Enzymatic Asymmetric Isomerization of α- to β-Amino Acids

Key words

amino acids - isomerization - phenylalanine aminomutase (PAM)

Significance

A biocatalytic asymmetric approach to β-amino acids from the corresponding enantioenriched α-amino acids is reported. Native phenylalanine aminomutase (PAM) from Taxus mediates the stereospecific isomerization of (S)-α-arylalanines 1 to (R)-β-arylalanines 2 in varying catalytic efficiencies (six orders of magnitude), depending on the respective substrate. Various aromatic as well as heteroaromatic groups are tolerated.

Comment

Optically active β-amino acids are of great value due to their biological activity as well as their function as chiral building blocks for the synthesis of complex molecules, including β-lactams and β-peptides. While previously described protocols to prepare β-amino-β-arylpropionic acids (2) suffer from the requirement of multiple steps (G. Cardillo, C. Tomasini Chem. Soc. Rev. 1996, 25, 117), the present method involves only one step starting from readily available precursors 1. A possible extension to the use of aliphatic α-alanine derivatives or racemic starting materials would render the process even more attractive.