Used in peptide synthesis as a protecting group for cysteine residues. The benzyl (Bzl) group shields the thiol functionality during the reaction process, preventing unwanted side reactions. The para-nitrophenyl (ONp) ester acts as an activating group, facilitating the coupling of the cysteine derivative with other amino acids or peptides. This compound is particularly useful in solid-phase peptide synthesis (SPPS) where selective deprotection and coupling steps are critical. It ensures the integrity and correct sequence of the peptide chain, making it valuable in the production of peptides for research, pharmaceuticals, and biotechnology applications.