Compounds of formula (I), wherein R is a substituted nitrogen, oxygen or sulphur atom or a radical C=R3, C(R4)R5 or CH-R6; R1 is a hydroxy radical, polyfluoroalkoxy, carboxy, alkoxycarbonyl, -NH-CHO or -NH-CO-N(alk)Ar where Ar is optionally substituted, -N(alk)-CO-NR8R9, -N(alk-Ar)-CO-NR8R9, -NH-CO-NR9R12, -NH-CS-NR8R9, -N(alk)-CS-NR8R9, -NH-CO-R10, -NH-CS-R20, -NH-C(=NR21)-NR7R9, -N(alk)-C(=NR21)-NR7R9, -NH-SO2-NR7R9, -N(alk)-SO2-NR7R9, -CO-NR7R9, -NH-SO2-CF3, -NH-SO2-alk, -NR9R11, -S(O)m-alk-Ar, -SO2-NR7R9, optionally 3-substituted 2-oxo-1-imidazolidinyl or optionally 3-substituted 2-oxo-1 perhydropyrimidinyl; R2 is a hydrogen or halogen atom or an akyl radical, alkoxy, amino, -NH-CO-NH-Ar, N=CH-N(alk)alk', nitro, cyano, phenyl, imidazolyl, acylamino, SO3H, hydroxy, polyfluoroalkoxy, carboxy, alkoxycarbonyl, -NH-CHO, -NH-CO-N(alk)Ar where Ar is optionally substituted, -N(alk)-CO-NR8R9, -N(alk-Ar)-CO-NR8R9, -NH-CO-NR9R12, -NH-CS-NR8R9, -N(alk)-CS-NR8R9, -NH-CO-R10, -NH-CS-R20, -NH-C(=NR21)-NR7R9, -N(alk)-C(=NR21)-NR7R9, -NH-SO2-NR7R9, -N(alk)-SO2-NR7R9, -CO-NR7R9, -NH-SO2-CF3, -NH-SO2-alk, -NR9R11, -S(O)m-alk-Ar, -SO2-NR7R9, optionally 3-substituted 2-oxo-1-imidazolidinyl or optionally 3-substituted 2-oxo-1-perhydropyrimidinyl; R3 is an oxygen atom or a NOH, NO-alk-COOX or CH-R13 radical; R4 is an alkyl radical, -alk-Het or -alk-Ar; R5 is a straight or branched C1-11 alkyl radical, -alk-Het or -alk-Ar, or R4 and R5, taken together with the carbon atom to which they are attached, form a cycloalkyl radical; R6 is a hydrogen atom radical or a hydroxy radical, straight or branched C1-11 alkyl, -NR14R15, -alk-OH, -alk-NR14R15, -alk-Ar or -alk-Het; and salts thereof. The compounds of formula (I) are non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, particularly NMDA receptor glycine modulation site ligands, and are alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonists, said receptor also being known as the quisqualate receptor.