- PQXdpap: Helical Poly(quinoxaline-2,3-diyl)s Bearing 4-(Dipropylamino)pyridin-3-yl Pendants as Chirality-Switchable Nucleophilic Catalysts for the Kinetic Resolution of Secondary Alcohols
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Helically chiral poly(quinoxaline-2,3-diyl)s bearing 4-(dipropylamino)pyridin-3-yl pendants at the 5-position of the quinoxaline ring (PQXdpap) exhibited high catalytic activities and moderate to high selectivities (up to s = 87) in the acylative kinetic resolution of secondary alcohols. The solvent-dependent helical chirality switching of PQXdpap between pure toluene and a 1:1 mixture of toluene and 1,1,2-trichloroethane enabled the preparation of either compound of a pair of enantiomerically pure alcohols (>99% ee) from a single catalyst.
- Murakami, Ryo,Suginome, Michinori,Yamamoto, Takeshi
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supporting information
p. 8711 - 8716
(2021/11/24)
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- Rh-catalyzed asymmetric hydrogenation of α-aryl-β-alkylvinyl esters with chiral ferrocenylphosphine-phosphoramidite ligand
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An enantioselective Rh-catalyzed hydrogenation of E/Z mixtures of trisubstituted vinyl esters has been disclosed. With a combination of [Rh(COD)2]BF4 and a structurally fine-tuning chiral ferrocenylphosphine-phosphoramidite ligand as the catalyst, a variety of E/Z mixtures of α-aryl-β-alkylvinyl esters have been successfully hydrogenated in high yields and with good to high enantioselectivities (up to 96% ee). The presence of a small amount of tBuOH proved to be beneficial to improve the hydrogenation outcome.
- Dong, Chao,Liu, Dao-Sheng,Zhang, Lei,Hu, Xiang-Ping
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- Evaluation of gem-Diacetates as Alternative Reagents for Enzymatic Regio-and Stereoselective Acylation of Alcohols
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Geminal diacetates have been used as sustainable acyl donors for enzymatic acylation of chiral and nonchiral alcohols. Especially, it was revealed that geminal diacetates showed higher reactivity than vinyl acetate for hydrolases that are sensitive to acetaldehyde. Under optimized conditions for enzymatic acylation, several synthetically relevant saturated and unsaturated acetates of various primary alcohols were obtained in very high yields up to 98% without E/Z isomerization of the double bond. Subsequently, the acyl donor was recreated from the resulting aldehyde and reused constantly in acylation. Therefore, the developed process is characterized by high atomic efficiency. Moreover, it was shown that acylation using geminal diacetates resulted in remarkable regioselectivity by discriminating among the primary and secondary hydroxyl groups in 1-phenyl-1,3-propanediol providing exclusively 3-acetoxy-1-phenyl-propan-1-ol in good yield. Further, enzymatic kinetic resolution (EKR) and chemoenzymatic dynamic kinetic resolution (DKR) protocols were developed using geminal diacetate as an acylating agent, resulting in chiral acetates in high yields up to 94% with enantiomeric excesses exceeding 99%.
- Koszelewski, Dominik,Brodzka, Anna,Madej, Arleta,Trzepizur, Damian,Ostaszewski, Ryszard
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p. 6331 - 6342
(2021/05/06)
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- Synthesis of task-specific imidazolium ionic liquid as an efficient catalyst in acetylation of alcohols, phenols, and amines
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Herein, we report the synthesis of task-specific amino-functionalized imidazolium ionic liquid, acetate1-(2-tert-butoxycarbonylamino-ethyl)-3-methyl-3H-imidazol-1-ium; (Boc-NH-EMIM.OAc), as an efficient catalyst for the acetylation of alcohols, phenols, and amines in the presence of acetic anhydride (acetylating reagent). Remarkably, acetic anhydride in the presence of 10?molpercent of catalyst (Boc-NH-EMIM.OAc) under solvent-free conditions showed excellent acetylation activity in shorter duration of time. On the basis of this, a general procedure for acetylation of alcohols, phenols, and amines has been developed. The ionic liquid (Boc-NH-EMIM.OAc) can be readily recovered and reused successfully up to four consecutive cycles without any significant loss of its catalytic activity. We have been able to show that this acetylating method has many advantages. It gives high yields, takes shorter time, and develops the possibility of benign environmental-friendly process.
- Chaubey, Snehkrishn A.,Mishra, Roli
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p. 3259 - 3268
(2020/04/17)
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- Activity and specificity studies of the new thermostable esterase EstDZ2
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In this paper, we study the activity and specificity of EstDZ2, a new thermostable carboxyl esterase of unknown function, which was isolated from a metagenome library from a Russian hot spring. The biocatalytic reaction employing EstDZ2 proved to be an efficient method for the hydrolysis of aryl p-, o- or m-substituted esters of butyric acid and esters of secondary alcohols. Docking studies revealed structural features of the enzyme that led to activity differences among the different substrates.
- Myrtollari, Kamela,Katsoulakis, Nikolaos,Zarafeta, Dimitra,Pavlidis, Ioannis V.,Skretas, Georgios,Smonou, Ioulia
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- Highly Focused Library-Based Engineering of Candida antarctica Lipase B with (S)-Selectivity Towards sec-Alcohols
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Candida antarctica lipase B (CALB) is one of the most extensively used biocatalysts in both academia and industry and exhibits remarkable (R)-enantioselectivity for various chiral sec-alcohols. Considering the significance of tailor-made stereoselectivity in organic synthesis, a discovery of enantiocomplementary lipase mutants with high (R)- and (S)-selectivity is valuable and highly desired. Herein, we report a highly efficient directed evolution strategy, using only 4 representative amino acids, namely, alanine (A), leucine (L), lysine (K), tryptophan (W) at each mutated site to create an extremely small library of CALB variants requiring notably less screening. The obtained best mutant with three mutations W104V/A281L/A282K displayed highly reversed (S)-selectivity towards a series of sec-alcohol with E values up to 115 (conv. 50%, ee 94%). Compared with the previously reported (S)-selective CALB variant, W104A, a single mutation provided less selectivity, while the synergistic effects of three mutations in the best variant endow better (S)-selectivity and a broader substrate scope than the W104A variant. Structural analysis and molecular dynamics simulation unveiled the source of reversed enantioselectivity. (Figure presented.).
