3-((((9H-Fluoren-9-yl)methoxy)carbonyl)amino)oxetane-3-carboxylic acid is a specialty chemical used as an Fmoc-protected non-natural amino acid building block in solid-phase peptide synthesis (SPPS). The fluorenylmethoxycarbonyl (Fmoc) group protects the 3-amino functionality, enabling orthogonal deprotection under mild basic conditions (e.g., piperidine in DMF) for stepwise peptide chain assembly. The oxetane ring at the 3-position introduces conformational rigidity and metabolic stability to the peptide backbone, facilitating studies of structure-activity relationships (SAR). It is essential for developing pharmaceutical peptides and peptidomimetics requiring precise sequences and enhanced properties.