Lanostane triterpenes

Widespread reports indicate that, in addition to their anti-inflammatory role, triterpenes have other activities. Triterpenoids have been found to possess cytotoxic, antimicrobial and interesting effects on metabolism. Triterpenoids with antitumour activity include oleanane, lanostane, lupane, friedelane, hopane and quassionoid types. Glycyrrhetinic acid has been described as an antiviral, hypolipidemic and anti-atherosclerotic agent. Cucurbitacins B and E, and oleanolic acid possess a potent protective action on the liver, and ganoderic acid and its derivatives have been shown to be inhibitors of cholesterol biosynthesis. Lanostane derivatives, like suberosol, have also been found to inhibit HIV replication in H9 lymphocytes [1,3]. 

The main kind of anti-inflammatory triterpenes isolated have oleanane, ursane, taraxastane, lupane and lanostane skeletons (Table 1). Some minor compounds such as hopane are included in other structural groups. Other anti-inflammatory triterpenes like the different cucurbitacins are not included in this review because of their high toxicity. 

The lanostanes are the most relevant group of the tetracyclic triterpenes (Tables 12-13). Many of this type of compounds are described as antiinflammatories and their mechanism of action has been studied frequently. Cycloartenol and some 3,4-seco-lanostane derivatives have been reported to have activity also. 

Dimethylsterols (lanostane series, also known as triterpene alcohols)... 

As part of an investigation into the synthesis of tetracyclic triterpenes of the lanostane (27)-cycloartane (28) group, Packer and Whitehurst described the synthesis of the indan-2-one 29. Compound 29 has potential as a key intermediate in the synthesis of tetracyclic triterpenes, possessing the trans-CD ring junction and a carbonyl suitably positioned for introduction of the side chain at C-17. 

These highly oxygenated triterpenes have been recently shown to be interrelated chemically to the lanostane series. They also are products of a chair-boat-chair-boat squalene condensation. A biogenetic sequence for cucurbitacins based on Coates (1976) is proposed (Fig. 23.23). 

Cueurbitacins tetracyclic triterpenes found as their glycosides in the Cucurbitaceae and Cruciferae. These toxic, bitter compounds are structurally related to the parent hydrocarbon, cucurbitane [19(10-9P)-abeo-5p-lanostane], which differs from lanostane (see Lanosterol) in the formal shift of the 10-methyl group to the 9p-position. Cucurbitacin E was formerly known as elaterin. C. have a laxative action some serve as insect attractants, and a few have antineo-plastic and antigibberellin activity. 

Lanoatarol, kryptosterol 5a-lanosta-8(9),24-dien-3P-ol, a tetracyclic triterpene alcohol. M, 426.7, m.p. 140 °C, [o]i3 + 60° (CHCI3). L. is also a zoosterol (see Sterols) present in large amounts in the wool fat of sheep. Structurally, it is based on the hydrocarbon 5a-lanostane ring system. It is biosynthesized from squalene, via 2,3-epoxysqualene, and is an important intermediate in the synthesis of all further tetracyclic triterpenes of the lanostane type and of the steroids. 

Polyporanic acid, polyporenic acid A a tetracyclic triterpene carboxylic acid. A/, 486.74, m.p. 200°C, [ ]d + 74°. P a. is structurally related to 5a-lanostane (see Lanosterol). It occurs in the fungus Polypoms spp. growing on birch trees. 

Sterol fractions of holothurians are complex and show the presence of AO sterols (stanols), A5, A7 and A9(ll) as well as 4a-methylsterols and triterpenes of the lanostane series. In studies carried out by Djerassi s group since the mid-1970s using a method based on the incorporation of tritium-labeled tracers," it was shown that the species Stichopus califomicus ... 

Kitagawa, I., Kobayashi, M., Son, B.W., Susuki, S., and Kyogoku, Y. (1989) Marine natural products. XIX. Pervicosides A, B, and C, lanostane-type triterpene-oligoglycoside sulfates from the sea cucumber Holothuria pervicax. Chem. Pham. Bull, 37, 1230-1234. 

Kobayashi, M., Hori, M., Kan, K., Yasuzawa, T., Matsui, M., Suzuki, S., and Kitagawa, I. (1991) Marine natural products. XXVII. Distribution of lanostane-type triterpene oligoglycosides in ten kinds of Okinawan sea cucumbers. Chem. Pham. BuU., 39, 2282-2287. 

The euphane and tirucallane triterpenes differ from the lanostanes only in having the opposite stereochemical dispositions at C13, C14, and Ci7 and are themselves epimeric at C20 384). The stereochemistry is considered to be a consequence of enzymatic cyclization of squalene epoxide (305) from a chair, chair, chair conformation (Scheme 29). The two stereoisomeric forms arise from 17->20 hydrogen shift to the dia-stereotopic faces of the carbonium ion at C20. ... 

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