The present invention relates to compounds of general formula wherein R1 is phenyl or pyridinyl, which are optionally substituted by one, two or three substituents, selected from halogen, lower alkyl substituted by halogen, lower alkoxy, lower alkoxy substituted by halogen, cyano or S(O)2-lower alkyl, or is morpholinyl, dihydropyranyl or piperidinyl, wherein piperidinyl is optionally substituted by halogen, or is C(O)O-lower alkyl； R2 is hydrogen； R3 is hydrogen, lower alkyl substituted by halogen, -(CH2)n-S(O)2-lower alkyl, -(CH2)n- cycloalkyl or -(CH2)n-lower alkoxy； R4 is hydrogen or lower alkyl； n is 0, 1 or 2； or to a pharmaceutically acceptable acid addition salt, to a racemic mixture or to its corresponding enantiomer and/or optical isomers thereof. The compounds may be used for the treatment of schizophrenia, obsessive-compulsive personality disorder, major depression, bipolar disorders, anxiety disorders, normal aging, epilepsy, retinal degeneration, traumatic brain injury, spinal cord injury, post-traumatic stress disorder, panic disorder, Parkinson’s disease, dementia, Alzheimer’s disease, cognitive impairment, chemotherapy-induced cognitive dysfunction ("chemobrain"), Down syndrome, autism spectrum disorders, hearing loss, tinnitus, spinocerebellar ataxia, amyotrophic lateral sclerosis, multiple sclerosis, Huntington’s disease, stroke, and disturbances due to radiation therapy, chronic stress, optic neuropathy or macular degeneration, or abuse of neuro-active drugs, selected from alcohol, opiates, methamphetamine, phencyclidine and cocaine.本發明係關於如下通式之化合物，其中：R1 係苯基或吡啶基，其可視情況經一個、兩個或三個選自鹵素、經鹵素取代之低碳數烷基、低碳數烷氧基、經鹵素取代之低碳數烷氧基、氰基或S(O)2-低碳數烷基之取代基取代，或係：嗎啉基、二氫吡喃基或哌啶基，其中哌啶基可視情況經鹵素取代，或係：C(O)O-低碳數烷基；R2 係氫；R3 係氫、經鹵素取代之低碳數烷基、-(CH2)n-S(O)2-低碳數烷基、-(CH2)n-環烷基或-(CH2)n-低碳數烷氧基；R4 係氫或低碳數烷基；n 係0、1或2；或其醫藥上可接受之酸加成鹽、外消旋混合物或其相應的對映異構體及/或其光學異構體。該等化合物可用於治療精神分裂症、強迫型人格障礙、重性抑鬱症、躁鬱症、焦慮症、正常老化、癲癇症、視網膜變性、腦外傷、脊椎損傷、創傷後壓力症、恐慌症、帕金森氏(Parkinson's)病、癡呆、阿茲海默氏(Alzheimer's)病、認知障礙、化療引起之認知功能障
