ACPT-II is a general competitive antagonist of metabotropic glutamate (mGlu) receptors. The K values for mGlu1a, mGlu2, and mGlu4a receptors are 115, 88, and 77 µM, respectively. It binds to the large extracellular domain called a Venus flytrap module, where agonists bind. ACPT-II is a stereoisomer of the group III mGlu receptor-selective antagonist, ACPT-I.