(S)-Benzyl (1-amino-4-methyl-1-oxopentan-2-yl)carbamate, commonly known as Cbz-L-Leu-NH₂ or N-(benzyloxycarbonyl)-L-leucinamide, is a protected derivative of L-leucinamide primarily used in peptide synthesis. The Cbz (benzyloxycarbonyl) protecting group safeguards the α-amino functionality, enabling selective coupling reactions at the carboxamide group for constructing C-terminal amidated peptides and peptidomimetics. It exhibits excellent stability under standard peptide coupling conditions (e.g., with DIC/HOBt or HBTU) and is orthogonally deprotected via hydrogenation or strong acid. This reagent is essential in pharmaceutical development for complex peptide drugs and in research on peptide-protein interactions, enzyme inhibitors, and biochemical mechanisms.