- H-Atom Abstraction vs Addition: Accounting for the Diverse Product Distribution in the Autoxidation of Cholesterol and Its Esters
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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.
- Zielinski, Zosia A. M.,Pratt, Derek A.
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p. 3037 - 3051
(2019/02/19)
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- Additional pathways of sterol metabolism: Evidence from analysis of Cyp27a1?/? mouse brain and plasma
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Cytochrome P450 (CYP) 27A1 is a key enzyme in both the acidic and neutral pathways of bile acid biosynthesis accepting cholesterol and ring-hydroxylated sterols as substrates introducing a (25R)26-hydroxy and ultimately a (25R)26-acid group to the sterol side-chain. In human, mutations in the CYP27A1 gene are the cause of the autosomal recessive disease cerebrotendinous xanthomatosis (CTX). Surprisingly, Cyp27a1 knockout mice (Cyp27a1?/?) do not present a CTX phenotype despite generating a similar global pattern of sterols. Using liquid chromatography – mass spectrometry and exploiting a charge-tagging approach for oxysterol analysis we identified over 50 cholesterol metabolites and precursors in the brain and circulation of Cyp27a1?/? mice. Notably, we identified (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids, indicating the presence of an additional sterol 26-hydroxylase in mouse. Importantly, our analysis also revealed elevated levels of 7α-hydroxycholest-4-en-3-one, which we found increased the number of oculomotor neurons in primary mouse brain cultures. 7α-Hydroxycholest-4-en-3-one is a ligand for the pregnane X receptor (PXR), activation of which is known to up-regulate the expression of CYP3A11, which we confirm has sterol 26-hydroxylase activity. This can explain the formation of (25R)26,7α- and (25S)26,7α-dihydroxy epimers of oxysterols and cholestenoic acids; the acid with the former stereochemistry is a liver X receptor (LXR) ligand that increases the number of oculomotor neurons in primary brain cultures. We hereby suggest that a lack of a motor neuron phenotype in some CTX patients and Cyp27a1?/? mice may involve increased levels of 7α-hydroxycholest-4-en-3-one and activation PXR, as well as increased levels of sterol 26-hydroxylase and the production of neuroprotective sterols capable of activating LXR.
- Griffiths, William J.,Crick, Peter J.,Meljon, Anna,Theofilopoulos, Spyridon,Abdel-Khalik, Jonas,Yutuc, Eylan,Parker, Josie E.,Kelly, Diane E.,Kelly, Steven L.,Arenas, Ernest,Wang, Yuqin
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p. 191 - 211
(2019/01/03)
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- Effect of Eleven Antioxidants in Inhibiting Thermal Oxidation of Cholesterol
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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.
- Xu, Guihua,Liu, Donghong,Zhao, Gongling,Chen, Shiguo,Wang, Jun,Ye, Xingqian
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p. 215 - 225
(2016/02/03)
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- Cholesterol transformations during heat treatment
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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.
- Derewiaka,Molińska
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p. 233 - 240
(2015/01/09)
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- Improved synthesis and in vitro evaluation of the cytotoxic profile of oxysterols oxidized at C4 (4α- and 4β-hydroxycholesterol) and C7 (7-ketocholesterol, 7α- and 7β-hydroxycholesterol) on cells of the central nervous system
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Whereas the biological activities of oxysterols oxidized at C7 (7-ketocholesterol (7KC), 7β-hydroxycholesterol (7β-OHC), 7α-hydroxycholesterol (7α-OHC)) are well documented, those of oxysterols oxidized at C4 (4β-hydroxycholesterol (4β-OHC), 4α-hydroxycholesterol (4α-OHC)) are not well known, especially on the cells of the central nervous system. Therefore, an improved methodology has been validated for 4β-OHC and 4α-OHC synthesis, and the effects on cell viability and cell growth of these molecules were studied on immortalized, tumoral and normal brain cells (158N, C6 and SK-N-BE cells, and mixed primary cultures of astrocytes and oligodendrocytes). Whereas inhibition of cell growth with 7KC, 7β-OHC, and 7α-OHC is associated with a decrease of cell viability (cytotoxic activities), our data establish that 4β-OHC and 4α-OHC have no effect on cell viability, and no or minor effect on cell growth evocating cytostatic properties. Thus, comparatively to oxysterols oxidized at C7, the toxicity of oxysterols oxidized at C4 is in the following range of order: 7KC ≥ 7β-OHC > 7α-OHC > (4β-OHC ≥ 4α-OHC). Interestingly, to date, 4β-OHC and 4α-OHC are the only oxysterols identified with cytostatic properties suggesting that these molecules, whereas not cytotoxic, may have some interests to counteract cell proliferation.
