Efficacy switching SAR of mGluR5 allosteric modulators: Highly potent positive and negative modulators from one chemotype

A series of metabotropic glutamate 5 receptor (mGluR5) allosteric ligands with positive, negative or no modulatory efficacy is described. The ability of this series to yield both mGluR5 PAMs and NAMs with single-digit nanomolar potency is unusual, and the underlying SAR is detailed.