- SYNTHESIS OF OPTICALLY ACTIVE 2-ARYLALKANOIC ACIDS BY THE USE OF 1,2-REARRANGEMENT OF THE ARYL GROUP
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A new route to the synthesis of optically active 2-arylalkanoic acids was accomplished by using stereospecific 1,2-rearrangement of the aryl group in chiral 1-aryl-2-sulfonyloxy-1-alkanone acetals.
- Tsuchihashi, Gen-ichi,Mitamura, Shuichi,Kitajima, Kouji,Kobayashi, Kumi
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- Preparation of One-Pot Immobilized Lipase with Fe3O4 Nanoparticles Into Metal-Organic Framework For Enantioselective Hydrolysis of (R,S)-Naproxen Methyl Ester
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Immobilization of enzyme to magnetic metal-organic frameworks (MOF) can preserve biological functionality in harsh environments to increase enzymes activity, stability, and improve reusability. The magnetic Fe3O4 nanoparticles were treated with calix[4]arene tetracarboxylic acid (Calix) and Candida rugosa lipase (CRL), and then encapsulated into the zeolitic imidazole framework-8 (Fe3O4@Calix-ZIF-8@CRL). The lipase activity data of Fe3O4@Calix-ZIF-8@CRL was 2.88 times higher than that of the Fe3O4@ZIF-8@CRL (without Calix). The catalytic properties of immobilized lipases were studied on the enantioselective hydrolysis of R/S-naproxen methyl ester. It was also observed that Fe3O4@Calix-ZIF-8@CRL has excellent enantioselectivity (E=371) compared to Fe3O4@ZIF-8@CRL (E=131). Furthermore, Fe3O4@Calix-ZIF-8@CRL was seen to still retain 30 % of the conversion rate after the fifth reuse. This work may also be useful for the pharmaceutical industry due to the increased reusability and stability of enzymes, the enantiomeric selectivity exhibited by MOF-enzyme biocomposites, and the significant differences in the biological activities of the enantiomers.
- Ozyilmaz, Elif,Ascioglu, Sebahat,Yilmaz, Mustafa
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p. 3687 - 3694
(2021/06/25)
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- Reshaping the active pocket of esterase Est816 for resolution of economically important racemates
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Bacterial esterases are potential biocatalysts for the production of optically pure compounds. However, the substrate promiscuity and chiral selectivity of esterases usually have a negative correlation, which limits their commercial value. Herein, an efficient and versatile esterase (Est816) was identified as a promising catalyst for the hydrolysis of a wide range of economically important substrates with low enantioselectivity. We rationally designed several variants with up to 11-fold increased catalytic efficiency towards ethyl 2-arylpropionates, mostly retaining the initial substrate scope and enantioselectivity. These variants provided a dramatic increase in efficiency for biocatalytic applications. Based on the best variant Est816-M1, several variants with higher or inverted enantioselectivity were designed through careful analysis of the structural information and molecular docking. Two stereoselectively complementary mutants, Est816-M3 and Est816-M4, successfully overcame and even reversed the low enantioselectivity, and several 2-arylpropionic acid derivatives with highEvalues were obtained. Our results offer potential industrial biocatalysts for the preparation of structurally diverse chiral carboxylic acids and further lay the foundation for improving the catalytic efficiency and enantioselectivity of esterases.
- Fan, Xinjiong,Fu, Yao,Liu, Xiaolong,Zhao, Meng
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p. 6126 - 6133
(2021/09/28)
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- Nickel-catalyzed asymmetric reductive cross-coupling of α-chloroesters with (hetero)aryl iodides
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An asymmetric reductive cross-coupling of α-chloroesters and (hetero)aryl iodides is reported. This nickel-catalyzed reaction proceeds with a chiral BiOX ligand under mild conditions, affording α-arylesters in good yields and enantioselectivities. The reaction is tolerant of a variety of functional groups, and the resulting products can be converted to pharmaceutically-relevant chiral building blocks. A multivariate linear regression model was developed to quantitatively relate the influence of the α-chloroester substrate and ligand on enantioselectivity.
- Cleary, Leah,DeLano, Travis J.,Dibrell, Sara E.,Lacker, Caitlin R.,Pancoast, Adam R.,Poremba, Kelsey E.,Reisman, Sarah E.,Sigman, Matthew S.
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p. 7758 - 7762
(2021/06/16)
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- Bidentate phosphine-phosphine oxide ligand and intermediate, preparation method and application thereof
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The invention discloses a bidentate phosphine-phosphine oxide ligand and an intermediate, a preparation method and application thereof. The phosphine oxide compound is shown as a formula I and/or ent-I. The phosphine oxide compound is used as a metal ligand and is applied to Suzuki-Miyaura coupling reaction so that generation of self-coupled by-products is avoided, and an alpha-aryl carbonyl compound is obtained; and the dosages of the ligand and the metal catalyst are less.
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Paragraph 0431-0438
(2020/11/10)
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- Enantioselective Palladium-Catalyzed Cross-Coupling of α-Bromo Carboxamides and Aryl Boronic Acids
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We herein report an enantioselective palladium-catalyzed cross-coupling between α-bromo carboxamides and aryl boronic acids, generating a series of chiral α-aryl carboxamides in good yields and excellent enantioselectivities. The development of a chiral P,P=O ligand was critical in overcoming the second transmetalation issue and allows the first asymmetric palladium-catalyzed coupling of α-bromo carbonyl compounds.
- Li, Bowen,Li, Tiejun,Aliyu, Muinat A.,Li, Zhen Hua,Tang, Wenjun
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supporting information
p. 11355 - 11359
(2019/07/12)
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- Deracemizing α-Branched Carboxylic Acids by Catalytic Asymmetric Protonation of Bis-Silyl Ketene Acetals with Water or Methanol
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We report a highly enantioselective catalytic protonation of bis-silyl ketene acetals. Our method delivers α-branched carboxylic acids, including nonsteroidal anti-inflammatory arylpropionic acids such as Ibuprofen, in high enantiomeric purity and high yields. The process can be incorporated in an overall deracemization of α-branched carboxylic acids, involving a double deprotonation and silylation followed by the catalytic asymmetric protonation.
