- One-Step Chemo-, Regio- and Stereoselective Reduction of Ketosteroids to Hydroxysteroids over Zr-Containing MOF-808 Metal-Organic Frameworks
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Zr-containing MOF-808 is a very promising heterogeneous catalyst for the selective reduction of ketosteroids to the corresponding hydroxysteroids through a Meerwein-Ponndorf-Verley (MPV) reaction. Interestingly, the process leads to the diastereoselective synthesis of elusive 17α-hydroxy derivatives in one step, whereas most chemical and biological transformations produce the 17β-OH compounds, or they require several additional steps to convert 17β-OH into 17α-OH by inverting the configuration of the 17 center. Moreover, MOF-808 is found to be stable and reusable; it is also chemoselective (only keto groups are reduced, even in the presence of other reducible groups such as C=C bonds) and regioselective (in 3,17-diketosteroids only the keto group in position 17 is reduced, while the 3-keto group remains almost intact). The kinetic rate constant and thermodynamic parameters of estrone reduction to estradiol have been obtained by a detailed temperature-dependent kinetic analysis. The results evidence a major contribution of the entropic term, thus suggesting that the diastereoselectivity of the process is controlled by the confinement of the reaction inside the MOF cavities, where the Zr4+ active sites are located.
- Llabrés i Xamena, F. X.,Mautschke, H.-H.
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p. 10766 - 10775
(2021/06/15)
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- Biotransformation of androst-4-ene-3,17-dione by some fungi
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The incubations of androst-4-ene-3,17-dione with Aspergillus candidus MRC 200634, Aspergillus tamarii MRC 72400, Aspergillus wentii MRC 200316 and Mucor hiemalis MRC 70325 for 5 days are reported. A. candidus MRC 200634 mainly hydroxylated androst-4-ene-3,17-dione at C-11α, C-15α and C-15β whilst A. wentii MRC 200316 hydroxylated it mainly at C-6β. A. tamarii MRC 72400 showed predominately a Baeyer–Villiger monooxygenase activity. M. hiemalis MRC 70325 hydroxylated the substrate at C-14α and reduced most of it at C-17.
- Yildirim, Kudret,Kuru, Ali,Keskin, Ece,Salihoglu, Aylin,Bukum, Neslihan
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p. 594 - 597
(2017/11/14)
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- Endogenous boldenone-formation in cattle: Alternative invertebrate organisms to elucidate the enzymatic pathway and the potential role of edible fungi on cattle's feed
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Although β-boldenone (bBol) used to be a marker of illegal steroid administration in calves, its endogenous formation has recently been demonstrated in these vertebrates. However, research on the pathway leading to bBol remains scarce. This study shows the usefulness of in vivo invertebrate models as alternatives to vertebrate animal experiments, using Neomysis integer and Lucilia sericata. In accordance with vertebrates, androstenedione (AED) was the main metabolite of β-testosterone (bT) produced by these invertebrates, and bBol was also frequently detected. Moreover, in vitro experiments using feed-borne fungi and microsomes were useful to perform the pathway from bT to bBol. Even the conversion of phytosterols into steroids was shown in vitro. Both in vivo and in vitro, the conversion of bT into bBol could be demonstrated in this study. Metabolism of phytosterols by feed-borne fungi may be of particular importance to explain the endogenous bBol-formation by cattle. To the best of our knowledge, it is the first time the latter pathway is described in literature.
- Verheyden,Noppe,Zorn,Van Immerseel,Bussche, J. Vanden,Wille,Bekaert,Janssen,De Brabander,Vanhaecke
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p. 161 - 170
(2011/03/19)
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- 2-(Prenyloxymethyl)benzoyl (POMB) group: a new temporary protecting group removable by intramolecular cyclization
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2-(Prenyloxymethyl)benzoates can be prepared from alcohols and readily available 2-(prenyloxymethyl)benzoic acid by standard acylation techniques or by Mitsunobu reaction with inversion of configuration. The POMB group can be cleaved first by oxidative removal of the prenyl group with DDQ followed by lactonization with expulsion of the alcohol catalyzed by Yb(OTf)3. These reaction conditions are compatible with the presence of a large number of common protecting groups.
- Vatèle, Jean-Michel
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p. 10921 - 10929
(2008/02/12)
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- Efficient method for inversion of secondary alcohols by reaction of chloromethanesulfonates with cesium acetate
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Inversion of a variety of secondary alcohols using the (chloromethylsulfonyl)oxy group as a favorable leaving group with cesium acetate in the presence of 18-crown-6 has been performed to give the inverted acetates in high yields.
- Shimizu, Takeshi,Hiranuma, Sayoko,Nakata, Tadashi
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p. 6145 - 6148
(2007/10/03)
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- PREPARATION OF UNLABELLED AND 3H>-LABELLED EPITESTOSTERONE AND ITS METABOLITES
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Cold as well as 3H>-labelled substrates and metabolites IX-XI, XV, XVI, XX-XXII, XXIV, XXV and XXVIII were prepared by catalytic hydrogenation of epitestosterone (VIII) and Λ1-dehydroepitestosterone (XIII).The key step in the preparation of compound XXVIII was reaction of 3β-tosylates XXVI and XXX with potassium nitrite in dimethyl sulfoxide.
- Kasal, Alexander,Fuksova, Kveta,Pouzar, Vladimir
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p. 600 - 611
(2007/10/02)
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- A GENERAL METHOD FOR THE SELECTIVE REDUCTION OF KETONES IN THE PRESENCE OF ENONES.
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Ketones can be reduced in the presence of conjugated enones by sodium borohydride in 50percent methanol in dichloromethane at -78 deg C.The selectivity is generally excellent.In favorable cases the reaction can be carried out at room temperature in dichloromethane with acetic acid as catalyst.
- Ward, Dale E.,Rhee, Chung K.,Zoghaib, Wajdi M.
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p. 517 - 520
(2007/10/02)
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