Synthesis of (2S,2 ' R,3 ' R)-2-(1 '-[H-3],2 ',3 '-dicarboxylcyclopropyl)-glycine ([H-3]-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 gro up II mGluR agonist. In order to study the distribution of group IImGluRs i n 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 aldehyd e 7, was prepared in four steps starting from (-)-Feist's acid (3). The inc orporation of tritium was performed by reaction of 7 with tri-n-butyltin tr itide to give 8, which was transformed in two steps into 2a.