Conformationally constrained NR2B selective NMDA receptor antagonists derived from ifenprodil: Synthesis and biological evaluation of tetrahydro-3-benzazepine-1,7-diols

NR2B selective NMDA receptor antagonists with tetrahydro-3-benzazepine-1,7-diol scaffold have been designed by formal cleavage and reconstitution of the piperidine ring of the lead compound ifenprodil ( 1). The secondary amine 10 represents the central building block for the synthesis of more than 25 tetrahydro-3-benzazepin-1-ols. Generally 7-hydroxy derivatives display higher NR2B receptor affinities than the corresponding 7-benzyloxy compounds. A distance of four atoms (five bond lengths) between the basic amino group and the terminal aryl moiety led to highest NR2B affinity. 3-(4-Phenylbutyl)-2,3,4,5-tetrahydro-1 H-3-benzazepine-1,7-diol (WMS-1410, 25) represents the most promising NR2B antagonist of this series showing a K i-value of 14 nM. Compound 25 reveals excellent selectivity over more than 100 further relevant target proteins, antagonizes glutamate induced excitotoxicity (IC 50 = 18.4 nM) and is metabolically more stable than ifenprodil. Up to a dose of 100 mg/kg 25 is well tolerated by mice and it shows dose dependent analgesic activity in the late neuropathic pain phase of the formalin assay.