3CL protease (3CLpro), a key enzyme of SARS-CoV-2 replication, is one of the most selective targets of antivirals, as no homologous protease has been recognized in the human body. As proteolysis-targeting chimeras (PROTACs) are superior to traditional inhibitors, based on the reported cereblon (CRBN) ligands thalidomide and lenalidomide, 3CLpro ligands of peptidomimetic inhibitors, and suitable linkers, we aimed to develop novel PROTACs that may trigger efficient intracellular 3CLpro degradation through a balance of hydrophilicity and lipophilicity. In brief, we designed and synthesized 5 PROTAC molecules. The 3CLpro degradation efficiency of the PROTACs was assayed in stable SARS-CoV-2 3CLpro expression HEK293 cell models and evaluated by Western blot. All compounds showed prominent 3CLpro degradation activity with tolerable HEK293 cytotoxicity. The most prominent PROTAC compounds, 15 and 16, have DC50 values of approximately 1 µM, and Dmax of 89.3% and 75% respectively, indicating good potential for further application.
