Fmoc-HoCit-OH is widely used in peptide synthesis as a building block for introducing hydroxycitrulline residues into peptides. It is particularly valuable in the study of post-translational modifications, especially in the context of citrullination, which plays a role in autoimmune diseases like rheumatoid arthritis. The Fmoc protecting group ensures selective deprotection during solid-phase peptide synthesis, allowing for the precise construction of complex peptide sequences. Additionally, it is employed in the development of peptide-based drugs and biomaterials, where the incorporation of hydroxycitrulline can influence peptide stability, solubility, and biological activity. Its application extends to research in protein-protein interactions and the design of enzyme inhibitors.