Novel 2-(2-phenalkyl)-1H-benzo[d]imidazoles as antitubercular agents. Synthesis, biological evaluation and structure-activity relationship.

A series of novel 2-(2-phenalkyl)-1H-benzo[d]imidazole derivatives and analogues (2a-3l) have been synthesized and evaluated for tuberculostatic activity. Benzimidazoles substituted at the C-2 position with phenethyl, styryl and 3,5-dichlorophenethyl moiety were obtained. Compounds 2g, 2h and 2i bearing methyl groups at the benzimidazole system and phenalkyl substituent at the C-2 position showed high tuberculostatic activity against Mycobacterium tuberculosis strains with MIC values ranging from 0.8 to 6.2 μg/mL (2.5-25 μM). More importantly, derivatives 2g (5,6-dimethyl-2-phenethyl-1H-benzo[d]imidazole) and 2i (2-(3,5-dichlorophenethyl)-5,6-dimethyl-1H-benzo[d]imidazole) appeared selective for M. tuberculosis as compared with eukaryotic cells: non-malignant (neonatal human dermal fibroblasts) and malignant (mouse melanoma B16-F10 cell line). These compounds may thus represent a novel, selective class of anti-tubercular agents. SAR studies resulted in interesting conclusions on structural factors affecting tuberculostatic activity.