Used in solid-phase peptide synthesis to introduce a protected guanidinated phenylalanine residue, enabling the construction of peptides with modified side chains for enhanced stability or biological activity. The Fmoc group allows for mild base deprotection, while the Boc2 protection on the guanidine moiety ensures compatibility with standard peptide coupling conditions. Commonly applied in the development of enzyme inhibitors, receptor agonists/antagonists, and bioactive peptides where arginine-like functionality is needed with tailored steric or electronic properties. Also useful in medicinal chemistry for probing protein-protein interactions or improving cell permeability in peptide-based drug candidates.