Synthesis and antimicrobial testing of 4H-1,2,4-triazole, 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole and 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine derivatives of 1H-benzimidazole.

Three novel series of benzimidazole derivatives namely 6-substituted 3-[1-(2-alkyl-1 H-benzimidazolyl)methyl]-1,2,4-triazolo[3,4-b][1,3,4] thiadiazoles 5a-h, 6-substituted 3-[1-(2-alkyl-1H-benzimidazolyl)methyl]-7H-1,2,4 -triazolo[3,4-b]-[1,3,4]thiadiazines 6a-j and 6-thioxo-3-[1-(2-alkyl-1H-benzimidazolyl)methyl]-5,6-dihydro-1,2,4 -triazolo[3,4-b][1,3,4]-thiadiazoles 7a, b have been prepared by cyclization of the key intermediate 1-[(4-amino-5-mercapto-4 H-1,2,4-triazol-3-yl)methyl]-2-alkyl-1 H-benzimidazoles 3a, b. Furthermore, 1-[(4-arylideneamino-5-mercapto- 4H-1,2,4-triazol-3-yl)-methyl]-2-alkyl- 1 H-benzimidazoles 4a-h have been prepared and some of them were cyclized to 6-substituted 3-[1-(2-alkyl-1H-benzimidazolyl)methyl]-1,2,4-triazolo [3,4-b][1,3,4]thiadiazoles 5d, h using thionyl chloride. The prepared compounds were tested for antimicrobial activity in vitro; they showed moderate activity.