H-Lys-OMe·2HCl (L-Lysine methyl ester dihydrochloride, CAS 26348-70-9) is a protected derivative of the essential amino acid L-lysine. It is a white to off-white crystalline powder, characterized by the esterification of the carboxyl group and the presence of two hydrochloride salts on the side-chain amino group. This modification enhances its solubility in organic solvents and alters its reactivity profile compared to free lysine. This compound is primarily used as a key building block in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS) and solution-phase methods. The methyl ester protects the C-terminus, while the side-chain amino group, protected as a salt, can be selectively deprotected for further coupling. It serves as a crucial intermediate for introducing the lysine residue into peptides and proteins, which is important for creating structures with specific biological activities, such as antimicrobial peptides, enzyme inhibitors, and diagnostic probes. Beyond peptide chemistry, it finds application in biochemical research as a substrate or precursor for studying enzymatic processes involving lysine, such as methylation and acetylation. It is also explored in material science for the preparation of functional polymers and hydrogels. As a chemical reagent, it requires careful handling due to its potential to cause irritation to the skin, eyes, and respiratory system.