Design, Synthesis, and in vitro Biological Evaluation of 3,5‐Dimethylisoxazole Derivatives as BRD4 Inhibitors

: BRD4 has been identified as a potential target for blocking proliferation in a variety of cancer cell lines. In this study, 3,5-dimethylisoxazole derivatives were designed and synthesized with excellent stability in liver microsomes as potent BRD4 inhibitors, and were evaluated for their BRD4 inhibitory activities in vitro. Gratifyingly, compound 11 h [3-((1-(2,4-difluorophenyl)-1H-1,2,3-triazol-4-yl)methyl)-6-(3,5-dimethylisoxazol-4-yl)-4-phenyl-3,4-dihydroquinazolin-2(1H)-one] exhibited robust potency for BRD4(1) and BRD4(2) inhibition with IC50 values of 27.0 and 180 nm, respectively. Docking studies were performed to illustrate the strategy of modification and analyze the conformation in detail. Furthermore, compound 11 h was found to potently inhibit cell proliferation in the BRD4-sensitive cell lines HL-60 and MV4-11, with IC50 values of 0.120 and 0.09 μm, respectively. Compound 11 h was further demonstrated to downregulate c-Myc levels in HL-60 cells. In summary, these results suggest that compound 11 h is most likely a potential BRD4 inhibitor and is a lead compound for further investigations.