Boc-Aminooxy-PEG4-CH2CO2H is a PEG-based PROTAC linker that can be used in the synthesis of PROTACs[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[1].
[1]. Zhao B, et al. Protein Engineering in the Ubiquitin System: Tools for Discovery and Beyond. Pharmacol Rev. 2020 Apr;72(2):380-413.