Synthesis of (2S,2′R,3′R)-2-(1′-[3H],2′,3′-dicarboxylcyclopropyl)-glycine ([3H]-DCG-IV)

The conformationally restricted analog of L-glutamic acid (L-Glu, 1), (2S,2'R,3'R)-2-(2',3'-dicarboxylcyclopropyl)-glycine (DCG-IV, 2) is a potent group II mGluR agonist. In order to study the distribution of group IImGluRs in the brain and to establish a radioligand binding assay we have developed a synthesis of [H-3]-DCG-IV (2a). The key intermediate, alpha-bromo aldehyde 7, was prepared in four steps starting from (-)-Feist's acid (3). The incorporation of tritium was performed by reaction of 7 with tri-n-butyltin tritide to give 8, which was transformed in two steps into 2a.