Fig. 3.
Epimerization of 20(S)-ginseng saponins to 20(R)-isomers in acid. The dehydration reaction produced a carbocation intermediate at C-20 of 20(S)-ginseng saponins. Upon rehydration, an oxonium ion was generated, resulting in the conversion of the configuration at C-20 and the creation of 20(R)-ginseng saponins.