Design and synthesis of novel derivatives of bioactive sesquiterpenes Dehydrocostus lactone and Costunolide and their evaluation as leishmanicidal agents with an improved safety profile.

The marker compounds sesquiterpene lactones, Dehydrocostus lactone, and Costunolide have been isolated from Aucklandia costus Falc. The α-methylene-γ-Lactone (αMγL) moiety is a highly reactive functional group in sesquiterpene lactones and is responsible for biological effects. However, the αMγL group is alkylated by -SH groups of enzymes as well as amino acids like cysteine, and glutathione that leads to alterations in biological systems. In the present work a series of derivatives have been synthesised by Michael addition reaction between substituted piperazines and isolated sesqueterpene lactones Dehydrocostuslactone and Costunolide across the αMγL group in a site and stereo-selective fashion. Further, we have assessed the isolated sesquiterpene lactones and their synthesised derivatives for anti-leishmanial potential and cytotoxic effects on the J774A.1 and RAW 264.7 cell lines. Results demonstrated that the synthetic modification introduced in the isolated sesquiterpene lactones led to better leishmanicidal potency and significantly improved the selectivity index (SI) as compared to parent molecules. The most potent hits 1po (IC50 4-7 μM, SI 13-21) and 2pp (IC50 4-6 μM, SI 17-31) were selected for in-depth mechanistic insights. Various studies suggested that potent hits (1po and 2pp) caused alterations in structural morphology, generation of oxidative stress, depletion of intracellular ATP pool which is linked to mitochondrial dysfunction, and accumulation of lipid bodies; ultimately leading to cell death. Moreover, computational studies and sterol quantification assays confirmed that these potent hits inhibit leishmanial sterol 14-α demethylase protein. Thus, the present study highlighted potent plant-based sesquiterpene lactones (Dehydrocostus lactone and Costunolide) as potential anti-leishmanial candidates, which may be further developed as novel therapeutic alternatives to fight leishmaniasis.