HG-12-6 has a better binding affinity for the unphosphorylated inactive IRAK4 kinase domain (IC50 of 165 nM) than the phosphorylated active IRAK4 kinase domain (IC50 of 2876 nM).The in-house compound HG-12-6 has a similar chemical scaffold as Ponatinib.?The most differentiating components are the head of the inhibitor and the lack of a methyl substituent on ring A. Without the methyl substituent on ring A, the entire HG-12-6 molecule shifts inward to the ATP pocket in comparison with the binding mode of Ponatinib.