- An Amphiphilic (salen)Co Complex – Utilizing Hydrophobic Interactions to Enhance the Efficiency of a Cooperative Catalyst
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An amphiphilic (salen)Co(III) complex is presented that accelerates the hydrolytic kinetic resolution (HKR) of epoxides almost 10 times faster than catalysts from commercially available sources. This was achieved by introducing hydrophobic chains that increase the rate of reaction in one of two ways – by enhancing cooperativity under homogeneous conditions, and increasing the interfacial area under biphasic reaction conditions. While numerous strategies have been employed to increase the efficiency of cooperative catalysts, the utilization of hydrophobic interactions is scarce. With the recent upsurge in green chemistry methods that conduct reactions ‘on water’ and at the oil-water interface, the introduction of hydrophobic interactions has potential to become a general strategy for enhancing the catalytic efficiency of cooperative catalytic systems. (Figure presented.).
- Solís-Mu?ana, Pablo,Salam, Joanne,Ren, Chloe Z.-J.,Carr, Bronte,Whitten, Andrew E.,Warr, Gregory G.,Chen, Jack L.-Y.
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supporting information
p. 3207 - 3213
(2021/06/01)
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- Aromatic donor-acceptor interaction promoted catalyst assemblies for hydrolytic kinetic resolution of epichlorohydrin
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Three generations of Co(iii)-salen complexes containing electron-deficient aromatic moieties (acceptors) have been synthesized. When electron-rich aromatic compounds (donors) were introduced, these complexes were designed to form catalyst assemblies through aromatic donor-acceptor interaction. For all three generations of complexes, the addition of a proper donor led to higher catalytic efficiency in the hydrolytic kinetic resolution (HKR) of epichlorohydrin. The reaction rates are in the following order: Generation 3 > Generation 2 > Generation 1. The aromatic donor-acceptor interaction was verified by NMR spectroscopy and UV-vis absorption spectroscopy studies. These results demonstrated that aromatic donor-acceptor interaction can be a valuable driving force in the assembly of supramolecular catalysts.
- Blechschmidt, Daniel R.,Woodhouse, Matthew D.,Inagaki, Sebastien,Whitfield, Melita,Ogunsanya, Ayokunnumi,Yoder, Aaron,Lilly, Daniel,Heim, Eric W.,Soucie, Luke N.,Liang, Jian,Liu, Yu
-
supporting information
p. 172 - 180
(2019/01/04)
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- Exploring the Biocatalytic Scope of a Novel Enantioselective Halohydrin Dehalogenase from an Alphaproteobacterium
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A gene encoding halohydrin dehalogenase from an alphaproteobacterium (AbHHDH) was identified, cloned and over-expressed in Escherichia coli. AbHHDH was able to catalyze the stereoselective dehalogenation of prochiral and racemic halohydrins. It showed the highest enantioselectivity in the dehalogenation of 20?mM (R,S)-2-bromo-1-phenylethanol, which yielded (S)-2-bromo-1-phenylethanol with 99% ee and 34.5% yield. Moreover, AbHHDH catalyzed the azidolysis of epoxides with low to moderate (S)-enantioselectivity. The highest enantioselectivity (E = 18.6) was observed when (R,S)-benzyl glycidyl ether was used as the substrate. A sequential kinetic resolution catalyzed by HHDH was employed for the synthesis of chiral 1-chloro-3-phenoxy-2-propanol. We prepared enantiopure (S)-isomer with a high enantiopurity of ee > 99% and a yield of 30.7% (E-value: 21.3) by kinetic resolution of 20?mM substrate. The (S)-isomer with 99% ee readily obtained from 40 to 150?mM (R,S)-1-chloro-3-phenoxy-2-propanol. Taken together, the results of this study demonstrate the applicability of this HHDH for the production of optically active compounds. [Figure not available: see fulltext.].
- Xue, Feng,Ya, Xiangju,Xiu, Yuansong,Tong, Qi,Wang, Yuqi,Zhu, Xinhai,Huang, He
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p. 629 - 637
(2019/01/25)
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- Molecular modification of a halohydrin dehalogenase for kinetic regulation to synthesize optically pure (S)-epichlorohydrin
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Asymmetric synthesis of chiral epichlorohydrin (ECH) from 1,3-dichloro-2-propanol (1,3-DCP) using halohydrin dehalogenases (HHDHs) is of great value due to the 100% theoretical yield and high enantioselectivity. The vital problem in the asymmetric synthesis is to prepare optically pure ECH. In this study, key amino acid residues located at halide ion channels of HheC (P175S/W249P) (HheCPS) were modified to regulate the kinetic parameters. HheCPS I81W, F86N and V94R were constructed with the corresponding halide ion channels destroyed. The catalytically efficiencies (kcat/Km) of the three mutants exhibited 0.38-, 0.23- and 0.23-fold decrease toward (S)-ECH and the reverse reaction was significantly inhibited. As the results, (S)-ECH was synthesized with >99% enantiomeric excess (e.e.) and 63.42%, 67.08% and 57.01% yields, respectively, under 20 mM 1,3-DCP as substrate. To our knowledge, this is the first investigation of the molecule kinetic modification of HHDHs and also the first report for the biosynthesis of optically pure (S)-ECH from 1,3-DCP using HHDHs.
- Zhang, Xiao-Jian,Deng, Han-Zhong,Liu, Nan,Gong, Yi-Chuan,Liu, Zhi-Qiang,Zheng, Yu-Guo
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p. 154 - 160
(2019/01/08)
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- Aromatic Donor-Acceptor Interaction-Based Co(III)-salen Self-Assemblies and Their Applications in Asymmetric Ring Opening of Epoxides
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Aromatic donor-acceptor interaction as the driving force to assemble cooperative catalysts is described. Pyrene/naphthalenediimide functionalized Co(III)-salen complexes self-assembled into bimetallic catalysts through aromatic donor-acceptor interactions and showed high catalytic activity and selectivity in the asymmetric ring opening of various epoxides. Control experiments, nuclear magnetic resonance (NMR) spectroscopy titrations, mass spectrometry measurement, and X-ray crystal structure analysis confirmed that the catalysts assembled based on the aromatic donor-acceptor interaction, which can be a valuable noncovalent interaction in supramolecular catalyst development.
- Liang, Jian,Soucie, Luke N.,Blechschmidt, Daniel R.,Yoder, Aaron,Gustafson, Addie,Liu, Yu
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supporting information
p. 513 - 518
(2019/01/14)
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- Imido-P(v) trianion supported enantiopure neutral tetrahedral Pd(II) cages
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Charge-neutral chiral hosts are attractive due to their ability to recognize a wide range of guest functionalities and support enantioselective processes. However, reports on such charge-neutral cages are very scarce in the literature. Here, we report an enantiomeric pair of tetrahedral Pd(ii) cages built from chiral tris(imido)phosphate trianions and oxalate linkers, which exhibit enantioselective separation capabilities for epichlorohydrin, β-butyrolactone, and 3-methyl- and 3-ethyl cyclopentanone.
