- Retention of Configuration in Oxidation of a Chiral Boronic Acid by the Flavoenzyme Cyclohexanone Oxygenase
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The first study of flavoenzyme oxygenation of chiral boronic acids has been carried out and found to occur with retention of configuration at the migrating carbon centre; this is analogous to the migration found in peroxide-mediated oxidations.
- Latham, John A.,Walsh, Christopher
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Read Online
- (+)- and (-)-myrtanylborane. Solid and Stable Monoalkylboranes for Asymmetric Hydroboration
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Both (+)- and (-)-myrtenyldithiane were independently prepared from commercially available chiral precursors and were easily, and in one step, converted by means of borane complexes into solid and stable chiral monoalkylboranes: (+)- and (-)-2-(1,3-dithianyl)myrtanylborane (MDBH2).These new chiral reagents, when tested on representative classes of olefins, present a reactivity profile similar to IpcBH2: they achieve the asymmetric hydroboration of trisubstituted double bonds with high asymmetric induction.Reduction of asymmetric prochiral ketones with MDBH2 achieves high diastereoselectivity but low enantioselectivity.The likely intramolecular stabilization of MDBH2 not only accounts for the easy access to monoalkylboranes but also for its remarkable physical properties, whereas its efficiency in asymmetric hydroboration is at the same level as that of similar reagents.
- Richter, Renaud Kiesgen de,Bonato, Marc,Follet, Michel,Kamenka, Jean-Marc
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Read Online
- A crystalline, internally-coordinated chloroborane for asymmetric hydroboration
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Asymmetric hydroboration is an important method in the preparation of enantiomerically-enriched compounds that are necessary in many areas of chemistry. Here is reported the preparation of a unique chiral chloroborane-internal ether complex and its applic
- Garner, Charles M.,Jones, Andrew J.,Savage, Quentin R.,Wood, John L.,von Dollen, Breanna
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supporting information
(2022/02/01)
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- Direct Asymmetric Hydrogenation and Dynamic Kinetic Resolution of Aryl Ketones Catalyzed by an Iridium-NHC Exhibiting High Enantio- and Diastereoselectivity
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A chiral iridium carbene-oxazoline catalyst is reported that is able to directly and efficiently hydrogenate a wide variety of ketones in excellent yields and good enantioselectivity (up to 93 % ee). Moreover, when using racemic α-substituted ketones, excellent diastereoselectivities were obtained (dr 99:1) by dynamic kinetic resolution of the in situ formed enolate. Overall, the herein described hydrogenation occurs under ambient conditions using low hydrogen pressures, providing a direct and atom efficient method towards chiral secondary alcohols.
- Ayya Swamy P, Chinna,Varenikov, Andrii,de Ruiter, Graham
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supporting information
p. 2333 - 2337
(2020/02/11)
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- Asymmetric Induction via a Helically Chiral Anion: Enantioselective Pentacarboxycyclopentadiene Br?nsted Acid-Catalyzed Inverse-Electron-Demand Diels-Alder Cycloaddition of Oxocarbenium Ions
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An enantioselective catalytic inverse-electron-demand Diels-Alder reaction of salicylaldehyde acetal-derived oxocarbenium ions and vinyl ethers to generate 2,4-dioxychromanes is described. Chiral pentacarboxycyclopentadiene (PCCP) acids are found to be effective for a variety of substrates. Computational and X-ray crystallographic analyses support the unique hypothesis that an anion with point-chirality-induced helical chirality dictates the absolute sense of stereochemistry in this reaction.
- Gheewala, Chirag D.,Hirschi, Jennifer S.,Lee, Wai-Hang,Paley, Daniel W.,Vetticatt, Mathew J.,Lambert, Tristan H.
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supporting information
p. 3523 - 3527
(2018/03/21)
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- Catalytic carbonyl hydrosilylations: Via a titanocene borohydride-PMHS reagent system
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Reduction of a wide range of aldehydes and ketones with catalytic amounts of titanocene borohydride in concert with a stoichiometric poly(methylhydrosiloxane) (PMHS) reductant is reported. Preliminary mechanistic studies demonstrate that the reaction is mediated by a reactive titanocene(iii) complex, whose oxidation state remains constant throughout the reaction.
- Fianu, Godfred D.,Schipper, Kyle C.,Flowers, Robert A.
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p. 3469 - 3473
(2017/08/21)
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- Diastereoselective and Enantioselective Silylation of 2-Arylcyclohexanols
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The silylation-based kinetic resolution of trans 2-arylcyclohexanols was accomplished by employing a triaryl silyl chloride as the derivatizing reagent with a commercially available isothiourea catalyst. The methodology is selective for the trans diastereomer over the cis, which provides an opportunity to selectively derivatize one stereoisomer out of a mixture of four. By employing this technology, a facile, convenient method to form a highly enantiomerically enriched silylated alcohol was accomplished through a one-pot reduction-silylation sequence that started with a 2-aryl-substituted ketone.
