Studies on Absorption, Distribution, Excretion and Metabolism of Ginseng Saponins. VII. Comparison of the Decomposition Modes of Ginsenoside-Rb_1 and -Rb_2 in the Digestive Tract of Rats

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In order to clarify some similarities and differences of decomposition modes between 20(S)-protopanaxadiol (20(S)-ppd) saponins, represented by ginsenoside Rb_1 (Rb_1) and ginsenoside Rb_2 (Rb_2), the devompositions of Rb_1 and Rb_2 in the rat gastrointestinal tract, 0.1 N NCl and crude hesperidinase were investigated in detail. As in the case of Rb_2 reported previously, Rb_1 was hydrolyzed to 20(R, S)-ginsenoside Rg_3 in 0.1 N HCl. On the other hand, hydroperoxidation of Rb_1 occurred in rat stomach; the major hydroperoxide was separated and identifed as the 25-hydroperoxy-23-ene derivative of Rb_1 (VIII) by ^1H- and ^<13>C-nuclear magnetic resonance and fast atom bombardment mass spectrometry. The decomposition modes of 20(S)-ppd saponins (Rb_1 and Rb_2) differed from that of 20(S)-protopanaxatriol saponin (Rg_1) in rat stomach. In rat large intestine, five decomposition products of Rb_1 were observed by thin-layer chromatography, and these were identified as gypenoside XVII (G-XVII), ginesenoside Rd (Rd), ginsenoside F_2 (F_2), compound K (C-K) and VIII. The decomposition modes of Rb_1 and Rb_2,both 20(S)-ppd saponins, are considered to be different because of the hydrolysis rate in the terminal sugar moiety at the C-20 hydroxyl group in the rat large intestine. Using crude hesperidinase, Rb_1 was decomposed to G-XVII, F_2 and C-K, and Rb_2 was decomposed to 3-O-β-D-glucopyranosyl-20-O-[α-L-arabinopyranosyl(1→6)-β-D-glucopyranosyl]-20(S)-ppd, F_2 and C-K. Consequently, it appears that hydrolysis by β-glucosidase, which is present in the rat large intestine, is distinct from that by crude hesperidinase. Tetracycline-resistant bacteria decomposed both Rb_1 and Rb_2 to their respective prosapogenins, except for Rd, and their respective hydroperoxides, while Rd and hydroperoxides of Rb_1 and Rb_2 were produced by enteric enzymes.

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  • Chem. Pharm. Bull.

    Chem. Pharm. Bull. 39 2357-2361, 1991

    公益社団法人日本薬学会

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