Synthesis and biological evaluation of 2-benzylamino-4(5)-(6-methylpyridin-2-yl)-5(4)-([1,2,4]triazolo[1,5-a]-pyridin-6-yl)thiazoles as transforming growth factor-β type 1 receptor kinase inhibitors

► A series of 34 novel compounds were prepared and chemically characterized. ► The compounds were evaluated for their ALK5 inhibitory activity in enzyme assay and in cell-based luciferase reporter assay. ► Compounds 12b and 12g exhibited highly potent ALK5 inhibitory activity and selectivity indices of >400 over p38α MAP kinase.