The Experts below are selected from a list of 21570 Experts worldwide ranked by ideXlab platform
Qiaqing Wu - One of the best experts on this subject based on the ideXlab platform.
-
engineering of l threonine aldolase for the preparation of 4 methylsulfonyl phenylserine an important intermediate for the synthesis of florfenicol and thiamphenicol
Enzyme and Microbial Technology, 2020Co-Authors: Xi Chen, Qijia Chen, Jinhui Feng, Min Wang, Qiaqing WuAbstract:Abstract l -Threonine aldolases ( l -TAs) catalyze the aldol condensation of aldehyde and glycine, offering direct enzymatic synthesis of β-hydroxy-α-amino acids under mild conditions. However, this method suffers from moderate yield and low Stereoselectivity at the β-carbon. Given the importance of 4-(methylsulfonyl)phenylserine for the synthesis of florfenicol and thiamphenicol, mutations of a l -threonine aldolase from Pseudomonas sp. ( l -PsTA) were performed in this study by error-prone PCR and combinatorial mutation. Some beneficial mutants were obtained by screening the mutant library using a stepwise visual method. 4-(Methylsulfonyl)phenylserine was synthesized in up to 71 % diastereomeric excess (de), which are much higher than the previously reported 2 % de value, by using the newly identified mutants. The mutants V200I and C187S/V200I were found to improve the product yield and Stereoselectivity for the aldol condensation of various benzaldehydes with glycine. These results show that the amino acid residues outside of the substrate-binding cavity of l -PsTA play an important role in determining its Cβ-stereoseletivity.
-
improving and inverting cβ Stereoselectivity of threonine aldolase via substrate binding guided mutagenesis and a stepwise visual screening
ACS Catalysis, 2019Co-Authors: Qijia Chen, Xi Chen, Jinhui Feng, Qiaqing WuAbstract:Threonine aldolase (TA)-catalyzed aldol condensation is a powerful tool for C–C bond formation under mild conditions, but the low Cβ-Stereoselectivity has hampered its wide application. A stepwise visual screening method was developed to measure the activity and Stereoselectivity of threonine aldolase-catalyzed aldol condensation by employing a stereoselective phenylserine dehydratase, enabling direct selection of mutants with higher Cβ-Stereoselectivity. Mutants of l-PsTA from Pseudomonas sp. with improved or inverted Stereoselectivity toward aromatic aldehydes were obtained by simultaneously mutating amino acid residues which interact with the amino and hydroxyl groups of the substrate and screening the resulting mutant libraries with this method. The mutation and enzyme–substrate docking studies provided some insights into the regulation of the Cβ-Stereoselectivity by the enzyme–substrate interactions. This study offers a tool and useful guidance for further engineering of TAs to address the Cβ-stereos...
Jiaxi Xu - One of the best experts on this subject based on the ideXlab platform.
-
diaStereoselectivity in the staudinger reaction a useful probe for investigation of nonthermal microwave effects
Tetrahedron, 2007Co-Authors: Libo Hu, Yikai Wang, Daming Du, Bonan Li, Jiaxi XuAbstract:Abstract The effect of microwave irradiation on the selectivity, especially Stereoselectivity, is one of the most important issues in microwave-assisted organic reactions. The diaStereoselectivity in Staudinger reactions involving the representative ketenes and the corresponding matched imines has been used as a probe to investigate carefully the existence of the specific nonthermal microwave effects. The results indicate that the microwave irradiation-controlled Stereoselectivity in the Staudinger reaction is in fact the contribution of temperature. No specific nonthermal microwave effect was found in the Staudinger reaction.
-
do reaction conditions affect the Stereoselectivity in the staudinger reaction
Journal of Organic Chemistry, 2006Co-Authors: Yikai Wang, Daming Du, Yong Liang, Lei Jiao, Jiaxi XuAbstract:The stereochemistry is one of the critical issues in the Staudinger reaction. We have proposed the origin of the Stereoselectivity recently. The effects of solvents, additives, and pathways of ketene generation on the Stereoselectivity were investigated by using a clean Staudinger reaction, which is a sensitive reaction system to the Stereoselectivity. The results indicate that the additives, usually existed and generated in the Staudinger reaction, and the pathways of the ketene generation do not generally affect the Stereoselectivity. The solvent affects the Stereoselectivity. The polar solvent is favorable to the formation of trans-β-lactams. The addition orders of the reagents affect the Stereoselectivity in the Staudinger reaction between acyl chlorides and imines. The addition of a tertiary amine into a solution of the acyl chloride and the imine generally decreases the Stereoselectivity, which is affected by the interval between additions of the acyl chloride and the tertiary amine, and the imine s...
