SYNTHESIS OF 3- (1 – BENZYL – 1H – BENZO [D] IMIDAZOL – 2 – L AMINO) – 2 – (3 – ARYL – 1- PHENYL – 1H – PYRAZOL – 4 – YL) THIAZOLIDIN – 4- ONES AND THEIR ANTIMICROBIAL ACTIVITIES

SYNTHESIS OF 3- (1 – BENZYL - 1H - BENZO [D] IMIDAZOL – 2 - L AMINO) – 2 - (3 – ARYL - 1- PHENYL - 1H - PYRAZOL - 4 - YL) THIAZOLIDIN - 4- ONES AND THEIR ANTIMICROBIAL ACTIVITIES

Sharanabasappa B. Patil and Naganna M. Goudgaon*

Department of Studies and Research in Chemistry, Gulbarga University, Gulbarga (Karnataka), India

ABSTRACT

Reaction of 1- (1- benzyl- 1H- benzo [d] imidazol- 2- yl) hydrazine (1) with 3-aryl-1-phenyl-1H-pyrazole-4-carbaldehydes (2a-f) in ethanol yielded the corresponding Schiff bases (3a-f). Further, cyclization of compounds 3a- f with thioglycollic acid in benzene in presence of anhydrous ZnCl₂ furnished desired novel compounds 3- (1 – Benzyl - 1h - Benzo [D] Imidazol – 2 - L Amino) – 2 - (3 – Aryl - 1- Phenyl - 1h - Pyrazol - 4 - Yl) Thiazolidin - 4- Ones (4a- f) in 41-65% yield. All the synthesized compounds were screened for antibacterial and antifungal activities. Among the synthesized compounds 3b, 3d, 4a and 4f have shown good activity against bacteria P. aeruginosa, S. aureus and P. vulgaris, where as other compounds have shown moderate to poor activity against all the organisms. The compounds 3a and 3c exhibited good activity against fungal strains A. niger and A. flavus. All remaining synthesized compounds exhibited moderate to poor activity against all the organisms. The structures of synthesized compounds have been established by spectral studies and elemental analysis.

INTRODUCTION: Benzimidazoles constitute an important group of heterocyclic compounds and have been shown to exhibit wide range of pharmacological activities such as antifungal, antibacterial, antiparasitic and anthelmintic ^1-3. Some of the benzimidazole analogs like thiabendazole, mebendazloe and albebdazole are widely used as anthelmintic drugs ⁴.  In addition, N₁ and C₂- subtituted benzimidazoles and their derivatives have been found to be potent biologically active compounds as well. Further, N₁-subtituted benzimidazoles have exhibited anti-microbial ⁵ and also antiviral activity ⁶ against human cytomegalovirus and herpes simplex virus type-1. The biological activities of these compounds depend upon the substitution on the benzimidazole at the N-1 or C-2 position. In addition, pyrazole and thiazolidinone derivatives are also known to exhibit a wide range of biological activities such as anti-hyperglycaemic, analgesics, anti-inflammatory, antipyretic, antibacterial and sedative-hypnotics ^7-11. In continuation of our research work on benzimidazoles ^12-14 and pyrazoles ¹⁵, we report here the synthesis and antimicrobial activity of some novel 3 (1- benzyl- 1H- benzo [d] imidazole- 2-yl amino)- 2- (3- aryl- 1- phenyl- 1H- pyrazole- 4-yl) thiazolidine- 4- ones.

EXPERIMENTAL:

Chemistry: Melting points were recorded by using Thomas-Hoover melting point apparatus and were uncorrected. IR spectra in KBr disc were recorded on Perkin- Elmer- Spectrum- one FTIR spectrophotometer (ν_max in cm^-1) and ¹H NMR in DMSO-d₆ on amx 400 MHz spectrophotometer using TMS as internal standard (chemical shift in δ or ppm). Mass spectra were recorded on a JEOL SX 102 Mass spectrometer using Argon/Xenon (6kv, 10 mA) as the FAB gas. Purity of the compounds was checked by TLC using silica gel ‘G’ plates obtained from Whatman Inc, and a fluorescent indicator. 3- aryl- 1- phenyl- 1H- pyrazole- 4-carbaldehydes were prepared by known literature method ¹⁶.

