7.30 (m, 5H, Ar-

H)

MS m/z: 311.11(M+)

57

3.6.2b Synthesis of ethyl 2-methyl-5-oxo-4-p-tolyl-1,4,5,6,7,8-hexahydroquinoline-3-

carboxylate (5a)

Yield: 87%

Appearance: White amorphous solid

m.p: 242˚C

IR (KBr): 3298, 3200, 3078, 1717, 1629, 1609 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 1.20 (t, J=7.2 Hz, 3H, CH3), 1.50 (s, 3H,

CH3), 1.80-2.00 (m, 2H, CH2), 2.25 (s, 3H,

CH3), 2.32- 2.42 (m, 4H, 2CH2), 4.10 (q, J=7.0

Hz, 2H, CH2), 5.10 (s, 1H, CH), 6.0 (s, 1H, NH),

7.00 (d, J=8.0Hz, 2H, Ar-H), 7.10 (d, J=8.0Hz,

2H, Ar-H )

MS m/z: 325.17(M+)

3.6.2c Synthesis of ethyl 4-(4-chlorophenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline -3-carboxylate (5b)

Yield: 80%

Appearance: dull white amorphous material

58

IR (KBr): 3292, 3208, 3079, 1700, 1628, 1606 cm-1

m.p: 235˚C

1H-NMR (CDCl3, 400 MHz): δ: 1.12 (t, J=7.2 Hz, 3H, CH3), 1.80-2.00 (m,

2H, CH2), 2.20 (s, 3H, CH3), 2.32-2.40 (m, 4H,

2CH2), 4.00 (q, J=7.1 Hz, 2H, CH2), 5.00 (s, 1H,

CH), 5.8 (s, 1H, NH), 7.10 (d, J=8.8Hz, 2H, Ar-

H), 7.20 (d, J=8.8Hz, 2H, Ar-H)

MS m/z: 346.09(M+)

3.6.2d Synthesis of ethyl 4-(4-hydroxyphenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5c)

Yield: 95%

Appearance: dark green colour

m.p: 234˚C

IR (KBr): 390, 3201, 2965, 1698, 1613 cm-1

1H-NMR (DMSO-d6, 400 MHz): δ:1.15 (t, J=7.2Hz, 3H,CH3), 1.56 (s, 3H, CH3),

1.70-2.00 (m, 6H, CH2), 4.00 (q, J=7.0Hz, 2H,

CH2), 4.90 (s, 1H, CH), 6.8-6.91 (m, 4H , Ar-H),

8.34 (s, H, NH), 9.70 (s, H, OH).

MS m/z: 327.14(M+)

59

3.5.3e Synthesis of ethyl 2-methyl-5-oxo-4-m-tolyl-1,4,5,6,7,8-hexahydroquinoline-3-

carboxylate (5d)

Yield: 83%

Appearance: yellow solid

m.p: 245˚C

1H-NMR (CDCl3, 400 MHz): δ:1.11 (t, J=7.1 Hz, 3H, CH3), 1.70-1.96 (m,

4H, 2CH2), 2.20 (s, 3H, CH3), 2.30 (s, 3H, CH3),

2.50 (t, J= 6.2Hz, 2H, CH2), 4.00 (q, J= 7.1 Hz,

2H, CH2), 4.89 (s, 1H, CH), 6.9-7.10 (m, 4H,

Ar-H), 9.1 (s, 1H, NH)

MS m/z: 325.14(M+)

3.6.2f Synthesis of ethyl 4-(3-chloro phenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5e)

Yield: 77%

Appearance: Yellow solid

m.p: 202˚C

1H-NMR (DMSO-d6, 400 MHz): δ: 1.21 (t, J=7.0 Hz, 3H, CH3), 1.78-1.98 (m,

4H, 2CH2), 2.19-2.29 (m, 2H, CH2), 2.32 (s, 3H,

60

CH3), 4.02 (q, J= 7.0 Hz, 2H, CH2), 5.00 (s, 1H,

CH), 7.49 (d, J= 8.0Hz, 2H, Ar-H), 8.20 (d,

J=8.0Hz, 2H, Ar-H), 9.6 (s, 1H, NH)

MS m/z: 345.11(M+)

3.6.2g Synthesis of ethyl 2-methyl-4-(4-nitrophenyl)-5-oxo-4-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5f)

Yield: 83%

Appearance: Bright yellow colour

m.p: 205˚C

IR (KBr): 3293, 3209, 3080, 1708, 1620, 1175 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 1.17 (t, J=6.9Hz, 3H, CH3), 1.85-2.00 (m, 2H,

CH2), 2.10 (s, 3H, CH3), 2.29-2.32 (m, 4H, 2CH2),

4.00 (q, J=6.8 Hz, 2H, CH2), 5.00 (s, 1H, CH),

7.20-7.22 (d, J=8.0Hz, 2H, Ar-H), 7.25-7.30 (d,

J=8.0Hz, 2H, Ar-H), 9.6 (s, 1H, NH)

MS m/z: 356.14(M+)

61

3.6.2h Synthesis of ethyl 4-(2-bromophenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5g)

Yield: 83%

Appearance: yellow solid

m.p: above 300˚C

1H-NMR (DMSO-d6, 400 MHz): δ:1.25 (t, J=7.0 Hz, 3H, CH3), 2.10 (s, 3H, CH3)

2.20-2.32 (m, 4H, 2CH2), 3.80 (t, J= 6.0Hz,

2H, CH2), 4.03 (q, J=7.0 Hz, 2H, CH2), 5.10 (s,

1H, CH), 6.90-7.40 (m, 4H, Ar-H), 9.49 (s, 1H,

NH)

MS m/z: 390.27(M+)

3.6.2i Synthesis of ethyl 4-(4-fluorophenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5h)

Yield: 85%

Appearance: Yellow solid

m.p: 244˚C

62

IR (KBr): 3282, 3190, 3077, 1690, 1600, 1206 cm-1

1H-NMR (DMSO-d6, 400 MHz): δ: 1.24 (t, J=7.2 Hz, 3H, CH3), 1.60-1.78 (m,

4H, 2CH2), 1.90-2.03 (m, 2H,CH2), 2.40 (s, 3H,

CH3), 4.02 (q, J=7.0 Hz, 2H, CH2), 4.98 (s, 1H,

CH), 7.05-7.15 (m, 2H, Ar-H), 7.30-7.34 (m,

2H, Ar-H), 9.3 (s, 1H, NH)

MS m/z: 330.15[M+ H+]

3.6.2j Synthesis of ethyl 4-(4-bromophenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5i)

Yield: 85%

Appearance: yellow solid

m.p: 254˚C

1H-NMR (DMSO-d6, 400 MHz): δ: 1.70 (t, J=7.0 Hz, 3H, CH3), 1.85-2.00 (m,

2H, CH2), 2.20-2.32 (m, 4H, CH2 ), 4.12 (q,

J=6.8 Hz, 2H, CH2), 4.85 (s, 1H, CH), 4.90 (s,

3H, CH3), 7.1 (d, J=8.0Hz, 2H, Ar-H), 7.4 (d,

J=8.0Hz, 2H, Ar-H), 9.5 (s, 1H, NH)

MS m/z: 390.27(M+)

63

3.6.2k Synthesis of ethyl 4-(4-methoxyphenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5j)

Yield: 76%

Appearance: yellow colour

m.p: 195˚C

IR (KBr): 3392, 3290, 3078, 1708, 1618 cm-1

1H-NMR (DMSO-d6, 400 MHz): δ: 1.20 (t, J= 6.8 Hz, 3H, CH3), 1.85-2.00 (m,

2H, CH2), 2.10-2.23 (m, 4H, 2CH2), 2.26 (s, 3H,

CH3) 3.65 (s, 3H, OCH3) 4.00 (q, J=7.0 Hz, 2H,

CH2), 4.87 (s, 1H, CH), 7.10 (d, J=8.5, 2H, Ar-

H), 7.20 (d, J= 8.5, 2H, Ar-H), 9.41 (s, 1H, NH)

MS m/z: 364.13(M +Na+)

3.6.2l Synthesis of ethyl 2-methyl-4-(4-(methylsulfonyl)phenyl)-5-oxo-4-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5k)

Yield: 69%

Appearance: light yellow solid

64

m.p: 251˚C

1H-NMR(CDCl3, 400 MHz): δ: 1.19 (t, J= 7.0 Hz, 3H, CH3), 1.71-1.80 (m,

6H, 3CH2), 2.00 (s, 3H, CH3), 2.30 (s, 3H, CH3)

4.00 (q, J=7.0 Hz, 2H, CH2), 4.70 (s, 1H, CH),

4.90 (s, 1H, NH), 7.10 (d, J 8.0, 2H, Ar-H), 7.50

(d, J=8.0, 2H, Ar-H)

MS m/z: 389.12(M+)

3.6.2m Synthesis of ethyl 4-(3-fluorophenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5l)

Yield: 82%

Appearance: light yellow solid

m.p: 260˚C

1H-NMR (CDCl3, 400 MHz): δ: 1.20 (t, J=7.0 Hz, 3H, CH3), 1.90-2.00 (m,

4H, 2CH2), 2.16 (s, 3H, CH3), 2.20-2.29 (m, 2H,

CH2), 3.50 (t, J=6.2Hz, 2H, CH2), 4.00 (q,

J=6.9 Hz, 2H, CH2), 5.00 (s, 1H, CH), 5.7(s, 1H,

NH), 6.70-7.10 (m, 4H, Ar-H)

MS m/z: 330.15[M+ H+]

65

3.6.3 Synthesis of hexahydroquinoline-3-carboxylate by using guanidine HCl as

catalyst

Scheme 3.8: Synthesis of hexahydroquinoline-3-carboxylate by using guanidine HCl as

catalyst

Method D: Use of guanidine HCl as catalyst

A mixture of dimedone (0.01mol, 1.4g), ammonium acetate (0.01mol, 0.77g), ethyl

acetoacetate (0.01mol, 1.27cm3), benzaldehyde (0.01mol, 1.08cm3) and salts of guanidine

(0.0015 mol, 0.143g) were taken in catalytic amounts in 20 ml ethanol. The reaction mixture

was refluxed and monitored by TLC (ethyl acetate: n-hexane) and stirred after completion of

the reaction at room temperature. The precipitate was filtered and the pure product was

obtained by recrystallization with ethanol.

3.6.3a Synthesis of 2,7,7-trimethyl-5-oxo-4-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-

carboxylic acid ethyl ester (6)

Yield: 96%

Appearance: white amorphous solid

m.p: 203˚C

IR (KBr): 3290, 3070, 2960, 1701, 1613 cm-1

66

1H-NMR (CDCl3, 400 MHz): δ: 0.90 (s, 3H, CH3), 1.02 (s, 3H, CH3), 1.22 (t,

J=7.0 Hz, 3H, CH3), 1.50 (s, 3H, CH3), 2.10-

2.28 (m, 4H, 2CH2), 4.00 (q, J=7.1 Hz, 2H,

CH2), 4.98 (s,1H, CH), 5.60 (s, 1H, NH), 7.00-

7.30 (m, 5H, Ar-H)

13C NMR (CDCl3, 100 MHz): δ: 14.9, 19.3, 27.4, 29.7, 33.1, 36.5, 40.2, 51.1,

59.7, 104.9, 111.0, 126.3, 127.3, 128.5, 145.8,

148.7, 150.8, 167.9 and 196.0

MS m/z: 339.17 [M+].

HR-MS: 339.1669 (M+H+)

X-Ray Structure

Figure 3.3: ORTEP diagram of compound 6

67

3 .7 Preparation of substituted 2-chloro-3-formyl quinolines

3.7.1 N-Acetylation of substituted anilines

To 0.1 mol of the substituted aniline, 0.2 mol of glacial acetic acid was added in a 250 ml

flask. Catalytic amounts of ortho-phosphoric acid were added to this mixture and the mixture

was refluxed for 5-6 hrs. After the completion of the reaction as monitored by TLC, the

mixture was poured in ice water and stirred well. The product precipitated immediely. The

precipitates were filtered and washed with cold water. The pure product was obtained by

recrystallization from boiling water.

3.7.2 Synthesis of 2-chloro-3-formylquinolines (7-9)

Scheme 3.9: Synthesis of 2-chloro-3-formylquinolines

The Vilsmeier reagent was prepared by adding POCl3 (107.4 g, 64.4 ml, 0.70 mol) dropwise

to DMF (18.26 g, 19.2 ml, 0.25 mol) at 0 ºC with constant stirring. To this solution was

added the acetanilide (0.10mol). The resulting mixture was stirred (15 min) at room

temperature. Then this mixture was refluxed at 70-80ºC for the time period as mentioned.

After the completion of the reaction by TLC monitoring, the mixture was poured in to ice

water (500 ml) and stirred vigorously (30 min) at 0-10°C. The 2-chloro-3-quinoline

carbaldehyde precipitated. It was filtered, washed with water (200 ml), dried and

recrystallized from ethyl acetate.

