Synthesis, characterization and in vitro antimicrobial screening of quinoline nucleus containing 1,3,4-oxadiazole and 2-azetidinone derivatives Academic research paper on "Chemical sciences"

ORIGINAL ARTICLE

Synthesis, characterization and in vitro antimicrobial screening of quinoline nucleus containing 1,3,4-oxadiazole and 2-azetidinone derivatives

N.C. Desai *, Amit M. Dodiya

Medicinal Chemistry Division, Department of Chemistry, Mahatma Gandhi Campus, Bhavnagar University, Bhavnagar 364 002, India

Received 10 May 2011; accepted 2 September 2011

KEYWORDS

Antimicrobial activity of quinoline;

Quinoline-oxadiazole-azetidinone

Abstract A series of 3-chloro-1-(aryl)-4-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-ethyl-azetidin-2-ones (V)i 12 have been synthesized and characterized by IR, 1H NMR, 13C NMR and mass spectra. Synthesized compounds were screened for their antibacterial activity against four different strains like Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Streptococcus pyogenes, while antifungal activity was determined against three different strains like Candida albicans, Aspergillus niger and Aspergillus clavatus. On the basis of statistical analysis, it has been observed that compounds gave significant co-relation.

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1. Introduction

Chemical modification of bioactive components is one of the most common approaches in drug discovery with improved therapeutic effect (Tan et al., 2006) and the wide occurrence of heterocycles in bioactive natural products and pharmaceuticals have made them important synthetic targets.

* Corresponding author.

E-mail address: dnisheeth@rediffmail.com (N.C. Desai).

1319-6103 © 2011 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

Peer review under responsibility of King Saud University. doi:10.1016/j.jscs.2011.09.005

Quinoline nucleus containing antibacterial agents are among the most attractive drugs in anti-infective chemotherapy. These antibiotics exert their antimicrobial activity by binding to type II bacterial topoisomerase enzymes, DNA gyrase (subunits encoded by gyrA and gyrB) and topoisomerase IV (subunits encoded by grlA and grlB for Staphylococcus aureus). This binding induces permanent double stranded DNA breaks, and results in cell death (Domagala et al., 1986). However, toxic dose-related side effects such as myelosuppresion and cardiotoxicity limited their clinical applications (Cheng and Zee-Cheng, 1983; Murray, 2000). The potent anticancer activity as well as toxic effects described for these compounds is normally ascribed, at least, to two main mechanisms. One, which is associated with protein, involves trapping of a protein enzyme-DNA cleavable intermediate, whereas the other, a non-protein-associated mechanism, is related to redox cycling of the quinoline moiety, which produces damaging free-radical species (Murray, 2000). In search of more potential bioactive molecules with improved pharmacokinetic properties, potency

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and lower side effects, a large number of quinoline derivatives and related compounds have been prepared and several of the quinolines are promising in clinical trials (Lown, 1988).

1,3,4-Oxadiazole derivatives have been found to exhibit diverse biological activities such as antibacterial, antifungal, anti-inflammatory and antihypertensive (Tully et al., 1991; Manjunatha et al., 2010; Holla et al., 2000). Antihypertensive agents available in the market such as tiodazosin (Vardan et al., 1983) and antibiotics such as furamizole possess oxadi-azole nucleus. The widespread use of 1,3,4-oxadiazoles as a scaffold in medicinal chemistry establishes this moiety as an important bio-active class of heterocycles. These molecules are also utilized as pharmacophores due to their favorable metabolic profile in the human body and the ability to engage in hydrogen bonding. They are also useful as HIV integrase inhibitors and as angiogenesis inhibitors (Johns, 2004). Several methods have been reported in the literature for the synthesis of 1,3,4-oxadiazoles (Baxendale et al., 2005; Coppo et al., 2004; Brain et al., 1999; Wang et al., 2006).

Azetidin-2-one (ß-lactam) ring is present in several widely used families of antibiotics such as penicillins, cephalosporins, carbapenems, and monocyclic ß-lactams (for example aztreo-nam). Recent discoveries have proved that ß-lactams can serve as mechanism based inhibitors of serine protease (Abell and Oldham, 1999; Annunziata et al., 2002) and as inhibitors of acyl-CoA cholesterol acyltransferase (ACAT) (Rosenblum

et al., 2000) which is responsible for atherosclerotic coronary heart disease. This has stimulated considerable research efforts toward stereoselective routes for the synthesis of this important building block. Moreover, additional impetus has been provided by the introduction of b-lactam synthon methodology (Ojima et al., 1992; Palomo et al., 1997; Boge and Georg, 1997), according to which enantiomerically pure b-lactams can be employed as useful intermediates for organic synthesis. One of the most popular methods for the preparation of the b-lac-tam ring involves venerable [2+2] cycloaddition of ketenes and imines (Taggi et al., 2002; Hegedus et al., 1991).

