Abstract: Novel 5-fluoro/chloro/bromo-N`-(4-aryl-1, 3-thiazol-2-yl)-1H-indole-2-carbohydrazide derivatives (4a-I) were prepared by treating corresponding 5-fluoro/chloro/bromo thiosemicarbazide with aromatic acylbromides. The newly synthesized compounds were characterized by analytical and spectral data. All the compounds were screened for antifungal and antibacterial activities. Most of the compounds exhibited promising antimicrobial activity.
Introduction
The indole nucleus is an important element in many pharmacologically active compounds. A number of indole derivatives are reported to exhibit antibacterial, antifungal, antituberculosis, antithrombotic, anticancer and antiinflammatory activities (Forbes et al., 1993; Murphy et al., 1997; Young et al., 2001; Mackman et al., 2002; Narayana et al., 2005). Various indolyl thiazoles were synthesized and reported for their CNS depressant, anti-inflammatory and anticancer activities (Arya et al., 1977; Gu et al., 1999). Antimicrobial activity of thiazole derivatives is extensively studied by many researchers (Demirayak et al., 1997; Katsura et al., 1999; Vingkar et al., 2001; Holla et al., 2003). As a continuation of the present study to explore potent biologically active thiazole containing molecules (Narayana et al., 2004, 2006a, 2006b), we synthesized some new 5-fluoro/chloro/bromo-N'-(4-aryl-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide derivatives and screened for their antifungal and antibacterial activities.
Materials and Methods
Melting points were taken in open capillary tubes and are uncorrected. The purity of the compounds confirmed by thin layer chromatography using Merck silica gel 60 F254 coated aluminium plates. IR spectra were recorded on Shimadzu-FTIR Infrared spectrometer in KBr (vmax in cm-1). 1H NMR spectra were recorded in CDCl3 and in DMSO-d6 on a Varian (300 MHZ) spectrometer using TMS as internal standard and 13C NMR spectra were recorded in CDCl3 and in DMSO-d 6 on a Varian (75 MHZ) spectrometer. FABMS spectra were recorded on a JEOL SX 102/DA-6000 Mass spectrometer using argon/xenon (6 kv, 10 mA) as the FAB gas.
Synthesis of 1-[(5-fluoro/chloro/bromo-1H-indol-2-yl) carbonyl] thiosemicarbazide
(2a-c)
5-Fluoro/chloro/bromo indole-2-carbohydrazide (0.01 mole) was refluxed with
10 mL 10% HCl and potassium thiocyanate (0.012 mole) for 2-3 h. The solid separated
was filtered and washed with sufficient quantity of water and then dried. All
the compounds were taken for next step without further purification
2a. 1-[(5-Fluoro-1H-indol-2-yl) carbonyl] thiosemicarbazide
This compound was isolated as yellowish orange powder with a yield of 78%,
m.p 223-225°C; IR (KBr, v in cm-1): 3417.6 and 3244.0 (-NHNH2),
3124.5 and 2970.2 (-CH), 1670.2 (-C = O), 1542.9 (-C = N), 1240.1 (-C = S).
2b. 1-[(5-Chloro-1H-indol-2-yl) carbonyl] thiosemicarbazide
This compound was isolated as brown crystals with a yield of 80%, m.p 229-230°C;
IR (Kbr, v in cm-1): 3484.8 (-NHNH2), 3163.0 (-CH), 1676.0
(-C = O), 1560.3 (-C = N), 1234.4 (-C = S).
2c. 1-[(5-Bromo-1H-indol-2-yl) carbonyl] thiosemicarbazide
This compound was isolated as yellow crystals with a yield of 82%, m.p 222-223°C;
IR (KBr, v in cm-1): 3516.0 and 3421.5 (-NHNH2), 3139.9
(-CH), 1658.7 (-C = O), 1541.90 (-C = N), 1244.0 (-C = S).
Synthesis of 5-fluoro/chloro/bromo-N'-(4-aryl-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
(4a-I)
1-[(5-Fluoro/chloro/bromo-1H-indol-2-yl) carbonyl] thiosemicarbazide
(0.001 mole) and appropriate aromatic acyl bromide (0.0012 mole) was refluxed
in methanol for 6-8 h. The reaction mixture was then kept overnight. The solid
separated was filtered and then recrystallized in ethanol, dimethylformamide
mixture.
Spectral Data
4a. 5-Fluoro-N'-(4-(2-chloropyridin-4-yl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
IR (KBr, v in cm-1): 3285.0 (-NH), 1708.9 (-C = O); 1H-NMR
(300MHz, DMSO-d6): δ 6.99 (m, 1H, ArH), 7.26 (s, 1H, ArH), 7.42
(m, 2H, ArH), 7.72 (m, 2H, ArH), 7.83 (m, 1H, ArH), 8.35 (s, 1H, ArH), 9.82
(bs, 1H, NH), 10.80 (s,1H, NH) and 11.56 (1H, NH); FABMS: m/z 388 (I = 50%,
M+), 389 (I = 50%, M+1).
