Studies on Absorption, Distribution, Excretion and Metabolism of Ginseng Saponins. VI. The Decomposition Products of Ginsenoside Rb₂ in the Stomach of Rats

Abstract

The decomposition of ginsenoside Rb₂ (Rb₂) in rat stomach (in vivo) and in 0.1 N HCl solution (in vitro) was investigated in detail. By treating with 0.1 N HCl, the acidity of which is similar to that of gastric juice, a part of Rb₂ was hydrolyzed to 20(R, S)-ginsenoside Rg₃. On the other hand, Rb₂ was little decomposed in rat stomach and a small quantity of an unidentified metabolite, which was different from the hydrolyzed products in 0.1 N HCl, was observed. The metabolite was separated into four compounds, which were identified by ¹H-and ¹³C-nuclear magnetic resonance and fast atom bombardment mass spectrometry. These compounds were determined to be 25-hydroxy-23-ene (IV), 24-hydroxy-25-ene (V), 25-hydroperoxy-23-ene (VI) and 24-hydroperoxy-25-ene (VII) derivative of Rb₂, respectively.In this study, it is suggested that 20(S)-protopanaxatriol saponins undergo hydrolysis of the C-20 glycosyl moiety and hydration of the side chain, on the other hand, 20(S)-protopanaxadiol saponins undergo oxygenation of the side chain.