NH2-PEG4-Val-Cit-PAB-OH is a cleavable ADC linker that features a primary amine, a hydrophilic PEG spacer, a Val-Cit dipeptide, and a PAB group. The benzyl alcohol on the PAB component is suitable for attaching reactive groups (such as PNP) to facilitate binding with drug payloads. The primary amine is versatile for reactions such as coupling with carboxylic acids, reductive amination with ketones or aldehydes, or other specialized applications like SNAr reactions or heterocyclic chemistry. The Val-Cit dipeptide is cleaved by intracellular cathepsins, allowing efficient payload delivery via an elimination mechanism through the PAB structure.