Used in peptide synthesis as a protected form of cysteine, allowing selective formation of disulfide bonds without unwanted side reactions. The BOC (tert-butyloxycarbonyl) group protects the amino terminus, while the carboxylic acid remains available for coupling. Commonly applied in the production of therapeutic peptides, research compounds, and in solid-phase peptide synthesis. Its protection strategy enables controlled deprotection under mild acidic conditions, preserving other sensitive functional groups in complex molecules.