(2S,4R)-1-(tert-Butoxycarbonyl)-4-(hydroxymethyl)pyrrolidine-2-carboxylic acid is a chiral, non-proteinogenic amino acid derivative featuring a pyrrolidine ring. It serves as a crucial building block in the synthesis of peptidomimetics and constrained peptides. The compound contains both a carboxylic acid and a hydroxymethyl group on the pyrrolidine scaffold, which are amenable to further chemical modifications, allowing for the introduction of diverse side chains and functionalities. This intermediate is extensively utilized in medicinal chemistry for the development of protease inhibitors and other bioactive peptides. Its rigid, proline-like structure is valuable for inducing specific conformational constraints in peptide backbones, thereby enhancing metabolic stability, bioavailability, and target selectivity. It is a key precursor in the synthesis of complex molecules for pharmaceutical research. The Boc-protected amine and the orthogonal protecting groups on the carboxylic acid and alcohol functionalities make it a versatile and widely used synthon in solid-phase peptide synthesis (SPPS) and solution-phase chemistry. It is commercially available from several fine chemical suppliers catering to the life sciences and drug discovery sectors.