Protein kinases are involved in most physiological processes and in numerous diseases. Therefore, inhibitors of protein kinases have therefore a wide therapeutic potential. While screening for inhibitors of cyclin-depent kinases (CDK's) and glycogen synthase kinase-3 (GSK-3), we identified pyrazolo [3, 4-b] quinoxalines as sub-micromolar inhibitors of CDK1/cyclin B. A preliminary structure–activity relationship study suggests that this family ...