Optimization of labeling conditions to produce N-isopropyl-p-[123I]-iodoamphetamine: a radiopharmaceutical for brain perfusion imaging

Brain SPECT tracers, such as [123I]-labeled amines and technetium-labeled compounds, offer high resolution SPECT images after intravenous injection using conventional rotating gamma cameras. The aim of this study was to optimize labeling conditions to produce N-isopropyl-p-[123I]-iodoamphetamine) and to propose an easy, rapid and inexpensive chromatography quality control procedure to determine radiochemical purity. [123I]-Imp was produced by isotopic exchange in presence of Cu(II) as catalyst and an excess of ascorbic acid as reducing agent. In order to obtain good radiochemical yield in a minimal reaction time, labeling reaction parameters were evaluated, with the study of different reaction temperatures and time, mass of ascorbic acid, reaction pH and [131I]NaI/IMP ratio. [123I]-IMP was obtained with radiochemical yield greater than 97 per cent using 3 mg of IMP.HCl, 3.15 mol of Cu++ and an excess of ascorbic acid in acid medium (pH 2.0) at 175oC and 30 minutes. Radiochemical purity was determined by paper chromatography with high resolution. Biological distribution studies in animals showed high and persistent cerebral uptake and in vivo stability of the compound (Au)