In this paper, we have reported the synthesis of a new class of heterocyclic molecules in which quinoline, 1,3,4-oxadiazole and azetidinone moieties were present in one frame work. The structures of synthesized compounds were assigned on the basis of IR, NMR, 13C NMR and mass spectral data. These compounds were evaluated for their antimicrobial screening on different strains of bacteria and fungi, (Scheme 1).

2. Experimental

2.1. Materials and methods

The percentage composition of elements (CHN) for the compounds was determined using an elemental analyzer Fisons EA-1108-CHNS-O, Fisons Instruments, Milano, Italy. Infra-

conhnh2

Sr. No. r Sr. No. r

V, -2-C1 v7 -2-OCH,

v2 -3-C1 v8 -3-OCft

v3 -4-C1 v9 -4-OCH,

v4 -2-N02 V,o -4-CH3

v5 -3-N02 v„ -2-F

V6 -4-N02 v,2 -4-F

(V)l-12

R = Different substituents

Scheme 1 Synthetic route of the title compounds (V)i_i2.

red spectra were recorded on KBr disk using Perkin-Elmer spectrophotometer GX. The and 13C nuclear magnetic resonance spectra were recorded using JEOL JNM-ECP 400 NMR spectrometer (JEOL, Japan). Mass spectra were recorded on Shimadzu GCMSQP5050A, spectrometer, Japan, DB-1 glass column 30, 0.25 mm, ionization energy 70 eV. The purity of the synthesized compounds were checked by TLC silica gel coated plates obtained from Merck as stationary phase and solvent mixture of n-hexane-ethyl acetate used as mobile phase at 25 0C. 2-Chloro-6-methylquinoline-3-carbal-dehyde (I) was synthesized by following the procedure (Meth-Cohn, 1993). The progress of the reaction and the purity of compounds were routinely checked on TLC aluminium sheet silica gel 60 F245 (E. Merck) using benzene-acetonitrile (4:1 v/v) as an irrigator and was developed in an iodine chamber.

2.2. Preparation and physical data of synthesized compounds (II- V1-12)

2.2.1. N'-((2-Chloro-6-methylquinolin-3-yl)methylene) isonicotinohydrazide (II)

A mixture of equal amounts of 2-chloro-6-methylquinoline-3-carbaldehyde and isoniazide was taken and dissolved in 1,4-dioxane (25 mL) and refluxed for 5-6 h. After cooling, the crystals formed were filtered off and recrystallized from alcohol (95%) to give compound-(II). Yield 78%, m.p.: 154-156 oc. Anal. Calcd for C17H13ClN4O. C, 62.87; H, 4.03; N, 17.25. Found: C, 62.93; H, 4.08; N, 17.32.

2.2.2. 1-(2-( 2-Chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)ethanone (III)

Acetic anhydride was added to aroylhydrazone (II) and the mixture was refluxed for 2 h. After cooling, the reaction mixture was poured into ice water. The precipitate was filtered off, washed with water, dried, and recrystallized from mixed solvents DMF and ethanol (95%) to give compound-(III). Yield 71%, m.p.: 212-214 oc. Anal. Calcd for C19H15ClN4O2: C, 62.21; H, 4.12; N, 15.27. Found: C, 62.26; H, 4.18; N, 15.33.

2.2.3. 4-Chloro-N-( 1-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1 ,3 ,4-oxadiazol-3(2H)-yl)ethylidene)aniline

A mixture of (III) (0.01 mol) and p-chloroaniline (0.01 mol) in ethanol (30 ml) containing a catalytic amount of glacial acetic acid was refluxed for 8 h at 80 oc. The solid that separated out on cooling was filtered, washed with water and recrystallized from alcohol (95%) to afford compound - (IV)3. Yield 72%, m.p.: 211-213 oc. Anal. Calcd for C25H19Cl2N5O: C, 63.03; H, 4.02; N, 14.70. Found: C, 63.08; H, 4.08; N, 14.77.

2.2.4. General procedure for 3-chloro-1-(4-chlorophenyl)-4-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H) -yl)-4-methylazetidin-2-one (V)3

A mixture of compound-(IV)3 (0.01 mol) and triethylamine (TEA) (1.02 ml, 0.01 mol) was dissolved in 1,4-dioxane (30 ml) and kept it in an ice bath and stirred for half an hour. To this, a cold solution of chloroacetyl chloride (0.72 ml, 0.01 mol) was added slowly at 0-5 oc and further stirred for half an hour, then refluxed and stirred it for 10-12 h at

95 oc. Then it was left for 2-3 h. The precipitated triethylam-monium chloride was filtered off and 1,4-dioxane was removed by distillation. Residue was poured into cold water, the resulting solid was washed well with water, then dried and crystallized from alcohol (95%) to afford the final product - (V)3.

