Improvementof Transpeptidative Protein Ligation viaSelective Nucleophile Quenching using 2‑Cyano-6-hydroxybenzothiazole

Here, we report a new method that employs a simple and readily available small molecule, 2-cyano-6-hydroxybenzothiazole (CBT), to selectively quench the nucleophilicity of an N-terminal Cys-containing leaving group, thereby shifting the equilibrium of peptidyl asparaginyl ligase (PAL)-mediated ligation toward the product side. This method can be applied not only to the N- and C-terminal modifications of proteins but also to efficiently mediate protein–protein ligation.