68

3.7.3 Procedure for the synthesis of chalcone from 2-chloro-quinoline 3-carbaldehyde

Scheme 3.10: Synthesis of quinolinyl chalcone by using NaOH

A mixture of quinolone carbaldehyde 7, 8 or 9 (10 mmol) and an aromatic or heteroaromatic

ketone (10 mmol) were taken in methanol (50 ml) and stirred at room temperature, followed

by dropwise addition of aq. NaOH (4 ml, 40%). The stirring was continued for 24 h and the

reaction mixture was then kept at 0°C (24 h). Subsequently, it was poured into water (200

ml). The precipitates were collected by filtration, washed with cold water followed by cold

MeOH. The resulting chalcones were recrystallized from CHCl3.

3.7.4 Method for the synthesis of quinolinyl chalcones

3.7.4a Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-furan-2-yl-propenone (7a)

Yield: 96%

Appearance: brown solid

m.p: 164 ˚C

IR (KBr): 1655, 1594 cm-1

1H-NMR (DMSO, 400 MHz): δ: 3.85 (3H, s, OCH3), 6.70 (d,1H, Ar-H, J=

3.0Hz), 7.30 (d, 1H, J=3.2 Hz, Ar-H), 7.34 (d,

1H, Ar-H, J=9.2Hz), 7.40 (d, 1H, J=15.1 Hz,

Hα), 7.49 (s, 1H, Ar-H), 7.81 (d, 1H, Ar-H,

J=9.2 Hz), 7.98 (d, 1H, Hβ, J=15.9Hz), 8.34

(d,1H, Ar-H, J=3.8 Hz), 8.45 (s, 1H, Ar-H)

69

MS m/z: 313(M+)

3.7.4b Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-(2,5-dimethyl-furan-2-yl)-

propenone (7b)

Yield: 70%

Appearance: yellow solid

m.p: 121˚C

IR (KBr): 1650, 1590 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 2.25 (s, 3H, CH3), 2.60 (s, 3H, CH3), 3.90

(3H, s, OCH3), 6.34 (s, 1H, Ar-H), 7.05 (d,

J=15.9Hz, 1H, Hα), 7.20 (d, 1H, Ar-H,

J=2.7Hz), 7.45 (d, 1H, Ar-H, J=9.2Hz), 7.89

(d, 1H, Ar-H, J=9.2Hz), 8.12 (d,1H, Hβ,

J=15.9Hz), 8.30 (s, 1H, Ar-H).

MS m/z: 341(M+)

3.7.4c Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-(5-chloro-thiophen-2-yl)-

propenone (7c)

Yield: 93%

Appearance: yellowish grey solid

m.p: 179˚C

IR (KBr): 1660, 1600 cm-1

70

1H-NMR (CDCl3, 400 MHz): δ: 3.85 (3H, s, OCH3), 6.35 (1H, d, Ar-H, J=

4.1Hz), 6.50 (1H, d, Ar-H, J=2.6Hz), 6.70 (1H, d,

Ar-H, J=9.2Hz), 6.89 (1H, d, Hα, J=15.7Hz), 7.49

(1H, d, Ar-H, J=4.1Hz), 7.50 (1H, d, Ar-H,

J=9.2Hz), 7.60 (1H, d, Hβ, J=15.7Hz), 8.00 (1H, s,

Ar-H)

MS m/z: 363(M+)

3.7.4d Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-(1H-pyrrol-2-yl)-propenone

(7d)

Yield: 91%

Appearance: Yellow solid

m.p: 170˚C

IR (KBr): 3215, 1650, 1590 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 3.90 (3H, s, OCH3), 6.34 (d, 1H, Ar-H, J=

3.0Hz), 7.04 (d, Ar-H, 1H, J=3.0Hz), 7.1 (d, 1H ,

J=3.9Hz, Ar-H), 7.30 (d, 1H, Hα, J=15.0Hz), 7.40

(d, 1H, Ar-H, J=8.0 Hz), 7.49 (d, 1H, Ar-H,

J=2.9Hz), 7.85 (d,1H, Ar-H, J=8.0Hz), 8.02 (d, 1H,

Hβ, J=15.0Hz), 8.88 (s, 1H, Ar-H), 9.5 (s, 1H, NH)

MS m/z: 312(M+)

71

3.7.4e Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-pyridine-2-yl-propenone

(7e)

Yield: 70%

Appearance: dull white

m.p: 129˚C

1H-NMR (CDCl3, 400 MHz): δ: 3.81 (s, 3H, OCH3), 6.90 (s, 1H, Ar-H), 7.20

(d, 1H, Ar-H, J=7.1Hz), 7.40 (d, 1H, Ar-H,

J=7.1Hz), 7.40 (d, 1H, Hα, J=15.1Hz), 7.63-

7.85 (m, 3H, Ar-H), 7.90 (d, 1H, Hβ, J=15.1Hz),

8.00 (s, 1H, Ar-H), 8.60 (d,1H, Ar-H, J=7.0Hz)

MS m/z: 324(M+)

3.7.4f Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-(2-methoxy-phenyl)-

propenone (7f)

Yield: 72%

Appearance: yellow

m.p: 142˚C

1H-NMR (CDCl3, 300 MHz): δ: 3.73 (s, 6H, 2OCH3), 6.96 (d, 1H, ArH, J=

2.9Hz), 6.98 (s, 1H, Ar-H), 7.20 (t, , J=7.1Hz 1H,

Ar-H), 7.31 (d 1H, Ar-H), 7.35 (t, , J=7.1Hz 1H,

Ar-H), 7.43 (s, 1H, Ar-H), 7.60 (d, 1H, Ar-H), 7.63

(d, 1H, Hα, J=16.2Hz), 7.90 (d, 1H, Hβ, J=16.2Hz),

7.98 (d, 1H, Ar-H, J= 9.0Hz), 8.26 (s, 1H, H4)

72

MS m/z: 353(M+)

3.7.4g Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-(3-methoxy-phenyl)-

propenone (7g)

Yield: 68%

Appearance: deep yellow

m.p: 141˚C

1H-NMR (CDCl3, 300MHz): δ: 3.83 (s, 6H, 2OCH3), 7.05 (d, 1H, Ar-H,

J=2.7Hz), 7.19 (s, 1H, Ar-H), 7.32-7.55 (m, 5H,

Ar-H, Hα), 7.4 (s, 1H, Ar-H), 7.85(d, 1H, Ar-H,

J= 9.0Hz), 8.0 (d, 1H, Hβ, J=16.2Hz), 8.31 (s,

1H, Ar-H)

MS m/z: 353(M+)

3.7.4h Synthesis of 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-naphthalen-1-yl-propenone

(7h)

Yield: 90%

Appearance: yellow solid

m.p: 161˚C

IR (KBr): 1660, 1592cm-1

1H-NMR (CDCl3, 400 MHz): δ: 3.92 (3H, s, OCH3), 7.05 (1H, d, Ar-H,

J=2.7Hz), 7.37 (1H, d, Hα, J=15.9 Hz), 7.37

(1H, d, Ar-H, J=9.2Hz), 7.53-7.61 (3H, m, Ar-

H), 7.83-7.90 (3H, m, Ar-H), 8.00 (1H, d, Ar-H,

J=9.2Hz), 8.10 (1H, d, Hβ, J=16.1Hz), 8.35 (1H,

s, Ar-H), 8.40 (1H, d, Ar-H, J=8.2Hz)

73

MS m/z: 373(M+)

3.7.4i Synthesis of 1-benzofuran-2-yl-3-(2-chloro-6-methoxy-quinolin-3-yl)-propenone

(7i)

Yield: 63%

Appearance: Off white solid

m.p: 160˚C

IR (KBr): 1661, 1590 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 3.87 (s, 3H, OCH3), 6.80 (1H, d, Ar-H,

J=2.8Hz), 7.10 (t, 1H, Ar-H), 7.30 (d, 1H, Hα,

J=15.9Hz), 7.40-7.51 (4H, m, Ar-H), 7.65 (1H,

d, Ar-H, J=9.2Hz), 7.80 (1H, d, Ar-H, J=9.2

Hz), 8.06 (1H, d, Hβ, J=15.9 Hz), 8.20 (1H, s,

Ar-H).

MS m/z: 363(M+)

3.7.5j Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-furan-2-yl-propenone (8a)

Yield: 71%

Appearance: light yellow

m.p: 152 ˚C

IR (KBr): 1668, 1596 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 2.34 (3H, s, CH3), 6.20 (dd, 1H, Ar-H ,

J=3.2Hz), 7.20 (d, 1H, J=3.2 Hz, Ar-H), 7.35

74

(dd, 1H, Ar-H, J=9.0Hz), 7.39 (d, 1H, J=15.0

Hz, Hα), 7.50 (s,1H, Ar-H), 7.80 (d, 1H, Ar-H,

J=9.0 Hz), 7.96 (d, 1H, Hβ, J=15.9Hz), 8.34

(d,1H, Ar-H, J=3.9 Hz), 8.40 (s, 1H, Ar-H)

MS m/z: 297(M+)

3.7.5k Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-(2,5-dimethyl-furan-2-yl)-

propenone (8b)

Yield: 90 %

Appearance: yellow solid

m.p: 146 ˚C

IR (KBr): 1645, 1598 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 2.30-2.62 (s, 9H, 3CH3), 6.37 (s, 1H, Ar-H),

7.10 (d, J=15.7Hz, 1H, Hα), 7.23 (d,1H, Ar-H,

J=2.9Hz), 7.48 (d,1H, Ar-H, J=9.0Hz), 7.90 (d,

1H, Ar-H, J=9.0Hz), 8.17 (d, 1H, Hβ,

J=15.7Hz), 8.33 (s, 1H, Ar-H)

MS m/z: 325(M+)

3.7.5l Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-(5-chloro-thiophen-2-yl)-

propenone (3c)

Yield: 90%

Appearance: yellow solid

75

m.p: 180˚C

IR (KBr): 1656, 1596 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 1.50 (s, 3H, CH3), 6.37 (1H, d, J=4.0Hz,

Ar-H), 6.52 (1H, d, Ar-H, J=2.6Hz), 6.75(1H,

dd, Ar-H, J=9.0Hz), 6.93 (1H, d, Hα,

J=15.9Hz), 7.50 (1H, d, Ar-H, J=4.1Hz), 7.55

(1H, d, Ar-H, J=9.0Hz), 7.63 (1H, d, Hβ,

J=15.9Hz), 8.03 (1H, s, Ar-H)

MS m/z: 347(M+)

3.7.5m Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-(1H-pyrrol-2-yl)-propenone

(8d)

Yield: 70%

Appearance: yellow solid

m.p: 214 ˚C

IR (KBr): 3217, 1652, 1592 cm-1

1H-NMR (CDCl3, 400MHz): δ: 2.5 (s, 3H, CH3), 6.30 (d, 1H, Ar-H,

J=3.0Hz), 7.09 (d, Ar-H, 1H, J=3.0Hz), 7.20

(d, 1H, Ar-H, J=3.9Hz), 7.36 (d, 1H, Hα,

J=15.2Hz), 7.42 (d, 1H, Ar-H, J=8.2 Hz), 7.56

(d,1H, Ar-H, J=2.9Hz), 7.89 (d, 1H, Ar-H,

J=8.2Hz), 8.00 (d, 1H, Hβ, J=15.0Hz), 8.89 (s,

1H, Ar-HS), 9.6 (s, 1H, NH)

MS m/z: 295(M+)

76

3.7.5n Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-pyridine-2-yl-propenone (8e)

Yield: 68%

Appearance: dull white

m.p: 129˚C

1H-NMR (CDCl3, 400 MHz): δ: 2.30 (s, 3H,CH3), 5.90 (s, 1H, Ar-H), 7.22 (d,

1H, Ar-H, J=7.0Hz), 7.45 (d, 1H, Ar-H,

J=7.0Hz), 7.50 (d, 1H, Hα, J=15.0Hz), 7.63-7.85

(m, 3H, Ar-H), 7.90 (d, 1H, Hβ, J=15.0Hz),

8.00 (s, 1H, Ar-H), 8.60 (d, 1H, Ar-H, J=7.0Hz)

MS m/z: 308(M+)

3.7.5o Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-(2-methoxy-phenyl)-

propenone (8f)

Yield: 70%

Appearance: yellow solid

m.p: 137˚C

1H-NMR (CDCl3, 300 MHz): δ: 2.34 (s, 3H, CH3), 3.70 (s, 3H, OCH3), 6.98

(d, 1H, ArH, J=2.7Hz), 7.00 (s, 1H, Ar-H), 7.25

(t, 1H, Ar-H), 7.35(d 1H, Ar-H), 7.40 (t, 1H,Ar-

H),7.43 (s, 1H, Ar-H),7.55 (d, 1H, Ar-H), 7.63

(d, 1H, Hα, J=16.2Hz), 7.85 (d, 1H, Hβ,

77

J=16.1Hz), 7.98 (d, 1H, Ar-H, J=9.0Hz), 8.26

(s, 1H, Ar-H)

