Used in solid-phase peptide synthesis as a protected amino acid building block, particularly in the preparation of antibody-drug conjugates (ADCs). The Alloc group allows for orthogonal deprotection, enabling selective modification during multi-step syntheses. The PAB (para-aminobenzyloxycarbonyl) linker serves as a spacer that can be cleaved under mild conditions, typically by palladium-catalyzed deprotection, releasing the active drug molecule upon internalization in target cells. The PNP (p-nitrophenyl) ester acts as an activated leaving group, facilitating efficient amide bond formation with nucleophiles such as amines on antibodies or other biomolecules. This compound is especially valuable in constructing prodrugs and linker systems where controlled release and high specificity are required.