Thioester Ligation with AAHO Peptides

We report herein a new chemoselective ligation reaction between a peptide thioester and an aminoacyl-<i>N</i>-hydroxy peptide (AAHO peptide). In this ligation scheme, the thioester engages the nucleophilic <i>N</i>-hydroxyl group of the AAHO peptide in a thio-to-oxo transesterification reaction to form a transient <i>O</i>-acyl intermediate that rapidly rearranges to form a native peptide bond at the ligation junction. The <i>N</i>-hydroxyl auxiliary on the peptide bond next to the junction can be easily removed through the reductive cleavage of the N-O bond. Ubiquitination was demonstrated on a synthetic peptide containing Lys(<i>N</i>^ε-glycyl-<i>N</i>^ε-OH), an AAHO-modified lysine residue.