Fmoc-PEG2-Val-Cit-PAB-OH is a cleavable ADC linker that features a Boc-protected amine, hydrophilic PEG spacer, and a Val-Cit-PAB dipeptide. The benzyl alcohol on the PAB can be used for conjugating reactive groups (e.g., PNP) to attach a payload. The Fmoc protecting group is removable with piperidine, revealing a primary amine for amide bond formation in conjugation reactions. The Val-Cit-PAB segment is cleaved by cellular proteases to efficiently release the payload inside cells.