The present invention relates to a compound of general formula (I) wherein R, R and R are independently from each other hydrogen, lower alkyl, lower alkoxy, cycloalkyl, lower alkyl substituted by halogen or S-lower alkyl； or to a pharmaceutically acceptable acid addition salt, to a racemic mixture, or to its corresponding enantiomer and/or optical isomer thereof. It has been found that the compounds of general formula (I) are good inhibitors of the glycine transporter 1 (GlyT-1), and that they have a good selectivity to glycine transporter 2 (GlyT-2) inhibitors. The compounds may be used in the treatment of neurological and neuropsychiatric disorders.
