Radiopharmaceuticals

By nucleophilic isotope exchange, 6-¹²³I-nicotinic acid diethylamide (6-¹²³I-NADA) was synthesized in a solution of the starting compound and catalytic amounts of CuCl in acetic acid. After purification by high pressure liquid chromatography radiochemical yields up to 97% could be obtained within 10 minutes. In mice the radioactivity was rapidly accumulated in the brain reaching the maximum (4.16%/g) 0.5 minutes after i.v. injection and eliminated by a fast and a slow phase. At the maximum of accumulation the brain/blood ratio was 1.21, decreasing to less than 0.15 already after one hour.