Structure of saponins

An essential prerequisite for deducing the structures of saponins by NMR spectroscopic studies is the unambiguous assignment of H and 13C... 

Chart 9. Structure of Saponin constituents from Kidny Bean... 

Structures of Saponins (1-9) from Aralia spittifolia and Nothopanax davidii... 

Table 2. Structure of Saponins (GlcA = Glucuronopyranosyl, Glu = Glucopyranosyl, Api = Apiofuranosyl, Ara = Arabinopyranosyel, Gal = Galactopyranosyl, Rha = Rhamnopyranosyl, Xyl = Xylopyranosyl)...

The different plant source and structure of saponins, structure of algycone, length and position of sugar moiety may contribute various activities toward bacteria, fungi, protozoa and further studies are warranted. 

Figure 12.1 Basic structures of saponins (a) triterpene saponin QS-21 from Quillaya saponaria (b) steroidal saponin from Yucca schidigera (c) hederagenin glycoside from Sapindus mukurossi (d) soyasaponin I from soybean (Glycine max).

Saponins. Although the hypocholesterolemic activity of saponins has been known since the 1950s, thek low potency and difficult purification sparked Htde interest in natural saponins as hypolipidemic agents. Synthetic steroids (292, 293) that are structurally related to saponins have been shown to lower plasma cholesterol in a variety of different species (252). Steroid (292) is designated CP-88,818 [99759-19-0]. The hypocholesterolemic agent CP-148,623 [150332-35-7] (293) is not absorbed into the systemic ckculation and does not inhibit enzymes involved in cholesterol synthesis, release, or uptake. Rather, (293) specifically inhibits cholesterol absorption into the intestinal mucosa (253). As of late 1996, CP-148,623 is in clinical trials as an agent that lowers blood concentrations of cholesterol (254). 

There has been considerable discussion regarding the mode of action of the sea cucumber and starfish saponins. Both the triterpene and steroidal glycosides inhibit both Na/K ATPase and Ca/Mg ATPase 06) possibly as a result of their aglycone structures. However, their detergent properties cause membrane disruption which will influence the activity of membrane-bound enzymes such as the ATPases. In investigating the actions of saponins on multilamellar liposomes, it was found that cholesterol serves as the binding site for such saponins and that cholesterol-free lip-somes are not lysed by saponins 107). 

COSTELLO, C.E., Application of tandem mass spectral approach to structural determination of saponins. In Advances in Experimental Medicine and Biology (G. R. Waller and K. Yamaski, eds.), 405, Plenum Publishing, New York. 1996, pp. 317-329... 

Saponins are glycosylated secondary metabolites that are widely distributed in the Plant Kingdom.3,4 They are a diverse and chemically complex family of compounds that can be divided into three major groups depending on the structure of the aglycone, which may be a steroid, a steroidal alkaloid, or a triterpenoid. These molecules have been proposed to contribute to plant defense.3 6 Saponins are also exploited as drugs and medicines and for a variety of other purposes.4 Despite the considerable commercial interest in this important group of natural products, little is known about their biosynthesis. This is due in part to the complexity of the molecules, and also to the lack of pathway intermediates for biochemical studies. 

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. 

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. 

Fig. 2.1 Strucnires of some common saponins. The strucnires of some of the saponins described in the text are shown, including aescin from horse chesnut, avenacin A-1 and avenacoside A from oat, and a-tomatine from tomato. The glucose molecule enclosed in square brackets in the structure of avenacoside A highlights the glucose moiety that is cleaved off by hydrolysis by glycosidases in disrupted oat leaf tissue, leading to the fungitoxic 26-desglucosyl avenacoside A. Redrawn from [94]...

CS021 Murakami, T., J. Nakamura, H. Mat-suda and M. Yoshikawa. Bioactive saponins and glycosides. XV. Saponin constituents with gastroprotective effect from the seeds of tea plant, Camellia sinensis L. var. assamica Pierre, cultivated in Sri Lanka structures of assamsaponins A, B, C, D and E. Chem Pharm Bull 1999 47(12) 1759-1764. 

The distribution and structural elucidation of saponins have been reviewed. Glucuronides with a free carboxy-group and carbohydrate residues at C-2 and C-4 are readily cleaved with acetic anhydride in refluxing pyridine to give the genuine aglycone (see Vol. 7, p. 145). Details of the mass spectra of a series of permethylated oleanane saponins have been discussed. 

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. 

The numerous biological activities of saponins, as well as their widespread occurrence in the plants and the hundreds structures described so far, prompted the development of a strategy for their rapid, highly sensitive and, if possible, non degradative, structure elucidation. 

Saponins are widely distributed in plants and are a particular form of glycosides. They are so-called because of their soaplike effect, which is due to their surfactant properties. They also have hemolytic properties and, when injected into the bloodstream, are highly toxic. When taken by mouth, saponins are comparatively harmless. According to the structure of the aglycone or sapo-genin two kinds of saponin are recognized, the steroidal and triterpenoid type. 

FIG. 4 Structure of representative saponins found in soybeans (triterpenoid) and eggplant (steroid). The R group represents one or more carbohydrate linkages that may contain rhamnose, xylose, arabinose, galactose, glucose, or glucuronic acid. 

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