Derivatives of pyrimido[6.1-a]isoquinolin-4-one

The present invention relates to derivatives of pyrimido[6,1-a]isoquinolin-4-one and their application as inhibitors of phosphodiesterase (PDE) isoenzymes. More particularly the invention relates to derivatives of pyrimido[6,1-a]isoquinolin-4-one and their use in medicine for example as bronchodilators with anti-inflammatory properties. The invention provides compounds or salts thereof of the general formula (I): wherein each of Rand Rindependently represents a Calkyl or Cacyl group; X represents OCHor a group CRR; wherein each of Ror Rindependently represents a hydrogen atom or a Calkyl group; Rrepresents a hydrogen atom or a Calkyl, Calkenyl or Calkynyl group; Rrepresents a hydrogen atom or a Calkyl, Calkenyl, Calkynyl, amino, Calkylamino, di(C) alkylamino or Cacylamino group; each of Rand Rindependently represents a hydrogen or halogen atom or a hydroxy, trifluoromethyl, Calkyl, Calkenyl, Calkynyl, Cacyl, Calkylthio, Calkoxy, Ccycloalkyl; and Rrepresents a hydrogen or halogen atom or a hydroxy, trifluoromethyl, Calkyl, Calkenyl, Calkynyl, Cacyl, Calkylthio, Calkoxy or Ccycloalkyl group. The compounds or salts thereof are useful for treatment of respiratory disorders such as asthma. Compounds of the invention have a longer duration of action than the known compound trequinsin (9,10-dimethoxy-3 methyl-2-mesitylimino-2,3,6,7-tetrahydro--H-pyrimido[6,1-a]isoquinolin-4-one).