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ISSN: 2161-0444
Medicinal Chemistry
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Synthesis, Antifungal and Toxicity Screening of Newer Isoniazid Derivatives

Sadaf Jamal Gilani1*, Kandasamy Nagarajan1, Divya Prakash Maurya2, Deepti Katiyar3, Richa Goel3 and Suroor A Khan4

1Department of Pharmaceutical Chemistry, KIET School of Pharmacy, Ghaziabad, UP, India

2Dept. of Pharmaceutical Sciences, Sam Higginbottom Institute of Agiculture, Technology and Science, Allahabad, UP, India

3Department of Pharmacognosy, KIET School of Pharmacy, Ghaziabad, UP, India

4Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Jamia Hamdard, New Delhi, India

*Corresponding Author:
Sadaf Jamal Gilani
Department of Pharmaceutical Chemistry
KIET School of Pharmacy
Ghaziabad, UP, India
Tel: 919891128162
E-mail: [email protected]

Received date: March 04, 2014; Accepted date: April 15, 2014; Published date: April 17, 2014

Citation: Gilani SJ, Nagarajan K, Maurya DP, Katiyar D, Goel R, et al. (2014) Synthesis, Antifungal and Toxicity Screening of Newer Isoniazid Derivatives. Med chem 4:428-434. doi:10.4172/2161-0444.1000174

Copyright: © 2014 Gilani SJ, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

A series of Isoninicotinic acid hydrazide (INH) incorporated derivatives of thiazolidin-4-one (2a-h, 3a-h), azetidin-2- one (4a-h) and 1,3,4-oxadiazole (5a-h) were synthesized in satisfactory yield and pharmacologically evaluated for their in vitro antifungal activity. All the synthesized compounds were in good agreement with elemental and spectral data. A majority of the tested compounds showed good to moderate antifungal activity against all tested pathogenic fungal strains. To evaluate the toxicity of the compounds on liver, estimation of enzymes was also carried out.

Keywords

Thiazolidin-4-one; Azetidin-2-one; 1,3,4-oxadiazole; Isoniazid; Antifungal activity; Enzyme estimation

Introduction

Antimicrobial agents are those inhibitory chemicals which are employed to kill microorganisms or prevent their growth. Infectious diseases account for approximately one-half of all deaths in tropical countries. Although deaths from bacterial and fungal infections have dropped in the developed world, these are still major causes of death in the developing world [1]. In addition, primary and opportunistic fungal infections continue to increase rapidly because of the increased number of immunocompromised patients (AIDS, cancer and transplants) [2]. Antimicrobials reduce or completely block the growth and multiplication of bacteria. This has made them unique for the control of deadly infectious diseases caused by a variety of pathogens. They have transformed our ability to treat infectious diseases such as pneumonia, meningitis, tuberculosis, malaria and AIDS [3]. Literature survey revealed that thiazolidin-4-ones are a class of heterocycles which have attracted significant interest in medicinal chemistry and they have a wide range of pharmaceutical and biological activities including antimicrobial [4], anti-inflammatory, analgesic, antitubercular and antidiabetic [5-8]. Similarly, The azetidin-2-one derivatives have been reported to possess a wide range of biological activities like antibacterial, antifungal, anti-inflammatory, anticonvulsant, anticancer and antitubercular [9-14]. In addition, 1,3,4-oxadiazoles are a class of heterocycles which have attracted significant interest in medicinal chemistry and they have a wide range of pharmaceutical and biological activities including antimicrobial, anti-inflammatory and analgesic [15-17]. In the design of new compounds, development of hybrid molecules through the combination of different pharmacophores in one structure may lead to compounds with increased antifungal activity. In view of the above mentioned facts and in continuation of our interest in the synthesis of heterocycles containing isoniazid moiety, to identify new candidates that may be of value in designing new, potent, selective and less toxic antifungal agents, we report herein the synthesis and antifungal evaluation of some novel structural hybrids incorporating both the isoniazid moiety with thiazolidin-4-one, azetidin-2- one and 1,3,4-oxadiazole ring systems through different linkages. Further, Enzyme estimation was also carried out to assess the toxicity effects of the compounds on liver.

Experimental

All the solvents were of AR grade and were obtained from Merck, CDH and S.D. Fine chemicals. Melting points were determined in open capillary tubes and are uncorrected. All the compounds were subjected to elemental analysis (CHN) and the measured values agreed within ± 0.4% with the calculated ones. Thin layer chromatography was performed on silica gel G (Merck). The spots were developed in an iodine chamber and visualized with an ultraviolet lamp. The solvent systems used were benzene:acetone (8:2, v/v) and toluene:ethyl acetate:formic acid (5:4:1, v/v). Ashless Whatman No. 1 filter paper was used for vacuum filtration. The IR spectra were recorded in KBr pellets on a (BIO-RAD FTS 135) WIN-IR spectrophotometer. The FAB mass spectra of all the compounds were recorded on a JEOL SX102/DA-600 mass spectrometer using argon/xenon (6 kV, 10 mA) as the FAB gas. The 1H-NMR spectra were recorded on a Bruker model DPX 300 FTNMR spectrometer in CDCl3 using tetramethylsilane (Me4Si, TMS) as an internal standard. The chemical shifts are reported in the δ ppm scale [18].

General procedure for the synthesis of (E)-N’- (substitutedbenzylidene)isonicotinohydrazide (1a-h)

To an equimolar methanolic solution of isonicotinic acid hydrazide (0.1mol) and substituted benzaldehyde (0.1mol), a few drops of glacial acetic acid were added. The mixture was then refluxed on water bath for 5-6 h. It was then allowed to cool and poured into crushed ice. Recrystallisation of the dried compounds from methanol yielded compounds 1a-h.

(E)-N’-(2-Chlorobenzylidene)isonicotinohydrazide(1a): Yield: 90%; m.p.184-186°C. Anal. Calcd. for C13H10N3OCl (MW 259.69): C, 60.12; H, 3.88; N,16.18%. Found: C, 60.10; H, 3.86; N, 16.16%. IR (KBr, cm-1): 3300 (N-H stretching), 1680 (C=O stretching of carbonyl), 1600 (-N=CH-Ar stretching of aromatic ring), 830 (C-Cl stretching of chlorine). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.9 (1H, s, -N=CH), 7.72, 8.63 (4H, m, Py), 7.12-7.15 (4H, m, J = 9 Hz, aromatic), 6.1 (1H, s, NH). MS (m/z): 259 [M]+.

(E)-N’-(4-Chlorobenzylidene) isonicotinohydrazide (1b). Yield: 90%; m.p.192-194°C. Anal. Calcd. for C13H10N3OCl (MW 259.69): C, 60.12; H, 3.88; N,16.18%. Found: C, 60.11; H, 3.87; N, 16.17%. IR (KBr, cm-1): 3310 (N-H stretching), 1676 (C=O stretching of carbonyl), 1615 (-N=CH-Ar stretching of aromatic ring), 822 (C-Cl stretching of chlorine). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.72, 8.63 (4H, m, Py), 7.12-7.15 (4H, m, J = 9 Hz, aromatic,), 7.7 (1H, bs, -N=CH), 6.4 (1H, s, NH). MS (m/z): 259 [M]+.

