Cytotoxic flavanes from Uraria clarkei.

Two new flavanes, (2R)-4'-hydroxy-2',5,7-trimethoxyflavane (1) and (2R,4R)-2',4'-dihydroxy-5,7-dimethoxyflavan-4-ol (2), were isolated from Uraria clarkei, together with two known compounds 5,7-dimethoxy-4'-hydroxyflavan (3) and 5,7,4'-trimethoxyflavan (4). The structures of the new flavanes were characterized by analyses of the MS, IR, UV, CD, 1D, and 2D NMR data. Cytotoxicity test suggested that compounds 1-4 possessed slight activity against K-562 and Hela cell lines, with the IC50 values ranging from 26.6 to 56.3 μM.