This compound is the hydrochloride salt of (S)-tert-butyl 2-amino-6-{[(9H-fluoren-9-ylmethoxy)carbonyl]amino}hexanoate, a protected derivative of L-lysine. It has a free α-amino group (protonated as HCl salt), a tert-butyl ester protecting the carboxylic acid, and an Fmoc group specifically protecting the ε-amino group on the lysine side chain. This unique protection pattern is employed in peptide synthesis, particularly in solution-phase approaches or for orthogonal deprotection strategies where the side chain needs temporary protection. The Fmoc group is removed under mild basic conditions (e.g., piperidine), while the tert-butyl ester remains stable to bases but can be cleaved with mild acids (e.g., TFA). The free α-amino allows for direct coupling in synthetic sequences. It is valuable as a key intermediate in constructing lysine-containing peptides for pharmaceutical research, drug development, and biochemical studies, enabling precise control over side-chain reactivity and high-purity peptide production.