Synthesis of the trisaccharide portion of soyasaponin βg: evaluation of a new glucuronic acid acceptor Original Research Article

The synthesis of the trisaccharide portion of soyasaponin βg was successfully achieved using a new glucuronic acid acceptor: methyl 1-O-allyl-3,4-di-O-methoxymethyl-β-d-glucuronate (9). This compound and methyl 1-O-allyl-3,4-di-O-tert-butyldimethylsilyl-β-d-glucuronate (8) were both prepared from glucuronolactone via a glycal intermediate. The former compound 9 was successfully coupled to ethyl 2-O-benzoyl-3,4,6-tri-O-benzyl-1-thio-β-d-galactopyranoside (13) in excellent yield. Synthesis of the protected trisaccharide was then completed by the addition of a suitably protected rhamnose derivative to the disaccharide portion. The reactivity of the glucuronic acid derivative 9 was also explored with trichloroacetimidate and fluoride donors.