- Lipase mediated enzymatic kinetic resolution of phenylethyl halohydrins acetates: A case of study and rationalization
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Racemic phenylethyl halohydrins acetates containing several groups attached to the aromatic ring were resolved via hydrolysis reaction in the presence of lipase B from Candida antarctica (Novozym 435). In all cases, the kinetic resolution was highly selective (E > 200) leading to the corresponding (S)-β-halohydrin with ee > 99 %. However, the time required for an ideal 50 % conversion ranged from 15 min for 2,4-dichlorophenyl chlorohydrin acetate to 216 h for 2-chlorophenyl bromohydrin acetate. Six chlorohydrins and five bromohydrins were evaluated, the latter being less reactive. For the β-brominated substrates, steric hindrance on the aromatic ring played a crucial role, which was not observed for the β-chlorinated derivatives. To shed light on the different reaction rates, docking studies were carried out with all the substrates using MD simulations. The computational data obtained for the β-brominated substrates, based on the parameters analysed such as NAC (near attack conformation), distance between Ser-O and carbonyl-C and oxyanion site stabilization were in agreement with the experimental results. On the other hand, the data obtained for β-chlorinated substrates suggested that physical aspects such as high hydrophobicity or induced change in the conformation of the enzymatic active site are more relevant aspects when compared to steric hindrance effects.
- Fonseca, Thiago de Sousa,Vega, Kimberly Benedetti,da Silva, Marcos Reinaldo,de Oliveira, Maria da Concei??o Ferreira,de Lemos, Telma Leda Gomes,Contente, Martina Letizia,Molinari, Francesco,Cespugli, Marco,Fortuna, Sara,Gardossi, Lucia,de Mattos, Marcos Carlos
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- Intermolecular Halogenation/Esterification of Alkenes with N-Halosuccinimide and Acetic Acid Catalyzed by 1,4-Diazabicyclo[2.2.2]octane
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1,4-Diazabicyclo[2.2.2]octane (DABCO) is a suitable Lewis base that acts as an organocatalyst in the activation of N-chlorosuccinimide (NCS) towards the chlorination of alkenes. The chloriranium ion formed from NCS and the alkene, can be intermolecularly opened by a nucleophile, such as acetic acid, to produce highly functionalized trans-chloro esters in high yields. The protocol is also applied to the synthesis of chlorohydrins and chloro ethers using water or methanol as nucleophiles instead of acetic acid. Brominated analogs can also be synthesized from alkenes and N-bromosuccinimide (NBS) in the presence of various basic catalysts. However, the reaction patterns seem to be remarkably different. The catalytic performance of bases in the bromoesterification of alkenes was found to be strongly affected by their Br?nsted basicity, suggesting that acetyl hypobromite, formed in situ from NBS and acetic acid, acts as a real brominating agent in these systems. (Figure presented.).
- Pimenta, Laura S.,Gusevskaya, Elena V.,Alberto, Eduardo E.
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supporting information
p. 2297 - 2303
(2017/07/07)
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- Immobilization of Amano lipase from Pseudomonas fluorescens on silk fibroin spheres: an alternative protocol for the enantioselective synthesis of halohydrins
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The search for a new, efficient, cheaper and sustainable matrix for lipase immobilization is a growing area in biotechnology. Amano lipase from Pseudomonas fluorescens was immobilized on silk fibroin spheres and used in the enzymatic kinetic resolution of halohydrins, to obtain optically active epoxides (up to 99% ee), important precursors in the synthesis of derivative antifungal azoles. This paper reinforces the versatility of silk fibroin as a support for heterogeneous catalysts.
- Ferreira, Irlon M.,Yoshioka, Sergio A.,Comasseto, Jo?o V.,Porto, André L. M.
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p. 12650 - 12658
(2017/03/11)
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- Highly enantioselective acylation of chlorohydrins using Amano AK lipase from P. fluorescens immobilized on silk fibroin-alginate spheres
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Aromatic, allylic, and aliphatic compounds containing a chlorohydrin group were selected as substrates for the enzymatic kinetic resolution mediated by Amano AK lipase from Pseudomonas fluorescens immobilized in silk friboin-alginate spheres. Thus, the en
- Ferreira, Irlon M.,Nishimura, Rodolfo H.V.,Souza, Ana B. Dos A.,Clososki, Giuliano C.,Yoshioka, Sergio A.,Porto, André L.M.
