- Practical access to (S)-heterocyclic aromatic acetates via CAL-B/Na2CO3-deacylation and Mitsunobu reaction protocol
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Herein, we report the preparation of enantiomerically pure forms of 2,3-dihydrobenzofuran-3-ol (1), chroman-4-ol (2), thiochroman-4-ol (3), 1-(furan-2-yl) ethanol (5) and 1-(thiophen-2-yl) ethanol (6), through a kinetic resolution catalysed by Candida antarctica lipase B/Na2CO3 hydrolysis sequence in organic media. The (R)-furnished alcohols and the (S)-remained acetates are recovered enantiopures (ee?>99%, E???200, Conv = 50%). Those ideal enzymatic kinetic resolution (EKRs) are well incorporated to the Mitsunobu inversion protocol in a one pot procedure to give (S)-heterocyclic acetates (1a–3a) in good to high enantiomeric excess (88%–92% ee). Whilst, the (S)-heteroaromatic acetates (5a and 6a) are given with moderate enantiomeric excess (51%–62% ee). All the (S)-acetates are given in good isolated chemical yields (>80%) allowing to overcome the maximum of 50% yield which could be usually reached in a regular kinetic resolution processes.
- Aribi-Zouioueche, Louisa,Bra?a, Nabila,Merabet-Khelassi, Mounia,Toffano, Martial
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- Supported ionic liquids in Burkholderia cepacia lipase-catalyzed asymmetric acylation
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Lipase PS from Burkholderia cepacia was successfully immobilized on Kynol ACC 507-15 active carbon cloth with and without ionic liquids as SILE catalysts. Activity, enantioselectivity and reuse of the catalysts were evaluated in the acylation of 1-phenylethanol with vinyl acetate in toluene and in hexane over the temperature range 25-60 °C. The presence of [EMIM][NTf2] clearly stabilized the enzyme against inactivation and preserved enantioselectivity in reuse in a process which is affected by the nature of the IL, solvent and substrate structure.
- Hara, Piia,Mikkola, Jyri-Pekka,Murzin, Dmitry Yu.,Kanerva, Liisa T.
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scheme or table
p. 129 - 134
(2011/02/24)
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- Lipase-catalysed kinetic resolutions of secondary alcohols in pressurised liquid hydrofluorocarbons
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Three model secondary alcohols have been subjected to enzymatic kinetic resolution using three common lipases and a typical acyl donor. The resolutions were performed in two pressurised low-boiling hydrofluorocarbons, which are novel media for enzymatic reactions, and five conventional organic solvents. In general, higher yields, ee's and rates of reaction were observed in the hydrofluorocarbons.
- Ball, Anthony J.,Corr, Stuart,Micklefield, Jason
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supporting information; experimental part
p. 3543 - 3546
(2009/10/26)
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- Enhancement of enantioselectivity in the optical resolution of primary alcohols with modified cyclodextrin colyophilized lipase
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Colyophilization of lipase was carried out with immobilized β-cyclodextrins (β-CyD) bearing methyl, acetyl, benzoyl, and nicotinoyl substituents. The colyophilizates enhanced stereoselectivity in the acylation of several alcohols. The enantioselectivity in the acylation of ethyl-1-hydroxymethyl-phenylphosphine oxide using colyophilized lipase with nicotinoyl-β-CyD increased approximately threefold (from E=34 to E=113). The amphiphilic character of modified CyDs has been found to influence the enhancement of enantioselectivity. Copyright Taylor & Francis Group, LLC.
- Shioji, Kosei,Kurauchi, Yoshimitsu,Terada, Keiko,Kodera, Yasushi,Okuma, Kentaro
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p. 2163 - 2170
(2008/02/07)
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- A divergent synthesis of uncommon sugars from furanaldehyde
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A practical synthetic strategy has been developed for producing uncommon sugars. This method employed kinetic enzymatic resolution of 1-(2-furyl)ethanol, and followed by NBS-mediated Achmatowicz rearrangement to construct α,β-unsaturated lactones. After further derivatization, five representative uncommon sugar units were successfully synthesized. Georg Thieme Verlag Stuttgart.
