- Optimized Reaction Conditions Enable the Hydration of Non-natural Substrates by the Oleate Hydratase from Elizabethkingia meningoseptica
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The oleate hydratase from Elizabethkingia meningoseptica (Em-OAH) catalyzes the hydration of oleic acid (C18) to (R)-10-hydroxystearic acid. In previous work, low activity of Em-OAH towards chemically synthesized (Z)-undec-9-enoic acid (C11) was observed. Product formation in the hydration of the truncated C11 substrate was improved by optimizing the reaction conditions by applying statistical experiment design. Optimized reaction conditions resulted in a 2.8-fold increase in product formation in just one quarter of the time (64 % conversion in 28 h). The applicability has been assessed in the upscaling of the conversion of (Z)-undec-9-enoic acid to (S)-10-hydroxyundecanoic acid (132 mg product, >95 % purity). Reaction conditions developed for the hydration of C11 facilitated the first hydration of non-natural alkenes. By using a fatty acid dummy substrate, 1-decene was successfully hydrated to (S)-2-decanol with excellent stereoselectivity and 50 % conversion after four days of incubation.
- Demming, Rebecca M.,Otte, Konrad B.,Nestl, Bettina M.,Hauer, Bernhard
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Read Online
- Asymmetric Enzymatic Hydration of Unactivated, Aliphatic Alkenes
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The direct enantioselective addition of water to unactivated alkenes could simplify the synthesis of chiral alcohols and solve a long-standing challenge in catalysis. Here we report that an engineered fatty acid hydratase can catalyze the asymmetric hydration of various terminal and internal alkenes. In the presence of a carboxylic acid decoy molecule for activation of the oleate hydratase from E. meningoseptica, asymmetric hydration of unactivated alkenes was achieved with up to 93 % conversion, excellent selectivity (>99 % ee, >95 % regioselectivity), and on a preparative scale.
- Demming, Rebecca M.,Hammer, Stephan C.,Nestl, Bettina M.,Gergel, Sebastian,Fademrecht, Silvia,Pleiss, Jürgen,Hauer, Bernhard
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supporting information
p. 173 - 177
(2018/12/11)
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- Identification of a Robust Carbonyl Reductase for Diastereoselectively Building syn-3,5-Dihydroxy Hexanoate: A Bulky Side Chain of Atorvastatin
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t-Butyl-6-cyano-(3R,5R)-dihydroxyhexanoate is an advanced chiral precursor for the synthesis of the side chain pharmacophore of cholesterol-lowering drug atorvastatin. Herein, a robust carbonyl reductase (LbCR) was newly identified from Lactobacillus brevis, which displays high activity and excellent diastereoselectivity toward bulky t-butyl 6-cyano-(5R)-hydroxy-3-oxo-hexanoate (7). The engineered Escherichia coli cells harboring LbCR and glucose dehydrogenase (for cofactor regeneration) were employed as biocatalysts for the asymmetric reduction of substrate 7. As a result, as much as 300 g L-1 of water-insoluble substrate was completely converted to the corresponding chiral diol with >99.5% de in a space-time yield of 351 g L-1 d-1, indicating a great potential of LbCR for practical synthesis of the very bulky and bi-chiral 3,5-dihydroxy carboxylate side chain of best-selling statin drugs.
- Gong, Xu-Min,Zheng, Gao-Wei,Liu, You-Yan,Xu, Jian-He
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supporting information
p. 1349 - 1354
(2017/09/23)
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- Chiral Surfactant-Type Catalyst: Enantioselective Reduction of Long-Chain Aliphatic Ketoesters in Water
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A series of amphiphilic ligands were designed and synthesized. The rhodium complexes with the ligands were applied to the asymmetric transfer hydrogenation of broad range of long-chained aliphatic ketoesters in neat water. Quantitative conversion and excellent enantioselectivity (up to 99% ee) was observed for α-, β-, γ-, δ- and ε-ketoesters as well as for α- and β-acyloxyketone using chiral surfactant-type catalyst 2. The CH/π interaction and the strong hydrophobic interaction of long aliphatic chains between the catalyst and the substrate in the metallomicelle core played a key role in the catalytic transition state. Synergistic effects between the metal-catalyzed site and the hydrophobic microenvironment of the core in the micelle contributed to high stereoselectivity. (Chemical Equation Presented).
