Fmoc-Phe(4-Br)-OH is primarily used in peptide synthesis as a building block for creating peptide chains. The Fmoc group serves as a protecting group for the amine functionality, ensuring selective reactions during the synthesis process. The bromine atom on the phenyl ring allows for further functionalization, such as cross-coupling reactions, making it valuable in the development of modified peptides or peptide-based drugs. Its application is particularly significant in solid-phase peptide synthesis (SPPS), where it contributes to the production of peptides with specific structural or functional properties for research, therapeutic, or diagnostic purposes.