Cholesteryl oxide acetate

A solution of 10 g (0.023 mole) of cholesteryl acetate (mp 112-114°) in ether (50 ml) is mixed with a solution containing 8.4 g (0.046 mole) of monoperphthalic acid (Chapter 17, Section II) in 250 ml of ether. The solution is maintained at reflux for 6 hours, following which the solvent is removed by distillation (steam bath). The residue is dried under vacuum and digested with 250 ml of dry chloroform. Filtration of the mixture gives 6.7 g of phthalic acid (87% recovery). The solvent is evaporated from the filtrate under reduced pressure and the residue is crystallized from 30 ml of methanol, giving 6.0 g (58% yield) of -cholesteryl oxide acetate. Recrystallization affords the pure product, mp 111-112°. Concentration of the filtrate yields 1.55 g (15% yield) of a-cholesteryl oxide acetate which has a mp of 101-103° after crystallization from ethanol. 

Chloro-a,/3-unsaturated aldehydes condense with ammonium thiocyanate to give isothiazoles (76EGP122249). 2,3-Diphenylcyclopropenone reacts with iV-sulfinyl-cyclohexylamine in the presence of nickel tetracarbonyl to give the isothiazolin-3-one 1-oxide (197) (79SST(5)345). Cholesteryl acetate reacts with trithiazyl trichloride in pyridine to give the isothiazolo steroid (198) (77JCS(P1)916). 

A) From Cholesieryl Acetate (Note 6).-—Five grams of cholesteryl acetate (Note 7) and o.r g. of platinum oxide are... 

The hydroperoxides obtained on thermal oxidation of cholesteryl acetate (191e) can be selectively separated by SPE and elution with a polar solvent. After reduction to the corresponding alcohols by NaBH4 and further derivatization to the trimethylsilyl ether, the products can be subjected to GLC with ion-trap MS detection. It can be thus demonstrated with the aid of standards that under the oxidation conditions (160 °C for 90 min) only the 7-position is attacked, leading to the la- and 7/3-hydroperoxy derivatives, while the plausible 4-position remains unscathed . Treatment of erythrocite ghosts with t-BuOOH causes a manyfold content increase of 5-hydroxyeicosatetraenoic acid (5-HETE), 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and 5-oxoeicosatetraenoic acid (5-oxo-ETE) residues of phospholipids. These acids can be separated by HPLC, identified and quantitized by tandem MS . ... 

Physical Barriers. Wu et al (46) observed that the inclusion of palmitic acid or cholesteryl acetate in linoleic acid monolayers on silica, exerted a protective effect against oxidation. They suggested that these compounds act as a spacer keeping the linoleic acid molecules farther apart while being only slowly oxidized themselves. Similarly, our recent work with cholesterol oxidation appears to indicate that carbohydrates do not change the pathway of cholesterol oxidation but rather act as a physical barrier against the migration of reactive species. 

However, the oxidation of other steroid alkenes with Cr02X2 (X Cl, F) is affected by the structure of substrates. For example, cholesteryl acetate (22), when treated at -70 to -30 C, produces 3p-acetoxy-5a-chlorocholestan-6-one (23 12%), a mixture of a> and p-cholesteryl acetate epoxides (24 acetoxy>6p-chlorocholestan-6a-ol (25 9%) and 3p-acetoxy-5a-chlorocholestan-63-ol (25 equation 8). 

AUylic oxidatiau (3, 35). Dr. Thomson has informed us that dioxane is the only suitable solvent for allylic oxidation and that high yield.s arc obtainable only when the double bond is highly hindered, For example, 4,4-dimethylcholesteryl acetate gives a quantitative yield of the 7-keto derivative, and cholesteryl acetate gives 7-ketocholesteryl acetate in 80% yield. However, cholestene-1, -2, and -3 give no products of allylic oxidation, but rather bromohydrins, dibromides, and transformation products therefrom. The use of calcium carbonate is not necessary. 