- Rajasekar, Prabhakaran,Pandey, Swechchha,Paithankar, Harshad,Chugh, Jeetender,Steiner, Alexander,Boomishankar, Ramamoorthy
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supporting information
p. 1873 - 1876
(2018/02/23)
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- Homochiral Metal-Organic Cage for Gas Chromatographic Separations
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Metal-organic cages (MOCs) as a new type of porous material with well-defined cavities were extensively pursued because of their relative ease of synthesis and their potential applications in host-guest chemistry, molecular recognition, separation, catalysis, gas storage, and drug delivery. Here, we first reported that a homochiral MOC [Zn3L2] is explored to fabricate [Zn3L2] coated capillary column for high-resolution gas chromatographic separation of a wide range of analytes, including n-alkanes, polycyclic aromatic hydrocarbons, and positional isomers, especially for racemates. Various kinds of racemates such as alcohols, diols, epoxides, ethers, halohydrocarbons, and esters were separated with good enantioselectivity and reproducibility on the [Zn3L2] coated capillary column. The fabricated [Zn3L2] coated capillary column exhibited significant chiral recognition complementary to that of a commercial β-DEX 120 column and our recently reported homochiral porous organic cage CC3-R coated column. The results show that the homochiral MOCs will be very attractive as a new type of chiral selector in separation science.
- Xie, Sheng-Ming,Fu, Nan,Li, Li,Yuan, Bao-Yan,Zhang, Jun-Hui,Li, Yan-Xia,Yuan, Li-Ming
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p. 9182 - 9188
(2018/07/21)
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- Asymmetric Hydrolytic and Aminolytic Kinetic Resolution of Racemic Epoxides using Recyclable Macrocyclic Chiral Cobalt(III) Salen Complexes
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New chiral macrocyclic cobalt(III) salen complexes were synthesized and used as catalyst for the asymmetric kinetic resolution (AKR) of terminal epoxides and glycidyl ethers with aromatic/aliphatic amines and water as nucleophiles. This is the first occasion where a Co(III) salen complex demonstrated its ability to catalyze AKR as well as hydrolytic kinetic resolution (HKR) reactions. Excellent enantiomeric excesses of the epoxides, the corresponding amino alcohols and diols (upto 99%) with quantitative yields were achieved by using the chiral Co(III) salen complexes in dichloromethane at room temperature. This protocol was further extended for the synthesis of two important drug molecules, i.e., (S)-propranolol and (R)-naftopidil. The catalytic system was also explored for the synthesis of chirally pure diols and chiral cyclic carbonates using carbon dioxide as a greener renewable C1 source. The catalyst was recycled for upto 5 catalytic cycles with retention of enantioselectivity. (Figure presented.).
- Tak, Rajkumar,Kumar, Manish,Menapara, Tusharkumar,Gupta, Naveen,Kureshy, Rukhsana I.,Khan, Noor-ul H.,Suresh
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supporting information
p. 3990 - 4001
(2017/11/22)
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- Dinuclear salen cobalt complex incorporating Y(OTf)3: enhanced enantioselectivity in the hydrolytic kinetic resolution of epoxides
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The activation of inactive Jacobsen's chiral salen Co(ii) (salen = N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine) compound is attained by dinuclear chiral salen Co(iii)-OTf complex formation with yttrium triflate. The yttrium metal not only displays a promoting effect on electron transfer, but also assists in forming two stereocentres of a Lewis acid complex with Co(iii)-OTf. We found that the binuclear Co-complex significantly enhanced reactivity and enantioselectivity in the hydrolytic kinetic resolution of terminal epoxides compared to its analogous monomer and kinetic data are also consistent with these results.
- Patel, Deepak,Kurrey, Ganesh Ram,Shinde, Sandip S.,Kumar, Pradeep,Kim, Geon-Joong,Thakur, Santosh Singh
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p. 82699 - 82703
(2015/10/19)
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- Engineering the epoxide hydrolase from Agromyces mediolanus for enhanced enantioselectivity and activity in the kinetic resolution of racemic epichlorohydrin
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The biocatalytic production of enantiopure epichlorohydrin (ECH) has been steadily attracting more attention. For industrial applications, it is important to obtain an epoxide hydrolase (EH) that possesses the desired enantioselectivity. Site-saturation and site-directed mutagenesis of the Ser207, Asn240 and Trp182 positions were used to generate variants of EH from Agromyces mediolanus ZJB120203 with enhanced enantioselectivity for the kinetic resolution of racemic ECH. The best variant, VDF (W182F/S207V/N240D), displayed a 7-fold enhanced enantioselectivity toward racemic ECH, with an increase in the enantiomeric ratio value (E value) preferring the (R)-ECH enantiomer from 12.9 of wild-type to 90.0, as well as a 1.7-fold improvement in activity. Furthermore, we successfully applied the created recombinant Escherichia coli whole cells expressing variant VDF in the kinetic resolution of racemic ECH. Enantiopure (S)-ECH could be obtained with an enantiopurity of >99% ee and a yield of 40.5% from 450 mM racemic ECH, which is better than those of other reported EHs. These results demonstrated that the EH obtained in this study could be applied for the efficient resolution of racemic ECH.
- Xue, Feng,Liu, Zhi-Qiang,Wan, Nan-Wei,Zhu, Hang-Qin,Zheng, Yu-Guo
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p. 31525 - 31532
(2015/04/22)
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- Efficient synthesis of (S)-epichlorohydrin in high yield by cascade biocatalysis with halohydrin dehalogenase and epoxide hydrolase mutants
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Enantioselective biotransformation of prochiral 1,3-DCP by halohydrin dehalogenases (HHDHs) is particularly attractive since 100% yield of chiral epichlorohydrin (ECH) may be obtained. HheC mutant (P175S/W249P) displayed greatly improved enantiomeric excess (ee) of (S)-ECH from 5% to 95.3% in the catalyzed dehalogenation of 1,3-DCP at pH 8.0. (S)-ECH was enantioselectively biotransformed from 40 mM 1,3-DCP with 92.3% ee and 93.2% yield at pH 10.0. To increase the ee of (S)-ECH, the catalysis was carried out using HheC mutant coupled with epoxide hydrolase mutant and the maximum yield and ee of (S)-ECH reached 91.2% and > 99%.