- Cen, Yixin,Li, Danyang,Xu, Jian,Wu, Qiongsi,Wu, Qi,Lin, Xianfu
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p. 126 - 134
(2018/12/05)
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- LipG9-mediated enzymatic kinetic resolution of racemates: Expanding the substrate-scope for a metagenomic lipase
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Enzymes are the main biocatalysts of biological systems and nowadays they play an important role in asymmetric organic synthesis. Microorganisms are the main source for enzymes, however, just a very small portion of them are culturable at lab conditions and, as an alternative, metagenomics approaches allow new enzymes to be accessed from so-called “non-culturable” microorganisms. Several classes of metagenomic enzymes have been described in literature. Nevertheless, studies about their potential for asymmetric biotransformation are underexploited. Therefore, we present our recent efforts to establish the substrate-scope of LipG9, a metagenomic lipase, in enzymatic kinetic resolution (EKR) of chiral substances. LipG9 was previously isolated, immobilized and successfully applied in EKR of aliphatic alcohols. In this study, a series of resolvable chiral substances were assayed with LipG9, and secondary benzyl alcohols/esters were preferentially resolved in a much superior enantioselectivity (E > 200) than those described for aliphatic alcohols (E from 4 to 63). In an opposite way, Im-LipG9 did not present activity for tertiary alcohols, amines and lactones. When compared to commercial lipases, Im-LipG9 enantioselectivity was superior to Candida rugosa lipase and equivalent to Candida antarctica lipase B. Thus, the chemo and enantioselectivity of LipG9 in EKR reactions were identified and its potential for asymmetric synthetic approaches was demonstrated.
- Thomas, Juliana Christina,Alnoch, Robson Carlos,Costa, Allen Carolina dos Santos,Bandeira, Pamela Taisline,Burich, Martha Daniela,Campos, Suelem Kluconski,de Oliveira, Alfredo Ricardo Marques,de Souza, Emanuel Maltempi,Pedrosa, Fabio de Oliveira,Krieger, Nadia,Piovan, Leandro
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- Decarboxylative Acetoxylation of Aliphatic Carboxylic Acids
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Organic molecules bearing acetoxy moieties are important functionalities in natural products, drugs, and agricultural chemicals. Synthesis of such molecules via transition metal-catalyzed C-O bond formation can be achieved in the presence of a carefully chosen directing group to alleviate the challenges associated with regioselectivity. An alternative approach is to use ubiquitous carboxylic acids as starting materials and perform a decarboxylative coupling. Herein, we report conditions for a photocatalytic decarboxylative C-O bond formation reaction that provides rapid and facile access to the corresponding acetoxylated products. Mechanistic investigations suggest that the reaction operates via oxidation of the carboxylate followed by rapid decarboxylation and oxidation by Cu(OAc)2
- Senaweera, Sameera,Cartwright, Kaitie C.,Tunge, Jon A.
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p. 12553 - 12561
(2019/10/14)
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- Selective benzylic C–H monooxygenation mediated by iodine oxides
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A method for the selective monooxdiation of secondary benzylic C–H bonds is described using an N-oxyl catalyst and a hypervalent iodine species as a terminal oxidant. Combinations of ammonium iodate and catalytic N-hydroxyphthalimide (NHPI) were shown to be effective in the selective oxidation of n-butylbenzene directly to 1-phenylbutyl acetate in high yield (86%). This method shows moderate substrate tolerance in the oxygenation of substrates containing secondary benzylic C–H bonds, yielding the corresponding benzylic acetates in good to moderate yield. Tertiary benzylic C–H bonds were shown to be unreactive under similar conditions, despite the weaker C–H bond. A preliminary mechanistic analysis suggests that this NHPI-iodate system is functioning by a radical-based mechanism where iodine generated in situ captures formed benzylic radicals. The benzylic iodide intermediate then solvolyzes to yield the product ester.
- LaMartina, Kelsey B.,Kuck, Haley K.,Oglesbee, Linda S.,Al-Odaini, Asma,Boaz, Nicholas C.
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supporting information
p. 602 - 609
(2019/04/17)
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- A designer natural deep eutectic solvent to recycle the cofactor in alcohol dehydrogenase-catalysed processes
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Deep eutectic solvents (DESs) nowadays represent a sustainable alternative to traditional organic solvents in (bio)transformations. Herein, the use of a solvent composed of an aqueous buffer and choline chloride:glucose (1.5:1 mol/mol) is proposed, a natural DES (NADES) serving as both a cosolvent and efficient system to recycle the nicotinamide cofactor. Thus, glucose from the NADES served as a co-substrate required for several alcohol dehydrogenases to reduce different prochiral ketones, and also helped to solubilise the organic compounds to develop effective biotransformations at higher substrate concentrations.
- Mourelle-Insua, ángela,Lavandera, Iván,Gotor-Fernández, Vicente
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supporting information
p. 2946 - 2951
(2019/06/18)
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- Base-catalyzed selective esterification of alcohols with unactivated esters
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A practical and efficient base-catalyzed esterification has been developed for the facile synthesis of a broad range of esters from simple alcohols with unactivated tert-butyl esters. This protocol could be conducted at mild conditions, providing esters in high to excellent yields with good functional tolerance. Mechanistic studies provided evidence of an exchange of the tert-butyl alkoxide metal with the alcohol, producing a new alkoxide to participate in the transesterification reaction.
- Zhang, Chunyan,Zhang, Guoying,Luo, Shizhong,Wang, Chunfu,Li, Huiping
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supporting information
p. 8467 - 8471
(2018/12/01)
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- Pore Environment Control and Enhanced Performance of Enzymes Infiltrated in Covalent Organic Frameworks
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In the drive toward green and sustainable methodologies for chemicals manufacturing, biocatalysts are predicted to have much to offer in the years to come. That being said, their practical applications are often hampered by a lack of long-term operational stability, limited operating range, and a low recyclability for the enzymes utilized. Herein, we show how covalent organic frameworks (COFs) possess all the necessary requirements needed to serve as ideal host materials for enzymes. The resultant biocomposites of this study have shown the ability boost the stability and robustness of the enzyme in question, namely lipase PS, while also displaying activities far outperforming the free enzyme and biocomposites made from other types of porous materials, such as mesoporous silica and metal-organic frameworks, exemplified in the kinetic resolution of the alcohol assays performed. The ability to easily tune the pore environment of a COF using monomers bearing specific functional groups can improve its compatibility with a given enzyme. As a result, the orientation of the enzyme active site can be modulated through designed interactions between both components, thus improving the enzymatic activity of the biocomposites. Moreover, in comparison with their amorphous analogues, the well-defined COF pore channels not only make the accommodated enzymes more accessible to the reagents but also serve as stronger shields to safeguard the enzymes from deactivation, as evidenced by superior activities and tolerance to harsh environments. The amenability of COFs, along with our increasing understanding of the design rules for stabilizing enzymes in an accessible fashion, gives great promise for providing "off the shelf" biocatalysts for synthetic transformations.
