NH2-PEG9-acid is a non-cleavable 9 unit PEG ADC linker used in the synthesis of antibody-drug conjugates (ADCs). NH2-PEG9-acid also is a PEG-based PROTAC linker that can be used in the synthesis of PROTACs[2].In Vitro: ADCs are comprised of an antibody to which is attached an ADC cytotoxin through an ADC linker. 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].