Boc-PEG4-Val-Ala-PAB-PNP is an ADC linker featuring a Boc-protected amine, a hydrophilic PEG spacer, a Val-Ala dipeptide, a PAB group, and a PNP carbonate. The PNP carbonate is a leaving group that is highly activated towards attack from amines to form carbamates with the target molecule, while the Boc protecting group may be removed with acid to reveal a primary amine which can be used to couple with carboxylic acids. The Val-Ala dipeptide is cleaved by proteases to release a given drug payload via an elimination mechanism within the PAB group.
