Z-D-Lys(Boc)-OSu is the N-hydroxysuccinimide active ester of N^α-Z-N^ε-Boc-D-lysine, a fully protected D-lysine building block used in peptide synthesis. The OSu group enables efficient and selective coupling to N-terminal amines of growing peptide chains, primarily in solution-phase synthesis but also compatible with solid-phase methods. The orthogonal protecting groups—Z (Cbz) on the α-amino (removable by hydrogenation or HBr/AcOH) and Boc on the ε-amino (removable by TFA)—provide precise control for sequential deprotection and side-chain modification. This reagent is essential for constructing complex peptides, peptide conjugates, and bioactive molecules in research and pharmaceutical applications.