New cytotoxic 19-norbufadienolide and bufogargarizin isolated from Chan Su

One new 19-norbufadienolide (1) and one new bufogargarizin (2), together with twelve known bufadienolides (3-14, resp.) were isolated from Chan Su, a traditional Chinese medicine that is used in the treatment of cancer. Their structures were elucidated on the basis of detailed spectroscopic analysis and comparison of corresponding data that is previously reported. The cytotoxic activities of the isolated compounds were evaluated on HeLa and A549 cell lines. Though 1 and 2 showed weak cytotoxic activities on both cell lines, compounds 4 and 5 showed lower IC50 values than bufalin, the most widely studied bufadienolide in Chan Su. Furthermore, four 3-ester derivatives (15-18) of compound 4 were synthesized and their cytotoxic activities were also evaluated. Analysis of the structure-activity relationship indicated that bufadienolides with aldehyde group at C-10 or α-hydroxyl group at C-11 exhibit stronger cytotoxic activities on both cell lines. The cytotoxic activity of arenobufagin-3-ester derivative 17 was 4-fold higher than compound 4.