Scientific paper
Synthesis and Biological Evaluation of some new Imidazo[1,2-tf]pyridines
Zafer Cesur,1* Nesrin Cesur,1 Seher Birteksöz2 and Gülten Ötük2
1	University of Istanbul, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, 34116 Istanbul, TURKEY
2	University of Istanbul, Faculty of Pharmacy, Department Pharmaceutical Microbiology, 34116 Istanbul, TURKEY
* Corresponding author: E-mail: cesurzfr@istanbul.edu.tr Fax:+90-2124400265
Received: 11-09-2009
Abstract
A series of new 1-[(2,8-dimethylimidazo[1,2-a]pyridine-3-yl)carbonyl]-4-aIkyl/arylthiosemicarbazides, 2-[(2,8-di-methylimidazo[1,2-a]pyridine-3-yl)carbonyl]hydrazono-3-alkyl thiazolidin-4-ones, 2-(2,8-dimethylimidazo[1,2-a]pyridine-3-yl)-5-arylamino-1,3,4-oxadiazoles and 4-alkyl/aryl-2,4-dihydro-5-(2,8-dimethylimidazo[1,2-a]pyridine-3-yl)-3_ff-1,2,4-triazole-3-thiones were synthesized. The structures of the compounds have been elucidated by IR, 1H NMR, EI mass spectra and elemental analysis. Antibacterial, antifungal and antimycobacterial activities of compounds were evaluated against various microorganisms and some of them were found to be active in varying degrees against Staphylococcus aureus, Staphylococcus epidermidis or Mycobacterium tuberculosis H37Rv.
Keywords: Imidazo[1,2-a]pyridine, 4-thiazolidinone, 1,3,4-oxadiazole, 1,2,4-triazole-3-thione, antimicrobial activity
1.	Introduction
Imidazo[1,2-a]pyridines have been shown to possess diverse biological activities including antibacterial, antifungal, antituberculous, antiviral, anticonvulsant, antiinflammatory, analgesic and antipyretic.1-6 Also many reports indicate that acyl thiosemicarbazides and their corresponding cyclized derivatives, such as 4-thiazolidi-nones, 1,3,4-oxadiazoles and 1,2,4-triazole-3-thiones, possess antibacterial, antifungal, antiviral, anticonvulsant, antiinflammatory and hypnotic activities.7-15
As a continuation of our programme on imida-zo[1,2-a]pyridine ring system,2-4,8,16,17 we synthesized some new acylthiosemicarbazides, 4-thiazolidinones, 1,3,4-oxadiazoles and 1,2,4-triazole-3-thiones incorporating an imidazo[1,2-a]pyridine substituent to screen their antimicrobial activity.
2.	Experimental
2. 1. Chemistry
Melting points were determined on a Buchi 530 apparatus in open capillary tubes and are uncorrected. IR
spectra were recorded on KBr discs, using a Perkin Elmer 1600 FT-IR spectrophotometer. 1H NMR spectra were obtained in DMSO-d6 on a Bruker AC 200 (200 MHz) spectrophotometer using TMS as the internal standard. EI-MS were performed on a VG Zab Spec (70 eV) instrument. Elemental analyses were performed on a Carlo Erba 1106 elemental analyzer. Compounds 2a, 5a and the starting materials were either commercially available or synthesized according to the references cited.
2. 1. 1. 1-[(2,8-Dimethylimidazo[1,2-a]pyridine-3-yl)carbonyl]-4-alkyl/arylthiosemicarbazi-de (2a-j)
0.01 mol of 2,8-dimethylimidazo[1,2-a]pyridine-3-carbohydrazide 1,18 0.01 mol of appropriate isothiocyana-te and absolute ethanol (15 mL) were refluxed for 3 h. The separated solid was filtered and recrystallized from etha-nol (96%).
2-[(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]-N-methylhydrazinecarbothioamide (2a): Yield: 91%, mp 225-228 °C. IR v (cm-1): 3316, 3170 (N-H), 1652 (C=O), 1226 (C=S). 1H NMR 8 ppm: 9.57 (s, 1H, N1-H),
9.32 (s, 1H, N2-H), 8.85 (d, J = 6.9 Hz, 1H, C5-H), 8.04 (br s, 1H, N4-H), 7.23 (d, J = 6.8 Hz, 1H, C7-H), 6.95 (t, J = 6.8 Hz, 1H, C6-H), 2.90 (d, 3H, N-CH3), 2.63 (s, 3H, C8-CH3), 2.49 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 2777 (M+, 43), 247 (4), 246 (13), 244 (24), 243 (72), 204 (1), 189 (27), 186 (39), 174 (22), 173 (100), 171 (19), 158
(23),	157 (13), 146 (19), 118 (29), 92 (18), 73 (4), 65 (20). Anal. Calcd for C12H15N5OS x 2 H2O: C, 45.99; H, 6.11; N, 22.33. Found: C, 4(5.37; H, 5.87; N, 21.93.
