Synthesis of tritium labelled [2′,6′]‐ L ‐tyrosine

The synthesis of a specifically ring labelled isotopomer of L‐tyrosine, (L‐Tyr), using a combination of chemical and enzymatic methods is reported. The tritium labelled [2′,6′]‐L‐Tyr has been synthesized via catalytic exchange of phenol with tritiated water in the presence of K2PtCl4, reverse acid catalysed removal of tritium from the o‐ and p‐positions of phenol, and subsequent condensation of the resulting [3′,5‐3H2]‐phenol with S‐methyl‐L‐cysteine using the enzyme β‐tyrosinase from Citrobacter freundii.