- Nury, Thomas,Samadi, Mohammad,Zarrouk, Amira,Riedinger, Jean Marc,Lizard, Gérard
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p. 558 - 567
(2013/12/04)
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- Synthesis of 7-hydroperoxycholesterol and its separation, identification, and quantification in cholesterol heated model systems
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7-Hydroperoxycholesterol is considered to be an intermediate compound of the cholesterol oxidation path as the first product formed when cholesterol is oxidized by triplet oxygen. However, there is a limitation on cholesterol mechanism studies because of the lack of 7-hydroperoxycholesterol analytical standard due to its low stability. To verify the formation of hydroperoxides in cholesterol model systems heated at 140, 180, and 220 °C, 7α-hydroperoxycholesterol was synthesized by cholesterol photooxidation followed by rearrangement at room temperature in chloroform. Its structure was confirmed on the basis of 13C NMR and mass spectra obtained by APCI-LC-MS. The synthesized compound was also used as standard for the quantification of 7-hydroperoxycholesterol as the sum of 7α-and 7β-hydroperoxycholesterol. The results demonstrated that 7-hydroperoxycholesterol is the first compound formed when the temperature is lower (140 °C). However, the concentration of the 7-hydroperoxycholesterol depends on the temperature and time of exposure: the higher the time, the higher the amount of 7-hydroperoxycholesterol at lower temperatures, and the lower the time, the lower the amount of 7-hydroperoxycholesterol at higher temperatures (180 and 220 °C). By the formation of 7-hydroperoxycholesterol, the known cholesterol oxidation mechanism in three phases (initiation, propagation, and termination) could be confirmed; once at lower temperatures, the stage of cholesterol oxidation is at initiation, at which hydroperoxide formation predominates.
- Nogueira, Gislaine C.,Costa, Bruna Z.,Crotti, Antonio E. M.,Bragagnolo, Neura
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experimental part
p. 10226 - 10230
(2011/05/05)
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- Allylic oxidations catalyzed by dirhodium caprolactamate via aqueous tert-butyl hydroperoxide: The role of the tert-butylperoxy radical
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Dirhodium(II) caprolactamate exhibits optimal efficiency for the production of the tert-butylperoxy radical, which is a selective reagent for hydrogen atom abstraction. These oxidation reactions occur with aqueous tert-butyl hydroperoxide (TBHP) without rapid hydrolysis of the caprolactamate ligands on dirhodium. Allylic oxidations of enones yield the corresponding enedione in moderate to high yields, and applications include allylic oxidations of steroidal enones. Although methylene oxidation to a ketone is more effective, methyl oxidation to a carboxylic acid can also be achieved. The superior efficiency of dirhodium(II) caprolactamate as a catalyst for allylic oxidations by TBHP (mol % of catalyst, % conversion) is described in comparative studies with other metal catalysts that are also reported to be effective for allylic oxidations. That different catalysts produce essentially the same mixture of products with the same relative yields suggests that the catalyst is not involved in product-forming steps. Mechanistic implications arising from studies of allylic oxidation with enones provide new insights into factors that control product formation. A previously undisclosed disproportionation pathway, catalyzed by the tert-butoxy radical, of mixed peroxides for the formation of ketone products via allylic oxidation has been uncovered.
- McLaughlin, Emily C.,Choi, Hojae,Wang, Kan,Chiou, Grace,Doyle, Michael P.
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supporting information; experimental part
p. 730 - 738
(2009/07/04)
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- Efficient chemoenzymatic synthesis, cytotoxic evaluation, and SAR of epoxysterols
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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.
