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

A total synthesis of flaccidoside II, 3-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-xylopyranosyloleanolic acid 28-O-alpha-L-rhamnopyranosyl-(1-->4)-beta-D-glucopyranosyl-(1-->6)-beta-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-beta-D-xylopyranoside, 2,3,4-tri-O-benzoyl-alpha-L-rhamnopyranosyl trichloroacetimidate, oleanolic acid trityl ester, ethyl 2,3-di-O-acetyl-6-O-benzoyl-1-thio-beta-D-glucopyranoside and 4-methoxyphenyl 2,3,4-tri-O-acetyl-beta-D-glucopyranoside. The use of a partially protected thioglycosyl donor significantly simplified the synthesis of the target saponin.