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including chikusetsusaponin IVa, pseudoginsenoside RQ, malonyl-ginsenoside Rbi and the notoginsenosides A, C and K together with 5 new dammarane-type triterpene oligoglycosides named quinquenosides I-V. Four common polyacetylenic compounds and 6'-O-acetyl-ginsenoside-Rg1 were isolated from the corresponding methanolic extract. Further study of these compounds is essential as the extracts exhibit protective activity on hepatic injury induced in mice by D-galactosamine or lipopolysaccharide. Reported yields of individual saponins in Panax quinquefolium roots are summarised in Table 5.33.

Amongst other chemical components occurring in the roots are palmitic acid, oleanolic acid, daucosterin, sugars (sucrose and ginseng trisaccharide), polysaccharides and amino acids. Yuan and Ouyang (1993) reported that root cell cultures and roots yielded similar saponins and polysaccharides, roots producing 8.42 per cent total saponins and 15.02 per cent polysaccharides and cell cultures 7.12 per cent total saponins and 13.93 per cent polysaccharides.

Re-evaluation of the oil content of both Chinese-grown and American-grown P. quinquefolium roots by Zheng et al. (1989b) shewed a yield of 0.04-0.097 per cent and similarity in chemical content. Sesquiterpenes were shewn to comprise about 75 per cent of the oil (Shen et al., 1991). Nevertheless the composition can vary dependent on the extracting solvent e.g. 80 per cent methanol, diethylether.

As well as the common vital trace elements sodium, potassium, magnesium and calcium, P. quinquefolium roots contain, in order of decreasing amount, zinc (53.6 p.p.m.), barium, manganese (16.7 p.p.m.), titanium, lead (1.36 p.p.m.), chromium, cobalt, nickel and selenium (0.02 p.p.m.) (Liu et al., 1987). Larger amounts of trace elements occur in the aerial parts of the plant and rhizomes and fibrous roots yield more than the roots.

Saponins of Panax quinquefolium Stems and Leaves

Staba's team investigated the quantitative occurrence of saponins in the aerial parts of P. quinquefolium (Chen et al., 1981). The reported yields of the protopanaxadiol derived ginsenosides Rb3 and Rd were 0.1 and 0.2 per cent respectively; the protopanaxatriol derived ginsenoside Re occurred at 0.1 per cent yield and the ocotillol compound pseudoginsenoside F11 also formed 0.1 per cent.

Ma et al. (1993) discovered nine saponins viz. ginsenosides Rb2, Rb3, Rd, Re, Rg1, Rh1, Rh 2, F2 and pseudoginsenoside Fu in the stems and leaves of P. quinquefolium. Ginsenosides Rh1, Rh2 and F2 had not previously been located in this species. Li and his coworkers (1996b) reported 1.33-2.64 g total ginsenosides per 100 g of dried leaves for 1 month-old leaves and 4.14-5.58 g per 100 g dried leaves for mature 4 month-old leaves. The principal ginsenosides were Rd and Re, each accounting for about 40 per cent of the total ginsenosides.

The leaves also yield polysaccharides, one of which was isolated by Miao et al. (1993); water-soluble polysaccharide PN had a molecular weight of 7400 and comprised main chains of ^-(1^4(-linked glucose with 25 per cent of the main chains having sidechains at O-6 with a branching rate of 47.8 per cent.

The seed oil of P. quinquefolium contains sterols as the main unsaponifiable lipid fraction unlike P. ginseng seed oil which yields predominantly squalene (54%) in the unsaponifiable lipid fraction. Significantly the sterol fractions were different, P. ginseng yielding 28-isofucosterol (40%) and P. quinquefolium 24-ethyl-22E-dehydrocholesterol (66%) (Matsumoto et al., 1986).

(General reference sources for P. quinquefolium saponins:- Shoji, 1985 and references therein; Thompson, 1987 and references therein; Tang and Eisenbrand (1992); for chemical nomenclature see Appendix to Chapter 5).

5) Panax trifolium L.

The roots of P. trifolium were shewn to yield the ginsenosides Re (0.0005%), Rf (0.0008%), Rg1 (present), Rg2 (0.0008%) and Ro (0.0004%). Investigating the leaves of this species Lui and Staba (1980) noted high concentrations of oleanane Ro-ginsenosides and panaxadiol ginsenosides and Lee and Der Marderosian (1988) reported the presence of ginsenosides Rb3, Rc and Rd and notoginsenoside Fe as well as the flavonoids kaempferol-3,7-dirhamnoside and kaempferol-3-gluco-7-rhamnoside. Thus the common aglycones were (20S)-protopanaxadiol and kaempferol. Subsequent work revealed the presence of ginsenosides Rb1, Rb2, Rb 3, Rc, Rd and Ro and notoginsenoside Fe.

6) Panax vietnamensis Ha et Grushv.

This species entered the chemical literature when Lutomski (1992) published a review of the taxonomy, chemical composition and therapeutic action of a new species of Panax from Vietnam. His group had discovered seven polyacetylene compounds including two main compounds, falcarinol and heptadeca-1,8

fE/)-diene-4,6-diyne-3,10-diol, and also some isomers of the latter (Lutomski and Luan, 1991). Falcarinol. a substance related to allergic contact dermatitis, had earlier been isolated from other Araliaceous species e.g. Hedera helix L. and related ivy species, Schefflera arboricola (Boll et al., 1987).

Another team including Duc and Tanaka (1993-1994) investigated the occurrence of saponin glycosides isolating known dammarane glycosides including ginsenosides Rb1, Rb2, Rb 3, Rc, Rd, Re, 20-gluco-ginsenoside Rf, ginsenosides Rg1, and Rh1, 20(R)-ginsenoside Rh1, pseudoginsenoside RS1 (=monoacetyl-ginsenoside Re), gypenoside XVII, quinquenoside R1, majonoside F1 and notoginsenosides R1, R6 and Fa. The ocotillol type saponins detected were pseudoginsenoside RT4, 24(S)-pseudoginsenoside F11 and majonosides R1 and R2. Oleanolic type glycosides included ginsenoside Ro and hemsloside Ma3, a glycoside previously isolated from the Cucurbitaceous plant Hemsleya macrosperma. The subterranean plant parts yielded mainly dammarane glycosides with a small amount of oleanolic saponins. However, the yield of majonoside R2 the principal glycoside present, was conspicuously high being >5 per cent and comprised about 50 per cent of the total saponins.

Additional new compounds discovered were the vina-ginsenosides R1 to R14. Vina-ginsenoside R1 was shewn to be monoacetyl-24(S)-pseudoginsenoside F11 and vina-ginsenoside R2 was monoacetyl-majonoside R2. Vina-ginsenoside R3 is the first reported naturally-occurring dammarendiol and vina-ginsenosides R5 and R 6 are ocotillol-type saponins revealing the rare -glucosyl unit (Nguyen et al., 1994).

Apart from polyacetylenes and saponins these plants also yielded the sterol ^-sitosteryl-3-O-^-D-glucopyranoside.

Future Propects

It is inevitable that more chemical compounds from ginseng plants will be reported and that synonymy of some compounds will be confirmed; improved isolation and analytical techniques will provide a better understanding of the readily hydrolysed sugar sidechains of the glycosides and of the structures of the complex polysaccharides. So far 6 Panax species have featured in current research reports and only 3 commercially useful species have been extensively investigated. The chemical and pharmacological reports do reveal differences between the species. Ko et al. (1995) compared these species and reported that

Table 5.34. Crude saponin content and panaxadiol/panaxatriol ratios in common ginseng roots

Species

Crude saponin content per cent

Diol/triol ratio

P. ginseng

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