- Carvalho, Jo?o F. S.,Cruz Silva, M. Manuel,Moreira, Jo?o N.,Sim?es, Sérgio,Sá E Melo, M. Luisa
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experimental part
p. 4007 - 4019
(2009/12/26)
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- Allylic Oxidations Catalyzed by Dirhodium Catalysts under Aqueous Conditions
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The present invention relates to compositions and methods for achieving the efficient allylic oxidation of organic molecules, especially olefins and steroids, under aqueous conditions. The invention concerns the use of dirhodium (II,II) “paddlewheel complexes, and in particular, dirhodium carboximate and tert-butyl hydroperoxide as catalysts for the reaction. The use of aqueous conditions is particularly advantageous in the allylic oxidation of 7-keto steroids, which could not be effectively oxidized using anhydrous methods, and in extending allylic oxidation to enamides and enol ethers.
- -
-
Page/Page column 16-18; 20
(2009/04/24)
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- J-based analysis and DFT-NMR assignments of natural complex molecules: Application to 3β,7-dihydroxy-5,6-epoxycholestanes
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In order to reproduce the stereochemical dispositions of the epoxy and hydroxy functionalities, four 3β,7-hydroxy-5,6-epoxycholestanes were easily prepared from cholesterol, and their NMR spectroscopic data were experimentally obtained from 1D and 2D NMR experiments. An exhaustive QM-J-based analysis was then performed to replicate the experimental H-H and C-H coupling constants as well as the 13C NMR chemical shifts. The B3LYP GIAO methodology with the 6-311-G(d,p) basis set was chosen and showed that the data obtained from rings A and B were sufficient to calculate the correct stereochemistry of the 5,6-epoxy and 7-hydroxy groups. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Poza, Jesus Javier,Jimenez, Carlos,Rodriguez, Jaime
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experimental part
p. 3960 - 3969
(2009/04/08)
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- A comparison of the potential unfavorable effects of oxycholesterol and oxyphytosterol in mice: Different effects, on cerebral 24S-hydroxychoelsterol and serum triacylglycerols levels
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Sterol oxidation products derived from cholesterol and phytosterol are formed during the processing and storage of foods. The objective of the present study was to assess the potential unfavorable effects of oxysterols in mice. C57BL/6J mice were fed an AIN-93G-based diet containing 0.2 g/kg of oxycholesterol or oxyphytosterol for 4 weeks. The most abundant oxysterol in the diet was 7-ketosterol, but α-epoxycholesterol, β-epoxycholesterol, or 7α-hydroxyphytosterol, and 7β-hydroxyphytosterol were more prominent than 7-ketosterol in the serum and liver respectively. Consumption of both oxysterols resulted in an increased in 4β-hydroxycholesterol and total oxycholesterol in the liver, but the oxycholesterol-fed mice had a lower level of cerebral 24S-hydroxycholesterol and a higher level of the serum triacylglycerols than the control and oxyphytosterol groups. These results indicate that both oxysterols in the diet are accumulated in the body, but that the biological effect of oxycholesterol is different from that of oxyphytosterol.
- Bang, Hyun-Jung,Arakawa, Chiyo,Takada, Michihiro,Sato, Masao,Imaizumi, Katsumi
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experimental part
p. 3128 - 3133
(2009/05/09)
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- Synthesis and evaluation of new 6-hydroximinosteroid analogs as cytotoxic agents
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Taking into account the structural requirements for cytotoxicity, several new hydroximinosteroid derivatives have been prepared and evaluated for their cytotoxic activity against A-549, H116, PSN1, and T98G cultured tumor cell lines in order to obtain further information on the potential pharmacophoric core of this type of compound. The influence of the oxygenated position in the A ring, the presence of an additional oxygenated position at C-7 and C-16, and a fluorinated position at C-5 were considered in order to study the structure-activity relationships. The results reveal the importance of oxygenated positions in the A ring (e.g., 4,5-epoxide showed an IC50 value against HCT-116 under micromolar level) for an increase in cytotoxic activity in this type of compound. Furthermore, they showed an important selectivity toward colon tumor line (HCT-116).
