Lenalidomide-PEG3-iodine is a synthesized E3 ligase ligand-linker conjugate that incorporates the Lenalidomide based cereblon ligand and a 3-unit PEG linker. Lenalidomide-PEG3-iodine can be used in the synthesis of a series of PROTACs , such as SJF620. SJF620 is a potent PROTAC BTK degrader with a DC 50 of 7.9 nM.