Cytotoxic Biflavonoids from Selaginella braunii

A new biflavonoid, (2 '' S)-8 ''-C-methyl-2 '',3 ''-dihydrorobustaflavone-4 '-methyl ether (1) and 5 known robustaflavones (2-6) were isolated from the 70% EtOH extract of Selaginella braunii for the first time. The structures of 1 and the known compounds were identified by performing a comprehensive analysis of spectroscopic data including ultraviolet-visible, high-resolution electrospray ionization mass spectrometry, 1-dimensional and 2-dimensional nuclear magnetic resonance, and circular dichroism spectra. Compounds 1-6 were determined for cytotoxic activity against 3 human cancer cell lines (SMMC-7721, MCF-7, and A549). Compound 1 exerted apparent antiproliferative effects on SMMC-7721, MCF-7, and A549 cells, with IC50 values of 18.6, 16.7, and 25.5 mu M, respectively.