All other compounds of this series were prepared by using the same method.

2.2.4.1. 3-Chloro-1-(2-chlorophenyl)-4-(2-(2-chloro-6-methyl-quinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)1. Yield: 75%, m.p. 245-247 oc. IR (KBr): 3084, 3065 (Ar-H, Qu-H stret.,), 2893, 2875 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 1713 (C=O, stret.,), 1614, 1604 (C=C, C=N, aromatic ring), 1465, 1457 (-C-H bend., b-lactam-CH3 and quinoline-CH3 group), 1212 (C-O-C linkage), 766, 755 cm"1 (C-Cl stretching). NMR (400 MHz, DMSO-d6): d = 1.69 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 7.32-8.66 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 124.1, 123.0, 125.8, 126.6, 127.0, 130.1, 130.9, 131.2, 131.4, 136.2, 136.4, 138.4, 140.2, 141.1, 145.4, 149.4, 151.9, 157.0, 161.9 ppm; MS: m/z = 552.84. Anal. Calcd for C27H20Cl3N5O2: C, 58.66; H, 3.65; N, 12.67. Found: C, 58.72; H, 3.71; N, 12.72.

2.2.4.2. 3-Chloro-1-(3-chlorophenyl)-4-(2-(2-chloro-6-methyl-quinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)2. Yield: 68%, m.p. 195-197 oc. IR (KBr): 3080, 3063 (Ar-H, Qu-H stret.,), 2894, 2875 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 1715 (C=O, stret.), 1612, 1605 (C=C, C=N, aromatic ring), 1464, 1458 (-C-H bend., b-lactam-CH3 and quinoline-CH3 group), 1215 (C-O-C linkage), 767, 756 cm"1 (C-Cl stretching). NMR (400 MHz, DMSO-d6): d = 1.64 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.65 (s, 1H, -N-CH-O linkage), 5.26 (s, 1H, -CH-Cl azetidinone ring), 7.15-8.66 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 124.1, 125.6, 125.8, 126.6, 127.9, 130.3, 130.9, 134.5, 135.8, 131.4, 136.2, 136.4, 138.4, 143.1, 145.4, 149.4, 151.9, 157.0, 161.8 ppm; MS: m/z = 552.84. Anal. Calcd for C27H20Cl3N5O2: C, 58.66; H, 3.65; N, 12.67. Found: C, 58.71; H, 3.72; N, 12.74.

2.2.4.3. 3-Chloro-1-(4-chlorophenyl)-4-(2-(2-chloro-6-methyl-quinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)3. Yield: 65%, m.p. 222-223 oc. IR (KBr): 3085, 3060 (Ar-H, Qu-H stret.,), 2892, 2873 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 1716 (C=O, stret.), 1615, 1598 (C=C, C=N, aromatic ring), 1469, 1456 (-C-H bend., b-lactam-CH3 and quinoline-CH3 group), 1210 (C-O-C linkage), 768, 754 cm"1 (C-Cl stretching). 1H NMR (400 MHz, DMSO-d6): d = 1.68 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 7.34-8.66 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 124.1, 125.6, 125.8, 126.6, 129.0, 130.9, 133.3, 131.4, 136.2, 136.4, 138.4, 139.8, 145.4, 149.4, 151.9, 157.0, 161.9 ppm; MS: m/z = 552.84. Anal. Calcd for C27H20Cl3N5O2: C, 58.66; H, 3.65; N, 12.67. Found: C, 58.70; H, 3.69; N, 12.71.

2.2.4.4. 3-Chloro-1-(2-nitrophenyl)-4-(2-(2-chloro-6-methyl-quinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)4. Yield: 60%, m.p. 187-188 0C. IR (KBr): 3087, 3062 (Ar-H, Qu-H stret.), 2889, 2877 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 1713 (C=O, stret.), 1612, 1604 (C=C, C=N, aromatic ring), 1475 (-NO2 group asymmetric stretching), 1465, 1458 (-C-H bend., b-lac-tam-CH3 and quinoline-CH3 group), 1310 (-NO2 group symmetric stretching), 1215 (C-O-C linkage), 765, 756 cm-1 (C-Cl stretching). *H NMR (400 MHz, DMSO-d6): d = 1.65 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 7.588.64 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 113.3, 124.1, 125.4, 125.8, 126.6, 130.9, 125.2, 131.4, 136.2, 136.4, 137.7, 138.4, 136.9, 142.4, 145.4, 149.4, 151.9, 157.0, 161.2 ppm; MS: m/z = 594.36. Anal. Calcd for C27H20Cl2N6O4: C, 57.56; H, 3.58; N, 14.92. Found: C, 57.63; H, 3.66; N, 14.97.

