- 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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- Copper-catalysed allylic oxidation of Δ5-steroids by t-butyl hydroperoxide
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Δ5-7-Oxosteroids are efficiently prepared from Δ5-steroids with t-BuOOH and a copper catalyst, either Cu(II) and Cu(I) salts or Cu metal; selectivity in the presence of a secondary alcohol is observed.
- Salvador,E Melo,Campos Neves
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- CrO3/NHPI adsorbed on activated clay: A new supported reagent for allylic selective oxidation of Δ5-sterols
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Chromium trioxide and N-hydroxyphthalimide (NHPI) supported on activated clay could serve as an efficient and mild oxidant for allylic selective oxidation of Δ5-sterols. Thus, a ketone group could be easily introduced into the allylic position of Δ5-sterols with the existence of a sensitive 3β-hydroxyl group. The oxidant residue can be removed easily from the reaction mixture by filtration and reused after reactivation at 120δC for 4-6 h. Copyright Taylor & Francis Group, LLC.
- Liu, Jin,Zhu, Hong-You,Cheng, Xiao-Hong
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- Recyclable Dirhodium(II) Catalyst Rh2(esp)2 for the Allylic Oxidation of Δ5-Steroids
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The chelating dirhodium(II) catalyst Rh2(esp)2 was shown to efficiently catalyze the allylic oxidation of Δ5-steroids using T-HYDRO (70% tert-butyl hydroperoxide in water) as oxidant. Reaction yields were affected by the coordination ability of the solvent. The noncoordinating solvent n-heptane was determined to be an optimal solvent. At gram scale, the product, Δ5-en-7-one steroid, precipitated from the reaction mixture. The Rh2(esp)2 complex did not undergo catalytic degradation and was recycled using Merrifield-pyridine resin for further allylic oxidation cycles. The results of ultraviolet/visible spectral analysis suggested that the Rh2(II,II) species, rather than the Rh2(II,III) species, was in the catalyst resting state during the reaction, which helps to explain the high durability of the catalyst.
- Wang, Yi,Kuang, Yi,Zhang, Hongyang,Ma, Ruocheng,Wang, Yuanhua
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- Bismuth-catalyzed allylic oxidation using t-butyl hydroperoxide
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Bismuth(III) salts are efficient catalysts for the selective allylic oxidation using tert-butyl hydroperoxide. BiCl3 is especially effective and can be easily recovered and reused as BiOCl. Using BiCl 3/K-10 as catalyst, an increase in the reaction rate was observed.
- Salvador, Jorge A.R.,Silvestre, Samuel M.
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- Biohydroxylation of 7-oxo-DHEA, a natural metabolite of DHEA, resulting in formation of new metabolites of potential pharmaceutical interest
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Metabolism of steroids in healthy and unhealthy human organs is the subject of extensive clinical and biomedical studies. For this kind of investigations, it is essential that the reference samples of new derivatives of natural, physiologically active steroids (especially those difficult to achieve in the chemical synthesis) become available. This study demonstrated for the first time transformation of 7-oxo-DHEA—a natural metabolite of DHEA, using Syncephalastrum racemosum cells. The single-pulse fermentation of substrate produced two new hydroxy metabolites: 1β,3β-dihydroxy-androst-5-en-7,17-dione and 3β,12β-dihydroxy-androst-5-en-7,17-dione, along with the earlier reported 3β,9α-dihydroxy-androst-5-en-7,17-dione and 3β,17β-dihydroxy-androst-5-en-7-one. Simultaneously, the same metabolites, together with small quantities of 7α- and 7β-hydroxy-DHEA, as well as the products of their reduction at the C-17 were obtained after transformation of DHEA under pulse-feeding of the substrate. The observed reactions suggested that this micro-organism contains enzymes exhibiting similar activity to those present in human cells. Thus, the resulting compounds can be considered as potential components of the eukaryotic, including human, metabolome.
