Used in antibody-drug conjugate (ADC) development as a linker-payload component. The PEG3 spacer enhances solubility and flexibility, improving conjugation efficiency and stability. Fmoc group allows for controlled deprotection in solid-phase synthesis, enabling stepwise assembly. The Ala-Ala-Asn(Trt) sequence serves as a cathepsin-cleavable dipeptide substrate, facilitating targeted drug release inside lysosomes. PAB (para-aminobenzyl alcohol) acts as a self-immolative spacer, releasing the active drug upon cleavage. Commonly employed in constructing prodrugs and bioconjugates where enzyme-triggered payload release is required.