2-[(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]-N-ethylhydrazinecarbothioamide (2b): Yield: 90%, mp 205-207 °C. IR v (cm 1): 3334, 3173 (N-H), 1636 (C=O), 1225 (C=S). 1H NMR 8 ppm: 9.58 (s, 1H, N1-H), 9.26 (s, 1H, N2-H), 8.83 (d, J = 6.9 Hz, 1H, C5-H), 8.07 (br s, 1H, N4-H), 7.23 (d, J = 6.7 Hz, 1H, C7-H) 6.95 (t, J = 7.6 Hz, 1H, C6-H), 3.42-3.55 (m, 2H, ethyl CH2), 2.64 (s, 3H, C8-CH3), 2.49 (s, 3H, C2-CH3), 1.08 (t, J = 7.1 Hz, 3H, ethyl CH3). EI-MS m/z (rel. intensity): 291 (M+, 43), 258
(24),	257 (72), 247 (3), 246 (15), 204 (23), 189 (26), 186 (45), 174 (31), 173 (100), 158 (24), 146 (26), 118 (31), 104 (18), 87 (16), 65 (23). Anal. Calcd for C13H17N5OS: C, 53.59; H, 5.88; N, 24.04. Found: C, 54.11; H, 6.28; N, 24.35.
N -Allyl-2-[(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]hydrazinecarbothioamide (2c): Yield: 76%, mp 203-205 °C. IR v (cm-1): 3310, 3206 (N-H), 1645 (C=O), 1218 (C=S). 1H NMR 8 ppm: 9.56 (s, 1H, N1-H), 9.23 (s, 1H, N2-H), 8.80 (d, J = 6.8 Hz, 1H, C5-H), 8.01 (br s, 1H, N4-H), 7.28 (d, J = 6.8 Hz, 1H, C7-H), 6.95 (t, J = 7.6 Hz, 1H, C6-H), 5.90-5.85 (m, 1H, CH2-CH=CH2) 5.22 (d, J = 16.1 Hz, 1H, trans CH2-CH=CH2), 5.17 (d, J = 10.3 Hz, 1H, cis CH2-CH=CH2), 4.16 (s, 2 H, CH2-CH=CH2), 2.68 (s, 3H, C8-CH3), 2.4 6 (s, 3H, C2-CH3). Anal. Calcd for C14H17N5OS x 2 H2O: C, 49.54; H, 6.23; N, 20.62. Found: C, 50.06; H, 6.27; N, 19.68.
2-[(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]-N-propylhydrazinecarbothioamide (2d): Yield: 82%, mp 203-205 °C. IR v (cm-1): 3330, 3166 (N-H), 1637 (C=O), 1223 (C=S). 1H NMR 8 ppm: 9.58 (s, 1H, N1-H), 9.25 (s, 1H, N2-H), 8.82 (d, J = 6.8 Hz, 1H, C5-H), 8.03 (br s, 1H, N4-H), 7.26 (d, J = 6.8 Hz, 1H, C7-H) 6.95 (t, J = 6.8 Hz, 1H, C6-H), 3.72-3.68 (m, 2H, N-CH2), 2.60 (s, 3H, C8-CH3), 248 (s, 3H, C2-CH3), 1.51-1.30 (m, 2H, CH2CH2CH3), 0.60 (t, J = 7.3 Hz, 3H, CH2CH2CH3). Anal. Calcd for C14H19N5OS x 0.5 H2O: C, 53.48; H, 6.41; N, 22.26. Found: C, 53.60; H, 6.48; N, 22.28.
N-Butyl-2-[(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]hydrazinecarbothioamide (2e): Yield: 90%, mp 185 °C. IR v (cm-1): 3313, 3158 (N-H), 1637 (C=O), 1219 (C=S). 1H NMR 8 ppm: 9.60 (s, 1H, N1-H), 9.30 (s, 1H, N2-H), 8.83 (d, J = 6.8 Hz, 1H, C5-H), 8.00
(br s, 1H, N4-H), 7.25 (d, J = 6.8 Hz, 1H, C7-H), 6.96 (t, J = 6.8 Hz, 1H, C6-H), 3.43-3.32 (m, 2H, N-CH2), 2.64 (s, 3H, C8-CH3), 2.46 (s, 3H, C2-CH3), 1.47-1.40 (m, 2H, CH2CH2CH2CH3), 1.30-1.25 (m, 2H, CH2CH2CH2CH3), 0.8(5 (t, J = 7.3 Hz, 3H, CH2CH2CH2CH3). Anal Calcd for C15H21N5OS: C, 56.40; H, 6.63; N, 21.92. Found: C, 551.90; H, 6.97; N, 21.85.
2-[(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]-N-phenylhydrazinecarbothioamide (2f): Yield: 96%, mp >268 °C. IR v (cm-1): 3378, 3218 (N-H), 1627 (C=O), 1236 (C=S). 1H NMR 8 ppm: 9.78 (broad s, 3H, N1-H, N2-H, N4-H), 8.90 (d, J = 6.6 Hz, 1H, C5-H), 7.50 (d, J = 7.9 Hz, 1H, C7-H), 7.11-7.37 (m, 5H, C6H5), 6.95 (t, J = 7.0 Hz, 1H, C6-H), 2.69 (s, 3H, C8-CH3X 2.50 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 2773 (43), 247 (4), 2426 (13), 244 (24), 243 (72), 204 (1), 189 (27), 186 (39), 174 (22), 173 (100), 171 (19), 158 (23), 157 (13), 146 (19), 118 (29), 92 (18), 73 (4), 65 (20). Anal. Calcd for C17H17N5OS x H2O: C, 57.12; H, 5.35; N, 19.58. Found: C, 57.23; H, 5.76; N, 19.91.
