Fast Protein Modification in the Nanomolar Concentration Range Using an Oxalyl Amide as Latent Thioester**

Abstract

We show that latent oxalyl thioester surrogates are a powerful means to modify peptides and proteins in highly dilute conditions in purified aqueous media or in mixtures as complex as cell lysates. Designed to be shelf‐stable reagents, they can be activated on demand to enable ligation reactions with peptide concentrations as low as a few hundred nM at rates approaching 30 M−1 s−1.