Cytotoxic activity of Pulsatilla chinensis saponins and their structure-activity relationship

The cytotoxic activity of 36 saponins isolated from roots of Pulsatilla chinensis (Bunge) Regel against the human cancer cell lines (A549, SGC-7901) and the human hepatic cell line (HL-7702) was tested by 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide assay. Saponins 1-14 showed considerable cytotoxic activity, whereas saponins 15-36 showed no significant activity, which suggested that a free carboxylic group located at C-28 of aglycon is essential for their cytotoxic activity. Moreover, the analysis of structure-activity relationships also suggested that the oleanane-type saponins showed better cytotoxic activity than lupane-type saponins, and the length and linkage of glycolic chain attached to C-3 of aglycon displayed an important effect to the potent cytotoxicity. In conclusion, oleanolic acid 3-O-α-l-rhamnopyranosyl-(1 → 2)-[β-d-glucopyranosyl-(1 → 4)]-α-l-arabinopyranoside (5) exhibited the most significant cytotoxic activity.