Pyridopyrimidine or naphthyridine derivative

摘要

A pyridopyrimidine or a naphthyridine derivative of the formula (I): wherein R¹ is an optionally substituted nitrogen-containing heterocyclic group, etc.; R² is H or a lower alkyl group; R³ is H or an optionally substituted lower alkyl group, etc.; R⁴ is H, a lower alkyl group, COOH, etc.; R⁵ is a lower alkyl group which may optionally be substituted by an optionally substituted aryl etc.; one of X and Y is CH and the other is nitrogen, or both of X and Y are nitrogen; or a pharmaceutically acceptable salt thereof, these compounds exhibiting excellent PDE V inhibitory activities, and being useful in the prophylaxis or treatment of penile erectile dysfunction, etc.