Facile synthesis and cytotoxicity of triterpenoid saponins bearing a unique disaccharide moiety: hederacolchiside A1 and its analogues

An improved synthetic approach toward hederacolchiside A1, an antitumor triterpenoid saponin bearing a unique disaccharide moiety, was established. This approach began from a partially protected intermediate and avoided tedious protection–deprotection manipulation. An abnormal ring conformation (1C4) of the center arabinose residue was found in the intermediate, which may account for the unusual regioselectivity between 3-OH and 4-OH of arabinose. Two analogues of hederacolchiside A1 were then facilely prepared by this approach and exhibited significant cytotoxicity in preliminary in vitro assay.