Fmoc-S-xanthyl-L-cysteine is primarily used in peptide synthesis as a protecting group for cysteine residues. The Fmoc group ensures selective deprotection during solid-phase peptide synthesis, allowing for the controlled assembly of complex peptides. The xanthyl moiety provides additional stability and protection, particularly in preventing unwanted disulfide bond formation, which is crucial for maintaining the integrity of cysteine-containing peptides. This compound is especially valuable in the synthesis of peptides for pharmaceutical research, where precise control over cysteine reactivity is essential. Its application extends to the development of therapeutic peptides, protein engineering, and biochemical studies involving cysteine-rich proteins.