-
origin of the relative Stereoselectivity of the β lactam formation in the staudinger reaction
Journal of the American Chemical Society, 2006Co-Authors: Lei Jiao, Yong Liang, Jiaxi XuAbstract:The relative (cis, trans) Stereoselectivity of the β-lactam formation is one of the critical issues in the Staudinger reaction. Although many attempts have been made to explain and to predict the stereochemical outcomes, the origin of the Stereoselectivity remains obscure. We are proposing a model that explains the relative Stereoselectivity based on a kinetic analysis of the cis/trans ratios of reaction products. The results were derived from detailed Hammett analyses. Cyclic imines were employed to investigate the electronic effect of the ketene substituents, and it was found that the Stereoselectivity could not be simply attributed to the torquoelectronic model. Based on our results, the origin of the relative Stereoselectivity can be described as follows: (1) the Stereoselectivity is generated as a result of the competition between the direct ring closure and the isomerization of the imine moiety in the zwitterionic intermediate; (2) the ring closure step is most likely an intramolecular nucleophilic...
Jinhui Feng - One of the best experts on this subject based on the ideXlab platform.
-
engineering of l threonine aldolase for the preparation of 4 methylsulfonyl phenylserine an important intermediate for the synthesis of florfenicol and thiamphenicol
Enzyme and Microbial Technology, 2020Co-Authors: Xi Chen, Qijia Chen, Jinhui Feng, Min Wang, Qiaqing WuAbstract:Abstract l -Threonine aldolases ( l -TAs) catalyze the aldol condensation of aldehyde and glycine, offering direct enzymatic synthesis of β-hydroxy-α-amino acids under mild conditions. However, this method suffers from moderate yield and low Stereoselectivity at the β-carbon. Given the importance of 4-(methylsulfonyl)phenylserine for the synthesis of florfenicol and thiamphenicol, mutations of a l -threonine aldolase from Pseudomonas sp. ( l -PsTA) were performed in this study by error-prone PCR and combinatorial mutation. Some beneficial mutants were obtained by screening the mutant library using a stepwise visual method. 4-(Methylsulfonyl)phenylserine was synthesized in up to 71 % diastereomeric excess (de), which are much higher than the previously reported 2 % de value, by using the newly identified mutants. The mutants V200I and C187S/V200I were found to improve the product yield and Stereoselectivity for the aldol condensation of various benzaldehydes with glycine. These results show that the amino acid residues outside of the substrate-binding cavity of l -PsTA play an important role in determining its Cβ-stereoseletivity.
-
improving and inverting cβ Stereoselectivity of threonine aldolase via substrate binding guided mutagenesis and a stepwise visual screening
ACS Catalysis, 2019Co-Authors: Qijia Chen, Xi Chen, Jinhui Feng, Qiaqing WuAbstract:Threonine aldolase (TA)-catalyzed aldol condensation is a powerful tool for C–C bond formation under mild conditions, but the low Cβ-Stereoselectivity has hampered its wide application. A stepwise visual screening method was developed to measure the activity and Stereoselectivity of threonine aldolase-catalyzed aldol condensation by employing a stereoselective phenylserine dehydratase, enabling direct selection of mutants with higher Cβ-Stereoselectivity. Mutants of l-PsTA from Pseudomonas sp. with improved or inverted Stereoselectivity toward aromatic aldehydes were obtained by simultaneously mutating amino acid residues which interact with the amino and hydroxyl groups of the substrate and screening the resulting mutant libraries with this method. The mutation and enzyme–substrate docking studies provided some insights into the regulation of the Cβ-Stereoselectivity by the enzyme–substrate interactions. This study offers a tool and useful guidance for further engineering of TAs to address the Cβ-stereos...