- Poza, Javier,Rega, Miriam,Paz, Vanessa,Alonso, Beatriz,Rodriguez, Jaime,Salvador, Nelida,Fernandez, Antonio,Jimenez, Carlos
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p. 4722 - 4740
(2008/03/13)
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- Synthesis and antifungal activity of oxygenated cholesterol derivatives
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A series of oxygenated cholesterol derivatives were prepared from new synthetic methods and evaluated for their in vitro antimicrobial properties against human pathogens. The activity was highly dependent on the structure of the different compounds involved. The best results were obtained with hydroxy ketones 2, 4 and 5 and diketone 7 exhibiting activities against S. cerevisiae (ATCC 28383) and Candida albicans (CIP 1663-86). For example, compound 2 exhibited high activities against C. albicans (CIP 1663-86) and Amphotericine B and miconazole resistant strain C. albicans (CIP 1180-79) at a concentration of 1.5 μg/mL.
- Brunel, Jean Michel,Loncle, Celine,Vidal, Nicolas,Dherbomez, Michel,Letourneux, Yves
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p. 907 - 912
(2007/10/03)
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- New efficient and totally stereoselective copper allylic benzoyloxylation of sterol derivatives
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A new efficient and totally stereoselective copper allylic benzoyloxylation of sterol derivatives has been developed. This methodology has been successfully applied to the synthesis of 7α-hydroxy DHEA and 7α-hydroxy cholesterol in a two-step synthesis with high chemical yields (77% and 61% overall yield, respectively). A mechanistic rationale justifying the total stereoselectivity encountered has been proposed.
- Brunel, Jean Michel,Billottet, Ludovic,Letourneux, Yves
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p. 3036 - 3041
(2007/10/03)
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- Sensitized photooxygenation of cholesterol and pseudo-cholesterol derivatives via singlet oxygen
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3-Substituted cholesterols and 7-substituted pseudocholesterols undergo a facile photooxygenation sensitized by 9, 10-dicyanoanthracene (DCA) and lumiflavin (LF) to give similar, oppositely-positioned enol derivatives. Both steroids showed the same reaction pattern associated with the endocyclic 5- and 4-olefin units, respectively. The reaction was proposed to proceed via the ene reaction of singlet oxygen and subsequent rearrangement of the initially formed 5α-hydroperoxides.
- Shuping, Wu,Zhiqin, Jiang,Heting, Li,Li, Yang,Daixun, Zeng
-
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- Singlet-oxygen ene reaction with 3β-substituted stigmastanes. An alternative pathway for the classical Schenck rearrangement
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The course of the singlet-oxygen ene reaction with stigmasta-5,22-dienes may be controlled if in the substrate a good leaving group as substituent is present at 3-C. Thus when the 5α-hydroperoxystigmasta-5,22-diene is formed instead of the well known allylic rearrangement to yield the 7α-hydroperoxystigmasta-5,22-diene isomer an intramolecular nucleophilic substitution can then occur yielding 5α-hydroxystigmasta-6,22-dien-3-one. Various stigmasta-5,22-dienes were chosen to elucidate which feature of the stigmastane is necessary to control the course of the reaction. Thus, 3β-F, 3β-Cl, 3β-Br, 3β-I and 3α-Br-stigmasta-5,22-dienes were firstly prepared and fully characterized in order to study their reaction with 1O2 under different experimental conditions. 3β-Acetoxy- and 3β-mesyloxy-stigmasta-5,22-diene derivatives were also prepared and studied.
- Ponce, Maria A.,Ramirez, Javier A.,Galagovsky, Lydia R.,Gros, Eduardo G.,Erra-Balsells, Rosa
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p. 2351 - 2357
(2007/10/03)
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- Sterol synthesis. Preparation and characterization of fluorinated and deuterated analogs of oxygenated derivatives of cholesterol
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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.
- Li, Shengrong,Pang, Jihai,Wilson, William K.,Schroepfer Jr., George J.
