- Optical Rotatory Dispersion Studies. 134. Absolute Configuration and Circular Dichroism Spectrum of (R)-Cyclopentanone. Demonstration of a Conformational Isotope Effect
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The absolute configuration of (R)-cyclopentanone is established through synthesis using as the key step chiral epoxidation with the Sharpless reagent.Its circular dichroism (CD) spectrum is unusual in that it exhibits a bisignate Cotton effect being negative at 310 and positive at 275 nm.From the interpretation on the variable-temperature CD measurements, the unexpected conclusion is reached that the twist conformation with the deuterium in the quasi-equatorial position is energetically preferred by ca. 10 +/- 2 cal/mol.Evidently, even at room temperature, the contribution toward the spectrum resulting from the conformational isotope effect is of the same or larger amplitude but opposite sign compared to the difference between the partial octant contributions of an α-quasi-equatorial and α-quasi-axial deuterium substituent.
- Sundararaman, P.,Barth, Guenter,Djerassi, Carl
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- A novel ene-reductase from Synechococcus sp. PCC 7942 for the asymmetric reduction of alkenes
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The increasing demand for enantiopure molecules in the pharmaceutical and fine-chemical industry requires the availability of well-characterized and efficient biocatalysts for asymmetric syntheses. Thereby, asymmetric reduction of alkenes represents one of the most employed reactions for the production of chiral molecules. Here, we present a novel ene-reductase from the cyanobacterium Synechococcus sp. PCC 7942, a member of the old yellow enzyme family, capable of reducing CC bonds in a anti-specific fashion. We evaluated its biocatalytic potential by characterizing the substrate spectrum, cofactor preference, stereoselectivity and biochemical properties. This NADPH-dependent flavoprotein accepted a wide range of activated alkenes and displayed a pH optimum between pH 7.6 and pH 8.6. A C-terminal His6-tag decreased the enzyme activity 2.7-fold, but did not influence the stereoselectivity. The reduction of (R)-carvone and 2-methylmaleimide yielded (R)-products with high optical purities (98% de and >99% ee, respectively), pointing out the applicability of this new biocatalyst in the stereoselective production of chiral compounds.
- Fu, Yilei,Hoelsch, Kathrin,Weuster-Botz, Dirk
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- Synthesis of cycloalkanones from dienes and allylamines through C-H and C-C bond activation catalyzed by a rhodium(I) complex
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Formaldehyde in disguise: The allylic amine 1 is used as a masked form of formaldehyde in the rhodium-catalyzed cyclization of dienes 2. The reaction provides access to various cycloalkanones 3 through chelation-assisted C-H- and C-C-bond activation.
- Lee, Dae-Yon,Kim, In-Jung,Jun, Chul-Ho
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- ATTEMPTED GENERATION OF HALOCARBENES: PROTODESILYLATION OF DIHALOMETHYLSILANES
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Attempts to generate chlorocarbene or bromocarbene from (dichloromethyl)trimethylsilane and (dibromomethyl)trimethylsilane, respectively, under phase transfer conditions results in protodesilylation.The protodesilylation of 1,1-dihalosilanes under phase transfer conditions appears to be general.Phase transfer conditions are also useful for the protodesilylation of other organosilanes.
- Larson, Gerald L.,Cadiz, Carlos
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- The alkylation of silyl enol ethers with SN1-unreactive iodides in the presence of silver trifluoroacetate
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Silyl enol ethers can be effectively alkylated with primary n-alkyl iodides in the presence of silver trifluoro-acetate to give monoalkyl ketones.
- Jefford, Charles W.,Sledeski, Adam W.,Lelandais, Patrick,Boukouvalas, John
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- Studies on the chemistry of diols and cyclic ethers-53. Dehydration of 1,1-bishydroxymethylcycloalkanes: A quest for a 1,3-hydride shift
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A study of the sulphuric acid-catalysed dehydrations of 1,1-bishydroxymethyl-cyclopropane, - cyclobutane, - cyclopentane and -cyclohexane (1a-1d) revealed that the product distributions are determined by the relative stabilities of carbenium ions and der kinetic control furnished evidence of a 1,3-hydride shift.
- Molnar, Arpad,Bucsi, Imre,Bartok, Mihaly
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- Conversion of furfural into cyclopentanone over Ni-Cu bimetallic catalysts
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The conversion of furfural into cyclopentanone over Ni-Cu bimetallic catalysts was studied under hydrogen atmosphere. Furfuryl alcohol, 4-hydroxy-2-cyclopentenone and 2-cyclopentenone were verified as three key intermediates. Rearrangement of the furan ring was independent of hydrogenation, starting from furfuryl alcohol rather than furfural. The opening and closure of the furan ring were closely related to the attack of a H2O molecule on the 5-position of furfuryl alcohol. Prior hydrogenation of the aldehyde group accounted for the different reactivity of furfural and furfuryl alcohol. The high selectivity of cyclopentanone was ascribed to the presence of 2-cyclopentenone.
- Yang, Yanliang,Du, Zhongtian,Huang, Yizheng,Lu, Fang,Wang, Feng,Gao, Jin,Xu, Jie
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- Effects of HMPA on the Structure and Reactivity of the Lithium Enolate of Cyclopentanone in THF: The Dimer is Responsible for Alkylation and Proton Exchange Reactions
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The structure and reactivity of the lithium enolate of cyclopentanone are strongly influenced by coexisting HMPA molecules. Detailed low-temperature 7Li, 31P, and 13C NMR studies of the 0.04-0.2 M THF solutions indicate that excess quantities of HMPA act primarily to form a bis-HMPA coordinated dimer. Tetrameric, trimeric, and monomeric enolates were not detected by HMPA titration. The convergency on the dimeric aggregate has been monitored by the successive displacement of THF with HMPA molecules. Even at a high concentration of HMPA, the formation of monomeric enolate was not observed. Kinetic experiments, combined with the structural information, showed that alkylation of the enolate by methyl iodide proceeds via the dimer with the assistance of HMPA. Proton exchange between the enolate and 2-methylcyclopentanone also occurs via the dimer, but without the participation of additional HMPA. These findings explain the role of HMPA in the selective monoalkylation of lithium enolate.
- Suzuki, Masaaki,Koyama, Hiroko,Noyori, Ryoji
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- Efficient and selective hydrogenation of biomass-derived furfural to cyclopentanone using Ru catalysts
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The selective hydrogenation of furfural into cyclopentanone is an attractive transformation to advance in the sustainable synthesis of important chemicals from biomass. A supported Ru nanoparticle catalyst on an acidic MOF material (Ru/MIL-101) was designed for the highly active and selective conversion of furfural to cyclopentanone in aqueous media. Complete conversion of furfural with a selectivity higher than 96% was achieved within 2.5 h at 160 °C and 4.0 MPa H2 pressure.
- Fang, Ruiqi,Liu, Hongli,Luque, Rafael,Li, Yingwei
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- Asymmetric intramolecular C-H/Olefin coupling: Asymmetric cyclization reactions of 1,5-dienes catalyzed by rhodium complexes
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Asymmetric intramolecular C-H/olefin coupling reactions of 1-(2-pyridyl)- or 1-(1-methyl-2-imidazolyl)-1,5-dienes are catalyzed by a rhodium complex having a homochiral monodentate phosphine ligand.
