The Experts below are selected from a list of 2310 Experts worldwide ranked by ideXlab platform
Roger A. Sheldon - One of the best experts on this subject based on the ideXlab platform.
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a green and expedient synthesis of enantiopure diketopiperazines via enzymatic resolution of unnatural amino acids
ChemInform, 2015Co-Authors: Pedro C Pereira, Isabel W C E Arends, Roger A. SheldonAbstract:Dipeptides (III) are stereoselectively prepared from D-Phenylglycine amide and racemic amino acids in the presence of an immobilized form of penicillin G acylase in aqueous medium.
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a green and expedient synthesis of enantiopure diketopiperazines via enzymatic resolution of unnatural amino acids
Tetrahedron Letters, 2014Co-Authors: Pedro C Pereira, Isabel W C E Arends, Roger A. SheldonAbstract:Abstract Dipeptides comprising a d -phenylglycyl moiety coupled to the l -enantiomer of 2-amino butyric acid, norvaline, norleucine, and homocysteine were successfully synthesized from d -Phenylglycine amide and the racemate of the corresponding unnatural amino acid. The reaction is catalyzed by an immobilized form of penicillin G acylase in an aqueous medium. The dipeptides were subsequently converted into the corresponding enantiopure diketopiperazines in overall isolated yields of 22–33%.
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penicillin acylase catalyzed peptide synthesis in aqueous medium a chemo enzymatic route to stereoisomerically pure diketopiperazines
Tetrahedron-asymmetry, 2003Co-Authors: Andrei Y Khimiuk, Roger A. Sheldon, Alexei V Korennykh, Luuk M Van Langen, Fred Van Rantwijk, V K SvedasAbstract:Abstract A range of non-natural dipeptides of the general formula d -(−)-phenylglycyl- l -X, where X is a natural α-amino acid, have been prepared by penicillin acylase-catalyzed synthesis in aqueous medium from d -(−)-Phenylglycine amide and the corresponding amino acids. The conversion of the dipeptides to the corresponding dipeptide esters, followed by their subsequent spontaneous cyclization afforded the corresponding stereoisomerically pure diketopiperazines.
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penicillin acylase catalyzed synthesis of ampicillin in aqueous solution precipitate systems high substrate concentration and supersaturation effect
Journal of Molecular Catalysis B-enzymatic, 2000Co-Authors: M I Youshko, Harold Monro Moody, Roger A. Sheldon, Luuk M Van Langen, Fred Van Rantwijk, Erik De Vroom, V K SvedasAbstract:Abstract Penicillin acylase-catalyzed ampicillin synthesis via acyl group transfer in aqueous solution is highly dependent on the initial substrate concentration. The solubility of one substrate, 6-aminopenicillanic acid (6-APA), can be advantageously enhanced by the presence of acyl donor, the second substrate. Furthermore, a comparison of enzymatic synthesis in homogeneous solution with synthesis in a heterogeneous system having partially undissolved reactants, reveals major advantages for the latter approach. In this “aqueous solution–precipitate” system, accumulation of both products, ampicillin and d -(−)-Phenylglycine, proceeds through the formation of their supersaturated solutions. Subsequent precipitation of the product ampicillin positively influences the efficiency of the biocatalytic process. As a result, ampicillin synthesis proceeds in 93% conversion on 6-APA and in 60% conversion on d -(−)-Phenylglycine methyl ester.
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dynamic kinetic resolution of Phenylglycine esters via lipase catalysed ammonolysis
Tetrahedron-asymmetry, 1999Co-Authors: M A Wegman, M A P J Hacking, J Rops, Pedro C Pereira, F Van Rantwijk, Roger A. SheldonAbstract:Abstract Ammonolysis of d , l -Phenylglycine methyl ester catalysed by Novozym 435 at 40°C in tert -butyl alcohol gave d -Phenylglycine amide in 78% ee at 46% conversion, corresponding to an enantiomeric ratio ( E ) of 16. Lowering the temperature improved the enantioselectivity ( E =52 at −20°C). Combination of ammonolysis with pyridoxal-catalysed in situ racemisation of the unconverted ester (dynamic kinetic resolution), at −20°C, gave d -Phenylglycine amide with 88% ee at 85% conversion. The amide racemised much slower than the ester at this low temperature.
Jose M Sansano - One of the best experts on this subject based on the ideXlab platform.
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microwave assisted multicomponent diastereoselective 1 3 dipolar cycloaddition of ethyl glyoxylate derived azomethine ylides
Organic and Biomolecular Chemistry, 2013Co-Authors: Juan Manceboaracil, Carmen Najera, Jose M SansanoAbstract:The thermal multicomponent 1,3-dipolar cycloaddition (1,3-DC) of diethyl aminomalonate or α-amino esters (derived from glycine, alanine, phenylalanine, and Phenylglycine) with ethyl glyoxylate and the corresponding dipolarophile such as maleimides, methyl acrylate, methyl fumarate, (E)-1,2-bis(phenylsulfonyl)ethylene, and electron deficient alkynes allows the diastereoselective synthesis of new polysubstituted pyrrolidine derivatives. Microwave-assisted heating processes give better results than conventional heating ones, affording endo-cycloadducts as major stereoisomers. In general, 2,5-cis-cycloadducts are preferentially formed according to the previous formation of the W-shaped dipole. Only in the 1,3-DC of the disulfone with Phenylglycine and ethyl glyoxylate the corresponding exo-trans-cycloadduct was isolated. The compound endo-cis-4b, derived from phenylalanine, ethyl glyoxylate and N-benzylmaleimide, has been further transformed into a very complex diazabicyclo[2.2.1]octane skeleton with potential biological activity.
