[2.2]Paracyclophane-Based TCN-201 Analogs as GluN2A-Selective NMDA Receptor Antagonists

Discovery of GluN2A subtype-selective N-methyl-d-aspartate (NMDA) receptor ligands

The N-methyl-d-aspartate (NMDA) receptors, which belong to the ionotropic Glutamate receptors, constitute a family of ligand-gated ion channels. Within the various subtypes of NMDA receptors, the GluN1/2A subtype plays a significant role in central nervous system (CNS) disorders. The present article aims to provide a comprehensive review of ligands targeting GluN2A-containing NMDA receptors, encompassing negative allosteric modulators (NAMs), positive allosteric modulators (PAMs) and competitive antagonists. Moreover, the ligands' structure-activity relationships (SARs) and the binding models of representative ligands are also discussed, providing valuable insights for the clinical rational design of effective drugs targeting CNS diseases.

Progresses in GluN2A-containing NMDA Receptors and their Selective Regulators

NMDA receptors play an important physiological role in regulating synaptic plasticity, learning and memory. GluN2A subunits are the most abundant functional subunits of NMDA receptors expressed in mature brain, and their dysfunction is related to various neurological diseases. According to subunit composition, GluN2A-containing NMDA receptors can be divided into two types: diheteromeric and triheteromeric receptors. In this review, the expression, functional and pharmacological properties of different kinds of GluN2A-containing NMDA receptors as well as selective GluN2A regulators were described to further understand this type of NMDA receptors.

GluN2A-Selective NMDA Receptor Antagonists: Mimicking the U-Shaped Bioactive Conformation of TCN-201 by a [2.2]Paracyclophane System

Under physiological conditions, N-Methyl-D-Aspartate (NMDA) receptors play a crucial role for synaptic plasticity, long-term potentiation and long-term depression. However, overactivation of NMDA receptors can result in excitotoxicity, which is associated with various neurological and neurodegenerative diseases. The physiological properties of NMDA receptors are strongly dependent on the GluN2 subunit incorporated into the heterotetrameric NMDA receptor. Therefore, subtype selective NMDA receptor modulators are of high interest. Since prototypical GluN2A-NMDA receptor antagonists TCN-201 and its MPX-analogs adopt a U-shaped conformation within the binding pocket, paracyclophanes were designed containing the phenyl rings in an already parallel orientation. Docking studies of the designed paracyclophanes show a similar binding pose as TCN-201. [2.2]Paracyclophanes with a benzoate or benzamide side chain were prepared in four-step synthesis, respectively, starting with a radical bromination in benzylic 1-position of [2.2]paracyclophane. In two-electrode voltage clamp experiments using Xenopus laevis oocytes transfected with cRNAs for the GluN1-4a and GluN2A subunits, the esters and amides (conc. 10 μM) did not show considerable inhibition of ion flux. It can be concluded that the GluN2A-NMDA receptor does not accept ligands with a paracyclophane scaffold functionalized in benzylic 1-position, although docking studies had revealed promising binding poses for benzoic acid esters and benzamides.

The concise synthesis and resolution of planar chiral [2.2]paracyclophane oxazolines by C-H activation

Planar chiral [2.2]paracyclophanes are resolved through the direct C–H arylation of enantiopure oxazolines, providing a convenient route to ligands and chiral materials. Preliminary results show that hydrolysis followed by decarboxylative phosphorylation leads to enantiopure [2.2]paracyclophane derivatives that are otherwise challenging to prepare.

Racemic bromo[2.2]paracyclophanes are directly transformed into enantiomerically pure planar chiral oxazolines in one step with simultaneous resolution of planar chirality.