Fmoc-Leu-OH is widely used in peptide synthesis as a building block for constructing peptides. It is particularly valuable in solid-phase peptide synthesis (SPPS), where the Fmoc (fluorenylmethyloxycarbonyl) group serves as a protecting group for the amino acid leucine. This allows for the stepwise addition of amino acids to grow the peptide chain. The Fmoc group can be easily removed under mild basic conditions, making it a preferred choice for synthesizing complex peptides and proteins. Its application is critical in pharmaceutical research, biotechnology, and the development of therapeutic peptides, where precise control over peptide structure is essential. Additionally, it is used in the production of peptide-based drugs, vaccines, and diagnostic agents.