4b. 5-Fluoro-N'-(4-(6-bromocoumarin-3-yl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
IR (KBr, v in cm-1): 3286.5 (-NH), 1718.5 and 1650.0 (-C = O);
1H-NMR (300MHz, DMSO-d6): δ 7.09 (dt (J = 9.0,2.7),
1H, ArH), 7.27 (s,1H, ArH), 7.43 (m, 3H, ArH), 7.74 (m, 2H, ArH), 8.17 (d(J=2.1),
1H, ArH), 8.52 (s, 1H, ArH), 9.8(bs, 1H, NH), 10.99 (s, 1H, NH) and 11.90 (1H,
NH); FABMS: m/z 499 (I = 45%, M+), 501 (I = 50%, M+1).
4c. 5-Chloro-N'-(4-(6-bromocoumarin-3-yl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
IR(KBr, v in cm-1): 3390.6 and 3313.5 (-NH), 1722.3 and1629.7(-C
= O); 1H-NMR (300MHz, DMSO-d6): δ 7.15 (d (J
= 8.7), 1H, Ar-H), 7.26 (s, 1H, ArH), 7.32 (d(J = 9.0), 1H,
ArH), 7.45 (d (J = 8.70), 1H, ArH), 7.66 (dd (J = 9.3),
2H, ArH), 7.75 (s,1H, ArH), 7.99 (s,1H, ArH), 8.09 (s,1H, ArH), 8.53 (s, 1H,
ArH), 9.72 (bs, 1H, NH),10.92 (s,1H, NH) and 11.84 (1H, NH); FABMS: m/z 516
(I = 48%, M+1), 517 (I = 75%, M+1).
4e. 5-Chloro-N'-(4-(3,4-dihydroxyphenyl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
IR(KBr, v in cm-1): 3390.0(-NH), 1720.0 and 1629.9(-C = O); 1H-NMR
(300MHz, DMSO-d6): δ 6.84 (d (J=6.9), 2H, Ar-H),
7.02 (dd (J=1.8,8.1), 1H, ArH), 7.32 (dd(J=1.8,8.7),2H,
ArH), 7.30 (s, 1H, ArH), 7.46 (d (J=8.7), 1H, ArH), 7.63 (d(J=1.5)
1H, ArH), 7.93 (s, 1H, ArH), 8.09 (s, 1H, ArH), 8.53 (s, 1H, ArH), 11.34 (s,
1H, NH),11.87 (1H, NH); FABMS: m/z 400 (I = 30%, M+), 401 (I = 60%,
M+1).
4g. 5-Bromo-N'-(4-(coumarin-3-yl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
IR(KBr, v in cm-1): 3408.0 and 3155.3(-NH), 1725.0 and 1678.0(-C
= O); 1H-NMR (300MHz, DMSO-d6): δ 7.28 (d (J=6.6),
2H, Ar-H), 7.35 (d (J=9.6), 1H, ArH), 7.32 (d(J=8.4),2H,
ArH), 7.57 (t (J=7.5),1H, ArH), 7.70 (dd (J=7.2), 1H,
ArH), 7.73 (s, 1H, ArH), 7.79 (s,1H, ArH), 7.98 (s, 1H, ArH), 8.58 (s, 1H, ArH),
10.92 (s, 1H, NH),11.79 (1H, NH); FABMS: m/z 481 (I = 45%, M+),482
(I = 30%, M+1). 483 (I = 52%, M+2).
4h. 5-Bromo-N'-(4-(6-bromocoumarin-3-yl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
IR(KBr, v in cm-1): 3301.9 (-NH), 1732.0 and 1641.3 (-C = O);
1H-NMR (300MHz, DMSO-d6): δ 7.27 (d (J=8.7),2H,
ArH), 7.42 (d(J=9.0), 1H, ArH), 7.62 (dd(J=2.4,9.0), 1H,
ArH), 7.76 (s, 1H, ArH), 7.85 (d(J=11.1), 2H, ArH), 8.50 (s, 1H,
Ar-H), 9.8 (bs, 1H, NH), 10.84(s, 1H, NH) and 11.68 (1H, NH);FABMS:
m/z 560 (I = 75%, M-2), 561(I = 100%, M-1), 562 (I = 70%, M+), 307
(I = 30%, C17H13N3OS).
