Trypanocidal activity of piperazine-linked bisbenzamidines and bisbenzamidoxime, an orally active prodrug

A series of 32 piperazine-linked bisbenzamidines (and related analogues) were analysed for their in vitro and in vivo trypanocidal activity against a drug-sensitive strain of Trypanosoma brucei brucei and a drug-resistant strain of Trypanosoma brucei rhodesiense. The compounds showed similar potencies against both strains. The most potent compounds were bisbenzamidines substituted at the amidinium nitrogens with a linear pentyl group (8, inhibitory concentration for 50% (IC50) = 1.7-3.0 nM) or cyclic octyl group (17, IC50 = 2.3-4.6 nM). Replacement of the diamidine groups with diamidoxime groups resulted in a prodrug (22) that was effective orally against T. b. brucei-infected mice. Three compounds (7, 11 and 15) provided 100% cure when administered parenterally. The results indicate that the nature of the substituents at the amidinium nitrogens of bisbenzamidines strongly influence their trypanocidal activity.