New triterpenoid saponins from the whole plants of Clematis heracleifolia

Three new triterpenoid saponins, heracleifolianosides A-C (1-3), together with seven known compounds (4-10), were isolated from the whole plants of Clematis heracleifolia. Moreover, three new secondary saponins (1a, 2a and 3a), two known secondary metabolites (5a and 7a) were obtained by alkaline hydrolysis. Their structures were elucidated by extensive spectroscopic analysis and chemical evidences. The cytotoxicity of eight native saponins and five prosapogenins against human breast tumor MDA-MB-231 and gastric carcinoma SGC-7901 cell lines were evaluated by MTT method. Remarkably, the prosapogenin monodesmosidic saponin 7a showed significant cytotoxicity against MDA-MB-231 or SGC-7901 cell lines with IC₅₀ values in the range of 6.05-6.32 μmol/L. It is suggested that it might be a feasible way to change the inactive bisdesmosic triterpenoid saponins to active monodesmosic saponins by a simple procedure of alkaline hydrolysis.