- Structure and catalytic mechanism of 3-ketosteroid-Δ4-(5α)- dehydrogenase from Rhodococcus jostii RHA1 genome
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3-Ketosteroid Δ4-(5α)-dehydrogenases (Δ4-(5α)- KSTDs) are enzymes that introduce a double bond between the C4 and C5 atoms of 3-keto-(5α)-steroids. Here we show that the ro05698 gene from Rhodococcus jostii RHA1 codes for a flavoprotein with Δ4-(5α)-KSTD activity. The 1.6 A resolution crystal structure of the enzyme revealed three conserved residues (Tyr-319, Tyr-466, and Ser-468) in a pocket near the isoalloxazine ring system of the FAD co-factor. Site-directed mutagenesis of these residues confirmed that they are absolutely essential for catalytic activity. A crystal structure with bound product 4-androstene-3,17-dione showed that Ser-468 is in a position in which it can serve as the base abstracting the 4β-proton from the C4 atom of the substrate. Ser-468 is assisted by Tyr-319, which possibly is involved in shuttling the proton to the solvent. Tyr-466 is at hydrogen bonding distance to the C3 oxygen atom of the substrate and can stabilize the keto-enol intermediate occurring during the reaction. Finally, the FAD N5 atom is in a position to be able to abstract the 5α-hydrogen of the substrate as a hydride ion. These features fully explain the reaction catalyzed by Δ4-(5α)-KSTDs.
- Van Oosterwijk, Niels,Dijkstra, Bauke W.,Knol, Jan,Dijkhuizen, Lubbert,Van Der Geize, Robert
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p. 30975 - 30983,9
(2012)
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- 2-Iodoxybenzoic Acid Tosylates: the Alternative to Dess–Martin Periodinane Oxidizing Reagents
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Two powerful hypervalent iodine(V) oxidants, DMP-OTs (1-tosyloxy-1,1-diacetoxy-1H-1λ5-benzo[d][1,2]iodoxol-3-one) and IBX-OTs (1-tosyloxy-1-oxo-1H-1λ5-benzo[d][1,2]iodoxol-3-one) show high reactivity in the oxidation of structurally complex primary and secondary alcohols, which are highly functionalized polyketide or terpene fragments or steroids. The yields of the corresponding carbonyl compounds are even higher for the protocol that uses pyridine as additive. The oxidations proceed very rapidly at room temperature leaving the protective groups and π-systems intact and affording the corresponding carbonyl compounds in good to excellent yields. Moreover, IBX-OTs is an efficient reagent for the oxidative dehydrogenation of steroidal alcohols to the corresponding enones. (Figure presented.).
- Yusubov, Mekhman S.,Postnikov, Pavel S.,Yusubova, Roza Ya.,Yoshimura, Akira,Jürjens, Gerrit,Kirschning, Andreas,Zhdankin, Viktor V.
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p. 3207 - 3216
(2017/09/11)
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- Microbial transformation of epiandrosterone by Aspergillus sydowii
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Incubation of epiandrosterone with Aspergillus sydowii MRC 200653 afforded ten metabolites. The fungal dehydrogenation of epiandrosterone is reported for the first time. The formation of the major metabolite, 6?-hydroxyandrost-4-ene-3,17-dione, involved first dehydrogenation to give a 4-ene and then hydroxylation at C-6?. Small amounts of the substrate were hydroxylated at C-1α, C-7α, C-7β and C-11α.
- Yildirim, Kudret,Kuru, Ali
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p. 718 - 721
(2016/12/30)
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- Regioselective dehydrogenation of 3-keto-steroids to form conjugated enones using o-iodoxybenzoic acid and trifluoroacetic acid catalysis
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Mild and regioselective conversion of 3-keto-5α- and 3-keto-5β-steroids (trans A/B- and cis A/B-ring juncture, respectively) to the corresponding enones (Δ1- and Δ4-3- ketones) by treatment with o-iodoxybenzoic acid (IBX) catalyzed by trifluoroacetic acid (TFA) in DMSO, is described. The IBX-mediated reaction involved dehydrogenation of the α- and β-hydrogen atoms of the 3-ketones to give the enones regioselectively in good isolated yields without concomitant formation of related dienones and trienones.
- Iida, Takashi,Omura, Kaoru,Sakiyama, Ryou,Kodomari, Mitsuo
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- Synthesis of cyclic enones via direct palladium-catalyzed aerobic dehydrogenation of ketones
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α,β-Unsaturated carbonyl compounds are versatile intermediates in the synthesis of pharmaceuticals and biologically active compounds. Here, we report the discovery and application of Pd(DMSO)2(TFA)2 as a catalyst for direct dehydrogenation of cyclohexanones and other cyclic ketones to the corresponding enones, using O2 as the oxidant. The substrate scope includes heterocyclic ketones and several natural-product precursors.
- Diao, Tianning,Stahl, Shannon S.
