Heterocyclic bibenzimidazole derivatives as topoisomerase I inhibitors

A series of 2′-heterocyclic derivatives of 5-phenyl-2,5′-1H-bibenzimidazoles were evaluated for topoisomerase I poisoning activity and cytotoxicity. Topo I poisoning activity was associated with 2′-derivatives that possessed a hydrogen atom capable of hydrogen bond formation, suggesting that the interatomic distances between such hydrogen atoms and the heteroatoms on the adjacent benzimidazole influence activity.