Dammarane triterpenoids

In addition, negative dietary correlations can afford clues to drug discovery. Thus, the potent immunosuppressant dammarane triterpenoid 36 was discovered because of epidemiological correlations between the incidence of cancer and the consumption of Palmyrah flour (Borassus flabellifer), a staple for Sri Lankan Tamils.97... 

In addition to diacetylpyxinol (501), Yosioka, Yamauchi, and Kitagawa 345) have identified three new dammarane triterpenoids from Pyxine endochrysina pyxinol (502), 3-0-acetylpyxinol (503) and 12-desoxydiacetylpyxinol (504). 

More recently Huneck 176) identified two further dammarane triterpenoids from the related species Pyxine coccifera, namely 25-acetoxy-20( S),24(i )-epoxy-3-oxodammarane (505) and 25-acetoxy-3p-hydroxy-20(5),24(i )-epoxy-dammarane (506). 

Figure 3.34 Outline biosynthesis of the dammarane triterpenoids including ginsenosides and limonoids.

Dammar resin was introduced into Europe in the nineteenth century, mainly as a paint varnish It is still used today since it has good optical properties and low acidity. It is derived from various species (the genus Hopea and Shorea of the Dipterocarpaceae family). It is characterised by tetracyclic triterpenoids of the dammarane series and contains minor amounts of pentacyclic triterpenoids of the series of olanane, ursane and hopane. It also contains a polymeric fraction named polycadinene or [S-resene. Dammar resin triterpenoids undergo oxidation with ageing, as described for the components of mastic resin. 

Figure 5.5 Norrish reaction of a triterpenoid (e.g. dammarane, oleanane or ursane type) leading to ring opening and subsequent oxidation of the ketone to the corresponding acid...

Dammar is produced by trees belonging to the Dipterocarpaceae family. It is mainly composed of triterpenoids, but it also contains a polymeric fraction based on polycadinene, a polysesquiterpene [37,38]. The main components of the triterpene fraction are compounds with a dammarane type skeleton and oleane/ursane type molecules [39,40]. 

Triterpenoid saponins are synthesized via the isoprenoid pathway.4 The first committed step in triterpenoid saponin biosynthesis involves the cyclization of 2,3-oxidosqualene to one of a number of different potential products (Fig. 5.1).4,8 Most plant triterpenoid saponins are derived from oleanane or dammarane skeletons although lupanes are also common 4 This cyclization event forms a branchpoint with the sterol biosynthetic pathway in which 2,3-oxidosqualene is cyclized to cycloartenol in plants, or to lanosterol in animals and fungi. 

Triterpenoids are a major group of natural products in higher plants. The tetracyclic triterpenoids, based on the lanostane, euphane, onocer-ane, and dammarane skeletons, are found mostly in vascular plants and... 

Alfhough bearing a sterane nucleus, fhe biosyntheses of cucurbitacins and dammaran-type saponins will not be reviewed here. Both groups belong to the triterpenoids, the chemistry, biosynthesis and biological activities of which have been described elsewhere (Charlwood and Banthorpe, 1991 ... 

Cyclocarioside A (46) is a dammarane-type triterpenoid glycoside sweet principle from the leaves of Cyclocarya paliurus (Batal.) Iljinsk (Juglandaceae), a plant used in the People s Republic of China in the treatment for diabetes [81]. Recently, another sweet-tasting principle, cyclocarioside I (47), was isolated from the same plant along with two other compounds with the same dammarane-type triterpenoid aglycone structure [82]. Cyclocarioside I was rated as about 250 times sweeter than sucrose [82]. 

Subsequent to the isolation of the dammarane-type triterpenoid glycosides jujuboside B (112), hodulosides I-V (113-117), hovenoside I, and saponins C2, E, and H (122-125) as sweetness inhibitors from the leaves of Hovenia dulcis Thunb. var. tomentella Makino [139], hodulosides VII-X (118-121) were isolated as sweetness-inhibitory agents [140]. Hodulosides I (113) and II (114) have hovenolactone (151) as their aglycone which is the same compoimd as in saponins E (124) and H (125). Hodulosides Ill-V and VII-X (115-121) are based on two different danunarane-type aglycone structures, however [139,140]. The sweetness-inhibitory potencies of hodulosides are shown in Table 2. The sweetness-inhibitory potency of hoduloside X (121) was not determined [140]. 

The bark of Rhus javanica (Anacardiaceae) contains rhuslactone (57), a novel dammarane-type triterpenoid with an a-oriented side chain. The structure followed... 

The interesting biological properties shown by many saponins, coupled with improvements in spectroscopic methods of structure determination have led to the increased study of this class of compound. The following papers deal with saponins and prosapogenins which are based on known triterpenoids of the following groups dammarane-euphane,158 lupane,159 oleanane,160 and ursane.161... 

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]. 

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