General procedure for the synthesis of Schiff bases (3a- f): A mixture 1- (1- benzyl- 1H-benzo [d] imidazol- 2- yl) hydrazine (1) (0.01 mol) and 3- aryl- 1- phenyl- 1H- pyrazole- 4- carbaldehydes (2a-f) (0.01 mol) in ethanol (20 ml) containing 3-4 drops of conc. HCl was refluxed on a water bath for 8 hours. Concentrated and the residue was recrystalized from methanol yielded desired compounds 3a-f.

1- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl)- 2-((1, 3- diphenyl- 1H- pyrazol- 4-yl) methylene) hydrazine (3a): Yield 1.5 g (60%). IR (KBr): 3253, 3182 (NH). ¹H NMR: 10.0 (s, 1H, N₁H), 7.9-7.6 ( 2H 1 N=CH, C₅H of pyrazole), 7.5-7.0 (m, 19H, ArH), 5.2 (s, 2H, methylene proton). Mass (m/z) = 468 (M⁺, 10%). Anal. Calcd for C₃₀H₂₄N₆ : C, 76.90; H, 5.16; N, 17.94. Found: C, 75.90; H, 5.15; N, 16.94.

1- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl)- 2- ((3- (4- nitrophenyl)- 1- phenyl- 1H- pyrazol- 4-yl) methylene) hydrazine (3b): Yield 1.2 g (55%). IR (KBr): 3139, 3121 (NH). ¹H NMR: 10.2 (s, 1H, N₁H), 7.8-7.6 ( 2H 1 N=CH, C₅H of pyrazole), 7.5-7.0 (m, 18H, ArH), 5.2 (s, 2H, methylene proton). Mass (m/z) = 513 (M⁺, 10%). Anal. Calcd for C₃₀H₂₃N₇O₂ : C, 70.16; H, 4.51; N, 19.09. Found: C, 69.16; H, 4.50; N, 19.08.

1- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl)- 2- ((1-phenyl- 3- p- tolyl- 1H- pyrazol- 4-yl) methylene) hydrazine (3c): Yield 1.2 g (65%). IR (KBr): 3413, 3123 (NH). ¹H NMR: 10.1 (s, 1H, N₁H), 7.8-7.6 ( 2H, 1 N=CH, C₅H of pyrazole), 7.5-7.0 (m, 18H, ArH), 5.2 (s, 2H, methylene proton), 2.2(s, 3H, CH₃). Mass (m/z) = 482 (M⁺, 10%). Anal. Calcd for C₃₁H₂₆N₆: C, 77.15; H, 5.43; N, 17.41. Found: C, 77.14; H, 5.42; N, 17.40.

1- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl)- 2- ((3-(2, 4- dimethoxyphenyl)- 1- phenyl- 1H- pyrazol- 4-yl) methylene)hydrazine (3d): Yield 1.4 g (45%). IR (KBr): 3123, 3113 (NH). ¹H NMR: 9.9 (s, 1H, N₁H), 8.0-7.6( 2H, 1 N=CH, C₅H of pyrazole), 7.5-7.2 (m, 17H, ArH), 5.3 (s, 2H, methylene proton), 3.8 (s, 6H, OCH₃). Mass (m/z) = 528 (M⁺, 15%). Anal. Calcd for C₃₂H₂₈N₆O₂: C, 72.71; H, 5.34; N, 15.90. Found: C, 72.70; H, 5.32; N, 15.89.

1- (1- Benzyl- 1H- Benzo [d] imidazol- 2- yl)- 2- ((3-(2, 5- dimethoxyphenyl)- 1- phenyl- 1H- pyrazol- 4-yl) methylene) hydrazine (3e): Yield 1.5 g (50%). IR (KBr): 3213, 3113 (NH). ¹H NMR: 10.0 (s, 1H, N₁H), 8.0-7.6 ( 2H, 1 N=CH, C₅H of pyrazole), 7.5-7.2 (m, 17H, ArH), 5.2 (s, 2H, methylene proton), 3.8 (s, 6H, OCH₃). Mass (m/z) = 528 (M⁺, 10%). Anal. Calcd for C₃₂H₂₈N₆O₂: C, 72.71; H, 5.34; N, 15.90. Found: C, 72.69; H, 5.31; N, 15.88.

