The present invention relates to a compound of general formula (I) wherein X is O or CH X is O or CH with the proviso that one of X or X is always O and the other is CH.It has been found that the compounds of general formula (I) are good inhibitors of the glycine transporter 1 (GIyT 1) and therefore they may be used for the treatment of schizophrenia psychoses and other neurological conditions including pain.