Benzimidazoles have a broad spectrum of biological and pharmacological properties, including anticancer activity. This study reports the facile synthesis and cytotoxic evaluation of twenty-eight 1,2-disubstituted benzimidazoles (6a-β), based on condensation reactions between N-benzyl o-phenylenediamine and benzylamine. The reactions were solvent-free, with the use of Na2S2O5 as an inexpensive and environmentally friendly oxidizing agent, and progressed rapidly. Cytotoxicity assessments using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay were performed against the A549, HeLa, and MCF-7 cell lines for all synthesized compounds (6a-β). Among them, 6j, 6k, 6l, and 6n displayed good activities against the A549 and MCF-7 cell lines. These compounds possessed IC50 values ranging from 2.55 to 4.50 µM, corresponding to 1.4-fold to 2.4-fold stronger potencies than that of the positive control 5-fluorouracil (5-FU) (IC50 = 6.08 µM) against MCF-7 cells, while 6k (IC50 = 3.22 µM) was consistent with 5-FU on the A549 cell line (IC50 = 3.77 µM). Structure-activity relationship analyses revealed the 3-pyridinyl moiety at C-2 and the CH3, OCH3, or 1,3-dioxolyl groups on the benzene ring at the N-1 position of the benzimidazole heterocycle as key structural features effectuating the observed cytotoxicities.
Keywords: benzimidazole; benzylamine; cytotoxicity; o-phenylenediamine; sodium metabisulfite; solvent-free organic synthesis.