- Xue, Feng,Liu, Zhi-Qiang,Wang, Ya-Jun,Zhu, Hang-Qin,Wan, Nan-Wei,Zheng, Yu-Guo
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p. 147 - 149
(2015/10/19)
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- Design and synthesis of binuclear Co-salen catalysts for the hydrolytic kinetic resolution of epoxides
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Three binuclear Co(III)-salen complexes have been synthesized based on a series of hydrophilic cyclic frameworks with different ring sizes. The catalytic performance of Co-salen complexes have further been evaluated in the hydrolytic kinetic resolution of racemic epoxides. And kinetic studies reveal that the binuclear Co-salen catalysts show a higher reactivity and better enantioselectivity in comparison to monometallic reference complex, indicating the two Co-salen units on the cyclic framework may work in a cooperative manner. Specifically, Co3, with the most flexible cyclic framework exhibits the best catalytic performance among the three catalysts, due to the efficient cooperative interactions between two cobalt centers.
- Wu, Fengshou,Wang, Kai,Li, Zaoying,Zhu, Xunjin
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p. 101 - 104
(2015/05/27)
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- Application of Mesoporous Silica Foam for Immobilization of Salen Complexes in Chiral Intermediates Synthesis
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A route to synthesize porous materials with a hierarchical micro/meso/macroscopic pore system was investigated. Meso/macroporous monolithic silica foams with a large pore size could be fabricated from a mixture of monodispersed PMMA beads and SBA-15, -16 sol solutions. The size, bulk shape and density of the mesoporous monolithic foam could be controlled by the container and the heat treatment temperature. Drying at temperatures higher than 300°C resulted in an expansion of the SBA silica sol and its solidification to form the mesoporous foams. In contrast, only a dense silica monolith was obtained after full evaporation of the solvent at room temperature without releasing the foam structure in the monolithic body. A large fraction of macroporosity in three dimensions was formed in the monolith body, and the remaining silica walls exhibited uniform mesoporosity. Hydrolytic and phenolic ring-opening of epoxides were performed successfully using chiral (salen)Co-BF3 complex-immobilized catalysts in the packed bed of a continuous flow system. Very high catalytic activity with desirable enantioselectivity was obtained in asymmetric catalysis.
- Jeon, Hoon-Gi,Choi, Seong Dae,Jeon, Sang Kwon,Park, Geun Woo,Yang, Jin Young,Kim, Geon-Joong
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p. 1396 - 1404
(2015/07/15)
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- A One-Step Biocatalytic Process for (S)-4-Chloro-3-hydroxybutyronitrile using Halohydrin Dehalogenase: A Chiral Building Block for Atorvastatin
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(S)-4-Chloro-3-hydroxybutyronitrile [(S)-CHBN] was used as a chiral building block for the preparation of atorvastatin. In this study, (R,S)-epichlorohydrin [(R,S)-ECH] and 1,3-dichloro-2-propanol (1,3-DCP) were investigated to prepare (S)-CHBN by using the halohydrin dehalogenase HheC from Agrobacterium radiobacter AD1. Preparing (S)-CHBN from (R,S)-ECH gave a modest enantiomeric excess (ee), whereas by using 1,3-DCP as the substrate, (S)-CHBN was obtained with 97.3 % ee after pH optimization. However, a low ee value and low yield of (S)-CHBN were obtained if the substrate concentration was increased to 10 g L-1. To obtain a higher ee value and yield, 16 mutants were constructed and screened. The variant W249F with improvements in activity and enantioselectivity was identified and applied at a 1,3-DCP loading of 10 g L-1, which gave (S)-CHBN in 86 % yield with 97.5 % ee in 1 h. This is the first report of a one-step biocatalytic process for the preparation of (S)-CHBN from prochiral 1,3-DCP.
- Wan, Nan-Wei,Liu, Zhi-Qiang,Xue, Feng,Shen, Zhen-Yang,Zheng, Yu-Guo
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p. 2446 - 2450
(2015/08/24)
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- A novel enantioselective epoxide hydrolase from Agromyces mediolanus ZJB120203: Cloning, characterization and application
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A new strain Agromyces mediolanus ZJB120203, capable of enantioselective epoxide hydrolase (EH) activity was isolated employing a newly established colorimetric screening and chiral GC analysis method. The partial nucleotide sequence of an epoxide hydrolase (AmEH) gene from A. mediolanus ZJB120203 was obtained by PCR using degenerate primers designed based on the conserved domains of EHs. Subsequently, an open reading frame containing 1167 bp and encoding 388 amino acids polypeptide were identified. Expression of AmEH was carried out in Escherichia coli and purification was performed by Nickel-affinity chromatography. The purified AmEH had a molecular weight of 43 kDa and showed its optimum pH and temperature at 8.0 and 35 C, respectively. Moreover, this AmEH showed broad substrates specificity toward epoxides. In this study, it is demonstrated that the AmEH could unusually catalyze the hydrolysis of (R)-ECH to produce enantiopure (S)-ECH. Enantiopure (S)-ECH could be obtained with enantiomeric excess (ee) of >99% and yield of 21.5% from 64 mM (R,S)-ECH. It is indicated that AmEH from A. mediolanus is an attractive biocatalyst for the efficient preparation of optically active ECH.
- Xue, Feng,Liu, Zhi-Qiang,Zou, Shu-Ping,Wan, Nan-Wei,Zhu, Wen-Yuan,Zhu, Qing,Zheng, Yu-Guo
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p. 409 - 417
(2014/04/03)
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- Synthesis of enantiomerically pure 3-aryloxy-2-hydroxypropanoic acids, intermediate products in the synthesis of cis-4-Aminochroman-3-ols
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Oxidation of accessible (R)-3-chloropropane-1,2-diol to (R)-3-chloro-2-hydroxypropanoic acid and subsequent reaction of the latter with ortho-substituted sodium phenoxide gave a number of enantiomerically pure 3-aryloxy-2-hydroxypropanoic acid which are intermediate products in the synthesis of nonracemic 4-aminochroman-3-ols.
- Bredikhina,Pashagin,Kurenkov,Bredikhin
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p. 535 - 539
(2014/06/10)
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- Asymmetric hydrolytic kinetic resolution with recyclable polymeric Co(iii)-salen complexes: A practical strategy in the preparation of (S)-metoprolol, (S)-toliprolol and (S)-alprenolol: Computational rationale for enantioselectivity
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A series of chiral polymeric Co(iii)-salen complexes based on a number of achiral and chiral linkers were synthesized and their catalytic performances were assessed in the asymmetric hydrolytic kinetic resolution of terminal epoxides. The effects of the linker were judiciously studied and it was found that in the case of the chiral BINOL-based polymeric salen complex 1, there was an enrichment in catalyst reactivity and enantioselectivity of the unreacted epoxide, particularly in the case of short as well as long chain aliphatic epoxides. Good isolated yields of the unreacted epoxide (up to 46% compared to 50% theoretical yield) along with high enantioselectivity (up to 99%) were obtained in most cases using catalyst 1. Further studies showed that catalyst 1 could retain its catalytic activity for six cycles under the present reaction conditions without any significant loss in activity or enantioselectivity. To show the practical applicability of the above synthesized catalyst we have synthesised some potent chiral β-blockers in moderate yield and high enantioselectivity using complex 1. The DFT (M06-L/6-31+G??//ONIOM(B3LYP/6-31G?:STO-3G)) calculations revealed that the chiral BINOL linker influences the enantioselectivity achieved with Co(iii)-salen complexes. Further, the transition state calculations show that the R-BINOL linker with the (S,S)-Co(iii)-salen complex is energetically preferred over the corresponding S-BINOL linker with the (S,S)-Co(iii)-salen complex for the HKR of 1,2-epoxyhexane. The role of non-covalent C-H?π interactions and steric effects has been discussed to control the HKR reaction of 1,2-epoxyhexane.