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- Mass spectrometry characterization of the 5α-, 7α-, and 7β-hydroxy derivatives of β-sitosterol, campesterol, stigmasterol, and brassicasterol
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The 5α-hydroperoxides of β-sitosterol, campesterol, stigmasterol, and brassicasterol were obtained by photooxidation of the respective sterols in pyridine in the presence of hematoporphyrine as sensitizer. The reduction of the hydroperoxides gives the corresponding 5α-hydroxy derivatives. The 7α- and 7β-hydroperoxides of the sterols were obtained by allowing an aliquot of the 5α-hydroperoxides to isomerize to 7α-hydroperoxides, which in turn epimerize to 7β-hydroperoxides. The reduction gave the corresponding 7α- and 7β-hydroxy derivatives. The 5α-, 7α-, and 7β-hydroxy derivatives of β-sitosterol, campesterol, stigmasterol, and brassicasterol were identified by comparing thin-layer chromatography mobilities, specific color reactions, and mass spectral data with those of the corresponding hydroxy derivatives of cholesterol, which were synthesized in the same manner. The phytosterols had the same behavior to photooxidation as cholesterol and, moreover, the different phytosterols photooxidized at about the same rate. The mass spectra of the trimethylsilyl ethers of the hydroxy derivatives of the phytosterols investigated and of the corresponding hydroxy derivatives of cholesterol have the same fragmentation patterns and similar relative ion abundances.
- Bortolomeazzi, Renzo,De Zan, Michela,Pizzale, Lorena,Conte, Lanfranco S.
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p. 3069 - 3074
(2007/10/03)
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- Iron(III)picolinate-catalyzed oxygenation of cholesteryl acetate with hydrogen peroxide or peracetic acid
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The reaction of cholesteryl acetate 1 with a Fe(III)(PA; picolinate)3/H2O2/MeCN system (reagent system A), a simple model system for mono-oxygenases, gave mainly the 7α-hydroxylation product 2a, along with 7-ketonization product 3 and the 5,6-epoxidation product 4. On the other hand, reaction of 1 using a Fe(PA)3/peracetic acid (AcOOH)/MeCN system (reagent system c) or a Fe(III)(ClO4)3 · 9H2O-picolinic acid(PAH)- pyridine(Py)/AcOOH/MeCN system (reagent system F), provided 4 predominantly without formation of 2a. The former reaction may proceed via the dimeric Fe(III)-Fe(V) manifold complex, (PAH)(PA)2Fe(III)-O-O-Fe(V)=O(PA)2 (VII) as a hypothetically active species and a nonradical pathway, and the latter may proceed through monomeric iron complexes, [(PAH)(PA)2Fe(V)=O]+ (IX) and [(PAH)(PA)2Fe(V)(OH)(OOH)I+ (X).
- Takeya, Tetsuya,Egawa, Hirotaka,Inoue, Natsu,Miyamoto, Akiko,Chuma, Toichiro,Kotani, Eiichi
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- Cytotoxicity and suppression of immunoglobulin production against human Namalwa cells caused by oxidized cholesterol
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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.
