The invention provides for a compound of formula (I) or a pharmaceutically acceptable salt thereof: wherein R.sup.1, R.sup.2, R.sup.3, A, B, D, m, n, x, and y are defined as described in the specification. The invention additionally provides a pharmaceutically composition comprising the compound of formula I, together with a method of using the same to treat or prevent neurological and psychiatric disorders. The compounds are useful in therapy related to the treatment or prevention of mGluR2 receptor-mediated disorders.