- Wang, Li,Akhani, Ravish K.,Wiskur, Sheryl L.
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supporting information
p. 2408 - 2411
(2015/05/27)
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- P-Tolylimido rhenium(v) complexes with phenolate-based ligands: Synthesis, X-ray studies and catalytic activity in oxidation with tert-butylhydroperoxide
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The reactions of mer-[Re(p-NTol)X3(PPh3)2] (X = Cl, Br) with chelating phenolate-based ligands (2-(2-hydroxy-5-methylphenyl)benzotriazole (HL1), 2-(2-hydroxyphenyl)benzothiazole (HL2) or 2-(2-hydroxyphenyl)benzoxazole (HL3)) afforded a series of p-tolylimido rhenium(v) complexes cis- or trans-(X,X)-[Re(p-NTol)X2(L)(PPh3)]·yMeCN (where X = Cl, Br; L = L1, L2, L3 and y = 0-2) and [Re(p-NTol)X(L)(PPh3)2]Z·pPPh3 (where X = Cl, Br; Z = ReO4, PF6; L = L1, L2, L3 and p = 0 or 1). The reported compounds were characterized by elemental analysis, FT-IR, NMR (1H, 13C and 31P) and X-ray crystallography. Interestingly, the halide ions of [Re(p-NTol)Cl2(L1)(PPh3)]·MeCN (1) and [Re(p-NTol)Cl2(L2)(PPh3)]·2MeCN (3) are in cis relative dispositions, whereas the complexes [Re(p-NTol)Br2(L)(PPh3)] (L1 for 2, L2 for 4 and L3 for 6) and [Re(p-NTol)Cl2(L3)(PPh3)] (5) were found to be trans-(X,X) isomers. The compounds [Re(p-NTol)X(L)(PPh3)2](PF6) (X = Cl, Br; L = L1 and L2) and [Re(p-NTol)X(L3)(PPh3)2](PF6)·PPh3 (X = Cl, Br) have been tested in oxidative catalysis. A few compounds exhibited very good catalytic properties in oxidation of alcohols with tert-BuOOH (TBHP) in acetonitrile solution at moderate temperatures. Complex [Re(p-NTol)Cl(L2)(PPh3)2]PF6 (13) is the catalyst of choice for oxidation of 1-phenylethanol to acetophenone (in 80% yield; turnover number attained 290 after 30 h) and cyclooctanol to cyclooctanone (in 88% yield). Notably lower activity has been found in the oxidation of alkanes with TBHP. Product distribution in the oxidation of methylcyclohexane indicates some steric hindrance around the reaction center.
- Gryca, Izabela,Machura, Barbara,Malecki, Jan Grzegorz,Kusz, Joachim,Shul'Pina, Lidia S.,Ikonnikov, Nikolay S.,Shul'Pin, Georgiy B.
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p. 334 - 351
(2015/12/26)
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- Cytochrome P450 catalyzed oxidative hydroxylation of achiral organic compounds with simultaneous creation of two chirality centers in a single C-H activation step
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Regio- and stereoselective oxidative hydroxylation of achiral or chiral organic compounds mediated by synthetic reagents, catalysts, or enzymes generally leads to the formation of one new chiral center that appears in the respective enantiomeric or diastereomeric alcohols. By contrast, when subjecting appropriate achiral compounds to this type of C-H activation, the simultaneous creation of two chiral centers with a defined relative and absolute configuration may result, provided that control of the regio-, diastereo-, and enantioselectivity is ensured. The present study demonstrates that such control is possible by using wild type or mutant forms of the monooxygenase cytochrome P450 BM3 as catalysts in the oxidative hydroxylation of methylcyclohexane and seven other monosubstituted cyclohexane derivatives.
- Roiban, Gheorghe-Doru,Agudo, Ruben,Reetz, Manfred T.
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supporting information
p. 8659 - 8663
(2014/08/18)
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- New p-tolylimido rhenium(v) complexes with carboxylate-based ligands: Synthesis, structures and their catalytic potential in oxidations with peroxides
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Novel p-tolylimido rhenium(v) complexes trans-(Cl,Cl)-[Re(p-NC 6H4CH3)Cl2(pyz-2-COO)(PPh 3)]·MeCN (1), trans-(Cl,Cl)-[Re(p-NC6H 4CH3)Cl2(pyz-2-COO)(PPh
- Gryca,MacHura,Malecki,Shul'Pina, Lidia S.,Pombeiro, Armando J. L.,Shul'Pin, Georgiy B.