- Sun, Qi,Fu, Chung-Wei,Aguila, Briana,Perman, Jason,Wang, Sai,Huang, Hsi-Ya,Xiao, Feng-Shou,Ma, Shengqian
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p. 984 - 992
(2018/02/07)
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- Asymmetric Chemoenzymatic Reductive Acylation of Ketones by a Combined Iron-Catalyzed Hydrogenation–Racemization and Enzymatic Resolution Cascade
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A general and practical process for the conversion of prochiral ketones into the corresponding chiral acetates has been realized. An iron carbonyl complex is reported to catalyze the hydrogenation–dehydrogenation–hydrogenation of prochiral ketones. By merging the iron-catalyzed redox reactions with enantioselective enzymatic acylations a wide range of benzylic, aliphatic and (hetero)aromatic ketones, as well as diketones, were reductively acylated. The corresponding products were isolated with high yields and enantioselectivities. The use of an iron catalyst together with molecular hydrogen as the hydrogen donor and readily available ethyl acetate as acyl donor make this cascade process highly interesting in terms of both economic value and environmental credentials.
- El-Sepelgy, Osama,Brzozowska, Aleksandra,Rueping, Magnus
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p. 1664 - 1668
(2017/04/27)
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- Merging Iron Catalysis and Biocatalysis—Iron Carbonyl Complexes as Efficient Hydrogen Autotransfer Catalysts in Dynamic Kinetic Resolutions
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A dual catalytic iron/lipase system has been developed and applied in the dynamic kinetic resolution of benzylic and aliphatic secondary alcohols. A detailed study of the Kn?lker-type iron complexes demonstrated the hydrogen autotransfer of alcohols to proceed under mild reaction conditions and allowed the combination with the enzymatic resolution. Different racemic alcohols were efficiently converted to chiral acetates in good yields and with excellent enantioselectivities.
- El-Sepelgy, Osama,Alandini, Nurtalya,Rueping, Magnus
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supporting information
p. 13602 - 13605
(2016/10/21)
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- Mechanochemical Enzymatic Kinetic Resolution of Secondary Alcohols under Ball-Milling Conditions
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Mechanosynthesis is a valuable technique, offering attractive alternatives for the preparation of organic, inorganic, and organometallic products. Surprisingly, mechanochemical enzymatic transformations have only scarcely been studied until now. Here, we demonstrate the use of lipase B from Candida antarctica (CALB) in acylative kinetic resolutions of secondary alcohols in mixer and planetary mills. Despite the mechanical stress caused by the high-speed ball milling, the biocatalyst proved highly effective, stable, and, in part, recyclable under the applied mechanochemical conditions. Best milling practice: The compatibility of lipase B from Candida antarctica (CALB) in acylative kinetic resolutions of secondary alcohols in mixer and planetary mills has been explored. Despite the mechanical stress caused by the high-speed ball milling, the biocatalyst was found to be very effective, stable, and, in part, recyclable under the applied mechanochemical conditions.
- Hernández, José G.,Frings, Marcus,Bolm, Carsten
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p. 1769 - 1772
(2016/06/01)
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- Improved enantioselectivity of thermostable esterase ST0071 from archaeon Sulfolobus tokodaii by site-saturation mutagenesis
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An archaeon GGG(A)X-type esterase (ST0071) can catalyze the hydrolysis of various acetates of secondary alcohols, but shows low enantioselectivity. Using structure-guided site-saturation mutagenesis, we successfully identified a G274W variant that has excellent selectivity compared with that of wild-type ST0071.
- Ozaki, Masanaru,Kawakami, Norifumi,Ohta, Hiromichi,Miyamoto, Kenji
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p. 249 - 252
(2016/12/16)
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- Selectivity Enhancement in Dynamic Kinetic Resolution of Secondary Alcohols through Adjusting the Micro-Environment of Metal Complex Confined in Nanochannels: A Promising Strategy for Tandem Reactions
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(Figure Presented). Dichloro(η6-p-cymene) (1-butyl-3-cyclohexyl-imidazolin-2-ylidene) ruthenium(II) (RuL) was synthesized and confirmed. Five heterogeneous catalysts with similar ruthenium cores were prepared by chemical immobilization method using various silica-based supports, including mesoporous silica SBA-15 of different pore sizes (Ru/Si-9, Ru/Si-8, and Ru/Si-7), nonporous silica particles (Ru/SiO2), and surface trimethylsilylated SBA-15 (Ru/SiMe). The dynamic kinetic resolution (DKR) of 1-phenylethanol, which includes metal-enzyme bicatalytic racemization in tandem with stereoselective acylation, gave product in 99% yield and 0% ee with homogeneous catalyst RuL, whereas the heterogeneous Ru/Si-8 exhibited high catalytic activity and enantioselectivity (up to 96% yield and 99% ee). The racemization and acylation abilities of different catalysts were analyzed. The influences of pore size and surface properties for heterogeneous catalysts were investigated, and the nanocage effect was found to be the key factor in stereoselectivity. The catalyst Ru/Si-8 performed well in reactions with various substrates and can be reused for at least seven times.
