2-Methyltetrahydro-3-benzazepin-1-ols - The missing link in SAR of GluN2B selective NMDA receptor antagonists

The NMDA receptor containing GluN2B subunits represents a promising target for the development of drugs for the treatment of various neurological disorders including neurodegenerative diseases. In order to study the role of CH₃ and OH moieties trisubstituted tetrahydro-3-benzazepines 4 were designed as missing link between tetra- and disubstituted 3-benzazepines 2 and 5. The synthesis of 4 comprises eight reaction steps starting from alanine. The intramolecular Friedel-Crafts acylation to obtain the ketone 12 and the base-catalyzed elimination of trifluoromethanesulfinate (CF₃SO₂^-) followed by NaBH₄ reduction represent the key steps. The GluN2B affinity of the cis-configured 3-benzazepin-1-ol cis-4a with a 4-phenylbutyl side chain (K_i = 252 nM) is considerably lower than the GluN2B affinity of (R,R)-2 (K_i = 17 nM) indicating the importance of the phenolic OH moiety for the interaction with the receptor protein. Introduction of an additional CH₃ moiety in 2-position led to a slight decrease of GluN2B affinity as can be seen by comparing the affinity data of cis-4a and 5. The homologous phenylpentyl derivative cis-4b shows the highest GluN2B affinity (K_i = 56 nM) of this series of compounds. According to docking studies cis-4a adopts the same binding mode as the cocrystallized ligand ifenprodil-keto 1A and 5 at the interface of the GluN2B and GluN1a subunits. The same crucial H-bonds are formed between the C(O)NH₂ moiety of Gln110 within the GluN2B subunit and the protonated amino moiety and the OH moiety of (R,R)-cis-4a.