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We recently communicated that the free-radical-mediated oxidation (autoxidation) of cholesterol yields a more complex mixture of hydroperoxide products than previously appreciated. In addition to the epimers of the major product, cholesterol 7-hydroperoxide, the epimers of each of the regioisomeric 4- and 6-hydroperoxides are formed as is the 5α-hydroperoxide in the presence of a good H-atom donor. Herein, we complete the story by reporting the products resulting from competing peroxyl radical addition to cholesterol, the stereoisomeric cholesterol-5,6-epoxides, which account for 12% of the oxidation products, as well as electrophilic dehydration products of the cholesterol hydroperoxides, 4-, 6-, and 7-ketocholesterol. Moreover, we interrogate how their distribution - and abundance relative to the H-atom abstraction products - changes in the presence of good H-atom donors, which has serious implications for how these oxysterols are used as biomarkers. The resolution and quantification of all autoxidation products by LC-MS/MS was greatly enabled by the synthesis of a new isotopically labeled cholesterol standard and corresponding selected autoxidation products. The autoxidation of cholesteryl acetate was also investigated as a model for the cholesterol esters which abound in vivo. Although esterification of cholesterol imparts measurable stereoelectronic effects, most importantly reflected in the fact that it autoxidizes at 4 times the rate of unesterified cholesterol, the product distribution is largely similar to that of cholesterol. Deuteration of the allylic positions in cholesterol suppresses autoxidation by H-atom transfer (HAT) in favor of addition, such that the epoxides are the major products. The corresponding kinetic isotope effect (kH/kD ～ 20) indicates that tunneling underlies the preference for the HAT pathway.

A simple technique for the preparation of [18F]HF has been developed and applied to the generation of an [18F]FeF species for opening sterically hindered epoxides. This method has been successfully employed to prepare four drug-like molecules, including 5-[18F]fluoro-6-hydroxy-cholesterol, a potential adrenal/endocrine PET imaging agent. This easily automated one-pot procedure produces sterically hindered fluorohydrin PET imaging agents in good yields and high molar activities.

A new molecularly imprinted Ru-porphyrin complex catalyst on a SiO2 support was designed, prepared, and characterized in a step-by-step manner for the C5C6 epoxidation of cholesterol derivatives. High chemoselectivity for the C5C6 epoxidation of cholesterol derivatives without protecting the 3-position OH group and other oxidizable functional groups was achieved on the molecularly imprinted catalyst.

In this paper is described a synthetic route to 6β-phenylamino-cholestan-3β,5α-diol and (25R)-6β-phenylaminospirostan-3β,5α-diol, starting from cholesterol and diosgenin, respectively. The products were obtained in two steps by epoxidation followed by aminolysis, through an environmentally friendly and solvent-free method mediated by SZ (sulfated zirconia) as catalyst. The use of SZ allows chemo- and regioselective ring opening of the 5,6α-epoxide during the aminolysis reaction eliminating the required separation of the epoxide mixture. The products obtained were spectroscopically characterized by 1H, PENDANT 13C NMR and HETCOR experiments, and complemented with FTIR-ATR and HRMS. The antiproliferative effect of the β-aminoalcohols was evaluated on MCF-7 cells after 48 h of incubation, by MTT and CVS assays. These methodologies showed that both compounds have antiproliferative activity, being more active the cholesterol analogue. Additionally, the cell images obtained by Harris’ Hematoxylin and Eosin (H&E) staining protocol, evidenced formation of apoptotic bodies due to the presence of the obtained β-aminoalcohols in a dose-dependent manner.

Eleven antioxidants including nine phenolic compounds (rutin, quercetin, hesperidin, hesperetin, naringin, naringenin, chlorogenic acid, caffeic acid, ferulic acid), vitamin E (α-tocopherol), and butylated hydroxytoluene (BHT) were selected to investigate their inhibitory effects on thermal oxidation of cholesterol in air and lard. The results indicated that the unoxidized cholesterol decreased with heating time whilst cholesterol oxidation products (COPs) increased with heating time. The major COPs produced were 7α-hydroxycholesterol, 7β-hydroxycholesterol, 5,6β-epoxycholesterol, 5,6α-epoxycholesterol, and 7-ketocholesterol. When cholesterol was heated in air for an hour, rutin, quercetin, chlorogenic acid, and caffeic acid showed a strong inhibitory effect. When cholesterol was heated in lard, caffeic acid, quercetin, and chlorogenic acid demonstrated inhibitory action during the initial 0.5 h (p a high flame is recommended. If baking or deep fat frying food in oil, it is best to limit cooking time to within 0.5 h.