MS m/z: 337(M+)

3.7.5p Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-(2-methoxy-phenyl)-propenone

(8g)

Yield: 65%

Appearance: light yellow

m.p: 140˚C

1H-NMR (DMSO-d6, 300 MHz): δ: 2.35 (s, 3H, CH3), 3.74 (s, 3H, OCH3),

7.05 (d, 1H, ArH, J=2.8Hz), 7.20 (s, 1H, Ar-

H), 7.30-7.55 (m, 5H, ArH, Hα), 7.4 (s, 1H,

Ar-H), 7.89 (d, 1H, Ar-H, J= 9.0Hz), 8.0 (d,

1H, Hβ, J=16.0Hz), 8.37 (s, 1H, Ar-H)

MS m/z: 337(M+)

3.7.5q Synthesis of 3-(2-chloro-6-methyl-quinolin-3-yl)-1-naphthalen-1-yl-propenone

(8h)

Yield: 96%

Appearance: Yellow solid

m.p: 138˚C

IR (KBr): 1660, 1585cm-1

78

1H-NMR (CDCl3, 400 MHz): δ: 2.49 (3H, s, CH3), 7.05 (1H, d, Ar-H, J=2.7Hz ),

7.38 (1H, d, Hα, J=16.0 Hz), 7.39 (1H, dd, Ar-H,

J=9.0Hz), 7.53-7.61 (3H, m, Ar-H), 7.87-7.90

(3H, m, Ar-H), 8.00 (1H, d, Ar-H, J=9.0Hz), 8.30

(1H, d, Hβ, J=16.0Hz), 8.35 (1H, s, Ar-H), 8.39

(1H, d, Ar-H, J=8.2Hz)

MS m/z: 357(M+)

3.7.6r Synthesis of 3 - (2-chloro-quinolin-3-yl)-1-furan-2-yl-propenone (9a)

Yield: 65%

Appearance: light yellow

m.p: 125˚C

1H-NMR (CDCl3, 400 MHz): δ: 6.30 (d, 1H, Ar-H), 6.50 (d, 1H, Ar-H), 6.80

(d, 1H, Hα, J=15.7 Hz), 7.25-7.57(m,3H,

ArH),7.58 (d, 1H, Hβ, J=15.8 Hz), 7.72 (d, 1H,

Ar-H) 8.05 (d,1H, Ar-H, J=8.6 Hz), 8.33 (s,1H,

Ar-H)

MS m/z: 283(M+)

3.7.6s Synthesis of 3-(2-chloro-quinolin-3-yl)-1-(2,5-dimethyl-furan-2-yl)-propenone (9b)

Yield: 67%

Appearance: green solid

m.p: 112˚C

79

1H-NMR (CDCl3, 400 MHz): δ: 2.17 (s, 6H, 2CH3), 5.45 (d, 1H, Hα, J=15.9

Hz), 6.00 (s, 1H, Ar-H), 7.45-7.56 (m, 6H,

ArH), 7.60 (1H, d, Hβ, J=15.8 Hz), 7.80 (d, 1H,

Ar-H, J=8.4 Hz), 8.33 (1H, s, Ar-H)

MS m/z: 311(M+)

3.7.6t Synthesis of 3-(2-chloro-quinolin-3-yl)-1-(5-chloro-thiophen-3-yl)-propenone (9c)

Yield: 63%

Appearance: yellow

m.p: 221 ˚C

IR (KBr): 1658, 1593 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 6.67 (d, 1H, Hα, J=15.0 Hz), 6.81 (d, 1H, Ar-

H), 7.22 (d, 1H, Ar-H, J=8.2 Hz), 7.59 (1H, t,

Ar-H), 7.39 (1H, d, Ar-H),7.63 (1H, d, Ar-H)

7.68 (1H, d, Ar-H, J=8.0 Hz), 7.85 (1H, d, Hβ,

J=15.0 Hz), 8.30 (s, 1H, Ar-H)

MS m/z: 332(M+)

3.7.6u Synthesis of 3-(2-chloro-quinolin-3-yl)-1-(1H-pyrrol-2-yl)-propenone (9d)

Yield: 59%

Appearance: yellow solid

m.p: 286˚C

IR (KBr): 3222, 1653, 1589 cm-1

80

1H-NMR (CDCl3,400 MHz): δ: 6.32 (d, 1H, Ar-H), 6.64 (d, 1H, Hα, J=15.0

Hz), 6.98 (s, 1H, Ar-H), 7.20 (d, 1H, H5), 7.33

(d, 1H, Ar-H), 7.40 (d, 1H, Ar-H, J=8.2 Hz),

7.43 (t, 1H, Ar-H), 7.50 (d, 1H, Hβ, J=15.0 Hz),

7.8 (d, 1H, Ar-H, J=8.3Hz), 8.11 (s, 1H, Ar-H),

9.0 (s, 1H, NH)

MS m/z: 282(M+)

2.7.6v Synthesis of 3-(2-chloro-quinolin-3-yl)-1-pyridine-2-yl-propenone (9e)

Yield: 62%

Appearance: yellow

m.p: 171˚C

1H-NMR (CDCl3, 400 MHz): δ: 6.00 (s, 1H, Hα, J=15.2 Hz), 7.22 (d, 1H, Ar-

H, J=8.0 Hz), 7.43(d, 1H, Ar-H), 7.49 (d, 1H,

Hβ, J=15.2 Hz ), 7.68 (t, 1H, Ar-H), 7.70-7.85

(m, 3H, Ar-H), 7.90 (d, 1H, Ar-H, J=8.0 Hz ),

8.10 (s, 1H, Ar-H), 9.10 (d, 1H, Ar-H)

MS m/z: 294(M+)

3.7.6w Synthesis of 3-(2-chloro-quinolin-3-yl)-1-(3-methoxy-phenyl)-propenone (9g)

Yield: 64%

Appearance: light yellow solid

m.p: 138˚C

81

1H-NMR (CDCl3, 300 MHz): δ: 3.73 (s, 3H, OCH3), 6.9 (s, 1H, Ar-H), 7.0 (d,

1H, Hα, J=15.0 Hz), 7.00-7.19 (m, 3H, Ar-

H),7.29 (t, 1H, Ar-H), 7.30 (t, 1H, Ar-H, J=7.9

Hz), 7.40 (s, 1H, Ar-H), 7.49 (d, 1H, Ar-H,

J=7.9 Hz), 7.51 (d, 1H, Hβ, J=15.0 Hz), 8.0 (s,

1H, Ar-H)

MS m/z: 323(M+)

2.7.6x Synthesis of 3-(2-Chloro-quinolin-3-yl)-1-naphthalen-1-yl-propenone (9h)

Yield: 55%

Appearance: yellow

m.p: 165˚C

IR (KBr): 1775, 815 cm-1

1H-NMR (CDCl3, 400 MHz): δ: 7.38 (1H, d, Hα, J=15.0Hz), 7.51-7.90 (5H,

m, Ar-H), 7.80 (1H, d, Ar-H), 7.89 (1H, d, Ar-

H, J=8.0 Hz) ,7.93 (1H, s, Ar-H), 8.02 (1H, d,

Ar-H, J=8.0 Hz), 8.00 (1H, d, Hβ, J=15.0 Hz),

8.56 (1H, s, Ar-H), 8.89 (1H, d, Ar-H,)

MS m/z: 343(M+)

3.8 Protocols for Biological Studies

3.8.1 Antimicrobial assay

Screening of antibacterial activity was performed by standard disc diffusion method (Saeed et

al., 2007). All compounds 4a-4f, 5-5l, 7a-7i, 8a-8h and 9a-9h were screened for antibacterial

activity against Escherichia coli, Bacillus subtilis and Staphylococus aureus using

Ciprofloxazine (1.00 mmol/ml) as standard. DMSO poured disk was used as a negative

control. 20 μl of the test compound was impregnated in to sterile discs (7mm), allowed to dry

82

and was introduced on the upper layer of the seeded microbial plate. Then the plates were

incubated aerobically at 37°C for 24 h and the diameter of zone of inhibition of growth was

measured around each of the antibiotic disks to the nearest millimeter by a ruler.

3.8.2 Antioxidant activity

The antioxidant activities of the compounds 4a-4f, 5-5l, 7a-7i, 8a-8h and 9a-9l were

performed.

3.8.2a DPPH radical scavenging activity

The capacity of compounds to scavenge the “stable” free radical DPPH was monitored

according to the method of (Hatano et al., 1988). Briefly, a solution of DPPH (0.15 mM) in

methanol was prepared. The synthesized compounds were mixed at 100 mg mL-1(0.2 mL)

with the DPPH solution (1.8 mL); the mixture was shaken vigorously, incubated at (37 ̊C/30

min) in the dark (until stable absorption values were obtained). Then the absorbance was

measured at 517 nm against a blank, ascorbic acid and butylated hydroxytoluene (BHT) were

used as standard references. All the tests were performed in triplicate. The scavenging activity

was calculated by using the formula

DPPH inhibition (%) = [1-A1/A0] × 100 (Mothana et al., 2009)

Where

A1=absorbance of sample

A0= absorbance of control

3.8.2b Ferric reducing power assay

The reducing power was determined according to the method (reducing power assay) of

oyaizu (1986). 1.0µg of compound was mixed with 1 ml phosphate buffer (0.2M, pH 6.6) and

1 ml 1 % K3Fe(CN)6, shaken well and incubated at 50 ̊C for 20 min. After incubation, 1 ml

trichloro acetic acid (10%) was added to stop the reaction. It was centrifuged at 3000 rpm for

10 minutes 1.5 ml supernatant, 1.5 ml deionized water and 0.1 ml FeCl3 (0.1%) were mixed

and incubated for 10 min and absorbance was read at 700 nm on spectrophotometer. Distilled

water was used as a blank.

83

CHAPTER 4

RESULTS AND DISSCUSSIONS

The research project “Synthesis and Characterization of Potentially Biologically Active

Derivatives of Polyhydroquinoline and Quinoline Ring Systems” led us to plan many series

of this class of heterocyclic compounds. Firstly, the synthesis of 2-amino-5,6,7,8-

tetrahydroquinoline-3-carbonitrile was carried out without using any external catalyst.

Secondly, a series of 2-amino-5-oxo-hexahydroquinoline-3-carbonitrile (4a-f) were

synthesized. Thirdly, two series of 2-methyl, 5-oxo-4-substituted- phenyl

hexahydroquinoline-3-carboxylate (5a-5l) were prepared by using p-TSA as catalyst and also

by guanidine HCl. To bring novelty to the current work, we focus mainly on the synthesis of

polyhydroqinoline ring systems using UV-irradiation via a Hantzsch type condensation

reaction. Finally, an efficient synthetic approach of the synthesis of chalcone was introduced

7a-7i, 8a-8h and 9a-9h.

4.1 Chemistry of 2-amino 4-substituted phenyl polyhydroquinoline-3-

carbonitrile

4.1.1 Chemistry of 2-amino-4-methyl-5,6,7,8-tetrahydroquinoline-3-carbonitrile (1)

The interest in the synthesis of ortho-amino carbonitriles is due to the wide spectrum of their

pharmaceutical activities and their scope as precursors for the synthesis of novel compounds.

So, in this part of the study, we had decided to investigate the reactions of cyclohexanone and

malononitrile with different substituted aldehydes and ammonium acetate in ethanol without

using any catalyst. This reaction resulted in the production of 2-amino-4-methyl quinoline-3-

carbonitrile derivatives. As a control experiment, cyclohexanone and acetaldehyde were

reacted with malononitrile in the prescence of ammonium acetate under reflux conditions and

produced 2-amino-4-methyl-5,6,7,8-tetrahydroquinoline-3-carbonitrile 1 with 40% isolated

yield after 12 h (Scheme 3.1). The reaction succeeded only when the acetaldehyde reacts

with malononitrile to give an α,β-unsaturated nitrile intermediate which reacts with the

carbonyl group of cyclohexanone in the presence of ammonium acetate giving an

intermediate which upon intramolecular cyclization gave the compound 1.

Characterization of compounds 1 was confirmed by spectral data.. IR spectra showed bands

at 3400, 3320 cm-1 (NH2), (CN) at 2210, (CH) aliphatic 2933, 2870 cm-1 and 1H NMR

spectrum in CDCl3 revealed signals at 2.32ppm (CH3) and 5.16 ppm (NH2).

