Systematic variation of the benzoylhydrazine moiety of the GluN2A selective NMDA receptor antagonist TCN-201

Abstract

GluN2A containing N-methyl-D-aspartate receptors (NMDARs) are important ion channels in the central nervous system and highly involved in several different neurophysiological but also neuropathophysiological processes. However, current understanding of the contribution of GluN2A containing NMDARs in these processes is incomplete. Therefore, highly selective compounds are required to further investigate these ion channels. In 2010, TCN-201 (2), one of the first selective negative allosteric modulators was reported. While the binding site of 2 and the influence of the substitution pattern of the benzenesulfonamide part has been reported recently, detailed structure-activity-relationships of the diacylhydrazine part and the linked phenyl moiety are still missing. In order to examine the critical interactions between these moieties and the binding site, several TCN-201 analogs with modified diacylhydrazine part were synthesized. The negative allosteric effect was recorded by two-electrode voltage clamp (TEVC) experiments using GluN1a/GluN2A expressing Xenopus laevis oocytes. Our data led to the conclusion, that the terminal phenyl moiety is involved in a cation-π-interaction with the guanidinium moiety of Arg755 of the GluN1a subunit, which plays a crucial role for high activity. Additionally, structure optimization by replacing the phenyl moiety with a thiophen-2-yl (10c), indol-2-yl (10g) or indol-3-yl (10h) moiety significantly increased the activity of 2 by the factor 2.5. At a test compound concentration of 200 nM, the negative allosteric effect of the most potent ligands 10c, 10h and 17 was significantly influenced by the glycine concentration. Although glycine dependency is higher than those of the lead compound 4, 10c and 17 showed significantly higher negative allosteric effects than 4 at glycine concentrations from 1 μM up to 10 μM. The potent GluN2A-NMDA receptor inhibitors 10c, 10h and 17 did not influence the ion current of GluN2B-NMDA receptors.

Keywords: Electrophysiology; GluN2A selective antagonists; NMDA receptor; Synthesis; TCN-201; Two-electrode voltage clamp.