- Roy, Tamal,Barik, Sunirmal,Kumar, Manish,Kureshy, Rukhsana I.,Ganguly, Bishwajit,Khan, Noor-Ul H.,Abdi, Sayed H. R.,Bajaj, Hari C.
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p. 3899 - 3908
(2015/02/19)
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- A broadly applicable and practical oligomeric (salen)Co catalyst for enantioselective epoxide ring-opening reactions
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The (salen)Co catalyst (4a) can be prepared as a mixture of cyclic oligomers in a short, chromatography-free synthesis from inexpensive, commercially available precursors. This catalyst displays remarkable enhancements in reactivity and enantioselectivity relative to monomeric and other multimeric (salen)Co catalysts in a wide variety of enantioselective epoxide ring-opening reactions. The application of catalyst 4a is illustrated in the kinetic resolution of terminal epoxides by nucleophilic ring-opening with water, phenols, and primary alcohols; the desymmetrization of meso epoxides by addition of water and carbamates; and the desymmetrization of oxetanes by intramolecular ring opening with alcohols and phenols. The favorable solubility properties of complex 4a under the catalytic conditions facilitated mechanistic studies, allowing elucidation of the basis for the beneficial effect of oligomerization. Finally, a catalyst selection guide is provided to delineate the specific advantages of oligomeric catalyst 4a relative to (salen)Co monomer 1 for each reaction class.
- White, David E.,Tadross, Pamela M.,Lu, Zhe,Jacobsen, Eric N.
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p. 4165 - 4180
(2014/06/09)
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- Asymmetric aminolytic kinetic resolution of racemic epoxides using recyclable chiral polymeric Co(III)-salen complexes: A protocol for total utilization of racemic epoxide in the synthesis of (R)-naftopidil and (S)-propranolol
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Chiral polymeric Co(III) salen complexes with chiral ((R)/(S)-BINOL, diethyl tartrate) and achiral (piperazine and trigol) linkers with varying stereogenic centers were synthesized for the first time and used as catalysts for aminolytic kinetic resolution (AKR) of a variety of terminal epoxides and glycidyl ethers to get enantio-pure epoxides (ee, 99%) and N-protected β-amino alcohols (ee, 99%) with quantitative yield in 16 h at RT under optimized reaction conditions. This protocol was also used for the synthesis of two enantiomerically pure drug molecules (R)-Naftopidil (α1- blocker) and (S)-Propranolol (β-blocker) as a key step via AKR of single racemic naphthylglycidyl ether with Boc-protected isoproylamine with 100% epoxide utilization at 1 g level. The catalyst 1 was successfully recycled for a number of times.
- Kumar, Manish,Kureshy, Rukhsana I.,Shah, Arpan K.,Das, Anjan,Khan, Noor-Ul H.,Abdi, Sayed H. R.,Bajaj, Hari C.
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p. 9076 - 9084
(2013/10/08)
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- Immobilized Aspergillus niger epoxide hydrolases: Cost-effective biocatalysts for the prepation of enantiopure styrene oxide, propylene oxide and epichlorohydrin
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This study aimed to prepare robust immobilized epoxide hydrolase (EH) preparations for asymmetric hydrolysis of racemic epoxides such as styrene oxide, propylene oxide and epichlorohydrin. For this purpose, Aspergillus niger EH was immobilized onto Lewatit VP OC 1600 support by adsorption, modified Florisil and Eupergit C supports by covalently. The suitability of the supports was examined for protein binding capacity and rate of racemic styrene oxide hydrolysis. The protein-activity recovery yields were 75-85%, 82-78% and 90-75%, respectively for EH immobilized onto Lewatit VP OC 1600, modified Florisil and Eupergit C supports. All A. niger EH preparations catalyzed preferentially hydrolysis of (R)-epoxides. Although enantiomeric excess values of all the tested epoxides were 99%, the highest enantiopure epoxide yields were obtained as 48% for (S)-styrene oxide by the immobilized EHs onto modified Florisil and Eupergit C. The highest diol yield was obtained as 78% for 3-chloro-1,2-propanediol, however, its enantiomeric excess value was 28.2%. Enantioselectivity of A. niger EH was improved with the preparation of mentioned immobilized forms. The highest enantioselectivity value was obtained as 95 toward styrene oxide by A. niger EH immobilized onto modified Florisil . The results of reusability studies show that the immobilized EH preparations offer feasible potentials for the preparation of enantiopure epoxides than that of free form.
- Yildirim, Deniz,Tuekel, S. Seyhan,Alptekin, Oezlem,Alagoez, Dilek
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- Evaluation of enantiopure and non-enantiopure Co(III)-salen catalysts and their counter-ion effects in the hydrolytic kinetic resolution (HKR) of racemic epichlorohydrin
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Hydrolytic kinetic resolution (HKR) resolves racemic epoxides using water as the nucleophile and is most often catalyzed by chiral Co(III)-salens. 1 Previous studies have shown that the counter-ion of the Co(III)-salen has a direct effect on rate of HKR; when catalyzed by a 50:50 mix of (R,R)-Co(III)-salen-OH and (R,R)-Co(III)-salen-SbF6, the fastest HKR rates occurred. It has further been shown that the enantioselectivity is primarily associated with the reaction of (R,R)-Co(III)-salen-OH on the activated epoxide. Based on the aforementioned origin of selectivity, a catalyst containing a 50:50 mix of (R,R)-Co(III)-salen-OH and (±)-trans-Co(III)- salen-SbF6 could, in principle, give high activities and enantioselectivities for HKR comparable to a mixed counter-ion system containing both (R,R)-Co(III)-salens. Here, a series of experiments are described that demonstrate that highly selective catalysis is only achieved using 100% enantiopure ligand, and mixtures of (R,R)-Co(III)-salen and (±)-trans- Co(III)-salen yield lower activity and selectivity. Control experiments demonstrate this is due to rapid counter-ion scrambling under reaction conditions, precluding the possibility of effectively co-utilizing enantiopure (expensive) and racemic (inexpensive) catalysts with differing counter-ions. The mechanistic investigations resolving the counter-ion scrambling are consistent with the currently accepted mechanism for catalysis, involving cooperative activity of two Co(III)-salen species that activate the epoxide and water in the reaction.
