KHARKIV V.N. KARAZIN NATIONAL UNIVERSITY

OLEKSANDR S. DETISTOV

BIS-HETEROCYCLIC SYSTEMS CONTAINING 1,2,4-OXADIAZOLE RING: SYNTHESIS AND

REACTIVITY

Organic chemistry

Author abstract of Dissertation for a candidate's (Ph.D.) degree in chemical sciences by speciality 02.00.03 - organic chemistry

Kharkiv, Ukraine – 2012

1

INTRODUCTION

Detistov O. S. Bis-heterocyclic systems containing 1,2,4-oxadiazole ring: synthesis and reactivity. – Manuscript.

Author abstract of dissertation for a candidate's (Ph.D.) degree in chemical sciences by speciality 02.00.03 - organic chemistry – Kharkiv V.N. Karazin National University, Kharkiv, 2012.

The present work is devoted to the synthesis and study of the reactivity of the heteryl-1,2,4-oxadiazoles.

Here, we represent preparative methods for synthesis of isomeric 3-isoxadiazolylcoumarins and their derivatives. Two new synthetic methods have been developed for 3-[1,2,4-oxadiazol-5-yl]coumarins. The first method is based on a three-component condensation of coumarin-3-carboxylic acids, 1,1'-carbonyldiimidazole and amidoximes. The second method essentially uses the interaction of 5-cyanomethyl-1,2,4-oxadiazoles with salicylic aldehydes. General approach for preparation of 3-[1,2,4-oxadiazol-3-yl]coumarins has been worked out. Moreover, above mentioned synthetic schemes open the way for the synthesis of their 2-imino derivatives not described before. Thereafter 2-iminocoumarins were diversified by reaction of nucleophilic substitution of the 2-imino group with numerous amino compounds. Antimicrobial and antifungal activities of 3-[1,2,4-oxadiazol-5-yl]coumarins were estimated by experimental studies.

New method for synthesis of 4-[1,2,4-oxadiazol-5-yl]-1H-pyrazoles has been worked out. The direction, the reactivity and conditions for the alkylation, the acylation reactions and the condensation with derivatives of acetoacetic ether of such kind heterocyclic compounds were investigated. New 3-[1,2,4-oxadiazol-5-yl]-pyrazolo[1,5-a]pyrimidin-7(4H)-ones were prepared.

5-(1H-1,2,3-Triazol-4-yl)-1,2,4-oxadiazoles were obtained by Dimroth reaction of 1,2,3-triazole synthesis by means of cyclocondensation of arylazides with 5-cyanomethyl-1,2,4-oxadiazoles and 5-acetonyl-1,2,4-oxadiazoles. Dimroth rearrangement was realized by example of 5-(1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazole.

Key words: 1,2,4-oxadiazole, coumarin, 2H-pyrano-[2,3-c]pyridin-2-one,

pyrazole, 1,2,3-triazole, pyrazolo[1,5-a]pyrimidin-7(4H)-one, synthesis, biological activity.

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PRINCIPAL CONTENTS

ІSOMERIC 3-ISOXADIAZOLYLCOUMARINS AND THEIR DERIVATIVES

Formerly described methods for synthesis of 3-[1,2,4-oxadiazol-5-yl]coumarins

are mainly based on the interaction of functional derivatives of coumarin-3-carboxylic acids, such as anhydrides, chlorinanhydrides and esters, with amidoximes. However, those methods suffer from grave shortcomings. There is an additional step for modification of a carboxylic group into more reactive derivative and there is a necessity to separate out this product. It complicates synthetic rout and makes incompatible with several functional groups, such as amino, hydroxy, etc. Indicated factors stimulate the development of perfected methods. We chose two tracks to solve this task.

The first way (method A) is based on the formation 1,2,4-oxadiazole moiety based on a coumarin skeleton. It was implemented by in situ activation of coumarin-3-carboxylic acid by 1,1`-carbonyldiimidazole (CDI) with further addition of amidoxime component to a reaction mixture. This method affords a clean one-pot approach by consecutive addition of reagents, which is applicable to parallel solution-phase synthesis (Scheme 1).

NH2

N OHR2

CDI

O O

N

NOR2

R1

3a-c4a,b

5a-f Yields : 38 - 68 %

O

OHR1 +

O O

O O

O O

OH

O

R1

3a-c1a-c 2

5a-f : R1 = 6-Br, 7-CH3O, 7-(C2H5)2N

R2 = C6H5, 4-CH3O-C6H4.

DMF, 500C O O

O

N N

R1

DMF, 800C O O

O

ON

NH2

R2

R1

DMF, 1100C

Dioxane

I II

Scheme 1. Method A for 3-[1,2,4-oxadiazol-5-yl]coumarins synthesis.

