Boc-Cys(Fm)-OH is widely used in peptide synthesis as a protecting group for cysteine residues. The Boc (tert-butoxycarbonyl) group shields the amino group, while the Fm (fluorenylmethyl) group protects the thiol functionality of cysteine. This dual protection ensures selective reactions during peptide chain assembly, preventing unwanted side reactions. It is particularly valuable in solid-phase peptide synthesis (SPPS), where controlled deprotection and coupling steps are essential. Additionally, it finds application in the synthesis of complex peptides, including those with disulfide bonds, which are critical in bioactive peptides and proteins. Its stability under various reaction conditions makes it a reliable choice for researchers in peptide chemistry.