- Fujii, Naoaki,Kakiuchi, Fumitoshi,Yamada, Airi,Chatani, Naoto,Murai, Shinji
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- Deciphering Reactivity and Selectivity Patterns in Aliphatic C-H Bond Oxygenation of Cyclopentane and Cyclohexane Derivatives
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A kinetic, product, and computational study on the reactions of the cumyloxyl radical with monosubstituted cyclopentanes and cyclohexanes has been carried out. HAT rates, site-selectivities for C-H bond oxidation, and DFT computations provide quantitative information and theoretical models to explain the observed patterns. Cyclopentanes functionalize predominantly at C-1, and tertiary C-H bond activation barriers decrease on going from methyl- and tert-butylcyclopentane to phenylcyclopentane, in line with the computed C-H BDEs. With cyclohexanes, the relative importance of HAT from C-1 decreases on going from methyl- and phenylcyclohexane to ethyl-, isopropyl-, and tert-butylcyclohexane. Deactivation is also observed at C-2 with site-selectivity that progressively shifts to C-3 and C-4 with increasing substituent steric bulk. The site-selectivities observed in the corresponding oxidations promoted by ethyl(trifluoromethyl)dioxirane support this mechanistic picture. Comparison of these results with those obtained previously for C-H bond azidation and functionalizations promoted by the PINO radical of phenyl and tert-butylcyclohexane, together with new calculations, provides a mechanistic framework for understanding C-H bond functionalization of cycloalkanes. The nature of the HAT reagent, C-H bond strengths, and torsional effects are important determinants of site-selectivity, with the latter effects that play a major role in the reactions of oxygen-centered HAT reagents with monosubstituted cyclohexanes.
- Martin, Teo,Galeotti, Marco,Salamone, Michela,Liu, Fengjiao,Yu, Yanmin,Duan, Meng,Houk,Bietti, Massimo
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supporting information
p. 9925 - 9937
(2021/06/30)
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- METHOD FOR INTRODUCING SUBSTITUENT INTO alpha,beta-UNSATURATED KETONE AND METHOD FOR SYNTHESIZING PROSTAGLANDIN USING THE SAME
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The present invention provides a method for introducing substituents into the α-position and the β-position of an α,β-unsaturated ketone, which not only can be used for the synthesis of a prostaglandin by a three-component coupling process, but also enables synthesis of a prostaglandin in a high yield by one-pot operation without requiring the use of a large excess amount of any of the three components required for the synthesis or using a highly toxic heavy metal as a catalyst or a solvent that is highly toxic to living bodies, and a method for synthesizing a prostaglandin using the same technical means. The method for introducing substituents into an α,β-unsaturated ketone according to the present invention is a method for introducing substituents into the carbon at the α-position and the carbon at the β-position of an α,β-unsaturated ketone, including: a first step of mixing alkyllithium and trialkylalkenyl tin in which tin atom binds to the vinyl position of the alkenyl group; a second step of mixing the mixture of the first step and dialkylzinc; a third step of mixing the mixture of the second step and an α,β-unsaturated ketone; and a fourth step of mixing the mixture of the third step and a trifluoromethanesulfonate compound.
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Paragraph 0044-0046
(2021/11/20)
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- Selective α-Methylation of Ketones
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The convenient and scalable preparative approach for the two-step α-methylation of ketones is described. The optimized protocols for regioselective preparation of enaminones with further diastereoselective and functional groups tolerant hydrogenation to α-methylketones are developed. The scope and limitations of the proposed methodology are discussed. The advantages compared to known procedures are demonstrated. The unexpected role of acetone in the hydrogenation is suggested. The evaluation of the method for both early building block synthesis and late-stage CH-functionalization is shown. The elaborate procedures' preparability and scalability are demonstrated by the synthesis of several α-methyl ketones up to 100 g amount.
- Frolov, Andriy I.,Ostapchuk, Eugeniy N.,Pashenko, Alexander E.,Chuchvera, Yaroslav O.,Rusanov, Eduard B.,Volochnyuk, Dmitriy M.,Ryabukhin, Sergey V.
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p. 7333 - 7346
(2021/06/28)
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- Synthesis of Chiral Amines via a Bi-Enzymatic Cascade Using an Ene-Reductase and Amine Dehydrogenase
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Access to chiral amines with more than one stereocentre remains challenging, although an increasing number of methods are emerging. Here we developed a proof-of-concept bi-enzymatic cascade, consisting of an ene reductase and amine dehydrogenase (AmDH), to afford chiral diastereomerically enriched amines in one pot. The asymmetric reduction of unsaturated ketones and aldehydes by ene reductases from the Old Yellow Enzyme family (OYE) was adapted to reaction conditions for the reductive amination by amine dehydrogenases. By studying the substrate profiles of both reported biocatalysts, thirteen unsaturated carbonyl substrates were assayed against the best duo OYE/AmDH. Low (5 %) to high (97 %) conversion rates were obtained with enantiomeric and diastereomeric excess of up to 99 %. We expect our established bi-enzymatic cascade to allow access to chiral amines with both high enantiomeric and diastereomeric excess from varying alkene substrates depending on the combination of enzymes.
- Fossey-Jouenne, Aurélie,Jongkind, Ewald P. J.,Mayol, Ombeline,Paul, Caroline E.,Vergne-Vaxelaire, Carine,Zaparucha, Anne
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- A robust and stereocomplementary panel of ene-reductase variants for gram-scale asymmetric hydrogenation
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We report an engineered panel of ene-reductases (ERs) from Thermus scotoductus SA-01 (TsER) that combines control over facial selectivity in the reduction of electron deficient C[dbnd]C double bonds with thermostability (up to 70 °C), organic solvent tolerance (up to 40 % v/v) and a broad substrate scope (23 compounds, three new to literature). Substrate acceptance and facial selectivity of 3-methylcyclohexenone was rationalized by crystallisation of TsER C25D/I67T and in silico docking. The TsER variant panel shows excellent enantiomeric excess (ee) and yields during bi-phasic preparative scale synthesis, with isolated yield of up to 93 % for 2R,5S-dihydrocarvone (3.6 g). Turnover frequencies (TOF) of approximately 40 000 h?1 were achieved, which are comparable to rates in hetero- and homogeneous metal catalysed hydrogenations. Preliminary batch reactions also demonstrated the reusability of the reaction system by consecutively removing the organic phase (n-pentane) for product removal and replacing with fresh substrate. Four consecutive batches yielded ca. 27 g L?1 R-levodione from a 45 mL aqueous reaction, containing less than 17 mg (10 μM) enzyme and the reaction only stopping because of acidification. The TsER variant panel provides a robust, highly active and stereocomplementary base for further exploitation as a tool in preparative organic synthesis.