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Significantly, at the beginning coumarin-3-carboxylic acid forms reactive imidazole derivative I upon treatment with CDI. After addition of amidoxime, at 70–80 ºC O-heteroyl amidoxime II is generated, which then cyclizes at 110 ºС into the ultimate product. Intermediates I and II were not separated out by us in this case, but authors in earlier paper denoted exactly such mechanism for one-pot condensation of this type. Coumarin-3-carboxylic acids 3a-f necessary for this reaction are easily obtained by the reaction of salicylic aldehydes 1a-f with Meldrum`s acid 2 according to described before method. Arylamidoximes 4a,b (N'-hydroxybenzenecarboximidamides) synthesis was carried out from corresponding benzonitriles and hydroxylamine. 3-[1,2,4-Oxadiazol-5-yl]coumarins 5a-l were synthesized by method A with yields in a range of 38 – 72 % directly from coumarin-3-carboxylic acids and arylamidoximes without the stage of anhydrides, chlorinanhydrides and esters preparation and separation of intermediates.

The second approach (method В) for 3-[1,2,4-oxadiazol-5-yl]coumarins synthesis consists in the formation of a coumarin cycle by Knoevenagel condensation of 5-cyanomethyl-1,2,4-oxadiazoles with salicylic aldehydes. If to carry out this reaction under anhydrous conditions, 2-imino derivatives form as final a product. However, 2-imino group can be fully hydrolyzed by addition to reaction mixture concentrated aqueous solution of hydrochloric acid in the end. 5-Cyanomethyl-1,2,4-oxadiazoles 7a,b, required for this condensation, were prepared by reaction of amidoximes 4b,c with 1-(cyanoacetyl)-3,5-dimethyl-1H-pyrazole 6. 3-[1,2,4-Oxadiazol-5-yl]coumarins 5m-o were synthesized in such a manner with 58 – 67 yields (scheme 2).

NN

O

NN

O N

NR2

7a-dYields : 66 - 99 %

+

6

O O

N

NOR2

R1

5m-oYields : 58 - 67 %

1) Et-OH;2) HCl in H2O addition

7a,b +

5m-o: R1 = 8-OH, 8-C2H5O; R2 = 4-CH3O-C6H4, 4-CH3-C6H4;

NH2

N OHR2

4

O

OH

R1

Dioxane

Scheme 2. Method В for 3-[1,2,4-oxadiazol-5-yl]coumarins synthesis.

Method B makes possible to synthesize 3-[1,2,4-oxadiazol-5-yl]coumarins with

a hydroxyl group in a coumarin moiety for example, 8-hydroxycoumarin 5о. To

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expand synthetic availability of product class 5, coumarin 5о was alkylated by benzylchlorides 8a-e and series of respective 8-O-benzyl derivatives 5p-t was obtained with 43 – 57 % yields (scheme 3).

ClR3

O O

N

NO

O

R2

R3

5p-t Yields : 43 - 57 %

8a-e

+

5p-t : R2 = 4-CH3-C6H4; R3 = 2-F-C6H4, 3-F-C6H4, 4-F-C6H4, 3-CH3-C6H4, 4-CH3-C6H4.

O O

N

NO

OH

R2

DMF

K2CO3

Scheme 3. Alkylation of 8-hydroxy-3-[1,2,4-oxadiazol-5-yl]coumarin.

The structures of 3-[1,2,4-oxadiazol-5-yl]coumarins 5a-t synthesized by method A and B were confirmed by spectral data. The position and multiplicity of signals Н-4, Н-5, Н-6, Н-7 and Н-8 correspond with type of substitution in a coumarin nucleus. 1Н-NMR spectra of compounds 5m-o have no signal of imino group`s protons, so hydrolysis reaction proceeded completely. In IR-spectra of the compounds 5 characteristic bands of lacton`s С=О group valent oscillation (1740 – 1772 cm-1) and low-intensity bands of 1,2,4-oxadiazole cycle C=N bonds, which in most cases are overlapped with bands of С=С aromatic valent oscillation, are observed. The integration of two heterocyclic fragments into one molecule is revealed by batochrom displacement of the long-wave band in UV spectra.

The carrying out of the Knoevenagel condensation of 5-cyanomethyl-1,2,4-oxadiazoles with salicylic aldehydes into anhydrous solvents allow to obtain pure 2-iminocoumarins 9a,b (scheme 4). Those compounds are characterized by singlet signal in a field of δ: 9.90 - 10.10 ppm in NMR spectra recorded in СDCl3, whereas in DMSO-d6 they are unstable. Iminolacton fragment in a structure of obtained compounds 9a,b is reactive towards nucleophilic reagents; it enables to realize a number of substitution reactions by 2-imino group. Thereby, not described before 2-N-aryliminoderivatives 11а-с were obtained with 45 – 61 % yields by the reaction of 2-iminocoumarin 9a with substituted anilines 10a-c. The use of arylsulfonylhydrazides 12a-c in this reaction leads to formation of new 2-N-arylsulfonylhydrazono-3-[3-aryl-1,2,4-oxadiazol-5-yl]coumarins 13a-c with 59 – 76 % yields. The signal of imino group proton is not observed in 1Н-NMR spectra of compounds 11а-с and 13a-c, this fact indicates effective and complete reaction proceeding. NH proton of arylsulfonylhydrazide fragment in 1

Н-NMR spectra of compounds 13а-с is observed as singlet signal in a field of δ: 10.5 – 11.0 ppm (DMSO-d6). IR spectra of those substances show bands of S=O bonds valent oscillation in a range of ν: 1130 – 1170 cm-1.

