N-(9-Fluorenylmethoxycarbonyl)-D-lysine hydrochloride (Fmoc-D-Lys-OH·HCl), with CAS number 201002-47-3, is a protected derivative of the amino acid D-lysine. It features the acid-labile 9-fluorenylmethoxycarbonyl (Fmoc) group protecting the alpha-amino group, while the side-chain amino group is typically protected with a Boc (tert-butoxycarbonyl) group, though in this specific hydrochloride salt form, the side chain is not Boc-protected. This compound is a white to off-white crystalline powder. This derivative is a fundamental and essential building block in solid-phase peptide synthesis (SPPS) employing the Fmoc strategy. The Fmoc group allows for orthogonal deprotection under mild basic conditions (e.g., piperidine), enabling the sequential assembly of peptide chains on a resin. D-Lysine is a non-proteinogenic amino acid and its incorporation into peptides is crucial for creating peptidomimetics, studying enzyme-substrate interactions, and developing therapeutic peptides with enhanced stability or specific biological activities, such as antimicrobial peptides or hormone analogs. As a specialty amino acid derivative, it is not a commodity chemical but a high-value research and development reagent. Its primary use is confined to peptide chemistry laboratories and pharmaceutical development for constructing peptides containing D-configured lysine residues. Proper handling requires standard laboratory safety precautions for fine chemicals.