The first description of this reagent reported an excellent yield in the oxidation of cholesteryl acetate to 7-ketocholesteryl acetate but subsequent reports have not substantiated this claim. In a modified procedure found to be more satisfactory the reagent is prepared in carbon tetrachloride containing acetic acid and acetic anhydride. Some workers have found even the modified procedure to give poor yields others" have found the reagent us good ns or better than conventional... 

Diels acid is high melting and sparingly soluble and can be isolated easily even though present in very small amounts. One of us oxidized cholesterol with sodium dichromate dihydrate in benzene-acetic acid and isolated the Diels acid in yield of 2.97% along with 6 neutral oxidation products. One of these, A -cholestene-3-one, might be but is not a precursor of the Diels acid. Cholesteryl acid chromate would seem to offer an attractive possibility for intramolecular attack of the allylic /3-hydrogen at C,. The active species in the hypobromite oxidation may be the hypobromite of cholesterol. 

Carboxylation of ketones. In the Robinson-Cornforth1 formal total synthesis of epiandrosterone two relays were utilized. The second was the Koster-Logemann2 ketone (1), available as a by-product of the oxidation of cholesteryl acetate dibromide. Based on model experiments with alicyclic ketones, (1) was converted... 

Chlorotrifluoromethylcarbene, 223 N-Chlorourethane, 60, 61 AM-Cholestadiene-3,6-dione, 60 5a-Cliolestane-3,6-dione, 60 5oCholestane-2a , 3a-oxide, 135 5CfrCholestane-2j3,3(3-oxide, 135 5(3-Cholestanone-3,6-dione, 60 A4-Cholestene-3,6-dione, 60, 65 Al-5/3-Cholestene-3,6-dione, 60 A4-Cholestene-3-one, 98 A4-Cholestene-4-one, 60 -Cholestene-a-epoxide, 116 A5-Cholestenone, 65 Cholesteryl acetate, 35, 171 Cholesteryl acetate dibromide, 40 Chromic acid, 54, 246 Chromic anhydride, 54-57, 150 Chromic anhydride-Acetic acid, 56 Chromic anhydride-Dimethylformamide, 56 Chromic anhydride-Pyridine complex,... 

Allylic oxidation. A6-Steroids (cholesteryl acetate and diosgenyl acetate) undergo allylic acetoxylation at C7 when oxidized with lead tetraacetate in benzene or glacial acetic acid solution. 7/3-Acetoxy and 7 -acetoxy derivatives are formed in a ratio of 3 2.10... 

Thus it has been used as the first stage to obtain the starting material for the microbiological method with CSD-10 and simplified in more recent work leading to a synthesis of estrone in four steps from 3p-acetoxy-19-hydroxyandrost-5-en-17-one (ref. 116). Cholesteryl acetate was transformed by standard methods to the required androstane compound shown in the following scheme, which with hypobromous acid followed by lead tetraacetate and zinc reduction (cf. ref. 115) afforded the 19-hydroxy derivative. This with thallium nitrate in dioxan underwent loss of formaldehyde and hydration with water to afford the 19-nor-10p-alcohol in 70% yield. The diol obtained by saponification was converted by Oppenauer oxidation with N-methylpiperid-4-one as hydride aceptor (ref. 117) and afforded a 78% yield of the enone which was transformed almost quantitatively into... 

Cholesteryl acetate dibromide is first prepared by the acetylation of chloesterol and its subsequent bromination. This on oxidation with chromium-6-oxide reduces the 8-carbon side chain at C-17 to a mere CO moiety, which on reduction followed by hydrolysis yields dehydroepiandro-sterone. The resulting product on acetylation protects the acetyl moiety at C-3 and treatment with sodium propoxide introduces a hydroxy group at C-17. Benzoylation followed by mild hydrolysis causes the reappearances of free OH moiety at C-3 and a benzoxy function at C-17. Oppeanauer oxidation cuased by refluxing the resulting secondary alcohol with aluminium tertiary butoxide in excess of acetone affords a ketonic function at C-3, which upon hydrolysis in an alkaline medium yields the official compound. 