5

1g,h

O NH

N

NOR2

R1

7a,b9a,bYields : 78 - 83 %

i-Pr-OH

NH2

R4

O N

N

NOR2

R4

10a-c

11a-cYields : 45 - 61 %

R1

SNH

O

ONH2

R5

12a-c

O N

N

NO

NHS

O

O

R2

R5

13a-cYields : 59 - 76 %

R1

NH2 OH

O

N

NO

NOH

R2

14Yield : 45 %

R1

O

O

O

R6 R6

15a-c

O

N

NO

NO

R2

O

R6

R1

16a-cYields : 67 - 85 %

9a,b: R1 = H, 8-C2H5O; 10a-c, 13a-c: R1 = H; 14, 16a-c: R1 = 8-C2H5O.9a,b: R2 = 4-CH3O-C6H4, 4-CH3-C6H4; 14, 16a-c: R2 = 4-CH3-C6H4; 11a-c, 13a-c: R2 = 4-CH3O-C6H4.R4 = 4-CH3, 4-CH3CO, 4-CH3CONH;R5 = 4-CH3, 3,4-di(CH3O), 2,5-di(CH3O);R6 = CH3, C2H5, (CH3)2CH.

+

O

OR1

N

N

NOR2

CH3COOH

CH3COOH

CH3COOH

Scheme 4. Substitution reactions of 2-imino group of 2-imino-3-[1,2,4-

oxadiazol-5-yl]coumarins.

It should be noted that 2-imino group of compound 9b was successfully substituted by hydroxylamine. For the substitution reaction base of hydroxylamine was used, and 2-hydroxyiminocoumarin 14 was obtained with 45 % yield. Then target compound 14 was inputted into the reaction of acylation by various carboxylic acid anhydrides 15a-c. The acylation reaction was carried out in acid anhydrides media and 2-acyloxyiminocoumarins 16a-c were synthesized with 67 –

6

85 % yields. 1Н-NMR spectrum of 2-(hydroxyimino)-coumarin 14 shows a signal of hydroxyimino group proton at δ 10.88 ppm. That signal disappears in 1

Н-NMR spectra of 2-acyloxyiminocoumarins 16a-c and signals of acylgroups appear with corresponding multiplicity.

In a present work, the synthesis of 3-[5-aryl-1,2,4-oxadiazol-3-yl]coumarins 22a-f isomeric with respect to compounds 5 was realized. There are reports about syntheses of compounds 22 in the literature [23], but those are separated and singular. In connection with that we developed new preparative method permitting to synthesize a range of 3-[5-aryl-1,2,4-oxadiazol-3-yl]coumarins 22 and go over to synthesis of related 2-iminoderivatives 25. The method is based on the condensation of 2-(5-aryl-1,2,4-oxadiazol-3-yl)-acetamides 21a,b with salicylic aldehydes 1a,e, i (Scheme 5).

We chose 2-cyanoacetamide 17 as initial compound for modification of nitrile functionality. It makes possible to obtain amidoxime 18 with good yields by simple synthetic procedure. The use of malononitrile and ethyl cyanoacetate for amidoxime preparation did not lead to success. Then amidoxime 18 was inputted into the condensation analogous to be used for 3-[1,2,4-oxadiazol-5-yl]coumarins 5a-l preparation by method A. As a first step, О-aroylsubstituted amidoximes 20a,b were obtained by the reaction of amidoxime 18 with aromatic acids 19a,b activated by CDI in dioxane and separated out of reaction mixture. As a second one, compounds 20a,b were cyclized into 2-(5-aryl-1,2,4-oxadiazol-3-yl)-acetamides 21a,b in dimethylformamide under heating. Step by step approach in this case gave more yields of required functionalized 1,2,4-oxadiazoles 21a,b.

The condensation of heterylacetamides 21 with salicylic aldehydes 1a,e,i lead to formation of target compounds 22a-f. By the treatment of acetamide 21a with thionyl chloride corresponding 3-cyanomethyl-5-aryl-1,2,4-oxadiazole 23 was obtained. Product 23 formed 2-imino-3-[5-aryl-1,2,4-oxadiazol-3-yl]coumarin 24, isomeric with respect to compounds 9, by the reaction with salicylic aldehyde 1d. On the base of iminocoumarin 24 products of substitution at the 2-imino group 25a-c were obtained. Spectral characteristics of 3-[5-aryl-1,2,4-oxadiazol-3-yl]coumarins 22a-f and 2-imino derivatives 24 and 25a-c correspond to structures given.

7

OH

OR2 O

NH2

N

NH2

O

O R2

O

NH2

N O

NR2

O

N

ON

O

R2

NNH2

O

OH NH2

O

NH2

N

NH2

OH

17

19a,b

20a,bYields : 50 - 75 %

22a-fYields : 28 - 55 %

DMF, 1200C

1a,e, i

+ + CDI18

SOCl2

N O

NN R2

23Yield : 33 %

1d

O NH

N

ONR2

R1

24Yield : 76 %

10e-g

O N

N

ONR2

R1

R3

25a-cYields : 58 - 63 %

21a,bYields : 30 - 37 %

18Yield : 72 %

Dioxane, 800C

22a-f: R1 = H, 8-CH3O, 6-Cl; 23, 24, 25a-c: 7-CH3O. 19a,b, 20a,b, 21a,b, 22a-f: R2 = 4-CH3-C6H4, 4-CH3O-C6H4; 23, 24, 25a-c: R2 = 4-CH3-C6H4.R3 = 3,4-di(CH3)-C6H3 2-F-C6H4, 4-C2H5O-C6H4.