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p. 5759 - 5776
(2014/04/03)
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- Tetrahydroxynaphthalene reductase: Catalytic properties of an enzyme involved in reductive asymmetric naphthol dearomatization
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In reduced circumstances: Tetrahydroxynaphthalene reductase shows a broad substrate range including alternate phenolic compounds and cyclic ketones. Structural modeling reveals major enzyme-substrate interactions; C-terminal truncation of the enzyme causes an altered substrate preference, in accordance with stabilization of the substrate by the C-terminal carboxylate (see picture). This effect allows the identification of a homologous enzyme. Copyright
- Schaetzle, Michael A.,Flemming, Stephan,Husain, Syed Masood,Richter, Michael,Guenther, Stefan,Mueller, Michael
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supporting information; experimental part
p. 2643 - 2646
(2012/05/04)
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- CYCLIC AMINE-1-CARBOXYLIC ACID ESTER DERIVATIVE AND PHARMACEUTICAL COMPOSITION CONTAINING THE SAME
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Provided is a compound useful as a therapeutic drug for pain and inflammation caused by various pathological conditions such as neuropathic pain and rheumatoid arthritis. The compound of the formula (I) or a salt thereof [wherein R1 is a methyl group or a hydrogen atom, R2 represents a hydrogen atom, an alkyl group, an alkylcarbonyl group or an aryl carbonyl group, A represents a cycloalkyl group, a cycloalkenyl group, an aryl group or a heteroaryl group (each group may be substituted with a substituent selected from the group consisting of alkyl, alkenyl, cycloalkyl and halogen), n and m each represent an integer of 1, 2 or 3, and p represents an integer of 0, 1, 2 or 3].
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- CYCLIC AMINE-1-CARBOXYLIC ACID ESTER DERIVATIVE AND PHARMACEUTICAL COMPOSITION CONTAINING THE SAME
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Provided is a compound useful as a therapeutic drug for pain and inflammation caused by various pathological conditions such as neuropathic pain and rheumatoid arthritis. The compound of the formula (I) or a salt thereof [wherein R1 is a methyl group or a hydrogen atom, R2 represents a hydrogen atom, an alkyl group, an alkylcarbonyl group or an aryl carbonyl group, A represents a cycloalkyl group, a cycloalkenyl group, an aryl group or a heteroaryl group (each group may be substituted with a substituent selected from the group consisting of alkyl, alkenyl, cycloalkyl and halogen), n and m each represent an integer of 1, 2 or 3, and p represents an integer of 0, 1, 2 or 3].
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Page/Page column 25-26
(2011/02/19)
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- Reductions of cyclic β-keto esters by individual Saccharomyces cerevisiae dehydrogenases and a chemo-enzymatic route to (1R,2S)-2-methyl-1-cyclohexanol
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Twenty purified dehydrogenases cloned from bakers' yeast (Saccharomyces cerevisiae) and expressed as fusion proteins with glutathione (S)-transferase were tested for their ability to reduce three homologous cyclic β-keto esters. The majority of dehydrogenases reduced ethyl 2-oxo-cyclopentanecarboxylate, yielding a pair of diastereomeric alcohols with consistent (1R)-stereochemistry. Ethyl 2-oxo-cyclohexanecarboxylate reductions afforded only cis-alcohol enantiomers. Ethyl 2-oxo-cycloheptanecarboxylate was accepted by two enzymes in the collection, and both yielded mainly the cis-(1R,2S)-alcohol. Escherichia coli cells overexpressing the YDL124w gene were used in a dynamic kinetic resolution of ethyl 2-oxo-cyclohexanecarboxylate to produce the key intermediate in a chemo-enzymatic synthesis of (1R,2S)-2-methyl-1-cyclohexanol, an important chiral building block.
- Padhi, Santosh Kumar,Kaluzna, Iwona A.,Buisson, Didier,Azerad, Robert,Stewart, Jon D.
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p. 2133 - 2138
(2008/02/11)
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- Plants-mediated reduction in the synthesis of homochiral secondary alcohols
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The reduction of 5-hexen-2-one 1, 6-methyl-5-hepten-2-one 2, acetophenone 3, cis-bicyclo[3.2.0]hept-2-en-6-one 4 and 2-methylcyclohexanone 5 with various commercially available plants (i.e., Brassica oleracea botrytis, Cucurbita maxima, Cucurbita pepo, Cynara scolimus, Daucus carota, Foeniculum vulgare and Musa sapientum) is reported. In the reduction of ketones 1-3, both (S)- and (R)-enantiomers 6-8 were obtained in good yields and with appreciable enantiomeric excesses. With racemic ketones 4 and 5, both the diastereomeric endo/exo 9 and 10 and cis/trans 11 and 12 are produced with variable yields and enantiomeric excesses depending on the various plants used.
