Pan-bromodomain and extra terminal (Pan-BET) inhibitors show profound efficacy but exhibit pharmacology-driven toxicities in clinical trials. The representative Compound 8l (XY153), a novel BD2-selective BET inhibitor, potently binds to BRD4 BD2 with an IC50 value of 0.79 nM. XY153 displayed potent antiproliferative activity against multiple tumor cell lines. XY153 also demonstrated good metabolic stability in vitro. These data indicate that XY153 may serve as a new and valuable lead compound for the development of potential therapeutics against acute myeloid leukemia (AML). All liver microsome assays were performed by Medicilon.