(E)-N’-(2-Hydroxybenzylidene)isonicotinohydrazide (1c): Yield: 80%; m.p.168-170°C. Anal. Calcd. for C13H11N3O2 (MW 241.25): C, 64.72; H, 4.60; N,17.42%. Found: C, 64.70; H, 4.59; N, 17.40%. IR (KBr, cm-1): 3308 (N-H stretching), 1684 (C=O stretching of carbonyl), 1612 (-N=CH-Ar stretching of aromatic ring). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.40 (1H, br, OH), 7.8 (1H, s, -N=CH), 7.13-7.16 (4H, m, J = 9 Hz, aromatic), 7.70, 8.61 (4H, m, Py), 6.2 (1H, s, NH). MS (m/z): 241[M]+.

(E)-N’-(3-Hydroxybenzylidene)isonicotinohydrazide (1d): Yield: 75%; m.p.186-188°C. Anal. Calcd. for C13H11N3O2 (MW 241.25): C, 64.72; H, 4.60; N,17.42%. Found: C, 64.70; H, 4.59; N, 17.40%. IR (KBr, cm-1): 3318 (N-H stretching), 1688 (C=O stretching of carbonyl), 1607 (-N=CH-Ar stretching of aromatic ring). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.40 (1H, br, OH), 7.7 (1H, s, -N=CH), 7.74, 8.62 (4H, m, Py), 7.11-7.14 (4H, m, J = 9 Hz, aromatic), 6.3 (1H, s, NH). MS (m/z): 241 [M]+.

(E)-N’-(4-Methoxybenzylidene)isonicotinohydrazide (1e): Yield: 80%; m.p.194-196°C. Anal. Calcd. for C14H13N3O2 (MW 255.27): C, 65.87; H, 5.13; N, 16.46%. Found: C, 65.85; H, 5.10; N, 16.44%. IR (KBr, cm-1): 3314 (N-H stretching), 1687 (C=O stretching of carbonyl), 1604 (-N=CH-Ar stretching of aromatic ring). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.73, 8.64 (4H, m, Py), 7.3 (1H, s, -N=CH), 7.13-7.16 (4H, m, J = 9 Hz, aromatic), 6.4 (1H, s, NH), 3.83 (3H, s, OCH3). MS (m/z): 255 [M]+.

(E)-N’-(4-Fluorobenzylidene)isonicotinohydrazide (1f): Yield: 90%; m.p.182-184°C. Anal. Calcd. for C13H10FN3O (MW 243.24): C, 64.19; H, 4.14; N, 17.28%. Found: C, 64.16; H, 4.12; N, 17.26%. IR (KBr, cm-1): 3305 (N-H stretching), 1684 (C=O stretching of carbonyl), 1611 (-N=CH-Ar stretching of aromatic ring). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.70-8.61 (4H, m, Py), 7.6 (1H, s, -N=CH), 7.11-7.14 (4H, m, J = 9.0 Hz, aromatic), 6.3 (1H, s, NH). MS (m/z): 243 [M]+.

(E)-N’-(2-Nitrobenzylidene)isonicotinohydrazide (1g): Yield: 85%; m.p. 188-189°C. Anal. Calcd. for C13H10N4O3 (MW 270.24): C, 57.78; H, 3.73; N, 20.73%. Found: C, 57.76; H, 3.70; N, 20.71%. IR (KBr, cm-1): 3311 (N-H stretching), 1685 (C=O stretching of carbonyl), 1610 (-N=CH- Ar stretching of aromatic rings), 1366 (NO2). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.8 (1H, s, -N=CH), 7.73, 8.61 (4H, m, Py), 7.10- 7.13 (4H, m, J = 9.0 Hz, aromatic), 6.2 (1H, s, NH). MS (m/z): 270 [M]+.

E)-N’-(4-(Dimethylamino)benzylidene)isonicotinohydrazide (1H): Yield: 85%; m.p. 196-198°C. Anal. Calcd. for C15H16N4O (MW 268.31): C, 67.15; H,6.01; N, 20.88%. Found: C, 67.12; H, 6.00; N, 20.86%. IR (KBr, cm-1): 3313 (N-H stretching), 1683(C=O stretching of carbonyl), 1613 (-N=CH-Ar stretching of aromatic rings). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.9 (1H, s, -N=CH), 7.72, 8.63 (4H, m, Py), 7.12-7.15 (4H, m, J = 9.0 Hz aromatic), 6.1 (1H, s, NH), 2.63 (6H, s, N(CH3)2). MS (m/z): 268 [M]+.

General procedure for the synthesis of N-(2-(substituted phenyl)-4-oxothiazolidin-3-yl) isonicotinamide (2a-h)

A mixture of 1 (0.01 mol) and thioglycollic acid (0.01mol) was heated on an oil-bath at 120-25°C for 12h.The reaction mixture was cooled and treated witH10%sodium bicarbonate solution. The product was isolated and recrystallised from methanol-dioxane (4:1) to give compounds 2a-h.

N-(2-(2-Chlorophenyl)-4-oxothiazolidin-3-yl)isonicotinamide (2a): Yield: 85%; m.p. 198-200°C. Anal. Calcd. for C15H12ClN3O2S (MW 333.79): C, 53.97; H, 3.62; N, 12.59%. Found: C, 53.94; H, 3.60; N, 12.57%. IR (KBr, cm-1): 3300 (N-H stretching), 1700 (C=O thiazolidinone), 1670 (C=O stretching of carbonyl), 1610 (C=N), 1574 (C=C stretching of chlorine), 830 (C-Cl stretching of chlorine), 700 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.8 (1H, s, CONH-), 7.74-8.64 (4H, m, Py), 7.20 (1H, s, N-CH-), 7.12-7.15 (4H, m, aromatic), 5.96 (1H, s, -S-CH-), 3.50 (2H, s, CH2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 149.7, 140.8, 134.0, 130.1, 128.7, 128.5, 126.7, 121.7, 102.5, 59.2, 35.6. MS (m/z): 333 [M+].

