Activity of extracts and naphthoquinones from Kigelia pinnata against Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense

Dichloromethane extracts of the root bark and stem bark of Kigelia pinnata collected from Zimbabwe exhibited antitrypanosomal activity against Trypanosoma brucei brucei in vitro. Activity-guided fractionation led to the isolation of four naphthoquinones from both the root and stem bark of the plant. The compounds were identified as 2-(1-hydroxyethyl)-naphtho[2,3-b]furan-4,9-quinone (1), isopinnatal (2), kigelinol (3), and isokigelinol (4). Subsequently, the compounds were assessed for antitrypanosomal activity against T. brucei brucei and T. brucei rhodesiense bloodstream form trypomastigotes in vitro. Compound 1 with a furanonaphthoquinone structure was found to possess pronounced activity against both parasites with IC50 values of 0.12 and 0.045 microM, respectively, although it was less active than the standard drug pentamidine. Compounds 2, 3, and 4 also exhibited activity against the parasites, although to a lesser extent. The activities of the compounds were further assessed by comparison with the cytotoxic activities obtained against KB cell lines.