- ?wizdor, Alina,Panek, Anna,Milecka-Tronina, Natalia
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- Optimization of the allylic oxidation in the synthesis of 7-keto-Δ5-steroidal substrates
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A variety of Δ5-steroids were converted into α, β-unsaturated 7-ketones using a modification of the already known method of t-butyl hydroperoxide in the presence of copper iodide in acetonitrile. The same alteration was applied to another oxidative procedure, which had never been used before on steroidal substrates. The same oxidative agent was used in the presence of copper iodide, and tetra-n-butylammonium bromide was used as a phase-transfer catalyst in a two-phase system of water/methylene chloride. It was found that the allylic oxidation proceeded more efficiently when t-butyl hydroperoxide was added to the reaction mixture in portions. The initial addition of the total amount of oxidant or its dropwise addition afforded low yields. This observation contributes to the investigation of the reaction mechanism, and high-yield conversions of steroidal 5,6-enes into the corresponding conjugated 7-ones in short reaction times are reported.
- Arsenou, Evaggelia S.,Koutsourea, Anna I.,Fousteris, Manolis A.,Nikolaropoulos, Sotiris S.
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- N-Hydroxyphthalimide catalyzed allylic oxidation of steroids with t-butyl hydroperoxide
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A new and optimized procedure for the allylic oxidation of Δ5-steroids with t-butyl hydroperoxide in the presence of catalytic amounts of N-hydroxyphthalimide (NHPI) under mild conditions was developed, showing excellent regioselectivity and chemoselectivity (functional group compatibility). It was found that Co(OAc)2 could enhance the catalytic ability of NHPI resulting in better yields and shorter reaction times. The reaction mechanism and the scope of the reaction with a variety of Δ5-steroidal substrates were also investigated.
- Zhao, Qian,Qian, Chao,Chen, Xin-Zhi
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- Visible-Light-Enabled Allylic C-H Oxidation: Metal-free Photocatalytic Generation of Enones
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A practical and efficient method has been established for the direct oxidation of allylic C-H bonds catalyzed by visible-light-enabled photoredox agents. This protocol uses oxygen as the sole oxidant under metal-free conditions at room temperature and pro
- Liu, Chao,Liu, Hui,Zheng, Xuan,Chen, Shanyi,Lai, Qihong,Zheng, Changlong,Huang, Mingqiang,Cai, Kaicong,Cai, Zhixiong,Cai, Shunyou
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p. 1375 - 1381
(2022/02/07)
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- Iridium-catalysed highly selective reduction-elimination of steroidal 4-en-3-ones to 3,5-dienes in water
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Steroidal 3,5-diene is an important structural motif in steroid drugs. In this report, an iridium-catalyzed reduction-elimination of readily available steroidal 4-en-3-ones is realized to prepare steroidal 3,5-dienes. At a low catalyst loading (S/C = 200), heating 4-en-3-ones in a water-mixed organic solvent with formic acid without inert atmosphere protection afforded the desired 3,5-dienes in moderate to excellent yields. In a gram-scale preparation, recrystallization is used instead of column chromatography to purify products. Excellent functionality tolerance and regioselectivity are featured. Structural moieties such as alkanols (primary, secondary and tertiary), esters (except for formate), tolylates, and ketones (endocyclic or exocyclic) are not affected. Surprisingly, the reduction-elimination only takes place at A-ring 4-en-3-ones. In addition, bicyclic 4-en-3-ones are also viable substrates. Synthetic applications of steroidal 3,5-dienes are demonstrated. Our method can also lead to steroidal 3,5-dienes-3-d (>99% d-incorporation) when DCO2D and D2O are used together.
