Two new bufadienolides from the rhizomes of Helleborus thibetanus Franch

Two new bufadienolides, named tigencaoside A(1) and tigencaoside B(2), were isolated from the rhizomes of Helleborus thibetanus Franch., along with two known bufadienolides, hellebrigenin (3) and 5beta,14beta-dihydroxy-19-oxo-3beta-[(alpha-L-rhamnopyranosyl)oxy]bufa-20,22-dienolide (4). Their structures were elucidated on the basis of extensive spectroscopic analysis. Two new compounds were evaluated for their cytotoxic activities against four strains of cultured tumor cells.