- Nett, Nathalie,Duewel, Sabine,Schmermund, Luca,Benary, Gerrit E.,Ranaghan, Kara,Mulholland, Adrian,Opperman, Diederik J.,Hoebenreich, Sabrina
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- Aqueous chemoenzymatic one-pot enantioselective synthesis of tertiary α-aryl cycloketonesviaPd-catalyzed C-C formation and enzymatic C=C asymmetric hydrogenation
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An aqueous chemoenzymatic cascade reaction combining Pd-catalyzed C-C formation and enzymatic C=C asymmetric hydrogenation (AH) was developed for enantioselective synthesis of tertiary α-aryl cycloketones in good yields and excellent enantioselectivities. The stereopreference of the enzyme in AH of α-aryl cyclohexenones was studied. An enantiocomplementary enzyme was obtained by site-directed mutation.
- Luan, Pengqian,Liu, Yunting,Li, Yongxing,Chen, Ran,Huang, Chen,Gao, Jing,Hollmann, Frank,Jiang, Yanjun
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supporting information
p. 1960 - 1964
(2021/03/26)
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- Selective C-C Bond Cleavage of Cycloalkanones by NaNO2/HCl
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A novel selective fragmentation of cycloalkanones by NaNO2/HCl has been established. The C-C bond cleavage reaction proceeds smoothly under mild conditions, selectively affording versatile keto acids or oxime acids. The methodology can streamline the synthesis of valuable chiral molecules and isocoumarins from readily available feedstocks.
- He, Tianyu,Chen, Dengfeng,Qian, Shencheng,Zheng, Yu,Huang, Shenlin
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supporting information
p. 6525 - 6529
(2021/09/02)
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- Solvent-free, microwave assisted oxidation of alcohols with 4-hydroxypyridinium chlorochromate functionalized silica gel
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4-Hydroxypyridinium chlorochromate functionalized silica gel was found to be an efficient and reusable oxidant for the very fast oxidation of primary and secondary alcohols to the corresponding carbonyl compounds under solventfree conditions and microwave irradiation in excellent yields.
- AHMADI, Sayed Ali,GHALEHBANDI, Shermineh Sadat,GHAZANFARI, Dadkhoda,SHEIKHHOSSEINI, Enayatollah
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p. 283 - 289
(2020/10/06)
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- Metals in Biotechnology: Cr-Driven Stereoselective Reduction of Conjugated C=C Double Bonds
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Elemental metals are shown to be suitable sacrificial electron donors to drive the stereoselective reduction of conjugated C=C double bonds using Old Yellow Enzymes as catalysts. Both direct electron transfer from the metal to the enzyme as well as mediated electron transfer is feasible, although the latter excels by higher reaction rates. The general applicability of this new chemoenzymatic reduction method is demonstrated, and current limitations are outlined.
- Rauch, Marine C. R.,Gallou, Yann,Delorme, Léna,Paul, Caroline E.,Arends, Isabel W. C. E.,Hollmann, Frank
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p. 1112 - 1115
(2019/12/27)
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- Effect of pretreatment conditions on acidity and dehydration activity of CeO2-MeOx catalysts
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A series of MeOx-modified CeO2 (CeO2-MnOx, CeO2-ZnO, CeO2-MgO, CeO2-CaO, and CeO2-Na2O) catalysts were prepared by the impregnation of CeO2 with corresponding metal nitrates. Acidity and oxidation state of cerium were investigated on both oxidized and reduced catalysts by employing Fourier Transform Infrared spectroscopy (FTIR) on adsorbed pyridine and in situ H2-Temperature Programmed Reduction/X-ray Absorption Spectroscopy (H2-TPR/XAS) techniques, respectively. Metal oxide addition tended to alter both type and number of acid sites on ceria. EXAFS data showed a significant difference in NCe-O between unmodified and CeO2-MeOx, suggesting that added MeOx interferes with vacancy formation on ceria during reduction. In comparison with air-pretreated samples, H2-pretreated ones under similar conversion of 1,5 pentanediol exhibited a higher selectivity towards linear alcohols. Alcohol conversion found to correlate with total acidity (i.e., Br?nsted and Lewis). CeO2 benefited from the addition of alkali (Na) or alkaline earth metals (Mg, Ca) by producing unsaturated alcohols.
- Cronauer, Donald C.,Góra-Marek, Kinga,Garcia, Richard,Gnanamani, Muthu Kumaran,Jacobs, Gary,Kropf, A. Jeremy,Marshall, Christopher L.
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- Preparation method of metconazole (by machine translation)
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The method comprises the following steps: 2 - (2 - chlorobenzylidene) 2 - 2 -methylcyclopentanone and p-chlorobenzaldehyde react to obtain an epoxide; the epoxide reacts with triazole to obtain an epoxide; and the epoxide is reacted with triazole to obtain an open-loop product; and the ring-opening product 4 - is subjected -2 to 2 - catalytic hydrogenation to obtain the 2 - myclobutanil . 4 - beta-(4 -chlorbenzydrospirone; 5 -2 -5 -chlorobenzyl) 5 - and methylcyclopentanone react. Corey-Chayyyysky is obtained. The preparation method is low in cost, easy to obtain in the market; the reaction steps are all conventional reactions, reaction steps are simple, implementation; process is simple, reaction conditions are mild, operation; conversion rate is high, reaction time is short, control, and industrialization production. (by machine translation)
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Paragraph 0055-0057
(2019/10/01)
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- Organozinc-aided, HMPA-free, stoichiometric three-component coupling for the general synthesis of prostaglandins and stable prostacyclin analogs with biological significance
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A three-component coupling procedure was developed to construct the entire prostaglandin (PG) skeleton under HMPA-free and stoichiometric conditions via a combination of dimethylzinc-aided conjugate addition of an ω-side-chain vinyllithium with (R)-4-hydroxy-2-cyclopentenone and the direct trapping of the resulting enolate with an α-side-chain propargyl triflate. Dimethylzinc effectively regulated both the conjugate addition and alkynylation reactions. Thus, the method afforded protected 5,6-didehydro-PGE2, a common intermediate for the general synthesis of natural PGs and the stable artificial prostacyclin (PGI2) analog isocarbacyclin in 88% yield. The utility of the method was further applied to the syntheses of novel intermediates, which are useful for the straightforward synthesis of 15R-TIC and 15-deoxy-TIC in 79% and 86% yield, respectively.
- Koyama, Hiroko,Izumiseki, Atsuto,Suzuki, Masaaki
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p. 1467 - 1470
(2019/05/07)
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- Enantio- A nd regioselective: Ene-reductions using F420H2-dependent enzymes
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In the past decade it has become clear that many microbes harbor enzymes that employ an unusual flavin cofactor, the F420 deazaflavin cofactor. Herein we show that F420-dependent reductases (FDRs) can successfully perform enantio-, regio- A nd chemoselective ene-reductions. For the first time, we have demonstrated that F420H2-driven reductases can be used as biocatalysts for the reduction of α,β-unsaturated ketones and aldehydes with good conversions (>99%) and excellent regioselectivities and enantiomeric excesses (>99% ee). Noteworthily, FDRs typically display an opposite enantioselectivity when compared to the well established FMN-dependent Old Yellow Enzymes (OYEs).
- Mathew, Sam,Trajkovic, Milos,Kumar, Hemant,Nguyen, Quoc-Thai,Fraaije, Marco W.
