New cytotoxic biflavonoids from Selaginella delicatula

Five new biflavonoids, robustaflavone 7,4',4'''-trimethyl ether, robustaflavone 4,4'''-dimethyl ether, 2,3-diliydroamentoflavone 7,4',7"-trimethyl ether, 2,3-diliydroamentoflavone 7,4'-dimethyl ether, and 2",3'''-dihydroisocryptomerin 7-methyl ether, together with six known compounds have been isolated from the aerial parts of Selaginella delicatula. The structures of these new compounds were determined through spectral analyses. Among the isolates, robustaflavone 4',4'''-dimethyl ether, 2,3-dihydroamentoflavone 7,4'-dimethyl ether, and alpha-tocopheryl quinone exhibited cytotoxicities (ED50 values < 4 mu g/mL) against P-388 and/or HT-29 cell lines in vitro.