| abstract |
A compound represented by formula (I) or a pharmaceutically acceptable salt thereof that exerts an inhibitory effect on PDE9 and, therefore, can be expected to be able to increase the level of cGMP in the brain. Because the inhibitory effect on PDE9 and an increase in the level of cGMP contribute to improving learning and memory behavior, the above-mentioned compound or one of its pharmaceutically acceptable salts would be available as a remedy for cognitive dysfunction in Alzheimer's disease zzzzzla . In formula (I): R1 represents a hydrogen atom; R2 represents an aromatic ring group, etc .; R3 represents a hydrogen atom, etc .; R4 represents a hydrogen atom; R5 represents an oxepanyl group, etc .; and R6 represents a hydrogen atom. (see Formula). |