- Cholesterol degradation in archaeological pottery mediated by fired clay and fatty acid pro-oxidants
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Cholesterol is generally absent in animal fat residues preserved in archaeological ceramic vessels. It is known from edible oil refining that during bleaching with activated clay sterols are degraded, largely via oxidation. Laboratory heating experiments
- Hammann, Simon,Cramp, Lucy J.E.,Whittle, Mathilda,Evershed, Richard P.
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Read Online
- 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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- Metal-Free Allylic Oxidation of Steroids Using TBAI/TBHP Organocatalytic Protocol
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A mild, efficient and organocatalytic allylic oxidation of steroids using a TBAI/TBHP protocol has been developed. A range of bioactive Δ5-en-7-ones can be easily prepared from the corresponding Δ5-steroids. The methodology features several advantages, including readily available starting materials, environmentally benign oxidant, high functional group compatibility, and metal-free catalysis.
- Lam, Ying-Pong,Yeung, Ying-Yeung
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supporting information
p. 2369 - 2372
(2018/04/19)
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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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- Oxyphytosterols as active ingredients in wheat bran suppress human colon cancer cell growth: Identification, chemical synthesis, and biological evaluation
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Consumption of whole grains has been reported to be associated with a lower risk of colorectal cancer. Recent studies illustrated that phytochemicals in wheat bran (WB) may protect against colorectal cancer. There is a growing interest in the phytosterol contents of foods as either intrinsic or added components due to their beneficial health effects. However, little is known whether phytosterols in WB contribute the observed chemopreventative activity of the grain. In the present study, we directly purified and identified four oxyphytosterols 1-4 from sterol-enriched fraction of WB, and also successfully synthesized five sterol oxides 5-8 and 13. Using these nine compounds as references, we outlined a comprehensive profile of steroids in WB using tandem liquid chromatography mass spectrometry with electrospray ionization (LC-ESI/MSn, n = 2-3) techniques for the first time. Among them, three sterol oxides 13, 14, and 18 are novel compounds, and 14 compounds 3, 4, 6-11, 13, 14, 16, and 18-20 were reported in WB for the first time. Our results on the inhibitory effects of available sterol oxides 1-8 and 13 against the growth of human colon cancer cells HCT-116 and HT-29 showed that compounds 2-8 exerted significant antiproliferative effects, with oxysterol 8 being the most active one in both cells. We further demonstrated that four most active sterol oxides 5-8 could induce cell death through the apoptosis pathway. Our results showed that phytosterols, particularly oxyphytosterols, in WB possess significant antiproliferative properties, and thereby may greatly contribute the observed chemoprevention of the whole grain wheat.
- Zhu, Yingdong,Soroka, Dominique,Sang, Shengmin
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p. 2267 - 2276
(2015/03/14)
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- Structure-activity relationships of oxysterol-derived pharmacological chaperones for Niemann-Pick type C1 protein
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Niemann-Pick disease type C is a fatal neurodegenerative disease, and its major cause is mutations in NPC1 gene. This gene encodes NPC1 protein, a late endosomal polytopic membrane protein required for intracellular cholesterol trafficking. One prevalent mutation (I1061T) has been shown to cause a folding defect, which results in failure of endosomal localization of the protein, leading to loss-of-function phenotype. We have previously demonstrated that several oxysterols and their derivatives act as pharmacological chaperones; binding of these compounds to NPC1I1061T mutant protein corrects the localization/maturation defect of the mutant protein. Here, we disclose detailed structure-activity relationships of oxysterol derivatives as pharmacological chaperones for NPC1I1061T mutant.
- Ohgane, Kenji,Karaki, Fumika,Noguchi-Yachide, Tomomi,Dodo, Kosuke,Hashimoto, Yuichi
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supporting information
p. 3480 - 3485
(2014/07/22)
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- Novel synthesis strategy for the preparation of individual phytosterol oxides
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Sterols (cholesterol and phytosterols) are important structural components of cell membranes and major constituents of lipid metabolism. Research on their oxides, such as the factors affecting oxidation, oxides' structures, and qualitative and quantitative analysis, aroused more attention in this decade. However, the biological roles of individual phytosterol oxides are still unclear because no commercial individual phytosterol oxide standards are available. Different from the traditional chemical synthesis, in the present study, chemical synthesis from a starting phytosterol mixture followed with a semipreparative HPLC separation produced individual oxides. TLC and analytical HPLC were used here to not only monitor the reaction process but also specifically analyze the synthetic intermediates and oxides. The chromatographic results exhibited strict rules and similar characteristics. Finally, for the first time, four individual phytosterol oxides were successfully separated and collected by a semipreparative HPLC system, thus providing a novel strategy for the preparation of individual phytosterol oxides.
- Gao, Junlan,Yue, Qiulin,Ji, Yishun,Cheng, Beijiu,Zhang, Xin
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p. 982 - 988
(2013/08/24)
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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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- 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 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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- 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.
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Page/Page column 16-18; 20
(2009/04/24)
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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 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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- 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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