- Osada, Kyoichi,Kodama, Takehiro,Matsuo, Noritaka,Yamada, Koji,Sugano, Michihiro
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p. 1362 - 1364
(2007/10/03)
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- A convenient synthesis of 7α-hydroxycholest-4-en-3-one by the hydroxypropyl-β-cyclodextrin-facilitated cholesterol oxidase oxidation of 3β,7α-cholest-5-ene-3,7-diol
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The initial biosynthetic conversions of cholesterol to the bile acids involve sequential 7α-hydroxylation (catalyzed by cholesterol 7α-hydroxylase) followed by C-3 oxidation and concomittant double bond migration (to a Δ4-configuration, catalyzed by 3β-Δ5-C27-steroid oxidoreductase) to provide 7α-hydroxycholest-4-en-3-one.A straightforward, and economical, preparation (on a 0.1 g scale) of this pivotal biosynthetic intermediate has been devised.Reduction of 3β-(benzoyloxy)-cholest-5-en-7-one with LiB(sec-butyl)3H provided a 4:1 mixture, respectively, of the 7α- and 7β-hydroxy diastereomers, which were separated chromatographically.Solvolytic removal of the C-3 benzoyl group gave 3β,7α-cholest-5-ene-3,7-diol.A suspension of the 1:1 (v/v) complex (formed by mutual dissolution in MeOH, followed by evaporation of the solvent) of this diol with hydroxypropyl-β-cyclodextrin, at a concentration of 1 mg mL-1 (in neutral phosphate buffer), was converted by Brevibacterium sp cholesterol oxidase (0.25 U mg-1 of substrate) and catalase (70 U mg-1 of substrate, to recover O2 from the H2O2 produced by the enzymatic oxidation) to a suspension of 7α-hydroxycholest-4-en-3-one and the hydroxypropyl-β-cyclodextrin.The yield for the enzymatic conversion was in excess of 90percent.A much poorer and less reproducible yield ( 20percent) was seen in the absence of the hydroxypropyl-β-cyclodextrin.Routine extraction of this aqueous suspension, and chromatographic purification (85:15 CHCl3/acetone v/v on silica) of the residue, gave pure 7α-hydroxycholest-4-en-3-one in 68percent isolated yield.This route is a significant improvement, in terms of reaction scale and convenience, over the previous procedures for the preparation of this steroid. - Keywords: (7α)-hydroxycholesterol; hydroxypropyl-β-cyclodextrin; cholesterol oxidase; (7α)-hydroxycholest-4-en-3-one; bile acid biosynthesis; cholesterol 7α-hydroxylase
- Alexander, David L.,Fisher, Jed F.
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p. 290 - 294
(2007/10/02)
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- Oxidation of Cholesterol by Heating
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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.
- Osada, Kyoichi,Kodama, Takehiro,Yamada, Koji,Sugano, Michihiro
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p. 1198 - 1202
(2007/10/02)
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- Ene Reactions of Allylically Stannylated Cholestenes: Singlet Oxygenation of 7α-Triphenylstannylcholest-5-en-3β-ol, and of 7α-Triphenylstannyl- and 7α-Tributylstannyl-cholest-5-ene-3-one, and the Rearrangement of 5α-Tributylstannylperoxy-3β-benzyloxycholest-6-ene and of 7α-Trib...
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The reaction of some allylically stannylated steroids with singlet oxygen has been investigated. 7α-Triphenylstannylcholest-4-ene-3β-ol reacts on the β-face with shift of the 4β-hydrogen to give 6β-hydroperoxy-7α-triphenylstannylcholest-4-ene-3β-ol, whereas cholest-5-ene-3β-ol itself reacts on the α-face to give 5α-hydroperoxycholest-6-ene-3β-ol. 7α-Triphenylstannyl- and 7α-tributylstannylcholest-5-ene-3-one give the corresponding 6β-hydroperoxy-7α-stannylcholest-4-ene-3-one (50-55percent), together with the 4,6-dien-3-one which is formed by elimination.In contrast, the parent cholest-5-en-3-one under the same conditions gives some of the 6β-hydroperoxy-4-ene-3-one, but the principal product is the hemiperketal from the 5α-hydroperoxycholest-6-ene-3-one.In neither system was there any evidence for a metalloene reaction, nor for cycloaddition accompanied by a nucleophilic 1,2-shift of the tin. 3β-Benzoyloxy-5α-tributylstannylperoxycholest-6-ene undergoes the Schenck and Smith types of rearrangement by a radical chain mechanism to give successively the corresponding 7α- and 7β-stannylperoxy-5-enes.
- Dang, H.-S.,Davies, Alwyn G.
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p. 1095 - 1101
(2007/10/02)
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- Biomimetic oxidation of cholesterol and related sterols by chemical model for horseradish peroxidate (HRP) in AOT reverse micelles
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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).
