Iodine Mediated Synthesis of Thiabendazole Derivatives and Their Antimicrobial Evaluation

Background: Thiabendazole (TBZ; 4-(1H-benzimidazol-2-yl)-1,3-thiazole) is a well known anti-fungal and anti-helminthic agent. It has been observed that substitution pattern by different alkyl, aryl or heterocyclic functionalities at the various positions of benzimidazole as well as thiazole nucleus markedly influence the biological efficacy. In this study, we synthesized a novel series of TBZ derivatives with structure modifications involving incorporation of amino aryl moiety at 2nd position of thiazole nucleus as a trial to obtain safer and potent antimicrobial agents. Method: 2-Acetylbenzimidazole was prepared by oxidation of 2-(α-hydroxyethyl)benzimidazole with potassium dichromate in acidic condition. The latter was prepared from o-phenylenediamine on condensation with lactic acid using 4N HCl. The treatment of 2-acetylbenzimidazole with substituted phenylthioureas and iodine in isopropanol under reflux for 3.5 h afforded 4-(1H-benzo[d]imidazol-2- yl)-N-substituted phenylthiazol-2-amines. The structures of these compounds have been characterized from the rigorous analysis of their IR, 1H NMR, 13C NMR, MS and elemental analysis. These compounds were evaluated for their antibacterial and antifungal activities. Results: TBZ derivatives compounds 7a, 7b, 7c and 7e exhibited total inhibition of Candida albicans as evident by minimum inhibitory concentration (MIC) of 125 μg/ml. These derivatives were moderately active against Bacillus cereus, Escherichia coli, Yersinia enterocolitica and Staphylococcus aureus. Conclusion: By structural modification of TBZ by incorporation of amino aryl moiety at 2nd position of thiazole nucleus, we synthesized 4-(1H-benzo[d]imidazol-2-yl)-N-substituted phenylthiazol-2- amines and found antimicrobial action. Our findings suggest that there is a need for further substitutions to obtain potent antibacterial and antifungal derivatives of TBZ.