Design, Synthesis, and Biological Evaluation of 3-Benzazepin-1-ols as NR2B-Selective NMDA Receptor Antagonists

Cleavage and reconstitution of a bond in the piperidine ring of ifenprodil (1) leads to 7-methoxy-2,3,4,5-tetrahydro-1H-3-benzazepin-1-ols, a novel class of NR2B-selective NMDA receptor antagonists. The secondary amine 7-methoxy-2,3,4,5-tetrahydro-1H-3-benzazepin-1-ol (12), which was synthesized in six steps starting from 2-phenylethylamine 3, represents the central building block for the introduction of several N-linked residues. A distance of four methylene units between the basic nitrogen atom and the phenyl residue in the side chain results in high NR2B affinity. The 4-phenylbutyl derivative 13 (WMS-1405, K(i)=5.4 nM) and the conformationally restricted 4-phenylcyclohexyl derivative 31 (K(i)=10 nM) represent the most potent NR2B ligands of this series. Whereas 13 shows excellent selectivity, the 4-phenylcyclohexyl derivative 31 also interacts with sigma(1) (K(i)=33 nM) and sigma(2) receptors (K(i)=82 nM). In the excitotoxicity assay the phenylbutyl derivative 13 inhibits the glutamate-induced cytotoxicity with an IC(50) value of 360 nM, indicating that 13 is an NMDA antagonist.