Facile synthesis of four natural triterpene saponins with important antitumor activity

摘要

The first synthesis of four natural triterpene saponins, which exhibit significant antitumor activities, was concisely achieved by adopting a stepwise glycosylation. The key intermediate 13 was afforded via Bu2SnO-mediated regioseletive benzoylation. During the preparation of the target compounds, it was found that the α-L-arabinopyranosyl unit in intermediates 17 and 20 existed in the unusual ~1C_4 conformation, and after removing the benzoyl groups, the α-L-arabinopyranosyl unit was normal in a typical ~4C_1 form.