Used in the synthesis of antibody-drug conjugates (ADCs) as a linker-payload component. The Cbz and Alloc protecting groups allow for selective deprotection and stepwise assembly in solid-phase peptide synthesis. The PAB (para-aminobenzyloxycarbonyl) spacer acts as a cleavable linker, releasing the active drug upon intracellular enzymatic cleavage, typically by cathepsin B in lysosomes. The PNP (p-nitrophenyl) ester serves as a reactive handle for conjugation to antibodies or other biomolecules, enabling targeted delivery in cancer therapy. Its design supports controlled release and enhanced stability in circulation, making it valuable in developing highly specific and potent ADCs.