The invention provides a compound of formula (I) or a solvate thereof:
wherein R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, and n are as
defined in the specification, and uses of such compounds. The compounds
inhibit GlyT1 transporters and are useful in the treatment of certain
neurological and neuropsychiatric disorders, including schizophrenia.