84

X-Ray structure of 2-amino-4-methyl-5, 6, 7, 8-tetrahydroquinoline-3-carbonitrile (1)

The XRD data for the compound 2-amino-4-methyl-5, 6, 7, 8-tetrahydroquinoline-3-

carbonitrile (1) C11H13N3 showed amino and nitrile groups which are responsible for the

classical hydrogen bonding interactions. There is no non classical interaction in molecules. In

the crystal structure two carbon atoms (C3 and C4) of the cyclohexene ring are disordered

over two positions. The dihedral angle between the ring A and B is 9.38(2)° while these are

oriented at a dihedral angle of 4.65(2)° and 4.85(2)° with respect to the pyridine ring. The

amino and nitrile groups are involved in the formation of the dimers through N-H…N

interactions and generate eight and twelve membered rings.

85

4.1.2 Chemistry of 2-amino-4-methyl-5-oxo-5,6,7,8-tetrahydroquinoline-3-carbonitrile

(2)

Compound 2 was prepared in a similar fashion as that of compound 1 but 1,3-

cyclohexanedione was used instead of cyclohexanone resulting in the production of 2-amino-

4-methyl-5-oxo-5, 6, 7, 8-tetrahydroquinoline-3-carbonitrile (2) with 42% yield (Scheme 3.2)

Patil et al. (2014) reported that the ammonium acetate utilized in excess in this reaction act as

an inexpensive and neutral catalyst and no external catalyst is used in this reaction. The

proposed mechanism for this transformation proceeds via three different steps.

Step 1 involves the formation of enaminone 6 from 1,3-cyclohexandione and an excess of

ammonium acetate. The excess of ammonium acetate acts as a source of acetic acid, which

can protonate carbonyl groups to create a more reactive species. Enaminone contains the

nucleophilic character of the enamine and nucleophilic character of enone (Martins et al.,

2012).

Step 2 there is the formation of arylidene malononitrile 7 by a Knoevenagel reaction of an

aldehyde and malononitrile.

Step 3 involves a Michael addition reaction with intra molecular cyclization between

enaminone 6 and arylidene malononitrile 7 affording the final product hexahydroquinoline 5.

Scheme 4.1: Proposed mechanism for the synthesis of hexahydroquinoline

86

The characterization of compound 2 was confirmed from spectroscopic analysis. IR spectra

showed bands at 3315,3216 cm-1 (NH2), (CN) at 2180 cm-1(CH) aliphatic 2960 and 2878cm-1

for (C=O) 1683cm-1 and the 1HNMR spectrum in DMSO-d6 exhibited signals at δ =1.08

ppm (CH3) and 6.95 ppm (NH2).

4.1.3 Chemistry of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene- 1, 3, 3-

tricarbonitrile (3)

The synthesis of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene-1,3,3 tricarbonitrile

(3) was similar as that of compound 1 as acetaldehyde was replaced by benzaldehyde. As a

result instead of getting 2-amino-4-phenyl-5,6,7,8-tetrahydroquinoline-3-carbonitrile. We

accidently obtained a yellow amorphous solid of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-

naphthalene-1, 3,3-tricarbonitrile (3) with 62% isolated yield (Scheme 3.3).

2-amino-4-phenyl-4a, 5, 6, 7-tetrahydro-4H-naphthalene-1,3,3-tricarbonitrile (3)

The characterization of compound 3 was performed by spectroscopy. The formation of

compound 3 has also been confirmed by mass spectroscopy showing a molecular ion peak at

300 (M+).

87

X-Ray Structure of 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene-1,3,3-

tricarbonitrile (3)

The XRD data for the compound 2-amino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene-

1,3,3-tricarbonitrile (3) C19H16N4 showed that it contains amino and nitrile groups which are

responsible for the classical hydrogen bonding interactions. The crystal structure of 3

contains two fused cyclohexene rings (C7-C12) C and (C11-C16) D and an aromatic ring

(C1-C6) E. The r.m.s deviation values for ring C and D are 0.1969(2) Å and 0.1934(2) Å.

Two fused rings are twisted at an angle of 10.65(2)°. The aromatic ring (C1-C6) is oriented

with a dihedralangle of 73.09(9)° and 74.12(9)° with respect to C (C7-C12) and D (C11-

C16), respectively eters 19 for the planes defined by atoms of cyclohexene are Q =0.4824 (1)

Å, q = 52.25(3)° and j = 340.81(2)° for C, Q =0.4739 (5) Å, q = 130.62(3)° and j = 325.18

(8)° for D. The classical N-H…N interactions form dimers and generate twelve membered

rings which further are connected through another N-H…N interaction and form infinite two

dimensional networks along the (0 0 1) plane. The synthesis of the 2-amino-4-phenyl-4a, 5,

6, 7-tetrahydro-4H-naphthalene- 1, 3, 3-tricarbonitrile by the reaction of benzylidine

malanonitrile with cyclohexanone had been carried out and found that a pair of enantiomers

3A was formed [(4R, 4aS) and (4S, 4aR)]. The obtained spectra do not show any hints for a

diastereomeric pair of enantiomers (4R, 4aR) and (4S, 4aS)

88

The hydrogen atoms on C-4 and C-4a are trans and have both axial positions (3

J = 12.3 Hz).

The ortho protons and ortho carbon atoms of the phenyl group have different δ values in the

NMR spectrum at room temperature because of the “frozen” rotation of the phenyl group (Al-

Matar et al., 2008).

4.1.4 Chemistry of 2-amino-5-oxo-4-substituted phenyl-1,4,5,6,7,8- hexahydroquinoline-

3-carbonitrile (4-4f)

In this study, we decided to investigate the reactions of 1,3- cyclohexandione and

malononitrile with different substituted aromatic aldehydes and ammonium acetate in ethanol

using 10 mole % P-TSA as catalyst. This reaction resulted in the production of 2-amino-1,4-

dihydro-4-substituted aryl quinoline-3-carbonitrile (4-4f). Initially, in the first reaction step a

mixture of benzaldehyde, malanonitrile, 1,3-cyclohexanedione and ammonium acetate in

ethanol was refluxed. Yield: 42% of the product obtained due to incomplete conversion of

the reactants. To focus on the yield and reaction time, all further reaction steps were planned

to carry out in the presence of P-TSA catalyst which allowed the generation of the

heterocyclic product with a higher yield 95% and lower reaction time. P-TSA increased the

yield and accelerated the reaction rate and acted as a dehydrating agent in this Hantzsch type

one pot condensation reaction of polyhydroquinoline.

The most optimum reaction condition and the role of P-TSA to accelerate the reaction are

discussed in detail in this section

Initially, the reaction of 1,3-cyclohexane dione, 4-chloro benzaldehyde, malononitrile and

ammonium acetate was selected as a model reaction to optimize the reaction conditions in the

89

presence of different amounts of P-TSA (0–12.5mol%) in ethanol at room temperature to

100 ̊C (Table 4.1).

Table 4.1: Screening of the reaction conditions for the synthesis of 2-amino-4-(4-

chlorophenyl)-5-oxo-1,4,5,6,7,8- hexahydroquinoline-3-carbonitrile (4b)

Entry Mole % Solvent Time (h) Yield (%)

1 0.0 C2H5OH 6.0 42

2 2.5 C2H5OH 5.5 67

3 5.0 C2H5OH 4.0 77

4 7.5 C2H5OH 3.0 87

5 10.0 C2H5OH 1.5 95

6 12.5 C2H5OH 1.5 92

7 10.0 CH3OH 2.0 85

8 10.0 CH3CN 2.0 90

9 10.0 CH3COCH3 4.5 48

10 10.0 C6H5CH3 6.0 37

11 10.0 CH2Cl2 5.5 40

12 10.0 C6H12 7.5 34

a All reactions were carried out of 4-chloro benzaldehyde : 1,3 cyclohexane dione: malononitrile and ammonium

acetate 1: 1:1:1.5 (molar ratio) at reflux in P-TSA.

Upon investigating the influence of the amount of P-TSA on the reaction rate, it was found

that without P-TSA the reaction proceed only with 42 % isolated yield (Table 4.1). It was

observed that 10 mol% of P-TSA was sufficient to promote the reaction yield. When the

amount of P-TSA was increased over 10 mol% equivalent, no significant improvement in

reaction yield as well as in reaction rate was observed.

To optimize the procedure for the selection of more convenient solvent, we then continued

the model process by detecting the efficiency of different solvents (Table 4.1). By screening

of solvents in Table 4.1, the solvents such as ethanol, methanol and acetonitrile were

investigated much better than rest of the solvents due to the difference of polarity. Catalyst

and other reagents have much better solubility in the polar solvents as compared to non polar

solvents. It was investigated that the reaction proceeded readily with acetone but the obtained

precipitate contained other by-products which were due to some reactions promoted by P-

TSA in acetone.

90

To determine the scope of the designed protocol, a number of substituted aromatic aldehydes

were condensed with malononitrile and 1,3-cyclohexane dione by using the optimum

amount of a catalyst (10 mole%) at 80 ̊C reflux temperature in ethanol to decrease the

reaction time and to increase the yield and purity of the product. Yields and reaction times are

summarized in (Table 4.2).

Table 4.2: Synthesis of 2-amino-5-oxo-4-substituted phenyl-1, 4, 5, 6, 7,

hexahydroquinoline-3-carbonitrile (4-4f) by using P-TSA catalyst

Sr. No Products Ar Reaction time

(h)

Yield (%)

1 4 Phenyl 2.5 91

2 4a 4-methyl phenyl 2.0 89

3 4b 4-chloro phenyl 1.5 95

4 4c 4-hydroxy phenyl 2.5 92

5 4d 3-methylphenyl 2.0 87

6 4e 3-chloro phenyl 3.0 90

7 4f 4-nitro phenyl 3.0 96

As shown in Table 4.2, both electron-deficient and electron-rich aromatic aldehydes were

applicable to the reaction, affording the products in excellent yields. In addition, the existence

of electron-donating groups on the aromatic amines decreased the reaction times and also

increased the yield of products.

In the 3-amino carbonitrile unit, the basic site is the carbonitrile group rather than the amino

group. Also, the following equilibrium has been predicted for 3-amino carbonitrile moiety in

acidic media. In fact, in an acidic environment there is an equilibrium between the nitrilium

ion and iminium ion.

Scheme 4.2: The nitrilium- iminium quilibrium in 3-amino carbonitrile

91

IR Spectra

The characterization of 2-amino-5-oxo-4-substituted -phenyl-1, 4, 5, 6, 7, 8-

hexahydroquinoline-3-carbonitrile (4-4f) was performed by IR spectroscopy. Two

characteristic bands of the primary amine were observed in the range of 3224 and 3318 cm-1.

A characteristic band for carbonyl groups was observed in the range of 1645-1700 cm-1.

Another characteristic band of nitrile groups was observed at 2190-2214 cm-1 suggesting the

presence of the desired functional groups in the products.

Mass Spectra

The molecular ion, observed in the mass spectra of all polyhydroquinolines (4-4f), confirmed

their molecular masses.

1H NMR Spectral study

For 2-amino-5-oxo-4-p-tolyl-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4a), a

characteristic singlet was observed for the methyl group of the aromatic aldehyde at δ = 2.05

ppm and characteristic multiplets were observed for the methylene groups of the cyclohexane

ring at δ = 1.90-2.10 ppm and 2.78 ppm reveal in adjacent methine protons. A sharp singlet at

δ = 4.10 ppm revealed the C4-H. The singlet for the primary amine (-NH2) proton was

observed at δ = 5.75 ppm. The aromatic ring protons were observed at δ = 6.90-7.10 ppm

and coupling constant were found in accordance with the substitution pattern of the phenyl

ring. The singlet for the secondary amine (-NH) protons was observed at δ =8.90 ppm.

Characteristic multiplets for 2-amino-4-(4-chlorophenyl)-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carbonitrile (4b) were observed for the adjacent methane of the cyclic

ring at δ = 2.0-2.4 ppm. A sharp singlet at δ = 4.30 displayed 1 H at C4. The singlet for the

secondary amine at δ = 5.8 ppm and for the primary amine at δ = 7.10 ppm and for the

aromatic ring were doublet located at δ = 7.25 and 7.40 ppm. For 2-amino-4-(4-

hydroxyphenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4) characteristic single

was observed at δ = 9.43 ppm for the OH proton.

92

4.2 Chemistry of ethyl 2-methyl-5-oxo-4-substituted-phenyl-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5-5l)

In this study, we decided to investigate the reactions of 1,3- cyclohexandione, ethyl

acetoacetate with different substituted aromatic aldehydes and ammonium acetate without

any solvent and catalyst by simple grinding and secondly by using 10 mole % P-TSA as

catalyst and ethanol as solvent to compare the effect on yield, purity and reaction rate. This

reaction resulted in the production of ethyl 2-methyl-5-oxo-4-substituted-phenyl-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5-5l).

