Two New Cytotoxic Spirostane-Steroidal Saponins from the Roots of Bletilla striata

Two new spirostane-steroidal saponins, bletilnoside A (1) and bletilnoside B (2), together with five known compounds, 3-7, were isolated from the roots of Bletilla striata (Thunb.) Reichb. F. The structures of the new compounds were determined based on their 1D- and 2D-NMR spectral data. The isolated compounds 1-7 were tested for cytotoxicity against four human tumor cells (A549, SK-OV-3, SK-MEL-2, and HCT15) in vitro using a sulforhodamin B bioassay, and compounds 1, 2, and 5 showed significant cytotoxicities against all tested tumor cell lines with IC50 values ranging from 3.98 +/- 0.16 to 12.10 +/- 0.40 mu M.