Synthesis of β-hederin and Hederacolchiside A1: triterpenoid saponins bearing a unique cytotoxicity-inducing disaccharide moiety

A facile synthetic approach toward oleanolic acid glycoside bearing α-l-rhamnopyranosyl-(1→2)-α-l-arabinopyranosyl moiety, a unique oligosaccharide that strongly induces antitumor activity of oleanane-type triterpenoid saponins, was developed. Based on this approach β-hederin (oleanolic acid 3-O-α-l-rhamnopyranosyl-(1→2)-α-l-arabinopyranoside) was efficiently prepared from oleanolic acid through stepwise glycosylation in linear eight steps with 52% overall yield, while Hederacolchiside A1 (oleanolic acid 3-O-α-l-rhamnopyranosyl-(1→2)-[β-d-glucopyranosyl-(1→4)]-α-l-arabinopyranoside) in linear 13 steps with 20% overall yield.

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