Ginseng

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The roots of the herbaceous plants Panax ginseng (Araliaceae) from China, Korea, and Russia, and related Panax species, e.g. P. quinquefolium (American ginseng) from the USA

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and Canada, and P. notoginseng (Sanchi-ginseng) from China, have been widely used in China and Russia for the treatment of a number of diseases including anaemia, diabetes, gastritis, insomnia, sexual impotence, and as a general restorative. Interest in the drug has increased considerably in recent years and ginseng is widely available as a health food in the form of powders, extracts, and teas. The dried and usually peeled root provides white ginseng, whereas red ginseng is obtained by steaming the root, this process generating a reddish-brown caramel-like colour, and reputedly enhancing biological activity. Ginseng is classified as an 'adaptogen', helping the body to adapt to stress, improving stamina and concentration, and providing a normalizing and restorative effect. It is also widely promoted as an aphrodisiac. The Korean root is highly prized and the most expensive. Long term use of ginseng can lead to symptoms similar to those of corticosteroid poisoning, including hypertension, nervousness, and sleeplessness in some subjects, yet hypotension and tranquillizing effects in others.

The benefits of ginseng treatment are by no means confirmed at the pharmacological level, though CNS-stimulating, CNS-sedative, tranquillizing, antifatigue, hypotensive, and hypertensive activities have all been demonstrated. Many of the secondary metabolites present in the root have now been identified. It contains a large number of triterpenoid saponins based on the dammarane subgroup, saponins that have been termed ginsenosides by Japanese investigators, or panaxosides by Russian researchers. These are derivatives of two main aglycones, protopanaxadiol and protopanaxatriol (Figure 5.64), though the aglycones liberated on acid hydrolysis are panaxadiol and panaxatriol respectively. Acid-catalysed cyclization in the side-chain produces an ether ring (Figure 5.64). Sugars are present in the saponins on the 3- and 20-hydroxyls in the diol series, and the 6- and 20-hydroxyls in the triol series. About 30 ginsenosides have been characterized from the different varieties of ginseng, with ginsenoside Rb-1 (Figure 5.64) of the diol series typically being the most abundant constituent. Ginsenoside Rg-i (Figure 5.64) is usually the major component representative of the triol series. Other variants are shown in Figure 5.64. Particularly in white ginseng, many of the ginsenosides are also present as esters with malonic acid. Steaming to prepare red ginseng causes partial hydrolysis of esters and glycosides. Ginsenosides Rb-i and Rg-i appear to be the main representatives in Panax ginseng, ginsenosides Rb-i, Rg-i, and Rd in P. notoginseng, and ginsenosides Rb-i, Re, and malonylated Rb-i in P. quinquefolium. The pentacyclic triterpenoid sapogenin oleanolic acid (Figure 5.65) is also produced by hydrolysis of the total saponins of P. ginseng, and is present in some saponin structures (chikusetsusaponins). The saponin contents of Panax notoginseng (about 12%) and P. quinquefolium (about 6%) are generally higher than that of P. ginseng (1.5-2%).

The root of Eleutherococcus senticosus (Acanthopanax senticosus) (Araliaceae) is used as an inexpensive substitute for ginseng, and is known as Russian or Siberian ginseng. This material is held to have similar adaptogenic properties as Panax ginseng and a number of eleutherosides have been isolated. However, the term eleutheroside has been applied to compounds of different chemical classes, and the main active anti-stress constituents appear to be lignan glycosides, e.g. eleutheroside E (= syringaresinol diglucoside) (Figure 5.65) (see page 132) and phenylpropane glycosides, e.g. eleutheroside B (= syringin). The leaves of Russian ginseng contain a number of saponins based on oleanolic acid, but these are quite different to the ginsenosides/panaxosides found in Panax. Whilst there is sufficient evidence to support the beneficial adaptogen properties for Eleutherococcus senticosus, detailed pharmacological confirmation is not available.

OGly2

OGly2

Gly1O

protopanaxadiol protonation of double bond gives tertiary cation and allows formation of ether by attack of hydroxyl OH oh

Gly1O

ginsenoside (panaxoside)

ginsenoside Rb-2 Glc-Glc -

protopanaxadiol ginsenoside Rc ginsenoside Rd

Gly2

Glc both 20R- and 20S-panaxadiol are formed, with the 20R-epimer predominating; since both isomers are produced, this implies an equilibration, probably through loss of H2O and generation of a carbocation at C-20 in protopanaxadiol

panaxadiol

ginsenoside Re

OGly1 ginsenoside (panaxoside)

Glc-Glc-

ginsenoside Rf ginsenoside Rg-1 Glc

ginsenoside Rg-2 Rha-Glc-

Gly2

Glc H

protopanaxatriol panaxadiol

Tertiary Structure Ginsenoside

protopanaxatriol

OH panaxatriol

OH panaxatriol as mixture of 20R and 20S epimers; see notes on panaxadiol above

Figure 5.64

CO2H

oleanolic acid

CO2H

oleanolic acid

GlcO

Figure 5.64

GlcO

OGlc syringaresinol diglucoside OMe (eleutheroside E)

OGlc syringaresinol diglucoside OMe (eleutheroside E)

GlcO

GlcO

syringin (eleutheroside B)

(Figure 5.62). Several of these hydroxyls are ester-ified with aliphatic acids, e.g. acetic, tiglic, and angelic acids.

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