Used in solid-phase peptide synthesis to introduce a protected cysteine residue. The Fmoc group allows for mild base deprotection, compatible with standard peptide synthesis protocols. The Boc-methyl protection on the thiol side chain prevents unwanted oxidation or disulfide bond formation during synthesis. This makes it ideal for constructing complex peptides that require cysteine at specific positions, especially when later selective deprotection and disulfide pairing are needed. Commonly applied in research settings for synthesizing bioactive peptides, including hormones and enzyme inhibitors.