Selective, reversible, ATP-competitive Chk2 inhibitor (IC50 = 0.2 μM) that displays no effect on a range of other kinases including Chk1 (IC50 > 10 μM). Inhibits histone H1 phosphorylation (IC50 = 0.24 μM) and attenuates mitochondrial ATP synthesis. Exhibits antiproliferative activity in a number of leukemias in vivo.