Azido-PEG4-C2-acid, a PEG-based PROTAC linker, is utilized in the synthesis of vRucaparib-TP4. It serves as a non-cleavable 4 unit PEG ADC linker for antibody-drug conjugate (ADC) synthesis.

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. ADCs are comprised of an antibody to which is attached an ADC cytotoxin through an ADC linker.