- Mandrelli, Francesca,Blond, Aurélie,James, Thomas,Kim, Hyejin,List, Benjamin
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p. 11479 - 11482
(2019/07/18)
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- Iron-catalysed enantioselective Suzuki-Miyaura coupling of racemic alkyl bromides
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The first iron-catalysed enantioselective Suzuki-Miyaura coupling reaction has been developed. In the presence of catalytic amounts of FeCl2 and (R,R)-QuinoxP?, lithium arylborates are cross-coupled with tert-butyl α-bromopropionate in an enantioconvergent manner, enabling facile access to various optically active α-arylpropionic acids including several nonsteroidal anti-inflammatory drugs (NSAIDs) of commercial importance. (R,R)-QuinoxP? is specifically able to induce chirality when compared to analogous P-chiral ligands that give racemic products, highlighting the critical importance of transmetalation in the present asymmetric cross-coupling system.
- Iwamoto, Takahiro,Okuzono, Chiemi,Adak, Laksmikanta,Jin, Masayoshi,Nakamura, Masaharu
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supporting information
p. 1128 - 1131
(2019/01/28)
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- Structural insights into the ene-reductase synthesis of profens
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Reduction of double bonds of α,β-unsaturated carboxylic acids and esters by ene-reductases remains challenging and it typically requires activation by a second electron-withdrawing moiety, such as a halide or second carboxylate group. We showed that profen precursors, 2-arylpropenoic acids and their esters, were efficiently reduced by Old Yellow Enzymes (OYEs). The XenA and GYE enzymes showed activity towards acids, while a wider range of enzymes were active towards the equivalent methyl esters. Comparative co-crystal structural analysis of profen-bound OYEs highlighted key interactions important in determining substrate binding in a catalytically active conformation. The general utility of ene reductases for the synthesis of (R)-profens was established and this work will now drive future mutagenesis studies to screen for the production of pharmaceutically-active (S)-profens.
- Waller,Toogood,Karuppiah,Rattray,Mansell,Leys,Gardiner,Fryszkowska,Ahmed,Bandichhor,Reddy,Scrutton
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supporting information
p. 4440 - 4448
(2017/07/10)
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- Surface-mounted MOF templated fabrication of homochiral polymer thin film for enantioselective adsorption of drugs
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A self-polymerized chiral monomer 3,4-dihydroxy-l-phenylalanine (l-DOPA) has been introduced into the pores of an achiral surface-mounted metal organic framework (SURMOF), and then the homochiral poly(l-DOPA) thin film has been successfully formed after UV light irradiation and etching of the SURMOF. Remarkably, such a poly(l-DOPA) thin film exhibited enantioselective adsorption of naproxen. This study opened a SURMOF-templated approach for preparing porous polymer thin films.
- Gu, Zhi-Gang,Fu, Wen-Qiang,Liu, Min,Zhang, Jian
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p. 1470 - 1473
(2017/02/05)
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- Ultrafast chiral separations for high throughput enantiopurity analysis
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Recent developments in fast chromatographic enantioseparations now make high throughput analysis of enantiopurity on the order of a few seconds achievable. Nevertheless, routine chromatographic determinations of enantiopurity to support stereochemical investigations in pharmaceutical research and development, synthetic chemistry and bioanalysis are still typically performed on the 5-20 min timescale, with many practitioners believing that sub-minute enantioseparations are not representative of the molecules encountered in day to day research. In this study we develop ultrafast chromatographic enantioseparations for a variety of pharmaceutically-related drugs and intermediates, showing that sub-minute resolutions are now possible in the vast majority of cases by both supercritical fluid chromatography (SFC) and reversed phase liquid chromatography (RP-LC). Examples are provided illustrating how such methods can be routinely developed and used for ultrafast high throughput analysis to support enantioselective synthesis investigations.
- Barhate, Chandan L.,Joyce, Leo A.,Makarov, Alexey A.,Zawatzky, Kerstin,Bernardoni, Frank,Schafer, Wes A.,Armstrong, Daniel W.,Welch, Christopher J.,Regalado, Erik L.
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supporting information
p. 509 - 512
(2017/01/13)
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- Temperature-Controlled Bidirectional Enantioselectivity in Asymmetric Hydrogenation Reactions Utilizing Stereodynamic Iridium Complexes
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Stereochemically flexible 2,2(-bis(diphenylphosphino)biphenyl (BIPHEP) ligands were modified with chiral α-substituted carboxylic acid auxiliaries in the 3- and 3′-position. The resulting central-to-axial chirality transfer to the stereochemically flexible chiral axis of the BIPHEP core was investigated as well as complexation of these diastereomeric ligands to iridium(I). Solid-state structures of both ligand diastereomers and a diastereomerically pure iridium(I) BIPHEP complex were obtained. Thermal equilibration of the resulting iridium(I) complexes was studied to investigate the stereodynamic properties of the BIPHEP ligands. The iridium(I) complexes without and after pre-catalysis warming in solution - which induces a shift of the diastereomeric ratio - were applied for asymmetric hydrogenation of a prochiral α-substituted acrylic acid, resulting in temperature-controlled bidirectional enantioselectivity of iridium catalysts for the first time. In both cases, enantioenriched (R)-naproxen as well as (S)-naproxen - after re-equilibration of the catalyst at elevated temperatures - was obtained by using the same catalyst.
- Siebert, Max,Storch, Golo,Rominger, Frank,Trapp, Oliver
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supporting information
p. 3485 - 3494
(2017/07/27)
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- Efficient resolution of profen ethyl ester racemates by engineered Yarrowia lipolytica Lip2p lipase
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Enzyme-catalyzed enantiomer discrimination is still a great challenge for the development of industrial pharmaceutical processes. For the resolution of ibuprofen, naproxen and ketoprofen racemates, three major anti-inflammatory drugs, only lipases from Candida rugosa present a high selectivity if solvent and surfactant use is discarded. However, their catalytic activities are too low. In the present work, we demonstrate that the lipase Lip2p from the yeast Yarrowia lipolytica has a higher catalytic activity than C. rugosa lipases to hydrolyze the ethyl esters of ibuprofen, naproxen and ketoprofen, but its selectivity is not sufficient [E?=?52 (S); 11 (S) and 1.5 (R) respectively]. The enantioselectivity was further improved by site-directed mutagenesis, targeted at the substrate binding site and guided by molecular modelling studies. By investigating the binding modes of the (R)- and (S)-enantiomers in the active site, two amino acid residues located in the hydrophobic substrate binding site of the lipase, namely residues 232 and 235, were identified as crucial for enantiomer discrimination and enzyme activity. The (S) enantioselectivity of Lip2p towards ethyl ibuprofen esters was rendered infinite (E???300) by replacing V232 by an A or C residue. Substitution of V235 by C, M, S, or T amino acids led to a great increase in the (S)-enantioselectivity (E???300) towards naproxen ethyl ester. Finally, the variant V232F enabled the efficient kinetic resolution of ethyl ketoprofen ester enantiomers [(R)-enantiopreference; E???300]. In addition to the increase in selectivity, a remarkable increase in velocity by 2.6, 2.7 and 2.5?times, respectively, was found for ibuprofen, naproxen and ketoprofen ethyl esters.
