Two new bufadienolides from the rhizomes ofHelleborus thibetanuswith inhibitory activities against prostate cancer cells

Two new bufadienolide glycosides (1 and 2) with an A/B trans ring fusion together with nine known compounds (3-11) were isolated from the rhizomes of Helleborus thibetanus. The structures of new compounds were elucidated by extensive spectroscopic analyses in combination with single-crystal X-ray diffraction. The bufadienolides 1 and 3-6 exhibited potent cytotoxic activities against the prostate cancer cells.