grindstone chemistry approach: synthesis and characterization...

Grindstone Chemistry approach: synthesis and

characterization of

2-thioxopyrimidine derivatives and its mosquito

larvicidal activity Sakthivel Palanimuthu#1

#1 Research scholar, Department of Chemistry,PRIST University, Vallam Thanjavur- 613 403

[email protected]

[email protected]

Abstract

The one-pot multicomponent synthesis of 2-thioxopyrimidine analogues (1a-1d) via Biginelli reaction

with grindstone chemistry technique as a novel method by using CuCl2.2H2O as a simple and

inexpensive catalyst. The title compounds were confirmed by FT-IR, 1H NMR, 13C NMR, and elemental

analyses. Compounds (1a-1d) were screened for mosquito larvicidal activity against

Culexquinquefasciatus. Among the synthesized compounds (1a-1d), the compound 1b was extremely

active with the LD50 value 55.94 μg /mL than standard Permethrin with the the LD50 value 60.03 μg

/mL respectively.

Keywords: Grindstone chemistry, Thioxopyrimidine, Culexquinquefasciatus, Larvicidal activity.

Introduction

Heterocyclic compounds plays a major role in medicinal chemistry research, as a key component in bio-

active drugs. Pyrimidines are the significant class of heterocyclic blocks that widely distributed in

nature. The pyrimidine analogues thymine, cytosine, and uracil were present in nucleic acids (DNA and

RNA) of alive organisms [1]. Pyrimidines possess broad range of pharmacological activities for

The International journal of analytical and experimental modal analysis

Volume XI, Issue VIII, August/2019

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*2, Dr.M.Jerome Rozario

*2 Associate Professor, Department of Chemistry,PRIST Deemed to be University, Vallam Thanjavur - 613 403

instanceanticancer [2], antileishmanial [3], anti-inflammatory [4], antifungal [5], antihypertensive [6],

analgesic [7], antibacterial [8],anticonvulsant [9], central nervous system (CNS) depressant properties

[10], antihistaminic [11], antidiabetic [12], antiviral [13], antiallerggic [14], herbicidal [15], antioxidant

[16], and also act as calcium channel blockers[17]. Some bio active 2-thioxopyrimidine derivatives were

shown in Fig. 1. The catalytic ability of copper based compounds in organic synthesis impressed us to

design copper containing compound as a catalyst. The copper based compounds like Cu(NO3)2·3H2O

[18], Cu sulfamate[19], Cu(OTf)2[20], Cu nanoparticles [21], and poly(4-vinylpyridine-co-

divinylbenzene)-Cu(II) complex [22] were already employed as a catalyst for Biginelli reaction. From

the literature, we select CuCl2.2H2O as a simple, commercially available and inexpensive catalyst for the

synthesis of 2-thioxopyrimidine analogues via Biginelli reaction. Mosquitoes are the important vectors

for deadly diseases like malaria,yellow fever, dengue fever, chikungunya,filariasis, and encephalitis.

More than millions of people affected from these diseases around the world. Keeping this in mind, the

present study aimed to synthesize 2-thioxopyrimidine derivatives via Biginelli reaction and also

screened for mosquito larvicidal activity.

Materials and methods

Chemistry:All materials were purchased from Nice and Loba chemicals. Melting points were checked in

an open capillary tubes and were uncorrected. Shimadzu 8201pc within the range of (4000-400 cm-1)

was used to recordthe IR spectra. JEOL-300 MHz spectrophotometer was used to analyze the ¹H NMR

and 13C NMR spectra of the title compounds. Elementer analyzer model (Varian EL III) was used to

analyze the Elemental analysis (C, H, and N). The reaction progress was tested by thin layer

chromatography (TLC) with silica gel plates.



