ß-Phenylalanine Ester Synthesis from Stable ß-Keto Ester Substrate Using Engineered ω-Transaminases.

ABSTRACT

The successful synthesis of chiral amines from ketones using ω-transaminases has been shown in many cases in the last two decades. In contrast, the amination of ß-keto acids is a special and relatively new challenge, as they decompose easily in aqueous solution. To avoid this, transamination of the more stable ß-keto esters would be an interesting alternative. For this reason, ω-transaminases were tested in this study, which enabled the transamination of the ß-keto ester substrate ethyl benzoylacetate. Therefore, a ω-transaminase library was screened using a coloring o-xylylenediamine assay. The ω-transaminase mutants 3FCR_4M and ATA117 11Rd show great potential for further engineering experiments aiming at the synthesis of chiral (S)- and (R)-ß-phenylalanine esters. This alternative approach resulted in the conversion of 32% and 13% for the (S)- and (R)-enantiomer, respectively. Furthermore, the (S)-ß-phenylalanine ethyl ester was isolated by performing a semi-preparative synthesis.