N -Terminal Cysteine Bioconjugation with (2-Cyanamidophenyl)boronic Acids Enables the Direct Formation of Benzodiazaborines on Peptides.

Benzodiazaborines (BDABs) have emerged as a valuable tool to produce stable and functional bioconjugates via a click-type transformation. However, the current available methods to install them on peptides lack bioorthogonality, limiting their applications. Here, we report a strategy to install BDABs directly on peptide chains using (2-cyanamidophenyl)boronic acids (2CyPBAs). The resulting BDAB is stabilized through the formation of a key intramolecular B-N bond. This technology was applied in the selective modification of N -terminal cysteine-containing functional peptides.