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General procedure for the synthesis of compounds 1a and 1c

The combination of substituted aldehyde (1mmol), thiourea (1mmol),ethyl acetoacetate (1mmol), and

catalytic expanse of CuCl2·H2O was ground together for 2-5 min by using pestle and mortar. The

finishing of the reaction exhibited by TLC, the crude product was washed with cold water and

recrystallized from hot alcohol. The same method to be followed for the synthesis of compound 1c

General procedure for the synthesis of compounds 1b and 1d

The combination of ethyl acetoacetate (1mmol), hydrazine hydrate (1mmol),substituted aldehyde

(1mmol), thiourea (1mmol), and catalytic amount of CuCl2·H2O was ground together for 2-5 min by

using pestle and mortar. The finishing of the reaction exhibited by TLC, the crude product was washed

with cold water and recrystallized from hot alcohol. The same method to be followed for the synthesis of

compound 1d.

6-methyl -4-phenyl-2-thioxo-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid ethyl ester (1a)

White solid; mw: 276.35; mp 241°C; IR(cm-1): 3281.92 (NH), 3122.39 (Ar-H), 3023.01 (Ph-CHstr),

1643.30 (COOR), 1230.46 (C=S); 1H NMR (300MHz, DMSO- d6): δ 9.30 (2H, s, NH), 4.10 (1H, s,

CH), 7.03 (2H, d,J=6.21Hz, Ph), 7.08 (2H, t, Ph), 7.07(1H, t, Ph), 1.02 (3H, s,CH3), 5.01 (2H, q,CH2),

2.04 (3H, t,Ar); 13C NMR(300MHz, DMSO-d6): 176.0 (1C, C=S), 168.0 (1C, C=O), 160.0 (1C, 6C-H),

54.0 (1C, 4C-H), 144.0, 124.0, 128.0, 126.0 (6C, Ar ring), 100.2 (1C, 5C-H), 60.01 (1C, -CH2), 18.0

(1C, -CH3), 13.0 (1C, CH3); Elemental analysis: Calcd. For (C14H16N2O2S): C, 60.85; H, 5.84; N,

10.14,%; Found: C, 60.87; H, 5.82; N, 10.12%.

6-methyl -4-phenyl-2-thioxo-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid hydrazide (1b)

Black solid; mw: 262.33; mp 264°C; IR(cm-1): 3344.41 (NH), 3118.48 (Ar-H), 2957.62 (Ph-

CHstr),1725.72 (CONH), 1222.61 (C=S); 1H NMR (300MHz, DMSO- d6): δ 9.40 (1H, s, CONH), 9.20

(2H, s, NH), 7.20 (2H, t, Ph), 6.20 (2H, d,J=6.21Hz, Ph), 5.50 (1H, t, Ph), 4.20 (1H, s, CH), 2.1 (2H, s,



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NH2), 1.20 (3H, s,CH3); 13C NMR(300MHz, DMSO-d6): 174.2 (1C, C=S), 165.0 (1C, C=O), 158.0 (1C,

CH), 143.0, 127.1, 128.3, 126.5 (6C, Ar ring), 100.0 (1C, CH), 54.0 (1C, CH), 14.0 (1C, -CH3);

Elemental analysis: Calcd. For (C12H14N4OS): C, 54.94; H, 5.38; N, 21.36, %; Found: C, 54.90; H,

5.32; N, 21.34%.

6-methyl-4-styryl-2-thioxo-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid ethyl ester (1c)

Dust White solid; mw: 302.39; mp 283°C; IR(cm-1): 3426.12 (NH), 3245.05 (Ar-H), 3114.50 (Ph-

CHstr), 1651.15 (COOR), 1224.35 (C=S); 1H NMR (300MHz, DMSO- d6): δ 9.20 (2H, s, NH), 7.30

(2H, t, Ph), 7.14 (1H, t, Ph), 7.10 (2H, d, Ph),6.40 (1H, d, J=6.21Hz, CH=CH), 6.20 (1H,dd, J=7.33Hz,

J=7.37Hz, CH=CH), 4.10 (2H, q, CH2), 3.80 (1H, d,J=6.21Hz,-CH), 2.10 (3H, t,Ar), 1.20 (3H, s,CH3);

