NI-42 is a structurally orthogonal chemical probe for the BRPFs and is biased. It effective inhibitor of the BRD of the BRPFs (IC50s of BRPF1/2/3=7.9/48/260 nM; Kds of BRPF1/2/3=40/210/940 nM). It also has excellent selectivity over nonclass IV BRD proteins.