A highly selective agonist for the metabotropic glutamate receptor mGluR2

The three conformationally restricted cyclopropyl glutamate analogues (3, 4, 5) were synthesised and their affinity for ionotropic and activity at metabotropic glutamate receptors were probed. Compound 4 turned out to be a highly selective agonist at the metabotropic glutamate receptor mGluR2 with at least two orders of magnitude selectivity in potency compared to the very homologous mGluR3 as well as mGluR1, 4, 5, 7. We also tried to synthesise the two epimers of 6, but the two compounds underwent fast epimerisation in H2O. Furthermore, two cyclopropyl arginine analogues (7, 8) were synthesised and characterised pharmacologically at GPRC6A.