- Gérard, Doriane,Guéroult, Marc,Casas-Godoy, Leticia,Condoret, Jean-Stéphane,André, Isabelle,Marty, Alain,Duquesne, Sophie
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p. 433 - 441
(2017/03/24)
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- Facile one-pot preparation of chiral monoliths with a well-defined framework based on the thiol-ene click reaction for capillary liquid chromatography
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A novel chiral cyclodextrin (CD) monolith was easily prepared via a one-pot process based on the thiol-ene click reaction of allyl-β-CD with pentaerythritol tetra-(3-mercaptopropionate) in a fused-silica capillary. The effects of both the composition of prepolymerization solution and reaction temperature on the morphology, permeability, and selectivity of the β-CD chiral monolith were investigated in detail. The conditions were optimized to fabricate a homogeneous and permeable chiral monolith. In this study, the β-CD monolith was used as the stationary phase of capillary liquid chromatography for the chiral separation of several pharmaceutical enantiomers including flavanone, flurbiprofen, naproxen, synephrine, isoprenaline sulfate, ketoprofen, and atropine sulfate monohydrate. Compared to the previously reported two-step method, this one-pot method for the preparation of a β-CD chiral monolith is simple and time-saving. Moreover, good resolutions were obtained for chiral isomers in a shorter analysis time compared to that reported in the literatures. These results indicate that the thiol-ene click chemistry provides a simple and robust method for the preparation of a chiral β-CD monolith.
- Zhang, Peng,Wang, Jiannan,Yang, Haiguan,Su, Linjing,Xiong, Yuhao,Ye, Fanggui
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p. 24835 - 24842
(2016/03/22)
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- Carbene-Catalyzed Dynamic Kinetic Resolution of Carboxylic Esters
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Carbene-catalyzed reaction of carboxylic esters has the potential to offer effective synthetic solutions that cannot be readily achieved by using the more conventional aldehyde-Type substrates. Here we report the first carbene-catalyzed dynamic kinetic resolution of α,α-disubstituted carboxylic esters with up to 99:1 er and 99% yield. The present study clearly illustrates the unique power of carbene-catalyzed reactions of readily available and easy to handle carboxylic esters.
- Chen, Xingkuan,Fong, Jacqueline Zi Mei,Xu, Jianfeng,Mou, Chengli,Lu, Yunpeng,Yang, Song,Song, Bao-An,Chi, Yonggui Robin
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p. 7212 - 7215
(2016/07/06)
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- Engineered hydrophobic pocket of (S)-selective arylmalonate decarboxylase variant by simultaneous saturation mutagenesis to improve catalytic performance
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A bacterial arylmalonate decarboxylase (AMDase) catalyzes asymmetric decarboxylation of unnatural arylmalonates to produce optically pure (R)-arylcarboxylates without the addition of cofactors. Previously, we designed an AMDase variant G74C/C188S that displays totally inverted enantioselectivity. However, the variant showed a 20,000-fold reduction in activity compared with the wild-type AMDase. Further studies have demonstrated that iterative saturation mutagenesis targeting the active site residues in a hydrophobic pocket of G74C/C188S leads to considerable improvement in activity where all positive variants harbor only hydrophobic substitutions. In this study, simultaneous saturation mutagenesis with a restricted set of amino acids at each position was applied to further heighten the activity of the (S)-selective AMDase variant toward α-methyl-α-phenylmalonate. The best variant (V43I/G74C/A125P/V156L/M159L/C188G) showed 9,500-fold greater catalytic efficiency kcat/Km than that of G74C/C188S. Notably, a high level of decarboxylation of α-(4-isobutylphenyl)-α-methylmalonate by the sextuple variant produced optically pure (S)-ibuprofen, an analgesic compound which showed 2.5-fold greater activity than the (R)-selective wild-type AMDase.
- Yoshida, Shosuke,Enoki, Junichi,Kourist, Robert,Miyamoto, Kenji
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p. 1965 - 1971
(2015/11/24)
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- Simple azo dyes provide access to versatile chiroptical switches
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Azo dyes have played an important role in the development of the chemical industry for 150 years. The azo-core of these dyes can undergo trans to cis photoisomerization, which allows azobenzene derivatives to act as light triggered molecular switches. Here, we showed that simple derivatization of Sudan I provides access to chiroptical molecular switches, and that the properties of these switches can be readily tuned by modification of the molecular structure. The synthesis, characterization, photoisomerization, thermal stability, chiral HPLC resolution, determination of absolute configuration and chiroptical properties of chiroptical switches based on Sudan I are reported. ortho-difluorinated Sudan I derivatives have improved thermal stabilities and switching properties compared to switches based on Sudan I itself. Transfer of stereochemical information from a non-racemic chiral unit to the π-conjugated system of the dye and exciton-coupled circular dichroism are both observed. The chiral unit influences the geometry and hence the spectra of cis and trans-isomers differently, which is the mechanistic basis of chiroptical switching. The azo-core of dyes can undergo trans to cis photoisomerization, which allows azobenzene derivatives to act as light triggered molecular switches. Simple derivatization of Sudan I using a chiral auxiliary provides access to chiroptical molecular switches. The properties of these switches can be readily tuned by modification of the molecular structure.
- Anger, Emmanuel,Fletcher, Stephen P.
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p. 3651 - 3655
(2015/06/16)
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- Easily accessible TADDOL-derived bisphosphonite ligands: Synthesis and application in the asymmetric hydroformylation of vinylarenes
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The synthesis of chiral bidentate bisphosphonite ligands based on the TADDOL motif from readily available starting materials has been developed. Taking advantage of the modular nature of the building blocks, a diverse ligand library has been prepared. Their catalytic potential has been evaluated in the asymmetric hydroformylation of styrene and derivatives. These catalysts showed high activity and provided the aldehydes in high enantiomeric purity.
