Leishmaniasis is a neglected tropical disease posing significant global health challenges. Given the limited effective treatment options and associated constraints, many patients are unable to complete therapy. In this study, we report the remarkable leishmanicidal activity of onnamides derived from the marine sponge Theonella sp. against the promastigote form of Leishmania major (IC 50 = 0.2–140 nM) and demonstrate their sele...