Oleanane-type saponin

Astragalus genus is one of the richest source of cycloartane saponins. Oleanane type saponins are also found in Astragalus sp., but their occurrence is limited to structures common to Leguminosae. Fig (3) shows the naturally occurring cycloartanes and oleananes which have been isolated from different Astragalus species. 

Several natural products are known to modify the sense of sweet taste. Such compounds can be either sweetness inhibitors or sweetness inducers/enhancers. A review of Suttisri et al., 1995 summarizes data on phytochemistry and biological activity of more than 40 triterpenoid sweetness inhibitors based on the oleanane and dammarane skeletons. These saponins were isolated from the leaves of Gymnema sylvestre, Zizyphus jujuba and Hovenia dulcis [224]. Recently, antisweet oleanane-type saponins were isolated from Stephanotis lutchuensis vm. japonic a [225]. 

Glycyrrhetin from licoris have been well known as an oleanane type saponin which having the anti-tumor-promoting activity, and in our... 

Furthermore, from the knots of Wistaria brachybotrys, several kinds of oleanane type saponins (101 - 108) were isolated together with isoflavonoids. Of these saponins, wistariasaponins A, Bl, B2, C, D and G were found to be novel saponins, and their structures of sapogenols were elucidated by the long-range COSY spectra and difference NOE... 

Some oleanane-type saponins isolated from G. sylvestre exhibited antisweetness acti-vity/ When chewed, the leaves produce a prolonged desensitization effect for sweet and bitter tastes. The sour taste is not affected, while the salty taste is very slightly affected. The saponin fraction, and ethanolic extract of the leaves, showed significant antibacterial and antifungal activities. The aqueous extract of G. hestre possessed hypoglycemic activity. The leaf powder stimulates the heart and the circulatory system, increases the secretion of urine, and activates the uterus. 

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). 

I The saponins isolated in the plant possess aglycones of three skeletons cycloartane, ursane and oleanane, with some variation in each structure—type. It s very interesting to discover such cycloartane-type saponins, that its side-chain has been modified naturally to conjugated diene-carboxylic acid, which formed amide with 2 -amino-3, 4 -dimethyl-y-lactone moiety. 

Matsuda H, Morikawa T, Ueda H, Yoshikawa M (2001) Medical foodstuffs. XXVII. Saponin constitutes of gotu kola(2) structures of new ursane-and oleanane-type triterpene oligogly-cosidase, centell. Chem Pharm Bull 49 1368-1371... 

Morikawa T, Miyake S, Miki Y, Ninomiya K, Yoshikawa M, Muraoka O (2012) Quantitative analysis of acylated oleanane-type triterpene saponins, chakasaponins I-III and florathea-saponins A-F, in the flower buds of Camellia sinensis from different regional origins. J Nat Med 66 608... 

Yoshikawa M, Monkawa T, Nakamura S et til (2(X)7) Bioactive saponins and glycosides. XXV.l) Acylated oleanane-type triterpene saponins from the seeds of tea plant (Camellia sinensis). Chem Pharm Bidl 55 57-63... 

Glycyrrhizin has been found to concentrate in the woody parts of the thickened root and stolon of G. glabra. Betulinic acid and soya-saponins have been previously reported from G. glabra cell cultures. Recently, soyasapo-nins (oleanane-type triterpene glycosides) have been reported in all parts of the intact plant, especially the seeds and young roots, particularly rootlets. ... 

Marsileagenin A (750) which is a hexahydroxylated oleanane type triterpene is a major sapogenol of the saponins obtained from Marsilea-minuata (Marsileaceae) 409), Such highly oxidized triterpenes are quite unusual in ferns though they occur frequently in seed plants. 

Interestingly novel sweet-tasting saponins based on the cycloartane (from Abrus precatorius), oleanane (from Periandra dulcis), secodammarane (from Pterocarya paliurus) and steroid saponin types (from Polypodium glycyrrhiza) have been reported [226, 227]. These compounds which have been demonstrated safe were rated by a human taste panel as about 50 and 100 times sweeter than 2% sucrose respectively [227]. ... 

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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