IR Spectra

Various functional groups present in ethyl 2-methyl-5-oxo-4-substituted-phenyl-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate (5-5l) were identified by characteristic frequencies. A

characteristic band of the carbonyl group was observed in the range of 1640-1700 cm-1 and a

characteristic band of α, β unsaturated ester groups were observed at1730-1717cm-1. Also, N-

H stretching bands of secondary amines gave weak bands in the range of 3300-3000 cm-1.

Mass Spectra

The molecular ion, observed in the mass spectra for all polyhydroquinoline (5-5l), confirmed

their molecular masses.

1N MR Spectral study

For ethyl 2-methyl-5-oxo-4-substituted-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate

(5), a characteristic triplet at δ = 1.12 ppm revealed a methyl group for the ester and a

characteristic quartet was observed for the CH2 group of esters at δ = 4.00 ppm. A multiplets

located at δ = 1.70-2.30 ppm revealed the adjacent methine protons of the cyclic ring. The

singlet for the secondary amines (-NH) proton was observed at δ = 5.00 ppm. A sharp singlet

at δ = 5.70 ppm revealed the C4-H. The aromatic ring protons were observed at δ = 7.00-7.30

ppm and J values were found to be in accordance with the substitution pattern on the phenyl

ring. The characteristic singlet at δ = 5.00 and at 5.70 ppm indicated the presence of NH i.e

secondary amine at 1 position instead of a tertiary amine and 1H at carbon 4. This is a

significant proof for the formation of hexahydroquinoline instead of tetrahydroquinoline.

93

The 1H NMR spectrums of polyhydroquinoline 5-5l derivatives the number of protons and

their chemical shifts were found to support the structure of the synthesized compounds. The

characteristic signal which requires comments is the appearance of the C-H proton at C-4

appear as singlet at δ = 6.0, 5.0, 4.90, 4.89, 5.06, 5.10, 4.85, 4.87, 4.70 and at 5.00 ppm

respectively in compounds 5a-5l. The appearance of broad range singlet at δ = 5.10, 5.8,

8.34, 9.10, 9.60, 6.60, 9.49, 9.30, 9.50 and at 9.41 ppm in compounds 5a-5l for NH shows

that the dihydropyridine ring formed instead of pyridine ring. Formation of dihydropyridine

ring in all the synthesized polyhydroquinoline 4-4f and 5-5l instead of pyridine confirmed by

1H NMR and by ORTEP diagram of the compound 2, 7, 7-trimethyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylic acid ethyl ester (6).

In case of compound 5a-5l quartet appeared at range of 4.00 to 4.12 ppm with J values in the

range of 6.2-7.2Hz and triplet at range of 1.11 to 1.25 ppm is due to ester group. The

aromatic proton of substituted phenyl at C4 of polyhydroquinoline appeared at the range of

6.80-7.98 ppm with J value in the range of 8.0-8.7 Hz depending on the nature and the

position of the electron withdrawing or electron donating group attached on the phenyl.

94

Table 4.3: Synthesis of 2-amino-5-oxo-4-substituted phenyl-1, 4, 5, 6, 7,

hexahydroquinoline-3-carboxylate (5-5l) by using P-TSA catalyst

Sr.

No

Products Ar Mol.formula

(mol.wt)

Reaction time

(h)a

m.p ˚C

1 5 Phenyl C19H21NO3

(311)

2.0 241

2 5a 4-methyl phenyl C20H23NO3

(325)

1.5 242

3 5b 4-chloro phenyl C19H20NO3Cl

(345)

1.5 235

4 5c 4-hydroxy phenyl C19H21NO4

(327)

3.0 234

5 5d 3-methylphenyl C20H23NO3

(325)

2.5 245

6 5e 3-chloro phenyl C19H20NO3Cl

(345)

2.0 202

7 5f 4-nitro phenyl C19H20N2O5

(356)

2.0 205

8 5g 3-bromo phenyl C19H20NO3Br

(390)

2.5 Above

300

9 5h 4-flouro phenyl C19H20FNO3

(329.14)

2.0 244

10 5i 4- bromo phenyl C19H20NO3Br

(390)

3.0 254

11 5j 4-methoxy phenyl C20H23NO4

(341.40)

2.0 195

12 5k 4-methyl sulfonyl

phenyl

C20H23NO5S

(389.12)

3.5 251

13 5l 3- flouro phenyl C19H20FNO3

(329.14)

2.5 260

As shown in Table 4.3, both electron-deficient and electron-rich aromatic aldehydes were

applicable to the reaction, affording the products in excellent yields. In addition, the existence

95

of electron-donating groups on the aromatic amines decreased the reaction times and also

increased the yield of products. Using p-bromo- and p-chloro-aldehydes, the products were

obtained with excellent yields.

4.3 Chemistry of ethyl 2,7,7-trimethyl-5-oxo-4-substituted-phenyl-

1,4,5,6,7,8-hexahydroquinoline-3-carboxylate synthesized by a

guanidine HCl

In this section we investigated the effect of an external catalyst guanidine HCl on the reaction

rate, yield and purity of the product. Using the catalyst with only 5 mole %, the yield

increased even upto 96% and the reaction was carried out without conventional heating at

room temperature, stirring and small amount of this catalyst formed the pure product without

any side products.

IR Spectra

Various functional groups present in ethyl 2,7,7-trimethyl-5-oxo-4-substituted-phenyl-1, 4, 5,

6, 7,8-hexahydroquinoline-3-carboxylate (6) were identified by characteristic frequencies. A

characteristic band of the carbonyl group was observed in the range of 1613-1678 cm-1 and a

characteristic band of the, β unsaturated ester group was observed at 1701 cm-1. A weak N-H

stretching band of the secondary amine was observed in between 3290- 3070 cm-1.

Mass Spectra

The molecular ion, observed in the mass spectra of ethyl 2,7,7-trimethyl-5-oxo-4-substituted-

phenyl-1,4,5,6,7,8- hexahydroquinoline-3-carboxylate at m/e 337 confirmed the molecular

mass.

1H NMR Spectral study

For ethyl 2,7,7-trimethyl-5-oxo-4-substituted-phenyl-1,4,5,6,7,8-hexahydroquinoline-3-

carboxylate compound (6), two characteristic singlets were observed at δ= 0.90 and 1.02 ppm

for the two methyl groups. A triplet revealed a methyl group of the ester at δ = 1.22 ppm and

a characteristic quartet was observed for the CH2 group of the esters. Multiplets were located

at δ = 2.10-2.28 ppm and revealed the methine protons of the cyclic ring. A sharp singlet at δ

=4.98 ppm revealed the C4-H. The singlet for the secondary amine (-NH) proton was

observed at δ = 5.98 ppm.The aromatic ring protons were observed at δ= 6.90-7.10 ppm and J

values were found to be in accordance with the substitution pattern on the phenyl ring. The

96

characteristic singlets at δ = 4.98 ppm indicates the presence of 1H at carbon 4. This was a

significant proof for the absence of aromaticity in the compound. From the high resolution

mass spectrum it is confirmed that compound 6 had 1, 4-dihydropyridine ring instead of a

pyridine ring. An X-ray crystal analysis proofed the suggested structure.

4.3.1 Effect of a catalyst

In this section, reactions were carried out by three different methods to optimize the yield of

the products. The results are summarized in the Table 4.4.

Table 4.4: A comparison of yields with catalysts producing hexahydroquinoline

Entry

Products

Solvent Free grinding

(% yield)

P-TSA

(% yield)

Guainidine HCl

(% yield)

1 5 92 93 95

2 5a 92 92 93

3 5b 89 95 96

4 5c 88 87 90

5 5d 86 89 91

6 5e 85 87 92

7 5f 90 92 94

8 5g 90 91 92

9 5h 87 90 91

10 5i 90 93 94

11 5j 87 89 92

12 5k 85 87 90

13 5l 90 89 90

14 6 93 95 96

The amount of the product obtained in this reaction show that a maximum yield of 96% was

obtained with compound 6. In case of the solvent free grinding and P-TSA product has to be

pure by column chromatography but in case of guanidine HCl pure product was obtained.

97

XRD data ethyl 2,7,7-trimethyl-5-oxo-4-substituted-phenyl-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate compound (6)

The XRD data for the compound ethyl 2, 7, 7-trimethyl-5-oxo-4-substituted-phenyl-1, 4, 5, 6,

7, 8- hexahydroquinoline-3-carboxylate compound (6), C21H25NO3, showed that the 1,4-di

hydropyridine ring which is a part of the polyhydroquinoline fused-ring system adopts a sofa

conformation; the methine C atom deviates from the square plane defined by the remaining

five non-H atoms. The phenyl ring is aligned at 85.5 (1) with respect to this mean plane. In

the crystal, adjacent molecules are linked via an N—H---O hydrogen bond, involving the

amino group and the carbonyl O atom of the fused-ring system, forming chains [100]. The

order of ethyl groups is disturbed at two positions in a 0.609 (6):0.391 (6) ratio.

ORTEP diagram of the compound 2, 7, 7-trimethyl-5-oxo-1,4,5,6,7,8- hexahydroquinoline-

3-carboxylic acid ethyl ester (6)

Duque et al., (2000) determined crystal and molecular structure of methyl-2,7,7-trimethyl-4-

phenyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate , C20 H23 NO3, by X-ray

diffraction. He found that structure of compound is similar to that of related analogs; the 4-

aryl substituent, almost orthogonal to the dihydropyridine ring (87.6°), occupies a

pseudoaxial position. Due to sp2 hybridization of the dihydropyridine, ester group occupies

98

an "equatorial" arrangement. The ester group exhibits a preference to the double bond of the

dihydropyridine ring.

The 1,4-dihydropyridine ring adopts a "boat" conformation. The distorsion from planarity of

the atoms comprising the dihydropyridine ring can be clearly seen from the torsion angles

calculated about the ring bonds. The ester group is considered cis because the carbonyl group

eclipses the adjacent double bond (C2-C3) of the dihydropyridine.

4.3.2 Ultraviolet assisted synthesis of compounds (4-4f) and (5-5l)

We disclose a novel and expedient synthesis of polyhydroquinoline derivatives via a multi

component cyclocondensation of a series of substituted aromatic aldehyde, 1,3-

cyclohexanedione, ethylacetoacetate/malanonitrile, ammonium acetate in the presence of P-

TSA as a catalyst in ethanol under UV-irradiation. The synthesis of an array of 2-amino-5-

oxo-4-substituted phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (4-4f) and 2-amino-

5-oxo-4-substituted phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5-5l) derivatives

has carried out by UV radiation operated at 254 nm for 1-5 min cycle and led to the

cyclization, followed by the aromatized products, in a single step with good to excellent

yields.

Synthesis of hexahydroquinoline-3-carbonitrile assisted by ultraviolet radiation

Initially, we carried out the cyclocondensation reaction of benzaldehyde, malononitrile,

cyclohexane dione and ammonium acetate in excess without any catalyst at reflux

temperature for 6 h, which led to a poor yield (42%) of 4 (Table 4.1). In spite of increasing

the reaction time to 12h, no appreciable increment was observed in the yield of the desired

product. Therefore, an attempt was made to promote the target reaction by employing

Ultraviolet irradiation as the source of heating. To verify the effect of ultraviolet irradiation in

these reactions, the synthesis of ethyl 4-(4-chlorophenyl)-2-methyl-5-oxo-1,4,5,6,7,8-

hexahydroquinoline-3-carboxylate are taken as a model reaction in the presence of catalyst

under ultraviolet irradiation and reflux conditions (Table 4.5).

99

Table 4.5: Comparison of % yield and reaction time of compounds ethyl 4-(4-chlorophenyl)-

2-methyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate synthesized under

different reaction conditions

ENTRY Techniques used Time (min) Yield (%)

Sr. No

Techniques used

Reaction time (min)

Yield (%)

1

Solvent free grinding

30

89

2

Thermal method with catalyst

80

95

3

Ultraviolet assisted method with catalyst

4

97

The reaction was catalyzed by P-TSA and strongly accelerated by ultraviolet radiation. The

P-TSA was used for the synthesis of compounds ethyl 4-(4-chlorophenyl)-2-methyl-5-oxo-

1,4,5,6,7,8-hexahydroquinoline-3-carboxylate and the desired product was obtained in 97%

yields. The reaction does not require any additional catalyst because UV radiation itself acts

as an efficient catalyst, and hence the reaction proceeds well. In this methodology, Hantzsch

reaction was completed in a shorter time (4 min) and with excellent yields (97%). To

generalize this methodology, we subjected a series of different substituted aldehydes

possessing electron-donating as well as electron withdrawing functional groups to obtain the

corresponding polyhydroquinoline derivatives under ultraviolet radiation shown in (Table 4.6

and 4.7).

