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.