- Key, Rebecca E.,Venkatasubbaiah, Krishnan,Jones, Christopher W.
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-
- Novel highly active polymer supported chiral Co(III)-salen catalysts for hydrolytic kinetic resolution of epichlorohydrin
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A series of novel polymer supported chiral Co(III)-salen catalysts based on the hydroxyl functionalized gel-type resins, the HEMA resins, has been developed. The terpolymers used as supports for the immobilization of the salen catalysts were derived from the mixtures of 2-hydroxyethyl methacrylate (HEMA), styrene and different divinyl monomers (divinylbenzene, diethylene and triethylene glycol dimethacrylates, 1,4-butanediol and 1,6-hexanediol dimethacrylates). It was found that the novel catalysts show the high catalytic activity in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in the medium of THF, TBME, CH2Cl2 and CH3CN. tert-Butyl methyl ether appeared to be the best medium for performing the resolution. An effect of the nature of the polymer matrices on activity of the supported catalysts was also observed. The activity could be improved by optimization of HEMA concentration in the mixture of the monomers and by selection of the cross-linker. The most active catalyst was prepared based on the HEMA resin derived form 30 mol.% of HEMA and diethylene glycol dimethacrylate as a cross-linker. In the presence of this catalyst the HKR could be performed even at 0.01 mol.% concentration of Co(III) ions. The catalysts could be recycled 10th time at 0.5 mol.% concentration without any additional reactivation. It allowed conducting the HKR of epichlorohydrin within less than 60 min even in the 10th cycle. The catalyst with the highest loading of catalytic centers could be also used successfully for conducting the HKR of epichlorohydrin in solvent-free conditions. Its activity can be compared to the most active heterogeneous catalyst of the HKR described to date.
- Matkiewicz, Katarzyna,Bukowska, Agnieszka,Bukowski, Wiktor
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- Asymmetric hydrolytic kinetic resolution with recyclable macrocyclic CoIII-salen complexes: A practical strategy in the preparation of (R)-mexiletine and (S)-propranolol
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A chiral cobalt(III) complex (1 e) was synthesized by the interaction of cobalt(II) acetate and ferrocenium hexafluorophosphate with a chiral dinuclear macrocyclic salen ligand that was derived from 1R,2R-(-)-1,2-diaminocyclohexane with trigol bis-aldehyde. A variety of epoxides and glycidyl ethers were suitable substrates for the reaction with water in the presence of chiral macrocyclic salen complex 1 e at room temperature to afford chiral epoxides and diols by hydrolytic kinetic resolution (HKR). Excellent yields (47 % with respect to the epoxides, 53 % with respect to the diols) and high enantioselectivity (ee>99 % for the epoxides, up to 96 % for the diols) were achieved in 2.5-16 h. The CoIII macrocyclic salen complex (1 e) maintained its performance on a multigram scale and was expediently recycled a number of times. We further extended our study of chiral epoxides that were synthesized by using HKR to the synthesis of chiral drug molecules (R)-mexiletine and (S)-propranolol.
- Sadhukhan, Arghya,Khan, Noor-Ul H.,Roy, Tamal,Kureshy, Rukhsana I.,Abdi, Sayed H. R.,Bajaj, Hari C.
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supporting information; experimental part
p. 5256 - 5260
(2012/06/01)
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- Poly(styrene) resin-supported cobalt(III) salen cyclic oligomers as active heterogeneous HKR catalysts
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A cross-linked poly(styrene) support functionalized with cobalt(III) salen cyclic oligomers that can be used as a catalyst for the hydrolytic kinetic resolution (HKR) of terminal epoxides is reported. This catalyst is the most active heterogeneous catalyst to date for the HKR of terminal epoxides and can be recycled more than six times with excellent enantioselectivities for the HKR of epichlorohydrin. A 3-fold rate enhancement was observed when conducting the HKR reaction with 6 equivalents of water compared to 0.6 equivalents. We hypothesize that this rate enhancement is due to water sequestration of the diol product from the organic phase, thereby maintaining a high local concentration of epoxides and catalyst in the organic phase. Copyright
- Kahn, Michael G.C.,Stenlid, Joakim H.,Weck, Marcus
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supporting information
p. 3016 - 3024
(2013/01/15)
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- Asymmetric ring opening of terminal epoxides via kinetic resolution catalyzed by chiral (salen)Co mixture
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The highly enantioselective hydrolytic kinetic resolution (HKR) of racemic terminal epoxides by bimetallic chiral (salen)Co and (salen)Co(III)-OAc mixture provides a simple and effective method for the synthesis of enantiomerically enriched terminal epoxides (ee > 99%) and diols. At the equimolar amounts of bimetallic chiral (salen)Co and (salen)Co(II)-OAc, the catalytic activity increases more than two times in comparison with (salen)Co(III)-OAc used alone. The mixed catalytic system can be recycled and reused. No significant loss of catalytic activity was observed after three runs.
- Jiang, Chengjun
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experimental part
p. 691 - 696
(2011/11/30)
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- Shell cross-linked micelle-based nanoreactors for the substrate-selective hydrolytic kinetic resolution of epoxides
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Shell cross-linked micelles (SCMs) containing Co(III)-salen cores were prepared from amphiphilic poly(2-oxazoline) triblock copolymers. The catalytic activity of these nanoreactors for the hydrolytic kinetic resolution of various terminal epoxides was investigated. The SCM catalysts showed high catalytic efficiency and, more significantly, substrate selectivity based on the hydrophobic nature of the epoxide. Moreover, because of the nanoscale particle size and the high stability, the catalyst could be recovered easily by ultrafiltration and reused with high activity for eight cycles.
- Liu, Yu,Wang, Yu,Wang, Yufeng,Lu, Jie,Pinon, Victor,Weck, Marcus
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supporting information; experimental part
p. 14260 - 14263
(2011/11/05)
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- Stereoselective synthesis of (R)-glycidyl butyrate from racemic glycidyl butyrate or epichlorohydrin via hydrolytic kinetic resolution
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The differences of (R)-glycidyl butyrate synthesis via hydrolytic kinetic resolution of glycidyl butyrate directly or regioselective opening epichlorohydrin as key steps by using Jacobsen's hydrotic kinetic resolution are compared. In the view of separation problem, it is hard to get the pure (R)-glycidyl butyrate by kinetic resolution of glycidyl butyrate directly. Via kinetic resolution of epichlorohydrin, treatment with butyric acid in the presence of CrCl3 and then epoxidation with NaOH, the total yield of 38.5% and optical purity of 99% are obtained.
