Antiplasmodial Quinones from Pentas longiflora and Pentas lanceolata

The dichloromethane/methanol (1 : 1) extracts of the roots of Pentas longiflora and Pentas lanceolata showed low micromolar (IC50 = 0.9-3 micrograms/mL) in vitro antiplasmodial activity against chloroquine-resistant (W2) and chloroquine-sensitive (D6) strains of Plasmodium falciparum. Chromatographic separation of the extract of Pentas longiflora led to the isolation of the pyranonaphthoquinones pentalongin (1) and psychorubrin (2) with IC50 values below 1 µg/mL and the naphthalene derivative mollugin (3), which showed marginal activity. Similar treatment of Pentas lanceolata led to the isolation of eight anthraquinones (4-11, IC50 = 5-31 µg/mL) of which one is new (5,6-dihydroxydamnacanthol, 11), while three - nordamnacanthal (7), lucidin-ω-methyl ether (9), and damnacanthol (10) - are reported here for the first time from the genus Pentas. The compounds were identified by NMR and mass spectroscopic techniques.