Simplified Preparation of the Ginsenoside-Rh2 Minor Saponin from Ginseng.

Abstract Condensation of the 12- O -acetylderivative of 20(S)-protopanaxadiol [dammar-24-ene-3β,12β,20(S)-triol] with tetra- O -acetyl-α- d -glucopyranosyl bromide in the presence of silver oxide in dichloroethane, followed by deprotection with sodium methoxide in methanol, results in formation of the 3- O -β- d -glucopyranosyldammar-24-ene-3β,12β,20(S)-triol identical with natural ginsenoside-Rh 2 . The 12- O -acetyl-20(S)-protopanaxadiol is easily prepared from betulafolienetriol via the 3-keto-12- O -acetylderivative followed by NaBH 4 reduction. This comparatively simple five-step synthesis makes this hitherto rare ginsenoside relatively accessible.