The invention relates to novel pyrazolopyrimidinones according to formula (I) wherein R1 is a pyridyl or pyrimidinyl group and D is optionally substituted cyclopentyl, cyclohexyl, tetrahydrofuranyl, tetrahydropyranyl or 2-, 3- or 4-pyridyl. The new compounds are for use as the active entity of medicaments or for the manufacture of medicaments respectively, in particular medicaments for the treatment of conditions concerning deficits in perception, concentration, learning or memory. Such conditions may for example be associated with Alzheimer's disease, schizophrenia and other diseases. The new compounds are also for example for the manufacture of medicaments and/or for use in the treatment of these diseases, in particular for cognitive impairment associated with such disease. The compounds of the invention show PDE9 inhibiting properties.
