An efficient synthesis of 3′-indolyl substituted pyrido[1,2-a]benzimidazoles as potential antimicrobial and antioxidant agents

A new class of indole-based pyrido[1,2-a]benzimidazole derivatives 4a-r have been synthesized by one-pot cyclocondensation reaction of 2-phenyl-1H-indole-3-carboxaldehyde 1a-i, malononitrile 2 and 2-cyanomethylbenzimidazole 3a-b in the presence of catalytic amount of NaOH. In vitro antimicrobial activity of the synthesized compounds were investigated against a representative panel of pathogenic strains specifically three Gram-positive bacteria (Streptococcus pneumoniae, Clostridium tetani, Bacillus subtilis), three Gram-negative bacteria (Salmonella typhi, Vibrio cholerae, Escherichia coli) and two fungi (Aspergillus fumigatus, Candida albicans) using broth microdilution MIC (minimum inhibitory concentration) method. In vitro antioxidant activity was evaluated by ferric-reducing antioxidant power (FRAP) assay method. Compounds 4c, 4e, 4l and 4q have been found to be most efficient antimicrobial members while compounds 4h and 4p possess better ferric reducing antioxidant power.