Boc-L-Ser-OSu is an activated N-Boc-protected L-serine derivative, specifically the N-hydroxysuccinimide ester, used in peptide synthesis to incorporate serine residues into peptide chains. It serves as a coupling agent in solid-phase peptide synthesis (SPPS), where the active ester facilitates efficient amide bond formation with the N-terminal amine of the growing peptide, while the Boc group protects the α-amino function. This orthogonality allows selective deprotection of the Boc group under acidic conditions without affecting other protecting groups. The compound is widely employed in the synthesis of serine-containing peptides for biochemical, pharmaceutical, and medicinal chemistry applications, enabling the study of peptide folding, biological activity, and drug development. Its high reactivity and stability make it ideal for automated and manual peptide assembly.