Highly selective synthesis of d-amino acids from readily available l-amino acids by a one-pot biocatalytic stereoinversion cascade

Abstract

D-Amino acids are key intermediates required for the synthesis of important pharmaceuticals. However, establishing a universal enzymatic method for the general synthesis of D-amino acids from cheap and readily available precursors with few by-products is challenging. In this study, we constructed and optimized a cascade enzymatic route involving L-amino acid deaminase and D-amino acid dehydrogenase for the biocatalytic stereoinversions of L-amino acids into D-amino acids. Using L-phenylalanine (L-Phe) as a model substrate, this artificial biocatalytic cascade stereoinversion route first deaminates L-Phe to phenylpyruvic acid (PPA) through catalysis involving recombinant Escherichia coli cells that express L-amino acid deaminase from Proteus mirabilis (PmLAAD), followed by stereoselective reductive amination with recombinant meso-diaminopimelate dehydrogenase from Symbiobacterium thermophilum (StDAPDH) to produce D-phenylalanine (D-Phe). By incorporating a formate dehydrogenase-based NADPH-recycling system, D-Phe was obtained in quantitative yield with an enantiomeric excess greater than 99%. In addition, the cascade reaction system was also used to stereoinvert a variety of aromatic and aliphatic L-amino acids to the corresponding D-amino acids by combining the PmLAAD whole-cell biocatalyst with the StDAPDH variant. Hence, this method represents a concise and efficient route for the asymmetric synthesis of D-amino acids from the corresponding L-amino acids.