8-quinolinxanthine and 8-isoquinolinxanthine derivatives as pde 5 inhibitors

A compound of formula (I) in free or salt form, where R<1> is hydrogen or alkyl optionally substituted by hydroxy, alkoxy, or alkylthio, R<2> is hydrogen, alkyl, hydroxyalkyl, alkylcarbonyloxyalkyl, alkoxyalkyl, alkylthioalkyl, alkenyl, cycloalkylalkyl, heterocyclylalkyl, aralkyl in which the aryl ring thereof is optionally fused to a 5-membered heterocyclic group or is optionally substituted by one or more substituents selected from alkoxy, amino, alkylamino, dialkylamino, acylamino, halogen, hydroxy, aminosulfonyl, alkylaminosulfonyl, dialkylaminosulfonyl, alkylsulfonylamino or dialkylaminosulfonylamino, R<3> is hydrogen or alkyl optionally substituted by hydroxy, alkoxy, or alkylthio, R<4> is hydrogen or alkyl, R<5> is a quinolinyl, isoquinolinyl or oxodihydroisoquinolinyl group optionally fused to a 5-membered heterocyclic group and optionally substituted by one or more substituents selected from halogen, cyano, hydroxy, alkyl, hydroxyalkyl, alkoxyalkyl, alkylthioalkyl, alkoxy, alkylthio, alkenyl, alkoxycarbonyl, alkynyl, carboxyl, acyl, a group of formula -N(R<6>)R<7>, aryl optionally substituted by one or more substituents selected from halogen or alkoxy, or heteroaryl having 5 or 6 ring atoms attached through a ring carbon atom to the indicated carbon atom, and R<6> and R<7> are each independently hydrogen or alkyl optionally substituted by hydroxy or alkoxy or one of R<6> and R<7> is hydrogen and the other is acyl, or R<6> and R<7> together with the nitrogen atom to which they are attached denote a 5- or 6- membered heterocyclyl group.