2-[(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]-N-(4-methylphenyl)hydrazinecarbothioamide (2g):
Yield: 95%, mp 245 °C. IR v (cm-1): 3333, 3191 (N-H), 1639 (C=O), 1259 (C=S). 1H NMR 8 ppm: 9.71 (br s, 3H, N1-H, N2-H, N4-H), 8.87 (d, J = 6.8 Hz, 1H, C5-H), 7.35 (d, J = 7.9 Hz, 2H, tolyl C2-H, C6-H), 7.23 (d, J = 6.9 Hz, 1H, C7-H), 7.13 (d, J = 8.2 Hz6 2H, tolyl C3-H, C5-H), 6.95 (t, J = 6.9 Hz, 1H, C6-H), 2.67 (s, 3H, C8-CH3), 2.50 (s, 3H, C2-CH3), 2.28 (s, 3H, tolyl CH3). EI-MS m/z (rel. intensity): 353 (M+, 3), 295 (3), 247 (8), 246 (10), 205 (64), 204 (78), 189 (2), 173 (100), 147 (17), 145 (7), 117 (10), 91 (8), 65 (8). Anal. Cald for C18H19N5OS x 1.5 H2O: C, 56.82; H, 5.83; N, 18.39. Found: C, 56.82; H, 5.56; N, 18.40.
N-(4-Bromophenyl)-2-[(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]hydrazinecarbothioamide
(2h): Yield: 89%, mp 235 °C. IR v (cm-1): 3356, 3311 (N-H), 1635 (C=O), 1216 (C=S). 1H NMR 8 ppm: 9.80 (broad s, 3H, N1-H, N2-H, N4-H), 8.82 (d, J = 6.8 Hz,1H, C5-H), 7.60 (d, J = 8.1 Hz, 2H, phenyl C2-H, C6-H), 7.38 (d, J = 8.1 Hz, 2H, phenyl C3-H, C5-H), 7.23 (d, J = 6.9 Hz, 1H, C7-H), 6.94 (t, J = 6.8 Hz, 1H, C6-H), 2.65 (s, 3H, C8-CH3), 2.49 (s, 3H, C2-CH3). Anal. Calcd for C17H16BrN5OS: C, 48.81; H, 3.86; N, 16.74. Found: C, 481.97; H, 2.91; N, 16.95.
N-(4-Chlorophenyl)-2-[(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]hydrazinecarbothioamide
(2i): Yield: 92%, mp >268 °C. IR v (cm-1): 3359, 3136 (N-H), 1635 (C=O), 1254 (C=S). 1H NMR 8 ppm: 9.84 (br s, 3H, N1-H, N2-H, N4-H), 8.86 (d, J = 6.7 Hz, 1H, C5-H), 7.53 (d, J = 8.5 Hz, 2H, phenyl C2-H, C6-H), 7.38 (d, J = 8.7 Hz, 2H, phenyl C3-H, C5-H), 7.25 (d, J = 6.9
Hz, 1H, C7-H), 6.96 (t, J = 6.9 Hz, 1H, C6-H), 2.66 (s, 3H, C8-CH3), 27.50 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 3773 (M+, 2), 339 (3), 247 (1), 246 (3), 204 (25), 189 (2), 174 (15), 173 (100), 169 (39), 149 (9), 145 (8), 127 (4), 118 (6), 111 (12), 104 (11), 78 (9), 65 (9). Anal. Calcd for C17H16ClN5OS x H2O: C, 52.10; H, 4.62; N, 17.86. Found: C, 51.36; H, 3.89; N, 17.75.
2-[(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)carbonyl]-N-(4-fluorophenyl)hydrazinecarbothioamide (2j):
Yield: 54 %, mp 255 °C. IR v (cm-1): 3260 (N-H), 1668(C=O), 1209 (C=S). 1H NMR 8 ppm: 9.77 (broad s, 3H, N1-H, N2-H, N4-H), 8.87 (d, J = 6.8 Hz, 1H, C5-H), 7.40-7.33 (m, 3H, phenyl C2-H, C6-H, C7-H), 7.17-7.10 (m, 2H, phenyl C3-H, C5-H), 6.95 (t, J = 6.9 Hz, 1H, C6-H), 2.65 (s, 3H, C8-CH3), 2.49 (s, 3H, C2-CH3). Anal. Calcd for C17H16FN5OS x 0.5 H2O: C, 55.72; H, 4.67; N, 19.10. Found: C, 55.58; H, 4.57; N, 19.23.
2. 1. 2. 2-[(2,8-Dimethylimidazo[1,2-a]pyridine-3-yl)carbonyl]hydrazono-3-alkylthiazoli-din-4-one (3a-e)
0.01 mol of the appropriate thiosemicarbazide 2a-e and 0.011 mol of ethyl bromoacetate were refluxed in 30 mL of absolute ethanole in the presence of 0.04 mol of anhydrous CH3COONa for 2-4 h. The reaction mixture was cooled, diluted with water and allowed to stand overnight. The precipitate thus obtained was filtered, dried and re-crystallized from ethanol (96%).
2,8-Dimethyl-W-(3-methyl-4-oxo-1,3-thiazolidin-2-yli-dene)imidazo[1,2-a]pyridine-3-carbohydrazide (3a):
Yield: 78%, mp 258-259 °C IR v (cm-1): 3321, 3138 (N-H), 1711 (C=O, thiazolidinone), 1666 (C=O, hydrazi-de). 1H NMR 8 ppm: 10.28 (s, 1H, CONH), 8.81 (d, J = 6.4 Hz, 1H, C5-H), 7.21 (d, J = 6.3 Hz, 1H, C7-H), 6.94 (t, J = 6.8 Hz, 1H, C6-H), 4.06 (s, 2H, S-CH2), 3.17 (s, 3H, N-CH3), 2.63 (s, 3H, C8-CH3), 2.50 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 317 (M+, 100), 71 (2), 45 (8), 42 (16). Anal. Calcd for C14H15N5O2S: C, 52.98; H, 4.76; N, 22.07. Found: C, 52.70; H, 5.00; N, 22.05.