- Lin, Zechao,Li, Jiahong,Huang, Qingfei,Huang, Qiuya,Wang, Qiwei,Tang, Lei,Gong, Deying,Yang, Jun,Zhu, Jin,Deng, Jingen
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p. 4419 - 4429
(2015/05/13)
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- A novel P450-based biocatalyst for the selective production of chiral 2-alkanols
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A P450 monooxygenase from Nocardia farcinica (CYP154A8) catalyses the stereo- and regioselective hydroxylation of n-alkanes, still a challenging task in chemical catalysis. In a biphasic reaction system, the regioselectivity for the C2-position of C7-C9 alkanes was over 90%. The enzyme showed strict S-selectivity for all tested substrates, with enantiomeric excess (ee) of up to 91%. This journal is the Partner Organisations 2014.
- Von Bühler, Clemens J.,Urlacher, Vlada B.
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supporting information
p. 4089 - 4091
(2014/04/03)
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- Continuous biphasic enzymatic reduction of aliphatic ketones
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Biphasic reactions offer an attractive alternative for the utilisation of enzymes for conversion of hardly water soluble substrates. Especially, the alcohol dehydrogenase from Lactobacillus brevis was successfully used for the reductive synthesis of enantiopure secondary aliphatic alcohols. With the enzymatic catalyst and the cofactor effectively retained in the reactive aqueous phase, the continuous operation was demonstrated by continuous addition and withdrawal of the non-reactive phase. The four tested substrates 2-heptanone, 2-octanone, 2-nonanone, and 2-decanone showed that the space time yield and turnover numbers (TON) of the enzyme decrease as the availability of the substrate decreases with increasing partition coefficients. Nevertheless, a TONLbADH of up to 478 × 103 could be achieved. Remarkably, the cofactor utilisation turned out to be very high and a TON NADP+ of more than 20 × 103 was easily achievable for both 2-heptanone and 2-octanone by substrate coupled cofactor regeneration with excess of 2-propanol.
- Leuchs, Susanne,Nonnen, Thomas,Dechambre, Dominique,Na'Amnieh, Shukralla,Greiner, Lasse
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- Catalytic enantioselective addition of alkyl grignard reagents to aliphatic aldehydes
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Herein, we report an efficient catalytic system for the enantioselective addition of alkyl Grignard reagents to a broad range of aliphatic aldehydes with good yields and enantioselectivities. Remarkably, the challenging methylmagnesium bromide (MeMgBr) can also be added to a variety of aliphatic aldehydes, providing versatile chiral methyl carbinol units with unprecedented yields and enantioselectivities in a simple one-pot procedure under mild conditions. Copyright
- Fernandez-Mateos, Emilio,Macia, Beatriz,Yus, Miguel
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supporting information
p. 1249 - 1254
(2013/06/27)
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- Stereospecific inversion of secondary tosylates to yield chiral methyl-branched building blocks, applied to the asymmetric synthesis of leafminer sex pheromones
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All four of the possible stereoisomers of 5,9-dimethylheptadecane, the major sex pheromone component secreted by female moths of the mountain-ash bentwing (Leucoptera scitella), were synthesized by the coupling of two chiral blocks with a methyl branch at the 2- or 3-position. The blocks were prepared by applying the stereospecific inversion of secondary tosylates, which were derived from (R)- and (S)-propylene oxide, and their enantiopurities were confirmed by chiral HPLC analysis.
