On acid hydrolysis with boiling diI. mineral acid, Ginseng samnins, ginsenoside-Rb_1, -Rb_2, and-Rc, afforded panaxadiol (I), which was also obtained from protopanaxadiol (III) (=12-β-hydroxydammarendiol-I), by the acid treatment, whereas, treatment of these saponins with cold conc. HCl, a chloride (II) was formed. By the action of diethylaniline or silica gel, this chloride gave a mixture of III and isoprotopanaxadiol (IV), while t-BuO^- afforded mostly protopanaxadiol (III). This anomalous orientation of these elimination reactions would be due to the anchimeric assistance of C-20 -OH or O^-. Acid catalyzed epimerization of C-20 OH of betulafolienetriol (VI) (=3-epi-12β-hydroxydammarenediol-II) and betulafolianetriol (VIII) has been examined (see Fig. 2). Conversion of VIII to dihydroprotopanaxadiol (XI) has been achieved, and it has been confirmed that panaxadiol (I) has the same C-20 configuration as that of protopanaxadiol (III). The absolute configuration of C-20 of panaxadiol (I) has been established to be R by correlation with (-)-R-linalool (XIX) as shown in Fig.3. Consequently, it can be now concluded that the absolute configuration of C-20 of dammarenediol-I (XVII) as well as that of protopanaxadiol is represented as R, then that of dammarenediol-II (VII) and betulafolienetriol (VI) and their homologs is S configuration.