- Li, Jide,Tang, Weiping,Ren, Demin,Xu, Jiaxi,Yang, Zhanhui
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supporting information
p. 2088 - 2094
(2019/04/29)
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- Scalable and sustainable electrochemical allylic C-H oxidation
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New methods and strategies for the direct functionalization of C-H bonds are beginning to reshape the field of retrosynthetic analysis, affecting the synthesis of natural products, medicines and materials. The oxidation of allylic systems has played a prominent role in this context as possibly the most widely applied C-H functionalization, owing to the utility of enones and allylic alcohols as versatile intermediates, and their prevalence in natural and unnatural materials. Allylic oxidations have featured in hundreds of syntheses, including some natural product syntheses regarded as € classics €. Despite many attempts to improve the efficiency and practicality of this transformation, the majority of conditions still use highly toxic reagents (based around toxic elements such as chromium or selenium) or expensive catalysts (such as palladium or rhodium). These requirements are problematic in industrial settings; currently, no scalable and sustainable solution to allylic oxidation exists. This oxidation strategy is therefore rarely used for large-scale synthetic applications, limiting the adoption of this retrosynthetic strategy by industrial scientists. Here we describe an electrochemical C-H oxidation strategy that exhibits broad substrate scope, operational simplicity and high chemoselectivity. It uses inexpensive and readily available materials, and represents a scalable allylic C-H oxidation (demonstrated on 100 grams), enabling the adoption of this C-H oxidation strategy in large-scale industrial settings without substantial environmental impact.
- Horn, Evan J.,Rosen, Brandon R.,Chen, Yong,Tang, Jiaze,Chen, Ke,Eastgate, Martin D.,Baran, Phil S.
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- MnO2/TBHP: A Versatile and User-Friendly Combination of Reagents for the Oxidation of Allylic and Benzylic Methylene Functional Groups
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In the presence of activated MnO2, tert-butyl hydroperoxide (TBHP) in CH2Cl2 is able to oxidize the allylic and benzylic methylene groups of different classes of compounds. I describe a one-pot oxidation protocol based on two sequential steps. In the first step, carried out at low temperature, MnO2 catalyses the oxidation of the methylene group. This is followed by a second step where reaction temperature is increased, allowing MnO2 both to catalyse the decomposition of unreacted TBHP and to oxidize allylic alcohols that could possibly be formed. The proposed oxidation procedure is generally applicable, although its efficiency, regioselectivity, and chemoselectivity are strongly dependent on the structure of the substrate. A simple and user-friendly synthetic procedure for the oxidation of allylic and benzylic methylene groups to the corresponding conjugated carbonyl derivatives is described. The proposed oxidation protocol is based on the combined use of MnO2 and tert-butyl hydroperoxide, and is generally applicable.
- Serra, Stefano
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p. 6472 - 6478
(2015/10/19)
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- Highly stereoselective epoxidation with H2O2 catalyzed by electron-rich aminopyridine manganese catalysts
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Fast, efficient, and highly stereoselective epoxidation with H 2O2 is reached by manganese coordination complexes with e-rich aminopyridine tetradentate ligands. It is shown that the electronic properties of these catalysts vary systematically with the stereoselectivity of the O-atom transfer event and exert fine control over the activation of hydrogen peroxide, reducing the amount of carboxylic acid co-catalyst necessary for efficient operation.
- Cusso, Olaf,Garcia-Bosch, Isaac,Font, David,Ribas, Xavi,Lloret-Fillol, Julio,Costas, Miquel
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supporting information
p. 6158 - 6161
(2014/01/17)
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- An unprecedented method for the generation of tert -butylperoxy radical using DIB/TBHP protocol: Solvent effect and application on allylic oxidation
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Figure presented Tert-Butylperoxy radical was generated with PhI(OAc) 2 and tBuOOH. Ester solvent was found to be critical and the protocol was applied in the allylic oxidation of various olefinic substrates, which gave the corresponding α,β-unsaturated enones in good yield and regioselectivity.
- Zhao, Yi,Yeung, Ying-Yeung
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supporting information; experimental part
p. 2128 - 2131
(2010/08/05)
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- Optimal TBHP allylic oxidation of Δ5 - Steroids catalyzed by dirhodium caprolactamate
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Dirhodium caprolactamate is the most efficient catalyst for the oxidation of Δ5-steroids to 7-keto-Δ5-steroids by 70% tert-butyl hydroperoxide in water (T-HYDRO). Isolated product yields range from 38 to 87%.
- Choi, Hojae,Doyle, Michael P.
