Lanostanes derivatives

Whereas empirical force-field calculations predict a ring A boat conformation for lanost-8-en-3-one, combined empirical force-field-extended Hiickel molecular orbital calculations favour a ring A chair conformation. Europium-shift n.m.r. results indicate that the molecule adopts the latter conformation. Studies on the peracetic acid-boron trifluoride etherate Baeyer-Villiger oxidation of 4,4-dimethyl-3-keto-triterpenoids to 5-lactones (18) and their subsequent ring contraction to y-lactones have been reported. Dehydrogenation of lanost-8-en-3j8-ol with 2,3-dichloro-5,6-dicyanobenzoquinone afforded, in addition to the corresponding 7,9(1 l)-diene, the aromatic seco-lanostane derivatives (19)... 

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 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. 

Akhtar, M., K. Alexander, R.B. Boar, J.F. McGhie, and D.H.R. Barton (1978). Chemical and enzymic studies on the characterization of intermediates during the removal of the 14a-methyl group in cholesterol biosynthesis. The use of 32-fiinctionalized lanostane derivatives. Biochem. J. 169, 449-463. 

A short, high-yield sequence for the removal of one C-4 methyl group from lanostane derivatives has been published (see Scheme 1). The reaction probably... 

The medical uses of the T. are as yet very limited. For example, antitumor activities have been described for glycyrrhet(in)ic acid and betulinic acid (3/3-hy-droxy-lup-20(29)-ene-28-oic acid), various lanostane derivatives exhibit antimicrobial and cholesterol-lowering activities (e.g., lanost-8-ene-3,7-dione), and dammar resin T. have antiviral properties. Some cu-curbitacins show anti-Hiv activity. 

Hirotani, M., Tsutomu, F. and Shiro, M. 1985, Lanostane derivatives from Ganoderma lucidum , Phytochemistry 24 2055-2061. 

The nitrite photolysis reaction was utilized by Barton to prepare 19-substituted lanostane derivatives. The photolysis of 3P-acetoxylanostan-llp-yl nitrite 17 afforded the 3p-acetoxy-19-hydroxy-iminolanostan-lip-ol 18. 

The synthesis of 32-functionalized lanostane derivatives was accomplished by the photolysis of 25 to yield 26. ... 

The transformation of the lanostane keto-epoxide (72) into the cucurbitacin derivative (73) has been achieved with boron trifluoride in acetic anhydride. The presence of the acetic anhydride appears to favour the backbone rearrangement. The structure of (73) was confirmed by correlation with the oxidation product (74) of deoxybryogenin acetate. Two new cucurbitacin glycosides, arvenins 1 (75) and II (76) from Anagallis arvensis, have been reported. ... 

Lanostan-3j8-yl azidoformate (248) and its A -unsaturated derivative are thermolysed or photolysed to give the oxazolidinones (249) and the products (250), functionalized in the 4a-methyl group. Other reactions leading to heterocyclic derivatives of steroids are described on p. 305. 

An elegant correlation of the lanostane and cucurbitane series has been reported by Barton and his colleagues. Cucurbitacin A (46) was transformed into the cyclopropane derivative (47) by treatment of the tosylate (48) with sodium borohydride. The cyclopropane ring of the tetrahydro-compound (49) was opened by an anionic process which involved protonation of the incipient... 

The full paper on the synthesis of 32-functionalized lanostanes has appeared. The 32-norlanosterol derivative (34), prepared from 3jS-acetoxy-7a-hydroxy-lanostano-32-nitrile, was found to have the unnatural 14-jS-H configuration. 

Lophenol 4a-methyl-Sa-cholest-7-en-3p-ol, a zoo-and/or phytosterol (see Sterols), M, 400.69, m.p. 151 °C, [a]i, + 5° (CHCI3). L. has been isolated from rat tissues and feces, and from the cactus Lophocer-eus schotdL It has the structure of a tetracyclic triter-pene with a 3132-6frdemethyl-lanostane skeleton. Its structure is therefore intermediate between lanoster-ol and the sterols derived from lanosterol. 

The basic 4,4-dimethylsterols are Cjq steroids lanosterol (3-92) and cycloartenol with a cyclopropane ring (3-93), derived from lanostane (4,4,14-trimethylcholestane). Lanosterol is the building block for the biosynthesis of aU other zoosterols (including cholesterol), the biosynthesis of many other phytosterols is based on cycloartenol. Common compounds are also euphol (3-94) and its isomer butyrospermol (A -euphol or A -tirukaUol, 3-95) derived from the hydrocarbon euphane. 

The common Cjj 4,4-dimethylsterols are represented by isomeric compounds with a cyclopropane ring, such as cycloartenol and 24-methylenecycloartanol (3-105), cyclosadol (3-106), cyclo-branol (3-107) and cyclolaudenol (3-108), which are derived from the hydrocarbon lanostane. 

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