Twenty nine original 3-nitroimidazo­[1,2-a]­pyridine derivatives, bearing a phenylthio (or benzylthio) moiety at position 8 of the scaffold, were synthesized. In vitro evaluation highlighted compound 5 as an antiparasitic hit molecule displaying low cytotoxicity for the human HepG2 cell line (CC50 > 100 μM) alongside good antileishmanial activities (IC50 = 1–2.1 μM) against L. donovani, L. infantum, and L. major; and good antitrypanosomal activities (IC50 = 1.3–2.2 μM) against T. brucei brucei and T. cruzi, in comparison to several reference drugs such as miltefosine, fexinidazole, eflornithine, and benznidazole (IC50 = 0.6 to 13.3 μM). Molecule 5, presenting a low reduction potential (E° = −0.63 V), was shown to be selectively bioactivated by the L. donovani type 1 nitroreductase (NTR1). Importantly, molecule 5 was neither mutagenic (negative Ames test), nor genotoxic (negative comet assay), in contrast to many other nitroaromatics. Molecule 5 showed poor microsomal stability; however, its main metabolite (sulfoxide) remained both active and nonmutagenic, making 5 a good candidate for further in vivo studies.

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