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p. 5349 - 5352
(2008/09/17)
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- Allylic and benzylic oxidation reactions with sodium chlorite
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Various allylic and benzylic substrates were selectively oxidized to the corresponding enones in good yields using sodium chlorite, either in combination with tert-butyl hydroperoxide in stoichiometric conditions, or associated with N-hydroxyphthalimide as catalyst. These oxidation reactions were effectively and economically performed under mild, transition-metal free conditions and therefore the dual challenge of cost effectiveness and benign nature of the processes was met with.
- Silvestre, Samuel M.,Salvador, Jorge A.R.
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p. 2439 - 2445
(2007/10/03)
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- Mild manganese(III) acetate catalyzed allylic oxidation: Application to simple and complex alkenes
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Manganese(III) acetate catalyzed allylic oxidation of alkenes to the corresponding enones was investigated, showing excellent regioselectivity and chemoselectivity (functional group compatibility). Δ5-Steroids were transformed into bioactive Δ5-en-7-ones under a nitrogen atmosphere, whereas simple alkenes were converted into the corresponding enones under an oxygen atmosphere in good yields.
- Shing, Tony K. M.,Yeung, Ying-Yeung,Su, Pak L.
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p. 3149 - 3151
(2007/10/03)
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- Preparation of 3β-acetoxy-17a-oxo-androst-5-ene-7,17-dione, a biologically active impurity isolated from the production of 3β-acetoxyandrost-5-ene-7,17-dione
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An impurity isolated during the kilo-lab preparation of 3β-acetoxyandrost-5-ene-7,17-dione was identified as 3β-acetoxy-17a- oxo-androst-5-ene-7,17-dione. This novel D-ring secosteroid was postulated to be a Baeyer-Villiger oxidation by-product of the preparation reaction. A genuine sample was prepared by the selective peracid-mediated Baeyer-Villiger reaction on 3β-acetoxyandrost-5-ene-7,17-dione (7-oxo-DHEA acetate), confirming the novel structure.
- Coutts, Lisa D.,DeOrazio, Russell J.,Meckler, Harold
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p. 979 - 985
(2007/10/03)
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- Methods for preparing 7alpha-hydroxy-dehydroepiandrosterone
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The invention relates to new processes for preparing 7alpha-hydroxy-dehydroepiandrosterone of formula (1): 1
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- Microwave induced selective enolization of steroidal ketones and efficient acetylation of sterols in semisolid state
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Under microwave irradiation steroidal enones, more specifically, position three carbonyls were efficiently and selectively converted to the corresponding enol acetates in the presence of additional enolizable carbonyl functions at other positions, using acetic anhydride and a catalytic amount of toluene-p-sulfonic acid. Acetylation of hydroxyl groups of the sterols, including those at the hindered positions, was near quantitative. Strictly anhydrous conditions were not a pre-requisite for acetylation and the reaction system easily tolerated up to 10% (v/v) moisture.
- Marwah, Padma,Marwah, Ashok,Lardy, Henry A.
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p. 2273 - 2287
(2007/10/03)
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- Allylic and benzylic oxidation using cobalt(II) alkyl phosphonate modified silica
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The allylic and benzylic oxidation of a range of substrates proceeds in good yield using catalytic quantities of cobalt(II) alkyl phosphonate modified silica and tert-butyl hydroperoxide.
- Jurado-Gonzalez, Magdalena,Sullivan, Alice C.,Wilson, John R. H.
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p. 4283 - 4286
(2007/10/03)
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- Process for effecting allylic oxidation using dicarboxylic acid imides and chromium reagents
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A procedure for oxidizing organic compounds having allylic hydrogen atom(s) involving the steps of reactively contacting the organic compound with a combination of an N-hydroxy dicarboxylic acid imide and a chromium-containing oxidant. The reaction can conveniently be conducted under ambient temperature and pressure conditions, and is conveniently conducted in a co-solvent system of water and organic solvent(s).
