Compound of general formula I:
1
wherein R
1
, R
2
, R
3
, R
4
, X, Y and R
5
have the meanings given herein which are useful in the curative and prophylactic treatment of a medical condition for which inhibition of a cyclic guanosine 3′,5′-monophosphate phosphodiesterase (e.g. cGMP PDE5) is desired.