Synthetic Investigation toward D-ring Functionalized Cytotoxic Oleanane-Type Saponins Pitheduloside D and E

Leveraging on the orchestrated application of both Schmidt and Yu glycosylations, the first total syntheses of echinocystic acid saponins, pitheduloside D and E, the two antitumoral and representative D-ring functionalized oleanane-type saponins, were achieved. Benefited from the applied convergent synthetic strategy, the synthetic efficiency regarding the precious echinocystic acid could reach as high as 71% and 76% overall yields through 4 linear steps.