N'-(3-Ethyl-4-oxo-1,3-thiazolidin-2-ylidene)-2,8-di-methylimidazo[1,2-a]pyridine-3-carbohydrazide (3b):
Yield: 88%, mp 203-205 °C IR v (cm-1): 3470 (N-H), 1698 (C=O, thiazolidinone), 1651 (C=O, hydrazide). 1H NMR 8 ppm: 10.17 (s, 1H, CONH), 8.28 (d, J = 6.8 Hz, 1H, C5-H), 7.08 (d, J = 6.9 Hz, 1H, C7-H), 6.81 (t, J = 6.9 Hz, 1H, C6-H), 3.93 (s, 2H, S-CH2), 3.63 (s, 2H, N-CH2), 2.50 (s, 3H, C8-CH3), 2.36 (s, 3H, C2-CH3), 1.06 (t, J = 7.1 Hz, 3H, ethyl CH3). EI-MS m/z (rel. intensity): 331 (M+, 76), 257 (17), 189 (5), 186 (19), 174 (52), 173 (100), 146 (65), 118 (19), 104 (23), 92 (21), 65 (19). Anal. Calcd for C15H17N5O2S x 3 H2O: C, 46.73; H, 6.01; N, 18.16. Found: C, 47.41; H, 5.42; N, 18.05.
W-(3-Allyl-4-oxo-1,3-thiazolidin-2-ylidene)-2,8-di-methylimidazo[1,2-a]pyridine-3-carbohydrazide (3c): Yield: 56%, mp 198-200 °C. IR v (cm-1): 3448, 3127 (N-H), 1718 (C=O, thiazolidinone), 1644 (C=O, hydrazide). 1H NMR 8 ppm: 10.21 (s, 1H, CONH), 8.60 (d, J = 6.8 Hz, 1H, C5-H), 7.18 (d, J = 6.8 Hz, 1H, C7-H), 6.81 (t, J = 6.8 Hz, 1H, C6-H), 5.87-5.82 (m, 1H, CH2-CH=CH2), 5.23 (d, J = 16.1 Hz, 1H, trans CH2-CH=CH2), 5.16 (d, J = 10.3 Hz, 1H, cis CH2-CH=CH2), 4.40 (d, 2H, CH2-CH=CH2), 3.90 (s, 2H, S-CH2), 2.48 (s, 3H, C8-CH3), 2.30 (s, 3H, C2-CH3). Anal.Calcd for C86H17N5O2S x H2O: C, 53.16; H, 5.29; N, 19.37. Found: C, 52.75; H, 5.58; N, 19.22.
2,8-Dimethyl-W-(4-oxo-3-propyl-1,3-thiazolidin-2-yli-dene)imidazo[1,2-a]pyridine-3-carbohydrazide (3d):
Yield: 83%, mp 201-202 °C. IR v (cm-1): 3466, 3258 (N-H), 1704 (C=O, thiazolidinone), 1659 (C=O, hydrazide). 1H NMR 8 ppm: 10.25 (s, 1H, CONH), 8.32 (d, J = 6.8 Hz, 1H, C5-H), 7.16 (d, J = 6.9 Hz, 1H, C7-H), 6.82 (t, J = 6.8 Hz,1H, C6-H), 4.04 (s, 2H, S-CH2), 3.74 (t, J = 7.2 Hz, 2H, N-CH2), 2.49 (s, 3H, C8-C^3), 2.36 (s, 3H, C2-CH3), 1.49-1.31 (m, 2H, CH2CH2CH3), 0.58 (t, J = 7.4 Hz, 3H, CH2CH2CH3). Anal. Calcd for C16H19N5O2S x 3 H2O: C, 48.10; H, 6.30; N, 17.52. Found: C, 48.33; H, 6.39; N, 17.38.
W-(3-Butyl-4-oxo-1,3-thiazolidin-2-ylidene)-2,8-di-methylimidazo[1,2-a]pyridine-3-carbohydrazide (3e): Yield: 85%, mp 175-176 °C. IR v (cm-1): 3133 (N-H), 1717 (C=O, thiazolidinone), 1676 (C=O, hydrazide). 1H NMR 8 ppm: 10.19 (s, 1H, CONH), 8.26 (d, J = 6.9 Hz, 1H, C5-H), 7.12 (d, J = 6.9 Hz, 1H, C7-H), 6.81 (t, J = 6.9 Hz,1H, C6-H), 4.03 (s, 2H, S-CH2), 3.72 (t, J = 7.2 Hz, 2H, N-CH2), 2.52 (s, 3H, C8-CH3), 2.34 (s, 3H, C2-CH3), 1.73-1.56 (m, 2H, CH2CH2CH2CH3), 1.42-1.28 (m, 2H, CH2CH2CH2CH3), 0.90 (t, J = 7.2 Hz, 3H, CH2CH2CH2CH3). Anal. Calcd for C17H21N5O2S: C, 56.820; H, 5.89; N, 19.48. Found: C, 5657; H, 5.23; N, 19.22.