- Allmendinger, Simon,Kinuta, Hirotaka,Breit, Bernhard
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supporting information
p. 41 - 45
(2015/03/03)
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- Spirobenzylamine-Phosphine, Preparation Method Therefor And Use Thereof
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The present invention relates to a spirobenzylamine-phosphine, preparation method therefor and use thereof. The compound has a structure represented by formula (I), wherein n=0 to 3; R1, R2, R3, R4, R5, R6, R7, R8 and R9 having a value as defined in claim 1. Starting from the substituted 7-trifluoromesyloxy-7′-diarylphosphino-1,1′-spiro-dihydroindene, the compound is synthesized in a two-step or three-step reactions. The new spirobenzylamine-phosphine is complexed with an iridium precursor and is subjected to ion exchange, to give an Iridium/spirobenzylamine-phosphine complex comprising various anions. The spiro benzyl amine-phosphine/Iridium complex according to the present invention may be used for catalyzing asymmetry hydrogenation of a variety of alpha-substituted acrylic acids, has high activity and enantio-selectivity, and has a good prospect of industrialization.
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Paragraph 0078; 0079
(2014/07/22)
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- Catalytic enantioselective protoboration of disubstituted allenes. Access to alkenylboron compounds in high enantiomeric purity
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Proto-boryl additions to 1,1-disubstituted allenes in the presence of 1.0-5.0 mol % of chiral NHC-Cu complexes, B2(pin)2, and t-BuOH proceed to afford alkenyl-B(pin) products in up to 98% yield, >98:2 site selectivity, and 98:2 er. T
- Jang, Hwanjong,Jung, Byunghyuck,Hoveyda, Amir H.
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supporting information
p. 4658 - 4661
(2015/02/19)
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- Enhanced catalysis and enantioselective resolution of racemic naproxen methyl ester by lipase encapsulated within iron oxide nanoparticles coated with calix[8]arene valeric acid complexes
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In this study, two types of nanoparticles have been used as additives for the encapsulation of Candida rugosa lipase via the sol-gel method. In one case, the nanoparticles were covalently linked with a new synthesized calix[8]arene octa valeric acid derivative (C[8]-C4-COOH) to produce new calix[8]arene-adorned magnetite nanoparticles (NP-C[8]-C4-COOH), and then NP-C[8]-C4-COOH was used as an additive in the sol-gel encapsulation process. In the other case, iron oxide nanoparticles were directly added into the sol-gel encapsulation process in order to interact electrostatically with both C[8]-C4-COOH and Candida rugosa lipase. The catalytic activities and enantioselectivities of two novel encapsulated lipases (Enc-NP-C[8]-C4-COOH and Enc-C[8]-C4-COOH@Fe 3O4) in the hydrolysis reaction of racemic naproxen methyl ester were evaluated. The results showed that the activity and enantioselectivity of the lipase were improved when the lipase was encapsulated in the presence of calixarene-based additives. Indeed, the encapsulated lipases have an excellent rate of enantioselectivity, with E = 371 and 265, respectively, as compared to the free enzyme (E = 137). The lipases encapsulated with C[8]-C4-COOH and iron oxide nanoparticles (Enc-C[8]-C 4-COOH@Fe3O4) retained more than 86% of their initial activities after 5 repeated uses and 92% with NP-C[8]-C 4-COOH. This journal is the Partner Organisations 2014.
- Sayin, Serkan,Akoz, Enise,Yilmaz, Mustafa
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p. 6634 - 6642
(2014/08/18)
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- SPIROBENZYLAMINE-PHOSPHINE, PREPARATION METHOD THEREFOR AND USE THEREOF
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The present invention relates to a spirobenzylamine-phosphine, preparation method therefor and use thereof. The compound has a structure represented by formula (I), wherein n=0 to 3; R1, R2, R3, R4, R5, R6, R7, R8 and R9 having a value as defined in claim 1. Starting from the substituted 7-trifluoromesyloxy-7'-diarylphosphino-1, 1'-spiro-dihydroindene, the compound is synthesized in a two-step or three-step reactions. The new spirobenzylamine-phosphine is complexed with an iridium precursor and is subjected to ion exchange, to give an Iridium/spirobenzylamine-phosphine complex comprising various anions. The spiro benzyl amine-phosphine/Iridium complex according to the present invention may be used for catalyzing asymmetry hydrogenation of a variety of alpha-substituted acrylic acids, has high activity and enantio-selectivity, and has a good prospect of industrialization.
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Paragraph 0067
(2014/07/22)
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- Characterization of a new thermophilic and acid tolerant esterase from Thermotoga maritima capable of hydrolytic resolution of racemic ketoprofen ethyl ester
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A gene coding for a putative thermostable esterase (Tm1160) from the hyperthermophilic bacterium Thermotoga maritima was cloned and expressed in Escherichia coli. The purified enzyme displayed optimal activity at 70 °C and had a half-life of 60 min at 90 °C. It was stable over a range of pHs from 5.0 to 7.5 with an optimum around 5.0-5.5. The enzyme was found to have high acid tolerance and maintained about 50% of its activity even after 60 min of treatment at pH 4.5 and 70 °C. Furthermore, the enzyme exhibited the highest specific activity with p-nitrophenyl butyrate (318 ± 7 s -1 mM-1). Under native conditions, Tm1160 forms a ~74 kDa dimer in solution. In addition, the esterase Tm1160 could enantioselectively hydrolyze the racemic ketoprofen ethyl ester and with an enantiomeric excess (eep) of 91.4% at a conversion of 41.1%, which makes it as a promising biocatalyst for the chiral resolution of (S)-ketoprofen.
- Wei, Tao,Feng, Shengxue,Mao, Duobin,Yu, Xuan,Du, Congcong,Wang, Xihua
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- Thermally driven asymmetric domino reaction catalyzed by a thermostable esterase and its variants
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We have developed a thermally driven domino reaction for the synthesis of (S)-a-arylpropionates (profens) using a thermostable esterase from Sulfolobus tokodaii strain 7. Stereoselectivity was improved considerably by engineering of the active site. Stereoselective decarboxylation at the active site of an esterase is a new reaction for the synthesis of optically active carboxylic acids. Crown Copyright.
- Wada, Reina,Kumon, Takashi,Kourist, Robert,Ohta, Hiromichi,Uemura, Daisuke,Yoshida, Shosuke,Miyamoto, Kenji
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p. 1921 - 1923
(2013/04/10)
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- Process for the optical resolution of 1-(4-methoxybenzyl)-octahydro-isoquinoline
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The resolution of racemic 1-(4-methoxybenzyl)-octahydro-isoquinoline, a key intermediate in the synthesis of the antitussive agent dextromethorphan, is reported using (R)-2-(6-methoxy-2-naphthyl) propionic acid in good yields. The resolving agent and the undesired isomer of the octahydro-isoquinoline have been recovered in good yield.
