Biosynthesis of Chiral Amino Alcohols via an Engineered Amine Dehydrogenase in E. coli

Chiral amino alcohols are prevalent synthons in pharmaceuticals and synthetic bioactive compounds. The efficient synthesis of chiral amino alcohols using ammonia as the sole amino donor under mild conditions is highly desired and challenging in organic chemistry and biotechnology. Our previous work explored a panel of engineered amine dehydrogenases (AmDHs) derived from amino acid dehydrogenase (AADH), enabling the one-step synthesis of chiral amino alcohols via the asymmetric reductive amination of α-hydroxy ketones. Although the AmDH-directed asymmetric reduction is in a high stereoselective manner, the activity is yet fully excavated. Herein, an engineered AmDH derived from a leucine dehydrogenase from Sporosarcina psychrophila (SpAmDH) was recruited as the starting enzyme, and the combinatorial active-site saturation test/iterative saturation mutagenesis (CAST/ISM) strategy was applied to improve the activity. After three rounds of mutagenesis in an iterative fashion, the best variant wh84 was obtained and proved to be effective in the asymmetric reductive amination of 1-hydroxy-2-butanone with 4-fold improvements in kcat/Km and total turnover number (TTN) values compared to those of the starting enzyme, while maintaining high enantioselectivity (ee >99%) and thermostability (T5015 >53°C). In preparative-scale reaction, the conversion of 100 and 200 mM 1-hydroxy-2-butanone catalyzed by wh84 was up to 91–99%. Insights into the source of an enhanced activity were gained by the computational analysis. Our work expands the catalytic repertoire and toolbox of AmDHs.

Chiral Amino Alcohols via Catalytic Enantioselective Petasis Borono-Mannich Reactions

Chiral amino alcohols are valuable building blocks in the synthesis of drugs, natural products, and chiral ligands used in enantioselective catalysis. The Petasis borono-Mannich reaction is a multicomponent condensation reaction of aldehydes, amines, and boronic acids to afford chiral amines. This report describes a practical, easily scaled, enantioselective Petasis borono-Mannich reaction of glycolaldehyde, with primary or secondary amines, and boronates catalyzed by BINOLderived catalysts to afford chiral 1,2-amino alcohols in high yields and enantioselectivities. The reactions are executed at room temperature in ethanol or trifluorotoluene using commercially available reagents and leverage an inherently attractive feature of the multicomponent reaction; the ability to use amines and boronates that possess a wide range of structural and electronic properties. Computational modeling of the diastereomeric transition states using DFT calculations identified a non-conventional CH…O interaction as a key feature that selectively stabilizes the transition state leading to the major enantiomer. The enantioselective catalytic reaction exemplifies a truly practical multicomponent condensation to afford 1,2-amino alcohols in highly enantioenriched form.

Chiral Amino Alcohols via Catalytic Enantioselective Petasis Borono-Mannich Reactions

Chiral amino alcohols are valuable building blocks in the synthesis of drugs, natural products, and chiral ligands used in enantioselective catalysis. The Petasis borono-Mannich reaction is a multicomponent condensation reaction of aldehydes, amines, and boronic acids to afford chiral amines. This report describes a practical, easily scaled, enantioselective Petasis borono-Mannich reaction of glycolaldehyde, with primary or secondary amines, and boronates catalyzed by BINOLderived catalysts to afford chiral 1,2-amino alcohols in high yields and enantioselectivities. The reactions are executed at room temperature in ethanol or trifluorotoluene using commercially available reagents and leverage an inherently attractive feature of the multicomponent reaction; the ability to use amines and boronates that possess a wide range of structural and electronic properties. Computational modeling of the diastereomeric transition states using DFT calculations identified a non-conventional CH…O interaction as a key feature that selectively stabilizes the transition state leading to the major enantiomer. The enantioselective catalytic reaction exemplifies a truly practical multicomponent condensation to afford 1,2-amino alcohols in highly enantioenriched form.

Data mining of amine dehydrogenases for the synthesis of enantiopure amino alcohols

Five amine dehydrogenases (AmDHs) derived from amino acid dehydrogenases have been identified and evaluated for the stereoselective amination of α-/β-functionalized carbonyl compounds to synthesize chiral amino alcohols.

Enabling an atom-economic production of chiral amino alcohols by electrodialysis with bipolar membranes

Along with catalytic hydrogenation, producing pure chiral amino alcohols with a perfect atom economy is achieved by electrodialysis with bipolar membranes.