Table 4.6: Ultraviolet-accelerated synthesis of 2-amino-5-oxo-4-substituted phenyl-1, 4, 5,

6, 7, hexahydroquinoline-3-carbonitrile (4-4f) by using P-TSA catalyst

Sr. No Products Ar Reaction time (min) Yield (%)

1 4 Phenyl 3 97

2 4a 4-methyl phenyl 3 94

3 4b 4-chloro phenyl 4 96

4 4c 4-hydroxy phenyl 5 92

5 4d 3-methylphenyl 3 93

6 4e 3-chloro phenyl 4 95

7 4f 4-nitro phenyl 4 95

100

As Table 4.6 shows yields are good to excellent in most cases. The reactions were compatible

with various substituted aldehyde such as nitro, chloro, methyl. No any considerable

substituents effect was observed in the yield of product and reaction time. In all reactions, it

was found that the use of ultraviolet radiation leads to faster reaction (3-5 min) and higher

yields (92-97%). So it exhibits that use of the ultraviolet improves the rate of reaction and

also yields of products.

Now, we also decided to synthesized another series of ethyl 2-methyl-5-oxo-4-substituted-

phenyl-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate (5-5l) by the exposure of Ultraviolet

radiation of 254nm to mixture of 1,3- cyclohexandione, ethyl acetoacetate with different

substituted aromatic aldehydes, ammonium acetate and 10 mole % P-TSA as catalyst in

ethanol as solvent to compare the effect on yield, purity and reaction rate.

Synthesis of hexahydroquinoline-3-carboxylate assisted by ultraviolet radiation

The results with different substituted aromatic aldehydes are summarized in the Table 4.7

101

Table 4.7: Ultraviolet-accelerated synthesis of 2-amino-5-oxo-4-substituted phenyl-

1,4,5,6,7,8- hexahydroquinoline-3-carboxylate (5-5l) by using P-TSA catalyst

Entry Products Ar Reaction time (min) Yield (%)

1 5 Phenyl 3 96

2 5a 4-methyl phenyl 4 93

3 5b 4-chloro phenyl 4 94

4 5c 4-hydroxy phenyl 6 91

5 5d 3-methylphenyl 6 92

6 5e 3-chloro phenyl 4 93

7 5f 4-nitro phenyl 5 92

8 5g 3-bromo phenyl 5 92

9 5h 4-flouro phenyl 4 93

10 5i 4- bromo phenyl 4 94

11 5j 4-methoxy phenyl 5 95

12 5k 4-methyl sulfonyl phenyl 3 94

13 5l 3- flouro phenyl 5 92

Results display reduction in reaction time (3-6 min) and improvement the yields (91-96%) of

products under ultraviolet irradiation. It is evident from the Table 4.8 that electronically and

structurally differentially substituted aldehydes do not reveal any significant effect on the

product yield and reaction time. Almost all the products obtained in good to excellent yield in

relatively short reaction times. Ultraviolet irradiation causes the excitation of molecules that

creates a special chemical environment which ultimately changes the space structure of the

molecule, interatomic distance increases and molecular symmetry changes. Comparative

studies are carried out in different conditions: (1) under ultraviolet (2) without ultraviolet

radiation (thermal heating). It is investigated from this comparative study that ultraviolet

radiation has significant activation effect. The rate of the reaction and yields of the products

shows the sequence UV> thermal method.

102

The reaction time and % yield of synthesized compounds by using ultraviolet irradiation and

conventional methods are summarized in Table 4.8.

Table 4.8: Comparison of % yield and reaction time of compounds (4-4f) and (5-5l)

synthesized under ultraviolet irradiation and by conventional heating using P-

TSA catalyst

Sr. No

Products

Ar

Reaction

Time (h)a

Yield

(%)a

Reaction

time(min)b

Yield

(%)b

1 4 Phenyl 2.5 95 3 97

2 4a 4-methyl phenyl 2.0 89 3 94

3 4b 4-chloro phenyl 3.0 91 4 96

4 4c 4-hydroxy phenyl 2.5 92 5 92

5 4d 3-methylphenyl 2.0 87 3 93

6 4e 3-chloro phenyl 3.0 90 4 95

7 4f 4-nitro phenyl 3.0 96 4 95

8 5 Phenyl 2.0 93 3 96

9 5a 4-methyl phenyl 2.0 92 4 93

10 5b 4-chloro phenyl 2.0 90 4 94

11 5c 4-hydroxy phenyl 3.0 87 6 91

12 5d 3-methylphenyl 2.5 89 6 92

13 5e 3-chloro phenyl 2.0 87 4 93

14 5f 4-nitro phenyl 2.0 92 5 92

15 5g 3-bromo phenyl 2.5 91 5 92

16 5h 4-flouro phenyl 2.0 90 4 93

17 5i 4- bromo phenyl 3.0 93 4 94

18 5j 4-methoxy phenyl 2.0 89 5 95

19 5k 4-methyl sulfonyl

phenyl

3.5 87 3 94

20 5l 3- flouro phenyl 2.5 89 5 92

a: Reaction time (h); Yield (%) of thermal method ; b: Reaction time (min); Yield (%) of ultraviolet assisted

method

It is investigated from the Table 4.8 that by using ultraviolet radiation, the reaction time has

reduced considerably whereas % yield increased markedly. In case of ultraviolet irradiation,

103

the reaction time was reduced to 3-5 minutes instead of (120-180) minutes for thermal

method. Also the yield of the product was increased from (87-91%) in case of thermal

method to (91-97%) under ultraviolet irradiation. This exhibits the superiority of the

ultraviolet assisted protocol for the synthesis of polyhydroquinoline over thermal method.

Thus, ultraviolet is proved to be a better technique than conventional heating method. By

irradiating an organic molecule with ultraviolet light chemical reactions takes place and

ultimately leads to the production of complex organic products in a simple way.

In conclusion, we have developed a simple novel method for the synthesis of

polyhydroquinoline derivatives via one-pot four-component Hantzsch condensation of

dimedone/ 1,3-cyclohexane dione, aryl aldehydes, ethyl acetoacetate/ malanonitrile and

ammonium acetate in the presence of an efficient catalyst P-TSA assisted by ultraviolet

radiation. The present method serve as more convenient than the other conventional methods.

The method has the advantage of being a single step and easy operation with short reaction

times, mild reaction conditions and good to excellent yields. Moreover, this method further

expands the application of a new and efficient source of energy, UV irradiation, in organic

synthesis.We believe this applicability of UV radiation with mentioned advantages makes our

method superior over other reported methods to synthesis of polyhydroquinoline derivatives.

The improvement of the yields of potentially active compounds reveals the method as an

attractive approach for the synthesis of many similar compounds.

4.4 Chemistry of synthesized chalcone

4.4.1 Chemistry of the chalcones 7a-i, 8a-h and 9a-h

All chalcones were prepared by a Claisen-Schmidt condensation reaction between equimolar

quantities of 6-OMe or 6-Me- or 6-H substituted 2-chloro-3-formylquinolines with various

aromatic and heteroaromatic ketones in methanol in the presence of 40% NaOH solution. The

product precipitated out by stirring the mixture at room temperature. The crude product was

obtained by filtration and washing first with water and then with cold methanol. It was then

recrystallized from EtOH to give pure compounds 7a-i, 8a-h and 9a-h.

104

Table 4.9: Heteroaromatic ketones used in the chalcone synthesis (a-i)

Ketones

Ar

Ketones

Ar

Ketones

Ar

a

O

H3C

O

d

HN

H3C

O

g H3C

O

OCH3

b

O

H3CO

H3C

CH3

e NH3C

O

h H3C

O

c S

Cl

H3C

O

f H3C

O OCH3

i O

H3C

O

The general structure of these chalcones is given below:

All the prepared compounds were characterized by spectroscopic methods (1H NMR, IR and

MS). The MS was employed only for the molecular mass confirmation. For structure

elucidation,

1H NMR spectroscopy was used. All the synthesized chalcones were in agreement with the

proposed structures.

105

Table 4.10: Synthesis of a series of quinolinyl chalcones 7a-7i, 8a-8h

Sr. No Product M.formula(M.wt) Yield (%) M.point (˚C)

1 7a C17H12ClNO3 (313) 69 164

2 7b C19H16ClNO3 (341) 70 121

3 7c C17H11Cl2NO2S (364) 93 179

4 7d C17H13ClN2O2 (312) 91 170

5 7e C18H13ClN2O2 (324) 70 129

6 7f C20H16ClNO3 (353) 72 142

7 7g C20H16ClNO3 (353) 68 141

8 7h C23H16ClNO2 (373) 90 161

9 7i C21H14ClNO3 (363) 63 160

10 8a C17H12ClNO2 (297) 71 116

11 8b C19H16ClNO2 (325) 90 146

12 8c C17H11Cl2NOS (348) 90 180

13 8d C17H13ClN2O (296.75) 76 214

14 8e C18H13ClN2O2 (308) 68 129

15 8f C20H16ClNO2 (373) 70 137

16 8g C20H16ClNO2 (373) 65 140

17 8h C23H16ClNO (353) 96 138

IR Spectra

Selected diagnostic bands of the IR spectra of the chalcones 7a-i, 8a-h and 9a-h showed

useful information about the structure of the compounds. Two significant stretching bands

due to C=C and groups C=O were observed at 1585-1598 and 1645-1668 cm-1 respectively,

which are typical stretching regions for chalcone moieties. The quinoline C=N stretching

appeared at 1560-1575cm-1 in all title compounds. In addition, the spectra of 7d, 8d and 9d

showed stretching bands resulting from the NH stretching of the pyrrole moiety at 3215, 3217

and 3222 cm-1.

Mass Spectra

The molecular ion peak observed in the mass spectra for all chalcones confirmed their

molecular masses. The base peak in the mass spectra of most of compounds was obtained by

106

the cleavage of C-Cl bonds in 2-chloroquinoline moieties. The EIMS of chalcones also gives

rise to the unusual fragment ion [M-H+] involving a type of intramolecular aromatic

substitution reaction by the elimination of an ortho substitutent from an aromatic ring with

further cyclization.

1H-NMR

The 1H-NMR spectra of the chalcones 7a-i, 8a-h and 9a-h reveal, that the Cα-H and Cβ-H

protons are so much deshielded that their signal is shifted considerably downfield to such an

extent that they appear in the aromatic region (7.05-8.12) for 3-(2-Chloro-6-methoxy-

quinoline-3-yl)-1-(2,5- dimethyl-furan-2-yl)-propenone (7b). As a result, two very sharp

doublets around 7.05 ppm for Hα and 8.12ppm for Hβ, with a coupling constant 15.9Hz for

the trans chalcones were observed. The 3-(2-Chloro-6-methoxy-quinoline-3-yl)-1-(2,5-

dimethyl-furan-2-yl)-propenone (7b) also show three sharp singlet signals, for protons of

methyl group at δ = 2.25 ppm and at 2.60 ppm and one for methoxy group at δ = 3.90 ppm.

The most deshielded proton is located in the vicinity of carbonyl oxygen atom. The last

proton of heteroaromatic ring appeared as singlet at δ= 6.34 ppm.

(7b)

The 1H-NMR spectra of the chalcone 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-pyridine-2-yl-

propenone (7e) displayed a sharp singlet of methoxy proton at δ = 3.81ppm and a singlet at δ

= 6.90 ppm representing aromatic proton. One doublet at δ = 7.40 with coupling constant J=

7.1 Hz representing aromatic proton.One doublet with coupling constant J= 15.1 Hz appear at

δ = 7.40 and 7.90 ppm respectively. A singlet at δ =8.00 ppm represent aromatic proton and a

doublet with a coupling constant J = 7.0 Hz displayed a chemical shift at δ = 8.60 ppm.

(7e)

107

The 1H-NMR spectra of the compound 3-(2-chloro-6-methoxy-quinoline-3-yl)-1-(2-

methoxy-phenyl)-propenone (7g) reveal, that the Cα-H and Cβ-H protons are so much

deshielded that their signal is shifted considerably downfield. Cα-H appears in the aromatic

region (7.32-7.58) with coupling constant J =16.0 Hz. Cβ-H proton appear as sharp doublet at

δ = 8.00 ppm with coupling constant J = 16.2Hz. This coupling constant confirmed the trans

isomer of the synthesized derivatives. One doublet of aromatic proton appear at δ = 7.05 ppm

with coupling constant J = 2.7Hz and another doublet appear at δ = 7.85 ppm with coupling

constant J = 9.0 Hz. The compound also show three sharp singlet signals, for aromatic

protons at δ = 7.19 ppm, at 7.40 ppm and one at δ = 8.31ppm.

(7g)

4.5 Biological Studies of the Polyhydroquinoline Derivatives

4.5.1 Antimicrobial studies of polyhydroquinoline 4-4f and 5-5l

All synthesized polyhydroquinolines 4a-4f, 5-5l were evaluated for their in vitro antibacterial

activity against Staphylococcus aureu representing gram-positive bacteria, Escherichia coli

gram-negative bacteria. For evaluation of antifungal activity, Aspergillus niger was used.