13C NMR(300MHz, DMSO-d6): 174.0 (1C, C=S), 164.0 (1C, C=O), 160.0 (1C, 6C-H), 142.4, 134.9,

126.2, 128.4, 127.2 (6C, Ar ring), 124.0 (1C, C=CH),122.0 (1C, CH=C), 104.2 (1C, CH), 62.0 (1C, -

CH2), 53.0 (1C, CH), 18.0 (1C, -CH3), 13.0 (1C, -CH3); Elemental analysis: Calcd. For (C16H18N2O2S):

C, 60.85; H, 5.84; N, 10.14, %; Found: C, 60.75; H, 5.80; N, 10.26 %.

6-methyl-4-styryl-2-thioxo-1,2,3,4-tetrahydro-pyrimidine-5-carboxylic acid hydrazide (1d)

Yellow solid; mw: 288.37; mp 212°C; IR(cm-1): 3415.28 (NH), 3258.49 (Ar-H), 2926.75 (Ph-CHstr),

1649.42 (CONH),1400.22 (C=S); 1H NMR (300MHz, DMSO- d6): δ 9.60 (2H, s, NH), 8.10 (1H, s,

CONH), 7.40 (2H, d, J=6.21Hz,Ph), 7.21 (2H, t, Ph), 7.10 (1H, t, Ph), 6.50 (1H, d, J=6.21Hz,CH=CH),

6.10 (1H,dd, J=7.33Hz, J=7.37Hz, CH=CH), 3.70 (1H, s, CH), 2.10 (2H, s, NH2), 1.20 (3H, s,CH3);13C

NMR(300MHz, DMSO-d6): 174.0 (1C, C=S), 164.0 (1C, C=O), 158.0 (1C, CH), 142.4, 134.9, 126.2,

128.4, 127.2 (6C, Ar ring), 126.0 (1C, C=CH), 122.0 (1C, CH=C), 120.0 (1C, CH), 53.0 (1C, CH), 17.0

(1C, -CH3); Elemental analysis: Calcd. For (C14H16N4OS): C, 58.31; H, 5.59; N, 19.43, %; Found: C,

58.32; H, 5.59; N, 19.40%.

Larvicidal activity



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Larvicidal screening was performed by the method described previously [23]. The statistical calculations

were performed by using statistical software SPSS version 16.0.

Results and Discussion

The one-pot multi-component reaction proceeded smoothly to give the corresponding 2-

thioxopyrimidine in high yields, the reaction was outlined in scheme 1 and 2. The mechanism of

proposed compounds were shown in scheme 3.The optimization of reaction conditions were shown in

Table I and the catalyst optimization was shown in Table II.

The compounds (1a-1d) wereconfirmed by FT-IR, 1H, and 13C NMR. The key assignments of title

compounds displays that an IR spectrum indicated absorption bands at 3281.92-3426.12, 3118.48-

3258.49, 2926.75-3114.50, and 1222.61-1400.11 cm-1, in compliance to the NH, Ar-H, Ph-CHstr and

C=Sgroups individually. ¹H NMR spectrum displayed signals at δ 9.20-9.60, 3.70-4.20, and 1.02-1.20

ppm, in compliance to the NH, 4-CH, and CH3 protons individually. The 13C NMR spectrum displays

peaks at δ 174.0-176.0, 164.0-168.0, and 14.0-18.0 ppm, assenting to the C=S, C=O, and CH3 carbon

atoms, individually.

Larvicidal activity

Compounds (1a-1d)were screened for larvicidal activity on second instar mosquito

larvaeculexquinquefasciatus. The compound 1b has high toxic and compound 1 has very less toxic

compared with compounds1cand1d. Compounds1aand 1cshowslow activity compared with other

compounds1b and 1dat 24h. Compound 1b and 1dhad harmfulupshot and killed 50% of second instar

larvaeand their LD50 value was 55.94 76.54, μg/mL respectively. Larvicidalscreening of the

compounds1band1d containing hydrazine moietydisplay very high activity however low activity for

compound 1aand1c.The compound1bhas highly active with the LD50 value of 55.94 μg/mL than the

control Permethrinwith the LD50 value of 60.03 μg/mL.The values are abridged in Table III.



