L-Arginine ethyl ester dihydrochloride is a synthetic derivative of L-arginine, primarily used as a protected building block in peptide synthesis. It facilitates the incorporation of the arginine residue into peptides and proteins during solid-phase or solution-phase peptide assembly, making it essential in biochemical research and pharmaceutical development for creating bioactive peptides and enzyme substrates. The ethyl ester protects the carboxyl group, while the dihydrochloride form improves solubility in organic solvents. This compound is also employed in studies exploring nitric oxide pathways, as it can act as a substrate analog for nitric oxide synthase, though its main application is as a synthetic intermediate rather than a direct therapeutic agent. It is not typically used in cosmetics or supplements due to its esterified form, which alters its bioavailability compared to free L-arginine.