- Zhu, Lizhi,Talukdar, Arindam,Zhang, Guisheng,Kedenburg, James P.,Wang, Peng George
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p. 1547 - 1550
(2007/10/03)
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- Entrapment of Pseudomonas cepacia lipase with peracetylated β-cyclodextrin in sol-gel: Application to the kinetic resolution of secondary alcohols
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Co-lyophilized Pseudomonas cepacia lipase with peracetylated β-cyclodextrin was immobilized by the sol-gel process. The gel-entrapped lipase/cyclodextrin was prepared by the hydrolysis of methyltrimethoxysilane (MTMS) in the presence of the co-lyophilized lipase with peracetylated β-cyclodextrin prepared with different weight ratios (enzyme to CD). This type of enzyme preparation was subsequently used in the kinetic resolution of a set of secondary alcohols using isopropenyl acetate as an innocuous acyl donor in toluene as the organic medium. The resulting chiral alcohols (substrate) and the corresponding acetates (product) were baseline separated in one analysis without derivatization using gas chromatography on a new chiral stationary phase (CSP) Chirasil-β-Dex containing an undecamethylene spacer (C11-Chirasil-Dex).
- Ghanem, Ashraf,Schurig, Volker
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p. 2547 - 2555
(2007/10/03)
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- The utility of cyclodextrins in lipase-catalyzed transesterification in organic solvents: Enhanced reaction rate and enantioselectivity
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The use of enzymes as valuable catalysis in organic solvents has been well documented. However, some of their features limit their application in organic synthesis, especially the frequently lower enzyme activity under nonaqueous conditions, which constitutes a major drawback in the application of enzymes in organic solvents. In addition, many enzymatic reactions are subject to substrate or product inhibition, leading to a decrease in the reaction rate and enantioselectivity. To overcome these drawbacks and to make enzymes more appealing to organic chemists, we demonstrate the use of cyclodextrins as regulators for the Pseudomonas cepacia lipase (PSL) and macrocyclic additives to enhance the reaction rate and enantioselectivity E in lipase-catalyzed enantioselective transesterification of 1-(2-furyl)ethanol in organic solvents. Both reaction rate and enantioselectivity were significantly enhanced by several orders of magnitude when using co-lyophilized lipase in the presence of cyclodextrins. The effect of cyclodextrin derivatives as well as solvents on the improvement of the reaction parameters has been studied. The observed enhancement was tentatively interpreted in terms of their ability to give a certain flexibility to the enzyme and to form a host-guest complex, thus avoiding product inhibition and leading to enhancement of the reaction rate and enantioselectivity. The effect of cyclodextrin additives on the enzyme morphology has been studied using scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) of the co-lyophilized lipase with cyclodextrins. The ability of cyclodextrins to form a host-guest complex to avoid product inhibition, which leads to the observed enhancement, has been proved by NOESY, COSY, 13C and 1H NMR.
- Ghanem, Ashraf
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p. 1282 - 1291
(2007/10/03)
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- Asymmetric hydrogenation of itaconic acid and enol acetate derivatives with the Rh-TangPhos catalyst
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(Matrix presented) The Rh-TangPhos catalyst has been used for asymmetric hydrogenation of itaconic acid and enol acetate derivatives. A variety of chiral 2-substituted succinic acids and chiral acetates have been obtained in excellent ee values (up to 99% ee).
- Tang, Wenjun,Liu, Duan,Zhang, Xumu
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p. 205 - 207
(2007/10/03)
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- Highly Enantioselective Hydrogenation of Enol Acetates Catalyzed by Ru-TunaPhos Complexes
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(Matrix Presented) The chiral disphosphines with tunable dihedral angles (TunaPhos) have been used for asymmetric hydrogenation of enol acetates and dihedral-angle-dependent enantioselectivities were observed. C2-TunaPhos has been proved to be effective for Ru-catalyzed asymmetric hydrogenation of electron-deficient and other enol acetates.
- Wu, Shulin,Wang, Weimin,Tang, Wenjun,Lin, Min,Zhang, Xumu
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p. 4495 - 4497
(2007/10/03)
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- Peracetylated β-cyclodextrin as additive in enzymatic reactions: Enhanced reaction rate and enantiomeric ratio in lipase-catalyzed transesterifications in organic solvents
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Peracetylated β-cyclodextrin has been employed as a macrocyclic additive to enhance the enantiomeric ratio E and reaction rate in Pseudomonas cepacia lipase (PSL)-catalyzed enantioselective transesterification of 1-(2-furyl)ethanol in organic solvents. The beneficial action of the cyclodextrin used as a regulator of lipase was tentatively interpreted as increasing the conformational flexibility of the enzyme and undergoing host-guest complexation with the product, thereby preventing product inhibition and leading to an enhancement of the enantiomeric ratio E and the reaction rate. The effect of the organic solvent on the present cyclodextrin-mediated enzymatic transesterification has been studied.
- Ghanem, Ashraf,Schurig, Volker
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p. 2761 - 2766
(2007/10/03)
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