In order to develop novel and orally active phosphodiesterase (PDE) 4 inhibitors, random screening was performed using our chemical library to find YM-10335 possessing the 1, 8- naphthyridin-2 (1H)-one skeleton which is a completely different structure from rolipram. In this report, the syntheses and structure–activity relationships of the YM-10335 derivatives were described. Some compounds showed selective inhibitory activities for PDE 4 derived ...