-
improving the catalytic efficiency and Stereoselectivity of a nitrilase from synechocystis sp pcc6803 by semi rational engineering en route to chiral γ amino acids
Catalysis Science & Technology, 2019Co-Authors: Peiyuan Yao, Jinhui Feng, Dunming ZhuAbstract:Nitrilase-catalysed desymmetrization of 3-substituted glutaronitriles to optically active 3-substituted 4-cyanobutanoic acid offers an attractive approach to access chiral β-substituted γ-amino acids, an important moiety in pharmaceuticals. In this study, we employed enzyme-substrate docking and alanine scanning to determine the key amino acid residues which have a positive effect on the activity and Stereoselectivity of a nitrilase from Synechocystis sp. PCC6803 (SsNIT). Then, site-saturation mutagenesis and combinatorial mutagenesis of the positive amino acid residues (H141, P194, M197, I201 and F202) were performed, and a double mutant (P194A/F202V) and a triple mutant (P194A/I201A/F202V) with high activity and Stereoselectivity were identified for desymmetrization of 3-substituted glutaronitriles to afford (S)-3-substituted-4-cyanobutanoic acids with a high space–time productivity of up to 488 g L−1 d−1. Molecular calculation suggests that the enzymatic activity improvement may be due to the enlargement of the substrate binding cavity. It is interesting that the Stereoselectivity is enhanced simultaneously.
-
Improving and Inverting Cβ‑Stereoselectivity of Threonine Aldolase via Substrate-Binding-Guided Mutagenesis and a Stepwise Visual Screening
2019Co-Authors: Qijia Chen, Xi Chen, Jinhui Feng, Dunming ZhuAbstract:Threonine aldolase (TA)-catalyzed aldol condensation is a powerful tool for C–C bond formation under mild conditions, but the low Cβ-Stereoselectivity has hampered its wide application. A stepwise visual screening method was developed to measure the activity and Stereoselectivity of threonine aldolase-catalyzed aldol condensation by employing a stereoselective phenylserine dehydratase, enabling direct selection of mutants with higher Cβ-Stereoselectivity. Mutants of l-PsTA from Pseudomonas sp. with improved or inverted Stereoselectivity toward aromatic aldehydes were obtained by simultaneously mutating amino acid residues which interact with the amino and hydroxyl groups of the substrate and screening the resulting mutant libraries with this method. The mutation and enzyme–substrate docking studies provided some insights into the regulation of the Cβ-Stereoselectivity by the enzyme–substrate interactions. This study offers a tool and useful guidance for further engineering of TAs to address the Cβ-Stereoselectivity problem
Pan-pan Zhou - One of the best experts on this subject based on the ideXlab platform.
-
insights into the diels alder reaction between 3 vinylindoles and methyleneindolinone without and with the assistance of hydrogen bonding catalyst bisthiourea mechanism origin of Stereoselectivity and role of catalyst
Journal of Organic Chemistry, 2017Co-Authors: Chao-xian Yan, Fan Yang, Xing Yang, Da-gang Zhou, Pan-pan ZhouAbstract:The Diels–Alder reaction between 3-vinylindoles and methyleneindolinone can proceed both under catalyst-free conditions and with bisthiourea as the catalyst. The reaction with bisthiourea is much faster and results in higher Stereoselectivity of the product. The reaction mechanism, origin of Stereoselectivity, and role of the catalyst were elaborated based on quantum mechanical calculations and theoretical methods of reactivity indices, NCI, QTAIM, and distortion/interaction models. In the uncatalyzed reaction, the two C–C bonds that are formed undergo conversion from noncovalent to covalent bonding via a concerted asynchronous mechanism. The weak intermolecular interactions formed in the transition state play important roles. The difference between the interaction and distortion energies is responsible for the Stereoselectivity. In the catalyzed reaction, bisthiourea induces both the diene and dienophile to approach it via weak intermolecular interactions, which greatly lowers the energy barrier of the r...
-
Insights into the Diels–Alder Reaction between 3‑Vinylindoles and Methyleneindolinone without and with the Assistance of Hydrogen-Bonding Catalyst Bisthiourea: Mechanism, Origin of Stereoselectivity, and Role of Catalyst
2017Co-Authors: Chao-xian Yan, Fan Yang, Xing Yang, Da-gang Zhou, Pan-pan ZhouAbstract:The Diels–Alder reaction between 3-vinylindoles and methyleneindolinone can proceed both under catalyst-free conditions and with bisthiourea as the catalyst. The reaction with bisthiourea is much faster and results in higher Stereoselectivity of the product. The reaction mechanism, origin of Stereoselectivity, and role of the catalyst were elaborated based on quantum mechanical calculations and theoretical methods of reactivity indices, NCI, QTAIM, and distortion/interaction models. In the uncatalyzed reaction, the two C–C bonds that are formed undergo conversion from noncovalent to covalent bonding via a concerted asynchronous mechanism. The weak intermolecular interactions formed in the transition state play important roles. The difference between the interaction and distortion energies is responsible for the Stereoselectivity. In the catalyzed reaction, bisthiourea induces both the diene and dienophile to approach it via weak intermolecular interactions, which greatly lowers the energy barrier of the reaction and leads to the product with excellent Stereoselectivity. The possible pathways of this reaction were explored, which suggested that the formation of the two C–C bonds goes through either a stepwise or concerted asynchronous mechanism. These results detail the reaction mechanism and shed light on both the significant role of the bisthiourea catalyst and the origin of Stereoselectivity for this type of Diels–Alder reaction and related ones
Qijia Chen - One of the best experts on this subject based on the ideXlab platform.
