27 薬用人参のサポニンの化学的研究 : 真性サポゲニンの問題とginsenoside-Rg_1の構造

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Previously, the sapogenin of ginsenosides-Rb_1, -Rb_2, and -Rc has been reported to be protopanaxadiol(II). However, the finding of the acid catalyzed epimerization of C-20 OH of this type of compounds has prompted the further investigation of C-20 configuration of the genuine sapogenin of these saponins. On Smith's degradation of these saponins, 20-epi-protopanaxadiol(IV) was yielded but formation of II was not observed. Accordingly, it can be now concluded that the genuine sapogens of the above saponins should be represented by IV. Ginsenoside-Rg_1, another saponin of Ginseng, has been purified through its deca-acetate. On hydrolysis with dil. mineral acid, -Rg_1 gave panaxatriol (and its C-20 epimer) (IX) and D-glucose. Treatment of-Rg_1 with conc. HCl followed by dehydrochlorination gave protopanaxatriol(X) as well as its C-20 epimer (XI), whereas Smith's degradation of-Rg_1 yielded XI only. The strucures of X and XI including C-20 configuration have been established as being 6α-bydroxy-protopanaxadiol and 6α-hydroxy-20-epi-protopanaxadiol, respectively. On the basis of the above evidences and other experimental results, -Rg_1 was represented by diglucoside of XI. Methanolysis of permethyl ether of -Rg_1 afforded methyl 2,3,4,6-tri-O-methyl-glucoside. Acid hydrolysis of permethyl ether of hydrogenated -Rg_1 yielded 3,12-di-O-methyl-dihydroprotopanaxatriol(XXII) (or its C-20 epimer). Consequently, -Rg_1 can be formulated as 6,20-di-O-D-glucosyl-20-epi-protopanaxatriol.
天然有機化合物討論会の論文
1967-09-25

27 薬用人参のサポニンの化学的研究 : 真性サポゲニンの問題とginsenoside-Rg_1の構造

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