Purified cholesterol, all known initial and subsequent oxidation products of cholesterol and some related compounds were tested cholest-5-en-3-one 7a-diol 73-diol 7-keto cholesta-3,5-dien-7-one a-epoxide triol cholest-4-en-3-one 63-hydroperoxycholest-4-en-3-one 63 hydroxycholest-4-en-3-one cholest-4-ene-3,6-dione cholest-5-ene-33,43 diol 5a-cholest-6-ene-33,5a-diol 53 cholestan-33-ol cholesta-1,4-dien-3-one 5a-cholest-7-eii-33 ol cholesta-7,9-dien-33-ol acetate 7,8,9,11-diepoxy-22-isoallospirostan-33 ol acetate cholesteryl acetoace-tate and cholesteryl isoheptylate. Many were carcinogenic when administered subcutaneously into Marsh-Buffalo mice with sesame oil as the vehicle a-epoxide, 63-hydroperoxycholest-4-en-3-one and cholest-4-en-3,6-dione were most potent (34-66% incidence of fibrosarcoma verses 1.4% for vehicle control). All share the property of oxygen linkage at carbon 6. 63-hydroxycholest-... 

The oxidation of A -steroids to the A -7-oxo-compound with CrOs-pyridine 1 1 and 1 2 complexes revealed that the 1 1 complex gave faster reactions. The reaction conditions were optimized by using an excess of the oxidant in the presence of P2O5 in refluxing CH2Cl2. Direct oxidation of 3j8-acetoxy-5a-cholest-8(14)-ene to the 15-oxo-derivative was achieved in useful preparative yield with Cr03-3,5-dimethyIpyrazoIe complex. Cholesteryl acetate reacted with Bu OOH-Fe "(acac)3 to give a mixture of the 7-oxo-compound, the 5,6-epoxides, and the peroxides (27) and (28). 

Bortolomeazzi et al. (1994) used GC/EI/MS with an ion trap to identify the thermal oxidation products of cholesteryl acetate as the 7P-hydroperoxy and 7a-hydroperoxy cholesteryl acetate, 7keto-cholesteryl acetate, the a and P isomers of 7-hydroxycholesteryl acetate, the a- and P-5,6-epoxy isomers and several derivatives arising from the loss of acetate and water. Dzeletovic et al. (1995b) have observed that saponification during sample preparation did not hydrolyse all of the oxysterol esters completely and that separation of oxysterols from cholesterol by HPLC was tedious and incomplete. They developed a stable isotope dilution GC/EI/MS SIM method for the determination of cholesterol oxidation products in human plasma. Nine oxysterols were determined by using deuterium-labelled internal standards. 

Bortolomeazzi, R., Pizzale, L., Conte, L. S. and Lercker, G. (1994) Identification of thermal oxidation products of cholesteryl acetate. J. Chromatogr. Ay 683, 75-85. 

A soln. of cholesteryl acetate in f rr-butanol containing 1-2 moles HgBrg UV-irradiated several hrs. in an open quartz flask with 254 nm light -> product. Y 90%. F. e., also benzylic oxidation, s. N. Friedman, M. Gorodetsky, and Y. Mazur, Chem. Commun. 1971, 874. 

Human serum paraoxonase (PON 1) is an esterase that is physically associated with high-density lipoprotein (HDL) and is also distributed in tissues such as liver, kidney, and intestine [38,39]. Activities of PON 1, which are routinely measured, include hydrolysis of organophosphates, such as paraoxon (the active metabolite of the insecticide parathion) hydrolysis of arylesters, such as phenyl acetate and lactonase activities. Human serum paraoxonase activity has been shown to be inversely related to the risk of cardiovascular disease [40,41], as shown in atherosclerotic, hypercholester-olemic, and diabetic patients [42-44]. In 1998 HDL-associated PON 1 was shown to protect LDL, as well as the HDL particle itself, against oxidation induced by either copper ions or free radical generators [45,46], and this effect could be related to the hydrolysis of the specific lipoproteins oxidized lipids such as cholesteryl linoleate hydroperoxides and oxidized phospholipids. Protection of HDL from oxidation by PON 1 was shown to preserve... 

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