Many of the compounds exhibited potent antibacterial and/or antifungal activities as

compared to standard drugs ciprofloxacin (bacteria) and fluconazole (fungi) but failed to get

a common compound showing both types of activities.

108

Table 4.11: Antimicrobial activities of compounds 4-4f, 5-5l with their zone of inhibition in

mm

Compounds Ar group A.niger S.aureus E.coli

Zone of inhibition (mm)

4 Phenyl 2 5 7

4a 4-methyl phenyl 4 9 8

4b 4-chloro phenyl 6 10 9

4c 4-hydroxy phenyl 4 5 6

4d 3-methylphenyl 12 16 18

4e 3-chloro phenyl 10 15 14

4f 4-nitro phenyl 2 4 6

5 Phenyl 9 10 12

5a 4-methyl phenyl 16 19 18

5b 4-chloro phenyl 13 14 11

5c 4-hydroxy phenyl 8 14 10

5d 3-methylphenyl 20 18 16

5e 3-chloro phenyl 16 20 18

5f 4-nitro phenyl 11 13 11

5g 3-bromo phenyl 15 19 18

5h 4-flouro phenyl 11 14 16

5i 4- bromo phenyl 17 18 23

5j 4-methoxy phenyl 11 14 10

5k 4-methyl sulfonyl phenyl 11 16 16

5l 3- flouro phenyl 15 18 16

DMSO __ __ __

Standard 26 29 36

+ve indicates microbial growth. Control: DMSO (0.01% solution in distilled water).

Standard for antibacterial: Ciprofloxacin (1.00 mmol/ml).Standard for antifungal: fluconazole (1.00 mmol/ml)

All the synthesized polyhydroquinoline 4-4f and 5-5l as shown in Table 4.11 exhibited

moderate to low in vitro antimicrobial activity. Compound 4-4f showed significant activity

against Staphylococcus aureus, Escherichia coli, and very low activity against fungal strain

Aspergilus niger. Compound 5-5l showed significant activity against, Staphylococcus aureus

109

and Escherichia coli but moderate activity against fungal strain Aspergilus niger Compound

4d, 5d and 5e showed moderate activity against Staphylococcus aureus and Escherichia coli

and compound 5d, 5e, 5i and 5l showed significant activity against fungal strain Aspergilus

niger.

A close examination of the structure of the compounds in Table 4.11 revealed that

carbonitrile and ester groups at third position of polyhydroquinoline were found responsible

for variation in activity. Particularly the carbonitrile group was found accountable for

increasing antibacterial activity where as ester group was responsible for increased antifungal

activity. The substituted aryl at C4 position increased or selectively reduced the antibacterial

activity. Compound 4 and 5 displayed almost negligible activity against both bacterial and

fungal strain due to the unsubstituted phenyl group at C4 position. It was found that the

compounds 4d and 5d possessing 3-methyl group has the good overall antibacterial and

antifungal activities. It was concluded that m-substituted alkyl group possess good activity.

Compound 4c and 5c displayed less activity due to the p-substituted hydroxyl phenyl at 4

position of polyhydroquinoline.

4.5.2 Antioxidant activity

Oxygen is necessary for the production of energy in living organisms for various biological

processes (Mojarrab et al., 2013). However, human body produces reactive oxygen species

due to the oxygen consumption by various enzymatic processes (Lee et al., 2006). Oxidative

stress is due to the imbalance of the production of free radicals and defense system of the

body (Lobo et al., 2010). It has been proved that oxygen stress play a key role in the etiology

and occurrence of disease consisting Alzeimer’s disease (Rahman et al., 2012), multiple

sclerosis (MS) (Sherki et al., 2004), cancer, immunologic disorders (Zhang & Zehnder,

2013), rheumatologic disease (Sukkar & Rossi, 2004), cardiovascular disorders

(artherosclerosia) (Hwang, 2013) and cerebrovascular accident (CVA) (Aliev et al., 2014).

Oxidative stress could lead to DNA damages (both mitochondrial and nuclear) and eventually

carcinogensis (Henkleret al., 2010). The incident of above mentioned disorders is closely

related to intake of dietary antioxidants. However, there is strong demand for discovery and

development of potent antioxidants.

All synthesized polyhydroquinolines 4-4f, 5-5l were evaluated for antioxidant activities

through DPPH (2,2'-diphenyl-1-picrylhydrazyl) as well as reducing power method

110

(Fe3+/Fe2+). Anti-oxidant (DPPH and FRPA) activities of the synthesized compounds along

with the standard (ascorbic acid and BHT) are presented in Table 4.12.

Table 4.12: Antioxidant activities of compounds 4-4f, 5-5l with their % inhibition

Compounds Ar group DPPH (50

µg mL-1)

FRAP

Activity

4 Phenyl 3 4

4a 4-methyl phenyl 8 6

4b 4-chloro phenyl 11 9

4c 4-hydroxy phenyl 34.0 32.0

4d 3-methylphenyl 18.0 16.0

4e 3-chloro phenyl 9 7

4f 4-nitro phenyl 3 6

5 Phenyl 3 2

5a 4-methyl phenyl 5 3

5b 4-chloro phenyl 10 8

5c 4-hydroxy phenyl 46.0 44.0

5d 3-methylphenyl 20.0 18.00

5e 3-chloro phenyl 5 4

5f 4-nitro phenyl 4 3

5g 3-bromo phenyl 7 3

5h 4-flouro phenyl 3 5

5i 4- bromo phenyl 4 3

5j 4-methoxy phenyl 8 9

5k 4-methyl sulfonyl phenyl 11.0 22.0

5l 3- flouro phenyl 3 4

Ascorbic acid 35 39

BHT 37 40

Note: All the activity values are expressed in % age

DPPH is a stable free radical and accepts an electron or hydrogen radical to become a stable

diamagnetic molecule which is widely used to investigate radical scavenging activity. In

DPPH radical scavenging assay, antioxidants react with DPPH (deep violet color) and

111

convert it to yellow coloured α,α-diphenyl-β-picrylhydrazine. The degree of discoloration

indicates the radical-scavenging potential of the antioxidant (Blois, 1958; Huang et al., 2005).

The compounds displayed mild antioxidant activities, compound 4c and 5c showed good

activities as compared to the rest of the compounds which is due to the presence of electron

donating -OH, substituent at position 4 of the phenyl group. Compounds 4 and 5 displayed

less activity as compared to compound 4-4f, 5-5f due to the unsubstitutd phenyl ring.

The influence of electron donating and electron withdrawing substituted aryl group was

reflected by the results obtained for 4-4h and 5-5l polyhydroquinoline. It is worth mentioning

that the antioxidant activities of the target compounds depend not only on the ortho, meta and

para positions but also on the nature of the substituent attached.

From the table 4.13 two compounds, 4c and 5c were found to be better radical scavenger in

DPPH method while three compounds, 4c, 5c and 5k exhibited significant reducing ability in

FRAP method.

A close examination of the structure of the compounds in Table 4.13 suggested that

carbonitrile and ester group at third position were found responsible for variation in activity.

Whereas, the presence of substituent on phenyl at position 4 in polyhydroquinoline have a

major influence on their antioxidant activities.

Herein, we summarized the biological activities results of polyhydroquinoline derivatives 4-

4f, 5-5l tested for antibacterial activity, almost all the compounds were found weakly active

against the bacterial strains, S. aureus and E. coli except the compounds 4d, 5e, 5d, 5g, 5l

which selectively inhibited the bacterial strain. Antifungal studies were carried out for

compounds 4-4f, 5-5l and compounds 4d, 5d, 5e, 5g, 5i, 5l were found active against fungi

(Aspergillus niger) but rest of the compounds were found weakly active against fungal strain.

Amongst all the compounds 4-4f, 5-5l tested for anti-oxidant (DPPH radical scavenging)

activities and FRAP assay, compound 5c was the most active. Its % inhibition was 46.00 and

44.00 by DPPH and FRAP assay respectively, which was even greater than the reference

compound, BHT (37.00 and 40.00). Four other compounds 4c, 4d, 5d and 5k showed mild

antioxidant activity but rest of all the compounds showed negligible antioxidant activity.

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4.6 Biological Activities of Chalcones

4.6.1 Antimicrobial activity

A series of quinolinyl chalcones were prepared and tested for their in vitro antimicrobial

activity against the two strains of bacteria (gram +ve, gram -ve) and a strain of fungs. The

zone of inhibition was measured in mm. The results of these assays are summarized below.

4.6.1a Antibacterial activity

The antimicrobial activity of the synthesized quinolinyl chalcones was compared with

standard antibacterial drugs chloramphenicol and flucanazole antifungal standard.

Six compounds of the Table 4.14 showed high in vitro antimicrobial activity. Compound 7c,

7d showed excellent activity against Staphylococcus aureus, Escherichia coli, and against

fungal strain Aspergilus niger, compound 9c and 9d showed good activity against,

Staphylococcus aureus and Escherichia coli, compound 8c and 8d showed good to moderate

activity against Staphylococcus aureus and Escherichia coli and compound 7c and 9c showed

significant activity against fungal strain Aspergilus niger.

A close examination of the structures of the active compounds in Table 4.14 revealed that

their antimicrobial activity was strongly bound to the nature of the substituent at the

quinoline- C6. In general, it could be clearly recognized that compound with the quinoline

containing a methoxy substitutent (R= OCH3) 7a-7i showed the greatest activity compared to

the unsubstituted quinoline at position 6 of compounds 9a-9h. On the other hand, the

introduction of the methyl group at position 6 of the quinoline 8a-8h result a noticeable

decrease in the antimicrobial potential of these compounds.

The influence of heterocyclic ring on antibacterial activity was reflected by the results

obtained for 7a-7e, 8a-8e and 9a-9e chalcones. It is worth mentioning that the biological

activity of the target compounds depends not only on the hetroaromatic pharmacophore but

also on the nature of the substituent. The findings of this vigorous study suggested that the

increase in halo substitution in the basic nucleus enhances the inhibition of bacterial growth

significantly. The findings suggested that chalcones with thiophene moiety 7c bearing

electron withdrawing chloro group showed the greatest antibacterial activity (zone of

inhibition 42 mm).

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Table 4.13: Antimicrobial activities of compounds 7a-i, 8a-h and 9a-h zone of inhibition in mm

Compounds Ar group A.niger S.aureus E.coli

Zone of inhibition (mm)

7a 2-acetyl furan 3 39 11

7b 2,5- dimethyl 3-acetyl

furan

3 30 10

7c 2-chloro5-acetyl thiophene 19 42 38

7d 2-acetyl pyrole 14 40 28

7e 2-acetyl pyridine 2 6 9

7f o-methoxy ketone 5 6 8

7g m-mehoxy ketone 4 8 8

7h 2-acetyl naphthalein 10 36 23

7i 2-acetyl benzofuran 15 34 32

8a 2-acetyl furan 2 37 16

8b 2,5- dimethyl 3-acetyl

furan

11 32 9

8c 2-chloro5-acetyl thiophene 16 36 29

8d 2-acetyl pyrole 9 35 28

8e 2-acetyl pyridine 1 6 7

8f o-methoxy ketone 5 6 8

8g m-mehoxy ketone 4 5 7

8h 2-acetyl naphthalein 7 27 17

9a 2-acetyl furan 3 38 10

9b 2,5- dimethyl 3-acetyl

furan

3 34 9

9c 2-chloro5-acetyl thiophene 17 38 31

9d 2-acetyl pyrole 12 41 29

9e 2-acetyl pyridine 2 6 8

9f o-methoxy ketone 4 7 6

9g m-mehoxy ketone 3 8 7

9h 2-acetyl naphthalein 8 36 20

DMSO +ve +ve +ve

Standard 20 40 41

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+ve indicates microbial growth. Control: DMSO (0.01% solution in distilled water). Standard for antibacterial:

Chloramphenicol (1.00 mmol/ml). Standard for antifungal: Flucanazole (1.00 mmol/ml)

Compounds 7c, 8c and 9c, from substituted heteroaryl derivatives have shown promising

antibacterial activities (almost equivalent to standard) against all the two bacterial strains i.e.,

S. aureus and E. coli. Only 7c was found more active than the standard drug

chloramphenicol. In case of furanyl derivatives, incorporation of methyl group at position 2

and 5 7b, 8b and 9b considerably decreases the activity as compared to the unsubstituted one

7b, 8b and 9b. In addition, the furan-2-yl moieties 7a, 8a, 9a are more active than pyridine-

2-yl 7e, 8e and 9e against Staphylococcus aureus.

Introduction of aromatic ketone with methoxy substitutent decreases the activity against all

three strains of microorganisms but m-methoxy substituted chalcone 7g, 8g and 9g showed a

little better activity against Staphylococcus aureus and Escherichia coli as compared to o-

methoxy substituted chalcone7f, 8f and 9f.