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Page column 7-8
(2008/06/13)
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- Process for allylic oxidation using metal hypochlorite and alkyl hydroperoxide
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The present invention is directed to a process for effecting the allylic oxidation of an allylic compound having at least two allylic hydrogen atoms on the same carbon atom into corresponding α,β-unsaturated carbonyl compound, using a combination of a metal hypochlorite and an alkyl hydroperoxide in a mixture of suitable conventional organic solvent(s) and/or water at a temperature of between about ?5° C. to +25° C.
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- The allylic oxidation of unsaturated steroids by tert-butyl hydroperoxide using homogeneous and heterogeneous cobalt acetate
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Cobalt acetate is an effective catalyst for the selective allylic oxidation of unsaturated steroids using tert-butyl hydroperoxide especially when used in a supported form when it can be easily recovered and reused.
- Salvador,Clark
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- Steroid transformations with Fusarium oxysporum var. cubense and Colletotrichum musae
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The utility of two locally isolated fungi, pathogenic to banana, for steroid biotransformation has been studied. The deuteromycetes Fusarium oxysporum var. cubense (IMI 326069, UAMH 9013) and Colletotrichum musae (IMI 374528, UAMH 8929) had not been examined previously for this potential. In general, F. oxysporum var. cubense effected 7α hydroxylation on 3β-hydroxy- Δ5-steroids, 6β, 12β, and 15α hydroxylation on steroidal-4-ene-3-ones, side-chain degradation on 17α,21-dihydroxypregnene-3,20-diones, and 15α hydroxylation on estrone. Both strains were shown to perform redox reactions on alcohols and ketones.
- Wilson, Maureen R.,Gallimore, Winklet A.,Reese, Paul B.
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p. 834 - 843
(2007/10/03)
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- The Stereochemistry of Epoxidation of Δ5-Steroids with Sodium Perborate and Potassium Permanganate
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Sodium perborate, with potassium permanganate as a catalyst, has been shown to be a novel reagent for the epoxidation of steroidal 5-enes with the attack occurring predominantly on the β-face.
- Hanson, James R.,Terry, Nicolas,Uyanik, Cavit
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- The Stereochemistry of Oxidation of Some B-Norsteroids
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The oxidation of ring B of some B-norsteroids is shown to have a different stereochemistry when compared to the same reactions in the normal six-membered series and it is suggested that caution should be exercised in drawing general stereochemical conclusions solely on evidence from the six-membered series.
- Hanson, James R.,Manickavasagar, Revathy,Thangavelu, Vasuki
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p. 3245 - 3260
(2007/10/03)
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- Ergosteroids II: Biologically active metabolites and synthetic derivatives of dehydroepiandrosterone
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An improved procedure for the synthesis of 3β-hydroxyandrost-5-ene- 7,17-dione, a natural metabolite of dehydroepiandrosterone (DHEA) is described. The synthesis and magnetic resonance spectra of several other related steroids are presented. Feeding dehydroepiandrosterone to rats induces enhanced formation of several liver enzymes among which are mitochondrial sn-glycerol 3-phosphate dehydrogenase (GPDH) and cytosolic malic enzyme. The induction of these two enzymes, that complete a thermogenic system in rat liver, was used as an assay to search for derivatives of DHEA that might be more active than the parent steroid. Activity is retained in steroids that are reduced to the corresponding 17β-hydroxy derivative, or hydroxylated at 7α or 7β, and is considerably enhanced when the 17-hydroxy or 17-carbonyl steroid is converted to the 7-oxo derivative. Several derivatives of DHEA did not induce the thermogenic enzymes whereas the corresponding 7-oxo compounds did. Both short and long chain acyl esters of DHEA and of 7-oxo-DHEA are active inducers of the liver enzymes when fed to rats. 7-Oxo-DHEA-3-sulfate is as active as 7-oxo-DHEA or its 3-acetyl ester, whereas DHEA-3-sulfate is much less active than DHEA. Among many steroids tested, those possessing a carbonyl group at position 3, a methyl group at 7, a hydroxyl group at positions 1, 2, 4, 11, or 19, or a saturated B ring, with or without a 4-5 double bond, were inactive.
