Azide-PEG3-Tos is a PEG-based PROTAC linker utilized in the synthesis of PROTACs[1]. It is a non-cleavable 3 unit PEG ADC linker employed in the synthesis of antibody-drug conjugates (ADCs)[2].

PROTACs contain two different ligands connected by a linker; one is a ligand for an E3 ubiquitin ligase and the other is for the target protein. PROTACs exploit the intracellular ubiquitin-proteasome system to selectively degrade target proteins[1]. ADCs are comprised of an antibody to which is attached an ADC cytotoxin through an ADC linker[2].