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

Two new antiprotozoal diterpenes from the roots of Acacia nilotica

The powdered roots of the medicinal plant Acacia nilotica were extracted with hexane and ethyl acetate, and the extracts were subjected to column chromatography for the isolation of potentially bioactive compounds and their screening against kinetoplastid pathogens. NMR and HREI mass spectrometric analyses identified two new diterpenes, characterized as 16, 19-dihydroxycassa-12-en-15-one (Sandynone, 1) and (5S, 7R, 8R, 9R, 10S, 13Z, 17S)-7,8:7,17:16,17-triepoxy-7,8-seco-cassa-13-ene (niloticane B, 2). The previously reported (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-diene-7,17-diol (3), (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-dien-7-ol-17-al (4), and (5S,7R,8R,9R,10S) -(-)-7,8-seco-7, 8-oxacassa-13,15-dien-7-ol (5) a, mixture of stigmasterol (6a) and sitosterol (6b), and lupeol (7) were also isolated. Several column fractions displayed significant activity against a panel of Trypanosoma and Leishmania spp., and from the most active fraction, compound 4 was isolated with high purity. The compound displayed high activity, particularly against T. brucei, T. evansi, and L. mexicana (0.88–11.7 µM) but only a modest effect against human embryonic kidney cells and no cross-resistance with the commonly used melaminophenyl arsenical and diamidine classes of trypanocides. The effect of compound 4 against L. mexicana promastigotes was irreversible after a 5-h exposure, leading to the sterilization of the culture between 24 and 48 h