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supporting information
p. 11208 - 11211
(2018/10/15)
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- SYSTEMS AND METHODS FOR SYNTHESIS OF PHENOLICS AND KETONES
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Embodiments herein relate to apparatus and systems for phenolic and ketone synthesis and methods regarding the same. In an embodiment, a method of producing phenolics and ketones is included. The method can specifically include forming a reaction mixture comprising nanocrystalline cellulose (NCC) and water. The method can also include contacting the reaction mixture with a metal oxide catalyst at a temperature of 350 degrees Celsius or higher and a pressure of at least about 3200 psi to form a reaction product mixture. The reaction product mixture can include at least about 20 wt. % phenolics and at least about 10 wt. % ketones as a percentage of the total mass of nanocrystalline cellulose (NCC). Other embodiments are also included herein.
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Paragraph 0080-0088
(2018/11/21)
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- Regioselective Dialkylations of N-(tert-Butyl)iminocyclopentane via Deprotonating One-Pot Procedures
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The title compound (1) was chosen as a model for the α/α′-regioselectivity of deprotonation and subsequent alkylation adjacent to the C=N bond. With the bulky base lithium N,N-diisopropylamide (LDA) as a catalyst, the one-pot deprotonation steps can be performed through titration with methyllithium, using gas-volumetric observation of the liberated methane. In the first step with ensuing methylation by iodomethane, the primary product is born at ?40?°C in its metastable (Z) configuration (kinetic control) and may be either isolated or converted in?situ at 30?°C into its thermodynamically favored (E)-isomer via cis to trans stereoinversion at the N-atom. Being slow enough on the laboratory time scale, this stereoinversion process can serve to control the regioselectivity of the second deprotonation/alkylation sequence as follows. The α,α′-products are formed from the intermediate (Z)-imine, whereas α,α-products result from the intermediate (E)-imine; in either case, syn deprotonation (cis to tBu at nitrogen) by LDA is apparently disfavored by the tBu group, so that anti deprotonation becomes obligatory. If a third one-pot deprotonation step is too slow with LDA, it may be performed with the stronger base butyllithium/HMPA which, however, reacts regio-unselectively. Regioselective one-pot, LDA-catalyzed deprotonation with alkylation by oxiranes (alone, or alternatingly with iodomethane) opens a short access to spiro-[2.4]heptan-4-ones.
- Knorr, Rudolf,Neuner, Brigitte
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- Reactivity of Lithium β-Ketocarboxylates: The Role of Lithium Salts
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Lithium β-ketocarboxylates 1(COOLi), prepared by the reaction of lithium enolates 2(Li+) with carbon dioxide, readily undergo decarboxylative disproportionation in THF solution unless in the presence of lithium salts, in which case they are indefinitely stable at room temperature in inert atmosphere. The availability of stable THF solutions of lithium β-ketocarboxylates 1(COOLi) in the absence of carbon dioxide allowed reactions to take place with nitrogen bases and alkyl halides 3 to give α-alkyl ketones 1(R) after acidic hydrolysis. The sequence thus represents the use of carbon dioxide as a removable directing group for the selective monoalkylation of lithium enolates 2(Li+). The roles of lithium salts in preventing the disproportionation of lithium β-ketocarboxylates 1(COOLi) and in determining the course of the reaction with bases and alkyl halides 3 are discussed.
- Berton, Mateo,Mello, Rossella,Williard, Paul G.,González-Nú?ez, María Elena
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supporting information
p. 17414 - 17420
(2017/12/15)
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- In Situ Generation and Immobilization of an Activated Rh Complex Catalyst in a Metal–Organic Framework for Hydrogenation at Low H2 Pressure
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Hydrogenation reactions under low-pressure H2 atmosphere are highly relevant from the safety viewpoint, because H2 gas is highly flammable in air and explosions can be triggered by spark, heat, or sunlight. In this work, an Rh complex/MOF hybrid was synthesized and used as catalyst for the hydrogenation of alkene substrates. Thanks to the activation of the Rh complex catalyst during the immobilization process and the intrinsic gas-condensation property of MOFs, the resulting composite showed much higher catalytic activity than the complex catalyst itself. Moreover, the composite can maintain its catalytic activity even at low H2 pressures that cannot support the reaction with the complex catalyst alone. Furthermore, in contrast to the complex catalyst, the composite maintained its catalytic activity even without solvent, and thus provides an environmentally friendly approach to catalysis.
- Takashima, Yohei,Fukuhara, Yoshimasa,Sato, Yasushi,Tsuruoka, Takaaki,Akamatsu, Kensuke
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p. 5344 - 5349
(2017/12/04)
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- Method for preparing alicyclic ketone by catalytic oxidation of alicyclic alcohol compound
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The invention provides a method for preparing alicyclic ketone by catalytic oxidation of an alicyclic alcohol compound. The method takes air or oxygen as an oxidant and uses a catalyst system consisting two components of aza-adamantane free radical of nitroxide and a vanadium oxygen compound, and the alicyclic alcohol compound is oxidated into the corresponding alicyclic ketone with high selectivity at 50 to 120 DEG C. Compared with 2,2,6,6,-tetramethyl piperidine free radical of nitroxide, the aza-adamantane free radical of nitroxide has smaller influence of steric hindrance in a catalytic oxidation secondary alcohol reaction, and the catalyst system consisting of the vanadium oxygen compound has higher alicyclic alcohol oxidating efficiency. Compared with the conventional stoichiometric chemistry oxidation methods such as manganese dioxide, chromium trioxide and sodium hypochlorite, the method provided by the invention has the characteristics of few side products, mild reaction conditions, small environmental pollution and the like, and has very high practicability and economical efficiency.
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Paragraph 0025; 0026
(2016/12/01)
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- Two "classical" Old Yellow Enzymes from Chryseobacterium sp. CA49: Broad substrate specificity of Chr-OYE1 and limited activity of Chr-OYE2
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Two putative Old Yellow Enzyme (OYE) homologues, Chr-OYE1 and Chr-OYE2, were identified from the genome of Chryseobacterium sp. CA49 as new members of the "classical" subfamily. Chr-OYE1 and Chr-OYE2 were most closely related to the SYE4 from Shewanella oneidensis and NerA from Agrobacterium radiobacter with 41% and 45% identity, respectively. Both enzymes were expressed in Escherichia coli in soluble form, but their catalytic abilities as ene-reductases were quite different. Among the 19 substrate tested, Chr-OYE1 could catalyze the reduction of 18 of them including an ynone with excellent stereoselectivity for several prochiral ones, and its specific activity was roughly 1100-fold high than Chr-OYE2, which only catalyzed 3 of the substrates. After restoring the conserved tyrosine, Chr-OYE2 remained the same substrate spectrum, but showed significantly enhanced activity and stereoselectivity.