- Cao, Hui,Zhu, Xiao-Han,Wang, Dong,Sun, Zhenkun,Deng, Yonghui,Hou, Xiu-Feng,Zhao, Dongyuan
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- Ligand effect in racemization and dynamic kinetic resolution of alcohols: Mechanism on cymene ruthenium complexes
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A family of ruthenium complexes with different ligands was utilized in racemization of (R)-1-phenylethanol to investigate the potential influence of the ligands coordinated to the ruthenium center. Kinetic experiments showed that 16-electron cymene ruthenium complex with two chloro-bridge bonds and 18-electron ones with easily dissociative ligands are highly active for catalytic racemization of alcohols. Possible racemization mechanism for cymene ruthenium complexes was then proposed. Computational analysis of dissociation energy barrier, NBO analysis and reaction potential energy surface suggest that ligand-dissociation process is the vital step of the racemization catalyzed by cymene ruthenium complexes. Thereafter, these complexes were applied in the DKR of secondary alcohols to verify their efficiency and applicability.
- Cao, Hui,Cai, Li-Hua,Wang, Chen-Xi,Zhu, Xiao-Han,Li, Zhi-Ming,Hou, Xiu-Feng
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- Liquid carbon dioxide as an effective solvent for immobilized Candida antarctica lipase B catalyzed transesterification
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The transesterification of alcohols catalyzed by immobilized Candida antarctica lipase B (Novozym 435) was found to be effectively enhanced using a liquid CO2 medium when it was compared with that using organic solvents. The large-scale kinetic-resolution of secondary alcohol by the immobilized lipase was also successfully performed with a continuous packed-column reactor that stably afforded corresponding enantiopure products. Herein, liquid CO2 was proved for the first time to be superior to conventional organic solvents for biotransformation.
- Hoang, Hai Nam,Matsuda, Tomoko
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p. 639 - 641
(2015/02/19)
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- Cobalt-Catalyzed Decarboxylative Acetoxylation of Amino Acids and Arylacetic Acids
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The first cobalt-catalyzed decarboxylative acetoxylation reaction was accomplished. This methodology is applicable to a wide range of amino acids and arylacetic acids.
- Xu, Kun,Wang, Zhiqiang,Zhang, Jinjin,Yu, Lintao,Tan, Jiajing
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supporting information
p. 4476 - 4478
(2015/09/28)
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- A novel synthesis of isoeugenol, [ring-(U)-14C]
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A novel method for the preparation of isoeugenol, [ring-(U)-14C] is presented. Phenols and phenyl esters substituted in the para position with 1-hydroxyethyl or 1-hydroxypropyl acetate esters when treated with 1,8-diazabicyclo[5.4.0]undec-7-ene in dimethylformamide (DMF) eliminate the alkyl carboxylate function to give the unsaturated compound. The reaction fails with unsubstituted or ether substituted phenyl 1-hydroxyacetate esters.
- Immoos, John E.
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p. 419 - 424
(2015/11/18)
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- Substrate specificity of an esterase from the archaeon Sulfolobus tokodaii bearing a GGG(A)X motif
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A GGG(A)X-type esterase (Est0071) from an archaeon catalyzes asymmetric hydrolysis of prochiral bulky malonic diesters in good enantioselectivity. The selectivity of Est0071 was for the opposite enantiomer to that previously shown for pig liver esterase, and the resulting enantiomeric excess of the products was higher. Est0071 could also catalyze the hydrolysis of various acetates of secondary alcohols, and showed moderate enantioselectivity in these reactions.
- Wada, Reina,Ozaki, Masanaru,Kumon, Takashi,Ohta, Hiromichi,Miyamoto, Kenji
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p. 188 - 190
(2015/11/09)
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- Synthesis of sulfonic acid containing ionic-liquid-based periodic mesoporous organosilica and study of its catalytic performance in the esterification of carboxylic acids
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A new sulfonic acid containing ionic-liquid-based periodic mesoporous organosilica (PMO-IL-SO3H) material was prepared and its catalytic application was investigated in the esterification of carboxylic acids with alcohols. The PMO-IL-SO3H nanocatalyst was first characterized with diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and nitrogen sorption analysis. Then, the catalytic performance of this material was studied in the esterification of carboxylic acids with short- and long-chain aliphatic alcohols, cyclic alcohols, and benzylic alcohols under solvent-free conditions. The results showed that the catalyst has superior activity for the conversion of several alcohols to afford the corresponding ester products in excellent yields and high purity. Moreover, the catalyst could be recovered and reused several times without a significant decrease in activity and product selectivity. Copyright
- Elhamifar, Dawood,Karimi, Babak,Moradi, Abbas,Rastegar, Javad
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p. 1147 - 1152
(2014/10/16)
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- ZnAl2O4@SiO2 nanocomposite catalyst for the acetylation of alcohols, phenols and amines with acetic anhydride under solvent-free conditions
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A ZnAl2O4@SiO2 nanocomposite was prepared from metal nitrates and tetraethyl orthosilicate by the sol-gel process, and characterized by X-ray diffraction, Fourier transform infrared, transmission electron microscopy, and N2 adsorption-desorption measurements. The nanocomposite was tested as a heterogeneous catalyst for the acetylation of alcohols, phenols, and amines under solvent-free conditions. Under optimized conditions, efficient acetylation of these substrates with acetic anhydride over the ZnAl2O4@SiO2 nanocomposite was obtained. Acetylation of anilines and primary aliphatic amines proceeded rapidly at room temperature, while the reaction time was longer for the acetylation of alcohols and phenols, showing that an amine NH2 group can be selectively acetylated in the presence of alcoholic or phenolic OH groups. The catalyst can be reused without obvious loss of catalytic activity. The catalytic activity of the ZnAl2O4@SiO2 nanocomposite was higher than that of pure ZnAl2O4. The method gives high yields, and is clean, cost effective, compatible with substrates having other functional groups and it is suitable for practical organic synthesis.
- Farhadi, Saeed,Jahanara, Kosar
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p. 368 - 375
(2014/04/03)
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- Acetylation of alcohols and phenols by zinc zirconium phosphate as an efficient heterogeneous catalyst under solvent-free conditions
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An efficient method for the acetylation of a wide range of alcohols as well as phenols with acetic anhydride in good to excellent yields under solvent-free conditions, using zinc zirconium phosphate as the catalyst was investigated. The catalyst was characterized by XRD, inductivity coupled plasma-optical emission spectroscopy, and scanning electron microscope. Products are easily isolated and the protocol is mild and green, compared to the existing methods. Graphical abstract: [Figure not available: see fulltext.]
