FMOC-LEU-OSU is used in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS), as a protected and activated form of leucine. The FMOC group provides temporary protection for the amino group, allowing selective deprotection during the synthesis process. The OSU (N-hydroxysuccinimide ester) activates the carboxylic acid for efficient coupling to the amino group of other amino acids. It is especially useful for synthesizing complex peptides and proteins, ensuring high purity and yield. Commonly applied in pharmaceutical research, biotechnology, and the development of therapeutic peptides. Its stability, ease of removal, and coupling efficiency make it a preferred choice in modern peptide chemistry.