- Pei, Xiao-Qiong,Xu, Meng-Yu,Wu, Zhong-Liu
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- Mild and Selective Catalytic Hydrogenation of the C=C Bond in α,β-Unsaturated Carbonyl Compounds Using Supported Palladium Nanoparticles
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Chemoselective reduction of the C=C bond in a variety of α,β-unsaturated carbonyl compounds using supported palladium nanoparticles is reported. Three different heterogeneous catalysts were compared using 1 atm of H2: 1) nano-Pd on a metal-organic framework (MOF: Pd0-MIL-101-NH2(Cr)), 2) nano-Pd on a siliceous mesocellular foam (MCF: Pd0-AmP-MCF), and 3) commercially available palladium on carbon (Pd/C). Initial studies showed that the Pd@MOF and Pd@MCF nanocatalysts were superior in activity and selectivity compared to commercial Pd/C. Both Pd0-MIL-101-NH2(Cr) and Pd0-AmP-MCF were capable of delivering the desired products in very short reaction times (10-90 min) with low loadings of Pd (0.5-1 mol %). Additionally, the two catalytic systems exhibited high recyclability and very low levels of metal leaching.
- Nagendiran, Anuja,Pascanu, Vlad,Bermejo Gómez, Antonio,González Miera, Greco,Tai, Cheuk-Wai,Verho, Oscar,Martín-Matute, Belén,B?ckvall, Jan-E.
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p. 7184 - 7189
(2016/05/19)
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- Towards quantitative and scalable transformation of furfural to cyclopentanone with supported gold catalysts
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Given the vital importance of furfural (FFA) upgrading towards a sustainable bio-based economy, an eco-friendly aqueous route to produce a sole valuable product from FFA is highly desirable. We herein describe an efficient approach to quantitatively convert FFA into cyclopentanone (CPO) in neat water, employing H2 as the clean reductant and supported gold nanoparticles as a simple yet versatile catalyst. The use of anatase TiO2 featuring only mild Lewis acidic sites as the underlying support is essential, not only for preventing undesirable side reactions, but also for attaining high CPO selectivity. The feasibility of using biogenic CPO and CO2 as benign carbon sources to synthesize the industrially important feedstock dimethyl adipate is also demonstrated.
- Zhang, Gao-Shuo,Zhu, Ming-Ming,Zhang, Qi,Liu, Yong-Mei,He, He-Yong,Cao, Yong
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p. 2155 - 2164
(2016/04/19)
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- Pichia stipitis OYE 2.6 variants with improved catalytic efficiencies from site-saturation mutagenesis libraries
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An earlier directed evolution project using alkene reductase OYE 2.6 from Pichia stipitis yielded 13 active site variants with improved properties toward three homologous Baylis-Hillman adducts. Here, we probed the generality of these improvements by testing the wild-type and all 13 variants against a panel of 16 structurally-diverse electron-deficient alkenes. Several substrates were sterically demanding, and as hoped, creating additional active site volume yielded better conversions for these alkenes. The most impressive improvement was found for 2-butylidenecyclohexanone. The wild-type provided less than 20% conversion after 24 h; a triple mutant afforded more than 60% conversion in the same time period. Moreover, even wild-type OYE 2.6 can reduce cyclohexenones with very bulky 4-substituents efficiently.
- Patterson-Orazem, Athéna,Sullivan, Bradford,Stewart, Jon D.
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p. 5628 - 5632
(2015/01/09)
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- Heterologous expression and characterization of the ene-reductases from Deinococcus radiodurans and Ralstonia metallidurans
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The Old Yellow Enzyme (OYE) homologues or ene-reductases (ER) from Deinococcus radiodurans (DrER) and Ralstonia metallidurans (RmER) were cloned and characterized. Sequence and phylogenetic analysis revealed both these enzymes to belong to the YqjM-like or "thermophilic-like" group of OYEs, both sharing more than 60% sequence similarity to the ER from Thermus scotoductus. This group of OYEs is characterized by a conserved cysteine residue modulating the redox potential of the flavin cofactor as well as a conserved tyrosine residue located at the N-terminus region involved in binding certain ligands. The genes were recombinantly expressed in Escherichia coli as functional soluble proteins. Both ERs have monomer molecular weights of approximately 40 kDa, with DrER a homodimer in solution and RmER a monomer. DrER and RmER are optimally active at pH 7-7.5 at 30 C and 35 C respectively. Although the enzymes showed comparable affinities towards the ubiquitous ER substrate 2-cyclohexenone, the specific activity and catalytic efficiency of DrER were more than twice those observed for RmER. Similar to other members of this subclass of ERs, no conversion was detected with cyclic Cβ substituted enones, and only DrER was able to convert citral. Both DrER and RmER were highly active at reducing N-phenyl substituted maleimides. The selectivity of the ERs was assessed using both the isomers of carvone, which were converted with high diastereomeric excesses. Ketoisophorone and 2-methylcyclopentenone were converted to their (R)- and (S)-enantiomeric products respectively. Finally, a light-driven cofactor regeneration system was used to drive enzymatic reduction in the absence of NAD(P)H.
- Litthauer,Gargiulo,Van Heerden,Hollmann,Opperman
-
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- SPIROHYDANTOIN COMPOUNDS AND THEIR USE AS SELECTIVE ANDROGEN RECEPTOR MODULATORS
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The present invention relates to a compound of formula (1-1 ) in free form or in pharmaceutically acceptable salt form in which the substituents are as defined in the specification; to its preparation, to its use as a medicament and to medicaments comprising it. The present invention further provides a combination of pharmacologically active agents and a pharmaceutical composition.
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Page/Page column 86
(2013/09/12)
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- Graphene-supported Pd nanoparticles: Microwave-assisted synthesis and as microwave-active selective hydrogenation catalysts
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Facile synthesis of graphene-supported Pd nanoparticles (NPs) with an average size of 5 nm (Pd/G) was achieved by a microwave-assisted reduction approach; the obtained Pd/G can be very effectively coupled to the microwave field, making it a high-performance catalyst (with turnover frequency (TOF) of 158 465 h-1) for microwave-assisted selective hydrogenation of isophorone at low temperatures. The Royal Society of Chemistry 2013.
- Yang, Jing-He,Ma, Ding
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p. 10131 - 10134
(2013/09/02)
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- Mimicking nature: Synthetic nicotinamide cofactors for C=C bioreduction using enoate reductases
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A series of synthetic nicotinamide cofactors were synthesized to replace natural nicotinamide cofactors and promote enoate reductase (ER) catalyzed reactions without compromising the activity or stereoselectivity of the bioreduction process. Conversions and enantioselectivities of >99% were obtained for C=C bioreductions, and the process was successfully upscaled. Furthermore, high chemoselectivity was observed when employing these nicotinamide cofactor mimics (mNADs) with crude extracts in ER-catalyzed reactions.
