4-SUBSTIUTED PIPERODINE ANALOGS AND THEIR USE AS SUBTYPE SELECTIVE NMDA RECEPTOR ANTAGONISTS

1. A compound represented by the formula (I) or a pharmaceutically acceptable salt thereof wherein Ar and Ar are independently phenyl, naphthyl, piperidinyl, quinolinyl, quinoxalinyl, benzamidazolyl, benzoxazolyl, indolyl, thiophenyl group, either of which may be independently substituted by one or two groups, selected from C1-C6 alkyl, hydroxy, halogen, nitro, cyano, carboxaldehyde, C1-C6 alkoxy carbonylmethyl, hydroxy C1-C6 alkyl, amino, a C1-C6 alkyl amino group, di- C1-C6 alkyl amino, z is a single or double bond; X is -(CHR )m-, O, S or NR , wherein each R is independently hydrogen, hydroxy or an alkyl group having 1 to 6 carbon atoms, R is hydrogen or an alkyl group having 1 to 6 carbon atoms and m is 0, 1 or 2, provided that when z is a double bond then X is not O or NR ; R is independently hydrogen or hydroxy; each R is independently hydrogen, hydroxy or a C1-C6 alkyl group having 1 to 6 carbon atoms; n is 0, 1, 2, 3 or 4; Y is O, S, NR or a single bond; and R is hydrogen or hydroxy when z is a single bond, provided that: (i) R cannot be hydroxy in an α position to Ar ; (ii) if X is a single bond, z is a double bond or R is hydroxy and Ar is phenyl then Y cannot be O; (iii) if Y is O, n is 3 or 4, R is exclusively hydrogen, z is a single bond, R and R are hydrogen and Ar is phenyl, or halogen, methoxy or trifluoromethyl substituted phenyl then X cannot be methylene or ethylene; (iv) if X is - -(CHR )m-, m is 2 and R is exclusively hydrogen then Ar cannot be imidazolyl substituted; (v) if Y is O, n is 2, 3 or 4, R is hydrogen or hydroxy, z is a single bond, R and R are hydrogen and Ar is phenyl, or NO2, CN, 1-imidazoyl, or 1,2,4-triazol-1-yl substituted phenyl then X cannot be methylene, hydroxymethylene, or O; (vi) if Y is O or S, R and R are hydrogen and R is hydroxy then X is not methylene or a single bond; or (vii) if Y is a single bond, R is exclusively hydrogen and Ar is phenyl then either R or R must be hydroxy 2. A compound according to claim 1, wherein Y is O or a single bond. 3. A compound according to claim 2, wherein Ar is phenyl, naphthyl, piperidinyl, quinolinyl, quinoxalinyl, benzamidazolyl, benzoxazolyl, indolyl, thiophenyl group. 4. A compound according to claim 2, wherein R or R is hydroxy 5. A compound according to claim 1, said compound selected from the group consisting of: 4-Phenoxy-1-[(4-fluorophenoxy)propyl]piperidine; 1-(3-Phenoxypropyl)-4-phenylpiperidine; 1-(2-Phenoxyethyl)-4-phenylpiperidine; 1-(4-Phenoxybutyl)-4-phenylpi