Synthesis and Mechanistic Insights of Coumarinyl-Indolinone Hybrids as Potent Inhibitors of Leishmania major

Abstract

Leishmaniasis, recognized as a neglected tropical disease, is a major global health issue that impacts millions of individuals across the globe. The limitations of existing treatments underscore the urgent need for novel antileishmanial drugs. In response, this study synthesized and evaluated fifteen hybrid compounds (7a-c, 10a-j, and 13a-b) combining 4-hydroxycoumarin and pyrazolyl indolin-2-one motifs for their in vitro antileishmanial efficacy towards Leishmania major. These molecules demonstrated remarkable activity against the promastigote form, with IC₅₀ values ranging from 1.21 to 7.21 μM, surpassing the reference drug miltefosine (IC₅₀ = 7.83 μM). Assessment against the intracellular amastigote form revealed efficient inhibitory action (IC₅₀: 2.41-9.44 μM vs. 8.07 μM for miltefosine). Compounds 7a and 7b exhibited exceptional antileishmanial activity against both forms while maintaining favorable safety profiles. Mechanistic studies indicated that the most effective compounds act through an antifolate mechanism, targeting pteridine reductase 1 (PTR1) and dihydrofolate reductase-thymidylate synthase (DHFR-TS). Molecular docking and dynamics simulations of compounds 7a and 7b revealed strong in-silico binding and stable dynamics against PTR1, suggesting a high potential for enzyme inhibition. These findings present a promising new class of antileishmanial agents targeting the folate pathway.