Structures of Ginseng Saponins

In Fig. I, TLC patterns of the saponin fraction and each saponin of Ginseng are illustrated. Up to now, eighteen saponins have been isolated from White Ginseng these are ginsenosides-Ro, -Rai -Ra2, -Ras -Rbj, 

Bu0H-Ac0Et-H20(4 l 2, upper layer) Plate Silica Gel 100 F254(Merck) 

Ginsenosides-Rbi, -Rb2 and -Rc purified by preparative TLC were hydrolyzed with 50% aqueous acetic acid at 70° From the methanol-insoluble fraction of each reaction mixture, a common prosapogenin (30) was obtained in crystalline form 24) which was identical with Kotake s a-panaxin 4) mentioned in Chapter II. Later, (30) was also obtained from Rd by the same treatment. 

The structure of (30) was elucidated as follows 19, 24). Mineral acid hydrolysis of (30) yielded (1) and glucose, while Smith degradation of (30) afforded an aglycone which was identical not with the genuine sapogenin (26) but with its 20 epimer (11). The IR spectrum (in CCU) of an octaacetate of (30) exhibited a concentration independent -OH band at 3542 cm which was characteristic of the intramolecular hydrogen bond 

On the aforementioned evidence, Rb, Rb2, Rc and Rd can be formulated as 20-o-glycosides of 3-o-P-sophorosyl-20(5)-protopanaxadiol. The isolation of Ginseng saponins on a preparative scale was accomplished 

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Zhou, J., Wu, M., Taniyasu, S., Besso, H., Tanaka, O., Saruwatari, Y., and Fuwa, T. (1981). Dammarane-saponins of Sanchi-ginseng, roots of Panax notoginseng (Burk.) F. H. Chen (Araliaceae) Structures of new saponins, notoginsenosides-Rl and -R2, and identification of ginsenosides-Rg2 and -Rhi. Chem. Pharm. Bull. 29, 2844-2850. 

As regards the chemical constituents of Panax spp., the presence of saponins in American Ginseng was reported as early as 1854 (7). Since the beginning of this century, a number of Japanese, European and Korean chemists have concerned themselves with isolation and structure elucidation of Ginseng saponins these include Asahina (2), Kondo (i), Kotake (4 Wagner-Jauregg (5), Horhammer (6) and their coworkers. However, even the basic skeleton of the major sapogenin was not characterized until 1960. 

Ginsenoside-Rb3, one of the minor saponins of Ginseng afforded (26) on Smith degradation and yielded (30), (34) and a biose (glucose-xylose) on partial hydrolysis. The structure of this saponin was established in the way described in the previous paragraph and is shown in Table I 31). 

Kondo, N., J. Shoji, and O. Tanaka Studies on the Constituents of Himalayan Ginseng, Panax pseudo-ginseng I. The Structures of the Saponins (1). Chem. Pharm. Bull. (Japan) 21, 2702 (1973). 

Sanada, S. and Shoji, J. (1978). Studies on the saponins of ginseng. III. Structures of ginsenoside-Rb3 and 20-glucoginsenoside-Rf. Chem. Pharm. Bull. 26,1694-1697. 

Yoshikawa, M., Murakami, T., Yashiro, K., Yamahara, J., Matsuda, H., Saijoh, R., and Tanaka, O. (1998). Bioactive saponins and glycosides. XI. Structures of new dammarane-type triterpene oligoglycosides, Quinquenosides 1, II, III, IV, and V, from American ginseng, the roots of Panax quinquefolium L. Chem. Pharm. Bull. 46, 647-654. 

Y. Nagai, O. Tanaka, and S. Shibata, Chemical studies on the Oriental plant drugs — XXTV Structure of ginsenoside Rgj, a neutral saponin of ginseng root. Tetrahedron 27, 811, 1971. 

Publications on the structure and analytical detection of saponins of Panax ginseng and the effect of ginseng on cholesterol synthesis and pyruvate kinase activity in rats have appeared. New saponins include ginsenosides Rhi (46) and... 

M7cd (47) from P. ginseng and chikusetsusaponins LT5, LTg, and LN4 from the leaves of P. japonicus The latter are 3,20-glycosides of (20S)-dammar-24-ene-3/3,20-diol-12-one (48). The full structures of hovenosides D, G, and I, saponins based on jujubogenin (49) from the root bark of Hovenia dulcis, have been elucidated. 

Panax spp., especially Panax ginseng, are purported to possess various health benefit qualities. In oriental countries it has been used as a traditional panacea for numerous health disorders for several centuries. Saponins are generally recognised as the main effective components of ginseng. Because of their close similarities in terms of structure they offer a real challenge to the analytical chemist in terms of separation. Furthermore, the relative complexity of their structures makes them perfect candidates for in-depth structural characterisation work by NMR. 

Since 1958, Shibata and his successors have conducted chemical studies on the saponins of the crude drug. After many twists and turns, it was determined that the major saponins of Ginseng were not oleanane oligoglycosides which are very common in nature, but that the genuine sapogenins were represented by triterpenes of the dammarane type. This was the first example of the occurrence of dammarane saponins in nature. The complications encountered in the isolation and structure determination were mainly due to an unexpected acid catalyzed epimerization of the tertiary hydroxyl group on c-20 of the carbon skeleton which was followed by cyclization of the side chain. This undesirable reaction accompanied acid hydrolysis of the saponins to the sapogenins. 

It followed that the same epimerization probably occurred during acid hydrolysis of the Ginseng saponins. The chloro compound (10) was obtained from the ether insoluble fraction of the crude hydrolysate of the saponin mixture with cone. HCl. The ether soluble fraction of the hydrolysate was subjected to dehydrochlorination to give an 20-epimer of (11) named 20(S)-protopanaxadiol (26) (Chart 2), the structure of which was elucidated by correlating it with (13) as follows. The dihydro derivative (27) of (26) was oxidized to give a diketone (28) which was identical with the diketone derived from (13) via (16) 16, 17, 19). Crystalline substances (1) and (12) of the 20(R)-series were also readily obtained from the less soluble fractions of the hydrolysates of the saponin mixture and from the hydrogenated saponin mixture, respectively, while the corresponding 20 ( S)... 

By means of the new techniques described in the preceeding chapter as well as the modern separation procedures described in Chapter VI, isolation and structure elucidation of the minor saponins of Ginseng were accomplished recently. 

IiDA, Y., O. Tanaka, and S. Shibata Studies on Saponins of Ginseng The Structure of Ginsenoside-Rgi. Tetrahedron Letters 1968, 5449 Nagai (n ee Iida), Y., O. Tanaka, and S. Shibata Chemical Studies on the Oriental Plant Drugs XXIV. Structure of Ginsenoside-Rgi, a Neutral Saponin of Ginseng Roots. Tetrahedron 27, 881 (1971). 

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