The invention provides PDE9-inhibiting compounds of Formula (I),and pharmaceutically acceptable salts thereof, wherein R1, R2, R3, A, and n are as defined herein. Pharmaceutical compositions containing the compounds of Formula I, and uses thereof in treating neurodegenerative and cognitive disorders, such as Alzheimer's disease and schizophrenia, are also provided.本發明係提供式(I) PDE9-抑制化合物,及其藥學上可接受之鹽,其中R1,R2,R3,A及n均如本文中所定義。亦提供含有式I化合物之醫藥組合物,及其在治療神經變性與認知病症上之用途,譬如阿耳滋海默氏病與精神分裂症。