- Hajipour, Abdol Reza,Karimi, Hirbod,Karimzadeh, Morteza
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p. 1461 - 1472
(2014/09/30)
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- Sol-gel derived LaFeO3/SiO2 nanocomposite: Synthesis, characterization and its application as a new, green and recoverable heterogeneous catalyst for the efficient acetylation of amines, alcohols and phenols
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LaFeO3/SiO2 nanocomposite was synthesized by the sol-gel process from metal nitrates and tetraethyl orthosilicate (TEOS) as the SiO2 source. The nanocomposite product was characterized by XRD, FT-IR, SEM, and surface area measurements and was used as a heterogeneous catalyst for the efficient acetylation of amines, alcohols and phenols to the corresponding acetates using acetic anhydride under solvent-free conditions. Among the various substrates, acetylation of amines was preceded rapidly, so that an amine group could be selectively acetylated in the presence of alcoholic or phenolic hydroxyl groups by the appropriate choice of reaction time. The catalyst can also be reused several times without the loss of activity. In addition, the catalytic activity of the LaFeO3/SiO2 nanocomposite was higher than that of the pure LaFeO3 nanoparticles. The method is high yielding, clean, cost effective, compatible with the substrates having other functional groups and very suitable for the practical organic synthesis.
- Farhadi, Saeed,Jahanara, Kosar,Sepahdar, Asma
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p. 1103 - 1112
(2014/08/05)
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- Core-Shell Composite as the Racemization Catalyst in the Dynamic Kinetic Resolution of Secondary Alcohols
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Beta-Silicalite-1 core-shell microcomposites with controllable shell thickness were synthesized and used as racemization catalysts in the one-pot dynamic kinetic resolution (DKR) of secondary alcohols by using lipase-catalyzed transesterification. The inert Silicalite-1 shell covered the external acidic sites of the Beta zeolite core, suppressing dehydration and non-enantioselective transesterification of the alcohol. The alcohols could penetrate the Silicalite-1 shell to access the acidic sites at the core Beta for racemization, however, the enzymatically formed (R)-esters were excluded owing to their larger size. As a result, the high ee of the (R)-ester products was conserved and dehydration side products were minimized. Owing to the shape selective nature of the composite racemization catalyst, small and readily available acyl donors could be used in the enzyme-catalyzed transesterification to obtain the esters with high enantiopurity. The DKR of 1-phenylethanol with isopropenyl acetate using an optimized core-shell catalyst, CS-60, gave 92% selectivity to ester formation and the desired (R)-1-phenylethyl acetate was formed with 94% ee.
- Wang, Jie,Do, Dong-Minh,Chuah, Gaik-Khuan,Jaenicke, Stephan
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p. 247 - 254
(2013/03/13)
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- Separation of enantiopure m-substituted 1-phenylethanols in high space-time yield using Bacillus subtilis esterase
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A recombinant Bacillus subtilis esterase (BsE) expressed in E. coli was found to exhibit excellent enantioselectivity (E was always greater than 100) towards m-substituted 1-phenylethanol acetates in the enantioselective hydrolysis reaction. An explanation for the high enantioselectivity observed towards these substrates was provided by molecular modeling. Moreover, the BsE also showed strong tolerance towards a high concentration of m-substituted 1-phenylethanol acetates (up to 1 M). Based on these excellent catalytic properties of BsE, a kind of m-substituted 1-phenylethanols, (R)-1-(3-chlorophenyl)ethanol, was efficiently synthesized in space-time yield of 920 g per L per day and 97% ee, indicating that the BsE was considered as a potentially ideal and promising biocatalyst for large-scale production of optically active m-substituted 1-phenylethanols. The Royal Society of Chemistry 2013.
- Zheng, Gao-Wei,Liu, Xu-Yun,Zhang, Zhi-Jun,Tian, Ping,Lin, Guo-Qiang,Xu, Jian-He
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p. 20446 - 20449
(2013/11/06)
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- Alkene Oxyalkylation Enabled by Merging Rhenium Catalysis with Hypervalent Iodine(III) Reagents via Decarboxylation
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Rhenium-catalyzed oxyalkylation of alkenes is described, where hypervalent iodine(III) reagents derived from widely occurring aliphatic carboxylic acids were used as, for the first time, not only an oxygenation source but also an alkylation source via decarboxylation. The reaction also features a wide substrate scope, totally regiospecific difunctionalization, mild reaction conditions, and ready availability of both substrates. Mechanistic studies revealed a decarboxylation/radical-addition/cation-trapping cascade operating in the reaction.
- Wang, Yin,Zhang, Lei,Yang, Yunhui,Zhang, Ping,Du, Zhenting,Wang, Congyang
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supporting information
p. 18048 - 18051
(2014/01/06)
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- Nonenzymatic dynamic kinetic resolution of secondary alcohols via enantioselective acylation: Synthetic and mechanistic studies
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Because of the ubiquity of the secondary carbinol subunit, the development of new methods for its enantioselective synthesis remains an important ongoing challenge. In this report, we describe the first nonenzymatic method for the dynamic kinetic resolution (DKR) of secondary alcohols (specifically, aryl alkyl carbinols) through enantioselective acylation, and we substantially expand the scope of this approach, vis-a-vis enzymatic reactions. Simply combining an effective process for the kinetic resolution of alcohols with an active catalyst for the racemization of alcohols did not lead to DKR, due to the incompatibility of the ruthenium-based racemization catalyst with the acylating agent (Ac2O) used in the kinetic resolution. A mechanistic investigation revealed that the ruthenium catalyst is deactivated through the formation of a stable ruthenium-acetate complex; this deleterious pathway was circumvented through the appropriate choice of acylating agent (an acyl carbonate). Mechanistic studies of this new process point to reversible N-acylation of the nucleophilic catalyst, acyl transfer from the catalyst to the alcohol as the rate-determining step, and carbonate anion serving as the Bronsted base in that acyl-transfer step.
- Lee, Sarah Yunmi,Murphy, Jaclyn M.,Ukai, Atsushi,Fu, Gregory C.