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supporting information; experimental part
p. 14566 - 14569
(2011/10/17)
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- Steroidal isomers with uniform mass spectra of their per-TMS derivatives: Synthesis of 17-hydroxyandrostan-3-ones, androst-1-, and -4-ene-3,17-diols
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In human sports doping control analysis most of the steroids are analyzed after enzymatic hydrolysis of the glucuronides as per-trimethylsilyl (TMS) derivatives applying gas chromatography-mass spectrometry (GC-MS). According to the recommendations of the World Anti-Doping Agency the identification of analytes should be based on retention time and on mass spectrometric characterization. This study shows that the bis-TMS derivatives of 16 specific C19 steroids, namely the stereoisomers of 5ξ-androst-1-ene-3ξ,17ξ-diol (8 isomers), androst-4-ene-3ξ,17ξ-diol (4 isomers), and 17ξ-hydroxy-5ξ-androstan-3-one (4 isomers), reveal very similar mass spectra. As a rule, when taking the retention times, which are provided as Kovac indices for all these isomers, into account, a restriction to two or three possible isomers is possible. Reliable identification should additionally include a comparison of the retention times of the analytes with the reference compounds measured concomitantly. In some cases standard addition may be appropriate. Due to the limited availability, the above mentioned isomers were synthesized by reduction of the corresponding α,β-unsaturated oxo steroids either with K-Selectride or by catalytic hydrogenation (Pd/C as catalyst). The products of the reactions were identified by means of nuclear magnetic resonance (NMR) characterization and by further reduction to the corresponding 5ξ-androstane-3ξ,17ξ-diols and GC-MS comparison with commercially available reference standards.
- Parr, Maria K.,Zapp, Josef,Becker, Michael,Opfermann, Georg,Bartz, Ulrike,Schaenzer, Wilhelm
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p. 545 - 551
(2008/02/02)
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- An efficient synthesis of 5α-androst-1-ene-3,17-dione
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5α-Androst-1-ene-3,17-dione (5) as a prodrug of 1-testosterone (4) was prepared in four steps from 17β-Acetoxy-5α-androstan-3-one (stanolone acetate) (1) in high yield. Thus, stanolone acetate (1) was brominated in the presence of hydrogen chloride in acetic acid to give 17β-acetoxy-2-bromo-5α-androstan-3-one (2), which underwent dehydrobromination using lithium carbonate as base with lithium bromide as an additive to give 17β-acetoxy-5α-androst-1-en-3-one (3) in almost quantitative yield with 97% of purity. Compound (3) was hydrolyzed with sodium hydroxide to give 17β-hydroxy-5α-androst-1-en-3-one (4,1-testosterone), which was oxidized with chromium trioxide to afford 5α-androst-1-ene-3,17-dione (5). The overall yield of 5 was 78.2% with purity of 99%. In this method, the formation of 4-ene was diminished when 1-ene was introduced, and its mechanism was also discussed.
- Zhang, Huyue,Qiu, Zhuibai
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p. 1088 - 1090
(2007/10/03)
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- Iodine(V) reagents in organic synthesis. Part 4. o-Iodoxybenzoic acid as a chemospecific tool for single electron transfer-based oxidation processes
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o-Iodoxybenzoic acid (IBX), a readily available hypervalent iodine(V) reagent, was found to be highly effective in carrying out oxidations adjacent to carbonyl functionalities (to form α, β-unsaturated carbonyl compounds) and at benzylic and related carbon centers (to form conjugated aromatic carbonyl systems). Mechanistic investigations led to the conclusion that these new reactions are initiated by single electron transfer (SET) from the substrate to IBX to form a radical cation which reacts further to give the final products. Fine-tuning of the reaction conditions allowed remarkably selective transformations within multifunctional substrates, elevating the status of this reagent to that of a highly useful and chemoselective oxidant.
- Nicolaou,Montagnon,Baran,Zhong
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p. 2245 - 2258
(2007/10/03)
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- HIO3 and I2O5: Mild and selective alternative reagents to IBX for the dehydrogenation of aldehydes and ketones
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Economic and convenient: Iodic acid (1) and iodine pentoxide (2) form complexes 3 and 4, respectively, with DMSO when heated at 80°C for 1 h. The complexes are efficient agents for the dehydrogenation of ketones and aldehydes at 45-65°C. X-ray crystallographic analysis (see picture) shows that the iodine pentoxide. DMSO complex 4 self-assembles into a remarkable helix in the solid state.
- Nicolaou,Montagnon, Tamsyn,Baran, Phil S.
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p. 1386 - 1389
(2007/10/03)
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- Modulation of the reactivity profile of IBX by ligand complexation: Ambient temperature dehydrogenation of aldehydes and ketones to α,β-unsaturated carbonyl compounds
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The reactivity profile of IBX can be altered by complexation with various ligands (e. g. 1-4). A new complex, IBX·MPO, is a remarkably effective oxidant and allows the room-temperature dehydrogenation of carbonyl compounds, for example, the formation of cyclooctenones 6 and 7 from cyclooctanone 5. IBX = iodoxybenzoic acid; MPO = 4-methoxypyridine-N-oxide.
- Nicolaou,Montagnon, Tamsyn,Baran, Phil S.
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p. 993 - 996
(2007/10/03)
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- Unusual Enolizations in 19-Nor-3-ketosteroids
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The direction of enolization of 19-nor-3-ketosteroids was found to proceed predominantly towards C-2 irrespective of the ring junction at C-5.
- Abul-Hajj, Yusuf J.
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p. 1479 - 1481
(2007/10/02)
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