- Chauhan, S M S,Ray, P C,Satapathy, S,Vijayarahavan, B
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p. 837 - 843
(2007/10/02)
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- Reactivities of Some Allylic Hydroperoxides toward Allylic Rearrangement and Related Reactions
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The allylic rearrangement has been studied of the hydroperoxides that are formed when singlet oxygen reacts with epicholesterol, Δ9,10-octahydronaphthalene, 2,3-dimethylbut-2-ene, cyclopentylidenecyclopentane, and cyclohexylidenecyclohexane.The reactivity in this sense decreases in the above sequence. 1-(Cyclopent-1-enyl)cyclopentyl hydroperoxide rearranges only slowly, but in the presence of triplet oxygen it reacts to give 1-(5-hydroperoxycyclopent-1-enyl)cyclopentyl hydroperoxide, and 1-(cyclohex-1-enyl)cyclohexyl hydroperoxide does not rearrange and shows only the reaction with oxygen to give 1-(6-hydroperoxycyclohex-1-enyl)cyclohexyl hydroperoxide.The various factors that affect the rates of these reactions are discussed.It is suggested that the reactivity and regioselectivity in the autoxidation which leads to the formation of dihydroperoxides implies that the reaction involves not the usual two-step propagation sequence, but a three-step sequence in which the chain carriers are a cycloalkenyl radical, a cycloalkenylperoxyl radical, and a cycloalkylperoxyl radical.
- Dang, Hai-Shan,Davies, Alwyn G.,Davison, Ian G. E.,Schiesser, Carl H.
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p. 1432 - 1438
(2007/10/02)
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- The mechanisms of the rearrangements of allylic hydroperoxides: 5α-hydroperoxy-3β-hydroxycholest-6-ene and 7α-hydroperoxy- 3β-hydroxycholest-5-ene
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The rearrangement of 5α-hydroperoxy-3β-hydroxycholest-6-ene in solution under 18O2, gives isotopically normal 7α-hydroperoxy-3β-hydroxycholest-5-ene, whereas the epimerization of this product to give 7β-hydroperoxy-3β-hydroxycholest-5-ene involves incorporation of 73-83% of 18O2 into the hydroperoxy group. These two reactions proceed through the corresponding hydroperoxyl radicals, which have different e.s.r. spectra and which therefore must exist as separate and distinct species. The former reaction shows a first-order dependence on hydroperoxide concentration, and a half-order dependence on t-butyl hyponitrite which was added as an initiator. It is suggested that the first reaction involves a sigmatropic [2,3]-rearrangement, whereas the second reaction proceeds through a dissociative mechanism.
- Beckwith, Athelstan L. J.,Davies, Alwyn G.,Davison, Ian G. E.,Maccoll, Allan,Mruzek, Margaret H.
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p. 815 - 824
(2007/10/02)
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- Catalytic Oxygenation of Cholesterol with a Platinum Catalyst under Moderate Pressure of Oxygen
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The catalytic oxigenation of cholesterol 1 with a platinum black catalyst under moderate pressure (20-25 atm) of oxygen yielded eleven oxidation products, 3-13a.The reaction pathway of the catalytic oxygenation is discussed on the basis of the results for several reaction conditions.
- Sakamaki, Hiroshi,Take, Masa-aki,Akihisa, Toshihiro,Matsumoto, Taro,Ichinohe, Yoshiyuki
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p. 3023 - 3025
(2007/10/02)
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- Regio- and Stereo-Controlled Oxygen Functionalization of Cholesterol by Photooxygenation in the Presence of Titanium Tetraisopropoxide
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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.
- Adam, Waldemar,Staab, Eugen
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p. 757 - 760
(2007/10/02)
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- STEREOSPECIFIC SYNTHESES OF 7β- AND 7α-HYDROXYCHOLESTEROLS
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The stereospecific syntheses of 7β- and 7α-hydroxycholesterols from cholesterol are described.