R1

DMFi-Pr-OH

i-Pr-OH

i-Pr-OH

CH3COOH

O

OR1

O

OR1

NH2

R4

Scheme 5. Synthesis of 3-[1,2,4-oxadiazol-3-yl]coumarins and their 2-imino

derivatives.

To resume, new perfected methods of synthesis of 3-[1,2,4-oxadiazol-5-yl] and 3-[1,2,4-oxadiazol-3-yl] coumarins were worked out. Furthermore, represented approaches make possible to go over to synthesis of related 2-imino derivatives, which are not described before. The presence in structures given of several randomization points allow to use proposed synthetic procedures for obtainment of a considerable number of substances for carrying out of drug screening research.

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The investigations of antimicrobial and antifungal activities of synthesized 3-[1,2,4-oxadiazol-5-yl]coumarins 5c,d,f,i,j,l (Fig. 1) were implemented in the laboratory of antimicrobial agents of the research institute of microbiology and immunology named by I.I. Mechnikov (Kharkiv city). Antimicrobial activity was studied by twofold serial dilution method in liquid and solid nutrient media against gram-positive and gram-negative microorganisms. Minimum inhibitory (MICs, µg/ml) and bactericidal (MBCs, µg/ml) concentrations were determinated (Table 1).

O O

N

NOR2

R1

5c,d,f,i,j,l

Figure 1. 3-[1,2,4-Oxadiazol-5-yl]coumarins

Table 1. Antimicrobial activities of 3-R1- [3-R2-1,2,4-oxadiazol-5-yl]coumarins 5c,d,f,i,j,l

Strain

S. Aureus ATCC 25923

E. Coli ATCC 25922

Ps. Aeruginosa ATCC 27853

Pr. Vulgaris ATCC 4636

B. Anthracoides ATCC 1312

C. Albicans ATCC

885-653

Compound MIC / MBC

(µg/ml)

MIC / MBC (µg/ml)

MIC / MBC (µg/ml)

MIC / MBC (µg/ml)

MIC / MBC (µg/ml)

MIC / MBC

(µg/ml) 5c (R1 = 6-Br,

R2 = C6H5) 125.0 250.0

31.2 62.5

125.0 125.0

62.5 62.5

62.5 125.0

62.5 125.0

5d (R1 = 7-CH3O, R2 =

C6H5)

125.0 250.0

62.5 125.0

62.5 125.0

62.5 62.5

125.0 125.0

250.0 250.0

5i (R1 = 6-Br, R2 = 4-CH3O-

C6H4)

31.2 62.5

31.2 62.5

31.2 62.5

31.2 62.5

31.2 62.5

31.2 62.5

5f (R1 = 7-(C2H5)2N, R2 =

C6H5)

125.0 125.0

31.2 62.5

62.5 62.5

62.5 62.5

62.5 62.5

250.0 250.0

5j (R1 = 7-CH3O, R2 = 4-CH3O-C6H4)

62.5 125.0

31.2 62.5

125.0 125.0

62.5 62.5

31.2 62.5

62.5 125.0

5l (R1 = 7-(C2H5)2N, R2 = 4-CH3O-C6H4)

62.5 62.5

62.5 62.5

62.5 62.5

125.0 125.0

62.5 125.0

62.5 125.0

Screening conducted discovered, that synthesized substances have shown

medium and moderate activities in experiments. It should be noted, compounds with a methoxyl group in their structures demonstrated higher activity against S. Aureus and C. Albicans strains. In this row, compound 5i with methoxyl group and bromine atom as substituents has the lowest MIC and MBC. The activity of compound 5i towards E. Coli strain is congruent quantity to activity of penicillin G

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(MIC – 32 µg/ml) and it is in eight times lower than ampicillin activity (MIC – 4 µg/ml). However, penicillin G and ampicillin are inactive (MIC > 128 µg/ml) towards Ps. Aeruginosa strain, whereas compound 5i shows moderate activity in this case.

In conclusion, screening among 3-[1,2,4-oxadiazol-5-yl]coumarins for antimicrobial and antifungal activities demonstrated promising results.

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5-(1H-4-PYRAZOLYL)-1,2,4-OXADIAZOLES:

SYNTHESIS AND REACTIVITY

We have developed simple and effective synthetic methods for the preparation of diverse substituted 5-(1H-4-pyrazolyl)-1,2,4-oxadiazoles. We started from functionally substituted 1,2,4-oxadiazoles – 5-cyanomethyl-3-aryl-[1,2,4]oxadiazoles 7. These methylenactive nitriles interact with a carbon disulfide in alkaline media with consequent addition of methyl iodide and form 5-[1-cyano-2,2-bis(methylthio)vinyl]-[1,2,4]oxadiazoles 29. Corresponding 5-[1-cyano-2-(R2-amino)-2-(methylthio)vinyl]-[1,2,4]oxadiazoles 30 were obtained by two synthetic ways: reaction of compounds 29 with amines (method A) or reaction of substances 7 with isothiocyanates in a present of alkali with further addition of methyl iodide (method B) (Scheme 6).

