A Crystallization-Induced Asymmetric Transformation using Racemic Phenyl Alanine Methyl Ester Derivatives as Versatile Precursors to Prepare Amino Acids

Abstract

L-Tyrosine and L-Dopa are the precursors in the biological synthesis of amine neurotransmitters. On the other hand, phenylalanine as an aromatic amino acid (AAA) is a precursor in the synthesis of L-Tyrosine and L-Dopa. For some substrates such as amino acids, resolution by the formation of diastereomers offers an attractive alternative. Among different methods in this case, crystallization-induced asymmetric transformation (CIAT) that is <em>in situ</em> racemization and selective crystallization of a reaction product can be a good choice. Using this method, preparation of L-Tyrosine and L-Dopa has been reported. In the synthetic route, racemic phenyl alanine methyl ester derivatives as versatile precursors were prepared by reducing azlactone derivatives with Mg in methanol as a reducing reagent and then in the resolution step (S)- enantiomer of L-Dopa (3,4-dihydroxyphenylalanine) and L-Tyrosine (4-hydroxyphenylalanine) were achieved via salt formation with (2R,3R)-tartaric acid in the presence of 5-nitro salicylaldehyde in good yield and high optical purity.