2.2.4.5. 3-Chloro-1-(3-nitrophenyl)-4-(2-(2-chloro-6-methyl-quinolin-3-yl)-5-(pyridin-4-yl)-1 , 3, 4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)5. Yield: 64%, m.p. 175-177 0C. IR (KBr): 3078, 3058 (Ar-H, Qu-H stret.,), 2890, 2871 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 1714 (C=O, stret.), 1610, 1601 (C=C, C=N, aromatic ring), 1478 (-NO2 group asymmetric stretching), 1464, 1452 (-C-H bend., b-lac-tam-CH3 and quinoline-CH3 group), 1317 (-NO2 group symmetric stretching), 1208 (C-O-C linkage), 763, 751 cm-1 (C-Cl stretching). *H NMR (400 MHz, DMSO-d6): d = 1.62 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.63 (s, 1H, -N-CH-O linkage), 5.26 (s, 1H, -CH-Cl azetidinone ring), 7.58-8.67 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 119.5, 123.1, 124.1, 125.8, 126.6, 129.8, 130.9, 133.6, 131.4, 136.2, 136.4, 138.4, 142.6, 145.4, 148.1, 149.4, 151.9, 157.0, 161.1 ppm; MS: m/z = 594.36. Anal. Calcd for C27H20Cl2N6O4: C, 57.56; H, 3.58; N, 14.92. Found: C, 57.61; H, 3.64; N, 14.98.

2.2.4.6. 3-Chloro-1-(4-nitrophenyl)-4-(2-(2-chloro-6-methyl-quinolin-3-yl)-5-(pyridin-4-yl)-1 , 3, 4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)6. Yield: 70%, m.p. 256-258 0C. IR (KBr): 3081, 3067 (Ar-H, Qu-H stret.,), 2887, 2872 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 1712 (C=O, stret.), 1611, 1602 (C=C, C=N, aromatic ring), 1476 (-NO2 group asymmetric stretching), 1462, 1459 (-C-H bend., b-lac-tam-CH3 and quinoline-CH3 group), 1322 (-NO2 group symmetric stretching), 1214 (C-O-C linkage), 762, 758 cm-1 (CCl stretching). *H NMR (400 MHz, DMSO-d6): d = 1.69 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.66 (s, 1H, -N-CH-O linkage), 5.27 (s, 1H, -CH-Cl azetidinone ring), 6.86-8.68 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 124.1, 124.4, 124.7, 125.8, 126.6, 130.9, 131.1, 131.3, 131.4, 136.2, 136.4, 138.4, 143.5, 145.4, 147.6, 149.4, 151.9, 157.0, 161.3 ppm; MS: m/z = 594.36. Anal. Calcd for C27H20Cl2N6O4: C, 57.56; H, 3.58; N, 14.92. Found: C, 57.62; H, 3.64; N, 14.97.

2.2.4.7. 3-Chloro-1-(2-methoxyphenyl)-4-(2-(2-chloro-6-meth-ylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)7. Yield: 54%, m.p. 234-236 0C. IR (KBr): 3081, 3063 (Ar-H, Qu-H stret.,), 2890, 2872 (-C-H

stret., b-lactam-CH3 and quinoline-CH3 group), 2862 (-OCH3 stretching), 1714 (C=O, stret.), 1611, 1602 (C=C, C=N, aromatic ring), 1462, 1455 (-C-H bend., b-lactam-CH3 and quinoline-CH3 group), 1450 (-OCH3 bending), 1212 (C-O-C linkage), 762, 755 cm-1 (C-Cl stretching). *H NMR (400 MHz, DMSO-d6): d = 1.64 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 3.73 (s, 3H, -OCH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 6.978.66 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 17.8, 21.7, 65.9, 77.4, 90.2, 116.9,

124.1, 125.8, 125.9, 126.6, 129.3, 130.7, 130.9, 134.3, 131.4,

136.2, 136.4, 138.4, 138.6, 145.4, 149.4, 151.9, 157.0, 161.4 ppm; MS: m/z = 548.42. Anal. Calcd for C28H23Cl2N5O3: C, 61.32; H, 4.23; N, 12.77. Found: C, 61.38; H, 4.29; N, 12.83.