NO N

NR1

SS

7a-d

1. CS2 (26), NaOH2. CH3I (27)

1. R2NCS (28), NaOH2. CH3I

Method B

NO N

NR1

SNH

R2

Method A

29a-cYields : 88 - 95 %

30a-hYields : 72 - 98 % (A) 71 - 88 % (B)

29a, 30a,b: R1 = C6H5; 29b, 30c,d: R1 = 4-CH3-C6H4;29c: R1 = 4-CH3O-C6H4; 30e-h: R1 = 4-Cl-C6H4;

30a-h: R2 = CH3, C2H5, CH(CH3)2, CH2CHCH2, C6H5.

R2NH2

NO N

NR1

dioxane / H2O

i- Pr-OH

dioxane

Scheme 6. Synthesis of S,S-ketenacetales and N,S-ketenacetales of 1,2,4-oxadiazole row.

Method A has several advantages over method B: it makes possible to obtain

compounds 30 with wide diversity of an amine moiety, included secondary amines, and exclude toxic isothiocyanates. However, method B allows obtaining of N,S-ketenacetales 30 directly from starting methylenactive nitriles 7.

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The following reactions of S,S-ketenacetales 29 and N,S-ketenacetales 30 with hydrazine hydrate under reflux in an isopropyl alcohol lead to formation of 5-(1H-3-Х-5-amino-pyrazolyl-4)-1,2,4-oxadiazoles 31a-c (Х = SCH3) and 33a-h (NH-alkyl) with 76 – 96 % yields (Scheme 7).

29a-c

NH2 NH2

30a-h

O N

NR1

SNNH

NH2

31a-cYields : 76 - 90 %

+

O N

NR1

NH

NH2

NNH

NH2

32Yields : 8 - 10 %

O N

NR1

NNNH

NH2

R2

33a-hYields : 84 - 96 %

NH2R2

NH2 NH2

NH2 NH2

31a, 33a,b: R1 = C6H5; 31b, 33c,d: R1 = 4-CH3-C6H4;31c: R1 = 4-CH3O-C6H4; 33e-h: R1 = 4-Cl-C6H4.33a-h: R2 = CH3, C2H5, CH(CH3)2, CH2CHCH2, C6H5.

i- Pr-OH

i- Pr-OH

i- Pr-OH

NO N

NR1

SS

NO N

NR1

SNH

R2

i- Pr-OH

Scheme 7. Reaction of 5-(1H-5-amino-pyrazolyl-4)-1,2,4-oxadiazoles formation

It should be noted that excess of hydrazine hydrate led to impurities of

3-hydrazino-4-([1,2,4]oxadiazol-5-yl)-1Hpyrazol-5-amine 32 in crude 3-(methylthio)-4-([1,2,4]oxadiazol-5-yl)-1H-pyrazol-5-amines 31. However, when we refluxed isolated pure compounds 31 with hydrazine hydrate or amine derivative, reaction of direct substitution of the methylthio-group did not occur. So, this side reaction occurs possible only when two molecules of the hydrazine hydrate react with 5-[1-cyano-2,2-bis(methylthio)vinyl]-[1,2,4]oxadiazoles 29 before the pyrazole cycle formation. Described above impurities 32 can be easily separated by crystallization from hot isopropyl alcohol. The mother liquor contains pure desired product 31.

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In 1H NMR spectra of compounds 31 singlet of proton of the pyrazole ring NH group is observed at 11.95-12.15 ppm, signal of NH2 group at 6.50-6.55 ppm, but in case of compounds 33 signals of NH2 group protons are overlapped with NH-R2 and observed at 5.80-6.0 ppm, NH signal of the pyrazole ring observed at 10.95-11.0 ppm. All other proton signals are observed in their usual resonance areas.

We studied reactivity 5-(1H-5-amino-pyrazolyl-4)-1,2,4-oxadiazoles 31 and 33 in alkylation reaction. In a case of potassium carbonate (catalyst) – N,N-dimethylformamide (solvent) reaction media we achieved selective reaction proceeding. The alkylation occurred by N1 atom of a pyrazole ring near unsubstituted NH2 group in both cases. We chose 2-chloracetamides 34 as alkylation agents to synthesize small combinatorial libraries of substituted 5-[5-amino-1-{2-[amino]-2-oxoethyl}-3-(methylthio)-1H-pyrazol-4-yl]-1,2,4]-oxadiazoles 35 and 5-(5-amino-3-[amino]-1-{2-[ amino]-2-oxoethyl}-1H-pyrazol-4-yl)-[1,2,4]oxadiazoles 36 (Scheme 8).

