Boc-PEG2-Val-Cit-PAB-OH is an enzymatically cleavable ADC linker featuring a Boc-protected amine, a hydrophilic PEG spacer, and a Val-Cit-PAB dipeptide. The benzyl alcohol on PAB can be utilized for attachment to reactive groups (such as PNP) to connect with a drug payload. The Boc protecting group can be removed with acid, revealing a primary amine that serves for coupling reactions to form an amide. The Val-Cit-PAB segment is cleaved by cellular proteases, facilitating the effective release of the payload inside the cell.