Cis-3-Aminocyclobutanecarboxylic acid hydrochloride is a conformationally constrained, non-proteinogenic amino acid derivative. It features a cyclobutane ring with cis-oriented amino and carboxylic acid functional groups, which are presented as the hydrochloride salt for enhanced stability and solubility. This structural motif imparts significant rigidity compared to linear amino acids, making it a valuable scaffold in medicinal chemistry. Its primary application is as a key pharmaceutical intermediate and a versatile building block in drug discovery. The constrained cyclobutane core is utilized to modulate the peptide backbone conformation, thereby improving metabolic stability, bioavailability, and target selectivity of potential drug candidates. It is particularly relevant in the design and synthesis of peptidomimetics and novel bioactive compounds targeting various therapeutic areas. As a bifunctional synthon containing both a protected amine (as HCl salt) and a carboxylic acid, it is extensively used in solid-phase peptide synthesis (SPPS) and solution-phase coupling reactions to introduce the cyclobutane amino acid (Cba) residue. Its utility extends to materials science for creating foldamers and functional polymers. Standard safety precautions for handling amino acid derivatives and hydrochloride salts should be observed.