Fmoc-Leu-OH-15N is primarily used in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS) methodologies. The Fmoc (fluorenylmethyloxycarbonyl) group serves as a protective group for the amino acid's amine functionality, allowing for the sequential addition of amino acids to build peptides. The presence of the 15N isotope makes it valuable in NMR (nuclear magnetic resonance) spectroscopy studies, where it aids in the structural elucidation and dynamics of peptides and proteins. This labeled compound is especially useful in research involving isotopic labeling for tracking and analyzing molecular interactions, folding mechanisms, and conformational changes in biological systems. Its application is critical in fields like biochemistry, biophysics, and drug development, where precise peptide synthesis and detailed molecular analysis are essential.