N-(2-(4-Chlorophenyl)-4-oxothiazolidin-3-yl)isonicotinamide (2b): Yield: 85%; m.p. 202-204°C. Anal. Calcd. for C15H12ClN3O2S (MW 333.79): C, 53.97; H, 3.62; N, 12.59%. Found: C, 53.96; H, 3.61; N, 12.58%. IR (KBr, cm-1): 3310 (N-H stretching), 1706 (C=O thiazolidinone), 1666 (C=O stretching of carbonyl),1612 (C=N), 1573 (C=C), 830 (C-Cl stretching of chlorine), 700 (C-S-C).1H-NMR (300 MHz, CDCl3, δ/ppm): 9.8 (1H, s, CONH-), 7.74, 8.64 (4H, m, Py), 7.2 (1H, s, N-CH-), 7.12-7.15 (4H, m, aromatic), 5.96 (1H, s, -S-CH-), 3.50 (2H, s, CH2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 149.7, 140.8, 134.0, 130.1, 128.7, 128.5, 126.7, 121.7, 102.5, 59.2, 35.6. MS (m/z): 333 [M+].

N - ( 2 - ( 2 - H y d r o x y p h e n y l ) - 4 - o x o t h i a z o l i d i n - 3 - y l ) isonicotinamide (2c): Yield: 70%; m.p. 200-202°C. Anal. Calcd. for C15H13N3O3S (MW 315.07): C, 57.13; H, 4.16; N, 13.33%. Found: C, 57.11; H, 4.14; N, 13.31%. IR (KBr, cm-1): 3318 (N-H stretching), 1716 (C=O thiazolidinone), 1674 (C=O stretching of carbonyl), 1626 (C=N), 1587 (C=C), 644 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.41 (1H, br, OH), 9.14 (1H, s, CONH-), 7.77-8.68 (4H, m, Py), 7.20 (1H, s, N-CH-), 7.17-7.20 (4H, m, Ar-H), 5.16 (1H, s, -S-CH-), 3.50 (2H, s, CH2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 153.7,149.7, 140.8, 128.5, 128.0, 121.2, 121.7, 118.1,115.8, 58.1, 35.6. MS (m/z): 315 [M+].

N - ( 2 - ( 3 - H y d r o x y p h e n y l ) - 4 - o x o t h i a z o l i d i n - 3 - y l ) isonicotinamide (2d): Yield: 70%; m.p. 208-210°C. Anal. Calcd. for C15H13N3O3S (MW 315.07): C, 57.13; H, 4.16; N, 13.33%. Found: C, 57.10; H, 4.13; N, 13.32%. IR (KBr, cm-1): 3317 (N-H stretching), 1717 (C=O thiazolidinone), 1672 (C=O stretching of carbonyl), 1624 (C=N), 1588 (C=C), 642 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.42 (1H, br, OH), 9.13 (1H, s, CONH-), 7.76-8.67 (4H, m, Py), 7.10 (1H, s, N-CH-), 7.17-7.20 (4H, m, aromatic), 5.16 (1H, s, -S-CH-), 3.50 (2H, s, CH2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 153.7, 149.7, 140.8, 128.5, 128.0, 121.2, 121.7, 118.1, 115.8, 58.1, 35.6. MS (m/z): 315 [M+].

N- (2- (4-Me t hoxypheny l ) - 4 -oxot h ia zol idi n - 3 - y l ) isonicotinamide (2e): Yield: 75%; m.p. 204-206°C. Anal. Calcd. for C16H15N3O3S (MW 329.37): C, 58.34; H, 4.59; N, 12.76%. Found: C, 58.33; H, 4.58; N, 12.74%. IR (KBr, cm-1): 3302 (N-H stretching), 1760 (C=O thiazolidinone), 1632 (C=O stretching of carbonyl), 1667 (C=N), 1546 (C=C), 628 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.06 (1H, s, CONH-), 7.70, 8.64 (4H, m, Py), 7.40 (1H, s, N-CH-), 7.26- 7.32 (4H, m, aromatic), 5.22 (1H, s, -S-CH-), 3.84 (3H, s, OCH3), 3.80 (2H, s, CH2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 159.0, 149.7, 121.7, 140.8, 131.5, 129.7, 121.7, 114.2, 64.3, 55.8, 35.6. MS (m/z): 329 [M+].

N-(2-(4-Fluorophenyl)-4-oxothiazolidin-3-yl)isonicotinamide (2f): Yield: 85%; m.p. 196-200°C. Anal. Calcd. for C15H12FN3O2S (MW 317.34): C, 56.77; H,3.81; N, 5.99%. Found: C, 56.76; H, 3.80; N, 5.98%. IR (KBr, cm-1): 3316 (N-Hstretching), 1769 (C=O thiazolidinone), 1661 (C=N), 1649 (C=O stretching ofcarbonyl), 1535 (C=C), 623 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm):9.02 (1H, s, CONH-), 7.80 (1H, s, N-CH-), 7.75-8.60 (4H, m, Py), 7.30, 7.36(4H, m, aromatic), 5.28 (1H, s, -S-CH-), 3.10 (2H, s, CH2). 13C-NMR (100MHz, CDCl3, δ/ppm): 168.8, 163.7, 161.3, 149.7, 140.8, 134.8, 130.3, 121.7, 115.4, 64.3, 35.6. MS (m/z): 317 [M+].

N-(2-(2-Nitrophenyl)-4-oxothiazolidin-3-yl)isonicotinamide (2g): Yield: 80%; m.p. 210-212°C. Anal. Calcd. for C15H12N4O4S (MW 344.35): C, 52.32; H, 3.51; N, 16.27%. Found: C, 52.31; H, 3.50; N, 16.25%. IR (KBr, cm-1): 3328 (N-H stretching), 1774 (C=O thiazolidinone), 1660 (C=N), 1652 (C=O stretching of carbonyl), 1532 (C=C), 620 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.05 (1H, s, CONH-), 7.90 (1H, s, N-CH-), 7.78, 8.64 (4H, m, Py), 7.31-7.34 (4H, m, aromatic), 5.21 (1H, s, -S-CH-), 3.11 (2H, s, CH2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 149.7, 149.0, 140.8, 134.7, 133.4, 129.6, 128.0, 124.8, 121.7, 59.7, 35.6. MS (m/z): 344 [M+].

N-(2-(4-(Dimethylamino)phenyl)-4-oxothiazolidin-3-yl) isonicotinamide (2h): Yield: 75%; m.p. 204-206°C. Anal. Calcd. for C17H18N4O2S (MW 342.42): C, 59.63; H, 5.30; N, 16.36%. Found: C, 59.61; H, 5.29; N, 16.34%. IR (KBr, cm-1):3336 (N-H stretching), 1777 (C=O thiazolidinone), 1661 (C=N), 1635 (C=O stretching of carbonyl), 1539 (C=C), 625 (C-S-C). 1H-NMR (300 MHz, CDCl3,δ/ppm): 9.03 (1H, s, CONH-), 7.71, 8.60 (4H, m, Py), 7.70 (1H, s, N-CH-), 7.28-7.32 (4H, m, aromatic), 5.20 (1H, s, -S-CH-), 3.09 (2H, s, CH2), 2.65 (6H, s, N(CH3)2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 163.7, 149.7, 149.5, 140.8, 128.7, 127.4, 121.7, 112.8, 64.3, 41.3, 35.6. MS (m/z): 342 [M+].

