Cytotoxic flavonoids from Platymiscium floribundum

Two new isoflavonoids, 7-hydroxy-6,4'-dimethoxy-isoflavonequinone (1) and 2'-hydroxy-6,4',6",4"'-tetramethoxy-[7-O-7"]-bisisoflavone (2), and seven other known flavonoids, 3-hydroxy-9-methoxypterocarpan (medicarpin), 3,10-dihydroxy-9-methoxypterocarpan, 3,9-dimethoxypterocarpan (homopterocarpin) (3), 2,3,9-trimethoxypterocarpan (4), 3,4-dihydroxy-9-methoxypterocarpan (vesticarpan) (5), 2',4,4'-trihydroxychalcone (isoliquiritigenin), and 7,4'-dihydroxyflavanone (liquiritigenin) (6), were isolated from the heartwood of Platymiscium floribundum. The structures of compounds 1 and 2 were established by spectroscopic methods. Compounds 3-6 showed cytotoxic activity when evaluated against five human cancer cell lines in vitro.