Herein, we report a method for the continuous flow DKR of rac-1-phenylethanol catalyzed by CAL-B and VOSO4, using a single packed-bed containing both catalysts.
Unnatural amino acids attract growing attention for pharmaceutical applications as they are useful building blocks for the synthesis of a number of chiral drugs. Here, we describe a two‐step enzymatic method for the asymmetric synthesis of homoalanine from L‐methionine, a cheap and readily available natural amino acid. First, the enzyme L‐methionine γ‐lyase (METase), from Fusobacterium nucleatum, catalyzed the γ‐elimination of L‐methionine to 2‐oxobutyrate. Second, an amino acid aminotransferase catalyzed the asymmetric conversion of 2‐oxobutyrate to either L‐ or D‐homoalanine. The L‐branched chain amino acid aminotransferase from Escherichia coli (eBCAT), using L‐glutamate as amino donor, produced L‐homoalanine (32.5 % conv., 28 % y, 99 % ee) and the D‐amino acid aminotransferase from Bacillus sp. (DATA) used D‐alanine as amino donor to produce D‐homoalanine (87.5 % conv., 69 % y, 90 % ee). Thus, this concept allows for the first time the synthesis of both enantiomers of this important unnatural amino acid.
l-Methionine γ-lyase (MGL) is a PLP-dependent enzyme which catalyzes the α, γ-elimination reaction in sulfur containing amino acids, such as L-methionine and L-cysteine. Its major applications are on metabolic restriction of methionine to cancer cells, food industry (cheese flavor) and for the synthesis of d and l-homoalanine. Herein, we present the immobilization and use of this new immobilized biocatalyst under batch and continuous-flow conditions. The best optimized continuousflow condition allowed 89 % conversion in 30 min of residence time with good recyclability of the biocatalyst.
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