L-Glutamine methyl ester hydrochloride is a protected derivative of L-glutamine, commonly used as an intermediate in peptide synthesis and pharmaceutical development. The methyl ester group serves to protect the carboxylic acid, facilitating selective N-terminal modifications and coupling reactions in solid-phase or solution-phase peptide assembly. It is essential in biochemical research for investigating protein folding, enzyme kinetics, and cellular metabolism. Additionally, it plays a role in the synthesis of glutamine-based therapeutics and research probes, valued for its chemical stability and solubility in organic and aqueous media.