Fmoc-(S)-3-Amino-4-(4-fluoro-phenyl)-butyric acid is primarily used in peptide synthesis as a building block. The Fmoc group acts as a protective group for the amine functionality, allowing for controlled and sequential peptide chain elongation. This compound is particularly valuable in the synthesis of peptides containing fluorinated aromatic residues, which can enhance the stability, binding affinity, or biological activity of the resulting peptides. It is widely employed in pharmaceutical research and development, especially in the creation of peptide-based drugs, enzyme inhibitors, and probes for biochemical studies. The incorporation of the fluoro-phenyl group can also improve the pharmacokinetic properties of peptides, making it a useful tool in drug design.