- Kumar, Vijay,Amann, Alain,Ourisson, Guy,Luu, Bang
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p. 1279 - 1286
(2007/10/02)
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- Stereoselectivity in Reduction of Steroidal 7-Ketones
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Several 7-ketones of lanostane, 4,4-dimethylcholestane and cholestane derivatives were subjected to catalytic hydrogenation on platinum, reduction with complex hydrides and reduction with sodium in tert-butanol, and the product ratios (7α-ol/7β-ol) were determined by gas chromatography or high-performance liquid chromatography.Catalytic hydrogenation of 3β hydroxylanostan-7-one and 3β-hydroxy-4,4-dimethylcholestan-7one yielded the 7β-alcohols as the major products, whereas their 3-acetates gave prinsipally the 7α-alcohols.Reductionof various 7-ketones with sodium in tert-butanol gave mainly the 7β-equitoiral alcohols, while the epimeric 7α-ols were the major products on reduction with litium tri-sec- butilborohydride.The stereoselectivity of reduction with sodium borohydride and lihium aluminium hydride was highly dependent on the neighboring double bond and 4,4-dimethiyl and/or 14α-methyl substituent(s). Keywords---reduction; 7-oxygenated sterol; stereoselectivity; lithium tri-sec-butylborohydride; 3β-hydroxy-4,4-dimethylcholestan-7one
- Maruyama, Sanae,Ogihara, Noriko,Adachi, Itsuko,Ohotawa, Junko,Morisaki, Masuo
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p. 1847 - 1852
(2007/10/02)
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- Oxygenated sterol derivatives. Their identification from the fungus-infected silkworm carcass, Bombyx cum Botryte, and their effects on growth and sterol metabolism of the silkworm, Bombyx mori
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Several oxygenated sterols, e.g. ergosterol peroxide, 7-oxocholesterol and 7 β-hydroxycholesterol, were identified from the fungus-infected carcass of silkworm, Bombyx cum Botryte. However, they were nontoxic to the silkworm Bombyx mori reared on a diet containing these oxygenated sterols (0.01%) together with sitosterol or cholesterol (0.1%).
- Ying,Morisaki,Ikekawa
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p. 3003 - 3008
(2007/10/02)
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- Iron-catalyzed Autoxidation of Liposomal Cholesterol
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The autooxidation of cholesterol in a benzene solution of egg lecithin and Fe(acac)3, giving products variously oxygenated in the steroidal ring B, proceeded with consumption of the unsaturated long chain fatty acid moieties, particularly C18:2, in the lechitin molecule.The reaction showed a marked β-stereoselectivity of epoxidation and was inhibited by a radical scavenger (BHT).Cholesterol was highly susceptible to ferric iron-catalyzed autoxidation within liposomes prepared by using lechitin.The oxidative degradation of the unsaturated moieties, C18:1 and C18:2, in the lechitin led to allylic oxidation as well as the β-stereoselective epoxidation of cholesterol.A radical scavenger inhibited both the degradation of these moities and the oxygenation of cholesterol.The oxygenation was retarded in liposomes prepared by using saturated dipalmitoyl lecithin, and was dominated by allylic oxidation giving cholesteryl hydroperoxide as the main product.Cholesterol in the liposomes containing egg lecithin was, thus, assumed to be co-oxidized with the unsaturated fatty acid moieties by radical pathway, when the liposomes were autoxidized in the presence of ferric catalyst.Keywords - cholesterol; egg lecithin; liposome; liposomal cholesterol; autoxidation; stereoselective epoxidation; lipid peroxidation; co-oxidation; radical pathway; iron catalyst
- Muto, Toshiki,Tanaka, Jun,Miura, Toshiaki,Kimura, Michiya
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p. 1561 - 1566
(2007/10/02)
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- Synthesis of Cholestane-3β,5α,7α-triol
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7-Oxocholesteryl acetate (II) on reduction with LAH gives the epimeric diols of which Δ5-cholestane-3β,7α-diol (III) is predominant.The diol (III) on epoxidation with m-chloroperbenzoic acid gives a mixture of epoxides (VI) which is reduced with LAH to give the desired cholestane-3β,5α,7α-triol (VII).Structures of the compounds have been confirmed by spectroscopic data.
- Pai, K. G.,Sunthankar, S. V.
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p. 509 - 510
(2007/10/02)
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- A sterospecific synthesis of 7alpha-hydroxycholesterol.
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The five step synthesis of 7alpha-hydroxycholesterol utilizes the solvolysis of 7alpha-bromocholesterol benzoate with potassium acetate in acetic acid as the key step in controlling the stereospecificity of the reaction sequence. This reaction yields 7alpha-acetoxycholesterol benzoate with retention of configuration at position seven. The diester is readily reduced with lithium aluminum to 7alpha-hydroxycholesterol.
- Johnson,Lack
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