Concise synthesis of two trisaccharides related to the saponin isolated from Centratherum anthelminticum

Chemical synthesis of two trisaccharides related to the saponin isolated from Centratherum anthelminticum is reported. Stereoselective, high-yielding glycosylation strategies were developed using H2SO4 immobilized on silica for activation of trichloroacetimidate donors, or in conjunction with N-iodosuccinimide for activation of a thioglycoside. A late stage TEMPO-mediated oxidation was performed for the formation of the required uronic acid moiety.