Potent and selective CDK9 inhibitor (IC50 = 44 nM at CDK9-cyclin T1). Inhibits other CDKs in the micromolar range (IC50 values are 2.4, 5.5, 9.2, >10 and >10 μM for CDK2-cyclin A, CDK1-cyclin B1, CDK4-cyclin D1, CDK6-cyclin D3 and CDK7-cyclin H-MAT1, respectively). Inhibits P-TEFb-dependent in vitro transcription. Induces apoptosis in vitro and in vivo in combination with BI 894999. Purity 98%. MW (observed): 370.43