135635-66-4Relevant academic research and scientific papers
Characteristics of l-threonine transaldolase for asymmetric synthesis of β-hydroxy-α-amino acids
Xu, Lian,Wang, Li-Chao,Xu, Xin-Qi,Lin, Juan
, p. 5943 - 5952 (2019)
l-Threonine transaldolase (LTTA) is a putative serine hydroxymethyltransferase (SHMT) that can catalyze the trans-aldehyde reaction of l-threonine and aldehyde to produce l-threo-β-hydroxy-α-amino acids with excellent stereoselectivity. In the present study, an l-threonine transaldolase from Pseudomonas sp. (PsLTTA) was mined and expressed in Escherichia coli BL21 (DE3). A substrate spectrum assay indicated that PsLTTA only consumed l-threonine as the donor substrate and could accept a wide range of aromatic aldehydes as acceptor substrates. Among these substrates, PsLTTA could catalyze p-methylsulfonyl benzaldehyde and l-threonine to produce l-threo-p-methylsulfonylphenylserine with a high conversion rate (74.4%) and a high de value (79.9%). The conversion and stereoselectivity of PsLTTA were found to be dramatically influenced by the concentration of the whole cell, the co-solvent and the reaction temperature. Through conditional optimization, l-threo-p-methylsulfonylphenylserine was obtained with 67.1% conversion and a near-perfect de value (94.5%), the highest stereoselectivity for an l-threo-β-hydroxy-α-amino acid so far reported by enzymatic synthesis. Finally, synthesis of l-threo-p-methylsulfonylphenylserine at a 100 mL scale by whole-cell biocatalysis was conducted. This is the first systematic report of l-threonine transaldolase as a robust biocatalyst for preparation of β-hydroxy-α-amino acids, which can provide new insights for β-hydroxy-α-amino acids synthesis.
Improving and Inverting Cβ-Stereoselectivity of Threonine Aldolase via Substrate-Binding-Guided Mutagenesis and a Stepwise Visual Screening
Chen, Qijia,Chen, Xi,Feng, Jinhui,Wu, Qiaqing,Zhu, Dunming,Ma, Yanhe
, p. 4462 - 4469 (2019/05/10)
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.
Engineered L-serine hydroxymethyltransferase from streptococcus thermophilus for the synthesis of α,α-dialkyl-α-amino acids
Bujons, Jordi,Claps, Pere,Hernandez, Karel,Joglar, Jesffls,Zelen, Igor,Usn, Isabel,Petrillo, Giovanna,Wandtke, Claudia M.,Parella, Teodor
supporting information, p. 3013 - 3017 (2015/10/05)
α,α-Disubstituted a-amino acids are central to biotechnological and biomedical chemical processes for their own sake and as substructures of biologically active molecules for diverse biomedical applications. Structurally, these compounds contain a quaternary stereocenter, which is particularly challenging for stereoselective synthesis. The pyridoxal-5′-phosphate (PLP)-dependent l -serine hydroxymethyltransferase from Streptococcus thermophilus (SHMTSth; EC 2.1.2.1) was engineered to achieve the stereoselective synthesis of a broad structural variety of α,α-dialkyl-α-amino acids. This was accomplished by the formation of quaternary stereocenters through aldol addition of the amino acids D-Ala and D-Ser to a wide acceptor scope catalyzed by the minimalist SHMTSth Y55T variant overcoming the limitation of the native enzyme for Gly. The SHMTSth Y55T variant tolerates aromatic and aliphatic aldehydes as well as hydroxy- and nitrogen-containing aldehydes as acceptors.
Diastereo- And enantioselective synthesis of β-Hydroxy-α-amino acids: Application to the synthesis of a key intermediate for lactacystin
Li, Qiong,Yang, Shao-Bo,Zhang, Zhihui,Li, Lei,Xu, Peng-Fei
supporting information; experimental part, p. 1627 - 1631 (2009/09/24)
The development of a highly efficient and stereoselective methodology for the preparation of β-hydroxy-α- amino acids is described. Nucleophilic addition of enolates of tricyclic iminolactones 1a and 1b to aldehydes in the presence of 6 equiv of lithium chloride in THF at -78 °C leads to aldol adducts in good yield (63-86%) and high diastereoselectivity (up to >25:1 dr). Subsequently, hydrolysis of the aldol adducts under acidic conditions leads to the corresponding β-hydroxy-a-amino acids in good yields (up to 83%) and excellent enantiomeric excesses (99% ee) with good recovery yields of the chiral auxiliaries 6 and 7. This methodology was applied to the facile synthesis of the key intermediate for lactacystin along with several isomers.
Benzyl (R)- and (S)-tert-Butyl-5-oxo-oxazolidine-3-carboxylate for Convenient Preparation of D- and L-Threonine Analogs from Aldehydes
Blaser, Denis,Seebach, Dieter
, p. 1067 - 1078 (2007/10/02)
Lithium enolates of (R)- or (S)-oxazolidinones 1 (specified in the title) are generated with lithium hexamethyldisilazanide (LHMDS) in THF at -75 deg C and added to aliphatic or aromatic aldehydes (products 2-18 of hydroxyalkylation, yields mostly over 80percent, diastereoselectivities usually over 98percent; Scheme 2).The adducts can be cleaved to give threonine analogs (19-32) under salt-free conditions (H2/Pd-C, then H2O and evaporation of the solvents, Scheme 3).In some cases, the primary adducts may cyclize with elimination of benzyl alcohol to give bicyclic carbamates 33 which, in turn, can be hydrolyzed to 5-substituted trans-2-oxo-1,3-oxazolidine-4-carboxylic acids 34 (Scheme 4). - The essentially complete threo selectivity of the coupling step is proved by NMR spectroscopy and by chemical correlations.The stereochemical course of the reaction is opposite to that observed with carbocyclic enolates; possible reasons for this behavior are discussed (Scheme 5). - The starting material rac-1, prepared from glycine, pivalaldehyde and benzyl chloroformate, is readily resolved by chromatography on preparative scale by using the stationary phase Chiraspher and a Prepbar system (Scheme 1); The undesired enantiomer may be recycled by thermal racemization (heating at reflux in CH3CN for 8 h). Key Words: D- or L-Threonines / Aldol additions / Diastereoselective coupling of trigonal centers / 1,3-Oxazolidin-5-ones / 1,3-Oxazolidin-2-ones, 5-substituted, 4-carboxylic acid