4.6.1b Antifungal activity

By comparing the antifungal activity of series of chalcones 7a-i, 8a-h and 9a-h with the

standard drug fluconazole (20 mm and 1.00 mmol /ml for each) as zone of inhibition. It was

found that 7c, 8c and 9c compounds were showing significant activity against the fungal

strain A.niger which exhibits that prescence of sulphur in chalcones of heteroaromatic ring

(thiophene moity) influences the antifungal activity of chalcones.

The antifungal effects of the chalcones with aromatic ring was investigated and found that

compound 7g, 8g and 9g with electron donating methoxy substitutent (OCH3 group) in m-

position show almost negligible activity against fungus.

4.6.2 Antioxidant activity

A series of quinoline based chalcone were synthesized and their antioxidant activities were

assessed by DPPH radical scavenging activity and FRAP Assay.

4.6.2a DPPH radical scavenging activity of chalcone

A series of quinolinyl chalcone reported (7a-i, 8a-h and 9a-h) as potential antioxidants in

Table 4.15 and compared with commercial antioxidant butylated hydroxy toluene, (BHT) and

ascorbic acid). DPPH is a stable free radical and accepts an electron or hydrogen radical to

become a stable diamagnetic molecule. In the radical form, this molecule had an absorbance

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at 517 nm which disappeared after acceptance of an electron or hydrogen radical from an

antioxidant compound to become a stable 1,1-diphenyl 2- picrylhydrazine molecule.

The reported compounds displayed mild to good antioxidant activties, compound 7a-7i

showed good activities as compared to compound 8a-8h which is due to the presence of

electron donating -OCH3, substituent at 6 positions on the quinoline ring. Compounds 9a-9h

displayed less activity as compared to compound 8a-8h due to the unsubstitutd quinoline

ring.

The influence of heterocyclic ring on antioxidant activity was reflected by the results

obtained for 7a-7e, 8a-8e and 9a-9e chalcones. It is worth mentioning that the antioxidant

activities of the target compounds depend not only on the hetroaromatic pharmacophore but

also on the nature of the substituent attached.

DPPH radical scavenging activity at 50µg/ml displayed that the % inhibition of compounds

7b, 8b, 7i, 9b, 7a, 8a and 8h, 9b were 47.00, 40.00, 38.07, 36.00, 35.00, 32.00 and 31.06

respectively. Among 5 of these compounds found more active than ascorbic acid but only one

compound 7b has promising activity (almost equivalent to standard).

The increasing antioxidant activity of the compound 7b depicted that the introduction of two

methyl group on furan ring enhances its activity as compared to 7a unsubstituted furan ring.

The present study revealed that 7c exhibited moderate activity due to the influence of the

nature of the functional linkage and the position of the substituent on the hetrocyclic ring as

2-chloro thiophene chalcone. The least DPPH radical scavenging activity at 50µg/ml was

15.08 as shown by compound 9e due to the unsubstituted quinoline along with deactivating

nature of pyridine

Introduction of aromatic ring with methoxy substituted chalcones having methoxy group at

ortho-position 7f was found to be more active antioxidant with % inhibition 28.05 as

compared to m-OCH3 substituted chalcone 7g with % inhibition 23.09.

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Table 4.14: Antioxidant activities of compounds 7a-i, 8a-h and 9a-h with their % inhibition

Compounds Ar group DPPH

(50 µg mL-1)

FRAP activity

7a 2-acetyl furan 35.00 34.00

7b 2,5- dimethyl 3-acetyl furan 47.00 44.09

7c 2-chloro5-acetyl thiophene 22.00 20.00

7d 2-acetyl pyrole 25.06 24.08

7e 2-acetyl pyridine 20.00 17.09

7f o-methoxy ketone 28.05 25.08

7g m-mehoxy ketone 23.09 23.00

7h 2-acetyl naphthalein 32.08 30.00

7i 2-acetyl benzofuran 38.07 35.09

8a 2-acetyl furan 32.00 31.00

8b 2,5- dimethyl 3-acetyl furan 40.00 37.00

8c 2-chloro5-acetyl thiophene 21.00 18.09

8d 2-acetyl pyrole 23.06 21.07

8e 2-acetyl pyridine 19.00 15.08

8f o-methoxy ketone 26.05 24.08

8g m-mehoxy ketone 22.09 23.00

8h 2-acetyl naphthalein 31.06 28.09

9a 2-acetyl furan 28.00 27.00

9b 2,5- dimethyl 3-acetyl furan 36.00 34.00

9c 2-chloro5-acetyl thiophene 18.09 16.09

9d 2-acetyl pyrole 19.06 17.07

9e 2-acetyl pyridine 15.07 14.09

9f o-methoxy ketone 22.07 23.08

9g m-mehoxy ketone 18.09 17.00

9h 2-acetyl naphthalein 27.08 24.06

Ascorbic acid 33.58 38.06

BHT 48.0 45.43

Note: All the activity values are expressed in % age

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4.6.2b Ferric reducing power assay

Hence the antioxidant potential of any compound is related to its (i) hydrogen and electron

donation capacity, (ii) its ability to stabilize and delocalize the unpaired electron and (iii)

potential to cheleate the transition metal ions (Rice-Evans et al., 1997). The above three

actions are achieved either by the hydrogen atom or single electron transfer. In case of ferric

reducing antioxidant power assay (FRAP), it is due to the single electron transfer and in case

of superoxide radical scavenging, hydrogen peroxide scavenging, and in DPPH radical

scavenging activities, it is due to the transfer of hydrogen atom (Boutennoun et al., 2014).

Table 4.15 revealed that compound 7b displayed good ferric ion reducing activity almost

equivalent to standard butylated hydroxyl toluene but greater than ascorbic acid and

compound 9e showed the least activity in the series. Compounds 8b, 7i, 9b, 7a, 8a and 8h, 9b

showed good to moderate activity. It is investigated that the position of methoxy group on

aromatic ring as well as on quinoline ring greatly influences on the FRAP activity.

In short, we summarized the biological activities results of quinolinyl chalcone into

significant, moderate and weakly activated compounds. Amongst all the compounds 7a-i, 8a-

h and 9a-h tested for antibacterial activity, compounds 7e, 7f, 7g, 8e, 8f, 8g, 9e, 9f were

found weakly active against the bacterial strains, S. aureus and E. coli. On the other hand,

compounds 7c, 7d, 7h, 7i, 8c, 8d, 8h, 9a, 9b, 9c, 9h selectively inhibited the bacterial strain.

Antifungal studies were carried out for compounds 7a-i, 8a-h and 9a-h and compounds 7h,

7i, 8b, 8c, 9c, 9d were found active against fungi (Aspergillus, niger) but compounds 7a, 7b,

7e, 7f, 7g, 8a, 8d, 8e, 9f, 8g, 8h, 9a, 9b, 9e, 9f, 9g, 9h were found weakly active against fugal

strain.

Amongst all the compounds 7a-i, 8a-h and 9a-h tested for anti-oxidant (DPPH radical

scavenging) activities and FRAP assay, compound 7b was the most active. Its % inhibition

was 47.00 and 44.00 by DPPH and FRAP assay respectively, which was even greater than the

reference compound, BHT (48.00 and 45.43). Table 4.15 given below categorized the

synthesized compounds in the form of significant active compounds, moderately active and

weakly active.

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Table 4.15: Categorization of synthesized compounds on the basis of their antioxidant

activity 7a-i, 8a-h and 9a-h

Category Compounds

Significant 7b, 8b

Moderate 7a,7c, 7d, 7e, 7f, 7g, 7h, 7i, 8a, 8c, 8d, 8e, 8f, 8g, 8h, 9a, 9b,

9c, 9d, 9f, 9g, 9h

Weak 9e

It is important to mention that almost most of the quinolinyl chalcone exhibited moderate

activity.

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CHAPTER 5

SUMMARY

This thesis entitled “Synthesis And Characterization Of Potentially Biologically Active

Derivatives Of Polyhydroquinoline And Quinoline Ring Systems” describes the synthesis

and characterization of a variety of polyhydroquinoline and quinoline ring systems. Despite

of the availability of much literature on derivatives of quinoline, it was observed that the

synthesis of quinolinyl chalcone derivatives and their biological studies were least reported.

During this project of preparing potentially biologically active derivatives of

polyhydroquinolines and quinolines (section 3.4) and sufficiently characterized by NMR and

mass spectroscopic techniques as well as by XRD. Whereas, X-ray studies proved that it exist

as 1, 4- dihydropyridine or hexahydroquinoline nuclei (Section 4.3).

In this section 3.4.1, we had decided to investigate reactions of cyclohexanone and

malononitrile with different substituted aldehydes and ammonium acetate in ethanol without

using any catalyst. This reaction resulted in the production of 2-amino-4-methyl quinoline-3-

carbonitrile derivatives. The synthesis of 2-amino-4-phenyl-4a, 5, 6, 7-tetrahydro-4H-

naphthalene- 1, 3, 3 tricarbonitrile (3) was carried out by the same experiment as that of

compound 1 but acetaldehyde was replaced by benzaldehyde. As a result instead of getting 2-

amino-4-phenyl-5,6,7,8-tetrahydroquinoline-3-carbonitrile we accidently obtained a yellow

amorphous solid of 2- mino-4-phenyl-4a,5,6,7-tetrahydro-4H-naphthalene-1, 3, 3-

tricarbonitrile (3) with 62% isolated yield. This compound was discussed in detail in section

(3.4.1c).

In section 3.5 we investigated the reactions of 1,3-cyclohexandione, malononitrile with

different substituted aromatic aldehydes and ammonium acetate in ethanol using 10 mole %

P-TSA as catalyst. This reaction resulted in the production of the 2-amino-1,4-dihydro-4-

substituted aryl-quinoline-3-carbonitrile (4-4f).

Now the effect of a catalyst was investigated in these reactions of 1, 3- cyclohexandione,

ethyl acetoacetate with different substituted aromatic aldehydes and ammonium acetate

without any solvent and catalyst by simple grinding and secondly by using 10 mole % P-TSA

as catalyst and ethanol as solvent and thirdly by using guanidine HCl (section 3.6) to compare

the effect of a catalyst on yield, purity and reaction rate. This reaction resulted in the

120

production of ethyl 2-methyl-5-oxo-4-substituted-phenyl-1, 4, 5, 6, 7, 8-hexahydroquinoline-

3-carboxylate (5-5l).

In this section, we described a novel, expedient and fast synthesis of polyhydroquinoline

derivatives 4-4f and 5-5l assisted by P-TSA and ultraviolet irradiation. Comparative studies

of these compounds are carried out under different conditions: (1) under ultraviolet

irradiation (2) without ultraviolet irradiation (thermal heating). It is investigated from this

comparative study that ultraviolet radiation has significant activation effect. The rate of the

reaction and yield of the products exhibited the superiority of the ultraviolet assisted protocol

for the synthesis of polyhydroquinoline over thermal method (section 4.3.2).

At the end, heterocyclic chalcones were synthesized by a Claisen-Schmidt condensation

reaction of equimolar quantities of 6-OMe or 6-Me- or 6-H substituted 2-chloro-3-formyl

quinolines with various substituted heteroaromatic ketones in methanol in the presence of

40% NaOH solution (section 3.7). The formylquinolines were prepared by a Vilsmeier Haack

formylation of substituted acetanilides which were already synthesized by N-acetylation of

different substituted anilines with the help of acetic acid in the presence of ortho-phosphoric

acid. These chalcones 7a-7i, 8a-8h and 9a-9h were characterized by IR, NMR and mass

spectroscopic techniques (section 4.5).

At the end, all synthesized polyhydroquinolines 4a-4f, 5-5l and quinolinyl chalcone

derivatives 7a-i, 8a-h and 9a-h were evaluated for their in vitro antibacterial activity against

Staphylococcus aureu, Escherichia coli and for antifungal activity, Aspergillus niger was

used. Compounds 4a-4f, 5-5l exhibited mild antibacterial and/or antifungal activities (section

4.5). Many of the quinolinyl chalcone derivatives 7a-i, 8a-h and 9a-h exhibited potent

antibacterial and/or antifungal activities as compared to standard drugs ciprofloxacin

(bacteria) and fluconazole (fungi) but failed to get a common compound showing both types

of activities (section 4.6.1). Also polyhydroquinolines 4a-4f, 5-5l and quinolinyl chalcone

derivatives 7a-i, 8a-h and 9a-h were evaluated for antioxidant activities through DPPH (2,2'-

diphenyl-1-picrylhydrazyl) as well as reducing power method (Fe3+/Fe2+) and compared with

commercial antioxidant butylated hydroxy toluene (BHT) and ascorbic acid. Compounds 4a-

4f, 5-5l displayed mild antioxidant activities (section 4.5.2) and most of the quinolinyl

chalcone derivatives 7a-i, 8a-h and 9a-h exhibited potent DPPH radical scavenging and

FRAP antioxidant activity (section 4.6.2).