- Lardy, Henry,Kneer, Nancy,Wei, Yong,Partridge, Bruce,Marwah, Padma
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p. 158 - 165
(2007/10/03)
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- Some reaction safety aspects of ruthenium-catalyzed allylic oxidations of Δ-5-steroids in the pilot plant
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The ruthenium-catalyzed allylic oxidation of Δ-5-steroids with tert-butyl hydroperoxide to the corresponding unsaturated ketones was studied. During the scale-up to the pilot plant level, serious safety problems were detected, and the identified runaway potential of this reaction was studied. By modifying the original oxidation procedure, it was possible to establish this reaction safely in the pilot plant at 17-kg scale. Furthermore, the procedure was applied successfully to several other steroids on the laboratory scale.
- Harre, Michael,Haufe, Reinhard,Nickisch, Klaus,Weinig, Peter,Weinmann, Hilmar,Kinney, William A.,Zhang, Xuehai
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p. 100 - 104
(2013/09/08)
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- Stereoselective 7α-hydroxylation of 3β-acetoxy-Δ5-steroids by Fe(PA)3/H2O2/MeCN
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Stereoselective 7α-hydroxylation reaction of Δ5-steroids by a Fe(PA; picolinate)3/H2O2/MeCN system is presented. The 7α-hydroxylation reactions were achieved in 33-40% yields by addition of 30%-H2O2 to a solution of 3β-acetoxy-Δ5-steroids 1a-1d and a crystalline of Fe(PA)3 in MeCN.
- Kotani, Eiichi,Takeya, Tetsuya,Egawa, Hirotaka,Tobinaga, Seisho
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p. 750 - 752
(2007/10/03)
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- Hypervalent (tert-butylperoxy)iodanes generate iodine-centered radicals at room temperature in solution: Oxidation and deprotection of benzyl and allyl ethers, and evidence for generation of α-oxy carbon radicals
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1-(tert-Butylperoxy)-1,2-benziodoxol-3(1H)-one (1a) oxidizes benzyl and allyl ethers to the esters at room temperature in benzene or cyclohexane in the presence of alkali metal carbonates. Since this reaction is compatible with other protecting groups such as MOM, THP, and TBDMS ethers, and acetoxy groups, and because esters are readily hydrolyzed under basic conditions, this new method provides a convenient and effective alternative to the usual reductive deprotection. Oxidation with 1a occurs readily with C-H bonds activated by both enthalpic effects (benzylic, allylic, and propargylic C-H bonds) and/or polar effects (α-oxy C-H bonds), generating α-oxy carbon-centered radicals, which can be detected by nitroxyl radical trapping. Measurement of the relative rates of oxidation for a series of ring-substituted benzyl n-butyl ethers 2d and 2p-s indicated that electron-releasing groups such as p-MeO and p-Me groups increase the rate of oxidation, and Hammett correlation of the relative rate factors with the σ+ constants of substituents afforded the reaction constant ρ+ = -0.30. The large value of the isotope effect obtained for the oxidation of benzyl n-butyl ether 2d (k(H)/k(D) = 12-14) indicates that the rate-determining step of the reactions probably involves a high degree of benzylic C-H bond breaking. The effects of molecular dioxygen were examined, and the mechanism involving the intermediacy of the tert-butylperoxy acetal 5 and/or the hydroperoxy acetal 32 is proposed. Particularly noteworthy is the finding that (tert-butylperoxy)iodane 1a can generate the tert-butylperoxy radical and the iodine-centered radical 33a, even at room temperature in solution, via homolytic bond cleavage of the hypervalent iodine(III)-peroxy bond.