The aim of the study was to characterise products of cholesterol standard changes during thermal processing. Cholesterol was heated at 120 °C, 150 °C, 180 °C and 220 °C from 30 to 180 min. The highest losses of cholesterol content were found during thermal processing at 220 °C, whereas the highest content of cholesterol oxidation products was observed at temperature of 150 °C. The production of volatile compounds was stimulated by the increase of temperature. Treatment of cholesterol at higher temperatures i.e. 180 °C and 220 °C led to the formation of polymers and other products e.g. cholestadienes and fragmented cholesterol molecules. Further studies are required to identify the structure of cholesterol oligomers and to establish volatile compounds, which are markers of cholesterol transformations, mainly oxidation.

3β-Hydroxy-5β-cholestan-6-one was identified in the EtOAc extract of Ajuga hairy roots by micro-analysis using LC-MS/MS in the multiple reaction mode (MRM). Furthermore, administration of (2,2,4,4,7,7-2H6)- and (2,2,4,4,6,7,7-2H7)-cholesterols to the hairy roots followed by LC-MS/MS analysis of the EtOAc extract of the hairy roots indicated that cholesterol was converted to the 5β-ketone with hydrogen migration from the C-6 to the C-5 position. These findings, in conjunction with the previous observation that the ketone was efficiently converted to 20-hydroxyecdysone, strongly suggest that the 5β-ketone is an intermediate immediately formed after cholesterol during 20-hydroxyecdysone biosynthesis in Ajuga sp. In addition, the mechanism of the 5β-ketone formation from cholesterol is discussed.

A convenient, fast, and high-yielding process to synthesize 5α,6β-dihydroxysteroids directly from the correspondent Δ5-steroids is reported. The reaction protocol consists in the conjugation of a readily available and stable oxidant, magnesium bis(monoperoxyphthalate) hexahydrate, with the non-toxic bismuth(III) triflate in acetone to afford the trans-diaxial hydroxylation product in a stepwise manner and in excellent yields.

We describe here the syntheses and the biological properties of new alkylaminooxysterols. Compounds were synthesized through the trans-diaxial aminolysis of 5,6-α-epoxysterols with various natural amines including histamine, putrescine, spermidine, or spermine. The regioselective synthesis of these 16 new 5α-hydroxyl-6β-aminoalkylsterols is presented. Compounds were first screened for dendrite outgrowth and cytotoxicity in vitro, and two leads were selected and further characterized. 5α-Hydroxy-6β-[2- (1Himidazol-4-yl)ethylamino]cholestan-3β-ol, called dendrogenin A, induced growth control, differentiation, and the death of tumor cell lines representative of various cancers including metastatic melanoma and breast cancer. 5α-Hydroxy-6β-[3-(4-aminobutylamino)propylamino]cholest-7-en- 3β-ol, called dendrogenin B, induced neurite outgrowth on various cell lines, neuronal differentiation in pluripotent cells, and survival of normal neurones at nanomolar concentrations. In summary, we report that two new alkylaminooxysterols, dendrogenin A and dendrogenin B, are the first members of a class of compounds that induce cell differentiation at nanomolar concentrations and represent promising new leads for the treatment of cancer or neurodegenerative diseases.

Fast generation of epoxides from the corresponding homoallylic and allylic steroidal olefins was developed by using magnesium bis(monoperoxyphthalate) hexahydrate (MMPP) as oxidant suspended in acetonitrile (CH3CN) at reflux temperature. The protocol involves the use of a safe readily available oxidant along with an easy work-up, which renders the process very efficient. Selective 4,5- and 5,6-epoxidations of steroids are reported. Among them, highly stereoselective epoxidation of Δ5-B-nor-cholestanes was achieved. Moreover, the method is chemoselective for the 5,6-position and can be applied to the epoxidation of ring-A enones.