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Paragraph 0027
(2013/09/11)
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- Substrate-selective inhibition of cyclooxygenase-2: Development and evaluation of achiral profen probes
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Cyclooxygenase-2 (COX-2) oxygenates arachidonic acid and the endocannabinoids 2-arachidonoylglycerol (2-AG) and arachidonoylethanolamide (AEA). We recently reported that (R)-profens selectively inhibit endocannabinoid oxygenation but not arachidonic acid oxygenation. In this work, we synthesized achiral derivatives of five profen scaffolds and evaluated them for substrate-selective inhibition using in vitro and cellular assays. The size of the substituents dictated the inhibitory strength of the analogs, with smaller substituents enabling greater potency but less selectivity. Inhibitors based on the flurbiprofen scaffold possessed the greatest potency and selectivity, with desmethylflurbiprofen (3a) exhibiting an IC50 of 0.11 μM for inhibition of 2-AG oxygenation. The crystal structure of desmethylflurbiprofen complexed to mCOX-2 demonstrated a similar binding mode to other profens. Desmethylflurbiprofen exhibited a half-life in mice comparable to that of ibuprofen. The data presented suggest that achiral profens can act as lead molecules toward in vivo probes of substrate-selective COX-2 inhibition.
- Windsor, Matthew A.,Hermanson, Daniel J.,Kingsley, Philip J.,Xu, Shu,Crews, Brenda C.,Ho, Winnie,Keenan, Catherine M.,Banerjee, Surajit,Sharkey, Keith A.,Marnett, Lawrence J.
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supporting information
p. 759 - 763
(2012/10/29)
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- Enantioselective hydrogenation of α-substituted acrylic acids catalyzed by iridium complexes with chiral spiro aminophosphine ligands
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Highly active: Iridium complexes with chiral spiro aminophosphine ligands were synthesized and applied as catalysts for the asymmetric hydrogenation of α-substituted acrylic acids (see scheme). The complexes were highly active catalysts, showing turnover frequencies of up to 6000 h-1, and catalyst loadings could be reduced to 0.01 mol %. Copyright
- Zhu, Shou-Fei,Yu, Yan-Bo,Li, Shen,Wang, Li-Xin,Zhou, Qi-Lin
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supporting information; experimental part
p. 8872 - 8875
(2012/10/08)
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- Design and synthesis of Janus-type chiral dendritic diphosphanes and their applications in asymmetric hydrogenation
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A series of chiral diphosphane-functionalized Janus dendrimers (up to 16 BINAP units) have been readily synthesized by using liquid-phase organic synthesis with the third-generation Frechet-type poly(aryl ether) dendron as the soluble support. The resulting dendritic ligands were purified by simple solvent precipitation without the need for chromatographic separation at the end of reaction. Complete functionalization of the dendrimers with BINAP moieties was confirmed by 1H NMR, MALDI-TOF mass spectroscopy, and elemental analyses. Their ruthenium complexes were applied to the asymmetric hydrogenation of 2-arylacrylic acids. It was found that only slightly lower enantioselectivities were achieved than the corresponding small-molecular Ru catalyst. Interestingly, a clear increase in activity of the dendritic catalysts was observed on going to the higher generations. In addition, the third-generation catalyst could be recycled without significant loss of catalytic activity or enantioselectivity before the fifth catalytic run. A new kind of easily available Janus dendritic diphosphane ligand has been synthesized and their metal complexes were applied to the asymmetric hydrogenation of 2-arylacrylic acids. Interestingly, a clear increase in activity of the dendritic catalysts was observed on going to the higher generations. Furthermore, the third-generation catalyst could be recycled at least five times. Copyright
- Liu, Ji,Feng, Yu,Ma, Baode,He, Yan-Mei,Fan, Qing-Hua
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supporting information
p. 6737 - 6744
(2013/01/15)
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- Resolution of 1-(4-methoxybenzyl)-octahydro-isoquinoline
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The resolution of racemic 1-(4-methoxybenzyl)-octahydro-isoquinoline, a key intermediate in the synthesis of the antitussive agent dextromethorphan, is reported using (R)-2-(6-methoxy-2-naphthyl) propionic acid in good yields. The resolving agent and the undesired isomer of the octahydro-isoquinoline have been recovered in good yield.
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- Separation of naproxen enantiomers using hollow fiber molecularly imprinted membrane chromatography
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In this paper, the use of molecularly imprinted membrane (MIM) for chromatographic separation is described. Poly(vinylidene fluoride) hollow-fiber membranes were grafted on an imprinted polymer layer by using 4-vinylpyridine and trimethylolpropane triacrylate as monomer and crosslinker and were applied as the chromatographic media. During separation, naproxen enantiomers were separated efficiently, and the separation factor was 2.36. Molecularly imprinted membrane chromatography (MIMC) showed an apparently opposite transport behavior compared to molecularly imprinted polymer (MIP)-packed chromatography.
- Bing, Nai Ci,Tian, Zhen,Jin, Hai Ying,Wang, Li Jun,Zhu, Lu Ping,Xu, Zhen Liang
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body text
p. 266 - 267
(2011/05/13)
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- High-performance liquid chromatography separation of enantiomers of mandelic acid and its analogs on a chiral stationary phase
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The enantiomers of mandelic acid and its analogs have been chromatographically separated on a chiral stationary phase (CSP) derived from 4-(3,5-dinitrobenzamido) tetrahydrophenanthrene. The rationale of separations of these compounds is discussed with respect to the method development for determining enantiomeric purity and possibility of obtaining enantiomerically pure materials by high-pressure liquid chromatography. The relationship of analyte structure to the extent of enantiomeric separation has been examined and separation factors (a) are presented for various groups of structurally related compounds. Chiral recognition models have been suggested to account for the observed separations. These models provide mechanistic insights into the chiral recognition process.
