Discovery of highly potent and selective antiparasitic new oxadiazole and hydroxy-oxindole small molecule hybrids

A series of highly active hybrids were discovered as novel antiparasitic agents. Two heterocyclic scaffolds (1,2,4-oxadiazole and 3-hydroxy-2-oxindole) were linked, and the resulting compounds showed in vitro activities against intracellular amastigotes of two protozoan parasites, Trypanosoma cruzi and Leishmania infantum. Their cytotoxicity was assessed using HFF-1 fibroblasts and HepG2 hepatocytes. Compounds 5b, 5d, 8h and 8o showed selectivity against L. infantum (IC₅₀ values of 3.89, 2.38, 2.50 and 2.85 μM, respectively). Compounds 4c, 4q, 8a and 8k were the most potent against T. cruzi, exhibiting IC₅₀ values of 6.20, 2.20, 2.30 and 2.20 μM, respectively. Additionally, the most potent anti-T. cruzi compounds showed in vitro efficacies comparable or superior to that of benznidazole. These easy-to-synthesize molecules represent novel chemotypes for the design of potent and selective lead compounds for Chagas disease and leishmaniasis drug discovery.