- Paul, Caroline E.,Gargiulo, Serena,Opperman, Diederik J.,Lavandera, Iván,Gotor-Fernández, Vicente,Gotor, Vicente,Taglieber, Andreas,Arends, Isabel W. C. E.,Hollmann, Frank
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supporting information
p. 180 - 183
(2013/04/24)
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- Polydentate pyridyl ligands and the catalytic activity of their iron(II) complexes in oxidation reactions utilizing peroxides as the oxidants
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The paper describes the synthesis of iron(II) complexes bearing new polydentate N,O-coordinating pyridyl ligands and their catalytic application in oxidation reactions employing peroxides as the oxidants. The tridentate N,O,N (10) and N,N,O (11) ligands, the tetradentate N,N,O,N ligand 12 and the pentadentate N,N,N,O,N-coordinating ligand 16 were synthesized, and obtained as oils or solids in 74-93% isolated yields. The ligands were subsequently converted to the iron complexes [Fe(10)2](OTf)2, [Fe(11)2](OTf)2, [Fe(12)(OTf)2] and [Fe(16)(OTf)](OTf), which were obtained as tan powders in 90-94% yield and characterized by various instrumental techniques. Preliminary screening experiments revealed that all complexes are catalytically active in the oxidation of secondary alcohols and benzylic methylene groups to the corresponding ketones. Optimization experiments with the complex [Fe(12)(OTf)2] yielded a system that provided under mild condition ketones from benzylic methylene groups and secondary alcohols in 63-90% isolated yields (3 mol% catalyst loading, 3 equiv. H2O2 in CH 3CN for 2 h at room temperature). Similar conditions utilizing environmentally friendly acetone as the solvent and 4 equiv. tBuOOH resulted in 36-65% isolated yields for some of the substrates, indicating a somewhat lower catalytic activity in that solvent. For the complexes [Fe(10)2](OTf)2 (two tridentate ligands), [Fe(12)(OTf)2] (one tetradentate ligand) and [Fe(16)(OTf)](OTf) (one pentadentate ligand), the product formation for a test reaction was followed over time at significantly reduced catalyst loading to determine activities. Under these conditions, the complex [Fe(10)2](OTf)2 exhibited a somewhat lower catalytic activity compared to the other two complexes. Thus, the denticity seems to have an impact on catalytic activity although it is not dramatic, and a higher denticity appears to be beneficial for catalysis.
- Lenze, Matthew,Sedinkin, Sergey L.,Bauer, Eike B.
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p. 161 - 171
(2013/06/27)
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- Asymmetric bioreduction of activated carbon-carbon double bonds using Shewanella yellow enzyme (SYE-4) as novel enoate reductase
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Shewanella yellow enzyme (SYE-4), a novel recombinant enoate reductase, was screened against a variety of different substrates bearing an activated double bond, such as unsaturated cyclic ketones, diesters, and substituted imides. Dimethyl- and ethyl esters of 2-methylmaleic acid were selectively reduced to (R)-configured succinic acid derivatives and various N-substituted maleimides furnished the desired (R)-products in up to >99% enantiomeric excess. Naturally occurring (+)-carvone was selectively reduced to (-)-cis- dihydrocarvone and (-)-carvone was converted to the diastereomeric product, respectively. Overall SYE-4 proved to be a useful biocatalyst for the selective reduction of activated CC double bonds and complements the pool of synthetic valuable enoate reductases.
- Iqbal, Naseem,Rudroff, Florian,Brigé, Ann,Van Beeumen, Jozef,Mihovilovic, Marko D.
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experimental part
p. 7619 - 7623
(2012/09/07)
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- Nicotinamide-dependent Ene reductases as alternative biocatalysts for the reduction of activated alkenes
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Four NAD(P)H-dependent non-flavin ene reductases have been investigated for their ability to reduce activated C=C bonds in an asymmetric fashion by using 20 structurally diverse substrates. In comparison with flavin-dependent Old Yellow Enzyme homologues, a higher degree of electronic activation was required, because the best activities were obtained with enals and nitroalkenes rather than enones and carboxylic esters. Although FaEO from Fragaria x ananassa (strawberry) and its homologue SlEO from Solanum lycopersicum (tomato) exhibited a narrow substrate spectrum, progesterone 5β-reductase (At5β-StR) from Arabidopsis thaliana (thale cress) and leukotriene B4 12-hydroxydehydrogenase (LTB4DH/PGR) from Rattus norvegicus (rat) appear to be promising candidates, in particular for the asymmetric bioreduction of open-chain enals, nitroalkenes and α,β-unsaturated γ-butyrolactones. Competing nitro reduction and non-enzymatic Weitz-Scheffer epoxidation were largely suppressed. Electronically activated alkenes have been stereoselectively reduced by using a single-enzyme-cofactor system employing nicotinamide-dependent non-flavin ene reductases. Copyright
- Durchschein, Katharina,Wallner, Silvia,MacHeroux, Peter,Schwab, Wilfried,Winkler, Thorsten,Kreis, Wolfgang,Faber, Kurt
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p. 4963 - 4968
(2013/01/14)
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- Enantioselective route to ketones and lactones from exocyclic allylic alcohols via metal and enzyme catalysis
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A general and efficient route for the synthesis of enantiomerically pure α-substituted ketones and the corresponding lactones has been developed. Ruthenium- and enzyme-catalyzed dynamic kinetic resolution (DKR) with a subsequent Cu-catalyzed α-allylic substitution are the key steps of the route. The α-substituted ketones were obtained in high yields and with excellent enantiomeric excess. The methodology was applied to the synthesis of a naturally occurring caprolactone, (R)-10-methyl-6-undecanolide, via a subsequent Baeyer-Villiger oxidation.
- Warner, Madeleine C.,Nagendiran, Anuja,Bogár, Krisztián,B?ckvall, Jan-E.
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supporting information
p. 5094 - 5097
(2013/01/15)
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- Synthesis of dimethyl adipate from cyclopentanone and dimethyl carbonate over solid base catalysts
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A facile route for the synthesis of dimethyl adipate (DAP) from cyclopentanone and dimethyl carbonate (DMC) in the presence of solid base catalysts has been developed. It was found that the intermediate carbomethoxycyclopentanone (CMCP) was produced from cyclopentanone with DMC in the first step, and then CMCP was further converted to DAP by reacting with a methoxide group. The role of the basic catalysts can be mainly ascribed to the activation of cyclopentanone via the abstraction of a proton in the α-position by base sites, and solid bases with moderate strength, such as MgO, favor the formation of DAP.
- Wu, Dudu,Chen, Zhi,Jia, Zhenbin,Shuai, Li
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experimental part
p. 380 - 385
(2012/10/07)
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- Hydrosilylation of epoxides catalyzed by a cationic η1- silane iridium(iii) complex
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Cationic silane complex 2, catalyzes the hydrosilylation of epoxides and cyclic ethers to give the silyl-protected alcohols, regioselectively. A mechanistic study shows that the epoxide undergoes isomerization to the ketone, followed by hydrosilylation.
- Park, Sehoon,Brookhart, Maurice
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scheme or table
p. 3643 - 3645
(2011/05/04)
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- Asymmetric bioreduction of alkenes using ene-reductases YersER and KYE1 and effects of organic solvents
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Asymmetric trans-bioreduction of activated alkenes by KYE1 from Kluyveromyces lactis and Yers-ER from Yersinia bercovieri, two ene-reductases from the Old Yellow Enzyme family, showed a broad substrate spectrum with a moderate to excellent degree of stereoselectivity. Both substrate- and enzyme-based stereocontrols were observed to furnish opposite stereoisomeric products. The effects of organic solvents on enzyme activity and stereoselectivity were outlined in this study, where two-phase systems hexane and toluene are shown to sustain bioreduction efficiency even at high organic solvent content.
