Chemical Studies on the Oriental Plant Drugs. XXVIII. Saponins and Sapogenins of Ginseng : Stereochemistry of the Sapogenin of Ginsenosides-Rb1, -Rb2 and -Rc

Abstract

The sapogenin of Ginseng saponins, ginsenosides-Rb₁, -Rb₂ and -Rc, was once reported to be protopanaxadiol (III). But it was found recently that dammarane type triperpenes with hydroxyl or methoxyl group at C₍₁₂₎ and C₍₂₀₎ give an equilibrated mixture of epimeric compounds at C₍₂₀₎. On mild hydrolysis of the saponins 20-epi-protopanaxadiol has been obtained as the genuine sapogenin for which the name of 20 (S)-protopanaxadiol (V) is proposed. The prosapogenin (XI), which was obtained by the partial hydrolysis of the above mentioned three saponins is found to be 3-O-(2β-D-glucopyranosyl-β-D-glucopyranosyl)-20 (R)-protopanaxadiol. The remaining glycosidic linkage in ginsenosides-Rb₁, -Rb₂ and -Rc should be located at C₍₂₀₎-OH.