Azido-PEG6-NHS ester is a cleavable 6 unit polyethylene glycol (PEG) linker, commonly employed in the synthesis of antibody-drug conjugates (ADCs)[1]. Additionally, it serves as a PEG- and alkyl/ether based linker for the synthesis of proteolysis targeting chimeras (PROTACs)[2].

ADCs are comprised of an antibody to which is attached an ADC cytotoxin through an ADC linker[1]. 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[2].