- Bruni, Renato,Fantin, Giancarlo,Maietti, Silvia,Medici, Alessandro,Pedrini, Paola,Sacchetti, Gianni
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p. 2287 - 2291
(2007/10/03)
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- Synthesis of chiral building blocks for use in drug discovery
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In the past decade there has been a significant growth in the sales of pharmaceutical drugs worldwide, but more importantly there has been a dramatic growth in the sales of single enantiomer drugs. The pharmaceutical industry has a rising demand for chiral intermediates and research reagents because of the continuing imperative to improve drug efficacy. This in turn impacts on researchers involved in preclinical discovery work. Besides traditional chiral pool and resolution of racemates as sources of chiral building blocks, many new synthetic methods including a great variety of catalytic reactions have been developed which facilitate the production of complex chiral drug candidates for clinical trials. The most ambitious technique is to synthesise homochiral compounds from non-chiral starting materials using chiral metal catalysts and related chemistry. Examples of the synthesis of chiral building blocks from achiral materials utilizing asymmetric hydrogenation and asymmetric epoxidation are presented.
- Marino, Sharon T.,Stachurska-Buczek, Danuta,Huggins, Daniel A.,Krywult, Beata M.,Sheehan, Craig S.,Nguyen, Thao,Choi, Neil,Parsons, Jack G.,Griffiths, Peter G.,James, Ian W.,Bray, Andrew M.,White, Jonathan M.,Boyce, Rustum S.
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p. 405 - 426
(2007/10/03)
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- Asymmetric reduction of enones with Synechococcus sp. PCC 7942
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Synechococcus sp. PCC 7942, a cyanobacterium, reduced both the endocyclic C-C double bond of s-trans enones and the exocyclic C-C double bond of s-cis enones with high enantioselectivity to afford the corresponding (S)-ketones under illumination.
- Shimoda, Kei,Kubota, Naoji,Hamada, Hiroki,Kaji, Misato,Hirata, Toshifumi
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p. 1677 - 1679
(2007/10/03)
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- Asymmetric transformation of enones with Synechococcus sp. PCC 7942
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Asymmetric transformation of enones was investigated with cultured cells of Synechococcus sp. PCC 7942 (a cyanobacterium). The cells reduced both the endocyclic C-C double bond of s-trans enones and the exocyclic C-C double bond of s-cis enones with high enantioselectivity to afford optically active α-substituted (S)-ketones under illumination. In addition, the reduction of the double bond of these enones was accompanied by the formation of saturated alcohols. The cells preferentially reduced simple aliphatic ketones rather than cyclic ones to the corresponding (S)-alcohols with excellent enantioselectivity.
- Shimoda, Kei,Kubota, Naoji,Hamada, Hiroki,Yamane, Shin-Ya,Hirata, Toshifumi
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p. 2269 - 2272
(2007/10/03)
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- Plants in organic synthesis: An alternative to baker's yeast
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The reduction of acetophenone 1 and the hydrolysis of 1-acetoxy-2-methylcyclohexene 3 with various commercially available plants to the corresponding S-carbinol 2 and S-ketone 4 are described. The further incubation of 2-methylcyclohexanone 4 with some pl
- Bruni, Renato,Fantin, Giancarlo,Medici, Alessandro,Pedrini, Paola,Sacchetti, Gianni
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p. 3377 - 3379
(2007/10/03)
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- Enantioselective hydrolyses with Yarrowia lipolytica: A versatile strain for esters, enol esters, epoxides, and lactones
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Racemic secondary esters 1-3, γ-lactones 8-9, and styrene oxide 7 are kinetically resolved via hydrolysis with Yarrowia lipolytica YL2 strain. The enantioselective hydrolysis of prochiral enol esters 4-6 to the corresponding homochiral carbonyl compounds 13-15 is also described. Subsequent reduction of the ketone 13 and of the aldehyde 15 can be avoided using lyophilised cells.
- Fantin, Giancarlo,Fogagnolo, Marco,Guerrini, Alessandra,Medici, Alessandro,Pedrini, Paola,Fontana, Silvia
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p. 2709 - 2713
(2007/10/03)
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- Kinetic resolution of racemic secondary alcohols via oxidation with Yarrowia lipolytica strains
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Cyclic and alicyclic racemic secondary alcohols are kinetically resolved via oxidation with Yarrowia lipolytica strains. The comparison of the oxidation reactions with the reductions of the corresponding ketones supports the hypothesis of the presence of
- Fantin, Giancarlo,Fogagnolo, Marco,Medici, Alessandro,Pedrini, Paola,Fontana, Silvia
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p. 2367 - 2373
(2007/10/03)
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- A safe, scaleable method for the oxidation of carbon-boron bonds with Oxone
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A new procedure for the oxidation of carbon-boron bonds to the corresponding alcohol with Oxone is described. (C) 2000 Elsevier Science Ltd.
- Ripin, David H. Brown,Cai, Weiling,Brenek, Steven J.
