SYNTHESIS AND BIODISTRIBUTION OF [5-I-131]IODOTROPAPRIDE - A POTENTIAL D-2 DOPAMINE-RECEPTOR IMAGING AGENT

[5-I-131]Iodotropapride is a benzamidic compound which displays high a ffinity and selectivity for dopaminergic receptors. It was prepared fr om the corresponding brominated compound by a nucleophilic substitutio n with [I-131]iodine (t(1/2) = 8.02 days, E(gamma) = 364 keV) based on the use of Cu(I) as catalyst and high specific activity of [I-131]NaI . After i.v. injection in rats the tracer crosses the blood-brain barr ier (0.42 +/- 0.06% of injected dose in the total brain) and demonstra tes a high affinity binding to the striatum. The striatum-to-cerebellu m ratio increases with time and reaches values of 9 and 22 at 30 and 1 20 min after injection, respectively This specific uptake in the stria tum is saturable and can be blocked by pretreatment with different D-2 antagonists. When labeled with I-123 (t(1/2) = 13 h, E(gamma) = 159 k eV), the corresponding [I-123]iodotropapride may be useful for the inv estigation of the D, dopamine receptors in humans with single photon e mission computer tomography (SPECT).