Enhancing Antileishmanial Activity of Amidoxime-Based Compounds Bearing a 4,5-Dihydrofuran Scaffold: In Vitro Screening Against Leishmania amazonensis.

Leishmaniasis, a protozoan disease affecting humans, exposes significant shortcomings in current treatments. In continuation to our previous findings on amidoxime-based antileishmanial compounds bearing a 4,5-dihydrofuran scaffold, twelve new amidoxime derivatives substituted at position 3 with an amide bearing a nitrogen heterocycle were synthesized. This series was designed to replace the sulfone and aryl group on a previously reported HIT. The synthesis of these compounds involved the following three-step pathway: manganese (III) acetate-based cyclization of a β-ketoester, followed by amidation with LiHMDS and a final reaction with hydroxylamine. Three of them, containing either bromine, chlorine, or methyl substitutions and featuring a pyridine moiety, showed an interesting toxicity-activity relationship in vitro. They exhibited IC₅₀ values of 15.0 µM, 16.0 µM, and 17.0 µM against the promastigote form of the parasite and IC₅₀ values of 0.5 µM, 0.6 µM, and 0.3 µM against the intracellular amastigote form, respectively. A selectivity index (SI) greater than 300 was established between the cytotoxic concentrations (in murine macrophages) and the effective concentrations (against the intracellular form of Leishmania amazonensis). This SI is at least seventy times higher than that observed for Pentamidine and twenty-five times higher than that observed for the reference HIT, as previously reported.