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p. 5817 - 5819
(2007/10/03)
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- Asymmetric reduction of α,β-unsaturated cyclic ketones by a yeast
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The asymmetric reduction of the carbon-carbon double bond of α,β-unsaturated cyclic compounds proceeds with high enantioselectivity when catalyzed by Yamadazyma farinosa IFO 10896. Microbial reduction of 2-methyl-2-cyclohexen-1-one followed by PCC oxidati
- Matsumoto, Kazutsugu,Kawabata, Yoichi,Takahashi, Jun,Fujita, Yoshitomo,Hatanaka, Minoru
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p. 283 - 284
(2007/10/03)
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- Optical Analysis of Reduction Products of 2-Methylcyclohexanone by Aspergillus repens MA0197
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The products of reduction of 2-methylcyclohexanone by Aspergillus repens MA0197 were analyzed quantitatively by GC after conversion to corresponding diastereoisomeric (-)-menthyl carbonate derivatives. Although the contents varied considerably with time, the predominant production of S-alcohol was observed, that is, Prelog's rule was obeyed.
- Onishi, Hironobu,Doi, Mikiharu,Shuto, Yoshihiro,Kinoshita, Yoshiro
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p. 486 - 487
(2007/10/03)
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- Chiral catalyst controlled diastereoselection and regioselection in intramolecular carbon-hydrogen insertion reactions of diazoacetates
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Individual enantiomers of substituted cyclohexyl diazoacetates or 2-octyl diazoacetates matched with a configurationally suitable chiral dirhodium(II) carboxamidate catalyst provide an effective methodology for the synthesis of lactones with exceptional diastereo- and regiocontrol. Enantiomerically pure (1S,2R)-cis-2-methylcyclohexyl diazoacetate forms the all-cis-(1R,5R,9R)-9-methyl-2-oxabicyclo[4.3.0]nonan-3-one with complete diastereocontrol in reactions catalyzed by dirhodium(II) tetrakis[methyl 1-(3-phenylpropanoyl)-2-oxoimidazolidine-4(R)carboxylate], Rh2(4(S)-MPPIM)4, but the configurational mismatch results in a mixture of products. The same diazoacetate produces (1S,5R)-5-methyl-2-oxabicyclo[4.3.0]nonan-3-one with virtually complete selectivity by catalysis with dirhodium(II) tetrakis[methyl 2-oxopyrrolidine-5(S)-carboxylate], Rh2(5(S)-MEPY)4. Similarly high stereo- and regiocontrol is also achieved with enantiomerically pure trans-2-methylcyclohexyl diazoacetates. Product control from insertion reactions of d- or l-menthyl diazoacetate and (+)-neomenthyl diazoacetate from the configurational match with dirhodium(II) catalyst results in the formation of one C-H insertion product in high yield. The exceedingly high product diastereoselection observed in these reactions is consistent with virtually exclusive insertion into equatorial C-H bonds. The catalyst-dependent selective formation of a cis-disubstituted γ-butyrolactone or a β-lactone from 2-octyl diazoacetate has been achieved. Control of product diastereoselectivity and regioselectivity in C-H insertion reactions is explained by conformational suitability in configurational match/mismatch of catalyst and carbene.
- Doyle, Michael P.,Kalinin, Alexey V.,Ene, Doina G.
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p. 8837 - 8846
(2007/10/03)
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- Hydroboration. 92. Investigation of Practical Methods for the Synthesis of Optically Pure Isopinocampheylchloroborane for the Asymmetric Hydroboration of Representative Prochiral Alkenes
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A quantitative study was made of the preparation of the optically pure borane reagent, isopinocampheylchloroborane (IpcBHCl), potentially valuable for asymmetric hydroboration.IpcBHCl (87-90percent) in equilibrium with 5-6.5percent of IpcBCl2 and IpcBH2, respectively, can be prepared conveniently by a number of relatively simple operations: (1) the reaction of isopinocampheylborane (IcpBH2) with anhydrous hydrochloric acid (HCl) in ethyl ether (EE); (2) the reaction of stoichiometric amounts of IpcBH2 with isopinocampheyldichloroborane (IpcBCl2) in EE; and (3) the reduction of IpcBCl2 with trimethylsilane (Me3SiH) or lithium aluminum hydride (LAH) in EE.The reduction of IpcBCl2 with Me3SiH in pentane proceeds extremely slowly to provide the desired reagent, IpcBHCl.However, in EE, the reduction proceeds much faster, providing an equilibrium mixture of 90percent IpcBHCl, 5percent IpcBH2, and 5percent IpcBCl2.We also investigated the reduction of IpcBCl2 with Me3SiH in pentane and dichloromethane (CH2CL2) in the presence of known amounts of EE, tetrahydrofuran (THF), and dimethyl sulfide (SMe2), solvents which coordinate with the dichloroboranes.A comparative study of the rate of hydroboration of the alkene, 2-methyl-2-butene, with IpcBH2 and IpcBHCl, obtained as described above, was made in representative solvents, such as pentane, CH2Cl2, EE, and THF, at 0 deg C and, in many cases, also at 25 deg C.This study revealed that the rate of hydroboration is faster in THF for IpcBH2, while for IpcBHCl, the rate is faster in EE.Asymmetric hydroboration of prochiral alkenes was achieved by two methods, viz., IpcBHCl, produced by the reaction of IpcBH2 with HCl in EE (method A), and the reduction-hydroboration reaction of IpcBCl2 with LAH (0.25 equiv) in the presence of the prochiral alkene (method B) in EE.In both methods, the temperature of the reaction mixture was maintained at -25 deg C.Almost identical results were realized in these two procedures, with the enantiomeric excess (ee) realized with IpcBHCl, in some cases, considerably better than that achieved with IpcBH2.Although, IpcBHCl was obtained in onyl 87090percent purity along with IpcBH2 and IpcBCl2 as side products, the presence of the latter compound had no observable effect on the chiral outcome of the asymmetric hydroboration.