A library of diastereomerically pure epoxysterols, prepared by combining chemical and enzymatic methodologies, was evaluated for cytotoxicity toward human cancer and noncancer cell lines. Unsaturated steroids were oxidized by magnesium bis(monoperoxyphthalate) hexahydrate in acetonitrile, and the resulting epimeric epoxides were enzymatically separated using Novozym 435 or lipase AY. Some of the synthesized epoxysterols have potent cytotoxicity and higher activity on cancer cell lines HT29 and LAMA-84.

5,6-Epoxycholestan-3β-ol derivatives were hydrolyzed in a diastereoconvergent manner by growing and resting cells of several strains of Aspergillus niger, particularly A. niger ATCC 11394. These strains displayed opposite regioselectivity toward each isomer in an α and β epoxide mixture, thus, the nucleophilic attack took place at the less substituted and the most substituted carbon atom on each diasteromer, respectively. These biocatalysts opened trisubstituted oxiranes but were unable to hydrolyze the disubstituted oxiranes in the tested sterol derivatives. These findings suggest that A. niger strains possess another hydrolytic ability different from the commercial A. niger epoxide hydrolase (EH) that did not accept this kind of steroidal oxiranes as substrates.

[RuIV(2,6-Cl2tpp)Cl2], prepared in 90% yield from the reaction of [RuVI(2,6-Cl2tpp)O2] with Me3SiCl and structurally characterized by X-ray crystallography, is markedly superior to [RuIv(tmp)Cl2], [RuIV(ttp)Cl2], and [RuII(por)(CO)] (por = 2,6-Cl2tpp, F20-tpp, F28-tpp) as a catalyst for alkene epoxidation with 2,6-Cl2pyNO (2,6Cl2tpp = meso-tetrakis(2,6-dichlorophenyl)porphyrinato dianion; tmp = meso-tetramesitylporphyrinato dianion; ttp = meso-tetrakis(p-tolyl)porphyrinato dianion; F20-tpp = meso-tetrakis(pentafluorophenyl)porphyrinato dianion; F28-tpp = 2,3,7,8,12,13,17,18-octafluoro-5,10,15,20- tetrakis(pentafluorophenyl)-porphyrinato dianion). The "[Ru IV(2,6-Cl2tpp)Cl2] + 2,6-Cl 2pyNO" protocol oxidized, under acid-free conditions, a wide variety of hydrocarbons including 1) cycloalkenes, conjugated enynes, electron-deficient alkenes (to afford epoxides), 2) arenes (to afford quinones), and 3) Δ5-unsaturated steroids, Δ4-3- ketosteroids, and estratetraene derivatives (to afford epoxide/ketone derivatives of steroids) in up to 99% product yield within several hours with up to 100% substrate conversion and excellent regio- or diastereoselectivity. Catalyst [RuIv(2,6-Cl2tpp)Cl2] is remarkably active and robust toward the above oxidation reactions, and turnover numbers of up to 6.4 × 103, 2.0 × 104, and 1.6 × 104 were obtained for the oxidation of α,β-unsaturated ketones, arenes, and Δ5-unsaturated steroids, respectively.

A general, efficient, and environmentally friendly method is provided for producing mostly β-epoxides of Δ5-unsaturated steroids using certain ketones as the catalyst along with an oxidizing agent, or by using certain dioxiranes. In another aspect of the invention, a method is provided for producing mostly 5β,6β-epoxides of steroids from Δ5-unsaturated steroids having a substituent at the 3α-position by an epoxidation reaction using a ketone along with an oxidizing agent under conditions effective to generate epoxides, or using a dioxirane under conditions effective to generate epoxides. A whole range of Δ5-unsaturated steroids, bearing different functional groups such as hydroxy, carbonyl, acetyl or ketal group as well as different side chains, were conveniently converted to the corresponding synthetically and biologically interesting 5β,6β-epoxides with excellent β-selectivities and high yields.

