Phytochemical study of Piliostigma thonningii , a medicinal plant grown in Nigeria.

Piliostigma thonningii (Schumach.) Milne-Redhead. (Leguminosae) is used for various medicinal purposes in African countries. Phytochemical investigation of P. thonningii yielded two compounds newly isolated from natural sources, 2 β -methoxyclovan-9 α -ol ( 1 ), and methyl- ent -3 β -hydroxylabd-8(17)-en-15-oate ( 2 ), along with 14 known compounds ( 3 - 16 ). Compounds 1 and 4 (alepterolic acid) showed potential selectivity towards Trypanosoma brucei brucei with IC50 7.89 and 3.42 μM, respectively. Compound 2 showed activity towards T. brucei and Leishmania donovani Amastigote with IC50 3.84 and 7.82 μM, respectively. The structure activity relationship (SAR) of the isolated metabolites suggested that hydroxylation at C-2 enhances the antiprotozoal activity towards T. brucei in sesquiterpenes 1 and 3 . Similarly hydroxylation at C-3 in labdane diterpenes elevates the antiprotozoal activity towards T. brucei.