- Taguri, Tomonori,Yamakawa, Rei,Fujii, Toru,Muraki, Yuta,Ando, Tetsu
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experimental part
p. 852 - 858
(2012/09/22)
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- The substrate spectrum of the inverting sec-alkylsulfatase Pisa1
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The substrate spectrum of the inverting alkylsulfatase Pisa1 was investigated using a range of sec-alkyl sulfate esters bearing aromatic, olefinic and acetylenic moieties. Perfect enantioselectivities were obtained for substrates bearing groups of different size adjacent to the sulfate ester moiety. Insufficient selectivities could be doubled by using dimethyl sulfoxide (DMSO) as co-solvent. Hydrolytically unstable benzylic sulfate esters could be sufficiently stabilised by introduction of electron-withdrawing substituents. Overall, Pisa1 appears to be a very useful inverting alkylsulfatase for the deracemisation of rac-sec-alcohols via enzymatic hydrolysis of their corresponding sulfate esters, which furnishes homochiral products possessing the 'anti-Kazlauskas' configuration. Copyright
- Schober, Markus,Knaus, Tanja,Toesch, Michael,MacHeroux, Peter,Wagner, Ulrike,Faber, Kurt
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p. 1737 - 1742
(2012/07/31)
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- Chiral surfactant-type catalyst for asymmetric reduction of aliphatic ketones in water
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A novel chiral surfactant-type catalyst is developed. Micelles formed in water by association of the catalysts themselves, and this was confirmed by TEM analyses. Asymmetric transfer hydrogenation of aliphatic ketones catalyzed by the chiral metallomicellar catalyst gave good to excellent conversions and remarkable stereoselectivities (up to 95% ee). Synergistic effects between the metal-catalyzed center and the hydrophobic microenvironment of the core in the metallomicelle led to high enantioselectivities.
- Li, Jiahong,Tang, Yuanfu,Wang, Qiwei,Li, Xuefeng,Cun, Linfeng,Zhang, Xiaomei,Zhu, Jin,Li, Liangchun,Deng, Jingen
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supporting information
p. 18522 - 18525
(2013/01/15)
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- Ionic liquid facilitates biocatalytic conversion of hardly water soluble ketones
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Ionic liquids represent a promising alternative to conventional cosolvents as biocompatible solubilisers for biocatalysis. This was shown using water miscible ionic liquids to facilitate the stereoselective reduction of hardly water soluble, aliphatic ketones catalysed by the alcohol dehydrogenase from Lactobacillus brevis. Ten ionic liquids were screened for activity and solubility. Improved storage stabilities besides improved enzyme activities, as well as reduced substrate surplus and product inhibitions were found, while applying the most promising AMMOENG 101 in more detailed investigations. Batch reactions with cofactor regeneration via a glucose dehydrogenase showed increased reaction rates; thus underlining the positive influence of AMMOENG 101. For (R)-3-octanol, (R)-2-nonanol, (R)-2-decanol, and (R)-2-octanol space time yields between 250 and 350 mmol L-1 d -1 were achieved.
- Kohlmann, Christina,Robertz, Nora,Leuchs, Susanne,Dogan, Zuebeyde,Luetz, Stephan,Bitzer, Katrin,Na'Amnieh, Shukrallah,Greiner, Lasse
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experimental part
p. 147 - 153
(2011/10/08)
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- Utilising hardly-water soluble substrates as a second phase enables the straightforward synthesis of chiral alcohols
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So far, the alcohol dehydrogenase-catalysed conversion of longer chain aliphatic substrates has been challenging due to their low solubility in aqueous solution. However, by utilising the ketone directly as a second organic phase, the straightforward synthesis of long chain aliphatic chiral alcohols is enabled. The Royal Society of Chemistry.
- Kohlmann, Christina,Robertz, Nora,Leuchs, Susanne,Greiner, Lasse,Na'Amnieh, Shukralla
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supporting information; experimental part
p. 3093 - 3095
(2011/12/05)
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- Asymmetric anti-Prelog reduction of ketones catalysed by Paracoccus pantotrophus and Comamonas sp. cells via hydrogen transfer
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A broad range of ketones including methyl-aryl-, methyl-alkyl-, cyclic and sterically hindered ketones were reduced to the corresponding anti-Prelog alcohols with moderate to excellent stereoselectivities by employing lyophilised cells of Paracoccus pantotrophus DSM 11072 and Comamonas sp. DSM 15091 via hydrogen transfer. The reduction equivalents were provided using 2-propanol as a hydride donor. For instance, acetophenone was reduced to the corresponding (R)-enantiomer with >99% ee.
