Compounds having the formula I wherein R1, X1, X2, X3 and X4 as defined herein are inhibitors of ERK kinase. Also disclosed are compositions and methods for treating hyperproliferative disorders.具有式I之化合物為ERK激酶抑制劑,其中R1、X1、X2、X3及X4如本文中所定義。亦揭示用於治療過度增殖性病症之組合物及方法。