Inhibitors of sterol synthesis. A highly efficient and specific side-chain oxidation of 3 beta-acetoxy-5 alpha-cholest-8(14)-en-15-one for construction of metabolites and analogs of the 15-ketosterol

Oxysterols: modulators of cholesterol metabolism and other processes

Oxygenated derivatives of cholesterol (oxysterols) present a remarkably diverse profile of biological activities, including effects on sphingolipid metabolism, platelet aggregation, apoptosis, and protein prenylation. The most notable oxysterol activities center around the regulation of cholesterol homeostasis, which appears to be controlled in part by a complex series of interactions of oxysterol ligands with various receptors, such as the oxysterol binding protein, the cellular nucleic acid binding protein, the sterol regulatory element binding protein, the LXR nuclear orphan receptors, and the low-density lipoprotein receptor. Identification of the endogenous oxysterol ligands and elucidation of their enzymatic origins are topics of active investigation. Except for 24, 25-epoxysterols, most oxysterols arise from cholesterol by autoxidation or by specific microsomal or mitochondrial oxidations, usually involving cytochrome P-450 species. Oxysterols are variously metabolized to esters, bile acids, steroid hormones, cholesterol, or other sterols through pathways that may differ according to the type of cell and mode of experimentation (in vitro, in vivo, cell culture). Reliable measurements of oxysterol levels and activities are hampered by low physiological concentrations (approximately 0.01-0.1 microM plasma) relative to cholesterol (approximately 5,000 microM) and by the susceptibility of cholesterol to autoxidation, which produces artifactual oxysterols that may also have potent activities. Reports describing the occurrence and levels of oxysterols in plasma, low-density lipoproteins, various tissues, and food products include many unrealistic data resulting from inattention to autoxidation and to limitations of the analytical methodology. Because of the widespread lack of appreciation for the technical difficulties involved in oxysterol research, a rigorous evaluation of the chromatographic and spectroscopic methods used in the isolation, characterization, and quantitation of oxysterols has been included. This review comprises a detailed and critical assessment of current knowledge regarding the formation, occurrence, metabolism, regulatory properties, and other activities of oxysterols in mammalian systems.

An alternative synthesis of 4,4-dimethyl-5 alpha-cholesta-8,14,24-trien-3 beta-ol, an intermediate in sterol biosynthesis and a reported activator of meiosis and of nuclear orphan receptor LXR alpha

4,4-dimethyl-5 alpha-cholesta-8,14,24-trien-3 beta-ol, a sterol of current biological interest, has been synthesized in six steps from 3 beta-acetoxy-4,4-dimethyl-5 alpha-cholest-8(14)-en-15-one.

Remote functionalization of the steroid side-chain

By using classical methods of organic synthesis, the introduction of chemical modifications into the saturated side-chains of steroids usually requires a multistep synthesis to construct new side-chains to be added to the steroid nucleus. In order to circumvent these earlier methods, new procedures have been developed to directly introduce functionality onto the steroid side-chain to produce useful products. These initial products may also provide an entry toward the further modification of the side-chain to produce steroids which could previously be obtained only with great difficulty.

Inhibitors of sterol synthesis. Synthesis and spectral properties of 3 beta-hydroxy-25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestan-15-one

3 beta-Hydroxy-25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestan-15-one (4) has been prepared as part of a program to synthesize 15-ketosterols that are not readily metabolized to cholesterol or side-chain oxygenated species. Saponification of 3 beta-acetoxy-5 alpha-chola-8(14),23-dien-15-one (5) followed by lithium-ammonia reduction with a bromobenzene quench gave 3 beta-hydroxy-5 alpha-chol-23-en-15-one (6). Addition of (CF3)2CFI to 6 in the presence of triethylborane gave an iodide preparation, which was reduced to 4 with tributyltin hydride (71% overall yield of 4 from 5). The 23-iodide preparations consisted of 6:1 mixtures of (23R)-3 beta-hydroxy-23-iodo-25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestan-15-one (9a) and its C-23 epimer 9b with variable amounts of 4. Compound 4 was also prepared by lithium-ammonia reduction of the delta 8(14) analogs of 4 and iodides 9a and 9b. The presence of small amounts of 6 in the latter product suggested a side reaction involving cleavage of the C24-C25 bond with loss of a (CF3)2CF radical. Also prepared were 25,26,26,26,27,27,27-heptafluoro-5 alpha-cholestane-3 beta, 15 alpha-diol, its 15 beta epimer, the 7 alpha-methyl analog of 4, 3 beta-hydroxy-7 alpha-methyl-5 alpha-cholestan-15-one (16), and (25R)-3 beta,26-dihydroxy-5 alpha-cholestan-15-one. Full 1H and 13C-NMR data of high precision with complete signal assignments are given for all new compounds. Definitive 1H-NMR stereochemical assignments of the C-24 protons were established for most sterols with a C8H17 side chain based on analysis of the downfield H-24 resonance in a 750-MHz spectrum of 16. Detailed electron-impact mass spectral data are presented together with a summary of major fragmentation patterns for 15-hydroxy- and 15-ketosteroids with and without a delta 8(14) bond.

