Deracemization and Stereoinversion of α‐Amino Acids by l‐Amino Acid Deaminase

Abstract

AbstractEnantiomerically pure α‐amino acids are compounds of primary interest for the fine chemical, pharmaceutical, and agrochemical sectors. Amino acid oxidases are used for resolving d,l‐amino acids in biocatalysis. We recently demonstrated that l‐amino acid deaminase from Proteus myxofaciens (PmaLAAD) shows peculiar features for biotechnological applications, such as a high production level as soluble protein in Escherichia coli and a stable binding with the flavin cofactor. Since l‐amino acid deaminases are membrane‐bound enzymes, previous applications were mainly based on the use of cell‐based methods. Now, taking advantage of the broad substrate specificity of PmaLAAD, a number of natural and synthetic l‐amino acids were fully converted by the purified enzyme into the corresponding α‐keto acids: the fastest conversion was obtained for 4‐nitrophenylalanine. Analogously, starting from racemic solutions, the full resolution (ee >99%) was also achieved. Notably, d,l‐1‐naphthylalanine was resolved either into the d‐ or the l‐enantiomer by using PmaLAAD or the d‐amino acid oxidase variant having a glycine at position 213, respectively, and was fully deracemized when the two enzymes were used jointly. Moreover, the complete stereoinversion of l‐4‐nitrophenylalanine was achieved using PmaLAAD and a small molar excess of borane tert‐butylamine complex. Taken together, recombinant PmaLAAD represents an l‐specific amino acid deaminase suitable for producing the pure enantiomers of several natural and synthetic amino acids or the corresponding keto acids, compounds of biotechnological or pharmaceutical relevance.magnified image