- Aneja, Ritu,Luthra, Pratibha Mehta,Ahuja, Satinder
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experimental part
p. 479 - 485
(2010/08/20)
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- Kinetic resolution of (R,S)-pyrazolides containing substituents in the leaving pyrazole for increased lipase enantioselectivity
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With hydrolysis of (R,S)-azolides in water-saturated methyl tert-butyl ether (MTBE) via Candida antarctica lipase B (CALB) as the model system, (R,S)-pyrazolides containing a leaving 3-, 4- or 3,4-substituted-pyrazole moiety are selected as the best substrates for preparing various optically pure carboxylic acids containing an α-chiral center. Great improvements of enzyme activity for the (R)-enantiomers with excellent enantioselectivity (VR/VS > 100) are obtainable, if (R,S)-pyrazolides containing a leaving 3- or 3,4-substituted-pyrazole moiety are employed for the hydrolysis or alcoholysis by methanol in anhydrous MTBE. A detailed kinetic analysis for (R,S)-N-2-phenylpropionylpyrazoles indicates that a bulky 3-substituent such as 3-(3-bromophenyl) or 3-(2-pyridyl) in the leaving pyrazole moiety has profound effects on decreasing the nucleophilic attack and proton transfer of catalytic serine for the slow-reacting enantiomer in anhydrous MTBE, as well as that and substrate affinity for both enantiomers in water-saturated MTBE. The resolution platform is also successfully applied to the hydrolysis of (R,S)-pyrazolides in water-saturated cyclohexane via Candida rugosa lipase (Lipase MY) having opposite enantioselectivity to CALB.
- Wang, Pei-Yun,Wu, Chia-Hui,Ciou, Jyun-Fen,Wu, An-Chi,Tsai, Shau-Wei
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experimental part
p. 113 - 119
(2011/02/21)
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- Biocatalyzed irreversible esterification in the preparation of S-naproxen
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Dimethyl carbonate was used as alcohol donor in the esterification of naproxen in the presence of immobilised lipase B from Candida antarctica (Novozym 435). The conjugation of hydrolysis of dimethyl carbonate and esterification of acid, created irreversible operative conditions so permitting the recovery of S-naproxen in high ee (>98%). The adopted procedure has a general use.
- Morrone,D'Antona,Lambusta,Nicolosi
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experimental part
p. 49 - 51
(2010/12/19)
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- METHOD FOR PRODUCING OPTICALLY ACTIVE ESTER AND METHOD FOR PRODUCING OPTICALLY ACTIVE CARBOXYLIC ACID
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Disclosed is a method for producing an optically active ester by highly selectively esterifying one enantiomer of a racemic carboxylic acid, while producing an optically active carboxylic acid which is the other enantiomer. An optically active ester is produced while producing an optically active carboxylic acid at the same time by reacting a racemic carboxylic acid with a specific alcohol or phenol derivative in the presence of benzoic anhydride or a derivative thereof and a catalyst such as tetramisole or benzotetramisole, thereby selectively esterifying one enantiomer of the racemic carboxylic acid.
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Page/Page column 13-14
(2010/09/18)
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- An effective kinetic resolution of racemic α-arylpropanoic acids, α-arylbutanoic acids, and β-substituted-α-arylpropanoic acids with bis(9-phenanthryl)methanol as a new achiral nucleophile in the asymmetric esterification using carboxylic anhydrides and the acyl-transfer catalyst
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A general method for the kinetic resolution of racemic α-arylalkanoic acids with achiral alcohols is described. It was determined that bis(9-phenanthryl)methanol is a suitable nucleophile which reacts with the intermediary mixed anhydrides generated from aromatic anhydrides with α-arylpropanoic acids or β-substituted-α-arylpropanoic acids in the presence of (+)-benzotetramisole to produce the corresponding optically active esters with high ee's under very mild conditions.
- Nakata, Kenya,Onda, Yu-Suke,Ono, Keisuke,Shiina, Isamu
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experimental part
p. 5666 - 5669
(2010/11/18)
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- Iterative saturation mutagenesis accelerates laboratory evolution of enzyme stereoselectivity: Rigorous comparison with traditional methods
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Efficacy in laboratory evolution of enzymes is currently a pressing issue, making comparative studies of different methods and strategies mandatory. Recent reports indicate that iterative saturation mutagenesis (ISM) provides a means to accelerate directed evolution of stereoselectivity and thermostability, but statistically meaningful comparisons with other methods have not been documented to date. In the present study, the efficacy of ISM has been rigorously tested by applying it to the previously most systematically studied enzyme in directed evolution, the lipase from Pseudomonas aeruginosa as a catalyst in the stereoselective hydrolytic kinetic resolution of a chiral ester. Upon screening only 10 000 transformants, unprecedented enantioselectivity was achieved (E = 594). ISM proves to be considerably more efficient than all previous systematic efforts utilizing error-prone polymerase chain reaction at different mutation rates, saturation mutagenesis at hot spots, and/or DNA shuffling, pronounced positive epistatic effects being the underlying reason.
- Reetz, Manfred T.,Prasad, Shreenath,Carballeira, Jose D.,Gumulya, Yosephine,Bocola, Marco
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experimental part
p. 9144 - 9152
(2010/08/21)
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- Kinetic resolution of racemic α-arylalkanoic acids with achiral alcohols via the asymmetric esterification using carboxylic anhydrides and acyl-transfer catalysts
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A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic α-substituted carboxylic acids using achiral alcohols, aromatic or aliphatic carboxylic anhydrides, and chiral acyl-transfer catalysts. The combination of 4-methoxybenzoic anhydride (PMBA) or pivalic anhydride with the modified benzotetramisole-type catalyst ((S)-β-Np-BTM) is the most effective for promotion of the enantioselective coupling reaction between racemic carboxylic acids and a novel nucleophile, bis(α-naphthyl) methanol, to give the corresponding esters with high ees. This protocol was successfully applied to the production of nonracemic nonsteroidal anti-inflammatory drugs from racemic compounds utilizing the transacylation process to generate the mixed anhydrides from the acid components with the suitable carboxylic anhydrides.
- Shiina, Isamu,Nakata, Kenya,Ono, Keisuke,Onda, Yu-Suke,Itagaki, Makoto
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supporting information; experimental part
p. 11629 - 11641
(2010/10/04)
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- Lithium chloride-assisted selective hydrolysis of methyl esters under microwave irradiation
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A rapid and mild method for the selective hydrolysis of methyl ester in lithium chloride-N,N-dimethylformamide (LiCl-DMF) system under microwave irradiation has been developed. The effects of substituent, metal salt, and solvent on the reactivity and selectivity of the hydrolysis reaction have been investigated. Microwave irradiation significantly improves the reaction yield within a short time in an LiCl-DMF system. Moreover, the chiral-carbon of methyl esters retained its configuration during the reaction. Finally, the catalytic mechanism of hydrolysis by LiCl salt has also been proposed.