Review of progress in sterol oxidations: 1987-1995

Material dealing with the chemistry, biochemistry, and biological activities of oxysterols is reviewed for the period 1987-1995. Particular attention is paid to the presence of oxysterols in tissues and foods and to their physiological relevance.

Inhibitors of sterol synthesis: effects of a 7 alpha-alkyl analog of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in cultured mammalian cells and on serum cholesterol levels and other parameters in rats

The 7 alpha-methyl analog (II) of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15- one (I) was prepared by chemical synthesis and evaluated with respect to its effects on HMG-CoA reductase activity in CHO-K1 cells and on serum cholesterol levels in rats. The 7 alpha-methyl substitution had no detectable effect on the potency of I in lowering HMG-CoA reductase activity in the cultured cells. In contrast, the 7 alpha-methyl substitution had a marked effect on the action of I in the suppression of food consumption in rats. Whereas II was less potent than I in lowering serum cholesterol levels in rats, it did so at dosage levels at which only slight or moderate effects on food consumption were observed. Full 1H and 13C-NMR assignments for II and intermediates in its synthesis have been presented. Conformational analysis, based on 1H-1H coupling constants, NMR shieldings and force-field calculations, indicated that the 7 alpha-methyl substitution had virtually no effect on the conformation of the 15-ketosterol apart from minor distortions of ring B.

Efficient preparation of steroidal 5,7-dienes of high purity

Protected forms of dehydroepiandrosterone, delta 5 cholenic acid, (25R)-26-hydroxycholesterol and diosgenin were converted to the corresponding delta 5,7 dienes by successive treatment with 1,3-dibromo-5,5-dimethylhydantoin (dibromantin), tetrabutylammonium bromide and tetrabutylammonium fluoride. The crude products, which contained the delta 5,7 species contaminated by minor amounts of the delta 5 and delta 4,6 steroids, were purified by silica gel-AgNO3 chromatography to give the following steroids in approximately 99% purity and at least 50% yield: 3 beta-acetoxyandrosta-5,7-dien-17-one, methyl 3 beta-acetoxychola-5,7-dien-24-oate, (25R)-3 beta,26-diacetoxycholesta-5,7-diene and (25R)-3 beta-acetoxyspirosta-5,7-diene. Analogous treatment of acetate derivatives of pregnenolone and stigmasterol gave 3 beta-acetoxypregna-5,7-dien-20-one and 3 beta-acetoxystigmasta-5,7,22-triene in approximately 50% yield but of lower purity. Full 1H and 13C NMR assignments are given for seven delta 5,7 steroid acetates and the corresponding delta 5 starting materials. Coupling constants for rings A, B and C of delta 5,7 steroids are presented and stereochemical assignments have been made for the following 1H NMR signals: the C-11 protons of delta 5,7 steroids, the C-16 protons of sterols and bile acids, the C-22 and C-23 protons of bile acid esters and the C-28 protons of stigmasterol derivatives.

Inhibitors of sterol synthesis. Chemical syntheses and spectral properties of 26-oxygenated derivatives of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one and their effects on 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in CHO-K1 cells

26-Oxygenated derivatives of delta 8(14)-15-ketosterols have been synthesized from (25R)-3 beta,26-diacetoxy-5 alpha-cholest-8(14)-en-15-one (IX) as part of a program to prepare potential metabolites and analogs of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (I), a potent regulator of cholesterol metabolism. Partial hydrolysis of IX gave a mixture, from which the 3 beta,26-diol II and the 26-acetate (XI) and 3 beta-acetate (X) monoesters were isolated. Mitsunobu reaction of XI followed by hydrolysis gave (25R)-3 alpha,26-dihydroxy-5 alpha-cholest-8(14)-en-15-one (VI). Oxidation of XI with pyridinium chlorochromate followed by hydrolysis of the acetate gave (25R)-26-hydroxy-5 alpha-cholest-8(14)-ene-3,15-dione (VII). Oxidation of X with Jones reagent followed by hydrolysis of the acetate gave (25R)-3 beta-hydroxy-15-keto-5 alpha-cholest-8(14)-en-26-oic acid (IVa). Jones oxidation of II gave (25R)-3,15-diketo-5 alpha-cholest-8(14)-en-26-oic acid (VII). 1H and 13C nuclear magnetic resonance assignments and analyses of mass spectral fragmentation data are presented for each of the new compounds and their derivatives. The 3,15-diketone VII was found to be highly active in lowering the levels of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in CHO-K1 cells, with a potency comparable to that of I. In contrast, 3 alpha,26-diol VI was less potent than I or VII. The two carboxylic acid analogs IVa and VIII were considerably less potent than VI in lowering the levels of HMG-CoA reductase activity.