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supporting information
p. 15149 - 15153
(2012/10/30)
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- Redesign of enzyme for improving catalytic activity and enantioselectivity toward poor substrates: Manipulation of the transition state
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Secondary alcohols having bulky substituents on both sides of the hydroxy group are inherently poor substrates for most lipases. In view of this weakness, we redesigned a Burkholderia cepacia lipase to create a variant with improved enzymatic characteristics. The I287F/I290A double mutant showed a high conversion and a high E value (>200) for a poor substrate for which the wild-type enzyme showed a low conversion and a low E value (5). This enhancement of catalytic activity and enantioselectivity of the variant resulted from the cooperative action of two mutations: Phe287 contributed to both enhancement of the (R)-enantiomer reactivity and suppression of the (S)-enantiomer reactivity, while Ala290 created a space to facilitate the acylation of the (R)-enantiomer. The kinetic constants indicated that the mutations effectively altered the transition state. Substrate mapping analysis strongly suggested that the CH/π interaction partly enhanced the (R)-enantiomer reactivity, the estimated energy of the CH/π interaction being -0.4 kcal mol-1. The substrate scope of the I287F/I290A double mutant was broad. This biocatalyst was useful for the dynamic kinetic resolution of a variety of bulky secondary alcohols for which the wild-type enzyme shows little or no activity. The Royal Society of Chemistry 2012.
- Ema, Tadashi,Nakano, Yasuko,Yoshida, Daiki,Kamata, Shusuke,Sakai, Takashi
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supporting information; experimental part
p. 6299 - 6308
(2012/09/05)
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- Molecular recognition driven catalysis using polymeric nanoreactors
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The concept of using polymeric micelles to catalyze organic reactions in water is presented and compared to surfactant based micelles in the context of molecular recognition. We report for the first time enzyme-like specific catalysis by tethering the catalyst in the well-defined hydrophobic core of a polymeric micelle.
- Cotanda, Pepa,O'Reilly, Rachel K.
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supporting information
p. 10280 - 10282,3
(2020/09/09)
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- N-acyl 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) tetraphenylborate salts as O-acylating agents
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Air-stable and crystalline N-acyl DBN tetraphenylborate salts have been shown to be effective O-acylating agents, reacting with both primary and secondary alcohols to give the corresponding esters in good yields. In the case of diols, the N-acyl DBN·BPh4 salts have been shown to acylate regioselectively the primary alcohol functionality in the presence of a secondary alcohol. The DBN hydrotetraphenylborate side product can be readily removed by filtration, providing the ester products without the need for further purification.
- Taylor, James E.,Williams, Jonathan M.J.,Bull, Steven D.
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experimental part
p. 4074 - 4076
(2012/08/28)
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- Functionalized organocatalytic nanoreactors: Hydrophobic pockets for acylation reactions in water
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The effect of covalently attaching 4-(dimethylamino)pyridine (DMAP) functionality to the hydrophobic core of a polymeric micelle in water has been investigated in the context of acylation reactions employing non-water-soluble substrates. For this purpose a novel temperature-responsive polymeric micelle has been synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization techniques. The reactivity of the tethered organocatalyst within the nanostructure was found to be extremely high, improving in some cases the acylation rates up to 100 times compared to those for unsupported DMAP in organic solvents. Moreover, the catalytic nanoreactors have been demonstrated to be capable of reuse up to 6 times while maintaining high activity.
- Cotanda, Pepa,Lu, Annhelen,Patterson, Joseph P.,Petzetakis, Nikos,O'Reilly, Rachel K.
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scheme or table
p. 2377 - 2384
(2012/06/29)
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- Mutated variant of Candida antarctica lipase B in (S)-selective dynamic kinetic resolution of secondary alcohols
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An (S)-selective dynamic kinetic resolution of secondary alcohols, employing a mutated variant of Candida antarctica lipase B (CalB) gave products in 84-88% yield and in 90-97% ee.
- Engstroem, Karin,Vallin, Michaela,Syren, Per-Olof,Hult, Karl,Baeckvall, Jan-E.
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supporting information; experimental part
p. 81 - 82
(2011/02/23)
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- A tandem and fully enzymatic procedure for the green resolution of chiral alcohols: Acylation and deacylation in non-aqueous media
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A green and fully enzymatic procedure for the resolution of chiral alcohols through lipase/esterase-catalyzed acylation and subsequent lipase-catalyzed aminolysis using anhydrous ammonia was demonstrated. Both enantiomers can be obtained in high ee values (up to >99%) under ambient reaction conditions. The solvent and acyl donors can be recycled, and the enzyme can be reused for up to five times.
- Wang, Bo,Jiang, Ling,Wang, Jue,Ma, Jingbo,Liu, Min,Yu, Hongwei
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p. 980 - 985
(2011/10/04)
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- Dynamic kinetic resolution of a wide range of secondary alcohols: Cooperation of dicarbonylchlorido(pentabenzylcyclopentadienyl)ruthenium and CAL-B
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The substrate scope in the dynamic kinetic resolution ofsecondary alcohols was studied by using 31 structurallydifferent alcohols and isopropenyl acetate in the presence ofdicarbonylchlorido(pentabenzylcyclopentadienyl)rutheniumand Candida antarctica lipase B (Novozym 435, CAL-B) in toluene. The enzyme and the ruthenium complex were shown to function in a highly compatible manner allowing the conversion of the racemic alcohols into the (R)-acetates in practically theoretical yields and, in most cases, ee values exceeding 99%. The results are fully comparable to those published previously by using earlier reported, state-of-the-art ruthenium-based catalysts for the alcohol racemization. A clear benefit of the dicarbonylchlorido(pentabenzylcyclopentadienyl)ruthenium system, when compared to other (cyclopentadienyl)ruthenium racemization catalysts, is its simple and cost-efficient preparation. The substrate scope of 31 secondary alcohols was studied in the dynamic kinetic resolution by utilizing dicarbonylchlorido(pentabenzylcyclopentadienyl)rutheniumand Candida antarctica lipase B (CAL-B) in the acylation with isopropenyl acetate in toluene at room temperature. The secondary alcohols were transformed into highly enantiopure (R)-acetates (in most cases ee > 99%) in close to quantitative isolatedyields. Copyright
- Paeivioe, Mari,Mavrynsky, Denys,Leino, Reko,Kanerva, Liisa T.
