1-Methyl-4-aryl-urazole (MAUra) labels tyrosine in proximity to ruthenium photocatalysts.

We designed and synthesised peptides conjugated with proline linkers and ruthenium photocatalysts. These peptides were used as substrates to evaluate the photocatalyst-proximity dependences of candidates for tyrosine labelling reagents. The 1-methyl-4-aryl-urazole (MAUra) structure was found to be a novel tyrosyl radical trapping agent to label tyrosine residues effectively under the conditions where the ruthenium photocatalyst and tyrosine were in close proximity. Using a ruthenium photocatalyst conjugated to a carbonic anhydrase ligand, the target protein in a complex protein mixture was labelled with remarkable target selectivity by azide- or desthiobiotin-conjugated MAUra derivatives.