This compound, (2S,4R)-4-{[(tert-butoxy)carbonyl]amino}-1-{[(9H-fluoren-9-yl)methoxy]carbonyl}pyrrolidine-2-carboxylic acid, is a protected amino acid derivative featuring a pyrrolidine ring. It is a key chiral building block in solid-phase peptide synthesis (SPPS). The molecule incorporates two orthogonal protecting groups: the 9-fluorenylmethoxycarbonyl (Fmoc) group on the amine nitrogen and the tert-butoxycarbonyl (Boc) group on the side-chain amine. The Fmoc group is base-labile and is standardly used for temporary α-amino protection in Fmoc-SPPS, while the Boc group is acid-labile, providing orthogonal protection for the side chain functionality. Its primary and well-defined application is as a specialized, non-proteinogenic amino acid precursor for the synthesis of peptides and peptidomimetics. The (2S,4R) stereochemistry of the proline-like structure is crucial for introducing conformational constraints into peptide chains, which can enhance metabolic stability, receptor selectivity, and biological activity. It is extensively used in medicinal chemistry research for developing therapeutic peptides, protease inhibitors, and other bioactive molecules targeting various diseases. This compound is a high-value synthetic intermediate rather than a final API. It is commercially available from suppliers specializing in peptide synthesis reagents and advanced pharmaceutical intermediates. Handling requires standard precautions for laboratory chemicals, and it should be stored under inert conditions to preserve its stability.