General procedure for the synthesis of 2-(2-(2-substitutedphenyl)-3-(isonicotinamido)-4- oxothiazolidin-5-yl) acetic acid (3a-h)

A mixture of 1 (0.01mol) and thiomalic acid (0.01mol) was heated on an oil-bath at 120-125ºC for 12h. The reaction mixture was cooled and treated witH10%sodium bicarbonate solution. The product was isolated and recrystallised from methanol-dioxane (4:1) to give compounds 3a-h.

2-(2-(2-Chlorophenyl)-3-isonicotinamido-4-oxothiazolidin- 5-yl)acetic acid (3a): Yield: 80%; m.p. 210-212°C. Anal. Calcd. for C17H14ClN3O4S (MW 391.83): C, 52.11; H, 3.60; N, 10.72%. Found: C, 52.10; H, 3.59; N, 10.70%. IR (KBr, cm-1): 3200 (N-H stretching), 1700 (C=O thiazolidinone), 1666 (C=O stretching of carbonyl), 1610 (C=N), 1572 (C=C), 700 (C-S-C), 830 (C-Cl stretching of chlorine). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.00 (1H, s, COOH), 9.40 (1H, s, CONH-), 7.71-8.60 (4H, m, Py), 7.20 (1H, s, N-CH-), 6.17--6.15 (4H, m, Ar-H), 5.95 (1H, s, -S-CH-Ar). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7, 149.7, 140.8, 134.0, 130.1, 121.7, 128.7, 128.5, 126.7, 102.5, 56.7, 47.5, 39.2. MS (m/z): 391 [M+].

2-(2-(4-Chlorophenyl)-3-isonicotinamido-4-oxothiazolidin- 5-yl)acetic acid (3b): Yield: 85%; m.p. 216-218°C. Anal. Calcd. for C17H14ClN3O4S (MW 391.83): Calcd: C, 52.11; H, 3.60; N, 10.72%. Found: C, 52.09; H, 3.58; N, 10.71%. IR (KBr, cm-1): 3204 (N-H stretching), 1702 (C=O thiazolidinone), 1664 (C=O stretching of carbonyl), 1611 (C=N), 1572 (C=C), 701 (C-S-C), 832 (C-Cl stretching of chlorine). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.10 (1H, s, COOH), 9.50 (1H, s, CONH-), 7.72-8.61 (4H, m, Py), 7.10 (1H, s, N-CH-), 6.18- 6.16 (4H, m, aromatic), 5.94 (1H, s, -S-CH-Ar). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7, 149.7, 140.8, 134.0, 130.1, 121.7, 128.7, 128.5, 126.7, 102.5, 56.7, 47.5, 39.2. MS (m/z): 391 [M+].

2-(2-(2-Hydroxyphenyl)-3-isonicotinamido-4-oxothiazolidin- 5-yl)acetic acid (3c): Yield: 75%; m.p. 222-224°C. Anal. Calcd. for C17H15N3O5S (MW 373.38): C, 54.68; H, 4.05; N, 11.25%. Found: C, 54.67; H, 4.03; N, 10.23%. IR (KBr, cm-1): 3324 (N-H stretching), 1714 (C=O thiazolidinone), 1660 (C=O stretching of carbonyl), 1625 (C=N), 1579 (C=C), 710 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.02 (1H, s, COOH), 9.40 (1H, s, CONH-), 9.33 (1H, br, OH), 7.69-8.51 (4H, m, Py), 7.50 (1H, s, N-CH-), 6.20-6.17 (4H, m, aromatic), 5.90 (1H, s, -S-CH-Ar). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7,153.7, 149.7, 140.8, 128.5, 128.0, 121.2, 118.1, 55.6, 47.5, 39.2. MS (m/z): 373[M+].

2-(2-(3-Hydroxyphenyl)-3-isonicotinamido-4-oxothiazolidin- 5-yl)acetic acid (3d): Yield: 60%; m.p. 238-240°C. Anal. Calcd. for C17H15N3O5S (MW 373.38): C, 54.68; H, 4.05; N, 11.25%. Found: C, 54.66; H, 4.04; N, 10.24%. IR (KBr, cm-1): 3325 (N-H stretching), 1713 (C=O thiazolidinone), 1662 (C=O stretching of carbonyl), 1624 (C=N), 1580 (C=C), 711 (C-S-C). 1H-NMR (300MHz, CDCl3, δ/ppm): 10.02 (1H, s, COOH), 9.40 (1H, s, CONH-), 9.32 (1H,br, OH), 7.68-8.52 (4H, m, Py), 7.50 (1H, s, N-CH-), 6.20-6.17 (4H, m, aromatic), 5.90 (1H, s, -S-CH-Ar). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7, 153.7, 149.7, 140.8, 128.5, 128.0, 121.2, 118.1, 55.6, 47.5, 39.2. MS (m/z): 373 [M+].

2-(3-Isonicotinamido-2-(4-methoxyphenyl)-4-oxothiazolidin- 5-yl)acetic acid (3e): Yield: 65%; m.p. 220-222°C. Anal. Calcd. for C18H17N3O5S (MW 387.41): C, 55.80; H, 4.42; N, 10.85%. Found: C, 55.78; H, 4.41; N, 10.83%. IR (KBr, cm-1): 3330 (N-H stretching), 1720 (C=O thiazolidinone), 1669 (C=O stretching of carbonyl), 1629 (C=N), 1574 (C=C), 714 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.01 (1H, s, COOH), 9.60 (1H, s, CONH-), 7.70 (1H, s, N-CH-), 7.63, 8.55 (4H, m, Py), 6.22-6.18 (4H, m, Ar-H), 5.91 (1H, s, -S-CH-Ar), 3.80 (3H, s, -OCH3). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7, 159.0, 149.7, 140.8, 131.5, 129.7, 121.7, 114.2, 61.8, 55.8, 47.5, 39.2. MS (m/z): 387 [M+].

2-(2-(4-Fluorophenyl)-3-isonicotinamido-4-oxothiazolidin- 5-yl)acetic acid (3f): Yield: 75%; m.p. 190-192°C. Anal. Calcd. for C17H14FN3O4S (MW 375.37): C, 54.39; H, 3.76; N, 11.19%. Found: C, 54.38; H, 3.74; N, 11.18%. IR (KBr, cm-1): 3316 (N-H stretching), 1714 (C=O thiazolidinone), 1670 (C=O stretching of carbonyl), 1634 (C=N), 1578 (C=C), 720 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.04 (1H, s, COOH), 9.20 (1H, s, CONH-), 7.90 (1H, s, N-CH-),7.66-8.58 (4H, m, Py), 6.20-6.17 (4H, m, aromatic), 5.93 (1H, s, -S-CH-Ar). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7, 161.3, 149.7, 140.8, 134.8, 130.3, 121.7, 115.4, 61.8, 47.5, 39.2. MS (m/z): 375 [M+].