- Jiang, Chengjun,Yan, Jianbo
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scheme or table
p. 242 - 243
(2012/05/19)
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- Asymmetric synthesis of l-carnitine from (R)-3-chloro-1,2-propanediol
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A practical chemical synthesis of l-carnitine (1) has been accomplished from (R)-3-chloro-1,2-propanediol ((R)-4), which is a main by-product originated from (R,R)-Salen Co(III) catalyzed hydrolytic kinetic resolution (HKR) of (±)-epichlorohydrin. (R)-4 was utilized as a chiral starting material to prepare the key intermediate cyclic sulfite ((R)-5). The new synthetic approach demonstrated an efficient utilization of organic by-product for the asymmetric synthesis of bioactive compounds.
- Li, Xu Qin,Yang, Yun Xu,Wang, Wei Li,Hu, Bin,Xue, Hui Min,Zhang, Tian Yi,Zhang, Xue Tao
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scheme or table
p. 765 - 767
(2012/01/03)
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- Self-assembly approach toward chiral bimetallic catalysts: Bis-urea-functionalized (Salen)cobalt complexes for the hydrolytic kinetic resolution of epoxides
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A series of novel bis-urea-functionalized (salen)Co complexes has been developed. The complexes were designed to form self-assembled structures in solution through intermolecular urea-urea hydrogen-bonding interactions. These bis-urea (salen)Co catalysts resulted in rate acceleration (up to 13atimes) in the hydrolytic kinetic resolution (HKR) of rac-epichlorohydrin in THF by facilitating cooperative activation, compared to the monomeric catalyst. In addition, one of the bis-urea (salen)CoIII catalyst efficiently resolves various terminal epoxides even under solvent-free conditions by requiring much shorter reaction time at low catalyst loading (0.03-0.05amol %). A series of kinetic/mechanistic studies demonstrated that the self-association of two (salen)Co units through urea-urea hydrogen bonds was responsible for the observed rate acceleration. The self-assembly study with the bis-urea (salen)Co by FTIR spectroscopy and with the corresponding (salen)Ni complex by 1HaNMR spectroscopy showed that intermolecular hydrogen-bonding interactions exist between the bis-urea scaffolds in THF. This result demonstrates that self-assembly approach by using non-covalent interactions can be an alternative and useful strategy toward the efficient HKR catalysis.
- Park, Jongwoo,Lang, Kai,Abboud, Khalil A.,Hong, Sukwon
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supporting information; experimental part
p. 2236 - 2245
(2011/03/22)
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- Practical and efficient utilisation of (R)-3-chloro-1,2-propanediol in synthesis of L-carnitine
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As a by-product originating from Salen Co(III) catalysed hydrolytic kinetic resolution (HKR) of (±)-epichlorohydrin in the manufacturing procedure of L-Carnitine, (R)-3-chloro-1,2-propanediol was utilised as a starting chiral material to prepare via key nitrile intermediates and by a final hydrolysis L-Carnitine. The new synthetic approach demonstrated an efficient utilisation of the by-product.
- Yang, Yunxu,Wang, Weili,Wumaier, Aikeremu,Sheng, Ruilong,Zhang, Xuetao,Zhang, Tianyi
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scheme or table
p. 371 - 372
(2011/10/09)
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- Cooperative activation in the hydrolytic kinetic resolution of epoxides by a bis-cobalt(III)salen-calix[4]arene hybrid
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A chiral, bimetallic cobalt(III)salen-calix[4]arene hybrid structure was prepared and tested in the hydrolytic kinetic resolution (HKR) of racemic epoxides. Kinetic studies have revealed that the two catalytic units on the upper rim of the calixarene scaffold are able to activate the reactants in a cooperative and primarily intramolecular mode. High enantioselective behaviour was observed and besides, a higher stability was found for the bimetallic catalyst as compared to a monometallic reference complex.
- Wezenberg, Sander J.,Kleij, Arjan W.
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supporting information; experimental part
p. 85 - 91
(2010/06/21)
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- Factors influencing recyclability of Co(III)-salen catalysts in the hydrolytic kinetic resolution of epichlorohydrin
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The recyclability of Co(III)-salen catalysts, where salen is defined by (R,R)-N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediamine, for the hydrolytic kinetic resolution (HKR) of racemic epichlorohydrin is a strong function of the counterion of the Co(III)-salen catalyst. The nature of the counterion determines whether the HKR reaction follows primarily a bimetallic or monometallic reaction path, which significantly affects catalyst recyclability. For example, Co(III)-salen initially containing the nucleophilic Cl- counterion catalyzes the HKR of epichlorohydrin according to a bimetallic reaction path but loses activity upon recycle, as Cl- is replaced with OH- during the reaction. In contrast, a Co(III)-salen catalyst containing non-nucleophilic SbF6- counterion catalyzes the reaction according to a monometallic reaction path and is quite stable during multiple recycles, albeit at a low rate with less selectivity. A mixed catalyst system with Co(III)-salen initially containing Cl- to which Co(III)-salen with SbF6- is later added demonstrates high activity and high stability to recycling. Additional experiments with Co(III)-salen initially containing the acetate counterion reveal a progressive decline in activity with multiple recycles even after regeneration with acetic acid between runs, suggesting a destructive role of the regeneration process.
- Jain, Surbhi,Venkatasubbaiah, Krishnan,Jones, Christopher W.,Davis, Robert J.
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experimental part
p. 8 - 15
(2010/05/01)
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- Synthesis of carbon monolith with bimodal meso/macroscopic pore structure and its application in asymmetric catalysis
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Carbon monolith with bimodal meso/macroporous pore structures was synthesized by the nanocasting method, using corresponding monolith silica as templates. The pore system of this material was characterized by instrumental analysis. The adjacent macropores are interconnected through uniform-sized windows, and the walls of macrospheres consist of mesostructured pores. Chiral Co(III)-(BF3) salen immobilized on a meso/macroporous carbon monolith can be applied as an effective heterogeneous catalyst for an asymmetric reaction such as a hydrolytic kinetic reaction of terminal epoxides. The catalysts were prepared with different loading amounts of aluminium chloride to anchor the active salen complex, and the catalytic activity increased with increasing amount of aluminum chloride on the surfaces, showing up to 99 ee% of the product epichlorohydrin (ECH).
- Kim, Yong-Suk,Guo, Xiao-Feng,Kim, Geon-Joong
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experimental part
p. 91 - 99
(2010/11/17)
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- Highly efficient recyclable CoIII-salen complexes in the catalyzed asymmetric aminolytic kinetic resolution of aryloxy/terminal epoxides for the simultaneous production of N-protected 1,2-amino alcohols and the corresponding epoxides in high op
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Chiral CoIII-salen complexes 1-6 bearing different substituents at the 3,3′- and 5,5′-positions of the salen unit, namely H, tBu, morpholmomethyl, and piperidinomethyl, have been synthesized. These complexes were used as catalysts in an environ
- Kureshy, Rukhsana I.,Prathap, K. Jeya,Agrawal, Santosh,Kumar, Manish,Khan, Noor-Ul H.,Abdi, Sayed H. R.,Bajaj, Hari C.
