Saponins were found to be the principal medicinal components of Araliaceae. Different glycosides varying in their genins and carbohydrate moieties were discovered among Araliaceae saponins (see Fig. 6).

According to current concepts, all species of Russian Far East Aralia are combined in groups, each of which has its specific set of secondary compounds. For two major groups, such substances determining their biological activity are essentially triterpenoid saponins. Besides, glycosides of the protopanaxatriol row are major first group saponins, the said first-group being formed by two species of ginseng: P. ginseng and P. quinquefolium. In other representatives of the genus (creeping ginseng from Japan, two species from China, and Vietnamese ginseng), the content of triterpene glycosides is low or their genins are modified, and in most other genera protopanaxatriols have so far not been revealed. The structure of this row of metabolites is based on the protopanaxatriol nucleus (see Fig. 10.4), with which various carbohydrates can combine (Fig. 10.5). Carbohydrate radicals in various sets and ratios strongly change their chemical and biological properties.

The principal second-group compounds, which include species of Far East Aralia and Kalopanax, are glycosides of oleanolic acid and hederagenin. Oleanolic acid is more widespread in the plant kingdom than protopanaxatriols; in fact, its compounds are not as unique as gynsenosides. Oleanolic acid occurs in numerous representatives of various families, and has also isolated from beet sugar.

The third group of Araliaceae contains preferentially glycosides of other origin. This group includes O. elata, Eleuthero, and Acanthopanax. The main glycosides from this group are no longer triterpenoid, since they have genins of aromatic nature. The principal ones among them are acanthosides and eleutherosides. Acanthosides A and C, and also B and D, are distinguished in that they have, being lignan glycosides, mutually close genins. In this case, the genin of acanthosides B and D is represented by (-)-syringaresinol (Fig. 10.6); however, acanthoside B contains one molecule, and acanthoside D two molecules of ß-dglucopyranose. Syringaresinol and isofraxidin serve as genins of eleutherosides D, E, and B.

The division into groups is essentially based on the contents of principal plant substances. The basic compound of any of the groups may occur in plants from other groups as a minor component. Some individual glycosides, daucosterin, for instance, were found in representatives of all the three groups.

List of illustrations:

Fig. 10.1. Oleanan.

Fig. 10.2. 3ß -hydroxyolean-12-en-28-oic oleanolic acid (R1, R2) 3ß, 23-dihydroxyoleonan- 23-oic acid hederagenin (R1, R3).

Fig. 10.3. Panaxadiol.

Fig. 10.4. 20(S) protopanaxadiol (R=H; R1=24) and 20(S) protopanaxatriol (R=OH; R1=D 24)

Fig. 10.5. Arrangement of radicals in protopanaxatriols (tr) and protopanaxadiols (di).

Fig. 10.6. Syringaresinol.

Fig. 10.7. Triterpenoids-lupans from Acanthopanax trifoliatus: 3a , 11a dihydroxy-23- oxo-lup-20(29)-en-28-oic acid (R1=CHO; R2=H) and 3a , 11a -23-triol (R1=CH20H; R2=H).

Fig. 10.8. 24-nor-triterpenoids: 24-nor-3a ,11a -dihydroxy-lup-20(29)-en-28-oic acid (R1=H; R2=a -OH; ß-H; R3=a -OH; ß-H); 24-nor-11a -hydroxy-3-oxo-lup-20(29)-en-28-oic acid (R1=H; R2=0; R3=a -OH; ß-H).

Fig. 10.9. Major secondary metabolite pathway in plant cells.

Fig. 10.10. Synthesis of Araliaceae glycosides established with radioactive acetate and mevalonic acid (Price et al., 1987): 1 - acetic acid; 2 - mevalonic acid; 3 - farnesyl-pyrophosphate; 4 - squalene.