The present invention relates to compounds of the general formula (I): or a pharmaceutically acceptable acid addition salt thereof, a racemic mixture or a corresponding enantiomer and / or optical isomer thereof, (I) In this formula, R <； 1 >； is hydrogen； R 2 is hydrogen, lower alkyl, benzyl, lower alkyl substituted by hydroxy, or cycloalkyl optionally substituted by cyano； Or R <； 1 >； and R <； 2 >； together with the N-atom to which they are attached form a heterocycloalkyl group optionally containing additional N, O or S ring atoms, which is optionally substituted with hydroxy； R <； 3 >； is halogen, Phenyl optionally substituted by one or more halogens, cyano, lower alkyl substituted by halogen, lower alkoxy substituted by halogen, lower alkyl substituted by hydroxy, Lower alkyl or heteroaryl optionally substituted with halogen, 3,6-dihydro-pyran-4-yl, or Piperidinyl-1-yl optionally substituted with one or more halogens. The compounds of formula I are useful in the treatment of schizophrenia, compulsive personality disorder, depression, bipolar disorder, anxiety disorder, normal aging, epilepsy, retinal degeneration, traumatic brain injury, spinal cord injury, post traumatic stress disorder, panic disorder, Alzheimer's disease, cognitive disorders, chemotherapy-induced cognitive dysfunction, Down syndrome, autism spectrum disorders, hearing loss, tinnitus, spinal cord cerebellar ataxia, amyotrophic lateral sclerosis, multiple sclerosis, Huntington's disease, stroke, radiation therapy, Or an abuse of a neuro-active drug selected from alcohol, opiate, methamphetamine, phencyclidine and cocaine.본 발명은 하기 화학식 I의 화합물 또는 이의 약학적으로 허용가능한 산 부가 염, 라세미 혼합물 또는 이의 대응 거울상이성질체 및/또는 광학 이성질체에 관한 것이다:[화학식 I]상기 식에서, R1은 수소이고；R2는 수소, 저급 알킬, 벤질, 하이드록시로 치환된 저급 알킬, 또는 시아노로 임의적으로 치환된 사이클로알킬이고；또는 R1 및 R2는 이들이 부착된 N-원자와 함께, 임의적으로 추가의 N, O 또는 S 고리 원자를 함유하는 헤테로사이클로알킬 기를 형성하고, 이는 임의적으로 하이드록시로 치환되고；R3은, 할로겐이거나,하나 이상의 할로겐으로 임의적으로 치환된 페닐, 시아노, 할로겐으로 치환된 저급 알킬, 할로
