Used in the synthesis of antibody-drug conjugates (ADCs) as a linker-payload component. The PAB (para-aminobenzyloxycarbonyl) spacer enables efficient release of cytotoxic agents inside target cells through enzymatic cleavage, particularly by cathepsin B in lysosomes. The Fmoc and Boc protecting groups allow for stepwise solid-phase peptide synthesis, facilitating the construction of complex conjugates. The PNP (p-nitrophenyl) ester acts as an activated carboxylate for amide bond formation, commonly used to attach drugs or labels to antibodies or peptides. This compound is valuable in developing targeted cancer therapies due to its stability in circulation and controlled intracellular drug release.