Dammarane derivatives

The hexanor-dammarane derivative (58) [cf. (54)] has been synthesized" from hydroxyhopane (59) via the ditosylate (60). This represents a formal total synthesis of the dammarane skeletal type. 

Tori, M., Tsuyuri, T., and Takahashi, T., The reaction of dammarane derivatives. Reactions involving C-20 carbonium ions. Bull. Chem. Soc. Jpn., 50, 3349, 1977. 

Dammarane derivatives. Besides the isolation of oleanane -type triterpene glycosides several new dammarane-type saponins designated... 

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. 

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. 

Treatment of (11) with cone. HCl at room temperature yielded (10). Furthermore, catalytic hydrogenation of the saponin mixture in ethanol-acetic acid followed by hydrolysis with dilute mineral acid did not yield (1) but afforded the dihydro derivative (12). This evidence indicated that (1) and (10) must be artifacts formed during the process of acid hydrolysis thus, at that stage, the genuine sapogenin seemed to be substance (11) which was named protopanaxadiol (9,10,11). However, as will be described later, investigation of the acid-catalyzed isomerization of dammarane type triterpenes and subsequent study of the mild hydrolysis of the purified... 

It is relevant to note that 2- C-mevalonate is incorporated specifically into the methyl group of the isopropenyl side chain of the lupane triterpene betulinic acid (348, R = C02H) (447). Hence, in the biosynthesis the two methyl groups in postulated intermediate (347) are not randomized. A related chemical observation is the acid-catalyzed equilibration of two C20 epimeric dammarane diol derivatives (12p-hydroxy-24,25-dihydro version of 320 and 345) (448). 

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