Non-natural phenolic amino acids Synthesis and application in peptide chemistry.

Several non-natural phenolic amino acids have been synthesized.t-Butylated tyrosine and thyroxine derivatives, on one-electron oxidation, give persistent radicals which can be used as positional and/or spin labels for amino acids. Two-electron oxidation ofN-protected tyrosines leads to spirolactones, useful active esters for peptide coupling.