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supporting information
p. 5062 - 5065
(2015/01/09)
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- Catalyst-free, direct, high regio- and chemoselective conversion of epoxides to vicinal haloesters under mild, neutral, and solvent-free conditions
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A catalyst-free, high regio- and chemoselective method is described for the mild conversion of wide varieties of epoxides directly to their corresponding vicinal haloesters using quaternary ammonium halides R4N +X- (X equa
- Aghapour, Ghasem,Hatefipour, Razieh
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p. 1030 - 1040
(2013/03/14)
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- Addition of halide to π-bond directly from aqueous NaX solution: A general strategy for installation of two different functional groups
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Activation of π-bond with organic Lewis acid and cationic surfactant mediated direct transfer of halides to alkyne and alkene are demonstrated to afford α,α-dihaloketones and other valuable synthons with outstanding selectivities.
- Pandit, Palash,Gayen, Krishnanka S.,Khamarui, Saikat,Chatterjee, Nirbhik,Maiti, Dilip K.
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supporting information; experimental part
p. 6933 - 6935
(2011/08/06)
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- An algorithm for the deconvolution of mass spectrosopic patterns in isotope labeling studies. Evaluation for the hydrogen-deuterium exchange reaction in ketones
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(Graph Presented) An easy to use computerized algorithm for the determination of the amount of each labeled species differing in the number of incorporated isotope labels based on mass spectroscopic data is described and evaluated. Employing this algorithm, the microwave-assisted synthesis of various α-labeled deuterium ketones via hydrogen-deuterium exchange with deuterium oxide was optimized with respect to time, temperature, and degree of labeling. For thermally stable ketones the exchange of α-protons was achieved at 180°C within 40-200 min. Compared to reflux conditions, the microwave-assisted protocol led to a reduction of the required reaction time from 75-94 h to 40-200 min. The α-labeled deuterium ketones were reduced by biocatalytic hydrogen transfer to the corresponding enantiopure chiral alcohols and the deconvolution algorithm validated by regression analysis of a mixture of labeled and unlabeled ketones/alcohols.
- Gruber, Christian C.,Oberdorfer, Gustav,Voss, Constance V.,Kremsner, Jennifer M.,Kappe, C. Oliver,Kroutil, Wolfgang
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p. 5778 - 5783
(2008/02/10)
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- Trichloroisocyanuric Acid as a Cohalogenating Reagent: An Efficient Transformation of Alkenes into Chlorohydrins, β-Chloroethers and β-Chloroacetates
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The preparation of diverse β-chloroethers, β-chloroacetates, and chlorohydrins is efficiently achieved under mild conditions by reaction of alkenes with trichloroisocyanuric acid (0.34 mol equiv) in alcohols (MeOH, EtOH, i-PrOH, t-BuOH), acetic acid or aqueous acetone, respectively.
- Mendonca, Gabriela Fonseca,Sanseverino, Antonio Manzolillo,Mattos, Marcio C. S. de
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- Efficient and Regioselective Conversion of Epoxides into Vicinal Chloroesters with TiCl4 and Imidazole in Ethyl Acetate
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Epoxides can be cleaved easily in EtOAc with TiCl4 in the presence of imidazole to afford β-chloroesters with excellent yields and regioselectivity.
- Iranpoor,Zeynizadeh
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p. 582 - 583
(2007/10/03)
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- A facile 1,2-acetoxychlorination reaction of olefins by using the N,N-dimethtylacetamide/hydrogen chloride/m-chloroperbenzoic acid (or oxone) system
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Various alkenes underwent 1,2-acetoxychlorination by dimethylacetamide (DMA)/HCl/m-CPBA (or Oxone) system in good yields.
- Kim, Hyoung Rae,Oh, Hyun Sook,Park, Hyun Ju,Kim, Jae Nyoung,Jeon, Dong Ju,Ryu, Eung K.
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p. 159 - 165
(2007/10/03)
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- Yttrium compounds: New catalysts for the regioselective acylative cleavage of epoxides
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The use of Cp2YCl and YCl3 as effective catalysts for the regioselective acylative cleavage of epoxides, especially for the conversion of α,β- epoxyketones to α-chloroenones is described.