- Wu, Xiao-Ai,Ying, Ping,Liu, Jun-Yang,Shen, Heng-Shui,Chen, Yue,He, Ling
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experimental part
p. 3459 - 3470
(2009/12/03)
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- NEW CHIRAL STATIONARY PHASES FOR CHROMATOGRAPHY BASED ON AROMATIC ALLYL AMINES
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New chiral stationary phases (CSPs) based on chiral selectors covalently bound on a solid support were prepared. Chiral selectors were obtained from enantiomerically pure aromatic amines and 3,5-dinitrobenzoic acid and then linked to the support surface through the allylic double bond. Such obtained materials allow enantioseparation of racemates or enantiomerically enriched compounds. These chiral stationary phases can be used as fillings in chromatographic columns for enantiomer separation of naproxen type drugs and other similar non-steroidal anti-inflammatory drugs (NSAID) by means of high performance liquid chromatography on both the analytical and preparative scale.
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Page/Page column 18; Figure 8
(2009/10/22)
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- Homobenzotetramisole-catalyzed kinetic resolution of α-Aryl-, α-Aryloxy-, and α-Arylthioalkanoic acids
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Effective kinetic resolutions of α-aryl-, αaryloxy-, and α-arylthioalkanoic acids have been achieved via in situ generation of their symmetrical anhydrides and enantioselective alcoholysis in the presence of homobenzotetramisole (HBTM) 3.
- Yang, Xing,Birman, Vladimir B.
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supporting information; experimental part
p. 2301 - 2304
(2010/01/19)
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- (R,S)-azolides as novel substrates for lipase-catalyzed hydrolytic resolution in organic solvents
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Azolides, that is, N-acylazoles, as versatile acylation reagents are well characterized in the literature, in which the azole structure can not only act as a better leaving group but also make the carbonyl carbon more electrophilic and susceptible to nucleophilic attack. It is therefore desirable to combine this unique property and lipase resolution ability in the development of a new resolution process for preparing optically pure carboxylic acids. With the Candida antarctica lipase B (CALB)-catalyzed hydrolysis of (R,S)-N- profenylazoles in organic solvents as the model system, (R,S)-N-profenyl-l,2,4- triazoles instead of their corresponding ester analogues were exploited as the best substrates for preparing optically pure profens, i.e., 2-arylpropionic acids. The structure-reactivity correlations for the (R,S)-azolides in water-saturated methyl tert-butyl ether (MTBE) at 45°C coupled with a thorough kinetic analysis were further employed for elucidating the rate-limiting formation of a tetrahedral adduct without C-N bond breaking or with moderate C-N bond breaking concerted with C-O bond formation in the acylation step. The advantages of easy substrate preparation, high enzyme reactivity and enantioselectivity, and easy recovery of the product and remaining substrate by aqueous extraction demonstrate the potential of using (R,S)-azolides as novel substrates for the enzymatic resolution process.
- Wang, Pei-Yun,Chen, Ying-Ju,Wu, An-Chi,Lin, Yi-Sheng,Kao, Min-Fang,Chen, Jin-Ru,Ciou, Jyun-Fen,Tsai, Shau-Wei
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supporting information; scheme or table
p. 2333 - 2341
(2009/12/27)
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- Resolution of Racemic Organic Acids with (1S, 4S)-4[3,4-Dichlorophenyl]-1,2,3,4-Tetrahydro-N-Methyl-1-Naphthaloneamine
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The present invention relates to novel chiral resolving agents and a process for resolution of racemic organic acids and their derivatives of the formula (+, ?)—R1R2CHCOOR3 with Cis-(1S,4S)-4[3,4-dichlorophenyl]-1,2,3,4-tetrahydro-N-methyl-1-naphthaloneamine and its Cis-(1R,4R)-isomer as well as Trans-(1S,4R)-4[3,4-dichlorophenyl]-1,2,3,4-tetrahydro-N-methyl-1-naphthaloneamine and its Trans-(1R,4S)-isomer.
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Page/Page column 4
(2009/10/18)
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- Kinetic resolution of racemic carboxylic acids using achiral alcohols by the promotion of benzoic anhydrides and tetramisole derivatives: Production of chiral nonsteroidal anti-inflammatory drugs and their esters
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A variety of optically active carboxylic esters were produced by kinetic resolution of racemic carboxylic acids by using achiral alcohols, benzoic anhydrides, and Birman's tetramisole-type catalysts. Bis(α-naphthyl) methanol is a very effective reagent for producing the corresponding esters with high ee values in the presence of 4-methoxybenzoic anhydride (PMBA) as the coupling reagent by promotion of benzotetramisole derivatives (BTM, α-Np-BTM, and β-Np-BTM). This protocol directly provides chiral carboxylic esters from free carboxylic acids and achiral alcohols by utilizing a transacylation process to generate the mixed anhydrides from the acid components with benzoic anhydride derivatives in the presence of chiral catalysts. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Shiina, Isamu,Nakata, Kenya,Onda, Yu-Suke
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experimental part
p. 5887 - 5890
(2009/05/27)
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- Influence of {single bond}OR ester group length on the catalytic activity and enantioselectivity of free lipase and immobilized in membrane used for the kinetic resolution of naproxen esters
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Lipases are suitable catalysts for the kinetic resolution of racemic mixtures due to their ability to discriminate between enantiomers. For this reason, they have been studied largely to develop reactors for the production of optically pure enantiomers. The main problem in these productive systems is enzyme stability and enantiocatalytic selectivity as a function of time. In this work, the enantiocatalytic properties of lipase as a function of the {single bond}OR group length were studied. The methyl, butyl, and octyl esters of naproxen were synthesized and used as reagents. The lipase was used as a free agent and immobilized in a polymeric membrane reactor. The results show that selectivity and stability of the enzyme improved while catalytic activity decreased with the {single bond}OR length group. The immobilized enzyme had higher activity compared with the free enzyme.
- Giorno,D'Amore,Drioli,Cassano,Picci
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p. 194 - 200
(2008/03/12)
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- Asymmetric intermodular heck-type reaction of acyclic alkenes via oxidative palladium(II) catalysis
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Herein, we report an asymmetric intermolecular Heck-type reaction of acyclic alkenes by using a palladium-pyridinyl oxazoline diacetate complex under oxidative palladium(II) catalysis conditions. A premade palladium-ligand complex afforded higher enantioselectivities than a corresponding premixed palladium-ligand system, while offering enhanced asymmetric induction when compared to known intermolecular Heck-type protocols.