- Lavandera, Ivan,Hoeller, Brigitte,Kern, Alexander,Ellmer, Ursula,Glieder, Anton,de Wildeman, Stefaan,Kroutil, Wolfgang
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p. 1954 - 1958
(2008/12/22)
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- One-way biohydrogen transfer for oxidation of sec-alcohols
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(Chemical Equation Presented) Quasi-irreversible oxidation of sec-alcohols was achieved via biocatalytic hydrogen transfer reactions using alcohol dehydrogenases employing selected ketones as hydrogen acceptors, which can only be reduced but not oxidized. Thus, only 1 equiv of oxidant was required instead of a large excess. For the oxidation of both isomers of methylcarbinols a single nonstereoselective short-chain dehydrogenase/reductase from Sphingobium yanoikuyae was identified and overexpressed in E. coli.
- Lavandera, Ivan,Kern, Alexander,Resch, Verena,Ferreira-Silva, Bianca,Glieder, Anton,Fabian, Walter M. F.,De Wildeman, Stefaan,Kroutil, Wolfgang
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supporting information; experimental part
p. 2155 - 2158
(2009/05/27)
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- Orchestration of concurrent oxidation and reduction cycles for stereoinversion and deracemisation of sec-alcohols
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Black and white are opposites as are oxidation and reduction. Performing an oxidation, for example, of a sec-alcohol and a reduction of the corresponding ketone in the same vessel without separation of the reagents seems to be an impossible task. Here we show that oxidative cofactor recycling of NADP + and reductive regeneration of NADH can be performed simultaneously in the same compartment without significant interference. Regeneration cycles can be run in opposing directions beside each other enabling one-pot transformation of racemic alcohols to one enantiomer via concurrent enantioselective oxidation and asymmetric reduction employing defined alcohol dehydrogenases with opposite stereo- and cofactor-preference. Thus, by careful selection of appropriate enzymes, NADH recycling can be performed in the presence of NADP+ recycling to achieve overall, for example, deracemisation of sec-alcohols or stereoinversion representing a possible concept for a "green" equivalent to the chemical-intensive Mitsunobu inversion.
- Voss, Constance V.,Gruber, Christian C.,Faber, Kurt,Knaus, Tanja,Macheroux, Peter,Kroutil, Wolfgang
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supporting information; experimental part
p. 13969 - 13972
(2009/02/07)
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- Enantioselective transfer hydrogenation of aliphatic ketones catalyzed by ruthenium complexes linked to the secondary face of β-cyclodextrin
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Ruthenium-η-arene complexes attached to the secondary face of β-cyclodextrin catalyze the enantioselective reduction (ee up to 98%) of aliphatic and aromatic ketones in aqueous medium in the presence of sodium formate (HCOONa).
- Schlatter, Alain,Woggon, Wolf-D.
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scheme or table
p. 995 - 1000
(2009/05/30)
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- Deracemization of secondary alcohols through a concurrent tandem biocatalytic oxidation and reduction
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(Chemical Equation Presented) Breaking the mirror: A purified alcohol dehydrogenase (ADH) for stereoselective reduction and whole cells of a microorganism for enantioselective oxidation operated concurrently to effect the stereoinversion of one enantiomer of a racemic secondary alcohol and provide the optically pure alcohol in >99% yield (see scheme). R,R′ = alkyl.
- Voss, Constance V.,Gruber, Christian C.,Kroutil, Wolfgang
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p. 741 - 745
(2008/12/20)
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- A chiral Mn(III) salen complex immobilized onto ionic liquid modified mesoporous silica for oxidative kinetic resolution of secondary alcohols
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A supported ionic liquid strategy has been applied for the immobilization of a chiral Mn(III) salen complex onto ionic liquid modified mesoporous silica SBA-15. The immobilized catalyst demonstrated high enantioselectivity and activity in the oxidative kinetic resolution of secondary alcohols, and could be recycled five times without obvious loss of activity.
- Sahoo, Suman,Kumar, Pradeep,Lefebvre,Halligudi
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p. 4865 - 4868
(2008/09/21)
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- One-pot enzymatic resolution and separation of sec-alcohols based on ionic acylating agents
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(Figure Presented) Going their different ways: A simple, robust, efficient, and reusable system for the one-pot preparative resolution and separation of sec-alcohols is described. The system is based on the combination of sequential enzymatic kinetic resolution (lipase B from Candida Antarctica, CALB) and transesterification in ionic liquids (ILs) with an ionic acylating agent 1 and removal of each enantiomer by extraction with an organic solvent.
