SYNTHESIS OF [2-C-11]-6,7-DICHLORO-2,3-DIHYDROXYQUINOXALINE AND EVALUATION OF ITS IN-VIVO DISTRIBUTION IN RAT WITH PET

A method for labelling 6,7-dichloro-2,3-dihydroxyquinoxaline (DCQX) in position 2 with carbon-11 is presented. Diethyl [1-C-11]oxalate was s ynthesized in a two-step, microwave-assisted procedure from no-carrier -added [C-11]cyanide and was reacted with 4,5-dichloro-1,2-phenylenedi amine in sulfuric acid at 150 degrees C for 10 min. [2-C-11]DCQX, isol ated by semi-preparative HPLC, was >99% radiochemically pure with a sp ecific activity ranging between 19-26 TBq/mmol. The total time of synt hesis was 45-55 min and the isolated, decay-corrected yields were on t he order of 10%, based on the trapped [C-11]cyanide. A PET study of it s biodistribution after intravenous injection in a male rat revealed t hat the extraction of [2-C-11]DCQX across the intact blood-brain barri er was less than or equal to 2%.