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Saponins of P. pseudoginseng=Panax notoginseng Flowers and Flower Buds

Taniyasu et al. (1982) investigated Chinese Sanchi ginseng flower buds and reported the apparent absence of protopanaxatriol-type glycosides and the dominance of ginsenoside Rc (Table 5.32).

Later the flower buds were shewn to yield ginsenosides Rb3 and Rc, notoginsenoside Fd (gypenoside IX) and notoginsenoside Fe together with p-sitosterol and daucosterol (Zuo et al., 1991). The sapogenins panaxadiol, dammar-20(22)-en-3p,12p,25-triol and 20(%)-dammaran-3p,20p,25-tetrol and two unnamed compounds had been isolated earlier by silica gel chromatography (Wei et al., 1984b). The essential oil in the flowers comprised some 24 compounds which were principally terpenes and alkanes, dominant compounds being y-elemene, heptocosane and pentacosane (Shuai and Li, 1986).

The pedicels or flower stalks contained ginsenosides Rb3, Rc and Re and notoginsenosides R1, Fd (29.6%) and Fe (Wei and Cao, 1992).

Saponins of P. pseudoginseng=Panax notoginseng Seeds

The seeds were analysed by Yang et al. (1983) who reported that the protopanaxadiol-derived ginsenosides Rb1 (0.01%), Rb3 (1.2%), Rc (0.42%) and Rd (0.067%), gypenoside IX (0.014%) and notoginsenosides Fa (0.087%) and Fc (0.15%) occurred and again ginsenoside Rb3 was the principal saponin present.

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

4) Panax quinquefolium L.

As with the studies of Chinese and Korean ginsengs, progress in the investigation of the chemistry of American ginseng was slow. Long after Garriques' isolation of panaquilon in 1854, Wong in 1921, working in the United States, searched unsuccessfully for alkaloids but was able to report 0.8 per cent of a pale yellow ginseng oil as well as a dark brown saponin that yielded pentose sugar and a sapogenin on hydrolysis. The oil was further investigated in 1939 by Torney and Cheng. Japanese researchers in the 1930's had shewn the presence of more saponins, less oil and proteinaceous material in the American species when compared with the Chinese and Korean species (Hou, 1978). This was confirmed by Shibata et al. (1965).

A detailed study of American ginseng was undertaken by Staba and his co-workers at the University of Minnesota, U.S.A. in the 1970's and 1980's. Their work embraced the distribution of phytochemicals, particularly saponin glycosides, throughout the plant and corelated the Japanese and Russian findings concerning the chemical structures of ginsenosides and panaxosides with their newly-found panaquilins from P. quinquefolium. The name "panaquilin" was adopted for the 11 isolated saponins in deference to Garriques original separation of a compound "panaquilon" from the plant. Fractionation into ethereal and methanol extracts revealed the occurrence of -sitosterol and stigmasterol in the ether fraction and saponins and sugars in the methanolic extract. The saponins or panaquilins were labelled A, B, C, D, E1, E2, E3, G1, G2, (c) and (d). It was noted that panaquilins B, C, E2, E3 and G2 occurred in all parts of the plant whilst panaquilins D, E1 and G1 were found chiefly in the subterranean parts of the plants. The leaves were found to yield panaquilins B, C, (d), E2, E3 and G2. This qualitative variation was also age related, young roots presenting different saponin patterns to those found in older plants. Likewise a pattern variation occurred in the leaves at various times of the year. Subsequently, using advanced analytical methods, it was realised that these compounds were similar to or identical with known ginsenosides. Panaquilin B was a mixture of ginsenosides Rb1 and Rb 2, panaquilin C was identical with ginsenoside Rc, panaquilins D and E2 were ginsenoside Rd, panaquilin E3 was ginsenoside Re and panaquilins G1 and G2 were ginsenosides Rg1 and Rg2 respectively (Hou, 1978).

Hydrolysis of the separated saponins confirmed that these compounds were also based on panaxadiol, panaxatriol or oleanolic acid. Quantitative estimations indicated about 17.3 per cent panaxadiol, 0.44 per cent panaxatriol and 0.28 per cent oleanolic acid. Thus the ratio of panaxadiol to panaxatriol was roughly 40:1 although in P. ginseng the ratio was approximately 1:1 and the pharmacology of the two species was therefore not identical.

