1,3,5-Trisubstituted Pyrazoles as Potent Negative Allosteric Modulators of the mGlu_2/3 Receptors

The metabotropic glutamate subtype 2 (mGlu₂ ) receptor is a presynaptic membrane receptor distributed widely in brain that provides feedback inhibitory control of glutamate release. Inhibition of the mGlu₂ receptor function with a negative allosteric modulator (NAM) enhances activity-dependent glutamate release, which may be of therapeutic benefit for the treatment of neurological and psychiatric disorders. An attractive pyrazole hit was identified after a high-throughput screening (HTS) campaign. The evolution of this hit is described by structure-activity relationship (SAR) studies on specific parts of the molecule. From near micromolar potency we could obtain compounds with single-digit nanomolar activity in the mGlu₂ NAM GTPγS assay. In addition to SAR on in vitro potency, a more detailed overview is given with a specific set of compounds on the excellent agreement between in vitro potency, free brain concentration, and ex vivo mGlu₂ receptor occupancy. Finally, to obtain improved drug-like compounds, plans for future research are suggested toward increasing free brain concentration while maintaining high in vitro potency.