The present invention relates to a compound of general formula I-A or I-B wherein X is a bond or a CH2- group； R1, R2 and R3 are independently from each other hydrogen, lower alkoxy, 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 formulas I-A and I-B are good inhibitors of the glycine transporter 1 (GlyT-1), and that they have a good selectivity to glycine transporter 2 (GlyT-2) inhibitors, suitable in the treatment of neurological and neuropsychiatric disorders.
