This compound is an Fmoc-protected derivative of L-lysine, specifically (S)-Fmoc-Lys-OtBu hydrochloride, used primarily in solid-phase peptide synthesis. The fluorenylmethoxycarbonyl (Fmoc) group protects the α-amino functionality, enabling selective deprotection with base. The tert-butyl (OtBu) ester safeguards the carboxylic acid group, which is removed in the final global deprotection step with acid. The side-chain ε-amino group remains unprotected and is present as the hydrochloride salt, allowing for further modification if needed or incorporation into peptides where side-chain reactivity is desired. This specialty chemical intermediate is essential for constructing peptides with precise sequences in pharmaceutical research, drug development, and biochemical studies requiring defined structures.