N-(tert-Butoxycarbonyl)-L-cysteine methyl ester is a protected derivative of L-cysteine widely used in peptide synthesis. The Boc group protects the α-amino function, while the methyl ester safeguards the carboxylic acid, enabling selective deprotection and coupling in the assembly of peptides. The free thiol side chain remains unaffected, allowing it to participate in disulfide bond formation or other reactions as required. It is essential in solid-phase peptide synthesis (SPPS) for precise construction of cysteine-containing sequences. This compound is also utilized in biochemical research to investigate protein folding and disulfide linkages. Its robustness across diverse conditions positions it as a key reagent in organic synthesis and medicinal chemistry for creating bioactive peptides and proteins.