Fmoc-Arg(Pmc)-OH is a protected derivative of the amino acid L-arginine, featuring two orthogonal protecting groups: the base-labile 9-fluorenylmethoxycarbonyl (Fmoc) group on the α-amino function and the acid-labile 2,2,5,7,8-pentamethylchroman-6-sulfonyl (Pmc) group on the guanidino side chain. Its CAS number is 119831-72-0. This compound is a cornerstone building block in solid-phase peptide synthesis (SPPS) employing the Fmoc strategy. The Pmc group effectively protects the highly polar and nucleophilic guanidino group of arginine during the repetitive coupling cycles, preventing side reactions and ensuring high coupling efficiency. It is selectively removed under mild acidic conditions (e.g., with trifluoroacetic acid) during the final cleavage and deprotection step, while the Fmoc group is removed with piperidine during chain elongation. Due to the critical role of arginine in numerous biologically active peptides and proteins, Fmoc-Arg(Pmc)-OH is an essential and widely used reagent in pharmaceutical research, peptide drug development, and biochemical studies. It enables the reliable incorporation of arginine residues into synthetic peptide sequences.