Stereoisomerically pure 3β-hydroxy-5,6-epoxysteroids were obtained by combining selective chemical methods for α- and β-epoxidation of Δ5-unsaturated steroids with enzymatic stereoselective esterification of the 3β-hydroxyl group. 5β,6β-Epoxy-3β- hydroxysteroids were efficiently acylated by Novozym 435 and lipase AK, whereas 5α,6α-epoxy-3β-hydroxysteroids were good substrates for Candida rugosa lipase. Mild enzymatic deacylation of the 3β-acetoxy group in the presence of the epoxy functionality was also accomplished by C. rugosa lipase-mediated hydrolysis.

2,3,3-Trimethyl-7-nitro-3,4-dihydroisoquinolinium tetrafluoroborate is a highly efficient catalyst for the oxaziridinium-mediated epoxidation of a variety of olefins, including monosubstituted ones.

A general, efficient, and environmentally friendly method is provided for producing mostly β-epoxides of Δ5-unsaturated steroids using certain ketones as the catalyst along with an oxidizing agent, or by using certain dioxiranes. In another aspect of the invention, a method is provided for producing mostly 5β,6β-epoxides of steroids from Δ5-unsaturated steroids having a substituent at the 3α-position by an epoxidation reaction using a ketone along with an oxidizing agent under conditions effective to generate epoxides, or using a dioxirane under conditions effective to generate epoxides. A whole range of Δ5-unsaturated steroids, bearing different functional groups such as hydroxy, carbonyl, acetyl or ketal group as well as different side chains, were conveniently converted to the corresponding synthetically and biologically interesting 5β,6β-epoxides with excellent β-selectivities and high yields.

The nicely crystalline, easily prepared and handled, 3,3-dimethyl-3,4-dihydroisoquinolinium salt 6, is a convenient catalyst for the oxaziridinium-mediated epoxidation of alkenes by Oxone.

A general catalytic and environmentally friendly method for β-epoxidation of Δ5-unsaturated steroids has been developed, which uses ketones as the catalysts and Oxone as the terminal oxidant. A whole range of Δ5-unsaturated steroids, which bear different functional groups such as hydroxyl, carbonyl, acetyl, or ketal, as well as different side chains, were conveniently converted to the corresponding synthetically and biologically interesting 5β,5β-epoxides with excellent β-selectivities and high yields.

Oxygenated sterols, including both autoxidation products and sterol metabolites, have many important biological activities. Identification and quantitation of oxysterols by chromatographic and spectroscopic methods is greatly facilitated by the availability of authentic standards, and deuterated and fluorinated analogs are valuable as internal standards for quantitation. We describe the preparation, purification and characterization of 43 oxygenated sterols, including the 4β-hydroxy, 7α-hydroxy, 7β-hydroxy, 7-keto, and 19-hydroxy derivatives of cholesterol and their analogs with 25,26,26,26,27,27,27-heptafluoro (F7) and 26,26,26,27,27,27-hexadeuterio (d6) substitution. The 7α-hydroxy, 7β-hydroxy, and 7-keto derivatives of (25R)-cholest-5-ene-3β,26-diol (1d) and their 16,16-dideuterio analogs were also prepared. These d2-26-hydroxysterols and [16,16-2H2]-(25R)-cholest-5-ene-3β,26-diol (1e) were synthesized from [16,16-2H2]-(25R)-cholest-5-ene-3β,26-diol diacetate (2e), which can be prepared from diosgenin. The highly specific deuterium incorporation at C-16 in 1e and 2e should be useful in mass spectral analysis of 26-hydroxycholesterol samples by isotope dilution methods. The Δ5-3β,7α,26- and Δ5-3β,7β,26-triols were regioselectively oxidized/isomerized to the corresponding Δ4-3-ketosteroids with cholesterol oxidase. Also described are 5,6α-epoxy-5α-cholestan-3β-ol, its 5β,6β-isomer, cholestane-3β,5α,6β-triol, their F7 and d6 derivatives, and d3-25-hydroxycholesterol, which was prepared from 3β-acetoxy-27-norcholest-5-en-25-one (30). The 43 oxysterols and most synthetic intermediates were isolated in high purity and characterized by chromatographic and spectroscopic methods, including mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Detailed mass spectral assignments are presented, and 1H NMR stereochemical assignments are derived for the C-19 protons of 19-hydroxysterols and for the side chain protons of 30. Copyright (C) 1999 Elsevier Science Ireland Ltd.