- Dhokte, Ulhas P.,Kulkarni, Shekhar V.,Brown, Herbert C.
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p. 5140 - 5148
(2007/10/03)
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- Lipase-catalyzed enantioselective acylation of alcohols: A predictive active site model for lipase YS to identify which enantiomer of an alcohol reacts faster in this acylation
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Primary alcohols having a hydroxymethyl group at an S sterogemic center and secondary alcohols with an R configuration are preferentially acylated to give the corresponding acetates by lipase YS (from Pseudomonas fluorescens)-catalyzed acylation using isopropenyl acetate as the acylating agent in diisopropyl ether. On the basis of enantiomer selectivities observed, a predictive active site model for lipase YS is proposed for identifying which enantiomer of a primary or a secondary alcohol reacts faster in this acylation.
- Naemura,Fukuda,Murata,Konishi,Hirose,Tobe
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p. 2385 - 2394
(2007/10/03)
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- Lipase YS-catalysed Acylation of Alcohols: a Predictive Active Site Model for Lipase YS to Identify which Enantiomer of a Primary or a Secondary Alcohol Reacts Faster in this Acylation
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Primary alcohols having a hydroxymethyl group at an S chiral centre and secondary alcohols with an R configuration are preferentially acylated to give the corresponding acetates by lipase YS-catalysed acylation in diisopropyl ether; a predictive cubic-spaced active site model for lipase YS is proposed for identifying which enantiomer of a primary or a secondary alcohol reacts faster in this acylation.
- Naemura, Koichiro,Fukuda, Ritsuko,Konishi, Masayoshi,Hirose, Keiji,Tobe, Yoshito
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p. 1253 - 1256
(2007/10/02)
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- Enantioselective Hydrolysis of 2-Methylcyclohexanyl Acetates with the Cultured Cells of Marchantia polymorpha
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Enantioselectivity in the hydrolysis of trans- and cis-2-methylcyclohexanyl acetates with the cultured cells of Marchantia polymorpha was investigated.The cultured cells were found to hydrolyze preferentially the acetates having the R-configuration.
- Hirata, Toshifumi,Izumi, Shunsuke,Akita, Kenji,Yoshida, Hiroaki,Gotoh, Shisei
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p. 1465 - 1466
(2007/10/02)
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- Enantioselectivity of some lipases, control and prediction
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Different strategies for the resolution of racemates in lipase catalyzed hydrolyses, esterifications, and transesterifications are presented.The importance of the equilibrium conversion for the optimization of the enantiomeric excess is emphasized.Investigations have been carried out on esters of 1-phenylethanol and 2-methylalkanoic acids.Results are presented, which provide general information about important parameters for the enhancement of the enantiomeric excess and the reaction rates.The application of a "matched strategy" stereochemical control for increasingthe enantiomeric excess is presented, i.e. the use of a chiral acid for the resolution of chiral alcohols.Molecular modelling of lipase from Rhizomucor miehei as well as the use of a simple active site model of lipase from Candida cylindracea to obtain information for the prediction and modification of enzyme specificity is presented.
- Hult, Karl,Norin, Torbjoern
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p. 123 - 126
(2007/10/02)
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- Stereoselectivity in hydrosilylative reduction of substituted cyclohexanone derivatives with chiral rhodium-bis(oxazolinyl)pyridine catalyst
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Stereoselectivity in the reduction of substituted cyclohexanones, 4-tert-butylcyclohexanone, 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-methoxycarbonyl-methylcyclohexanone, was examined with chiral rhodium-bis(oxazolinyl)pyridine catalyst and diphenylsilane. 4-tert-Butylcyclohexanone gave the corresponding trans(equatorial)-alcohol predominantly; the ratio of the trans/cis alcohols, 67:33. Other 2-substituted cyclohexanones showed exclusive enantioselectivities for each diastereomer in terms of the kinetic resolution; e.g. from 2-phenylcyclohexanone, 99% ee of (1S,2R)-trans-2-phenylcyclohexanol and 96% ee of (1S,2S)-cis-2-phenylcyclohexanol in 92% yield (the trans/cis ratio = 51:49).