2-(3-Isonicotinamido-2-(2-nitrophenyl)-4-oxothiazolidin- 5-yl)acetic acid (3g): Yield: 80%; m.p. 232-234 °C. Anal. Calcd. for C17H14N4O6S (MW 402.38): C, 50.74; H, 3.51; N, 13.92%. Found: C, 50.73; H, 3.50; N, 13.91%. IR (KBr, cm-1): 3310 (N-H stretching), 1704 (C=O thiazolidinone), 1660 (C=O stretching of carbonyl), 1632 (C=N), 1580 (C=C), 727 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.03 (1H, s, COOH), 9.40 (1H, s, CONH-), 7.63, 8.31 (4H, m, Py), 7.50 (1H, s, N-CH), 6.24-6.20 (4H, m, Ar-H), 5.90 (1H, s, -S-CH-Ar). 13C-NMR (100 MHz, CDCl3, δ/ppm): 175.3, 173.3, 163.7, 149.0, 149.7, 140.8, 133.4, 134.7, 129.6, 128.0, 124.8, 121.7, 57.2, 47.5, 39.2. MS (m/z): 402 [M+].

2-(2-(4-(Dimethylamino)phenyl)-3-isonicotinamido-4- oxothiazolidin-5-yl)-acetic acid (3h): Yield: 70%; m.p. 248-250°C. Anal. Calcd. for C19H20N4O4S (MW 400.45): C, 56.99; H, 5.03; N, 13.99%. Found: C, 56.97; H, 5.01; N, 13.98%. IR (KBr, cm-1): 3315 (N-H stretching), 1710 (C=O thiazolidinone), 1666 (C=O stretching of carbonyl), 1632 (C=N), 1584 (C=C), 727 (C-S-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 10.06 (1H, s, COOH), 9.10 (1H, s, CONH-), 7.68-8.33 (4H, m, Py), 6.22-6.19 (4H, m, Ar-H), 7.10 (1H, s, N-CH-), 5.93 (1H, s, -S-CH-Ar), 2.72 (6H, s, N(CH3)2). 13C-NMR (100 MHz, CDCl3, δ/ ppm): 175.3, 173.3, 163.7, 149.7, 149.5, 140.8, 128.7, 127.4, 121.7, 112.8, 57.2, 47.5, 39.2. MS (m/z): 400 [M+].

General procedure for the synthesis of N-(3-chloro-2-(2- substitutedphenyl)-4-oxaazetidin-1-yl) isonicotinamide (4ah)

A solution of 1 (0.01 mol) in dioxane (20 mL) was added to a well stirred mixture of chloroacetylchloride (0.012 mol) and triethylamine (Et3N) (0.012 mol) in dioxane (10 mL) at 0-5ºC. The reaction mixture was then stirred for 8h, kept for 2days at room temperature and then treated with cold water. The solid thus obtained was filtered, washed with water and recrystallized from methanol to yield 4a-h.

N-(3-Chloro-2-(2-chlorophenyl)-4-oxoazetidin-1-yl) isonicotinamide (4a): Yield: 75%; m.p. 322-324°C. Anal. Calcd. for C15H11 C12N3O2 (MW 336.17): C, 53.59; H, 3.30; N, 12.50%. Found: C, 53.58; H, 3.29; N, 12.48%. IR (KBr, cm-1): 3250 (N-H stretching), 1745 (C=O β-lactam ring), 1616 (C=O stretching of carbonyl), 1600 (C=N), 1560 (C=C), 742 (C-Cl stretching of chlorine). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.40 (1H, s, CONH-), 7.70 (1H, s, N-CH-), 7.68-8.33 (4H, m, Py), 6.61-6.63 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 149.7, 143.5, 140.8, 132.2, 128.6, 128.1, 126.6, 121.7. MS (m/z): 335 [M+].

N-(3-Chloro-2-(4-chlorophenyl)-4-oxoazetidin-1-yl) isonicotinamide (4b): Yield: 65%; m.p. 328-330°C. Anal. Calcd. for C15H11C12N3O2 (MW 336.17): C, 53.59; H, 3.30; N, 12.50%. Found: C, 53.57; H, 3.27; N, 12.46%. IR (KBr, cm-1): 3252 (N-H stretching), 1746 (C=O β-lactam ring), 1612 (C=O stretching of carbonyl), 1599 (C=N), 1562 (C=C), 741 (C-Cl stretching of chlorine). 1H NMR (300 MHz, CDCl3, δ/ppm): 9.80 (1H, s, CONH-), 7.60 (1H, s, N-CH-), 7.67-8.32 (4H, m, Py), 6.62-6.64 (4H, m, Ar-H). 13C-NMR (100 MHz, CDCl3, δ/ ppm): 163.7, 163.5, 149.7, 143.5, 140.8, 132.2, 128.6, 128.1, 126.6, 121.7. MS (m/z): 335 [M+].

N-(3-Chloro-2-(2-hydroxyphenyl)-4-oxoazetidin-1-yl) isonicotinamide (4c): Yield: 70%; m.p. 346-348°C. Anal. Calcd. for C15H12ClN3O3 (MW 317.73): C, 56.70; H, 3.81; N, 13.23%. Found: C, 56.68; H, 3.80; N, 13.21%. IR (KBr, cm-1): 3256 (N-H stretching), 1749 (C=O β-lactam ring), 1614 (C=O stretching of carbonyl), 1602 (C=N), 1561 (C=C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.20 (1H, br, OH), 9.90 (1H, s, CONH-), 7.64-8.31 (4H, m, Py), 7.40 (1H, s, N-CH-), 6.60- 6.61 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 154.0, 149.7, 140.8, 130.9, 128.1, 126.5, 121.7, 121.1, 115.7, 64.4, 61.2. MS (m/z): 317 [M+].

N-(3-Chloro-2-(3-hydroxyphenyl)-4-oxoazetidin-1-yl) isonicotinamide (4d): Yield: 60%; m.p. 330-332°C. Anal. Calcd. for C15H12ClN3O3 (MW 317.73): C, 56.70; H, 3.81; N, 13.23%. Found: C, 56.69; H, 3.80; N, 13.22%. IR (KBr, cm-1): 3259 (N-H stretching), 1752 (C=O β-lactam ring), 1672 (C=O stretching of carbonyl), 1605 (C=N), 1562 (C=C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.30 (1H, br, OH), 9.80 (1H, s, CONH-), 7.64-8.31 (4H, m, Py), 7.40 (1H, s, N-CH-), 6.60- 6.61 (4H, m, Ar-H). 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 156.8, 149.7, 144.9, 140.8, 129.9, 121.7, 113.9, 112.6, 67.7, 64.1. MS (m/z): 317[M+].

