Fragment-Based Discovery of a Small Molecule Inhibitor of Bruton’s Tyrosine Kinase

The discovery and optimization of a series of 4-aminocinnoline-3-carboxamide inhibitors of Bruton's tyrosine kinase are reported. A fragment-based screening approach incorporating X-ray co-crystallography was used to identify a cinnoline fragment and characterize its binding mode in the ATP binding site of Btk. Optimization of the fragment hit resulted in the identification of a lead compound which reduced paw swelling in a dose- and exposure-dependent fashion in a rat model of collagen-induced arthritis.