Water Compatible Photoarylation of Amino Acids and Peptides

A novel photoarylation of amino acids and peptides is described, which tolerates the presence of water. Irradiation of Boc‐protected amino acids in the presence of N‐protected 2‐azidobenzimidazoles leads to selective arylation of carboxy termini or side chains. The new reaction also works for peptides. Irradiation of the nonapeptide H‐SPSYVYHQF‐OH also resulted in selective arylation of the tyrosine side chains, as indicated by ESI‐MS/MS fragmentation. Chemo‐ and regioselectivity could add the title reaction to the repertoire of photoaffinity labeling methods.