N-(3-Chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl) isonicotinamide (4e): Yield: 55%; m.p. 344-346 οC. Anal. Calcd. for C16H14ClN3O3 (MW 331.75): C, 57.93; H, 4.25; N, 12.67%. Found: C, 57.91; H, 4.22; N, 12.65%. IR (KBr, cm-1): 3260 (N-H stretching), 1748 (C=O β-lactam ring), 1670 (C=O stretching of carbonyl), 1603 (C=N), 1558 (C=C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.40 (1H, s, CONH-), 7.62, 8.31 (4H, m, Py), 7.20 (1H, s, N-CH-), 6.63-6.65 (4H, m, aromatic), 3.78 (3H, s, OCH3). 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 158.6, 149.7, 140.8, 135.8, 126.6, 121.7, 114.1, 67.4, 64.1. MS (m/z): 331 [M+].

N-(3-Chloro-2-(4-fluorophenyl)-4-oxoazetidin-1-yl) isonicotinamide (4f): Yield: 75%; m.p. 298-300°C. Anal. Calcd. for C15H11ClFN3O2 (MW 319.72): C, 56.35; H, 3.47; N, 13.14%. Found: C, 56.33; H, 3.46; N, 13.12%. IR (KBr, cm-1): 3264 (N-H stretching), 1747 (C=O β-lactam ring), 1672 (C=O stretching of carbonyl), 1613 (C=N), 1560 (C=C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.60 (1H, s, CONH- ), 7.60, 8.31 (4H, m, Py), 7.80 (1H, s, N-CH-), 6.62-6.67 (4H, m, Ar-H). 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 160.9, 149.7, 140.8, 139.1, 128.5, 121.7, 115.3, 67.4, 64.1. MS (m/z): 319 [M+].

N-(3-Chloro-2-(2-nitrophenyl)-4-oxoazetidin-1-yl) isonicotinamide (4g): Yield: 60%; m.p. 294-296°C. Anal. Calcd. for C15H11ClN4O4 (MW 346.73): C, 51.96; H, 3.20; N, 16.16%. Found: C, 51.94; H, 3.19; N, 16.14%. IR (KBr, cm-1): 3268 (N-H stretching), 1740 (C=O β-lactam ring), 1662 (C=O stretching of carbonyl), 1614 (C=N), 1562 (C=C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.40 (1H, s, CONH- ), 7.63, 8.34 (4H, m, Py), 7.30 (1H, s, N-CH-), 6.64-6.66 (4H, m, Ar-H). 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 149.7, 147.2, 140.8, 137.5, 134.6, 127.6, 124.7, 121.7, 63.1, 62.8. MS (m/z): 346 [M+].

N-(3-Chloro-2-(4-(dimethylamino)phenyl)-4-oxoazetidin-1-yl) isonicotinamide (4h): Yield: 65%; m.p. 360-362οC. Anal. Calcd. for C17H17ClN4O2 (MW 344.80): C, 59.22; H, 4.97; N, 16.25%. Found: C, 59.21; H, 4.96; N, 16.23%. IR (KBr, cm-1): 3266 (N-H stretching), 1747 (C=O β-lactam ring), 1668 (C=O stretching of carbonyl), 1611 (C=N), 1565 (C=C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.10 (1H, s, CONH- ), 7.90 (1H, s, N-CH-), 7.67, 8.32 (4H, m, Py), 6.65-6.69 (4H, m, Ar- H), 2.70 (6H, s, N(CH3)2. 13C-NMR (100 MHz, CDCl3, δ/ppm): 163.7, 163.5, 149.7, 149.1, 140.8, 133.0, 129.2, 121.7, 112.7, 67.4, 64.1, 41.3. MS (m/z): 344 [M+].

General procedure for the synthesis of 1-(2-(2-substitutedphenyl)-5-(pyridine-4-yl)-1,3,4- oxadiazol-3(2H)-yl)ethanone (5a-h)

A mixture of 1(0.003mol) and acetic anhydride (10mL) was heated under reflux for 4h. After the reaction mixture attained room temperature, excess acetic anhydride was decomposed by water and the mixture was stirred for further 30 min. The separated product was filtered, washed with water, dried and recrystallized in appropriate solvent systems to give the products 5a-h.

1-(2-(2-Chlorophenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)- yl)ethanone (5a): Yield: 65%; m.p. 182-184°C. Anal. Calcd. for C15H12ClN3O2 (MW 301.73): C, 59.71; H, 4.01; N, 13.93%. Found: C, 59.70; H, 4.00; N, 13.91%. IR (KBr, cm-1): 1660 (acetyl C=O), 1614 (C=N), 1560 (C=C), 830 (C-Cl stretching of chlorine), 1500 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.72-8.64 (4H, m, Py), 7.12-7.14 (4H, m, aromatic), 7.19 (1H, s, CH- oxadiazole). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 149.4, 142.8, 138.4, 132.2, 128.6, 128.3, 128.1, 126.6, 124.1, 78.4, 23.4. MS (m/z): 301 [M+].

1-(2-(4-Chlorophenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol- 3(2H)-yl)ethanone (5b): Yield: 60%; m.p. 186-188°C. Anal. Calcd. for C15H12ClN3O2 (MW 301.73): C, 59.22; H, 4.97; N, 16.25%. Found: C, 59.21; H, 4.95; N, 16.23. IR (KBr, cm-1): 1662 (acetyl C=O), 1616 (C=N), 1562 (C=C), 834 (C-Cl stretching of chlorine), 1504 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.73, 8.65 (4H, m, Py), 7.20 (1H, s, CH-oxadiazole), 7.13-7.15 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 149.4, 138.4, 132.3, 128.6, 128.3, 124.1, 83.5, 23.4. MS (m/z): 301 [M+].

1-(2-(2-Hydroxyphenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol- 3(2H)-yl)ethanone (5c): Yield: 50%; m.p. 198-200°C. Anal. Calcd. for C15H13N3O3 (MW 283.28): C, 63.60; H, 4.63; N, 14.83%. Found: C, 63.58; H, 4.61; N, 14.81%. IR (KBr, cm-1): 1664 (acetyl C=O), 1618 (C=N), 1563 (C=C), 1510 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.32 (1H, br, OH), 7.62, 8.34 (4H, m, Py), 7.20 (1H, s, CH-oxadiazole), 7.10- 7.13 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 149.4, 138.4, 129.6, 128.3, 128.1, 124.1, 121.1, 115.7, 77.3, 23.4. MS (m/z): 283 [M+].

