Used in peptide synthesis as an activated ester for introducing glutamine residues with orthogonal protection. Enables efficient coupling in solid-phase and solution-phase peptide assembly, particularly when Z (benzyloxycarbonyl) protection is desired. Its Osu (N-hydroxysuccinimide) ester group enhances reactivity and reduces racemization during amide bond formation. Commonly applied in the preparation of biologically active peptides and protein fragments where selective deprotection and chain elongation are required.