2.2.4.8. 3-Chloro-1-(3-methoxyphenyl)-4-(2-(2-chloro-6-meth-ylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)8. Yield: 66%, m.p. 233-235 0C. IR (KBr): 3078, 3057 (Ar-H, Qu-H stret.,), 2888, 2868 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 2856 (-OCH3 stretching), 1715 (C=O, stret.), 1613, 1604 (C=C, C=N, aromatic ring), 1464, 1452 (-C-H bend., b-lactam-CH3 and quinoline-CH3 group), 1448 (-OCH3 bending), 1214 (C-O-C linkage), 765, 750 cm-1 (C-Cl stretching). *H NMR (400 MHz, DMSO-d6): d = 1.66 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 3.73 (s, 3H, -OCH3), 5.64 (s, 1H, -N-CH-O linkage), 5.26 (s, 1H, -CH-Cl azetidinone ring), 6.978.68 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 55.8, 65.9, 77.4, 90.2, 116.4, 119.8, 124.1, 125.4, 125.8, 126.6, 124.0, 130.9, 131.4, 136.2, 136.4, 138.4, 142.7, 145.4, 149.4, 151.9, 157.0, 160.3, 161.7 ppm; MS: m/z = 548.42. Anal. Calcd for C28H23Cl2N5O3: C, 61.32; H, 4.23; N, 12.77. Found: C, 61.39; H, 4.30; N, 12.82.

2.2.4.9. 3-Chloro-1-(4-methoxyphenyl)-4-(2-(2-chloro-6-meth-ylquinolin-3-yl)-5-(pyridin-4-yl)-1, 3, 4-oxadiazol-3(2H)-yl)-4-methylazetidin-2-one (V)9. Yield: 68%, m.p. 176-178 0C. IR (KBr): 3087, 3056 (Ar-H, Qu-H stret.,), 2893, 2875 (-C-H stret., b-lactam-CH3 and quinoline-CH3 group), 2868 (-OCH3 stretching), 1716 (C=O, stret.), 1611, 1602 (C=C, C=N, aromatic ring), 1464, 1458 (-C-H bend., b-lactam-CH3 and quinoline-CH3 group), 1445 (-OCH3 bending), 1214 (C-O-C linkage), 763, 756 cm-1 (C-Cl stretching). *H NMR (400 MHz, DMSO-d6): d = 1.66 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 3.73 (s, 3H, -OCH3), 5.64 (s, 1H, -N-CH-O linkage), 5.27 (s, 1H, -CH-Cl azetidinone ring), 7.048.68 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 55.8, 65.9, 77.4, 90.2, 114.5, 124.1, 122.6, 125.8, 126.6, 130.9, 134.0, 131.4, 131.4, 136.2, 136.4, 136.4, 138.4, 145.4, 149.4, 151.9, 157.0, 158.9, 161.0 ppm; MS: m/z = 548.42. Anal. Calcd for C28H23 Cl2N5O3: C, 61.32; H, 4.23; N, 12.77. Found: C, 61.37; H, 4.31; N, 12.82.

2.2.4.10. 3-Chloro-4-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1 ,3 ,4-oxadiazol-3(2H)-yl)-4-methyl-1-2-tolylaz-etidin-2-one (V)10. Yield: 64%, m.p. 232-234 0C. IR (KBr): 3087, 3067 (Ar-H, Qu-H stret.), 2890, 2871 (-C-H stret., b-lac-tam-CH3 and quinoline-CH3 group), 1711 (C=O, stret.), 1611, 1602 (C=C, C=N, aromatic ring), 1463, 1454 (-C-H

bend., ß-lactam-CH3 and quinoline-CH3 group), 1212 (C-O-C linkage), 763, 754 cm"1 (C-Cl stretching). 1H NMR (400 MHz, DMSO-d6): d = 1.66 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 2.09 (s, 3H, phe-CH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 6.86-8.66 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 17.5, 21.7, 65.9, 77.4, 90.2, 116.9, 124.1, 125.7, 125.8, 126.6, 129.3, 130.7, 130.9, 131.4, 136.2, 136.4, 138.4, 138.6, 145.4, 149.4, 151.9, 157.0, 161.5 ppm; MS: m/z = 532.42. Anal. Calcd for C28H23Cl2N5O2: C, 63.16; H, 4.35; N, 13.15. Found: C, 63.22; H, 4.42; N, 13.21.

