Tetraethylene glycol (PROTAC Linker 18) is a PEG-based PROTAC linker can be used in the synthesis of PROTACs.In Vitro: 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.