CECXG (3'-ethyl-LY-341,495) is a research drug which acts as a potent and selective antagonist for the group II metabotropic glutamate receptors (mGluR<sub>2/3</sub>), with reasonable selectivity for mGluR<sub>3</sub>. While it is some five times less potent than LY-341,495 at mGluR<sub>3</sub>, it has 38x higher affinity for mGluR<sub>3</sub> over mGluR<sub>2</sub>, making it one of the few ligands available that is able to distinguish between these two closely related receptor subtypes.