1-(2-(3-Hydroxyphenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol- 3(2H)-yl)ethanone (5d): Yield: 65%; m.p. 210-212°C. Anal. Calcd. for C15H13N3O3 (MW 283.28): C, 63.60; H, 4.63; N, 14.83%. Found: C, 63.59; H, 4.62; N, 14.82. IR (KBr, cm-1): 1664 (acetyl C=O), 1618 (C=N), 1563 (C=C), 1510 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 9.32 (1H, br, OH), 7.62, 8.34 (4H, m, Py), 7.20 (1H, s, CH-oxadiazole), 7.10- 7.13 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 156.8, 149.4, 141.7, 138.4, 129.9, 124.1, 113.9, 112.6, 83.8, 23.4. MS (m/z): 283 [M+].

1-(2-(4-Methoxyphenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol- 3(2H)-yl)ethanone (5e): Yield: 55%; m.p. 202-204°C. Anal. Calcd. for C16H15N3O3 (MW 297.31): C, 64.64; H, 5.09; N, 14.13%. Found: C, 64.62; H, 5.07; N, 14.11%. IR (KBr, cm-1): 1667 (acetyl C=O), 1615 (C=N), 1561 (C=C), 1515 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ ppm): 7.66, 8.38 (4H, m, Py), 7.22 (1H, s, CH-oxadiazole), 7.14-7.17 (4H, m, aromatic), 3.71 (3H, s, OCH3). 13C-NMR (100 MHz, CDCl3, δ/ ppm): 168.8, 157.0, 156.5, 149.4, 138.4, 127.9, 127.7, 124.1, 120.8, 112.1, 77.6, 23.4. MS (m/z): 297 [M+].

1-(2-(4-Fluorophenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)- yl)ethanone (5f): Yield: 65%; m.p. 206-208°C. Anal. Calcd. for C15H12FN3O2 (MW 285.27): C, 63.15; H, 4.24; N, 14.73%. Found: C, 63.14; H, 4.23; N, 14.71%. IR (KBr, cm-1): 1663 (acetyl C=O), 1620 (C=N), 1565 (C=C), 1518 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ ppm): 7.69, 8.37 (4H, m, Py), 7.25 (1H, s, CH-oxadiazole), 7.13-7.18 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 159.4, 149.4, 138.4, 129.4, 128.5, 128.3, 124.1, 76.7, 23.4. MS(m/z): 285 [M+].

1-(2-(2-Nitrophenyl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)- yl)ethanone (5g): Yield: 70%; m.p. 196-198°C. Anal. Calcd. for C15H12N4O4 (MW 312.28): C, 57.69; H, 3.87; N, 17.94%. Found: C, 57.67; H, 3.85; N, 17.93%. IR (KBr, cm-1): 1669 (acetyl C=O), 1619 (C=N), 1563 (C=C), 1517 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ ppm): 7.67, 8.35 (4H, m, Py), 7.23 (1H, s, CH-oxadiazole), 7.12-7.15 (4H, m, aromatic). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 149.4, 148.2, 139.4, 138.4, 130.9, 129.4, 127.6, 124.7, 78.9, 23.4. MS (m/z): 312 [M+].

1-(2-(4-(Dimethylamino)phenyl)-5-(pyridin-4-yl)-1,3,4- oxadiazol-3(2H)-yl)-ethanone(5h): Yield: 75%; m.p. 204-206°C. Anal. Calcd. for C17H18N4O2 (MW 310.35): C, 65.79; H, 5.85; N, 18.05%. Found: C, 65.78; H, 5.83; N, 18.03%. IR (KBr, cm-1): 1664 (acetyl C=O), 1624 (C=N), 1570 (C=C), 1511 (C-O-C). 1H-NMR (300 MHz, CDCl3, δ/ppm): 7.65, 8.33 (4H, m, Py), 7.26 (1H, s, CH-oxadiazole), 7.14-7.18 (4H, m, aromatic), 2.73 (6H, s, N(CH3)2). 13C-NMR (100 MHz, CDCl3, δ/ppm): 168.8, 157.0, 149.4, 149.1, 138.4, 129.8, 127.8, 124.1, 83.5, 41.3, 23.4. MS (m/z): 310 [M+].

Biological Activity

Antifungal activity

Antifungal activity of the synthesized compounds were determined in vitro by using serial plate dilution method [19,20] against C. albicans (ATCC 2091), A. niger (MTCC 281), A. flavus (MTCC 277), M. purpureous (MTCC 369) and P. citrinum (NCIM 768) at 100 μg/ mL, 50 μg/mL, 25 μg/mL, 12.5 μg/mL and 6.25 μg/mL concentrations, respectively, in the nutrient agar media. Standard antibiotic ketoconazole was used as reference drug at 25 μg/mL, 12.5 μg/mL and 6.25 μg/mL. Solutions of required concentrations of test compounds were prepared by dissolving the compounds in DMSO. The minimum inhibitory concentration (MIC) obtained for the test compounds and standard drug are reported in Table 1. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of the compounds that inhibited visible growth of microorganisms on the plate.

Compounds MIC in μg/mL and zone of inhibition (%)
C. albicans A. niger A. flavus M. purpureous P. citrinum
2a 25 (67) 50(51) 25(67) 25(67) 50(51)
2b 6.25(100) 6.25(91) 6.25(97) 12.5 (86) 6.25(97)
2c 50(51) 50(51) 50(47) 12.5(80) 25(67)
2d 100(34) 100(30) 100(34) 100(34) 100(30)
2e 12.5(74) 12.5(77) 12.5(80) 6.25(86) 12.5(77)
2f 100(30) 100(24) 100(34) 100(27) 100(34)
2g 25(67) 50(51) 25(67) 50(51) 25(64)
2h 50(51) 50(41) 50(47) 12.5(83) 50(51)
3a 25(64) 50(47) 25(61) 25(64) 50(51)
3b 12.5 (77) 12.5 (74) 6.25(86) 6.25(86) 12.5(74)
3c 50(44) 25(57) 25(54) 25(61) 50(51)
3d 100(30) 100(27) 100(24) 100(27) 100(34)
3e 12.5(77) 6.25(86) 6.25(86) 12.5(74) 12.5 (77)
3f 100(30) 100(24) 100(21) 100(24) 100(27)
3g 50(47) 25(64) 25(67) 25(61) 50(51)
3h 25(64) 50(44) 25(67) 50(47) 50(54)
4a 25(57) 50(37) 50(41) 50(37) 12.5 (74)
4b 12.5 (77) 12.5 (80) 12.5 (74) 25(83) 25(74)
4c 25(57)5 50(41) 25(54) 25(54) 50(41)
4d 100(15) 100(12) 100(18) 100(24) 100(15)
4e 12.5 (74) 25(64) 12.5 (74) 12.5 (77) 25(64)6
4f 100(12) 100(15) 100(12) 100(18) 100(18)
4g 25(57) 25(57) 25(54) 25(57) 50(44)
4h 25(61) 50(41) 50(37) 50(41) 12.5 (77)
5a 12.5 (70) 25(54) 25(57) 25(61) 50(44)
5b 25(67) 12.5(70) 12.5(83) 25(67) 12.5(70)
5c 25(57) 50(54) 25(61) 25(54) 12.5 (74)
5d 100(18) 100(12) 100(15) 100(18) 100(12)
5e 12.5 (70) 25(67) 12.5 (70) 12.5 (77) 25(57)
5f 100(7) 100(7) 100(3) 100(12) 100(7)
5g 50(41) 25(61) 50(37) 25(61) 25(64)
5h 12.5 (74) 25(57) 25(57) 25(54) 12.5 (77)
Ketoconazole 6.25(100) 6.25(100) 6.25(100) 6.25(100) 6.25(100)
Isoniazid 25(67) 25(61) 25(67) 50 (51) 25(64)

Table 1: Antifungal activity of the synthesized compounds.

