Results of kinase assays of compounds 9–27.

<p>(A) Inhibitory activity of compounds <b>9–27</b> against EGFR and HER2 protein kinases were represented as a bar graph. The black bar represented the IC₅₀ values of all the compounds against EGFR tyrosine kinase <i>in vitro</i>, while the white one represented that of these compounds against HER2 tyrosine kinase. (B) Kinase selectivity profile of compound <b>21</b>. Potency is represented by pIC₅₀.