EN219 is a synthetic recruiter of the E3 ubiquitin ligase RNF114. It binds to cysteine 8 (C8) in the intrinsically disordered region of RNF114 (RNF114-C8; IC50 = 470 nM) and inhibits RNF114-induced autoubiquitination and p21 ubiquitination in a cell-free assay when used at a concentration of 50 µM. EN219 (1 µM) also interacts with cysteine residues in the tubulin β1 chain (TUBB1), heat shock protein 60 (Hsp60), also known as Hsp family D member 1 (HspD1), and histone H3.1 (HIST1H3A) in 231MFP human breast cancer cells in a proteomic profiling assay. It has been linked to the bromodomain and extra terminal domain (BET) inhibitor ligand (+)-JQ1 for use as a proteolysis-targeting chimera (PROTAC) to degrade bromodomain-containing protein 4 (BRD4) in 231MFP cells.