Cytotoxic biflavonoids from Selaginella delicatula

Four new biflavonoids-robustaflavone 4'-methyl ether (1), robustaflavone 7,4'-dimethyl ether (2), 2 ",3 "-dihydrorobustaflavone 7,4', -dimethyl ether (3), and 2 ",3 "-dihydrorobustaflavone 7,4', 7 "-trimethyl ether (4)-as well as two known biflavonoids, robustaflavone and amentoflavone, and three caffeoylquinic acids, 3,5-di-O-caffeoylquinic acid, 3,4-di-O-caffeoylquinic acid, and 4,5-di-O-caffeoylquinic acid, were isolated from Selaginella delicatula. The structures of the new compounds were established by spectroscopic analysis and chemical modification. The cytotoxic activity of these compounds on various tumor cell lines was evaluated, and both compounds 1 and 3 significantly suppressed the growth of Raji and Calu-1 tumor cell lines.