HJB97 is a high-affinity BET inhibitor with Kis of 0.9 nM (BRD2 BD1), 0.27 nM (BRD2 BD2), 0.18 nM (BRD3 BD1), 0.21 nM (BRD3 BD2), 0.5 nM (BRD4 BD1), 1.0 nM (BRD4 BD2), respectively. HJB97 is employed for the design of potential PROTAC BET degrader and has antitumor activity.