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supporting information; experimental part
p. 1452 - 1457
(2011/04/22)
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- Benzylic-acetoxylation of alkylbenzenes with PhI(OAc)2 in the presence of catalytic amounts of TsNH2 and I2
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Treatment of alkylbenzenes with (diacetoxyiodo)benzene in the presence of catalytic amounts of p-toluenesulfonamide or p-nitrobenzenesulfonamide, and molecular iodine in 1,2-dichloroethane at 60 °C gave the corresponding (α-acetoxy)alkylbenzenes in good to moderate yields. The present reaction is a simple method for the introduction of an acetoxy group to the benzylic position of alkylbenzenes.
- Baba, Haruka,Moriyama, Katsuhiko,Togo, Hideo
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experimental part
p. 4303 - 4307
(2011/08/22)
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- Optimization of lipase-catalyzed enantioselective production of 1-phenyl 1-propanol using response surface methodology
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Optically active 1-phenyl 1-propanol is used as a chiral building block and synthetic intermediate in the pharmaceutical industries. In this study, the enantioselective production of 1-phenyl 1-propanol was investigated systematically using response surface methodology (RSM). Before RSM was applied, the effects of the enzyme source, the type of acyl donor, and the type of solvent on the kinetic resolution of 1-phenyl 1-propanol were studied. The best results were obtained with Candida antartica lipase (commercially available as Novozym 435), vinyl laurate as the acyl donor, and isooctane as the solvent. In the RSM, substrate concentration, molar ratio of acyl donor to the substrate, amount of enzyme, temperature, and stirring rate were chosen as independent variables. The predicted optimum conditions for a higher enantiomeric excess (ee) were as follows: substrate concentration, 233mM; molar ratio of acyl donor to substrate, 1.5; enzyme amount, 116mg; temperature, 47°C; and stirring rate, 161rpm. A verification experiment conducted at these optimized conditions for maximum ee yielded 91% for 3hr, which is higher than the predicted value of 83%. The effect of microwave on the ee was also investigated and ee reached 87% at only 5min. Copyright Taylor & Francis Group, LLC.
- Soyer, Asl,Bayraktar, Emine,Mehmetoglu, Ulku
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experimental part
p. 389 - 404
(2012/05/19)
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- Mutant lipase-catalyzed kinetic resolution of bulky phenyl alkyl sec-alcohols: A thermodynamic analysis of enantioselectivity
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The size of the stereoselectivity pocket of Candida antarctica lipase B limits the range of alcohols that can be resolved with this enzyme. These steric constrains have been changed by increasing the size of the pocket by the mutation W104A. The mutated enzyme has good activity and enantioselectivity toward bulky secondary alcohols, such as 1-phenylalkanols, with alkyl chains up to eight carbon atoms. The S enantiomer was preferred in contrast to the wild-type enzyme, which has R selectivity. The magnitude of the enantioselectivity changes in an interesting way with the chain length of the alkyl moiety. It is governed by interplay between entropic and enthalpic contributions and substrates with long alkyl chains are resolved best with E values higher than 100. The enantioselectivity increases with temperature for the small substrates, but decreases for the long ones.
- Vallin, Michaela,Syren, Per-Olof,Hult, Karl
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experimental part
p. 411 - 416
(2010/12/19)
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- BVMO-catalysed dynamic kinetic resolution of racemic benzyl ketones in the presence of anion exchange resins
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4-Hydroxyacetophenone monooxygenase from Pseudomonas fluorescens ACB was employed in the presence of a weak anion exchange resin to perform dynamic kinetic resolutions of racemic benzyl ketones with high conversions and good optical purities. Different parameters that affect to the efficiency of the enzymatic Baeyer-Villiger oxidation and racemisation were analyzed in order to optimize the activity and selectivity of the biocatalytic system. The Royal Society of Chemistry.
- Rodriguez, Cristina,De Gonzalo, Gonzalo,Rioz-Martinez, Ana,Torres Pazmino, Daniel E.,Fraaije, Marco W.,Gotor, Vicente
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experimental part
p. 1121 - 1125
(2010/06/20)
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- A highly selective ferrocene-based planar chiral PIP (Fc-PIP) acyl transfer catalyst for the kinetic resolution of alcohols
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Novel planar chiral ferrocene nucleophilic catalysts (Fc-PIP) containing both central and planar chiral elements were designed and synthesized for catalytic enantioselective acyl transfer of secondary alcohols. A remarkably efficient catalyst with high selectivity factors (up to S = 1892) was identified. Comparing the combination of central and planar chirality revealed a strong requirement for the "matched" chiral elements, indicating that the stereogenic center of the imidazole rings should present itself on the same face as the ferrocenyl fragment; otherwise, the catalyst is completely inactive. An exclusively stacked transition state that accounts for the high selectivity of the kinetic resolution of secondary alcohols is proposed. Notably, this newly designed catalyst family is suitable for the catalytic kinetic resolution of bulky arylalkyl carbinols, producing esters with extremely high ee (>99%).
- Hu, Bin,Meng, Meng,Wang, Zheng,Du, Wenting,Fossey, John S.,Hu, Xinquan,Deng, Wei-Ping
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scheme or table
p. 17041 - 17044
(2011/02/16)
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- Asymmetric transfer hydrogenation of ketones in aqueous solution catalyzed by rhodium(III) complexes with C2-symmetric fluorene-ligands containing chiral (1R,2R)-cyclohexane-1,2-diamine
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Two C2-symmetric bis(sulfonamide) ligands containing fluorene-chiral (1R,2R)-cyclohexane- 1,2-diamine were complexed to Rh III(Cp*) and used as catalyst to reduce aromatic ketones. The corresponding chiral secondary alcohols were obtained in 87-100percent ee and 85-99percent yield, under asymmetric transfer hydrogenation (ATH) conditions using aqueous sodium formate as the hydride source. With acetophenone, 94percent ee and 86-97percent yield was achieved with substrate/catalyst (S/C) ratio of 10,000.
- Montalvo-Gonza?lez, Rube?n,Cha?vez, Daniel,Aguirre, Gerardo,Parra-Hakea, Miguel,Somanathan, Ratnasamy
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experimental part
p. 431 - 435
(2010/07/16)
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- One-pot sequence for reductive-acetylation of carbonyl compounds with (N-methylimidazole)(tetrahydroborato)zinc complex
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Reductive-acetylation of variety of aliphatic and aromatic aldehydes and ketones, α,β-unsaturated carbonyl compounds are examined efficiently with (N-methylimidazole)(tetrahydroborato)zinc complex, [Zn(BH4) 2(nmi)], under mild condition in THF at room temperature or reflux conditions. The corresponding acetates were obtained in excellent yields (90-98 %).