- Yanto, Yanto,Winkler, Christoph K.,Lohr, Stephanie,Hall, Melanie,Faber, Kurt,Bommarius, Andreas S.
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supporting information; experimental part
p. 2540 - 2543
(2011/06/25)
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- PROCESS INCLUDING HYDROGENOLYSIS OF BIOMASS FOLLOWED BY DEHYDROGENATION AND ALDOL CONDENSATION FOR PRODUCING ALKANES
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A method comprises providing a bio-based feedstock; contacting the bio-based feedstock with a solvent in a hydrolysis reaction to form an intermediate stream comprising carbohydrates; contacting the intermediate stream with an aqueous phase reforming catalyst to form a plurality of oxygenated intermediates, wherein a first portion of the oxygenated intermediates are recycled to form the solvent; and contacting at least a second portion of the oxygenated intermediates with a condensation catalyst comprising a base functionality to form a fuel blend.
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Page/Page column 34-37
(2011/12/02)
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- DEHYDROGENATION OF CYCLOHEXANONE TO PRODUCE PHENOL
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In a process for the dehydrogenation of cyclohexanone to produce phenol, a feed comprising cyclohexanone is contacted with a dehydrogenation catalyst under dehydrogenation conditions comprising a temperature of less than 4000C and a pressure of less than 690 kPa, gauge, such 0.1 to 50 wt% of the cyclohexanone in said feed is converted to phenol and the dehydrogenation product contains less than 100 ppm by weight of alkylbenzenes.
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Page/Page column 23; 25
(2011/09/14)
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- The substrate spectra of pentaerythritol tetranitrate reductase, morphinone reductase, N-ethylmaleimide reductase and estrogen-binding protein in the asymmetric bioreduction of activated alkenes
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Four flavoproteins from the old yellow enzyme (OYE) family, pentaerythritol tetranitrate (PETNR) reductase, N-ethylmaleimide reductase (NEMR), morphinone reductase (MorR) and estrogen-binding protein (EBP1), exhibited a broad substrate tolerance by accepting conjugated enals, enones, imides, dicarboxylic acids and esters, as well as a nitroalkene and therefore can be employed for the asymmetric bioreduction of carbon-carbon double (C=C) bonds. In particular, morphinone reductase and estrogen-binding protein often showed a complementary stereochemical preference in comparison to that of previously investigated OYES.
- Mueller, Nicole J.,Stueckler, Clemens,Hauer, Bernhard,Baudendistel, Nina,Housden, Hazel,Bruce, Neil C.,Faber, Kurt
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experimental part
p. 387 - 394
(2010/06/11)
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- Focused Directed Evolution of Pentaerythritol Tetranitrate Reductase by Using Automated Anaerobic Kinetic Screening of Site-Saturated Libraries
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This work describes the development of an automated robotic platform for the rapid screening of enzyme variants generated from directed evolution studies of pentraerythritol tetranitrate (PETN) reductase, a target for industrial biocatalysis. By using a 96-well format, near pure enzyme was recovered and was suitable for high throughput kinetic assays; this enabled rapid screening for improved and new activities from libraries of enzyme variants. Initial characterisation of several single site-saturation libraries targeted at active site residues of PETN reductase, are described. Two mutants (T26S and W102F) were shown to have switched in substrate enantiopreference against substrates (E)-2-aryl-1-nitropropene and α-methyl-trans-cinnamaldehyde, respectively, with an increase in ee (62 % (R) for W102F). In addition, the detection of mutants with weak activity against α,β-unsaturated carboxylic acid substrates showed progress in the expansion of the substrate range of PETN reductase. These methods can readily be adapted for rapid evolution of enzyme variants with other oxidoreductase enzymes.
- Hulley, Martyn E.,Toogood, Helen S.,Fryszkowska, Anna,Mansell, David,Stephens, Gill M.,Gardiner, John M.,Scrutton, Nigel S.
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experimental part
p. 2433 - 2447
(2011/07/08)
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- Biocatalysis with thermostable enzymes: Structure and properties of a thermophilic 'ene'-reductase related to old yellow enzyme
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We report the crystal structure of a thermophilic "ene" reductase (TOYE) isolated from Thermoanaerobacter pseudethanolicus E39. The crystal structure reveals a tetrameric enzyme and an active site that is relatively large compared to most other structurally determined and related Old Yellow Enzymes. The enzyme adopts higher order oligomeric states (octamers and dodecamers) in solution, as revealed by sedimentation velocity and multiangle laser light scattering. Bead modelling indicates that the solution structure is consistent with the basic tetrameric structure observed in crystallographic studies and electron microscopy. TOYE is stable at high temperatures (T m > 70°C) and shows increased resistance to denaturation in water-miscible organic solvents compared to the mesophilic Old Yellow Enzyme family member, pentaerythritol tetranitrate reductase. TOYE has typical ene-reductase properties of the Old Yellow Enzyme family. There is currently major interest in using Old Yellow Enzyme family members in the preparative biocatalysis of a number of activated alkenes. The increased stability of TOYE in organic solvents is advantageous for biotransformations in which water-miscible organic solvents and biphasic reaction conditions are required to both deliver novel substrates and minimize product racemisation.
- Adalbjoernsson, Bjoern V.,Toogood, Helen S.,Fryszkowska, Anna,Pudney, Christopher R.,Jowitt, Thomas A.,Leys, David,Scrutton, Nigel S.
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experimental part
p. 197 - 207
(2010/12/19)
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- Characterization of xenobiotic reductase A (XenA): Study of active site residues, substrate spectrum and stability
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Xenobiotic reductase A (XenA) has broad catalytic activity and reduces various α,β-unsaturated and nitro compounds with moderate to excellent stereoselectivity. Single mutants C25G and C25V are able to reduce nitrobenzene, a non-active substrate for the wild type, to produce aniline. Total turnover is dominated by chemical rather than thermal instability. The Royal Society of Chemistry 2010.
- Yanto, Yanto,Yu, Hua-Hsiang,Hall, Melanie,Bommarius, Andreas S.
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scheme or table
p. 8809 - 8811
(2011/02/28)
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- Asymmetrie reduction of activated alkenes by pentaerythritol tetranitrate reductase: Specificity and control of stereochemical outcome by reaction optimisation
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We show that pentaerythritol tetranitrate reductase (PETNR), a member of the 'ene' reductase old yellow enzyme family, catalyses the asymmetric reduction of a variety of industrially relevant activated α,β-unsaturated alkenes including enones, enals, maleimides and nitroalkenes. We have rationalised the broad substrate specificity and stereochemical outcome of these reductions by reference to molecular models of enzyme-substrate complexes based on the crystal complex of the PETNR with 2cyclohexenone 4a. The optical purity of products is variable (49-99% ee), depending on the substrate type and nature of substituents. Generally, high enantioselectivity was observed for reaction products with stereogenic centres at Cβ (>99% ee). However, for the substrates existing in two isomeric forms (e.g., citral 11a or nitroalkenes 18-19a), an enantio-divergent course of the reduction of E/Z-forms may lead to lower enantiopurities of the products. We also demonstrate that the poor optical purity obtained for products with stereogenic centres at Ca is due to non-enzymatic racemisation. In reactions with ketoisophorone 3a we show that product racemisation is prevented through reaction optimisation, specifically by shortening reaction time and through control of solution pH. We suggest this as a general strategy for improved recovery of optically pure products with other biocatalytic conversions where there is potential for product racemisation.
