Design, synthesis and structural studies of meta-xylyl linked bis-benzimidazolium salts: potential anticancer agents against ‘human colon cancer’

BACKGROUND: Benzimidazole derivatives are structurally bioisosteres of naturally occurring nucleotides, which makes them compatible with biopolymers of living systems. This property gives benzimidazole a biological and clinical importance. In the last decade, this class of compounds has been reported to possess anti-allergic, anti-diabatic, anti-HIV, anti-hypertensive, anti-inflammatory, anti-mycobacterial, anti-oxidant, anti-protozoal, and anti-viral properties. The researchers are now interested to explore their potential as anti-cancer agents. In the present study, an effort was made to further explore this area of research. Furthermore, in order to increase the solubility and efficacy of these heterocycles, the interest is now shifted to the salts of these compounds. With this background, we planned to synthesize a series of meta-xylyl linked bis-benzimidazolium salts to assess their anti-proliferation efficacy on human colon cancer cell line (HCT 116). RESULTS: A number of N-alkylbenzimidazoles were synthesized by reactions of benzimidazole with alkyl halides (i-PrBr, PrBr, EthBr, Pent-2-ylBr, BuBr, BenzCl, HeptBr). The subsequent treatment of the resulting N-alkylbenzimidazoles with 1,3-(bromomethylene)benzene afforded corresponding bis-benzimidazolium salts. All synthesized compounds were characterized by spectroscopic techniques (Additional file 1: NMR & FT-IR) and microanalysis. Molecular structures of selected compounds were established through single crystal x-ray diffraction studies. All the compounds were assessed for their anti-proliferation test on human colorectal cancer cell line (HCT 116). Results showed that the compounds exhibited dose dependent cytotoxicity towards the colon cancer cells with IC(50) ranges between 0.1 to 17.6 μM. The anti-proliferation activity of all compounds was more pronounced than that of standard reference drug 5-flourouracil (IC(50) =19.2 μM). CONCLUSIONS: All the synthesized bis-benzimidazolium salts showed potential anticancer activity. Out of them, some of these salts showed IC(50) value as low as 0.1–0.2 μM. Based on the results it can be concluded that, the bis-benzimidazolium salts could probably be the potential source of chemotherapeutic drugs.