31a,b

ClNH

OR3

34N

NO

NN NH2

S

NH

O

R1

R3

35a-gYields : 55 - 91 %

33e,f,h

34N

NO

NN NH2

NH

NH

O

R1

R2

R3

36a-gYields : 55 - 83 %

NOESY

NOESY

ClNH

OR3

35a: R1 = C6H5; 35b-g: R1 = 4-CH3-C6H4; 36a-g: R1 = 4-Cl-C6H4;36a-g: R2 = CH3, C2H5, CH(CH3)2, CH2CHCH2, C6H5.35: R3 = 3-CH3O-C6H4-CH2, 3-Cl-4-CH3-C6H3, 4-C2H5O-C6H4, 4-CH3-C6H4, 3-F-4-CH3-C6H3,3-Cl-4-F-C6H3, 4-CH3O-C6H4. 36:R3 = 3,5-di-CH3-C6H3, 2-CH3O-5-CH3-C6H3, 3-C2H5-C6H4, 2-Cl-C6H4-CH2, 4-Cl-C6H4-CH2,2,4,6-three-CH3-C6H2, 2,4,6-three-CH3-C6H2.

K2CO3, DMF

K2CO3, DMF

O N

NR1

SNNH

NH2

O N

NR1

NHNNH

NH2

R2

Scheme 8. Alkylation of 5-(1H-5-amino-pyrazolyl-4)-1,2,4-oxadiazoles The selective alkylation proceeding was proven by NOESY spectra of

products 35f and 36e. Cross-coupling peaks between CH2-protons of acetamide fragment and 5-amino group are observed (Figure 2, 3). Interaction between CH2-protons of the acetamide fragment and substitutes at third position of the pyrazole ring was absent in both cases.

13

Figure 2. 2D NOESY spectrum of compound 35f

Figure 3. 2D NOESY spectrum of compound 36e

14

Compounds 35 were loaded into acylation reaction. Monoacyl derivatives 38

were obtained with 56 – 71 % yields, when we used acylchlorides 37 in dioxane. In a case of acetic anhydride 15a without solvent, diacetyl derivatives 39 were formed and recovered with 59 – 73 % yields (Scheme 9).

35

Cl

OR4

N

NO

NN NH

S

NH

O

OR4

R1

R3

38a-dYields : 56 - 71 %

37a,b

O

O

O

39a,bYields : 59 - 73 %

15a

N

NO

NN N

S

NH

O

R1

R3

O

O

N

NO

NN NH2

S

NH

O

R1

R3

38a-d: R1 = 4-CH3-C6H4; 38a,b: R3 = 4-CH3O-C6H4;38c,d: R3 = 3,4-di-CH3-C6H3; 38a,c: R4 = CH3; 38b,d: R4 = n-C3H7;39a,b: R1 = C6H5; 39a: R3 = C6H5; 390b: R3 = 4-(CH3)2CH-C6H4.

dioxane

Scheme 9. Scheme of acylation of 5-[5-amino-1-{2-[R3-amino]-2-oxoethyl}-

3-(methylthio)-1H-pyrazol-4-yl]-3-R1-[1,2,4]oxadiazoles

In a case of monoacyl derivatives 38, in 1H NMR spectra NH-proton is observed about 10.20 ppm. In a case of diacetyl derivatives 39, in 1H NMR spectra NH-proton is absent and signal of acetyl protons was observed at 2.40-2.50 ppm with double integral intensity.

15

The following studied reaction of 5-(1H-5-amino-pyrazolyl-4)-1,2,4-oxadiazoles 31, 33 was the interaction with substituted acetylacetates 40 upon heating in a glacial acetic acid. This reaction leads to 2-(methylthio)-3-(-[1,2,4]oxadiazol-5-yl)pyrazolo[1,5a]pyrimidin-7(4H)-ones 41 and 2-[amino]-3-( [1,2,4]oxadiazol-5-yl)pyrazolo[1,5-a]pyrimidin-7(4H)-ones 42 correspondingly, with high yields and short time.

31

O

O

O

R6

R5

N

NO

N

S

N NH

O

R1

R5R6

33

40

40N

NO

N

NH

N NH

O

R1

R2

R5R6

41a,bYields : 63 - 90 %

42a-dYields : 85 - 93 %

.N

N

NO

N

NH2

N

O

R1

R5R6

R2

43

40

41a,b: R1 = 4-CH3-C6H4; R6 = H; R5 = CH3, C2H5;42a,b:R1 = C6H4; 42c,d:R1 = 4-Cl-C6H4; 42a-d: R2 = CH3, CH2CHCH2; R5 = CH3, C2H5; R6 = H, CH3, Cl.

O N

NR1

SNNH

NH2

O N

NR1

NHNNH

NH2

R2

CH3COOH

CH3COOH

Scheme 10. Reaction of 5-(1H-5-amino-pyrazolyl-4)-1,2,4-oxadiazoles with substituted acetylacetates

In 1H NMR spectra of products of the reaction of substances 33 with

acetylacetates 40 NH signal of a pyrimidine moiety at 11.9-12.4 ppm and doublet of NH-signal at 6.30-6.45 ppm, coupled on an alkyl moiety, are observed. These data prove the formation of isomer 42. The formation of isomeric pyrazolo[1,5-a]pyrimidin-7(4H)-ones 43 was not observed.

To conclude, efficient synthetic routes for solution-phase parallel synthesis of diverse 5-[1H-pyrazol-4-yl]-1,2,4-oxadiazoles and 1,2,4-oxadiazolyl-5-pyrazolo[1,5-a]pyrimidin-7(4H)-ones were developed. All reactions proposed allow obtaining of products with low levels of impurities, using simple isolation procedures.

