NU2058 (O6-(Cyclohexylmethyl)guanine) is a competitive inhibitor of CDK2 with respect to ATP (Ki value CDK2, 12 μM) that binds in the ATP binding pocket in a different orientation from other purine-based inhibitors, including olomoucine and roscovotine. NU2058 is the lead compound in a structure-based drug discovery program to develop more potent and selective CDK inhibitors.