2.2.4.11. 3-Chloro-4-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-1-(2-fluorophenyl)-4-methylazetidin-2-one (V)n. Yield: 63%, m.p. 205-207 0C. IR (KBr): 3083, 3064 (Ar-H, Qu-H stret.), 2890, 2876 (-C-H stret., ß-lactam-CH3 and quinoline-CH3 group), 1713 (C=O, stret.), 1614, 1604 (C=C, C=N, aromatic ring), 1465, 1458 (-C-H bend., ß-lactam-CH3 and quinoline-CH3 group), 1215 (C-O-C linkage), 765, 752 cm"1 (C-Cl stretching). 1H NMR (400 MHz, DMSO-d6): d = 1.66 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 7.22-8.67 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 115.7, 124.1, 123.2, 124.5, 125.8, 126.6, 127.8, 129.0, 130.9, 131.4, 136.2, 136.4, 138.4, 145.4, 149.4, 151.9, 157.0, 161.0, 162.8 ppm; MS: m/z = 536.38. Anal. Calcd for C27H20Cl2FN5O2: C, 60.46; H, 3.76; N, 13.06. Found: C, 60.53; H, 3.82; N, 13.11.

2.2.4.12. 3-Chloro-4-(2-(2-chloro-6-methylquinolin-3-yl)-5-(pyridin-4-yl)-1 , 3, 4-oxadiazol-3(2H)-yl)-1-(4-fluorophenyl)-4-methylazetidin-2-one (V)12. Yield: 75%, m.p. 228-230 0C. IR (KBr): 3083, 3057 (Ar-H, Qu-H stret.), 2896, 2873 (-C-H stret., ß-lactam-CH3 and quinoline-CH3 group), 1710 (C=O, stret.), 1615, 1602 (C=C, C=N, aromatic ring), 1467, 1453 (-C-H bend., ß-lactam-CH3 and quinoline-CH3 group), 1210 (C-O-C linkage), 765, 754 cm"1 (C-Cl stretching). 1H NMR (400 MHz, DMSO-d6): d = 1.66 (s, 3H, Aze-CH3), 2.43 (s, 3H, Qu-CH3), 5.64 (s, 1H, -N-CH-O linkage), 5.28 (s, 1H, -CH-Cl azetidinone ring), 7.25-8.66 (m, 12H, Qu-H and ph-H) ppm. 13C NMR (400 MHz, DMSO-d6): d = 17.0, 21.7, 65.9, 77.4, 90.2, 115.1, 115.7, 123.2, 123.5, 124.1, 125.8, 126.6, 130.9, 131.4, 136.2, 136.4, 137.3, 138.4, 145.4, 149.4, 151.9, 157.0, 161.0, 162.9 ppm; MS: m/z = 536.38. Anal. Calcd for C27H20Cl2FN5O2: C, 60.46; H, 3.76; N, 13.06. Found: C, 60.52; H, 3.83; N, 13.12.

3. Results and discussion

3.1. Synthesis

We have described the synthesis, characterization and biological evaluation of 3-chloro-1-(aryl)-4-(2-(2-chloro-6-methyl quinolin-3-yl)-5-(pyridin-4-yl)-1,3,4-oxadiazol-3(2H)-yl)-4-eth-yl-azetidin-2-ones (V)1-12. In the first step, 2-chloro-6-methyl-quinoline-3-carbaldehyde (I) reacted with isoniazide using 1,4-dioxane as a solvent to furnish aroyl hydrazone (II) as an intermediate. Then, compound (II) was reacted with acetic anhydride, which yielded intermediate (III), which on further treatment with different amines using ethanol (95%) in

the presence of glacial acetic acid as a catalyst, intermediate

(IV) was produced. Compound (IV) when reacted with an equal amount of triethylamine and chloroacetyl chloride in 1,4-dioxane as solvent, the product (V) was yielded. The solvent system used for TLC was n-hexane-ethyl acetate (7:3) for final step.

The IR spectrum of the compound-(V)3 (molecular formula C27H20Cl3N5O2, m.w. 552.84) has given vibrations at 3060 and 3085 cm"1 over the ranges, which showed multiple weak absorption peaks corresponding to Qu-H and Ar-H stretching vibration absorption peaks. The absorption peaks at 2892 and 2873 cm"1 are due to the stretching vibration of methyl group. The strong absorption at 1716 cm"1 is due to the stretching vibration of C=N which is present in b-lactam ring. The moderate intensity absorption at 1615 cm"1 corresponds to a C=N stretching vibration, and the stretching vibration of C=C linkage appeared at 1598 cm"1. The absorption peak at 1469 and 1456 cm"1 are due to bending vibrations of the methyl group. While in oxadiazole nucleus C-O-C linkage appeared at the range of 1210 cm"1. The absorption peaks at 754 and 768 cm"1 arises due to C-Cl groups present in the moiety.

