Abstract

A series of ten novel substituted Benzimidazole urea derivatives [5a (I-VIII), 5b and 7] have been synthesized by two different methods. In the first method (Conventional Method A) Benzimidazole urea derivatives 5a (I-VIII), 5b and 7 were prepared by reacting substituted 1R-benzimidazol-2-amine 4(a-c) with substituted phenyl isocynates, in toluene. In the second method (Improved Method B), the above reaction was carried out under microwave assistance. Various 1R-nitro anilines 2(a-c) were prepared by reacting 1-fluoro-2-nitrobenzene with cyclohexyl amine, 2-methoxy benzyl amine or 3,4-dimethoxy benzyl amine in ethanol by Method (A) and Method (B). Compared to the conventional method, the microwave-assisted syntheses demonstrated several advantages, in terms of reaction time and overall yield. 1R-nitro anilines 2(a-c) were further reduced and cyclized to form 1R-benzimidazol-2-amine 4(a-c). The structures were confirmed by IR, 1H NMR, CHN, and Mass spectral data. The synthesized compounds [5a (I-VIII), 5b and 7] were screened for their antimicrobial activity against six microorganisms: antibacterial strains viz. Staphylococcus aureus, Bacillus spisizenii, Escherichia coli and fungal strains Aspergillus niger, Aspergillus brasiliensis and Curvilaria lunata. The compounds were found to exhibit good to moderate antimicrobial activity. Among the compounds tested, compound 5a (VI) i.e. 1-(1-cyclohexyl-1H-benzimidazol-2-yl)-4-methoxy-3-phenylurea showed highest activity.