Used in solid-phase peptide synthesis as a linker system for the construction of antibody-drug conjugates (ADCs). The Alloc (allyloxycarbonyl) protecting group allows selective deprotection under mild conditions, enabling stepwise assembly of complex peptide-drug constructs. The PABC (para-aminobenzyloxycarbonyl) spacer acts as a self-immolative linker, releasing the active drug upon enzymatic cleavage in target cells. The PNP (p-nitrophenyl) ester serves as an activated leaving group, facilitating efficient conjugation to antibodies or other biomolecules. This system is particularly valuable in prodrug design and targeted cancer therapies where controlled drug release is critical.