It can be seen from the chemical structure of compound-

(V)3 that different pairs of carbons e.g. C-14 and C-17, C-15 and C-16 are attached to chemically equivalent protons. The protons which are attached to C-14 and C-17 appeared at d = 7.98 ppm, while the protons which are attached to C-15 and C-16 appeared at d = 8.66 ppm. The proton attached at C-5 position appeared as a singlet at d = 7.63 ppm. The proton of the methyl group which is attached with C-7 appeared as a singlet at d = 2.43 ppm. The proton which is attached to C-8 appeared as a doublet at d = 7.47 ppm having J value = 7.6 Hz, while another proton which is attached with C-9 also appeared as a doublet at d = 7.93 ppm having J value = 8.0 Hz. The proton which is attached to C-3 and present in the quinoline nucleus appeared as singlet at d = 8.24 ppm, while C-11 (-CH group) present in the oxadiazole nucleus appeared as a singlet at d = 5.64 ppm. The proton of C-20 of the b-lactam ring which is directly attached to chlorine atom appeared as a singlet at d = 5.28 ppm. The proton of the methyl group at C-19 gives a singlet and appeared at d = 1.68 ppm, because of the vicinity of the carbonyl group at C-21 and chlorine atom at C-20 present in the b-lactam ring. The other four protons attached to carbons in the phenyl ring are chemically equivalent protons, C-23 and C-27 appeared at d = 7.34 ppm, while other equivalent protons which are attached at C-24 and C-26 appeared at d = 7.54 ppm, respectively.

The chemical shifts of the final compound-(V)3 carbons vary from d = 161.9 to 17.0 ppm. The carbon nuclei under the influence of a strong electronegative environment appeared down-field, e.g. the C-21 carbonyl which is present in b-lactam ring and is directly linked to the nitrogen in the ring has a chemical shift value of d = 161.9 ppm, whereas C-1, linked to one chlorine and other nitrogen atom, appeared at d = 151.9 ppm. The chemical shift of the ring carbon at C-10 is affected by the presence of the directly attached ring nitrogen atom and appeared at d = 145.4 ppm. The alkane carbon at C-19 is directly attached to a carbon of the b-lactam ring and appeared at d = 17.0 ppm. While the carbon at C-20 directly attached to chlorine atom present in b-lactam ring records a downfield chemical shift at d = 65.9 ppm. The carbons of the phenyl ring which are attached to the nitrogen atom of the azetidinone ring

H3C 5 3 11/ \l2 17

2 O 13

8 ^10^ N^NC

14\^ N 15

Figure 1 Carbon numbering of the final compound - (V)3.

having equivalent carbons C-23 and C-27 appeared at d = 125.6 ppm. Other equivalent carbons C-24 and C-26 appeared at d = 129.0 ppm, while the carbon C-22 which is directly attached with the nitrogen atom of the azetidinone ring appeared at d = 139.8 ppm and C-25 which is directly attached to the chlorine atom appeared at d = 133.3 ppm. The carbons which are present in the oxadiazole nucleus C-11 and C-12 both are on one side directly attached to the oxygen atom and on the other side C-11 is attached to nitrogen by a single bond. Due to this reason, it gives chemical shift at d = 77.4 ppm, while on the other side C-12 attached to nitrogen atom by a double bond, gives a chemical shift at d = 157.0 ppm. The carbons of the quinoline ring (C-2 to C-5, C-8 and C-9) appeared between d = 125.8 and 136.2 ppm, respectively, while the carbon of quinoline ring C-6 which is directly attached with methyl group appeared at d = 136.4 ppm, while the carbon of the methyl group C-7 appeared at d = 21.7 ppm. The equivalent carbons C-14 and C-17 appeared at d = 124.1 ppm, while other equivalent carbons C-15 and C-16, which are directly attached to nitrogen atom of the pyridine appeared at 149.4 ppm. The carbon numbering is described in Fig. 1.

3.2. Biological activity

Minimum inhibitory concentration (MIC) for bacteria of (V)1-12 of all the synthesized compounds was determined against

four different strains, viz two gram positive bacteria (Staphylococcus aureus and Streptococcus pyogenes) and two gram negative bacteria (E. coli and Pseudomonas aeruginosa) as compared to the standard drug ampicillin by broth dilution method (Rattan, 2000; Desai and Dodiya, 2011). Minimum inhibitory concentration (MIC) for antifungal activity was carried out against Candida albicans, Aspergillus niger and Aspergillus clavatus organisms and the results were compared with the standard drug griseofulvin by the same method.