Results and Discussion
5-Fluoro/chloro/bromo indole-2-carbohydrazides (1a-c) on treatment with KSCN in acidic medium yielded 1-[(5-fluoro/chloro/bromo-1H-indol-2-yl) carbonyl]thiosemicarbazide (2a-c). The compounds (2a-c) on treatment with aromatic acyl bromides (3a-I) to give corresponding 5-fluoro/chloro/bromo-N'-(4-aryl-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide derivatives (4a-I); (Scheme-1). The structures of newly synthesized compounds were confirmed by recording IR, 1H NMR, 13C NMR, Mass spectra and elemental analysis. All the compounds were isolated in good yields after recrystallisation from methanol-DMF mixture. Few selected compounds were characterized by IR, 1H-NMR and mass spectral analysis. Characterization data are given in Table 1 and the spectral data are given in the experimental section.
| Scheme 1: | |
| Table 1: | Characterization data of the compound (4a-I) |
| *All the yields are on isolated basis | |
Antibacterial Activity
We investigated the newly synthesized 5-fluoro/chloro/bromo-N'-(4-aryl-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
(4a-I) for their antibacterial activity against Escherichia coli (ATTC-25922),
Staphyllococcus aureus (ATTC-25923), Psuedomonus aeruginosa (ATTC-27853)
and Klebsiella pneumoniae (recultured) bacterial strains by disc diffusion
method (Cruickshank et al., 1975; Arthington et al., 2000). Streptomycin
was used as standard drug. Solvent and growth controls were kept and the zone
of inhibition in mm was noted. The results of such studies are given in Table
2. It can be seen that most of the compounds are active against all the
bacterial strains.
| Table 2: | Antibacterial activity of newly synthesized compounds at the conc. 10-100 g mL-1 (Disc diffusion method) |
| Zone of inhibition in mm | |
| Table 3: | Antifungal activity of newly synthesized compounds at the conc. 10-100 g mL-1 (Serial plate dilution method) |
| Zone of inhibition in mm | |
The compound 4e, 5-chloro-N'-(4-(3,4-dihydroxyphenyl)-1, 3-thiazol-2-yl)-1H-indole-2-carbohydrazide exhibited the highest inhibition and the compound 4d, 5-chloro-N'-(4-(4-methoxyphenyl)-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide exhibited the least inhibition. Compounds 4a-c and h also exhibited promising antibacterial activity. It can be seen from the studies that the compounds with fluoro and chloro substitution exhibited more inhibition than the compounds with bromo substitution. A correlation between antibacterial activity and substitution at C-4 could not be made from our studies. The higher activity of 4e may be due to the presence of catechol moiety, which is the main moiety present in adrenaline.
Antifungal Activity
Newly synthesized compounds 5-fluoro/chloro/bromo-N'-(4-aryl-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide
(4a-I) were screened for their antifungal activity against Aspergilus flavus
(NCIM No. 524), Aspergilus fumigatus (NCIM No. 902), Candida albicans
(NCIM No. 3100), Penicillium marneffei (Recultured) and Trichophyton
mentagrophytes (Recultured) in DMSO by serial plate dilution method (Cruickshank
et al., 1975; Arthington et al., 2000). Antifungal activity was
determined by measuring the diameter of the inhibition zone. The results of
such studies are given in Table 3. Activity of each compound
was compared with Fluconozole as standard drug. The study reveals that most
of the compounds possess less inhibition against the fungal strains. The compound
4a, 5-fluoro-N'-(4-(2-chloropyridin-4-yl)-1, 3-thiazol-2-yl)-1H-indole-2-carbohydrazide
exhibited highest inhibition and the compound 4g, 5-bromo-N'-(4-(3-coumarinyl)-1,
3-thiazol-2-yl)-1H-indole-2-carbohydrazide exhibited least inhibition.
The compound 4b and 4f also exhibited moderate activity in comparison with other
compounds. It can be seen that compounds with fluoro substitution exhibited
more activity than bromo and chloro substitution. A correlation between antibacterial
activity and substitution at C-4 could not be made from our studies.
Conclusion
Novel 5-fluoro/chloro/bromo-N'-(4-aryl-1,3-thiazol-2-yl)-1H-indole-2-carbohydrazide derivatives were prepared and screened for their antifungal and antibacterial activities. The compound 4e, 5-chloro-N'-[4-(3,4-dihydroxyphenyl)-1,3-thiazol-2-yl]-1H-indole-2-carbohydrazide exhibited maximum antibacterial activity and the compound 4a, 5-fluoro-N'-[4-(2-chloropyridinyl)-1, 3-thiazol-2-yl]-1H-indole-2-carbohydrazide exhibited maximum antifungal activity. The compounds 4a and 4e can be recommended for further studies.
Acknowledgments
The authors are thankful to Dr. A. Srikrishna, Professor, Department of Organic Chemistry, IISc, Bangalore and The Head, SAIF, CDRI Luknow for IR, Mass and NMR analysis.