- Ochiai, Masahito,Ito, Takao,Takahashi, Hideo,Nakanishi, Akinobu,Toyonari, Mika,Sueda, Takuya,Goto, Satoru,Shiro, Motoo
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p. 7716 - 7730
(2007/10/03)
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- Preparation of 7-[O-(carboxymethyl)oxime] derivatives of dehydroepiandrosterone and pregnenolone
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Novel simple syntheses of 7-(O-carboxymethyloxime) derivatives of 3β-hydroxyandrost-5-en-17-one (dehydroepiandrosterone) and of 3β-hydroxypregn-5-en-20-one (pregnenolone) are reported. In the first one, 17-oxoandrost-5-en-3β-y1 acetate was oxidized to give the 7,17-dione which was then selectively reduced in the position 17. Oximation, reoxidation, and deacetylation yielded the desired oxime. The second synthesis started with (20R)-pregn-5-ene-3β,20-diol 3-acetate which was converted to the 20-nitrate, oxidized to the C-7 ketone, oximated, partially deprotected in position 20, reoxidized, and deacetylated. Both the 7-(O-carboxymethyloxime) derivatives have been devised as immunoassay components.
- Pouzar, Vladimir,Slavikova, Tereza,Cerny, Ivan
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p. 404 - 412
(2007/10/03)
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- BIMETALLIC OXIDATION CATALYSTS: OXIDATIONS WITH TERT.BUTYLHYDROPEROXIDE MEDIATED BY BIS-(TRIBUTYLTIN OXIDE) DIOXOCHROMIUM (VI)
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At 40-80 deg C, t.BuOOH in conjunction with catalytic amounts of (n.Bu3SnO)2CrO2 1 oxidizes benzylic alcohols, methylenes in α-position of aryl, ethylenic or acetylenic groups into ketones, anthracene into anthraquinone, adamantane into adamantan-1-ol and 2-one.Except for propargylic oxidations, yields are generally superior to those obtained when CrO3 is used as catalyst instead of 1.
- Muzart, Jacques
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p. 2061 - 2068
(2007/10/02)
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- SYNTHESIS, CRYSTAL AND MOLECULAR STRUCTURE, AND HYPERCONJUGATION OF THE ISOMERIC 17,20-EPOXY-17-PICOLYL DERIVATIVES OF 5-ANDROSTENE AND 5α-ANDROSTANE
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Three pairs of isomeric 17,20-epoxy-17-picolyl-derivatives of 5-androstene and 5α-androstane (3 - 8) have been prepared by an oxidation of 3β-acetoxy-17-picolinylidene-androst-5-ene (2) and 3β-acetoxy-17-picolinylidene-5α-androstane (2) with in situ prepared Cr(VI) oxide-pyridine-complex in methylene chloride at room temperature.X-Ray structural analysis of the suitably crystalline epoxides 5 and 6 revealed the structure of 5 being 17α,20α-epoxide, while structure of 6 corresponded to 17β,20β-epoxide.It was proved that in both cases E-geometrical isomers were formed.Based on the deduced absolute stereochemistry of 5 and 6, the structures of other two pairs (3-4, 7-8) were readily worked out by NMR-spectroscopy.A mechanism of the oxidation reaction was proposed, and some other relevant chemical experiments were described.Finally, an explanation was offered for the observed differences of the relevant bond lenghts and dihedral angles in 5 and 6 which indicated a slight ? - ? conjugation between the epoxide and the pyridine rings, which might be coupled with long range effect of the C-7 carbonyl group.
- Miljkovic, Dusan,Gasi, Katarina,Kindjer, Marija,Stankovic, Slobodanka,Argay, Gyula
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p. 631 - 641
(2007/10/02)
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- SYNTHESIS OF UNSATURATED CARBONYL COMPOUNDS VIA A CHROMIUM-MEDIATED ALLYLIC OXIDATION BY 70percent TERT.BUTYLHYDROPEROXIDE
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Alkenes were converted into α,β-unsaturated carbonyl compounds using excess of tert.butylhydroperoxide and catalytic amounts of chromiumVI oxide at room temperature.Fair yields and conversions were obtained from Δ5-steroids while allylic oxidation of acyclic alkenes was less efficient.Epoxidation of the double bond, sometimes observed, remained a minor reaction pathway.
- Muzart, Jacques
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p. 4665 - 4668
(2007/10/02)
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