3.2.1. Antibacterial activity

From screening results, It has been observed that final compounds (V)2, (V)3, (V)5, (V)8, (V)11 and (V)12 possess good activity against E. coli, compounds (V)4 and (V)7 possess very good activity against E. coli. Final compounds (V)1, (V)4, (V)6, (V)9 and (V)12 possess good activity against P. aeruginosa and compounds (V)3, (V)5 and (V)10 possess very good activity against P. aeruginosa. Final compounds (V)4, (V)8 and (V)10 possess good activity against S. aureus, while compounds (V)3, (V)5, (V)9 and (V)11 possess very good activity and compounds (V)2 and (V)6 possess excellent activity against S. aureus. Compounds (V)6 and (V)9 were shown to possess good activity against S. pyogenes, while compound (V)5 possesses very good activity and compound (V)3 possesses excellent activity. The remaining compounds of the entire series possess moderate to poor antibacterial activity. The discussion and comparison of antibacterial activity were given with respect to ampicillin antibiotic. The antibacterial activity is described in Table 1.

3.2.2. Antifungal activity

Antifungal screening data showed that final compounds (V)1, (V)2, (V)4, (V)7 and (V)11 possess good activity, while compounds (V)5, (V)9 and (V)12 possess very good activity and compounds (V)3 and (V)10 possess excellent activity against C. albicans. Compounds (V)1, (V)3 and (V)10 possess good activity against A. niger. Compounds (V)2, (V)4, (V)5 and (V)12 possess good activity against A. clavatus. The remaining compounds of the entire series possess moderate antifungal activity. The discussion and comparison of antifungal activity were compared with griseofulvin. The antifungal activity is described in Table 1.

Table 1 Results of antibacterial and antifungal screening of the compounds (V)1-12.

Sr. No. -R Minimum inhibitory concentration (MICb) lg/ml ± SD Minimum inhibitory concentration (MICf) in lg/ml ± SD

E. coli P. aeruginosa S. aureus S. pyogenes C. albicans A. niger A. clavatus

MTCC 443 MTCC 1688 MTCC 96 MTCC 442 MTCC 227 MTCC 282 MTCC 1323

(V)1 2-C1 200 ± 4.04* 100 ± 3.78* 500 ± 4* 500 ± 4.16* 500 ± 3.78* 100 ± 2.35* 500 ± 2.51*

(V)2 3-C1 100 ± 4.72* 500 ± 3.05* 50 ± 3.05* 200 ± 3.51* 500 ± 2.51* 1000 ± 3* 100 ± 4.08*

(V)3 4-C1 100 ± 3.78* 50 ± 2.64* 100 ± 4.55* 25 ± 2.21* 100 ± 4.04* 100 ± 1.24* 500 ± 2.35*

(V)4 2-NO2 62.5 ± 4.04* 100 ± 4.55* 200 ± 3.78* 200 ± 4* 500 ± 2.35* 500 ± 3.24* 100 ± 1.32*

(V)5 3-NO2 100 ± 3.65* 50 ± 4.04* 100 ± 3.05* 50 ± 1.24* 200 ± 4* 1000 ± 2.08* 100 ± 3.60*

(V)6 4-NO2 200 ± 4.51* 100 ± 2.51* 50 ± 2.51* 100 ± 3.51* 1000 ± 4.50* 1000 ± 4.58* 200 ± 4*

(V)7 2-OCH3 50 ± 4.93* 500 ± 4* 500 ± 3.51* 500 ± l* 500 ± 2.30* 500 ± 2.30* 500 ± 2.30*

(V)S 3-OCH3 100 ± 4.04* 500 ± 3.34* 250 ± 4.04* 200 ± 1.32* 1000 ± 3.54* 500 ± 3.05* 500 ± 4.04*

(V)9 4-OCH3 250 ± 3.78* 100 ± 4* 100 ± 3.21* 100 ± 4.04* 200 ± 3.51* 500 ± 3.55* 500 ± 3.55*

(V)10 4-CH3 500 ± 3.21* 50 ± 3.55* 200 ±3.54* 1000 ± 4.16* 100 ± 2.30* 100 ± 3.78* 500 ± 4.04*

(V)11 2-F 100 ± 3.05* 250 ± 3.78* 100 ± 3.05* 250 ± 2.08* 500 ± 3.05* 500 ± 4.21* 500 ± 2.08*

(V)l2 4-F 100 ± 4.55* 100 ± 3.51* 500 ± 3.01* 500 ± 3.60* 200 ± 3.78* 500 ± 3.05* 100 ± 3.46*

Ampicillin 100 100 250 100 - - -

Griseofulvin - - - - 500 100 100

SD = Standard deviation.

* p < 0.0001.

3.2.3. Statistical analysis

The standard deviation value is expressed in terms of ±SD. On the basis of the calculated value by using ANOVA method, it has been observed that differences below 0.0001 level (p 6 0.0001) were considered as statistically significant.

Acknowledgments

The authors are thankful to Department of Chemistry,

Bhavnagar University, Bhavnagar for providing research facilities. One of authors A.M.D. is thankful to University Grants

Commission, New Delhi for providing UGC-meritorious

scholarship.

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