Deconstruction - Reconstruction: Analysis of the Crucial Structural Elements of GluN2B-Selective, Negative Allosteric NMDA Receptor Modulators with 3-Benzazepine Scaffold

Abstract

The NMDA receptor plays a key role in the pathogenesis of neurodegenerative disorders including Alzheimer's and Huntington's disease, as well as depression and drug or alcohol dependence. Due to its participation in these pathologies, the development of selective modulators for this ion channel is a promising strategy for rational drug therapy. The prototypical negative allosteric modulator ifenprodil inhibits selectively GluN2B subunit containing NMDA receptors. It was conformationally restricted as 2-methyl-3-(4-phenylbutyl)-2,3,4,5-tetrahydro-1H-3-benzazepine-1,7-diol, which showed high GluN2B affinity and inhibitory activity. For a better understanding of the relevance of the functional groups and structural elements, the substituents of this 3-benzazepine were removed successively (deconstruction). Then, additional structural elements were introduced (reconstruction) with the aim to analyze, which additional modifications were tolerated by the GluN2B receptor. The GluN2B affinity was recorded in radioligand receptor binding studies with the radioligand [3H]ifenprodil. The activity of the ligands was determined in two-electrode voltage clamp experiments using Xenopus laevis oocytes transfected with cRNA encoding the GluN1-1a and GluN2B subunits of the NMDA receptor. Docking studies showed the crucial interactions with the NMDA receptor protein. The deconstruction approach showed that removal of the methyl moiety and the phenolic OH moiety in 7-positon resulted in almost the same GluN2B affinity as the parent 3-benzazepine. A considerably reduced GluN2B affinity was found for the 3-benzazepine without further substituents. However, removal of one or both OH moieties led to considerably reduced NMDA receptor inhibition. Introduction of a NO2 moiety or bioisosteric replacement of the phenol by a benzoxazolone resulted in comparable GluN2B affinity, but almost complete loss of inhibitory activity. An O-atom, a carbonyl moiety or a F-atom in the tetramethylene spacer led to 6-7-fold reduced ion channel inhibition.

Pharmacological Potential of 3-Benzazepines in NMDAR-Linked Pathophysiological Processes

“…Therefore, other ifenprodil derivatives were synthesized, and their inhibitory effects and modulatory effects on NMDARs were investigated. The ifenprodil-derived 3-benzazepine WMS-1410 (with an IC 50 of 18.4 nM and binding affinities of 84 nM for GluN1-1a/GluN2B [63,64]) was shown to be a potent antagonist of NMDA receptors with a GluN2B subunit [65]. A structurally modified 3-benzazepine antagonist targeting NM-DARs was investigated using WMS-1410 as a lead compound.…”

“…The resulting tetrahydro-3-benzazepine has a lower binding affinity but a higher inhibitory activity on NMDARs containing GluN1/GluN2B subunits in electrophysiological experiments than ifenprodil. As a result of further removing the phenolic and benzylic OH − moieties, WMS-1410 was obtained, which also exhibited GluN1/GluN2B inhibition and affinity [65,66]. In order to inhibit NMDARs, one of the two OH − groups in 3-benzazepine antagonists must be present [67].…”

“…The methyl moiety and the phenolic and benzylic OH moieties were removed to retrieve WMS-14-10. Adapted from Ritter et al 2021 [65].…”

Negative allosteric modulators of NMDA receptors with GluN2B subunit: Alanine‐derived benzoxazolone bioisosteres of 2‐methyl‐3‐benzazepine‐1,7‐diols

“…5b [37] -38% 47% 136 284 5c [37] - 3 (WMS-1410) [44] 84 ± 18 b Due to low GluN2B affinity, K i values were recorded only twice and the mean is given.…”