Enzymatic reductive amination of p-hydroxy- and phenylpyruvic acids as a method of synthesis of L-tyrosine and L-phenylalanine labelled with deuterium and tritium

We report the synthesis of isotopomers of L-phenylalanine and L-tyrosine selectively labelled with hydrogen isotopes in the 2-position of the side chain. The deuterium or tritium label was introduced using reductive amination activity of enzyme L-phenylalanine dehydrogenase (EC 1.4.1.20). This way p-phenylpyruvic acid was converted into [2-2H]-, [2-3H]-, and doubly labelled [2-2H/3H]-isotopomers of L-phenylalanine, using deuteriated, tritiated, and mixed (DTO) incubation media, respectively. Similarly, p-hydroxyphenylpyruvic acid was converted into [2-2H]-, [2-3H]-, and [2-2H/3H]-L-tyrosine. Deuterium labelled isotopomers of L-phenylalanine and --tyrosine can be used as markers in the investigation of abnormal metabolism of these amino acids observed in patients with inborn genetic diseases such as phenylketonuria and tyrosinemia.