Activity of extracts and naphthoquinones from Kigelia pinnata against Trypanosorna 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 Trypano soma brucei brucei in vitro. Activity-guided fractionation led to the isola tion 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). Subseq uently, 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 pos sess pronounced activity against both parasites with IC50 values of 0.12 an d 0.045 mu M, respectively, although it was less active than the standard d rug pentamidine. Compounds 2, 3, and 4 also exhibited activity against the parasites, although to a lesser extent. The activities of the compounds wer e further assessed by comparison with the cytotoxic activities obtained aga inst KB cell lines.