A cell-permeable pyrimidylpyrrole compound that acts as an active site-targeting, highly potent and selective ERK1/2 inhibitor ( K I <2nM against Erk2; [ATP] = 65μM), while inhibiting GSK-3, Aurora A, Cdk2 only at much higher concentrations ( K I = 395, 540, and 852 nM, respectively) and exhibiting much reduced or little potency toward a panel of more than 130 other kinases ( K