Pyrrolo[1,2-b]pyridazines, pyrrolo[2,1-f]triazin-4(3H)-ones, and related compounds as novel corticotropin-releasing factor 1 (CRF₁) receptor antagonists.

To identify structurally novel corticotropin-releasing factor 1 (CRF1) receptor antagonists, a series of bicyclic core analogs pyrrolo[1,2-b]pyridazines and pyrrolo[2,1-f]triazin-4(3H)-ones, which were designed based on a monocyclic core antagonist, was synthesized and evaluated. Among the compounds tested, 2-difluoromethoxy-4-methylpyridin-5-yl analog 27 was found to show efficacy in a dose-dependent manner in an elevated plus maze test in rats. The discovery process and structure–activity relationship is presented.