Dammarane-type triterpene saponins

Dou, D.-Q., Chen, Y.-J., Liang, L.-H., Pang, F.-G., Shimizu, N., and Takeda, T. (2001). Six new dammarane-type triterpene saponins from the leaves of Panax ginseng. Chem. Pharm. Bull. 49, 442-446. 

Yoshikawa, M., Murakami, T., Ueno, T., Yashiro, K., Hirokawa, N., Murakami, N., Yamahara, J., Matsuda, H., Saijoh, R., and Tanaka, O. (1997b). Bioactive saponins and glycosides. Vlll. Notoginseng (1) New dammarane-type triterpene oligoglycosides, Notoginsenosides-A, -B, -C, and -D, from the dried root of Panax notoginseng (Burk.) F. H. Chen. Chem. Pharm. Bull. 45,1039-1045. 

Treatment of (11) with cone. HCl at room temperature yielded (10). Furthermore, catalytic hydrogenation of the saponin mixture in ethanol-acetic acid followed by hydrolysis with dilute mineral acid did not yield (1) but afforded the dihydro derivative (12). This evidence indicated that (1) and (10) must be artifacts formed during the process of acid hydrolysis thus, at that stage, the genuine sapogenin seemed to be substance (11) which was named protopanaxadiol (9,10,11). However, as will be described later, investigation of the acid-catalyzed isomerization of dammarane type triterpenes and subsequent study of the mild hydrolysis of the purified... 

N-Trimethylsilylimidazole readily trimethylsilylates even the hindered 20-hydroxyl 49). Besides ions B and B, TMSi ethers of dammarane type triterpenes of their saponins having a free hydroxyl group at c-20 show the characteristic strong ions A and C (see Chart 11) which are also useful criteria for the absence of a glycosyl linkage at c-20. 

Chemical studies on most of these Panax spp. have only been carried out recently. The saponins of Group A species are mainly oligoglycosides of dammarane type triterpenes, while the rhizomes of Group B contain large amounts of the common oleanolic acid saponins (C-V etc. Table III) along with dammarane saponins which are characteristic of each species. 

Haemolytic activities of Ginseng saponins have been reported 194, 195) and cytotoxic activities of dammarane type triterpenes have been investigated 196). Of interest also is a Ginseng abuse syndrome 197) which was commented upon at the third International Ginseng Symposium in Seoul, Korea. 

Ohsawa, T., N. Tanaka, O. Tanaka, and S. Shibata Chemical Studies on the Oriental Plant Drugs XXIX. Saponins and Sapogenins of Ginseng Further Study on the Chemical Properties of the Side Chain of Dammarane Type Triterpenes. Chem. Pharm. Bull. (Japan) 20, 1890 (1972). 

FIGURE 1.4 Proposed biosynthetic route for the biosynthesis of (A) squalene oxide (squalene-2,3-oxide) via the isoprenoid pathway and (B) triterpene saponins of the dammarane-type and oleanane-type from squalene oxide. PP, diphosphate group GPS, geranyl phosphate synthase FPS, farnesyl phosphate synthase NADPH, nicotinamide adenine dinucleotide phosphate. 

Dammarane derivatives. Besides the isolation of oleanane -type triterpene glycosides several new dammarane-type saponins designated... 

A number of non-proteinaceous substances of plant origin are known that induce or inhibit the sensation of sweetness. Sweetness inducers and enhancers from plants include cynarin, chlorogenic acid, caffeic acid, and arabinogalactin (larch gum) (33). A synthetic compound, 2-(4-methoxyphenoxy)propanoic acid, which is also a constituent of roasted coffee beans, is currently on the market as a sweetness inhibitor (33). Several oleanane-type triterpene esters with sweetness-inhibitory activity occur in Gynmema sylvestre leaves (33,116,117), with dammarane-type saponins with similar effects having been reported recently from the leaves of Hovenia dulcis Thunb. (Rhamnaceae) (118) and Ziziphusjujuba Mill. (Rhamnaceae) (33,119,120). 

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. 

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