The present invention relates to compounds of formulas (IA) or (IB) wherein R1/R2 independently from each other hydrogen, lower alkyl, -(CH2)nNR5R5' or -(CH2)n+1OH; R5 and R5' are independently from each hydrogen, lower alkyl; R3/R4 are independently from each other hydrogen, lower alkyl, lower alkoxy, halogen, trifluoromethyl or hydroxy; Ar is phenyl or thiophenyl; the dotted line is -CH2-CH2-, -CH2-CHR'-, wherein R' is lower alkyl or are two hydrogen atoms, not forming a bridge and; n is 0, 1 or 2; and to pharmaceutically acceptable acid addition salts thereof, with the exception of 6-styryl-pyridin-2-yl-amine. The compounds of the present invention are NMDA (N-methyl-D-aspartate)-receptor subtype blockers and may be used in the treatment of diseases related to this receptor.