-
engineering of l threonine aldolase for the preparation of 4 methylsulfonyl phenylserine an important intermediate for the synthesis of florfenicol and thiamphenicol
Enzyme and Microbial Technology, 2020Co-Authors: Xi Chen, Qijia Chen, Jinhui Feng, Min Wang, Qiaqing WuAbstract:Abstract l -Threonine aldolases ( l -TAs) catalyze the aldol condensation of aldehyde and glycine, offering direct enzymatic synthesis of β-hydroxy-α-amino acids under mild conditions. However, this method suffers from moderate yield and low Stereoselectivity at the β-carbon. Given the importance of 4-(methylsulfonyl)phenylserine for the synthesis of florfenicol and thiamphenicol, mutations of a l -threonine aldolase from Pseudomonas sp. ( l -PsTA) were performed in this study by error-prone PCR and combinatorial mutation. Some beneficial mutants were obtained by screening the mutant library using a stepwise visual method. 4-(Methylsulfonyl)phenylserine was synthesized in up to 71 % diastereomeric excess (de), which are much higher than the previously reported 2 % de value, by using the newly identified mutants. The mutants V200I and C187S/V200I were found to improve the product yield and Stereoselectivity for the aldol condensation of various benzaldehydes with glycine. These results show that the amino acid residues outside of the substrate-binding cavity of l -PsTA play an important role in determining its Cβ-stereoseletivity.
-
improving and inverting cβ Stereoselectivity of threonine aldolase via substrate binding guided mutagenesis and a stepwise visual screening
ACS Catalysis, 2019Co-Authors: Qijia Chen, Xi Chen, Jinhui Feng, Qiaqing WuAbstract:Threonine aldolase (TA)-catalyzed aldol condensation is a powerful tool for C–C bond formation under mild conditions, but the low Cβ-Stereoselectivity has hampered its wide application. A stepwise visual screening method was developed to measure the activity and Stereoselectivity of threonine aldolase-catalyzed aldol condensation by employing a stereoselective phenylserine dehydratase, enabling direct selection of mutants with higher Cβ-Stereoselectivity. Mutants of l-PsTA from Pseudomonas sp. with improved or inverted Stereoselectivity toward aromatic aldehydes were obtained by simultaneously mutating amino acid residues which interact with the amino and hydroxyl groups of the substrate and screening the resulting mutant libraries with this method. The mutation and enzyme–substrate docking studies provided some insights into the regulation of the Cβ-Stereoselectivity by the enzyme–substrate interactions. This study offers a tool and useful guidance for further engineering of TAs to address the Cβ-stereos...
-
Improving and Inverting Cβ‑Stereoselectivity of Threonine Aldolase via Substrate-Binding-Guided Mutagenesis and a Stepwise Visual Screening
2019Co-Authors: Qijia Chen, Xi Chen, Jinhui Feng, Dunming ZhuAbstract:Threonine aldolase (TA)-catalyzed aldol condensation is a powerful tool for C–C bond formation under mild conditions, but the low Cβ-Stereoselectivity has hampered its wide application. A stepwise visual screening method was developed to measure the activity and Stereoselectivity of threonine aldolase-catalyzed aldol condensation by employing a stereoselective phenylserine dehydratase, enabling direct selection of mutants with higher Cβ-Stereoselectivity. Mutants of l-PsTA from Pseudomonas sp. with improved or inverted Stereoselectivity toward aromatic aldehydes were obtained by simultaneously mutating amino acid residues which interact with the amino and hydroxyl groups of the substrate and screening the resulting mutant libraries with this method. The mutation and enzyme–substrate docking studies provided some insights into the regulation of the Cβ-Stereoselectivity by the enzyme–substrate interactions. This study offers a tool and useful guidance for further engineering of TAs to address the Cβ-Stereoselectivity problem