The Discovery of VX-745: A Novel and Selective p38α Kinase Inhibitor

The synthesis of novel, selective, orally active 2,5-disubstituted 6H-pyrimido[1,6-b]pyridazin-6-one p38α inhibitors is described. Application of structural information from enzyme–ligand complexes guided the selection of screening compounds, leading to the identification of a novel class of p38α inhibitors containing a previously unreported bicyclic heterocycle core. Advancing the SAR of this series led to the eventual discovery of 5-(2,6-dichlorophenyl)-2-(2,4-difluorophenylthio)-6H-pyrimido[1,6-b]pyridazin-6-one (VX-745). VX-745 displays excellent enzyme activity and selectivity, has a favorable pharmacokinetic profile, and demonstrates good in vivo activity in models of inflammation.