Anti-parasitic activity and computational studies on a novel labdane diterpene from the roots of Vachellia nilotica

A new labdane diterpene characterized as 18 alpha-O-trans-p-feruloyl-15-methyl-8(17)-labdanoate has been isolated from the roots of Vachellia nilotica. Also isolated were p-coumaric acid, ferulic acid, stearic acid, lupeol, and a mixture of beta-sitosterol and stigmasterol. The compounds were obtained after a series of column chromatography on silica gel, and their structures were elucidated using NMR and LC-MS analyses. The new diterpene showed good anti-parasitic activity with an IC50 of 0.0177 mu M against Trypanosoma brucei and 0.0154 mu M against Leishmania major using an Alamar Blue assay. The compound also displayed very good inhibitory activity against Leishmania major compared to Trypanosoma brucei rhodesiense with a binding energy of -10.5 and -7.8 kcal/mol, respectively. Density functional theory analysis showed that the studied compound has low LUMO-HOMO energy, signifying a high chemical reactivity with the ability to donate electrons to electron-accepting species.