Manganese(III) acetate dihydrate is used as a catalyst for the epoxidation of various olefins with molecular oxygen/pivalaldehyde as an oxidant in perfluoro-2-butyltelrahydrofuran. Various types of olefins, including substituted styrenea, stilbenes and cyclic and acyclic alkenes were epoxidized in excellent yields at 25°C. The reaction is stereodependent. Regioselectivity is observed on epoxidation of limonene. Mono- and disubstituted olefins show interesting dichotomy in their reactivity in fluorous solvents such as perfluoro-2-butyltetrahydrofuran and 1,1,1,3,3,3- hexafluoro-2-propanol.

The reaction of ketones (acetone, 1,1,1-trifluoropropan-2-one) with the oxidation system (arene-sulfonyl)imidazole (2)/H2O2/NaOH permits the in situ generation of the corresponding dimethyl-and methyl(trifluoromethyl)dioxirane in various solvents. This has been established by the chemoselective oxidation of azomethines 6, the diastereoselective oxidation of cholesterol (12), and 18O-labeling experiments. Because only 5 equiv of ketone are used, the dioxirane oxidation pathway appears to be virtually exclusive one in this system. One example for the nonaqueous in situ generation of dimethyldioxirane (1a) is given.

Oxaziridinium 5 efficiently epoxidises olefins. It reacts as an electrophilic reagent and does not transfer its oxygen to deactivated double-bonds or carbonyl functions. Epoxidation of cyclic allylic acetates shows a remarkable diastereoselectivity leading to the syn isomer. We propose that the epoxidation reaction proceeds through a one-step process.

The effects of oxidized cholesterols on proliferation and IgM production of human lymphoblastoid Namalwa cells were examined. An oxidized cholesterol mixture, in contrast to cholesterol, was a potent cytotoxin to Namalwa cells. Among oxidized cholesterols examined, 25-hydroxycholesterol was the most cytotoxic. However, no oxidized cholesterol examined suppressed IgM production, although cholestanetriol and 7-ketocholesterol did suppress it. Thus, oxidized cholesterols are cytotoxic to lymphocytes, while the influence on the immunoglobulin production may be marginal.

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We have investigated the behaviour of sulfonic peracids 2 in situ generated towards olefins 7a, 7b, 9, 11, 14, 16, 18, allylic acid and homoallylic alcohols 20, 22, 24, 26, 28, 30, 33 and α,β-unsaturated ketones 35, 37, 39. Generally, the epoxidation proceeds in a peracid-like manner with greater diastereoselectivity than those by common oxidants. In particular, the epoxidation of Δ4 3-ketosteroids 39a-i led to 4α,5α-epoxides 40a-i with remarkable high de-values. Enhanced α-selectivity was also found in the epoxidation of cholesterol 28b. Due to the mild reaction conditions, even acid sensitive epoxides 8a, 8b, 10, 12, 13, 15, 17, 19 were obtained in good yields.

The oxidation of cholesterol and stigmasterol with iodosylbenzene catalyzed by 5,10,15,20 - α,α,α,α- [O - (4N-methylisonicotinamido) phenyl]porphyrinatomanganese(III) acetate gives 5α, 6α-epoxides and 5β, 6β-epoxides in homogeneous medium and phospholipid vesicles in different yields. The higher yield of 5β, 6β-epoxide of above steroids in phospholipid vesicles than homgeneous medium indicate that oxidation is more regioselective in phospholipid vesicles than the homogeneous medium. The incorporation of manganese(III) porphyrin and its metal free porphyrin in phospholip-id vesicles have been studied by the UV-visible, Fluorescence, Quasi Laser Light Scattering and Transmission Electron Microscopic techniques.

Photochemically induced HgO/I2 oxidation of cholest-5-en-3α-ol (6) and cholest-5-en-3β-ol (7) afforded (Scheme 3) products arising from the corresponding alkoxy radicals (12, 13 and 14a,b) and from attack of the I2O intermediate at the olefinic double bond (epoxides 15a and 16a,b, respectively).With cholest-5-ene-1α,3β-diol 3-acetate (8) and cholest-7-ene-3β,5α-diol 3-acetate (9) the HgO/I2 oxidation led to unresolvable complex mixtures (Scheme 5).With the same reagent cholest-5-en-3α-ol acetate (10) and cholest-5-en-3β-ol acetate (11) underwent exclusively attack by I2O, to give epoxides 20a,b, iodohydrin 21, and rearranged products 19 and 22 (scheme 7), in the case of 10, and predominantly epoxides 23a,b (scheme 8), in the case of 11.

