Synthesis and antiparasitic activity of new bis-arylimidamides : DB766 analogs modified in the terminal groups

Fifteen novel bis-arylimidamide derivatives with various 6-membered (7a-c) and 5-membered (7d-o) heterocyclic rings replacing the terminal pyridyl rings of the lead compound DB766{(2,5-bis[2-i-propoxy-4-(2-pyridylimino)aminophenylfuran]}, were prepared and evaluated versus Trypanosoma cruzi, Leishmania amazonensis, Trypanosoma brucei rhodesiense and Plasmodium falciparum. Compound 7a with pyrimidine replacing the pyridine rings showed good activity versus T. cruzi, T. brucei rhodesiense and P. falciparum (IC50 = 200 nM, 32 nM and 8.5 nM, respectively). Three compounds (7g, 7i, 7j) with thiazole replacing the pyridine rings gave low micromolar (0.17-0.3 μM) IC50 values versus L. amazonensis, however only 7g exhibited an acceptable selectivity index (SI = 27). Compounds 7a, 7j and 7m exhibited potent activity against T. brucei rhodesiense (IC50 = 12-60 nM). Ten of the 15 compounds with pyrimidine, pyrrole, thiazole and imidazole terminal units were highly active against P. falciparum (IC50 = 9-87 nM). Both pyrimidine and pyridine terminal groups are advantageous for anti-T. cruzi activity and several different heterocyclic terminal units are effective versus P. falciparum, both findings merit further investigation.