- Lourenco, Nuno M. T.,Afonso, Carlos A. M.
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p. 8178 - 8181
(2008/09/18)
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- A biocatalytic one-pot oxidation/reduction sequence for the deracemisation of a sec-alcohol
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Biocatalytic deracemisation via inversion of rac-2-decanol was accomplished by a combined oxidation/reduction sequence using the same 'single' catalyst for both steps. Overall, the (R)-alcohol was inverted to the corresponding (S)-alcohol. Lyophilised cells of various Rhodococci spp. were tested for the unselective oxidation of the racemic sec-alcohol using acetone as the hydrogen acceptor in the first step. For the second step, the stereoselective asymmetric reduction of the corresponding ketone, 2-propanol was employed as the hydrogen donor. Employing lyophilised cells of Rhodococcus sp. CBS 717.73 racemic 2-decanol was transformed to (S)-2-decanol with excellent enantiomeric excess (92% ee) and yield (82% isolated yield) in the combined one-pot oxidation/reduction sequence.
- Voss, Constance V.,Gruber, Christian C.,Kroutil, Wolfgang
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p. 276 - 281
(2007/10/03)
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- Highly enantioselective reduction of ketones by chiral diol-modified lithium aluminum hydride reagents
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Some readily available chiral diols from indene and d-mannitol were investigated as chiral modifiers in lithium aluminum hydride reduction of ketones, and it was discovered that further modification of these reducing reagents by a simple a-amino alcohol resulted in a remarkable increase in optical yield. Among the investigated chiral modifiers, chiral diol 1 gave the highest enantioselectivities.
- Ren, Yunlai,Tian, Xinzhe,Sun, Kunpeng,Xu, Jian,Xu, Xianlun,Lu, Shijie
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p. 463 - 465
(2007/10/03)
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- Enantioselective reduction of aromatic and aliphatic ketones catalyzed by ruthenium complexes attached to β-cyclodextrin
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Water-soluble chiral Ru complexes with a β-cyclodextrin unit have been shown to catalyze the reduction of aliphatic ketones (see scheme) with up to 97% ee and in good to excellent yields in the presence of sodium formate. The β-cyclodextrin unit is an essential component of the catalyst. It contributes to the unprecedented levels of enantioselectivity observed through the preorganization of the substrates in the hydrophobic cavity.
- Schlatter, Alain,Kundu, Mrinal K.,Woggon, Wolf-D.
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p. 6731 - 6734
(2007/10/03)
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- Preparative asymmetric reduction of ketones in a biphasic medium with an (S)-alcohol dehydrogenase under in situ-cofactor-recycling with a formate dehydrogenase
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The substrate range of a novel recombinant (S)-alcohol dehydrogenase from Rhodococcus erythropolis is described. In addition, an enzyme-compatible biphasic reaction medium for the asymmetric biocatalytic reduction of ketones with in situ-cofactor regeneration has been developed. Thus, reductions of poorly water soluble ketones in the presence of the alcohol dehydrogenase from R. erythropolis and a formate dehydrogenase from Candida boidinii can be carried out at higher substrate concentrations of 10-200 mM. The resulting (S)-alcohols were formed with moderate to good conversion rates, and with up to >99% ee.
- Gr?ger, Harald,Hummel, Werner,Rollmann, Claudia,Chamouleau, Francoise,Hüsken, Hendrik,Werner, Helge,Wunderlich, Christine,Abokitse, Kofi,Drauz, Karlheinz,Buchholz, Stefan
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p. 633 - 640
(2007/10/03)
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- Biocatalytic asymmetric hydrogen transfer employing Rhodococcus ruber DSM 44541
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Nonracemic sec-alcohols of opposite absolute configuration were obtained either by asymmetric reduction of the corresponding ketone using 2-propanol as hydrogen donor or by enantioselective oxidation through kinetic resolution of the rac-alcohol using acetone as hydrogen acceptor employing whole lyophilized cells of Rhodococcus ruber DSM 44541. The microbial oxidation/reduction system exhibits not only excellent stereo- and enantioselectivity but also a broad substrate spectrum. Due to the exceptional tolerance of the biocatalyst toward elevated concentrations of organic materials (solvents, substrates and cosubstrates), the process is highly efficient. The simple preparation of the biocatalyst and its ease of handling turns this system into a versatile tool for organic synthesis.