Molybdenyl(IV) acetylacetonate catalyses the conversion of various cholesterol esters into the corresponding β-epoxides in good yields with the combined use of molecular oxygen and i-butyraldehyde at room temperature.

Oxidation of pure cholesterol during heating in an air oven at high temperature was studied.Cholesterol was virtually stable during heating at 100 deg C for 24 h but was unstable at temperature above 120 deg C.In the heated choleaterol preparations, a number of oxidized derivatives were detected by a combination of thin-layer chromatography and capillary gas chromatography-mass spectrometry.Major oxidized sterols were 7α-hydroxycholesterol, 7β-hydroxycholesterol, 5α-epoxycholesterol, 5β-epoxycholesterol, cholestanetriol, and 7-ketocholesterol.Various oxidized cholesterol derivatives were produced during heating above 120 deg C within a relatively short time (1h).The composition of the oxidized products differed depending on temperature and time of heating.When cholesterol was heated at 150 deg C, the production of oxidized cholesterol was maximum, and 7-ketocholesterol was the most predominant oxidized product.Heating at 120 deg C also produced oxidized cholesterol to some extent, whereas only marginal amounts of oxidized cholesterols were produced at 100 deg C and at 200 deg C cholesterol was almost decomposed in a short time.

The biomimetic oxidation of cholesterol (4a) and sitosterol (4b) with H2O2 catalyzed with anionic water soluble iron (III) 5,10,15,20-tetraaryl porphyrins have been studied in AOT reverse micelles in differrent reaction conditions.The non-aggregating, non μ-oxodimer and electron withdrawing iron (III) 5,10,15,20-tetra(2',6'-dichloro-3'-sulphonatophenyl)porphyrin is better catalyst than simple iron (III) 5,10,15,20-tetra(4'-sulphonatophenyl)porphyrin and iron (III) 5,10,15,20-tetra(2',4',4'6'-trimethyl-3'-sulphonatophenylporphyrin .The higher yield of 4-en-3-one (6) of sterols (4) are obtained at lower pH and lower w0, whereas epoxides are also obtained at lower w0 but higher pH or in presence of N-methyl imidazole (NMI).

In the presence of catalytic amount of bis(dipivaloylmethanato)manganese(II) (= Mn(dpm)2), various cholesterol derivatives are smoothly converted into the corresponding β-epoxides in good to high yields with combined use of molecular oxygen and isobutyraldehyde.These stereoselectivities are the reversal of the cases using peracid such as mCPBA.

Dioxiranes generated in situ from a range of ketones afforded the 5,6-epoxides in high yield from cholesterol or its acetate. The α:β ratio was close to 1 in contrast to that observed for peroxyacids (ca. 4). 4,4-Dimethylcholesterol and its acetate were not epoxidised but were oxidised respectively to the 3,7-dioxo- and the 7-oxo-derivative respectively with dimethyldioxirane. Oxidations of steroidal alcohols were shown to proceed via an oxygen insertion mechanism by use of 18O-labelled substrates and 5α-cholestan-3α-ol was oxidised more quickly (>1.5 x) than its 3β-epimer.

A convenient "one-pot" procedure for the synthesis of the epoxy alcohols 1c and 2c by photooxygenation of cholesterol (1) in the presence of Ti(OiPr)4 was developed.The reaction proceeds regioselectively and stereospecifically.During the photooxygenation of 1 in the presence of Ti(IV) oxygen transfer 1a-->1c takes place much faster than the radical promoted isomerization 1a-->2a, thereby providing for regio-control.In contrast to tBuOOH/Ti(OiPr)4 epoxidations of the allylic alcohols 1b and 2b, derived from the reduction of the allylic hydroperoxides 1a and 2a, no further oxidation products, e.g. the keto epoxy alcohol 1d, were observed under the "one-pot" conditions.

