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DOI: 10.1055/s-0032-1321293
Antiprotozoal isoflavan quinones from Abrus precatorius
A library of 309 extracts from selected South African plants was screened in vitro against a panel of protozoan parasites. A CH2Cl2/MeOH (1:1) extract of Abrus precatorius L. ssp. africanus Verdc. (Fabaceae) strongly inhibited Plasmodium falciparum (97.8%), Trypanosoma brucei rhodesiense (100%), and Leishmania donovani (75.5%) when tested at 4.8mg/mL. Active constituents were tracked by HPLC-based activity profiling, and isolated by RP-HPLC. Structures were established by HRMS and NMR. The absolute configuration was determined by comparison of electronic circular dichroism (ECD) spectra with calculated ECD data. Five compounds were obtained and identified as isoflavan quinones and hydroquinones, among them two new natural products. (3R)-8-hydroxy-7,3',5'-trimethoxyisoflavan-1',4'-quinone and (3R)-6,7,8,2',3'-penta-methoxyisoflavan-1',4'-quinone showed strong in vitro activity against T. brucei rhodesiense (IC50s of 0.30µM±0.1 and 0.16µM±0.1, respectively). Selectivity indices (SI) as calculated from cytotoxicity data in L-6 cells were 78.3 and 61.3.