Discovery of Pyrrolo[3,2‑d]pyrimidin-4-one Derivatives as a New Class of Potent and Cell-Active Inhibitors of P300/CBP-Associated Factor Bromodomain

Herein, we report the discovery of a series of new P300/CBP-associated factor (PCAF) bromodomain (BRD) inhibitors, which were obtained through a hit discovery process and subsequent structure-based optimization and structure–activity relationship analyses toward a retrieved hit compound (12). Among these inhibitors, (R,R)-36n is the most potent one with an IC50 of 7 nM in homogeneous time-resolved fluorescence assay and a KD of 78 nM in isothermal titration calorimetry assay. This compound also exhibited activity against GCN5 and FALZ, but weak or no activity against other 29 BRD proteins and 422 kinases, indicating considerable selectivity. X-ray cocrystal structure analysis revealed the molecular interaction mode and the precise stereochemistry required for bioactivity. Cellular activity, preliminary RNA-seq analysis, and pharmacokinetic properties were also examined for this compound. Collectively, this study provides a versatile tool molecule to explore molecular mechanisms of PCAF BRD regulation and also offers a new lead compound for drug discovery targeting PCAF.