- Nishiyama,Park,Itoh
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p. 1029 - 1034
(2007/10/02)
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- Asymmetric Reductions of Prochiral Ketones with B-3-Pinanyl-9-borabicyclononane (Alpine-Borane) at Elevated Pressures
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The reduction of unhindered ketones, such as acetylenic ketones, with B-3-pinanyl-9-borabicyclononane (Alpine-Borane, prepared by hydroboration of α-pinene with 9-BBN) provides a simple means of forming chiral, nonracemic alcohols of known absolute configuration in high enantiomeric purity.A dehydroboration-reduction mechanism leading to racemic alcohol is believed to be responsible for erosion of the enantiomeric efficiency with more hindered ketones.The use of elevated pressures (2000-6000 atm) accelerates the asymmetric reduction mode while suppressing the undesired dehydroboration mode.The use of high pressure permits a studyof the scope and utility of Alpine-Borane in the absence of the competing side reaction.The reduction of ketones containing chiral centers was studied with use of the reagent from (+)-α-pinene. d-Carvone is reduced while l-carvone is not.Methyl-substituted cyclohexanones show no discrimination between enantiomers.For example, 2-methylcyclohexanone is reduced to a 1:1 mixture of cis- and trans-2-methylcyclohexanol, each of which is about 65 percent ee.In all cases, one may predict the absolute configuration of the product based on a simple model.The relative steric requirements of groups on the ketone may be catagorized as very small (CCH, CN, H, D); small (CH3, CO2CH3); medium (n-alkyl, trans-RHC=CH); medium large (CF3, i-Pr); large (Ar); and too large (tert-butyl).Effective asymmetric reductions are achieved when groups from nonadjacent catagories are attached to the carbonyl.
- Midland, M. Mark,McLoughlin, Jim I.,Gabriel, Josef
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p. 159 - 165
(2007/10/02)
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- Hydroboration. 83. Synthesis and Hydroboration of 2-Ethylapopinene. Comparison of Monoisopinocampheylborane and Its 2-Ethyl Analogue for the Chiral Hydroboration of Representative Alkenes
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Reduction of nopol tosylate gives the new chiral ligand (-)-2-ethylapopinene (90.2percent ee) with higher steric requirements than those of α-pinene.Reaction of borane with (-)-2-ethylapopinene in THF at 0 deg C, in a molar ratio of 1:2, provides an equilibrium mixture of mono- and dialkylboranes EapBH2 and Eap2BH.With an excess of (-)-2-ethylapopinene (1:10; BMS/2-ethylapopinene), the formation of bis(2-ethylapoisopinocampheyl)borane, Eap2BH, is essentially quantitative (ca. 98percent).Treatment of the equilibrium mixture of boranes (Eap2BH, EapBH2) with TMED at 34 deg C precipitates crystalline (EapBH2)2*TMED.Treatment of the crystalline product with BF3*OEt2 gives EapBH2 (mono(2-ethylapoisopinocampheyl)borane) of essentially 100percent ee, enantiomerically purer than the (-)-2-ethylapopinene (ca. 90percent ee) utilized for the preparation.Hydroboration of a series of olefins with EapBH2, followed by oxidation of the intermediate organoborane, produces the corresponding alcohols with significantly improved enantiomeric purities over those realized with IpcBH2 under the same conditions.Liberation of the olefin from purified EapBH2 provides (-)-2-ethylapopinene (D23 -46.2 deg (neat) in high optical purity (>99percent ee).Metalation of (+)-α-pinene (D23 +51.4 deg (neat)) with the Lochmann reagent, followed by alkylation with methyl iodide, provides in high optical purity (>99percent ee) (+)-2-ethylapopinene (D23 +46.4 deg (neat)), unavailable from commercial (-)-nopol.
- Brown, Herbert C.,Randad, Ramnarayan S.,Bhat, Krishna S.,Zaidlewicz, Marek,Weissman, Steven A.,et al.
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p. 5513 - 5518
(2007/10/02)
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- Production of optically pure organoboranes
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A process for upgrading to essentially 100% enantiomeric excess the optical purity of an organoborane intermediate represented by the formulae: or wherein Icp is isopinocampheyl and R* is a unsubstituted or substituted, acyclic or cyclic alkyl having from 4 to 30 carbon atoms, comprising the steps of hydroborating cis-alkene, a trans-alkene or a tertiary-alkene with monoisopinocampheylborane or diisopinocampheylborane, obtaining a solid organoborane and recrystallizing the solid organoborane to obtain an enantiomeric excess of essentially 100% ee of said organoborane.
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- ASYMMETRIC SYNTHESIS BY CHIRAL COBALT CATALYSTS: HOMOGENEOUS REDUCTION OF KETONES TO OPTICALLY ACTIVE ALCOHOLS
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The hydrogenation of ketones with Co2(CO)6(PR3)2 (PR3 = PPh2-neo-menthyl, PPh2-6-deoxo-1,2.3,4-diisopropylidene D-galactose and PMe2-menthyl)as catalysts gives optically active alcohols in optical yields of 1.6 to 5percent.