- Yoo, Kyung Soo,Park, Chan Pil,Yoon, Cheol Hwan,Sakaguchi, Satoshi,O'Neill, Justin,Jung, Kyung Woon
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p. 3933 - 3935
(2008/02/11)
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- A new class of versatile chiral-bridged atropisomeric diphosphine ligands: Remarkably efficient ligand syntheses and their applications in highly enantioselective hydrogenation reactions
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A series of chiral diphosphine ligands denoted as PQ-Phos was prepared by atropdiastereoselective Ullmann coupling and ring-closure reactions. The Ullmann coupling reaction of the biaryl diphosphine dioxides is featured by highly efficient central-to-axial chirality transfer with diastereomeric excess >99%. This substrate-directed diastereomeric biaryl coupling reaction is unprecedented for the preparation of chiral diphosphine dioxides, and our method precludes the tedious resolution procedures usually required for preparing enantiomerically pure diphosphine ligands. The effect of chiral recognition was also revealed in a relevant asymmetric ring-closure reaction. The chiral tether bridging the two aryl units creates a conformationally rigid scaffold essential for enantiofacial differentiation; fine-tuning of the ligand scaffold (e.g., dihedral angles) can be achieved by varying the chain length of the chiral tether. The enantiomerically pure Ru- and Ir-PQ-Phos complexes have been prepared and applied to the catalytic enantioselective hydrogenations of α- and β-ketoesters (C=O bond reduction), 2-(6′-methoxy- 2′-naphthyl)-propenoic acid, alkyl-substituted β-dehydroamino acids (C=C bond reduction), and N-heteroaromatic compounds (C=N bond reduction). An excellent level of enantioselection (up to 99.9% ee) has been attained for the catalytic reactions. In addition, the significant ligand dihedral angle effects on the Ir-catalyzed asymmetric hydrogenation of N-heteroaromatic compounds were also revealed.
- Qiu, Liqin,Kwong, Fuk Yee,Wu, Jing,Lam, Wai Har,Chan, Shusun,Yu, Wing-Yiu,Li, Yue-Ming,Guo, Rongwei,Zhou, Zhongyuan,Chan, Albert S. C.
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p. 5955 - 5965
(2007/10/03)
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- Polyethylene glycol as an environmentally friendly and recyclable reaction medium for enantioselective hydrogenation
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Polyethylene glycol (PEG) was found to be an inexpensive, non-toxic and recyclable reaction medium for ruthenium- and rhodium-catalyzed asymmetric hydrogenation of 2-arylacrylic acids (Ru-catalyzed C=C bond reduction), enamides (Rh-catalyzed C=C bond reduction), β-keto esters and simple aromatic ketones (Ru-catalyzed C=O bond reduction). In all cases, high catalytic activities and enantioselectivities have been achieved, which are comparable to those obtained in conventional organic solvent systems. The Ru and Rh catalysts prepared with commercially available chiral diphosphine ligands could be readily recycled by simple extraction, as in the case of ionic liquids, and reused up to nine times without obvious loss of catalytic activity and enantioselectivity. The reduced products were obtained from the extracts in high isolated yields. These results indicate that PEGs as new reaction media are attractive alternatives to room temperature ionic liquids.
- Zhou, Hai-Feng,Fan, Qing-Hua,Tang, Wei-Jun,Xu, Li-Jin,He, Yan-Mei,Deng, Guo-Jun,Zhao, Li-Wen,Gu, Lian-Quan,Chan, Albert S. C.
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p. 2172 - 2182
(2007/10/03)
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- Enantioselective synthesis of (S)-α-arylpropionic acids via Pd-catalyzed kinetic resolution of benzylic alcohols
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A convenient synthetic route for the synthesis of three (S)-α-propionic acids, (5)-naproxen (90% ee), (S)-ibuprofen (82% ee) and (5)-phenylpropionic acid (92% ee) is described. Pd-catalyzed oxidative kinetic resolution of the corresponding benzylic alcohols is used as a key step to introduce stereogenicity into the molecule.
- Thakur, Vinay V.,Sudalai
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p. 557 - 562
(2007/10/03)
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- A simple catalytic route to naproxen
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We report herein the asymmetric synthesis of naproxen involving catalytic enantioselective methylation for the first time. The reaction is conducted in a solid-liquid biphasic system using chiral quaternary ammonium salts.
- Kumar, Sanjeev,Ramachandran, Uma
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p. 647 - 649
(2007/10/03)
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- An efficient procedure for the resolution of α-cyano-α-fluoro- p-tolylacetic acid (CFTA) via the diastereomeric N-carbobenzyloxy-cis-1-amino-2- indanol esters
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Development of a new, efficient resolution method of α-cyano-α- fluoro-p-tolylacetic acid (CFTA) 2a has been successfully achieved, which has been troublesome to obtain by conventional methods, in spite of its outstanding ability as an NMR chiral derivatizing agent. Fractional recrystallization of a mixture of the diastereomeric CFTA esters prepared from racemic CFTA chloride and (1R,2S)-N-carbobenzyloxy-cis-1-amino-2-indanol (-)-B afforded the less-soluble diastereomer, which was hydrolyzed to give (S)-2a. It has also been demonstrated that optically active N-acetyl-cis-1-amino-2-indanol is effective for the chromatographic resolution of α-arylacetic acids including ibuprofen and naproxen.
- Fujiwara, Tomoya,Sasaki, Masaki,Omata, Kenji,Kabuto, Chizuko,Kabuto, Kuninobu,Takeuchi, Yoshio
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p. 555 - 563
(2007/10/03)
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- Regio- and enantiocontrol in the room-temperature hydroboration of vinyl arenes with pinacol borane
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The catalyzed hydroboration of vinyl arenes was carried out using pinacol borane instead of catechol borane, as the former reagent and the product boronates are significantly easier to handle. By careful choice of catalyst, either the branched or the linear product can be obtained in greater than 96% selectivity. Interestingly, common ligands such as BINAP and Josiphos give opposite asymmetric induction with pinacol borane as compared with catechol borane, while P,N-ligands such as Quinap gave the same sense of induction. The hydroboration of 6-methoxynaphthalene proceeded with the greatest regio- (95:5) and enantioselectivity (94:6) of all vinyl arenes examined. The hydroboration product was then employed in a concise synthesis of the nonsteroidal antiinflammatory agent, Naproxen. Copyright
- Crudden, Cathleen M.,Hleba, Yonek B.,Chen, Austin C.
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p. 9200 - 9201
(2007/10/03)
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