Studies on 2‐Formylphenylboronic Acid‐Based Ser/Thr Ligation and Cys/Pen Ligation†.

Main observation and conclusion: Developing an effective chemoselective ligation strategy for assembling unprotected peptide segments is important to peptide/protein synthesis. The ligation efficiency and selectivity depend on the chemistry between the C‐terminal active ester of the peptide (e.g., the thioester in Native Chemical Ligation or the salicylaldehyde ester in Ser/Thr Ligation and Cys/Pen Ligation) and N‐terminal functional groups of the second peptide (Cys or Ser/Thr). Increasing the reactivity of the ligation and decreasing the hydrolysis of the active ester are more like the opposite sites in balance. We investigated the potential application of the peptide acyl ester of 2‐formylphenylboronic acid (2‐FPBA) in the Ser/Thr ligation and Cys/Pen ligation. With the assistance of boronic acid group, the peptidyl FPBA ester showed remarkable stability in aqueous buffer and its reactivity towards Ser/Thr and Cys/Pen also improved. However, the strong coordination of the amine at the N‐terminus and boronic acid suppressed the acyl transfer process when the peptide acyl group was used. More effects should be made to enhance the ligation chemistry. [ABSTRACT FROM AUTHOR]