- Massonneau, V.,Maux, P. Le,Simonneaux, G.
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p. C59 - C60
(2007/10/02)
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- LIPASE-CATALYZED ESTER FORMATION IN ORGANIC SOLVENTS. AN EASY PREPARATIVE RESOLUTION OF α-SUBSTITUTED CYCLOHEXANOLS
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The commercial preparation "lipase My" catalyzes ester formation from an alcohol and a fatty acid in organic solvents.Preparative resolution of α-substituted cyclohexanols, including menthol, was achieved under these conditions.
- Langrand, Georges,Secchi, Michel,Buono, Gerard,Baratti, Jacques,Triantaphylides, Christian
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p. 1857 - 1860
(2007/10/02)
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- Resolution of Racemic Mixtures via Lipase Catalysis in Organic Solvents
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Yeast lipase and porcine pancreatic lipase have been found to vigorously function in nearly anhydrous organic solvents and catalyze the reactions of esterification and transesterification, respectively, in highly stereoselective manner.With use of these enzymatic processes, a number of optically active alcohols, carboxylic acids, and their esters have been prepared on a gram scale.
- Kirchner, Gerald,Scollar, Mark P.,Klibanov, Alexander M.
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p. 7072 - 7076
(2007/10/02)
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- Enantioselective Ester Hydrolyses Employing Rhizopus nigricans. A Method of Preparing and Assigning the Absolute Stereochemistry of Cyclic Alcohols
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The mold Rhizopus nigricans has been used to hydrolyze enantioselectively the acetates of several series of benzocycloalken-3-ols and 2-substituted cycloalkanols to yield chiral alcohols.The configurations of the alcohols formed were established.The absolute stereochemistries of 25 of the 26 alcohols obtained were found to conform to a generalization based on the effective sizes of substituents on the carbinol carbon.The relative sizes of substituents required for agreement were identical with those employed in Horeu's method of establishing the absolute stereochemistry of the same compounds.The use of these microbially mediated hydrolyses to assign the absolute stereochemistry of cyclic secondary alcohols is compared to Horeau's method and to the use of empirical relations between the absolute stereochemistry of an enantiomer and the order, relative to its antipode, in which it is eluted from a chiral (Pirkle) column.
- Kasai, Masaji,Kawai, Ken-ichi,Imuta, Mitsuru,Ziffer, Herman
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p. 675 - 679
(2007/10/02)
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- Enzymes in organic synthesis. 30. Reaction conditions - control of enantiomeric purities. Horse liver alcohol dehydrogenase-catalyzed reductions of 2-alkylcyclohexanones and their thiopyran analogs
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The effects of buffer, pH, reaction time, and / ratio on the enantiomeric purities of the alcohol products of horse liver alcohol dehydrogenase-catalyzed reductions of (+/-)-α-alkylcyclohexanones and -tetrahydrothiopyranones have been s
- Jones, J. Bryan,Takemura, Tetsuo
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- Enzymes in organic synthesis. 28. Reinvestigation of the horse liver alcohol dehydrogenase-catalyzed reductions of 2-alkylcyclohexanones. Identification of cis-alkylcyclohexanols as minor products.
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The formation of cis-2-alkylcyclohexanol products from horse liver alcohol dehydrogenase-catalyzed reductions of 2-alkylcyclohexanones has been detected for the first time.The cis-alcohols are minor (/ and pH conditions possible, and by minimizing the reaction time.The results parallel the cis-alcohol formation observed previously with the analogous 3-alkyltetrahydropyran-4-one substrates.
- Jones, J. Bryan,Takemura, Tetsuo
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p. 2950 - 2956
(2007/10/02)
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- ENZYMATIC "IN VITRO" REDUCTION OF KETONES VII. (1) Reduction rates and stereochemistry of the HLAD catalyzed reduction of 2-alkyl cyclohexanones, dimethyl cyclohexanones, cycloalkanones and bicycloalkanones.
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Values for the rate constants of the catalytic step HLAD-NADH + ketone -> HLAD-NAD1+ + alcohol in the HLAD catalyzed reduction of some 2-alkyl cyclohexanones, geminal dimethyl cyclohexanones, cycloalkanones and bicyclic ketones are presented.Also the thermodynamic parameters of activation are given and they are compared with the activation parameters of the NaBH4 reduction leading to a better understanding of some forces at work in enzymatic catalysis.The results are rationalized in the same way as was previously done for the 3-alkyl and 4-alkyl cyclohexanones.A reaction model is obtained in which steric hindrances and hydrophobic zones are responsible for rate decreasing, respectively increasing interactions between enzyme and substrates.
- Osselaer, T. A. Van,Lemiere, G. L.,Lepoivre, J. A.,Alderweireldt, F. C.
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p. 389 - 398
(2007/10/02)
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