Used in peptide synthesis for the selective protection of cysteine residues. The Boc (tert-butoxycarbonyl) group provides temporary amino protection, while the S-benzyl group protects the thiol side chain from oxidation or unwanted reactions during coupling steps. The N-hydroxysuccinimide (NHS) ester allows for efficient amide bond formation with primary amines under mild conditions, making it ideal for solid-phase or solution-phase peptide assembly. Commonly employed in the preparation of complex peptides and proteins where orthogonal protection strategies are required. Also useful in bioconjugation applications, such as labeling peptides with fluorescent tags or attaching peptides to surfaces or carriers through amine-reactive chemistry.