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supporting information; experimental part
p. 2863 - 2871
(2009/09/29)
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- Highly active new chiral Co(iii) salen catalysts immobilized by electrostatic interaction with sulfonic acid linkages on ordered mesoporous SBA-16 silica
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New chiral cobalt(iii) salen complexes immobilized via HO 3S-linkers on ordered SBA-16 by electrostatic interactions showed very high activity in enantioselective ring-opening reactions of racemic epoxides.
- Kim, Yong-Suk,Guo, Xiao-Feng,Kim, Geon-Joong
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scheme or table
p. 4296 - 4298
(2011/03/19)
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- Hydrolytic kinetic resolution of terminal epoxides catalyzed by novel bimetallic chiral Co (salen) complexes
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Novel bimetallic chiral Co (salen) complexes bearing transition-metal salts have been synthesized. The easily prepared complexes exhibited very high catalytic reactivity and enantioselectivity in hydrolytic kinetic resolution (HKR) of racemic terminal epoxides and consequently provided enantiomerically enriched epoxides (up to 99% ee). Copyright Taylor & Francis Group, LLC.
- Kawthekar, Rahul B.,Kim, Geon-Joong
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p. 1236 - 1248
(2008/09/18)
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- NEW CHIRAL SALEN CATALYSTS AND METHODS FOR THE PREPARATION OF CHIRAL COMPOUNDS FROM RACEMIC EPOXIDES BY USING THEM
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The present invention relates to new chiral salen catalysts and the preparation method of chiral compounds from racemic epoxides using the same. More specifically, it relates to new chiral salen catalysts that have high catalytic activity due to new molecular structures and have no or little racemization of the generated target chiral compounds even after the reaction is completed and can be also reused without catalyst regeneration treatment, and its economical preparation method to mass manufacture chiral compounds of high optical purity, which can be used as raw materials for chiral food additives, chiral drugs, or chiral crop protection agents, etc., using the new chiral salen catalysts.
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Page/Page column 41
(2009/01/24)
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- Formation of enantiopure 5-substituted oxazolidinones through enzyme-catalysed kinetic resolution of epoxides
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(Chemical Equation Presented) Halohydrin dehalogenase from Agrobacterium radiobacter catalyzed the enantioselective ring opening of terminal epoxides with cyanate as a nucleophile, yielding 5-substituted oxazolidinones in high yields and with high enantiopurity (69-98% ee). This is the first example of the biocatalytic conversion of a range of epoxides to the corresponding oxazolidinones.
- Elenkov, Maja Majeric,Tang, Lixia,Meetsma, Auke,Hauer, Bernhard,Janssen, Dick B.
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supporting information; experimental part
p. 2417 - 2420
(2009/05/26)
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- Enhanced cooperativity in hydrolytic kinetic resolution of epoxides using poly(styrene) resin-supported dendronized co-(salen) catalysts
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Excellent enantioselectivities and isolated yields have been achieved for the hydrolytic kinetic resolution of epoxides using a resin-supported dendronized R,R-(salen)Co catalyst with catalyst loadings as low as 0.04 mol%, the lowest metal loadings of any heterogeneous resin-supported (salen)Co catalyst reported to date. In addition, the supported catalysts can be recycled and reused with comparable enantioselectivities. It is hypothesized that the high catalytic activity can be attributed to the flexible linker and the dendronized framework supporting the (salen)Co moieties on the resin thereby promoting cooperativity between two metal centers. This work opens up new opportunities for the design of highly active resin-supported catalysts that catalyze transformations through a bimetallic pathway.
- Goyal, Poorva,Zheng, Xiaolai,Weck, Marcus
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experimental part
p. 1816 - 1822
(2009/08/07)
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- Enhanced cooperativity through design: Pendant CoIII-salen polymer brush catalysts for the hydrolytic kinetic resolution of epichlorohydrin (salen=N,N'-bis(salicylidene)ethylenediamine dianion)
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The CoIII-salen-catalyzed (salen = N,N'-bis(salicylidene) ethylenediamine dianion) hydrolytic kinetic resolution (HKR) of racemic epoxides has emerged as a highly attractive and efficient method of synthesizing chiral C3 building blocks for intermediates in larger, more complex molecules. HKR reaction rates have displayed a second order dependency on the concentration of active sites, and thus researchers have proposed a bimetallic transition state for the HKR mechanism. Here we report the utilization of pendant CoIII-salen catalysts on silica supported polymer brushes as a catalyst for the HKR of epichlorohydrin. The novel polymer brush architecture provided a unique framework for promoting site-site interactions as required in the proposed bimetallic transition state of the HKR mechanism. Furthermore, the polymer brushes mimic the environment of soluble polymer-based catalysts, whereas the silica support permitted facile recovery and reuse of the catalyst. The polymer brush catalyst displayed increased activities over the soluble Jacobsen Co-salen catalyst and was observed to retain its high enantioselectivities (> 99%) after each of five reactions despite decreasing activities. Analysis indicated decomposition of the salen ligand as an underlying cause of catalyst deactivation.
- Gill, Christopher S.,Venkatasubbaiah, Krishnan,Phan, Nam T. S.,Weck, Marcus,Jones, Christopher W.
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experimental part
p. 7306 - 7313
(2009/08/10)
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- 4(2)-Methoxyphenyl glycerol ethers in the synthesis of nonracemic di-O,O-acylglycerols
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Effective methods for the synthesis of nonracemic 4-and 2-methoxyphenyl glycerol ethers from nonracemic 3-chloropropanediols and by direct resolution of the racemate, respectively, were developed. Some existing discrepancies related to the to chiroptical properties of their derivatives were eliminated. Both ethers were used to synthesize nonracemic 3-O-aryloxy-1,2-di-O',O'-palmitoyl glycerols.
- Bredikhina,Novikova,Efremov,Sharafutdinova,Bredikhin
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experimental part
p. 2320 - 2323
(2010/02/15)
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- Asymmetric reactions on chiral catalysts entrapped within a mesoporous cage
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The encapsulation of homogeneous chiral catalysts, e.g. Co(Salen) and Ru-TsDPEN, in the mesoporous cage of SBA-16 is demonstrated; the encapsulated catalysts show performance as good as that of the homogeneous catalysts, and can be recycled for more than 10 times without significant loss of catalytic performance. The Royal Society of Chemistry.