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Conclusion

The one-pot multicomponent synthesis of 2-thioxopyrimidine derivatives (1a-1d) were attained with

good yields via Biginelli reaction by using novel grindstone chemistry technique. The simple, easily

available, and economical compound was CuCl2.2H2O employed as a catalyst. The title compounds (1a-

1d) were confirmed by FT-IR, 1H, 13C NMR and also screened for mosquito larvicidal activity against

Culexquinquefasciatus. Among the synthesized compounds (1a-1d), the compound 1b was highly active

than standard Permethrin. Therefore, compound 1b as a prospective candidate for mosquito control.

References

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Biginelli Reaction Catalyzed By Cu(NO3)2 .3H2O, Syn. Commun. 40 (2010) 1115–1122.

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Scheme 1. Synthesis of pyrimidine derivatives 1a and 1c

Scheme 2. Synthesis of Amine-connected pyrimidine derivatives 1b and 1d



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Scheme 3: Mechanism of preparation of 2-thioxo pyrimidine compounds



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Table I. Optimization of reaction condition

S.No. X R Ar Reaction

condition

Yield % Final product

structure

1 X=S EtO-

30 min, RT 47

N

NH

H

S

EtO

O

2 X=S H2N NH2

10 min, RT 88

N

NH

H

S

O

NH

H2N

3 X=S EtO-

30 min , RT 35

NHHN

S

OEtO

4 X=S H2N NH2

15 min, RT 33

NHHN

S

NH.NH2O

Table II. Optimization of catalyst

S. No. Catalysts Yield (%)

0.5 Mole % 1 Mole % 2 Mole %

1 TiCl2 - - -

2 SnCl2 - - 45

3 ZnCl2 16 34 47

4 ZrOCl2 - - 14

5 FeCl2 19 38 63

6 CuCl2.2H2O 68 98 -



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Table III. Larvicidal profile of compounds (1a-1d) on second instar larvae of

Culexquinquefasciatus

Positi

ve

contro

l:

Perme

thrin;

Negat

ive

contro

l:DM

SO; a

Value

were

the

means

of

three

replic

ates ± SD.

Comp.No

Mortality (%)Room temp LD50

μg /mL

Concentration (μg /mL)a

25 50 75 100

1a 10 ± 0.21 20±0.18 34±0.84 30±085 -

1b 38±0.81 51±0.87 66±0.35 80±0.65 55.94

1c 16±0.32 29±0.10 34±0.53 40±0.65 -

1d 22±0.45 46±0.32 51±0.74 60±0.14 76.34

Positive control 29±0.39 43±0.32 51±0.11 72±0.22 60.03

Negative control 0 ± 0.00 0 ± 0.00 0 ± 0.00 0 ± 0.00 -



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Fig. 1. Bioactive 2-thioxopyrimidine derivatives

Methylthiouracil



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Fig. 2. The IR spectrum of compound 1a



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Fig. 3. The 1H NMR spectrum of compound 1a



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Fig. 4. The13C NMR spectrum of compound 1a



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Fig. 5. The IR spectrum of compound 1b



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Fig. 6. The 1H NMR spectrum of compound 1b



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Fig. 7. The 13C NMR spectrum of compound 1b



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Fig. 8. The IR spectrum of compound 1c



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Fig. 9. The 1H NMR spectrum of compound 1c



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Fig. 10. The 13C NMR spectrum of compound 1c



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Fig. 11. The IR spectrum of compound 1d



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Fig. 12. The 1H NMR spectrum of compound 1d



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Fig. 13The 13C NMR spectrum of compound 1d



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