2. 1. 3. 2-(2,8-Dimethylimidazo[1,2-a]pyridine-3-yl)-5-arylamino-1,3,4-oxadiazole (4a-d)
4a-d were obtained from 2f,g,i,j as described for 3a-e. 5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-N-phenyl-1,3,4-oxadiazol-2-amine (4a): Yield: 85%, mp 265-266oC. IR v (cm-1): 3150-2866 (N-H). 1H NMR 8 ppm: 10.78 (s, 1H, NH), 9.09 (d, J = 6.0 Hz, 1H, C5-H), 7.64 (d, J = 6.0 Hz, 1H, C7-H), 7.40-7.09 (m, 5H, C6H5), 7.03 (t, J = 7.3 Hz, 1H, C6-H), 2.69 (s, 3H, C8-CH3), 2.55 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 305 (M+, 23), 187 (5), 186 (11), 173 (100), 170 (34), 158 (9), 156 (23), 146 (2), 145 (5), 133 (3). Anal. Calcd for C17H15N5O: C, 66.86; H, 4.95; N, 22.93. Found: C, 66.73; H, 4.92; N, 22.47.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-N-(4-methylphenyl)-1,3,4-oxadiazol-2-amine (4b): Yield: 67%, mp 268-269 °C. IR v (cm-1): 3200-2912 (N-H). 1H NMR 8 ppm: 10.35 (s, 1H, NH), 8.94 (d, J = 6.7 Hz, 1H, C5-H), 7.38 (d, J = 8.1 Hz, 2H, phenyl C2-H, C6-H), 7.16 (d, J = 6.7 Hz, 1H, C7-H), 7.04 (d, J = 8.0 Hz, 2H, phenyl C3-H, C5-H), 6.97 (t, J = 6.8 Hz, 1H, C6-H), 2.55 (3H, s, C8-CH3), 2.41 (s, 3H, C2-CH3), 2.14 (s, 3H, phenyl CH3). EI-MS m/z (rel. intensity): 319 (M+, 100), 262 (11), 187 (8), 186 (45), 174 (3), 173 (26), 172 (14), 171 (64), 158 (23), 146 (3), 145 (3), 133 (2). Anal. Calcd for C18H17N5O: C, 67.69; H, 5.36; N, 21.93. Found: C, 66.78; H, 5.97; N, 21.72.
N-(4-Chlorophenyl)-5-(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)-1,3,4-oxadiazol-2-amine (4c): Yield: 97%, mp 268 °C. IR v (cm-1): 3150-2925 (N-H). 1H NMR 8 ppm: 10.36 (s, 1H, NH), 8.90 (d, J = 6.8 Hz, 1H, C5-H), 7.56 (d, J = 8.5 Hz, 2H, phenyl C2-H, C6-H), 7.32 (d, J = 8.6 Hz, 2H, phenyl C3-H, C5-H), 7.16 (d, J = 6.8 Hz, 1H, C7-H), 6.89 (t, J = 6.8 Hz, 1H, C6-H), 2.50 (3H, s, C8-CH3), 22.39 (s, 3H, C2-CH3). Anal. Calcd for C17H14Cl-N5O: C, 60.09; H, 4.15; N, 20.61. Found: C, 59.39; H, 3.98; N, 19.94.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-N-(4-fluo-rophenyl)-1,3,4-oxadiazol-2-amine (4d): Yield: 80%, mp 265-268 °C. IR v (cm-1): 3178-2951 (N-H). 1H NMR 8 ppm: 10.65 (s, 1H, NH), 8.90 (d, J = 6.7 Hz, 1H, C5-H), 7.55-7.51 (m, 2H, phenyl C2-H, C6-H), 7.21-7.17 (m, 3H, phenyl C3-H, C5-H, C7-H), (5.96 (t, J = 6.8 Hz, 1H, C6-H), 2.60 (3H, s, C8-CH3), 2.45 (s, 3H, C2-CH3). Anal. Calcd for C17H14FN5O x (3.5 H2O: C, 61.43; H, 4.54; N, 21.07. Found: C, 62.10; H, 4.09; N, 21.09.
2. 1. 4. 4-Alkyl/aryl-2,4-dihydro-5-(2,8-dimethyli-midazo[1,2-a]pyridine-3-yl)-3#-1,2,4-tria-zole -3-thiones (5a-h)
A mixture of the thiosemicarbazide 2a-j (0.01 mol) and 2N NaOH (30 mL) was heated to reflux. After 3 h the mixture was poored into crushed ice and acidified with dilute HCl to pH 6-8. The precipitate was filtered, washed with water and recrystallized from ethanol (96%).