- Stampfer, Wolfgang,Kosjek, Birgit,Faber, Kurt,Kroutil, Wolfgang
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p. 402 - 406
(2007/10/03)
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- Asymmetric reduction of ketones by Geotrichum candidum in the presence of Amberlite Xad, A solid organic solvent
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Asymmetric reduction of ketones by Geotrichum candidum in the presence of Amberlite XAD, a solid organic solvent, was described. A hydrophobic polymer, XAD, was used as material to control the stereochemical course of microbial reductions. Aliphatic and aromatic ketones were reduced to the corresponding (S)-alcohols in excellent enantiomeric excess (ee) in the presence of XRD while low enantioselectivities were observed in the absence of the polymer.
- Nakamura, Kaoru,Fujii, Mikio,Ida, Yoshiteru
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p. 3205 - 3211
(2007/10/03)
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- Two Classes of Enzymes of Opposite Stereochemistry in an Organism: One for Fluorinated and Another for Nonfluorinated Substrates
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Reduction of methyl ketones by dried cells of Geotrichum candidum (APG4) afforded (S)-alcohols in excellent enantiomeric excess (ee), whereas the reduction of trifluoromethyl ketones gave the corresponding alcohols of the opposite configuration also in excellent ee. The replacement of the methyl moiety with a trifluoromethyl group alters both the bulkiness and the electronic properties, the effect of which on the stereoselectivity was examined. No inversion in stereochemistry was observed in the reduction of hindered ketones such as isopropyl ketone, while the stereoselectivity was inverted in the reduction of ketones with electron-withdrawing atoms such as chlorine. The mechanism for the inversion in stereochemistry was investigated by enzymatic studies. Several enzymes with different stereoselectivities were isolated; one of them catalyzed the reduction of methyl ketones, and another with the opposite stereoselectivity catalyzed the reduction of trifluoromethyl ketones. Furthermore, both APG4 and the isolated enzyme were applied to the reduction of fluorinated ketones on a preparative scale, which resulted in the synthesis of chiral fluorinated alcohols with excellent ee.
- Matsuda, Tomoko,Harada, Tadao,Nakajima, Nobuyoshi,Itoh, Toshiyuki,Nakamura, Kaoru
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p. 157 - 163
(2007/10/03)
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- Asymmetric reduction of ketones by the acetone powder of Geotrichum candidum
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Aromatic ketones, β-keto esters, and simple aliphatic ketones were reduced with excellent selectivity to the corresponding (S)-alcohols by using the acetone powder of Geotrichum candidum. This method is superior in reactivity and stereoselectivity to reduction by the whole-cell. The experimental conditions for the reduction system such as ratio of the biocatalyst to the substrate, kinds of coenzymes, alcohol for coenzyme regeneration, and buffer, pH, and reaction temperature were investigated, and stability and preservability of the biocatalyst were also examined. This method is very convenient for the synthesis of optically pure alcohols on a gram scale.
- Nakamura,Matsuda
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p. 8957 - 8964
(2007/10/03)
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- Optical resolution for producing optically active alcohol
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A process for producing an optically active alcohol comprising carrying out interesterification between a racemic alcohol and an ester selected from the group consisting of (a) a diester between a lower monohydric alcohol and a saturated dicarboxylic acid having 14 or more carbon atoms, (b) a triglyceride of a saturated fatty acid having 16 or more carbon atoms, and (c) a monoester between a lower monohydric alcohol and a saturated fatty acid having 18 or more carbon atoms in the presence of lipase, preferably heat-resistant lipase, and in the presence or absence of a solvent, preferably in the absence of a solvent, under a substantially water-free condition, separating an optically active alcohol rich in either one of R- and S-forms from the reaction mixture, and adding an optically inactive non-racemic alcohol to the residue of the previous step to carry out interesterification under the same conditions as in the previous reaction to separate the other enantiomer. According to the present invention a racemic alcohol can easily be resolved into each enantiomer with high purity in good yield.
