(S)-Cyclopropylalanine methyl ester hydrochloride is a chiral, non-proteinogenic amino acid derivative. It features a cyclopropane ring attached to the alpha carbon of an alanine methyl ester backbone, with the (S)-configuration at the stereocenter. The compound is supplied as a hydrochloride salt, enhancing its stability and solubility for synthetic applications. This compound serves as a crucial chiral building block in pharmaceutical research and development. Its primary application is as a key intermediate in the synthesis of complex bioactive molecules, particularly active pharmaceutical ingredients (APIs). The constrained cyclopropane ring is a valuable structural motif used to modulate the conformation, metabolic stability, and potency of drug candidates. It has been employed in the synthesis of protease inhibitors and other therapeutic agents targeting various diseases. As a protected amino acid ester, it is readily incorporated into peptide mimetics and small molecule libraries via standard amide coupling reactions. Its high enantiopurity makes it valuable for constructing stereochemically defined targets. Proper handling requires standard laboratory precautions for handling amine hydrochlorates.