16

5-(1H-1,2,3-TRIAZOL-4-YL)-1,2,4-OXADIAZOLES: DIMROTH REACTION AND REARRANGEMENT

We have developed a convenient method for preparation of 5-(1H-1,2,3-triazol-

4-yl)-1,2,4-oxadiazoles. Implemented approach is based on Dimroth reaction of 1,2,3-triazole synthesis using cycloaddition of organic azides to methylenactive nitriles and ketones.

If 5-Cyanomethyl-1,2,4-oxadiazoles 7 were used above as starting material for preparation of heteryl-1,2,4-oxadiazoles, 5-acetonyl-1,2,4-oxadiazoles 45 appear first. These substances were obtained by mild reaction of amidoximes 4 with 2,2,6-trimethyl-4H-1,3-dioxin-4-one 44 in dioxane with triethylamine as a catalyst (Scheme 11).

NH2

N OH

+ O O

O

R1

4e,f45a,bYields : 49 - 56 %

44

R1 = 3,4-CH2O2-C6H3, 2-Cl-C6H4.

N

ON

OR1

dioxane N

ON

OR1

H

H

Enol form

10 % in DMSO-d6

Keto form

90 % in DMSO-d6

TEA

Scheme 11. Synthesis of 5-acetonyl-1,2,4-oxadiazoles Interaction of methylenactive 1,2,4-oxadiazole derivatives 7a,с and 45a,b with

arylazides 46a-e,f-j occurs in methanol solution of sodium methylate and leads to formation of 5-(5-amino-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles 47a-j (68 – 93 % yields) and 5-(5-methyl-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles 48a-j (52 – 97 % yields) respectively (Scheme 12).

N

ON

YR1

+ N3R2

N

ON

N

NN

R1

R2T

46a-j

7a,c, 47a-j: Y = CN, R1 = C6H5, 4-CH3O-C6H4;47a-j: T = NH2, R2 = C6H5, 4-CH3-C6H4, 3-CH3O-C6H4, 2-Cl-C6H4, 3-F-C6H4.

48a-jYields : 52 - 97 %

47a-jYields : 68 - 93 %

45a,b, 48a-j: Y = COCH3, R1 = 3,4-CH2O2-C6H3, 2-Cl-C6H4;48a-j: T = CH3, R2 = 3,4-di-(CH3O)-C6H3, 2,5-di-(CH3O)-C6H3, 3-CF3-C6H4, 2,4-di-(F)-C6H3, 4-CH3OOC-C6H4.

7a,c

45a,b

MeONa

MeOH

Scheme 12. Formation of 5-(1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles

17

In 1H NMR spectra of 5-acetonyl-1,2,4-oxadiazoles 45 recorded in DMSO-d6 we observed signals of ketone and enol forms in 9:1 ratio. Thus signal of methylene protons CH2 group at 4.40 – 4.50 ppm (with integral intensity equal 2) and signal of vinyl proton CH group (with integral intensity equal 0.1) are observed.

1H NMR spectra confirm formation of 5-(1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles 47a-j and 48a-j. Signal of amino group protons of 5-(5-amino-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles 47a-j is observed at 6,83 – 7,05 ppm. Spectra of 5-(5-methyl-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles 48a-j contain speaks of methyl group at 2,48 – 2,74 ppm. Mass spectra prove structures of products 47a-j and 48a-j.

Based on a literature information regarding a mechanism of the Dimroth reaction of 1,2,3-triazole synthesis, we drew schematically formation of 5-(1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles (Scheme 13, 14). Interaction includes following stages: carbaniones generation of methylenactive nitrile and ketone under the influence of sodium methylate, consecutive cycloaddition of arylazide with following aromatization in 1H-1,2,3-triazole cycles.

N

ON

N

R1

N

ON

NH2N

NN

R1

R2

+ MeO-

- MeOH

N

ON

N

R1

N

ON

N

NN

N

H

R2

R1

- +

+ MeOH

- MeO-

N

N

N

R2

N

ON

N

R1

--

NNNR2

+ -

Scheme 13. Formation of 5-(5-amino-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles

N

ON

R3

O

+ MeO-

- MeOH

N

ON

O

R3

N

ON

O

NN

N

H

R2

R1

-+ NNN

R2

+ -

N

ON

N

NN

R1

R2

+ MeOHN

N

N

R2

N

ON

R1

O-

-

- MeOH- OH-

Scheme 14. Formation of 5-(5-methyl-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles

18

Dimroth rearrangement was realized by example of compound 47h. It was performed by heating of this substance in N,N-dimethylformamide at 150 ºC (Scheme 15). As a result, we obtained 5-(5-amino-1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazole 49 (32 % yield), where the aryl substituent was transferred from N1 atom to the 5-amino group of 1,2,3-triazole ring. As any other products were not recovered, reaction may be followed by a decomposition process. Signal of NH proton of 1,2,3-triazole cycle is observed at 15.55 ppm in 1H NMR spectrum of product 49.

N

ON

NH2N

NN

R1

R2

R1 = 3-C5H4N; R2 = 2-Cl-C6H4.

