Cytotoxic flavanones of Schizolaena hystrix from the Madagascar rainforest

Bioassay-guided fractionation of an ethanol extract of a Madagascar collection of Schizolaena hystrix afforded three new flavanones, schizolaenone A (1), schizolaenone B (2), and 4'-O-methylbonannione A (3), as well as three known flavanones, nymphaeol A, bonannione A, and macarangaflavanone B, and the flavanol bonanniol A. The structures of compounds 1-3 were determined by various one- and two-dimensional NMR techniques. All of the isolates were tested for cytotoxicity against the A2780 human ovarian cancer cell line. Nymphaeol A (IC(50) = 5.5 microg/mL) exhibited the greatest cytotoxicity, while the other flavanones were found to be only weakly active.