Methanolysis of triterpenoid saponin from Ardisia gigantifolia stapf. and structure–activity relationship study against cancer cells

Thirteen 13,28-epoxy triterpenoid saponins were isolated from Ardisia gigantifolia stapf. and one potential anti-tumor saponin was methanolysised by H2SO4 to afford four new compounds. The seventeen compounds were evaluated for their anti-proliferative activity on A549, HCT-8 and Bel-7402 cells. The structure–activity relationship analysis indicated that the incorporation of O group at C-16, l-rhamnose at R5 and acetyl group at OH-6 of the d-glucose lead to a significant increase of the cytotoxic activity on A549 and HCT-8 but significant reduction of the cytotoxic activity on Bel-7402 cells. The synthesized saponins losing 13,28-epoxy and CHO at C-30, losed their cytotoxicities on A549 and HCT-8 cells, suggesting that the two moieties play an essential role for activity. 3β-O-α-l-rhamnopyranosyl-(1→3)-[β-d-xylopyranosyl-(1→2)]-β-d-glucopyranosyl-(1→4)-[β-d-glucopyranosyl-(1→2)]-α-l-arabinopyranoside-16α-hydroxy-13,28-epoxy-oleanane (2) showed better inhibitory activity to Bel-7402 (IC50 0.86μM) than that of 5-FU (IC50 8.30μM), which indicate that five saccharide and methyl moiety at C-30 are important for anti-proliferative activity. The activities of saponins 15>14, 17>16, suggested that the configuration of 28,30-epoxy is preferable to be 30(R) rather than 30(S) on Bel-7402 cells. Further molecular mechanism studies of saponins 1 and 2 were carried out on the cell cycle distribution of Bel-7402 cells.