47h

N

ON

NHNH

NN

R1

R2

49Yield : 32 %

he at 150 C

DMF

Scheme 15. Rearrangement of 5-(5-amino-1H-1,2,3-triazol-4-yl)-1,2,4-

oxadiazole Thereby, we have developed the preparative method for synthesis of 5-(1H-

1,2,3-triazol-4-yl)-1,2,4-oxadiazoles. This method is based on the cycloaddition reaction of organic azides to 5-cyanomethyl-1,2,4-oxadiazoles and 5-acetonyl-1,2,4-oxadiazoles. Mild conditions, high yields, simple separation without necessity to purify final compounds: it makes method proposed convenient tool for preparation of these bicyclic compounds.

19

CONCLUSIONS

We have developed preparative methods for synthesis of bis-heterocyclic

compounds, containing in their structures 1,2,4-oxadiazole ring combined with coumarin, pyrazole and 1,2,3-triazole rings. Characterization of these substances has been done, and reactivity has been studied.

• Two new synthetic methods have been developed for 3-[1,2,4-oxadiazol-5-yl]coumarins. The first method is based on a three-component condensation of coumarin-3-carboxylic acids, 1,1'-carbonyldiimidazole and amidoximes. The second method essentially uses the interaction of 5-cyanomethyl-1,2,4-oxadiazoles with salicylic aldehydes.

• Condensation of 2-(1,2,4-oxadiazol-3-yl)-acetamides with salicylic aldehydes has opened the new way for preparation of 3-[1,2,4-oxadiazol-3-yl]coumarins.

• 2-Imino-3-[1,2,4-oxadiazol-5-yl]coumarins and 2-imino-3-[1,2,4-oxadiazol-3-yl]coumarins have been obtained for the first time. It has been shown, that 2-imino group in their structures is active in nucleophilic substitution reactions with aromatic amines, arylsulfonylhydrazides and hydroxylamine.

• Antimicrobial and antifungal activities of 3-[1,2,4-oxadiazol-5-yl]coumarins have been estimated by experimental studies.

• New method for synthesis of 4-[1,2,4-oxadiazol-5-yl]-1H-pyrazoles has been worked out. The direction, the reactivity and conditions for the alkylation, the acylation reactions and the condensation with derivatives of acetoacetic ether of such kind heterocyclic systems have been investigated. New 3-[1,2,4-oxadiazol-5-yl]-pyrazolo[1,5-a]pyrimidin-7(4H)-ones have been prepared.

• 5-(1H-1,2,3-Triazol-4-yl)-1,2,4-oxadiazoles have been obtained by Dimroth reaction of 1,2,3-triazole synthesis by cyclocondensation of arylazides with 5-cyanomethyl-1,2,4-oxadiazoles and 5-acetonyl-1,2,4-oxadiazoles. Dimroth rearrangement has been realized by example of 5-(1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazole.

20

PUBLICATIONS REGARDING DISSERTATION

1. O.S. Detistov, I.O. Zhuravel’, S.M. Kovalenko, V.V. Kazmirchuk. Synthesis and

biological activity of 3-[1,2,4-oxadiazol-5-yl]coumarins. // Journal of Organic and

pharmaceutical chemistry. – 2007. – V. 5 – Issue 4(20). – P. 41–43 (in Russian).

2. O.S. Detistov, I.O. Zhuravel’, V.D. Orlov. Cyclic systems containing 1,2,4-oxadiazole

ring. 1. Synthesis of 5-(1H-1,2,3-triazol-4-yl)-1,2,4-oxadiazoles – potential bioactive

compounds. // Kharkiv Univer. Bull. – 2007. – №770. Chemical Series, Issue 15(38). – P.

232–238 (in Russian).

3. Aleksandr V. Borisov, Oleksandr S. Detistov, Viktoriya I. Pukhovaya, Irina O. Zhuravel,

Sergey M. Kovalenko. A parallel liquid-phase synthesis of 5-(1H-4-pyrazolyl)-

[1,2,4]oxadiazole libraries. // J. Comb. Chem. – 2009. – Vol. 11 – P. 1023–1029.

(http://pubs.acs.org/doi/abs/10.1021/cc900070m)

4. O.S. Detistov, V.D. Orlov, I.O. Zhuravel`. Іsomeric 3-isoxadiazolylcoumarins and their

derivatives // J. Heterocyclic Chem. (DOI 10.1002/jhet.893).

5. Detistov A.S., Zaremba O.V., Kovalenko S.N. Combinatorial library of 5-(5-methyl-1H-

1,2,3-triazol-4-yl)-1,2,4-oxadiazoles. // III International Conference on the Chemistry and

Biological Activity of Nitrogen-Containing Heterocycles. – Chernogolovka Research

Center, Moscow Region, Russia. – 2006. – Vol. 2. – P. 102.

(http://www.cbcconf.com/conference/program.htm)

6. Oleksandr S. Detistov and Valeriy D. Orlov. Rational Design Of Combinatorial Libraries

Based On 1,2,4-Oxadiazole Scaffold. // 4th Annual Collaborative Drug Discovery UCSF

Community Meeting for Catalyzing Humanitarian and Commercial Research. – San

Francisco, CA, USA. – 2010. – P-20.

(http://www.acteva.com/booking.cfm?bevaID=204012)