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

A new labdane diterpene characterized as 18α-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 β-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 µM against Trypanosoma brucei and 0.0154 µM 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.