The Structure–Activity Relationship of a Tetrahydroisoquinoline Class of <i>N</i>‑Methyl‑d‑Aspartate Receptor Modulators that Potentiates GluN2B-Containing <i>N</i>‑Methyl‑d‑Aspartate Receptors

We have identified a series of positive allosteric NMDA receptor (NMDAR) modulators derived from a known class of GluN2C/D-selective tetrahydroisoquinoline analogues that includes CIQ. The prototypical compound of this series contains a single isopropoxy moiety in place of the two methoxy substituents present in CIQ. Modifications of this isopropoxy-containing scaffold led to the identification of analogues with enhanced activity at the GluN2B subunit. We identified molecules that potentiate the response of GluN2B/GluN2C/GluN2D, GluN2B/GluN2C, and GluN2C/GluN2D-containing NMDARs to maximally effective concentrations of agonist. Multiple compounds potentiate the response of NMDARs with submicromolar EC<sub>50</sub> values. Analysis of enantiomeric pairs revealed that the <i>S</i>-(−) enantiomer is active at the GluN2B, GluN2C, and/or GluN2D subunits, whereas the <i>R</i>-(+) enantiomer is only active at GluN2C/D subunits. These results provide a starting point for the development of selective positive allosteric modulators for GluN2B-containing receptors.