Inhibitors of phosphodiesterase 4 (PDE4) are an important class of anti-inflammatory drug that act by inhibiting the production of proinflammatory cytokines, including tumor necrosis factor-α (TNF-α). We have synthesized and evaluated a series of 2-substituted phthalazinone derivatives as PDE4 inhibitors. Structure–activity relationship studies led to the identification of benzylamine-substituted phthalazinones as potent PDE4 inhibitors ...