- Yang, Hengquan,Li, Jun,Yang, Jie,Liu, Zhimin,Yang, Qihua,Li, Can
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p. 1086 - 1088
(2008/01/03)
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- Continuous enantioselective kinetic resolution of terminal epoxides using immobilized chiral cobalt-salen complexes
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Jacobsen's cobalt-salen complex was covalently immobilized on polymer carriers that are part of different technical setups (polymer powder, composite Raschig rings, PASSflow microreactors) and employed for the enantioselective ring opening of terminal epoxides with water and phenols. The polymer-supported catalysts showed good activity and stereoselectivity and could be used repeatedly after a simple reactivation protocol in both batch as well as continuous-flow modes. Georg Thieme Verlag Stuttgart.
- Solodenko, Wladimir,Jas, Gerhard,Kunz, Ulrich,Kirschning, Andreas
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p. 583 - 589
(2007/12/25)
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- Asymmetric ring-opening of epoxides on chiral Co(Salen) catalyst synthesized in SBA-16 through the "ship in a bottle" strategy
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Chiral Co(Salen) complex was synthesized in the mesoporous cage of SBA-16 through the "ship in a bottle" method. The pore entrance size of SBA-16 was precisely tailored by varying the autoclaving time and silylation with phenyltrimethoxysilane to trap Co(Salen) complex in the cage of SBA-16. Chiral Co(Salen) trapped in SBA-16 shows enantioselectivity (up to 87-96% ee) as high as that of the homogeneous catalyst for the asymmetric ring opening of terminal epoxides and can be recycled at least 10 times with no apparent loss of activity. The activity for the catalyst trapped inside SBA-16 can be significantly increased when the surface is modified with organic groups. This work extends the "ship in a bottle" synthesis from microporous materials to mesoporous cage-like materials and develops an effective strategy to trap metal complex catalyst with large molecular size into the nanopores or cavities of mesoporous materials.
- Yang, Hengquan,Zhang, Lei,Su, Weiguang,Yang, Qihua,Li, Can
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p. 204 - 212
(2007/10/03)
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- Formal synthesis of herbarumin III
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An enantioselective synthesis of herbarumin III is described employing Jacobsen's hydrolytic kinetic resolution and Sharpless asymmetric dihydroxylation as the key steps.
- Gupta, Priti,Kumar, Pradeep
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p. 1688 - 1692
(2008/02/11)
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- Ring-expanding olefin metathesis: A route to highly active unsymmetrical macrocyclic oligomeric co-salen catalysts for the hydrolytic kinetic resolution of epoxides
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In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features - (i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the support - that facilitate rapid and efficient catalysis when a bimetallic transition state is required.
- Zheng, Xiaolai,Jones, Christopher W.,Weck, Marcus
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p. 1105 - 1112
(2007/10/03)
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- Modular approach for the development of supported, monofunctionalized, salen catalysts
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We report a modular approach toward polymer-supported, metalated, salen catalysts. This strategy is based on the synthesis of monofunctionalized Mn- and Co-salen complexes attached to a norbornene monomer via a stable phenylene-acetylene linker. The resulting functionalized monomers can be polymerized in a controlled fashion using ring-opening metathesis polymerization. This polymerization method allows for the synthesis of copolymers, resulting in an unprecedented control over the catalyst density and catalytic-site isolation. The obtained polymeric manganese and cobalt complexes were successfully used as supported catalysts for the asymmetric epoxidation of olefins and the hydrolytic kinetic resolution of epoxides. All polymeric catalysts showed outstanding catalytic activities and selectivities comparable to the original catalysts reported by Jacobsen. Moreover, the copolymer-supported catalysts are more active and selective than their homopolymer analogues, providing further proof that catalyst density and site isolation are key toward highly active and selective supported salen catalysts.
- Holbach, Michael,Weck, Marcus
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p. 1825 - 1836
(2007/10/03)
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- Poly(styrene)-supported co-salen complexes as efficient recyclable catalysts for the hydrolytic kinetic resolution of epichlorohydrin
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Here we describe an unprecedented synthetic approach to poly-(styrene)-supported chiral salen ligands by the free radical polymerization of an unsymmetrical styryl-substituted salen monomer (H2salen = bis(salicylidene)ethylenediamine). The new method allows for the attachment of salen moieties to the polymer main chain in a flexible, pendant fashion, avoiding grafting reactions that often introduce ill-defined species on the polymers. Moreover, the loading of the salen is controlled by the copolymerization of the styryl-substituted salen monomer with styrene in different ratios. The polymeric salen ligands are metallated with cobalt(II) acetate to afford the corresponding supported Co-salen complexes, which are used in the hydrolytic kinetic resolution of racemic epichlorohydrin, exhibiting high reactivity and enantioselectivity. Remarkably, the copolymer-supported Co-salen complexes showed a better catalytic performance (>99% ee, 54 % conversion, one hour) in comparison to the homopolymeric analogues and the small molecule Co-salen complex. The soluble poly(styrene)-supported catalysts were recovered by precipitation after the catalytic reactions and were recycled three times to afford almost identical enantiomeric excesses as the first run, with slightly reduced reaction rates.
- Zheng, Xiaolai,Jones, Christopher W.,Weck, Marcus
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p. 576 - 583
(2008/09/20)
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- Hydrolytic kinetic resolution of epoxides catalyzed by chromium(III)-endo, endo-2,5-diaminonorbornane-salen [Cr(III)-DIANANE-salen] complexes. Improved activity, low catalyst loading
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The hydrolytic kinetic resolution (HKR) of terminal epoxides, using chiral chromium(III)-salen catalysts based on DIANANE (endo,endo-2,5-diaminonorbornane) , was studied. A broad substrate scope was found for the chromium(III)-DIANANE catalysts, and very low loadings (down to 0.05 mol%) were needed to achieve high enantiomeric purities of both the remaining epoxides and the product diols (up to >99% ee). Besides monosubstituted epoxides, 2-methyl-2-n-pentyloxirane, which is an example for 2,2-disubstituted epoxides, could be ring-opened in an asymmetric fashion with water in the presence of an electronically tuned chromium-(III)-DIANANE complex.
- Berkessel, Albrecht,Ertuerk, Erkan
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p. 2619 - 2625
(2007/10/03)
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- Synthesis of optically pure terminal epoxide and 1,2-diol via hydrolytic kinetic resolution catalyzed by new heterometallic salen complexes
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The inactive chiral (salen)Co complex is easily activated by InCl 3 and TlCl3 Lewis acids by forming heterometallic salen complexes. These complexes show very high catalytic activity for the synthesis of enantiomerically enriched terminal epoxides (>99% ee) and 1,2-diols simultaneously via hydrolytic kinetic resolution. Strong synergistic effects of different Lewis acids, Co-In and Co-Tl, were exhibited in the catalytic process. The system described is very simple and efficient. Copyright Taylor & Francis Group, LLC.
- Thakur, Santosh Singh,Chen, Shu-Wei,Li, Wenji,Shin, Chang-Kyo,Koo, Yoon-Mo,Kim, Geon-Joong
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p. 2371 - 2383
(2007/10/03)
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