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- Highly enantioselective synthesis of long chain alkyl trifluoromethyl carbinols and β-thiotrifluoromethyl carbinols through lipases
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Among a variety of lipases tested, Candida antarctica lipase has been found to promote the enantioselective acylation of long chain alkyl trifluoromethyl carbinols 1a-4a and β-thiotrifluoromethyl carbinols 5a-7a, producing both R and S enantiomeric alcohols in good to excellent chemical yield and enantioselectivity. In all cases the lipase preferentially acylates the S enantiomer, irrespective the presence or not of a sulfur atom in β position to the hydroxyl group. When the reaction was carried out on the non-fluorinated substrates 1c-2c, the process occurred much faster and with higher e.e. of the less reacting enantiomer than when conducted on the fluorinated substrates.
- Petschen, Ines,Malo, Edi A.,Bosch,Guerrero, Angel
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p. 2135 - 2143
(2007/10/03)
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- Different stereochemistry for the reduction of trifluoromethyl ketones and methyl ketones catalyzed by alcohol dehydrogenase from Geotrichum
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Reduction of trifluoromethyl ketones by a crude alcohol dehydrogenase from Geotrichum affords (S)-trifluoromethyl carbinols in excellent ee, whereas the reduction of methyl ketones gives the corresponding alcohols of the opposite configuration in excellent ee.
- Nakamura, Kaoru,Matsuda, Tomoko,Itoh, Toshiyuki,Ohno, Atsuyoshi
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p. 5727 - 5730
(2007/10/03)
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- The asymmetric solvomercuration-demercuration of olefins in chiral micellar systems
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The solvomercuration-demercuration of olefins in chiral micelles were investigated. The chiral carbinols can be obtained by asymmetric oxymercuration of prochiral olefins with NaBH4. A satisfactory result was achieved. The highest e.e.% was up to 96%.
- Zhang,Bao,Dong
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p. 3029 - 3035
(2007/10/02)
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- Chiral N,N-Dialkylnorephedrines as Catalysts of the Highly Enantioselective Addition of Dialkylzincs to Aliphatic and Aromatic Aldehydes. The Asymmetric Synthesis of Secondary Aliphatic and Aromatic Alcohols of High Optical Purity
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The chiral N,N-dialkylnorephedrine-catalyzed addition of dialkylzincs to aliphatic and aromatic aldehydes afforded secondary alcohols of high optical purity (to > 95percent ee).Among the N,N-di(primary alkyl)norephedrines, N,N-di-n-butylnorephedrine (DBNE, 3d) was found to be the most effective catalyst. 1-Phenyl-2-(1-pyrrolidinyl)propan-1-ol (3i) and N,N-diallylnorephedrine (3j) were also highly effective catalysts.The method described provides optically active secondary aliphatic alcohols of high optical purity which cannot be prepared by conventional methods.
- Soai, Kenso,Yokoyama, Shuji,Hayasaka, Tomoiki
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p. 4264 - 4268
(2007/10/02)
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- ENANTIOFACE-DIFFERENTIATING HYDROGENATION OF 2-ALKANONES OVER MODIFIED RANEY NICKEL
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2-Octanone was hydrogenated over tartaric acid-NaBr-modified Raney nickel in the presence of pivalic acid at various temperatures.The hydrogenation at 50 60 deg C gave the best result with regard to the optical yield.Almost 80 percent of the optical yields were attained in the hydrogenations of various 2-alkanones.
- Osawa, Tsutomu
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p. 1609 - 1612
(2007/10/02)
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- ASYMMETRIC SYNTHESIS via CHIRAL ACETAL TEMPLATES. 8. REACTIONS WITH ORGANOMETALLIC REAGENTS
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The titanium tetrachloride catalyzed coupling of organometallic reagents with chiral acetals 1 is shown to provide a convenient route for the preparation of a variety of chiral alcohols 4 of high optical purity.
- Lindell, Stephen D.,Elliott, John D.,Johnson, William S.
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p. 3947 - 3950
(2007/10/02)
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