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-4-methyl-2,4-dihydro-3#-1,2,4-triazole-3-thione (5a): Yield: 72%, mp >268 °C. IR v (cm-1): 3088 (N-H), 1632 (C=N), 1285 (C=S). 1H NMR 8 ppm: 14.10 (s, 1H, NH), 8.19 (d, J = 6.7 Hz, 1H, C5-H), 7.20 (d, J = 6.7 Hz, 1H, C7-H), 6.88 (t, J = 6.9 Hz, 1H, C6-H), 3.27 (N-CH3 with H2O), 2.51 (s, 3H, C8-CH3), 2.35 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 259 (M+, 56), 258 (45), 245 (71), 186 (22), 172 (20), 171 (56), 155 (8), 91 (15), 59 (68), 41 (100). Anal. Calcd for C12H13N5S x 0.5 H2O: C, 53.71; H, 5.25; N, 26.08. Found: C, 543.33; H, 5.13; N, 26.23.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-4-ethyl-2,4-dihydro-3#-1,2,4-triazole-3-thione (5b): Yield: 88%, mp >268 °C. IR v (cm-1): 3080, 3026 (N-H), 1630 (C=N), 1277 (C=S). 1H NMR 8 ppm: 14.12 (s, 1H, NH), 8.12 (d, J = 6.7 Hz, 1H, C5-H), 7.20 (d, J = 6.7 Hz, 1H, C7-H), 6.86 (t, J = 6.8 Hz, 1H, C6-H), 3.80 (q, 2H, N-CH2), 2.52 (s, 3H, C8-CH3), 2.33 (s, 3H, C2-CH3), 1.00 (t, 3H ethyl CH3). Anal. Calcd for C13H15N5S: C, 57.12;
H,	5.53; N, 25.62. Found: C, 56.32; H, 5.87; N, 25.91.
4-Allyl-5-(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)-2,4-dihydro-3#-1,2,4-triazole-3-thione (5c): Yield: 78%, mp >268 °C. IR v (cm-1): 3080 (N-H), 1631 (C=N), 1281 (C=S). 1H NMR 8 ppm: 14.12 (s, 1H, NH), 8.15 (d, J = 6.7 Hz, 1H, C5-H), 7.20 (d, J = 6.7 Hz, 1H, C7-H), 6.87 (t, J = 6.9 Hz, 1H, C6-H), 5.85-5.80 (m, 1H, CH2-CH=CH2), 5.24 (d, J = 16.2 Hz, 1H, trans CH2-CH=CH2), 5.16 (d, J = 10.2 Hz, 1H, cis CH2-CH=CH2), 4.20 (d, J = 4.9 Hz, 2H, CH2-CH=CH2), 2.50 (s, 3H, C8-CH3), 2.33 (s, 3H, C2-CH3). Anal. Calcd for C14H15N5S x 0.5 H2O: C, 57.12; H, 5.47; N, 23.77. Found4 C, 57.83; H, 5.48; N, 24.11.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-4-propyl-2,4-dihydro-3#-1,2,4-triazole-3-thione (5d): Yield: 94%, mp >268 °C. IR v (cm-1): 3083, 3026 (N-H), 1629 (C=N), 1278 (C=S). 1H NMR 8 ppm: 14.13 (s, 1H, NH), 8.12 (d, J = 6.7 Hz, 1H, C5-H), 7.20 (d, J = 7.6 Hz, 1H, C7-H), 6.87 (t, J = 6.8 Hz, 1H, C6-H), 3.74 (t, J = 7.1 Hz, 2H, N-CH2), 2.52 (s, 3H, C^CH^, 2.33 (s, 3H, C2-CH3),
I.37-1.52	(m, 2H, C^C^CH^ 0.56 (t, J = 7.4 Hz, 3H, CH^H^Hj). Anal. Calcd for C14H17N5S x 0.5 H2O: C, 56.773; H, 6.12; N, 23.61. Found: C, 575.19; H, 5.98; N, 23.24.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-4-phenyl-2,4-dihydro-3#-1,2,4-triazole-3-thione (5e): Yield: 85%, mp >268 °C. IR v (cm-1): 3420, 3066 (N-H), 1629 (C=N), 1275 (C=S). 1H NMR 8 ppm: 14.30 (s, 1H, NH), 8.26 (d, J = 6.8 Hz,1H, C5-H), 7.34 (s, 5H, C6H5), 7.09 (d, J = 6.8 Hz, 1H, C7-H), 6.76 (t, J = 6.8 Hz, 1H, C6-H), 2.42 (s, 3H, C8-CH3), 2.01 (s, 3H, C2-CH3). EI-MS m/z (rel. intensity): 3281 (M+, 100), 262 (8), 248 (2), 244 (3),186 (4), 171 (24), 150 (2), 73 (6). Anal. Calcd for C17H15N5S: C, 63.53; H, 4.70; N, 21.79. Found: C, 63.72; H, 4.655; N, 21.41.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-4-(4-methylphenyl)-2,4-dihydro-3ff-1,2,4-triazole-3-thione
(5f): Yield: 48%, mp >268 °C. IR v (cm-1): 3390, 3065 (N-H), 1628 (C=N), 1273 (C=S). 1H NMR 8 ppm: 14.26 (s, 1H, NH), 8.25 (d, J = 6.7 Hz, 1H, C5-H), 7.12-7.22 (m, 4H, C6H4), 7.09 (d, J = 7.2 Hz, 1H, C7-H), 6.77 (d, J = 6.8 Hz, 1H, C6-H), 2.42 (s, 3H, C8-CH3), 2.26 (s, 3H, C2-CH3), 2.02 (s, 3H, phenyl CH3). EI-MS m/z (rel. inten-si2y): 335 (M+, 83), 334 (100), 276 (4), 262 (23), 244 (3), 186 (2), 171 (18), 164 (3), 91 (73), 65 (91). Anal. Calcd
for C18H17N5S x H2O: C, 61.16; H, 5.41; N, 19.80. Found: C, 61.99; H, 5.27; N, 20.00.
