The present invention relates to compounds of general formula (I), wherein R1 is hydrogen； R2 is hydrogen, lower alkyl, benzyl, lower alkyl substituted by hydroxy or is cycloalkyl optionally substituted by cyano； or R1 and R2 form together with the N-atom to which they are attached a heterocycloalkyl group, optionally containing an additional N, O or S ring atom, and which is optionally substituted by hydroxy； R3 is halogen, phenyl optionally substituted by one or more halogen, cyano, lower alkyl substituted by halogen, lower alkoxy substituted by halogen or by lower alkyl substituted by hydroxy, or is heteroaryl, optionally substituted by lower alkyl or halogen, or is 3,6-dihydro-pyran-4-yl, or is piperidin-1-yl optionally substituted by one or more halogen； or to a pharmaceutically acceptable acid addition salt, to a racemic mixture or to it corresponding enantiomer and/or optical isomer thereof. The compounds of formula I may be used in the treatment of schizophrenia, obsessive-compulsive personality disorder, 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, Down syndrome, autism spectrum disorders, hearing loss, tinnitus, spinocerebellar ataxia, amyotrophic lateral sclerosis, multiple sclerosis, Huntington's disease, stroke, radiation therapy, chronic stress, abuse of neuro-active drugs, selected from alcohol, opiates, methamphetamine, phencyclidine and cocaine.
