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. Copyright © 2004 John Wiley & Sons, Ltd.