(2S,1'S,2'R,3'R)-2(2'-Carboxy-3'-hydroxymethylcyclopropyl)glycine-[3H], a potent and selective radioligand for labeling group 2 and 3 metabotropic glutamate receptors.

We report herein the synthesis of the tritium labeled isotopomer of 1 and its use as a radioligand to label mGlu8 receptors in rat forebrain membranes as well as cloned human recombinant mGlu receptors. [(3)H]-1 was synthesized by the NaBT(4) reduction of an activated analog of 5. [(3)H]-1 bound appreciably to recombinant human mGlu2, mGlu3 and mGlu8 receptors and to rat forebrain membranes and was displaced by L-glutamate and L-(+)-2 amino-4-phosphonobutyric acid. The results indicate that [(3)H]-1 should be a useful ligand for the study of mGluR2, 3, and 8 receptors in cloned cell lines and possibly brain tissue.