Other Pentacyclic Triterpenes

Apart from the function of X-group itself, this mechanism also necessarily differs in stereochemical detail. It will be noted that the lupeol-like intermediate (7), in order to set the stage for the following anti-parallel rearrangements (8-> 9a and 9b l0), has the unnatural stereochemistry at C19 (ocH). Thus, this proposal suggests that lupeol (348) does not lie along the same biogenetic path as the other pentacyclic triterpenes. 

A novel interpretation of the chiroptical properties of cyclopropyl ketones has been proposed. " In addition to the two natural planes of symmetry of the carbonyl group, a third nodal surface is considered to be curved in a manner similar to that postulated last year for other carbonyl compounds, with its convex face towards oxygen. Cyclopropyl groups are then considered to obey a reversed octant rule i.e. one which reverses the signs of the original octant rule) with respect to the three boundary surfaces. O.r.d. and c.d. data are reported for a variety of pentacyclic triterpene derivatives with oxo-groups at C-3, C-12, and C-16, and for a series of compounds in the A-nor-2-oxo-series, including a,j8-epoxy-ketones and some lactones. ... 

In the oleanane-ursane group of triterpenes, postulated hydride shifts [as proposed by Eschenmoser and co-workers (1955)] have now been demonstrated. Incorporation of [4- C]MVA into oleanolic acid (56), ursolic acid (63), and several other metabolites was accomplished with tissue cultures of Isodon japonicus (Lamiaceae). Following introduction of [4- C]mevalonate and [l,2- C2]acetate, the pentacyclic triterpene compounds were examined by C-NMR spectroscopy. Rings D and E were formed by the routes predicted by Eschenmoser et al. (1955). The labeling pattern at carbons 4,23, and 24 of 3- p/-maslinic acid (64) indicates that this series is formed from (35)-squalene epoxide, rather than from the (3R)-epimer. 

Amyrin a pentacyclic triterpene alcohol with one double bond. a-A. (a formal derivative of the hydrocarbon, 5-a-ursane) is found free, esterified and as the aglycon of triterpene saponins of many plants, and has been isolated from many latexes, e.g. latex of the dandelion. Taraxacum officinale. P-A. (P-amyrenol, a-viscol) (a formal derivative of the hydrocarbon, 5-a-oleane) is present in mistletoe leaves, grapeseed oil, latex of Taraxacum officinale it is found free, esterified and as the aglycon of triterpene saponins in many other plants, especially in species which yield caoutchouc and gutta percha. 

Taraxa sterol, a-lactucerol, a-anthesterol a simple, unsaturated, pentacyclic triterpene alcohol, M, 426.73, m.p. 227 °C [a]D-r50°, structurally a derivative of the parent hydrocarbon, 5a-taraxastane. It occurs as the acetate in the latex of the dandelion (Taraxacum officinale) and other members of the Compo-sitae. 

A novel glycolipid (12) isolated from the extreme thermoacidophile Bacillus acidocaldarius is a 2-acylamino-2-deoxy-j3-D-glucopyranosyl derivative of 1,2,3,4-tetrahydroxypentane linked to hopane (a pentacyclic triterpene) at C-29. Three other glycolipids possess a common structure (13) having the hydroxy-groups of their glycerol residues unsubstituted, or monoacylated, or diacylated. 

The msyority of natural triterpenes are pentacyclic compounds. The next largest group are the tetracyclic triterpenes. There is also a smaller number of triterpenes with various other cyclic structures. The only important acyclic triterpene is squalene (and its 2,3-oxide as a metabolic intermediate). Most triterpenes are alcohols (3-OH). They are found free and as glycosides (saponins) (Karrer, 1958 Robinson, 1975) or esters. Free triterpenes are often components of resins, latex, or cuticle. Saponins are powerful surface-active agents and can cause lysis of red blood cells. Some of them have been... 

In C.halimii leaf wax triterpenoids were found in the very high amount of 72%,beside the wax lipids. The free triterpenols dominated with about 62%. Identified could be B-amyrin, a-amyrin and lupeol. In small amounts esters of B-amyrin and a-amyrin containing long chain fatty acids were found. Again triterpene ketones were isolated and detected with the aid of GC/MS. In this wax lupenone was present and also one other ketone named fridelanone in the remarkable amount of about 12%. They could be reduced to the corresponding alcohols. Fridelanone and fride-lanol have a pentacyclic structure without any double bond. Therefore these substances showed quite different Rf values in TLC and no colour reaction with carbazole (3)(Fig.l). 

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