The invention relates to compounds of formula (I). ##STR1## or a salt, or metabolically labile ester thereof wherein R.sub.1 represents a group selected from halogen, alkyl, alkoxy, amino, alkylamino, dialkylamino, hydroxy, trifluoromethyl, trifluoromethoxy, nitro, cyano, SO.sub.2 R.sub.3 or COR.sub.3 wherein R.sub.3 represents hydroxy, methoxy, or amino; m is zero or an integer 1 or 2; A represents an ethynyl group or an optionally substituted ethenyl group; X represents a bond or a C.sub.1-4 alkylene chain; R.sub.2 represents a bridged cycloalkyl or bridged heterocyclic group; which are antagonists of excitatory amino acids, to processes for their preparation and to their use in medicine.