 3- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl amino)- 2- (3- (2- hydroxyphenyl)- 1- phenyl- 1H-pyrazol- 4- yl) methylene) hydrazine (3f): Yield 1.2 g (55%). IR (KBr): 3135, 3123 (NH). ¹H NMR: 10.8 (s, 1H, N₁H), 8.0 (s, 1H, OH), 7.8-7.6 (2H, 1 N=CH, C₅H of pyrazole), 7.0-7.5 (m, 18H, ArH). Mass (m/z) = 484 (M⁺, 20%). Anal. Calcd for C₃₀H₂₄N₆O: C, 74.36; H, 4.99; N, 17.34. Found: C, 74.35; H, 4.97; N, 17.32;

General procedure for the synthesis of 3- (1-Benzyl- 1H- benzo [d] imidazol- 2- yl amino)- 2- (3-aryl-1-phenyl- 1H- pyrazol- 4- yl) thiazolidine- 4- one (4a- f): A mixture of Schiff base (0.001 mol), thioglycollic acid (0.001 mol) and a pinch of ZnCl₂ in 10 ml of benzene were refluxed for 24 hours. Concentrated the reaction product under reduced pressure yielded semisolid. It was then neutralized with NaHCO₃ (10%). Separated solid was filtered, dried and recrystallized from ethanol gave targeted compounds 4a-f.

3- (1 -Benzyl- 1H- benzo [d] imidazol- 2- yl amino)- 2- (1, 3- diphenyl- 1H- pyrazol- 4- yl) thiazolidin- 4- one (4a): Yield 0.4 g (45%). IR (KBr): 3172, 3123 (NH). 1676 C=O. ¹H NMR: 10.0 (s, 1H, N₁H), 7.8-7.2 (m, 20H, 19ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone). Mass (m/z) = 542 (M⁺, 10%). Anal. Calcd for C₃₂H₂₆N₆OS C, 70.83; H, 4.83; N, 15.49. Found: C, 70.82; H, 4.82; N, 15.48.

3- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl amino)-2- (3- (4- nitrophenyl)- 1-phenyl- 1H- pyrazol- 4- yl) thiazolidin- 4- one (4b): Yield 0.24 g (55%). IR (KBr): 3235, 3123 (NH). ¹H NMR: 10.0 (s, 1H, N₁H), 8.2-7.2 (m, 19H, 18ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone). Mass (m/z) = 587 (M⁺, 15%). Anal. Calcd for C₃₂H₂₅N₇O₃S: C, 65.40; H, 4.29; N, 16.68. Found: C, 65.39; H, 4.28; N, 16.66.

3- (1- Benzyl - 1H - benzo [d] imidazol- 2- ylamino) - 2 - (1- phenyl- 3- p- tolyl- 1H- pyrazol- 4- yl) thiazolidin- 4- one (4f): Yield 0.16 g (50%). IR (KBr): 3245, 3211 (NH). ¹H NMR:  9.9 (s, 1H, N₁H), 7.8-7.2 (m, 19H, 18ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone), 2.2 (s, 3H, CH₃). Mass (m/z) = 556 (M⁺, 15%). Anal. Calcd for C₃₃H₂₈N₆OS: C, 71.20; H, 5.07; N, 15.10. Found: C, 71.19; H, 5.08; N, 15.08.

3- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl amino)- 2- (3- (2, 4- dimethoxyphenyl)- 1- phenyl- 1H-pyrazol- 4- yl) thiazolidin- 4- one (4c): Yield 0.15 g (65%). IR (KBr): 3245, 3111 (NH). ¹H NMR: 10.0 (s, 1H, N₁H), 7.9-7.2 (m, 17H, 16ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone). Anal. Calcd for C₃₄H₃₀N₆O₃S: C, 67.76; H, 5.02; N, 13.94. Found: C, 67.75; H, 5.01; N, 13.92.

3- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl amino)- 2- (3- (2, 5- dimethoxyphenyl)- 1- phenyl- 1H-pyrazol- 4- yl) thiazolidin- 4- one (4d): Yield 0.25 g (41%). IR (KBr): 3268, 3112 (NH). ¹H NMR: 10.2 (s, 1H, N₁H), 7.8-7.2 (m, 17H, 16ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone). Anal. Calcd for C₃₄H₃₀N₆O₃S: C, 67.76; H, 5.02; N, 13.94. Found: C, 67.72; H, 5.02; N, 13.93.

3- (1- Benzyl- 1H- benzo [d] imidazol- 2- yl amino)- 2- (3- (2- hydroxyphenyl)- 1- phenyl- 1H- pyrazol-4- yl) thiazolidin- 4- one (4e): Yield 0.18 g (60%). IR (KBr): 3345, 3211 (NH). ¹H NMR: 10.2 (s, 1H, N₁H), 7.8-7.2 (m, 19H, 18ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone). Mass (m/z) = 558 (M⁺, 10%). Anal. Calcd for C₃₂H₂₆N₆O₂S: C, 68.80; H, 4.69; N, 15.04. Found: C, 68.79; H, 4.68; N, 15.02.

RESULTS AND DISCUSSION: The desired novel compounds 4a-f were synthesized in two steps starting from 2- hydrazinobenzimidazole (1) (Scheme- 1). Reaction of 1 with 3- aryl- 1- phenyl- 1H- pyrazole- 4-carbaldehydes (2a-f) in ethanol in the presence of 2-3-drops of conc. HCl under reflux for 8 hours gave the corresponding Schiff bases (3a-f) in 41-65% yield (Table-1). The IR spectrum of compound 3a shows absorptions at 3253 and 3182  cm^-1 due to NH and formation of compound 3a was further confirmed by its ¹H NMR spectrum shows signals at δ 10.0 (s, 1H, N₁H), 7.9-7.6( 2H 1 N=CH, C₅H of pyrazole), 7.5-7.0 (m, 19H, ArH), 5.2 (s, 2H, methylene proton ). Mass spectrum of compound 3a shows molecular ion peak at m/z = 468 (M⁺, 10%).

Cyclization of Schiff bases 3a-f with thioglycollic acid in refluxing benzene in the presence of ZnCl₂ for 24 hours furnished 3- (benzo [d] imidazol- 2- yl amino)- 2- (3- aryl- 1- phenyl- 1H- pyrazol- 4-yl) thiazolidin- 4- ones (4a-f). Formation of compound 4a was confirmed by the IR spectra shows absorptions at 3172, 3123  and 1676 cm^-1 due to NH and C=O group. ¹H NMR spectrum of compound 4a shows signals at δ10.0 (s, 1H, N₁H), 7.8-7.2 (m, 20H, 19ArH, C₅H of pyrazole), 5.6 (s, CH of thiazolidinone), 5.2 (s, 2H, methylene proton), 3.2 (d, CH₂ of thiazolidinone). Further formation of compound 4a was confirmed by mass spectra shows molecular ion peak at m/z = 542 (M⁺, 10%). Physical constants of all the synthesized compounds are tabulated in Table 1.

TABLE 1: PHYSICAL CONSTANT OF THE SYNTHESIZED COMPOUNDS

Antimicrobial Activity: The antimicrobial activities were performed by cup plate method. The sample was dissolved in DMF at the concentration of 1000 µg/ml. Antibacterial activity screened against P. aeruginosa, S. aureus and P. vulgaris. Antifungal activity was carried out against A. niger and A. flavus under aseptic conditions. Gentamycin and fluconazole were used as standard drug for antibacterial and antifungal activities respectively. The zone of inhibition was compared with standard drug after 24 hours of incubation at 25^oC for antibacterial activity and 48 hours at 30^oC for antifungal activity. Results are tabulated in Table 2.

CONCLUSION: A simple and convenient method has been developed to synthesize novel 3 - (benzo [d] imidazole – 2 - yl amino) - 2- (3 - aryl- 1 – phenyl - 1H - pyrazole - 4 - yl) thiazolidin- 4- one (4a- f). Further, it reveals that the presence of pyrazole moiety attached to benzimidazole ring enhances the antibacterial activity.

