Synthesis of flaccidoside II, a bidesmosidic triterpene saponin isolated from Chinese folk medicine Di Wu

A total synthesis of flaccidoside II, 3-O-α-l-rhamnopyranosyl-(1→2)-β-d-xylopyranosyloleanolic acid 28-O-α-l-rhamnopyranosyl-(1→4)-β-d-glucopyranosyl-(1→6)-β-d-glucopyranoside, isolated from Chinese folk medicine Di Wu, has been accomplished from building blocks isopropyl 2-O-acetyl-3,4-di-O-benzoyl-1-thio-β-d-xylopyranoside, 2,3,4-tri-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate, oleanolic acid trityl ester, ethyl 2,3-di-O-acetyl-6-O-benzoyl-1-thio-β-d-glucopyranoside and 4-methoxyphenyl 2,3,4-tri-O-acetyl-β-d-glucopyranoside. The use of a partially protected thioglycosyl donor significantly simplified the synthesis of the target saponin.

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