Thalidomide-piperazine-(S)-CH2-Pyrrolidine-C2-O-CH2-COO-C (CH3)3 is a synthetic E3 ligase ligand-Linker conjugate. Thalidomide-piperazine-(S)-Ch2-Pyrrolidine-C2-O-CH2-COO-C(CH3)3 includes Thalidomide-based cereblon ligands and linkers. Thalidomide-piperazine-(S)-CH2-Pyrrolidine-C2-O-CH2-COO-C(CH3)3 can be used to synthesize PROTAC BET.