Enhanced Conversion of Racemic α-Arylalanines to (R)β-Arylalaninesby Coupled Racemase/Aminomutase Catalysis

摘要

The Taxus phenylalanine aminomutase (PAM) enzyme converts several (S)-α-arylalanines to theircorresponding (R)-β-arylalanines. After incubating various racemic substrates with 100 μg of PAM for20 h at 31 °C, each (S)-α-arylalanine was enantioselectively isomerized to its corresponding (R)--pr oduct . With racemic starting materials, the ratio of (R)-β-arylalanine product to the (S)-α-substrate ranged between 0.4 and 1.8, the remaining nonproductive (R)-α-arylalanine becameenriched. To utilize the (R)-α-isomer, the catalysis of a promiscuous alanine racemase from Pseudo-monas putida (KT2440) was coupled with that of PAM to increase the production of enantiopure (R)-β-arylalaninesfrom racemic a-arylalanine substrates. The inclusion of a biocatalytic racemizationalong with the PAM-catalyzed reaction moderately increased the overall reaction yield of enantiopureβ-arylalanines between 4% and 19% (depending on the arylalanine), which corresponded to as much asa 63% increase compared to the turnover with the aminomutase reaction alone. The use of thesebiocatalysts, in tandem, could potentially find application in the production of chiral β-arylalaninebuilding blocks, particularly, as refinements to the process are made that increase reaction flux, such asby selectively removing the desired (R)-β-arylalanine product from the reaction mixture.