4-(4-Bromophenyl)-5-(2,8-dimethylimidazo[1,2-a]pyridin-3-yl)-2,4-dihydro-3ff-1,2,4-triazole-3-thione
(5g): Yield: 40%, mp >268 °C. IR v (cm-1): 3416, 3068 (N-H), 1628 (C=N), 1272 (C=S). 1H NMR 8 ppm: 14.16 (s, 1H, NH), 8.20 (d, J = 6.7 Hz, 1H, C5-H), 7.52 (d, J = 8.0 Hz, 2H, phenyl C2-H, C6-H), 7.46 (d, J = 8.0 Hz, 2H, phenyl C3-H, C5-H), 77.09 (d, J = 7.2 Hz, 1H, C7-H), 6.77 (d, J = 6.8 Hz, 1H, C6-H), 2.48 (s, 3H, C8-CH3), 2.30 (s, 3H, C2-CH3). Anal. Calcd for C17H14BrN5S x H2O: C, 48.81; H, 3.85; N, 16.74. Found: C, 49.42; H, 3.65; N, 16.39.
5-(2,8-Dimethylimidazo[1,2-a]pyridin-3-yl)-4-(4-fluo-rophenyl)-2,4-dihydro-3ff-1,2,4-triazole-3-thione (5h):
Yield: 63%, mp >268 °C. IR v (cm-1): 3408, 3078 (N-H), 1629 (C=N), 1277 (C=S). 1H NMR 8 ppm: 14.24 (s, 1H, NH), 8.20 (d, J = 6.8 Hz, 1H, C5-H), 7.45-7.33 (m, 3H, phenyl C2-H, C6-H, C7-H), 7.19-7.10 (m, 2H, phenyl C3-H, C5-H), 6.76 (d, J = 6.8 Hz, 1H, C6-H), 2.45 (s, 3H, C8-CH3), 2.34 (s, 3H, C2-CH3). Anal. Calcd for C17H14FN5S: C, 60.16; H, 42.16; N, 20.63. Found: C, 60.23; H, 44.19; N, 20.20.
2. 2. Microbiology
2. 2. 1. Antibacterial and Antifungal Activity
Disc diffusion method was used for antimicrobial activity. The cultures of bacteria and yeast strains were prepared in 4 mL of Mueller-Hinton broth at 37 °C. After 24 h of incubation, the turbidity of culture suspension was adjusted with sterile Mueller-Hinton broth in order to obtain a turbidity comparable to a No. 1 McFarland turbidity standard. One mL of this suspension was pipetted into the Mueller-Hinton agar plate and distributed evenly over the surface of the medium by gently rocking the plate. Excess suspension was pipetted off. The surface of the medium was allowed to dry for 15 min at room temperature. Compound (200 |^g) impregnated discs were applied to the surface of inoculated plates. The petri plates were placed in an incubator at 37 °C. After 18-24 h of incubation, the petri plates were examined.19
The minimum inhibitory concentrations (MIC) of the compounds were determined by the microbroth dilution technique using Mueller-Hinton broth. Serial twofold dilutions ranged from 2500 to 2.4 ^g mL-1 for compounds. The inoculum was prepared in broth which had been kept overnight at 37 °C and which had been diluted with Mueller-Hinton broth to give a final concentration of 105 cfu mL-1 in the test tray. The trays were covered and placed in plastic bags to prevent drying. After incubation at 37 °C for 18-20 h, the MIC was defined as the lowest concentration of the compound giving complete inhibition of visible growth.20
2.	2. 2. Antimycobacterial Activity
Primary screen was conducted at 12.5 |g mL-1 against M. tuberculosis H37Rv in BACTEC 12B medium using BACTEC 460 radiometric system. Compounds effecting <90% inhibition in the primary screen (MIC >12.5 |g mL-1) were not evaluated further.21
3. Results and Discussion
3.	1. Chemistry
1- [(2,8-Dimethylimidazo [ 1,2-a]pyridine-3-yl)car-bonyl]-4-alkyl/arylthiosemicarbazides 2a-j were obtained from 118 and corresponding alkyl/arylisothiocyanates. On treatment with ethyl bromoacetate, 2a-e yielded 4-thiazo-lidinones 3a-e. In the case of arylthiosemicarbazides 2f,g,i,j the same reaction resulted in 1,3,4-oxadiazole derivatives 4a-d.17 The thiosemicarbazides were cyclized to the corresponding 3H-1,2,4-triazole-3-thiones 5a-h by sodium hydroxide (Scheme).
The structures of the compounds were assigned by elemental analysis (CHN) and spectroscopic methods (IR, 1H NMR, EI-MS). The IR spectra of 2a-j showed the N-H and C=O vibrations at about 3136-3378 and 1627-1668 cm-1, respectively. 1H NMR spectra displayed N1-H, N2-H and N4-H resonances in the 8 9.57-9.84, 9.23-9.84 and 8.00-9.84 ppm regions, respectively.11,17 The C5-H, C7-H and C6-H resonances of the imidazo[1,2-a]pyridine residue in all compounds appeared in the 8.80-8.90, 7.23-7.50 and 6.94-6.96 ppm regions, respectively. New C=O bands (1698-1718 cm-1) in the IR spectra of 4-thiazolidinones 3a-e were particularly diagnostic for thiazolidinone formation.3,4,7,8,12,13 Further support was obtained from the 1H NMR spectra of 3a-e which showed signals due to the CH2 protons at the 5 position of the 4-thiazolidinone ring at about 3.90-4.06 ppm. After cycliza-tion, absence of resonances assigned to the N2-H and N4-H protons of the thiosemicarbazides 2a-e provided confirmatory evidence of thiazolidinone formation. Cycli-zation of 4-arylthiosemicarbazides 2f,g,i,j with ethyl bro-moacetate yielded unexpected products, which were identified as 2-(2,8-dimethylimidazo[1,2-a]pyridine-3-yl)-5-arylamino-1,3,4-oxadiazole (4a-d) on the basis of analytical and spectral data. Cyclization to 4-thiazolidinones involves the formation of an isothiosemicarbazide intermediate A (Scheme) following ene-thiolization. At this stage electronic effects or overall conformation of the isothiosemicarbazide intermediate can make the SCH2COOEt moiety a good leaving group and thus can lead to the formation of 4a-d.7,11,17 Compounds 4a-d exist as the amino tautomer (NH: 10.35-10.78 ppm). The absence of C=O bands in the IR spectra 4a-d also support the 1,3,4-oxadiazole structure.
