Simplified preparation of the ginsenoside-Rh2 minor saponin from ginseng

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-Rh2. The 12-O-acetyl-20(S)-protopanaxadiol is easily prepared from betulafolienetriol via the 3-keto-12-O-acetylderivative followed by NaBH4 reduction. This comparatively simple five-step synthesis makes this hitherto rare ginsenoside relatively accessible.