Animals

Male albino mice (Swiss, 18-25 gm) were used as experimental animals. The test compounds were suspended in polyethylene glycol (PEG). The animals were maintained on an adequate diet and allowed free access to food and water except during the short time they were removed from cages for testing. The animals were maintained at room temperature (25-30°C). All the experimental protocols were carried out with the permission from Institutional Animal Ethics Committee (IAEC). Animals were obtained from Central Animal House Facility, Hamdard University, New Delhi-110062, India. Registration number and date of registration of Animal House Facility (173/CPCSEA, 28, JAN-2000).

Assessment of liver function

Liver functions such as serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) were assessed by a reported method [21]. The alkaline phosphatase was also measured according to the reported procedures [22,23]. All data are recorded in Table 2.

Treatment Alkaline phosphatase ± SEM SGOT ± SEM SGPT ± SEM
Control 12.45±0.21 168.13±1.06 20.19±0.12
2b 14.32±0.11 169.12±1.11 28.10±0.13
4b 38.35±0.16** 187.32±1.01* 45.31±0.16**
5b 30.12 ± 0.13* 175.13*0.91 39.12±0.12*

Table 2: Enzyme estimation of the selected compounds.

Results and Discussion

Chemistry

The key intermediates used in the synthesis of thiazolidin-4- ones (2a-h) and (3a-h), azetidin-2-one (4a-h) and 1,3,4-oxadiazole derivatives (5a-h), (E)-N’-(2-substituted benzylidene) isonicotinohydrazides (1a-h) were prepared starting from isonicotinic acid hydrazide. The reaction of isonicotinic acid hydrazide with substituted benzaldehyde in refluxing methanol with few drops of glacial acetic acid gave the (E)-N’-(2-substituted benzylidene)isonicotinohydrazides (1a-h). In the present study, the reaction of the substituted benzylidene isonicotinohydrazides (1a-h) with thioglycolic acid, thiomalic acid, chloroacetyl chloride and acetic anhydride in presence of various reagents gave the new thiazolidin-4-ones (2a-h) and (3a-h), azetidin- 2-one (4a-h) and 1,3,4-oxadiazole derivatives (5a-h), respectively. The synthesis routes to the compounds are outlined in Scheme 1.

medicinal-chemistry-Synthetic-route-compounds

Scheme 1: Synthetic route for the title compounds.

Antifungal activity

The newly synthesized compounds 2a-h, 3a-h, 4a-h and 5a-h were screened for their antifungal activity. The results of antifungal effect of all the tested compounds were reported as minimal inhibitory concentrations (MICs, μg/mL). The compounds 2b, 2e, 3b, 3e, 4b, 4e, 5b and 5e showed comparatively good activity against all the fungal strains (Table 1). The good activity is attributed to the presence of pharmacologically active chloro (2b, 3b, 4b, 5b) and methoxy (2e, 3e, 4e, 5e) groups attached to phenyl group at fourth position respectively (MIC 6.25 μg/mL, 12.5 μg/mL & 25 μg/mL). When these groups were replaced by m-hydroxy and p-fluoro groups (2d, 2f, 3d, 3f, 4d, 4f,5d, 5f) it caused sharp decrease in activity against most of the strains (MIC 100 μg/mL). Rest of the compounds exhibited moderate activity compared to that of standard against all the fungal strains (MIC 25μg/mL & 50 μg/mL).

The antifungal activity study revealed that all the compounds tested showed good to moderate antifungal activity against all pathogenic strains (MIC 6.25 μg/mL, 12.5 μg/mL, 25 μg/mL and 50 μg/mL). Structure and biological activity relationship of title compounds showed that the presence of 4-chloro phenyl, 4-methoxy phenyl groups (MIC 6.25 and12.5 μg/mL) are responsible for good antifungal activity.

Thus, various thiazolidine (2a-h, 3a-h), azetidine (4a-h) and oxadiazole (5a-h) derivatives of isoniazid were prepared with the objective of developing better antifungal agents. The derivatives of the aforementioned rings were found to have a promising class of compounds with an interesting pharmacological profile. Further, it is clear from structure activity relationship (SAR), that the thiazolidine derivatives (2b, 2e, 3b, 3e) were found to be more active than azetidine (4b, 4e) and oxadiazole (5b, 5e) derivatives.

Assessment of liver function

The most active compounds (2b, 4b and 5b) of the series were evaluated further for their hepatotoxic effects by assessing the liver enzymes. Any significant changes in the level of enzymes are indicative of liver disorders. Levels of alkaline phosphatase, SGOT and SGPT enzymes were measured and the results are expressed as mean ± SEM. Compound 4b showed significant rise in the alkaline phosphatase and SGPT level with P<0.01 when compared to control. The rise in SGOT level was also found to be significant with P<0.05. Compound 5b was also found to increase the alkaline phosphatase and SGPT levels significantly with P<0.05. The rise in SGOT level was not significant with compound 5b. Compound 2b showed no significant change in all the three enzymes and can be considered to have no hepatotoxicity.

Conclusion

Thus, various thiazolidin-4-ones, (2a-h, 3a-h) azetidin-2-ones (4ah) and 1,3,4-oxadiazole (5a-h) derivatives of isoniazid were prepared with the objective of developing better antifungal agents. All the derivatives were found to have a promising class of compounds with an interesting pharmacological profile. Among these the compound N-(2-(4-Chlorophenyl)-4-oxothiazolidin-3-yl) isonicotinamide (2b) showed maximum antifungal activity with no hepatotoxicity effect. Hence, it is clear from structure activity relationship (SAR), that thiazolidin-4-ones derivatives were more active than azetidin-2-ones and 1,3,4-oxadiazole derivatives. Also a common result was obtained for parent drug isoniazid, which showed moderate activity against all pathogenic fungal strains. In conclusion, the isoniazid incorporated hydrazone derivatives can be regarded as a newer class of antifungal agents. They were also found to be less toxic which indicates better tolerability of the compounds having strong future prospects.

Acknowledgements

The authors are thankful to the Head of the Department, Pharmaceutical Chemistry for providing laboratory facilities, Central Drug Research Institute (CDRI) for spectral analysis of the compounds.

References

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