In a basic medium 1-acyl/aroyl-3-thiosemicarbazi-des are dehydrated by the condensation of the 4-amino group with the carbonyl function to give triazoline-3-
Scheme. General synthesis of compounds 2-5
thiones. The nucleophilicity of the terminal amino group of the thioamide determines whether it can undergo a condensation reaction or not. With a base, the sulfur function is ionized, and this increases the nucleophilicity of 4-amino group and promotes triazoline-3-thione formation.23 IR spectra of 5a-h provided definitive evidence for ring closure. The C=O absorption of the thiosemicar-bazides disappears as the group participates in ring formation and a new band in the 1632-1628 cm-1 region appeared which may be assigned to the C=N group of the triazoline ring.24 1H NMR spectra also supported ring closure as they showed only one low-field singlet in the
14.10-14.30 ppm region which is thus assigned to the N2-H of the ring. 5-Substituted 2,4-dihydro-3#-1,2,4-triazole-3-thiones may exist in tautomeric forms. 5a-h favored the thione form since no absorption indicative of an SH group (2500 cm-1) was displayed in the solid state IR spectra.10,11,23,25 The low field NH resonance in the 1H NMR spectra supported this form and the structure can be assigned to the thione form also in solution.25 The EI-MS of all representative examples showed moleculer ions of different intensity (except 2f) and fragmented in accordance with the fragmentation routes given in the literature 9,11,23,25,26
3. 2. Microbiology
Compounds 2-5 were evaluated for in vitro antibacterial activity against Staphylococcus aureus ATCC 6538, Staphylococcus epidermidis ATCC 12228, Escherichia coli ATCC 8739, Klebsiella pneumoniae ATCC 4352, Pseudomonas aeruginosa ATCC 1539, Salmonella typhi, Shigella flexneri, Proteus mirabilis ATCC 14153, Candida albicans ATCC 10231 using the disc diffusion method. Some of these compounds had appreciable activity for S. epidermidis and S. aureus (Table).
Compounds 2f-j were also evaluated for antimyco-bacterial activity against Mycobacterium tuberculosis H37Rv Only 2f exhibited 55% inhibition in the in vitro primary screen conducted at 12.5 ^g mL-1.
Table. MIC values of compounds 2-5
Compounds
MIC (|g mL1) S. epidermidis	S. aureus
2d	312	-
2e	312	-
2f	78	-
2g	62.5	312
2h	62.5	156
2i	31.25	312
2j	62.5	312
3c	62.5	-
3d	62.5	-
3e	78	-
4c	39	-
5g	312	-
4. Conclusion
In this study we reported the preparation of novel imidazo[1,2-a]pyridine derivatives containing thiosemi-carbazide, 4-thiazolidinone, 1,3,4-oxadiazole or 1,2,4-triazole-3-thione moieties and their antimicrobial activities. Some of the compounds, especially thiosemicarbazi-de derivatives, were found to be active against Staphylococcus aureus and/or Staphylococcus epidermidis and only compound 2f was found to be active against Myco-bacterium tuberculosis H37Rv
5. Acknowledgements
We thank Dr. Joseph A. Maddry from the Tuberculosis Antimicrobial Acquisition and Coordinating Facility (TAACF), National Institute of Allergy and Infectious Diseases Southern Research Institute, GWL Hansen's Disease Center, Colorado State University, Birmingham, Alabama, USA for the in vitro evaluation of antituberculosis activity. This work was partly supported by Istanbul University Research Fund, Project Number 1403 / 05 05 2000.
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Povzetek
Pripravili smo novo serijo 1-[(2,8-dimetilimidazo[1,2-a]piridin-3-il)karbonil]-4-alkil/aril- tiosemikarbazidov, 2-[(2,8-dimetilimidazo[1,2-a]piridin-3-il)karbonil]hidrazono-3-alkil tiazolidin-4-onov, 2-(2,8-dimethilimidazo[1,2-a]piridin-3-il)-5-arilamino-1,3,4-oksa-diazolov in 4-alkil/aril-2,4-dihidro-5-(2,8-dimetilimidazo[1,2-a]piridin-3-il)-3^-1,2,4-tria-zol-3-tionov. Strukture spojin smo določili z IR, 1H NMR, EI masno spektrometrijo in elementno analizo. Raziskali smo tudi aktivnosti proti bakterijam, glivam in mikobakterijam na različnih vrstah mikroorganizmov; nekatere spojine so bile v različni meri aktivne proti Staphylococcus aureus, Staphylococcus epidermidis in Mycobacterium tuberculosis H0,R .
37 v