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Cholesterol oxide hydrolase is recently described mammalian enzyme which catalyzes the hydration of Δ5-sterol oxides to 5,6-glycols in the liver.As the isomeric 7-dehydrocholesterol 5,6-oxides represent useful mechanistic probes of the action of the enzyme, synthetic procedures were sought for the stereoselective preparation of these unstable epoxides.Direct epoxidation of 7-dehydrocholesterol with peracid in the presence of aqueous buffer stereoselectively provided the α-oxide 2b in good yield.Synthesis of the β-oxide 12 proved more difficult in that attemptedformation of an intermediate bromohydrin with appropriate stereochemistry proved unsatisfactory.The finding that 7α-bromocholesteryl benzoate undergoes selective β-epoxidation and that the desired Δ7-double bond could be formed by treatment with potassium tert-butoxide resulted in the successful synthesis of the β- oxide 12.Both epoxides undergo cis addition of benzoic acid in chloroform at the allylic carbon and trans addition of 2-mercaptoethanol in base at the same position.Hydrolytic reactions prove to be more complex.Aqueous acid hydrolysis of the α-oxide 2b produced triol 5a and dienediol 6, which can further dehydrate to the trienol 7.Under identical conditions the β-oxide 12 hydrolyzes to a single product.Both epoxides, particulary the β-oxide 12, proved to be effective inhibitors of cholesterol oxide hydrolase.

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A new method for the synthesis of trans-β-halo carboxylates and trans-β-iodo ethers from alkenes using lead(IV)acetate-metal halide is described.KEYWORDS - lead(IV)acetate; metal halide; alkene; trans-β-halo carboxylate; trans-β-iodo ether

The ozonization of cholesterol in aqueous dispersion gave minor products 5,6α-epoxy-5α-cholestan-3β-ol and 5,6β-epoxy-5β-cholestan-3β-ol and major product 5ξ,6ξ-epidioxy-5,6-secocholestane-3β,5ξ,6ξ-triol, along with 3β-hydroxy-5-oxo-5,6-secocholestan-6-al and 3β,10-dihydroxy-5,6:5,10-disecocholestan-5-oic acid lactone (5->10) derived by decomposition of the major epidioxide product.Acetic anhydride/pyridine treatment of the epidioxide resulted in rearrangement, yielding 3β-acetoxy-10-hydroxy-6-oxo-5,6:5,10-disecocholest-3-en-5-oic acid lactone (5->10), and 6,6-diacetoxy-10-hydroxy-5,6;5,10-disecocholest-3-en-5-oic acid lactone (5->10).Acetylation of homologue 5ξ,6ξ-epidioxy-6ξ-methoxy-5,6-secocholestane-3β,5ξ-diol and its 3β-acetate also involved rearrangement to disecolactones, including 3β,6ξ-diacetoxy-10-hydroxy-6ξ-methoxy-5,6:5,10-disecocholestan-5-oic acid lactone (5->10).These results establish that 5,6-secosterol formation is the major ozonization process and 5,6-epoxidation a minor independent process and that ''anomalous'' lactone products derive by rearrangement of initially formed epidioxides.

A variety of O-alkylperoxycarbonic acids (2) were conveniently prepared in situ by utilizing alkyloxycarbonylimidazoles (1) as their precursors.Epoxidation of alkenes with such peroxy-acids was studied and their reactivities were compared with those of peroxycarboxylic acids.

The presence of an epoxide at the 4,5-position of a steroid accelerates the hydrolysis of an acetate group at the 3β or 6β-positions.This effect is also observed for a 1α-acetoxy-2β,3β-epoxide.A suitable fixed dipole-dipole orientation between the ester group and the adjacent polar group may be an important factor in the rate acceleration, since this neighbouring effect does not occur when a non-rigid side chain is present.Fliorine or bromine substitution at the 5α-position also enhances the rate of hydrolysis of 6β-acetoxy-group.

Good experimental procedures for the preparation of both (6α-2H)- and (6β-2H)-cholest-4-en-3-one are described, based on modification of methods described by Nambara and his coworkers.In addition, some less satisfactory literature methods are commented on and experiments based upon two proposed short, but unsuccessful, routes are described.

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