TABLE 2: ANTIMICROBIAL ACTIVITY OF SYNTHESIZED COMPOUNDS

** Zone of inhibition excluding well size 6mm

REFERENCES:

1. Puratchikody A, Sivajyothi V, Jaswanth K and Nallu M: Synthesis, Reactivity and Biological Activity of Benzimidazoles. Indian J Heterocyclic Chem. 2002; 11:
2. Pandey V. K and Raj N: Synthesis of α methylarylamido-ß-naphthyl-(1- Methylamino-2-methyl-benzimidazolyl)-ethers Curr, Sci. 1984; 53:256.
3. Sengupta A. K, Gupta A. and Chandra U: Synthesis of 1-(4-carboxy 3-hydroxy phenyl aminomethyl) benzimidazole. Indian Drugs. 1985; 18:233.
4. Wright J. B: Synthesis, Spectral Studies and Anti-inflammatory Activity of Some New 2-Aryloxybenzimidazoles Chem Rev. 1981; 48:
5. Preston P.N: Synthesis of some substituted benzimidazole with potential antimicrobial activity. Chem Rev. 1974; 74:
6. Zou R, Kawashima E, Freeman G.A, Koszalka G.W, Drach J.C and Townsend L.B: Design, Synthesis and Antiviral Evaluation of Some Polyhalogenated Indole C-nucleosides. Nucleosides Nucleotides and Nucleic acids. 2000; 19:125.
7. Abdullah S, El-Assiery, Hosni G, Ahmed Fouda: Synthesis of some new annulatedpyrazolo-pyrido (or pyrano) pyrimidine, pyrazolopyridine and pyranopyrazole derivatives. Acta Pharma, 2004; 54:143.
8. Lee K. Y, Kim J. M and J. N. Kim: Synthesis of 3-Benxyl-2-hydroxy-7, 8- dihydro-6H-quinolin-5-ones from Baylis-Hillman Adducts.Bull.Korean Chem. Soc.2005; 26:319.
9. Hogale M. B, Uthale A. C and Nikam B. P: Synthesis and biological activity studies of some thiazolidinones and azetidinone. Indian J Chem., 1991; 30B:717.
10. Asati K. C, Srivastava S. K and Srivastava D. S: Synthesis of 5-arylidene-2-aryl-3(benzotriazoloacetamidyl)-1, 3-thiazolidin-4-ones as analegesic and antimicrobial agents. Indian J Chem., 2006, 45B:526.

11. Cesur N and Gursoy A: Synthesis and anticonvulsant activity of clubbed thiazolidinone-barbituric acid and thiazolidinone-triazole derivatives Arch Pharm., 1992; 325:
12. Goudgaon N. M, Dhondiba V and Vijayalaxmi A: Synthesis and Antimicrobial Activity of N-1 Substituted Benzimidazoles. Indian J Heterocyclic Chem., 2004; 13:271.
13. Jeelan Basha N, Upendar Reddy CH and Goudgaon N. M: Cyclization of 4-(2-Aminoanilino)-2-Benzylthiopyrimidine to Novel 1-(2-Benxylthiopyrimidin-4-yl)-2-Subtituted Benzimidazoles. Heterocyclic Communications, 2008; 14:469.
14. Goudgaon N. M and Jeelan Basha N: Synthesis and Antimicrobial Activity of 2-(-Benzylthiopyrimidn-4-yl) substituted Benzimidazoles. Indian J Heterocyclic Chem., 2009; 18:353.
15. Goudgaon N. M, Jeelan Basha N and Sharanabasappa B. Patil: Synthesis of 2-Benzylthiopyrimidinyl Pyrazole Analogs and Their Antimicrobial Activities. Indian J Heterocyclic Chem., 2009; 18:349.
16. Jagath Reddy G, Latha D and Srinivas Rao K: Synthesis of some new Ethyl-4-(1, 3- Diarylpyrazol-4-yl)-6-Methyl-2-thioxo-1, 3, 4-trihydropyrimidine-5-carboxylates Heterocyclic Communications, 2004; 10:331.
    

    ---