- Setamdideh, Davood,Khezri, Behrooz
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experimental part
p. 5766 - 5772
(2012/07/28)
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- Spinel-type zinc aluminate (ZnAl2O4) nanoparticles prepared by the co-precipitation method: A novel, green and recyclable heterogeneous catalyst for the acetylation of amines, alcohols and phenols under solvent-free conditions
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Zinc aluminate (ZnAl2O4) nanoparticles with an average particle size of about 8 nm were easily prepared by the co-precipitation method using aqueous ammonia solution as the precipitating agent. This nanosized spinel-type oxide was characterized by TGA, XRD, FT-IR, TEM, and surface area measurement and used as the heterogeneous catalyst for the acetylation reaction. Efficient acetylation of various amines, alcohols and phenols was carried out over ZnAl2O4 nanoparticles using acetic anhydride and/or acetyl chloride as the acetylating agents at room temperature without the use of a solvent. The method is highly selective, allowing the alcoholic hydroxyl group to be protected while the phenolic hydroxyl group remains intact, and the amine group can be acetylated in the presence of the hydroxyl group. This method is fast and has a high yield. It is also clean, safe, cost effective, compatible with substrates that have other functional groups and very suitable for practical organic synthesis. In addition, the catalyst can be reused without significant loss of activity. Indeed, the catalytic activity of the ZnAl2O4 nanoparticles is higher than that of bulk ZnAl2O4.
- Farhadi, Saeid,Panahandehjoo, Somayeh
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scheme or table
p. 293 - 302
(2010/09/04)
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- Air-stable titanocene bis(perfluorooctanesulfonate) as a new catalyst for acylation of alcohols, phenols, thiols, and amines under solvent-free condition
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Air-stable titanocene bis(perfluorooctanesulfonate) [Cp2Ti(OSO2C8F17)2] that shows high Lewis acidity was prepared from Cp2TiCl2 and AgOSO2C8F17. The compound was characterized by different techniques, and examined as a catalyst for acylation reactions. It was found that using equimolar acetic anhydride as acetylating agent and under solvent-free condition, Cp2Ti(OSO2C8F17)2 exhibits high activity and selectivity in the acetylation of various alcohols, phenols, thiols, and amines. Also, good catalytic efficiency is observed in the acylation of 2-phenylethanol across various acylating reagents. The catalyst can be reused without loss of activity in a test of ten cycles. The Cp2Ti(OSO2C8F17)2 catalyst affords a simple, efficient and general method for the acylation of alcohols, phenols, thiols, and amines.
- Qiu, Renhua,Zhang, Guoping,Ren, Xiaofang,Xu, Xinhua,Yang, Ronghua,Luo, Shenglian,Yin, Shuangfeng
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experimental part
p. 1182 - 1188
(2010/06/13)
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- Synthesis of chiral aromatic alcohols: Use of new C2-symmetric RhIIICp*, RuII(cymene), or RuII(benzene) complexes containing chiral diaminocyclohexane ligand as asymmetric transfer hydrogenation catalyst
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Twelve chiral secondary alcohols were synthesized by asymmetric transfer hydrogenation (ATH) using C2-symmetric bis(sulfonamide) ligand (2) derived from (1R,2R)-cyclohexane-1,2-diamine and complexed with [RhCl 2CP*]2, [RuCl2(cymene)] 2, or [RuCl2(benzene)]2 and then used in situ in the reduction of prochiral ketones. The alcohols were obtained in 85-99% yield and 90-99% enantioselectivity with isopropanol as the hydrogen source. Two-fold rate enhancement and better yields were achieved (88-99%) with 80-99% enantioselectivity using the complex [RhCl2CP*] 2 and aqueous sodium formate as the hydrogen source.
- Montalvo-Gonzalez, Ruben,Chavez, Daniel,Aguirre, Gerardo,Parra-Hake, Miguel,Somanathan, Ratnasamy
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experimental part
p. 2737 - 2746
(2009/12/06)
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- A heterogeneous cobalt(II) Salen complex as an efficient and reusable catalyst for acetylation of alcohols and phenols
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Acetylation of various alcohols and phenols was performed successfully using an immobilized cobalt(II) catalyst in high yield. The catalyst shows high thermal stability and was also recovered and reused at least 10 times without any considerable loss of activity.
- Rajabi, Fatemeh
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scheme or table
p. 395 - 397
(2009/05/07)
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- Broensted acidic ionic liquid as an efficient catalyst for acetylation of alcohols and phenols
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A novel Broensted acidic room temperature ionic liquid (1-H-3-methyl-imidazolium bisulfate) is found to catalyze efficiently the acetylation of a wide rang of alcohols as well as phenols with acetic anhydride in good to excellent yields at 50°C under solvent-free conditions. Products are easily isolated by extraction with ether and the protocol is mild and green, compared to the existing method based on toxic solvents.
- Hajipour, Abdol R.,Khazdooz, Leila,Ruoho, Arnold E.
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experimental part
p. 398 - 403
(2009/12/06)
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- Immobilized Manihot esculenta preparation as a novel biocatalyst in the enantioselective acetylation of racemic alcohols
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The enzymatic preparation obtained from a discard of Manihot esculenta roots has been successfully immobilized on calcium alginate hydrogels. This preparation has been tested as a chiral biocatalyst in the enzymatic acylation of a set of racemic aromatic alcohols. Depending on the reaction conditions, excellent enantioselectivities can be achieved. Some parameters that can alter the biocatalytic properties of the enzyme, such as solvent, temperature, acyl donor and substrate structure have been studied exhaustively in order to establish a deeper knowledge of this novel biocatalyst.
- Machado, Luciana L.,Lemos, Telma L.G.,de Mattos, Marcos Carlos,de Oliveira, Maria da Conceicao F.,de Gonzalo, Gonzalo,Gotor-Fernandez, Vicente,Gotor, Vicente
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p. 1418 - 1423
(2008/12/20)
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