- Fryszkowska, Anna,Toogood, Helen,Sakuma, Michiyo,Gardiner, John M.,Stephens, Gill M.,Scrutton, Nigel S.
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experimental part
p. 2976 - 2990
(2010/03/25)
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- Asymmetric bioreduction of activated C=C bonds using Zymomonas mobilis NCR enoate reductase and old yellow enzymes OYE 1-3 from yeasts
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The asymmetric bioreduction of C=C-bonds bearing an electron-withdrawing group, such as an aldehyde, ketone, imide, nitro, carboxylic acid, or ester moiety by a novel enoate reductase from Zymomonas mobilis and Old Yellow Enzymes OYE 1-3 from yeasts furnished the corresponding saturated products in up to >99%ee. Depending on the substrate type, stereocontrol was achieved by variation of the substrate structure, by switching the (E/Z) geometry of the alkene or by choice of the appropriate enzyme. This substrate- or enzyme-based stereocontrol allowed access to the opposite enantiomeric products. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Hall, Melanie,Stueckler, Clemens,Hauer, Bernhard,Stuermer, Rainer,Friedrich, Thomas,Breuer, Michael,Kroutil, Wolfgang,Faber, Kurt
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scheme or table
p. 1511 - 1516
(2009/04/11)
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- pH-dependent catalytic activity and chemoselectivity in transfer hydrogenation catalyzed by iridium complex with 4,4′-dihydroxy-2,2′- bipyridine
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Transfer hydrogenation catalyzed by an iridium catalyst with 4,4′dihydroxy-2,2′-bipyridine (DHBP) in an aqueous formate solution exhibits highly pH-dependent catalytic activity and chemoselectivity. The substantial change in the activity is due to the electronic effect based on the acid-base equilibrium of the phenolic hydroxyl group of DHBP. Under basic conditions, high turnover frequency values of the DHBP complex, which can be more than 1000 times the value of the unsubstituted analogue, are obtained (up to 81000 h-1 at 80°C). In addition, the DHBP catalyst exhibits pH-dependent chemoselectivity for α,β-unsaturated carbonyl compounds. Selective reduction of the C=C bond of enone with high activity are observed under basic conditions. The ketone moieties can be reduced with satisfactory activity under acidic conditions. In particular, pH-selective chemoselectivity of the C=O versus C=C bond reduction was observed in the transfer hydrogenation of cinnamaldehyde.
- Himeda, Yuichiro,Onozawa-Komatsuzaki, Nobuko,Miyazawa, Satoru,Sugihara, Hideki,Hirose, Takuji,Kasuga, Kazuyuki
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scheme or table
p. 11076 - 11081
(2009/11/30)
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- Asymmetric bioreduction of C=C bonds using enoate reductases OPR1, OPR3 and YqjM: Enzyme-based stereocontrol
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Three cloned enoate reductases from the "old yellow enzyme" family of flavoproteins were investigated in the asymmetric bioreduction of activated alkenes. 12-Oxophytodienoate reductase isoenzymes OPR1 and OPR3 from Lycopersicon esculentum (tomato), and YqjM from Bacillus subtilis displayed a remarkably broad substrate spectrum by reducing α,β-unsaturated aldehydes, ketones, maleimides and nitroalkenes. The reaction proceeded with absolute chemoselectivity-only the conjugated C=C bond was reduced, while isolated olefins and carbonyl groups remained intact-with excellent stereoselectivities (ees up to >99%). Upon reduction of a nitroalkene, the stereochemical outcome could be determined via choice of the appropriate enzyme (OPR1 versus OPR3 or YqjM), which furnished the corresponding enantiomeric nitroalkanes in excellent ee. Molecular modelling suggests that this "enzyme-based stereocontrol" is caused by subtle differences within the active site geometries.
- Hall, Melanie,Stueckler, Clemens,Ehammer, Heidemarie,Pointner, Eva,Oberdorfer, Gustav,Gruber, Karl,Hauer, Bernard,Stuermer, Rainer,Kroutil, Wolfgang,Macheroux, Peter,Faber, Kurt
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experimental part
p. 411 - 418
(2009/04/10)
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- Asymmetric bioreduction of activated alkenes using cloned 12-oxophytodienoate reductase isoenzymes OPR-1 and OPR-3 from Lycopersicon esculentum (tomato): A striking change of stereoselectivity
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(Chemical Equation Presented) Tomato source: 12-Oxophytodienoate reductase isoenzymes OPR1 and OPR3 from tomato possess a broad substrate spectrum for the asymmetric bioreduction of α,β-unsaturated enals, enones, dicarboxylic acids, and N-substituted male-imides (see scheme). Stereocomplementary behavior of both isoenzymes was observed in the reduction of a nitroalkene that led to the formation of opposite stereoisomers in high enantiomeric excess.
- Hall, Melanie,Stueckler, Clemens,Kroutil, Wolfgang,Macheroux, Peter,Faber, Kurt
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p. 3934 - 3937
(2008/03/11)
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- Polymeric DABCO-bromine complex: a mild oxidant for the preparation of ketones and aldehydes
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A stable, shelf-ready polymeric oxidant was prepared from the addition of Br2 to DABCO in CCl4. This material was used to convert simple primary and secondary alcohols to the corresponding aldehydes and ketones in biphasic CH2Cl2/H2O.
- Struss, John A.,Barnhart, William D.,Velasco, Maria R.,Bronley-DeLancey, Apryl
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p. 6635 - 6636
(2007/10/03)
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- Semivolatile and volatile compounds in combustion of polyethylene
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The evolution of semivolatile and volatile compounds in the combustion of polyethylene (PE) was studied at different operating conditions in a horizontal quartz reactor. Four combustion runs at 500 and 850°C with two different sample mass/air flow ratios and two pyrolytic runs at the same temperatures were carried out. Thermal behavior of different compounds was analyzed and the data obtained were compared with those of literature. It was observed that α,ω-olefins, α-olefins and n-paraffins were formed from the pyrolytic decomposition at low temperatures. On the other hand, oxygenated compounds such as aldehydes were also formed in the presence of oxygen. High yields were obtained of carbon oxides and light hydrocarbons, too. At high temperatures, the formation of polycyclic aromatic hydrocarbons (PAHs) took place. These compounds are harmful and their presence in the combustion processes is related with the evolution of pyrolytic puffs inside the combustion chamber with a poor mixture of semivolatile compounds evolved with oxygen. Altogether, the yields of more than 200 compounds were determined. The collection of the semivolatile compounds was carried out with XAD-2 adsorbent and were analyzed by GC-MS, whereas volatile compounds and gases were collected in a Tedlar bag and analyzed by GC with thermal conductivity and flame ionization detectors.
- Font, Rafael,Aracil, Ignacio,Fullana, Andrés,Conesa, Juan A.
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p. 615 - 627
(2007/10/03)
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