We have developed a method for converting a transforming growth factor-β-activated kinase 1 (TAK1) type I inhibitor into a type II or c-helix-out inhibitor by structure-based drug design (SBDD) to achieve an effective strategy for developing these different types of kinase inhibitor in parallel. TAK1 plays a key role in inflammatory and immune signaling, and is therefore considered to be an attractive molecular target for the treatment of human diseases (inflammatory disease, cancer, etc.). We have already reported novel type I TAK1 inhibitor, so we utilized its X-ray information to design a new chemical class type II and c-helixout inhibitors. To develop the type II inhibitor, we superimposed the X-ray structure of our reported type I inhibitor onto a type II compound that inhibits multiple kinases, and used SBDD to design a new type II inhibitor. For the TAK1 c-helix-out inhibitor, we utilized the X-ray structure of a b-Raf c-helix-out inhibitor to design compounds, because TAK1 is located close to b-Raf in the Sugen kinase tree, so we considered that TAK1 would, similarly to b-Raf, form a c-helix-out conformation. The X-ray crystal structure of the inhibitors in complex with TAK1 confirmed the binding modes of the compounds we designed. This report is notable for being the first discovery of a c-helix-out inhibitor against TAK1.Key words transforming growth factor-β-activated kinase 1 (TAK1); inhibitor; type I; type II; c-helix-out; structure-based drug design Of over 500 kinases in human that maintain the functions of cells, 1) it is not completely clear which kinase inhibition causes an adverse event; therefore, it is important for kinase inhibitors to have a highly selective profile. However, in many cases, kinase inhibitors possess undesired off-target kinase activity, so multiple development candidates with different kinase selectivity profiles need to be prepared, and then a compound with a wide therapeutic window that has no severe adverse effects can be selected as a development candidate. In general, kinase inhibitors are classified into three different types 2,3) : a type I inhibitor binds to the active conformation (DFG-in conformation) of a kinase at the ATP-binding site and competes with ATP; a type II inhibitor binds to both the ATP binding site and its adjacent binding pocket in an inactive conformation (DFG-out conformation) of a kinase; a type III inhibitor is an allosteric inhibitor that has a binding site distinct from the ATP-binding site. Discovery of a type I inhibitor with high kinase selectivity is additionally challenging because amino acid residues in the ATP-binding site are highly conserved in many kinases. On the other hand, it is considered easier to identify a selective type II inhibitor because a type II inhibitor is able to utilize the lipophilic binding pocket derived from the DFG-out conformation, which is less conserved in terms of amino acid residues (though it has recently been reported that not all type II inhibitors possessed high kinase selectivity, 4) so this topic is...