H-Phe(4-Ac)-OH is primarily used in peptide synthesis as a building block for creating modified peptides. It is particularly valuable in research and development for studying peptide structure-activity relationships, as the acetyl group at the para position of the phenylalanine side chain can influence peptide interactions and stability. This compound is also employed in the design of peptide-based drugs and biomaterials, where specific modifications are needed to enhance bioavailability, target specificity, or resistance to enzymatic degradation. Additionally, it finds applications in organic chemistry as an intermediate for synthesizing more complex molecules with tailored properties.