Inhibitory activity of diospyrin derivatives against Leishmania major parasites in vitro

Objective: To evaluate the inhibitory activity of some new derivatives of diospyrin, a plant-derived bisnaphthoquinonoid compound, against the growth of Leishmania major, the causative parasites of cutaneous leishmaniasis. Methods: Diospyrin (I) was isolated from the stem bark of Diospyros montana Roxb., and its derivatives, viz. alkyl ethers (II-IV), hydroquinonoid (V) and amino (VI) were synthesized. Lawsone, another plant-derived naphthoquinonoid, was converted into an analogous dimeric compound (VII). The inhibitory activity of all these products was estimated against Leishmania major promastigotes. Parasites were grown in culture medium, with or without the test compounds, in 96-well plates in a CO₂- incubator. After 24 h, ³H- thymidine was added to each well, the parasites were further incubated for 18 h, and then harvested on glass microfibre filters. The growth inhibition of the parasites was estimated by measuring the resultant radioactivity on the filters in the control and the test compound-treated wells. Results: The modifications in the structure of diospyrin (I) produced variable effects. The compounds II and V were the most effective, causing nearly 98 % inhibition at a dose of 2.5 μg/ml. While all the derivatives (II - VI) showed enhanced antileishmanial activity in comparison to their precursor (I) the dimeric analogue, (VII) was found to be inactive in the assay. Conclusion: Diospyrin, an indigenous plant-product, could be used as a 'lead molecule' for drug-design based on the structure-activity relationship evolving in this series of novel naphthoquinonoid derivatives possessing significant antileishmanial activity in vitro against L. major parasites.