A cell permeable inhibitor of kinases that have been mutated, by a single base substitution, to become 'analog sensitive' (as), as compared to the wild type kinase; inhibits v-Src-as1, with an I338G substitution, preferentially over v-Src (IC50 = 4.2 nM versus 28 μM, respectively); used to elucidate functions of several kinases in both mammalian and yeast systems.