Using HPLC-spectrophotometric analysis Soldati and Sticher (1980) estimated the occurrence of 1.703 per cent total ginsenosides comprising ginsenosides Rb1 (0.263%), Rc (0.063%), Rd (0.095%), Re (1.043%) and Rg1 (0.239%). Ginsenosides Rb2, Rf and Rg2 were not detected. Besso and his coworkers (1982b) reported the presence in the roots of ginsenosides Ro, Rb1, Rb2, Rc, Rd and Re with the additional ginsenosides Rb3, Rg1, Rg2 and F2, pseudoginsenoside F11 and gypenoside XVII together with a new compound, quinquenoside R1 (=mono-O-acetyl-ginsenoside Rb1 with the acetyl group attached at the 6-OH position of the terminal glucosyl moiety of the ^-sophorosyl group). Liu et al. (1987) noted that the highest yield of ginsenosides occurred in the 4th and 5th years of growth and at the fruiting stage and that for 4-year old plants grown in

China the principal compounds were ginsenosides Rb1 (0.96%), Rb2 and Rc (0.97%), Rd and Re (2.93%) and Rg1 (0.44%).

The work of Zheng et al. (1989a), comparing the roots of P. quinquefolium grown in China with those imported from North America, indicated a similar ginsenoside composition in all samples, the overall yield being 6.21-7.35 per cent. This finding agreed with Guo et al. (1991) who reported total glycoside yields of 5.80 and 7.75 per cent respectively in roots and root hairs grown in China. Ginsenosides detected by Zheng et al. included ginsenosides Ro, Rb1, Rb2, Rc, Rd, Re, Rg1 and Rg 2. This was confirmed by Yang and his colleagues (1989) who analysed American ginseng grown in Yunnan Province, China and also noted the presence of the malonyl-ginsenosides Rb1, Rb2 and Rc. However they did stress that yields varied considerably dependent on the age of the plant, the time of harvesting, the commercial grade of the drug and the precise subterranean parts used. American seeds cultivated in India also produced plants yielding 9 saponins, the ginsenosides Rb being dominant. Sapogenins present after acid hydrolysis included ^-sitosterol, oleanolic acid, panaxadiol, panaxatriol, dammar-20(22)-en-3^,12^,25-triol and dammaran-3^,12^,20,25-tetrol (Saxena et al., 1994).

Subsequent investigations by Ko et al. (1995) indicated the absence of ginsenosides Ra, Rf, Rh1 and Rh2 from the P. quinquefolium samples analysed although such glycosides are present in P. ginseng and P. notoginseng roots. They reported the crude saponin yield as 7.01-7.25 per cent and that the diol/ triol saponin ratio was 2.12-2.5. Analysing by colorimetry 4-year old P. quinquefolium roots grown in Fujian Province, China, Li et al. (1995) recorded a yield of 9.50 per cent total saponins and 5.054 per cent ginsenoside Rb1.

Studying commercial samples obtained on the Taiwanese market Chuang et al. (1995) confirmed that the major saponins present were ginsenosides Rb1 and Re and malonyl ginsenoside Rb1. Also corroborating the occurrence of ginsenosides Rb1, Rb2, Rc, Rd, Re and Rg1, Li et al. (1996b) noted that in 4 years old roots the dominant ginsenosides were Re and Rb1, compounds forming about 75 per cent of the total glycosides present. A French crop grown by Le Men-Olivier et al. (1995) also yielded ginsenosides Rb1, Rd and Re, gypenoside XVII and pseudoginsenoside F11 as the main glycosides. In Canada Court et al. (1996) noted that the yield of ginsenosides Rb1, malonyl Rb1, Re and Ro increased with the age of the roots although the differences for ginsenosides Rb2, malonyl Rb2, Rc, malonyl Rc, Rd and Rg1 and gypenoside XVII due to root age were small. They also agreed that ginseng harvested after 3 years growth contained less total ginsenosides than 4 year old roots.

The Chinese researchers Xie et al. (1996) observed that, although roots could produce 2.79 and 4.57 per cent of total ginsenosides after one and two years growth respectively under natural conditions, callus cultures and suspension cultures could yield 4.43 and 4.82 per cent total ginsenosides respectively in a much shorter time.

Yoshikawa et al. (1998), investigating the occurrence of bioactive saponins and glycosides in P. quinquefolium roots, reported the presence in the butanol-soluble fraction of 14 known dammarane-type triterpene oligoglycosides

Table 5.33. Reported yields of individual saponins in Panax quinquefolium roots

Designation

Prosapogenin

Recorded yield per cent

Total ginsenosides

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