New cytotoxic flavonoids from Thelypteris torresiana

During our search for anti-tumor agents from pteridophytes, three new flavonoids, protoapigenone (1), 5',6'-dihydro-6'-methoxyprotoapigenone (2), and protoapigenin (3), along with four known compounds, protoapigenin 4'-O-beta-D-glucoside (4), apigenin 4'-O-beta-D-glucoside (5), kaempferol 3-O-alpha-L-rhamnopyranoside (6), kaempferol 3,7-di-O-alpha-L-rhamnopyranoside (7), were isolated from Thetypteris torresiana using bioactivity-guided fractionation methods. The structures of the new isolates were elucidated by 1D- and 2D-NMR spectral analysis. Among the 7 compounds, protoapigenone (1) exhibited significant antitumor activities toward Hep G2, Hep 3B, MCF-7, A549, and MDAMB-231 with IC50 values of 1.60, 0.23, 0.78, 3.88 and 0.27 mu g/mL, respectively.