Design, synthesis, bio-evaluation, and in silico studies of some N-substituted 6-(chloro/nitro)-1H-benzimidazole derivatives as antimicrobial and anticancer agents

A new series of 6-substituted 1H-benzimidazole derivatives were synthesized by reacting various substituted aromatic aldehydes with 4-nitro-o-phenylenediamine and 4-chloro-o-phenylenediamine through condensation using sodium metabisulfite as the oxidative reagent. The N-substituted 6-(chloro/nitro)-1H-benzimidazole derivatives were prepared from the 6-substituted 1H-benzimidazole derivatives and substituted halides using potassium carbonate by conventional methods as well as by exposure to microwave irradiation. Seventy-six 1H-benzimidazole derivatives have been synthesized in moderate to excellent yields with the microwave-assisted method (40 to 99%). Compounds 1d, 2d, 3s, 4b, and 4k showed potent antibacterial activity against Escherichia coli, Streptococcus faecalis, MSSA (methicillin-susceptible strains of Staphylococcus aureus), and MRSA (methicillin-resistant strains of Staphylococcus aureus) with MIC (the minimum inhibitory concentration) ranging between 2 and 16 μg mL(−1) as compared to ciprofloxacin (MIC = 8–16 μg mL(−1)), in particular compound 4k exhibits potent fungal activity against Candida albicans and Aspergillus niger with MIC ranging between 8 and 16 μg mL(−1) compared with the standard drug fluconazole (MIC = 4–128 μg mL(−1)). In addition, compounds 1d, 2d, 3s, 4b, and 4k also showed the strongest anticancer activity among the synthesized compounds against five tested cell lines with IC(50) (half-maximal inhibitory concentration) ranging between 1.84 and 10.28 μg mL(−1), comparable to paclitaxel (IC(50) = 1.38–6.13 μM). Furthermore, the five most active compounds showed a good ADMET (absorption, distribution, metabolism, excretion, and toxicity) profile in comparison to ciprofloxacin, fluconazole, and paclitaxel as reference drugs. Molecular docking predicted that dihydrofolate reductase protein from Staphylococcus aureus is the most suitable target for both antimicrobial and anticancer activities, and vascular endothelial growth factor receptor 2 and histone deacetylase 6 are the most suitable targets for anticancer activity of these potent compounds.