- Qian,Zhu
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p. 2203 - 2214
(2007/10/02)
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- Reaction of Epoxides with Chlorocarbonylated Compounds Catalyzed by Hexaalkylguanidinium Chloride
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Silica-supported guanidinium chloride (PBGSiCl) exhibits efficient chemo- and regiospecific catalytic activity in the ring opening of epoxides with various electrophiles.This reaction allows the preparation of β-chloro esters and β-chloro chloroformates in high yield under neutral conditions which offer product stability and ease of product isolation.
- Gros, P.,Perchec, P. Le,Senet, J. P.
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p. 4925 - 4930
(2007/10/02)
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- OXIDATIVE ADDITION OF ANIONS TO ALKENES BY THE ACTION OF COMPOUNDS OF TETRAVALENT LEAD IN THE PRESENCE OF CHLORIDE ION IN AN ACIDIC MEDIUM
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In the reaction of alkenes (cyclohexene, 1-hexene, styrene) with compounds of tetravalent lead in various acids (trifluoroacetic, acetic, methanesulfonic, perchloric) in the presence of metal chlorides the joint addition of the chloride anion and the anion of the respective acids to the alkenes takes place with a high degree of selectivity, leading to the formation of vicinal bifunctional derivatives of alkanes.The effectiveness of the addition of the anions of the acids to the alkenes under the given conditions varies directly with the strength of the acid and inversely with the nucleophilicity and the basicity of its anion.A new convenient method is proposed for the oxidative chlorofluorination of cyclohexene in aqueous hydrofluoric acid.
- Serguchev, Yu. A.,Gutsulyak, R. B.
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p. 1784 - 1790
(2007/10/02)
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- Three-Component Reactions. VIII. Chlorination of Olefines in N-Methylpyrrolidone
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The chlorination of cyclohexene, styrene and 1-dodecene in NMP gives immonium-chlorides 5 reacting with water to β-chloralkyl-γ-N-methylaminobutyrat-hydrochlorides.With cyclohexene the reaction proceeds stereospecifically as trans-addition.From styrene there is only formed the Markovnikov product, and from dodecene a mixture of isomeres is obtained containing about 30percent of the anti-Markovnikov product.
- Beger, J.,Jacobi, R.,Storch, A.,Ullmann, M.
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p. 394 - 400
(2007/10/02)
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- Kinetics and Stereochemistry of the Addition of Chlorine to Styrenes
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The chlorination of several ring- and side-chain-substituted styrenes has been studied in anhydrous acetic acid, in both the presence and absence of added perchlorate, chloride, and acetate salts.The reactions give three types of product: the 1,2-dichlorides arising from simple addition, 1-acetoxy-2-chloro compounds from addition followed by solvent incorporation, and β-chlorostyrenes from an addition-elimination process.The reactions are completely regiospecific in the Markownikoff sense, and the addition-elimination products are formed with high stereoselectivity.However, both types of addition product are formed nonstereospecifically.Both the product distribution and stereoselectivity are remarkably insensitive to added perchlorate, chloride, or acetate, and very high concentrations of these salts (ca. 1.0 M) are required to produce any significant change in product composition.These results are explicable in terms of a product-determining intermediate which consists of an intimate ion pair between an open β-chlorobenzyl carbonium ion and a tightly held chloride counterion.However, since (E)- and (Z)-1-phenylpropenes do not give similar product distributions under any conditions used, rotation of the Cα-Cβ bond in the carbonium ion must be highly restricted.The rates of reaction have been studied by a combination of potentiometric and stopped-flow spectrophotometric techiques.The reactions are first order in chlorine and first order in olefin and are generally very fast, with most of the rate constants being in the range 102-105 L mol-1 s-1.The rate constants for the ring-substituted styrenes give a good linear correlation against ?+ with a β value of -3.22.This value is less negative than expected from a comparison with other electrophilic additions and is discussed in terms of an earlier transition state with less charge development at Cα than in the analogous bromination reaction.The activation parameters obtained for two of the styrenes support this hypothesis.There is no direct evidence for chlorine bridging at either the transition state or the intermediate stage.
- Yates, Keith,Leung, Hei Wun
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p. 1401 - 1406
(2007/10/02)
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