Selective inhibitor of checkpoint kinases Chk1 and Wee1 (IC50 values are 47 and 97 nM respectively). Displays selectivity over a range of other protein kinases; IC50 values are 3.4, 3.75, > 5, > 50, > 50 and > 50 μM for PKC, CDK4, other CDKs, c-Src, PDGFR and FGFR respectively.