Andrea Trabocchi - One of the best experts on this subject based on the ideXlab platform.
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synthesis of diverse Phenylglycine derivatives via transformation of ugi four component condensation primary adducts
ChemInform, 2011Co-Authors: Stefano Marcaccini, Gloria Menchi, Andrea TrabocchiAbstract:A synthetically useful post-condensation of Ugi-4CC products (I) allows the preparation of diverse Phenylglycine derivatives.
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synthesis of diverse Phenylglycine derivatives via transformation of ugi four component condensation primary adducts
Tetrahedron Letters, 2011Co-Authors: Stefano Marcaccini, Gloria Menchi, Andrea TrabocchiAbstract:3-(N-Substituted)amino-4-arylamino-1H-isochromenones (isocoumarins) which can be regarded as the enediamine tautomers of the Ugi four-component condensation primary adducts between 2-formylbenzoic acids, arylamines, and isocyanides undergo a facile ring cleavage with amines to give a series of Phenylglycine derivatives. Thus, a synthetically useful post-condensation transformation of Ugi four-component condensation primary adducts is described for the first time.
Quirinus B Broxterman - One of the best experts on this subject based on the ideXlab platform.
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diastereoselective addition of allylzinc bromide to imines derived from r Phenylglycine amide
Organic Letters, 2001Co-Authors: Michiel Van Der Sluis, Quirinus B Broxterman, Richard M Kellogg, Jan Dalmolen, B De Lange, B KapteinAbstract:The highly diastereoselective addition of allylzinc bromide to imines derived from (R)-Phenylglycine amide is reported. Homoallylamines with high enantiomeric purity are obtained from the adducts in three steps on removal of the chiral auxiliary by means of a nonreductive protocol. Removal of the auxiliary by hydrogenation leads to the saturated amines, also in high enantiomeric purity.
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asymmetric strecker synthesis of α amino acids via a crystallization induced asymmetric transformation using r Phenylglycine amide as chiral auxiliary
Organic Letters, 2001Co-Authors: Wilhelmus Hubertus Joseph Boesten, Harold Monro Moody, Jeanpaul G Seerden, Ben De Lange, Hubertus Johannes Adrianus Dielemans, Henk Elsenberg, Bernard Kaptein, Richard M Kellogg, Quirinus B BroxtermanAbstract:[reaction: see text]. Diastereoselective Strecker reactions based on (R)-Phenylglycine amide as chiral auxiliary are reported. The Strecker reaction is accompanied by an in situ crystallization-induced asymmetric transformation, whereby one diastereomer selectively precipitates and can be isolated in 76-93% yield and dr > 99/1. The diastereomerically pure alpha-amino nitrile obtained from pivaldehyde (R1 = t-Bu, R2 = H) was converted in three steps to (S)-tert-leucine in 73% yield and >98% ee.
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dutch resolution of racemic 4 hydroxy and 4 fluoroPhenylglycine with mixtures of Phenylglycine and 10 camphorsulfonic acid
Tetrahedron-asymmetry, 2000Co-Authors: Bernard Kaptein, Quirinus B Broxterman, Henk Elsenberg, Reinier F. P. Grimbergen, Lumbertus A. Hulshof, Kees Pouwer, Ton VriesAbstract:Abstract 4-HydroxyPhenylglycine and 4-fluoroPhenylglycine can be resolved with (+)-10-camphorsulfonic acid only if dl - or d -(−)-Phenylglycine is added. When using dl -Phenylglycine this is co-resolved in this process. In this resolution process mixed crystals are formed of the (+)-10-camphorsulfonic acid salts of the d -(−)-enantiomers of Phenylglycine and the para substituted Phenylglycines. In the crystal lattice of the mixed salts approximately 25–30% of the d -(−)-Phenylglycine molecules can be randomly replaced by d -(−)-para substituted Phenylglycines, resulting in the desired resolution. The overall non-stoichiometric composition of the mixed crystals reflects to some extent the composition in solution. This behaviour is typical for solid solutions. The solid solution behaviour in this so called ‘Dutch resolution’ is proven by differential scanning calorimetry (DSC), X-ray crystal structure determination and powder diffraction.
Juan Manceboaracil - One of the best experts on this subject based on the ideXlab platform.
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microwave assisted multicomponent diastereoselective 1 3 dipolar cycloaddition of ethyl glyoxylate derived azomethine ylides
Organic and Biomolecular Chemistry, 2013Co-Authors: Juan Manceboaracil, Carmen Najera, Jose M SansanoAbstract:The thermal multicomponent 1,3-dipolar cycloaddition (1,3-DC) of diethyl aminomalonate or α-amino esters (derived from glycine, alanine, phenylalanine, and Phenylglycine) with ethyl glyoxylate and the corresponding dipolarophile such as maleimides, methyl acrylate, methyl fumarate, (E)-1,2-bis(phenylsulfonyl)ethylene, and electron deficient alkynes allows the diastereoselective synthesis of new polysubstituted pyrrolidine derivatives. Microwave-assisted heating processes give better results than conventional heating ones, affording endo-cycloadducts as major stereoisomers. In general, 2,5-cis-cycloadducts are preferentially formed according to the previous formation of the W-shaped dipole. Only in the 1,3-DC of the disulfone with Phenylglycine and ethyl glyoxylate the corresponding exo-trans-cycloadduct was isolated. The compound endo-cis-4b, derived from phenylalanine, ethyl glyoxylate and N-benzylmaleimide, has been further transformed into a very complex diazabicyclo[2.2.1]octane skeleton with potential biological activity.
