SUMMARY (S)-(-)-N-[( l-ethyl-2-pyrrolidinyl)methyl]-5-[ 1231]iodo-2,3-dimethoxy-benzamide (TDP 517) (proposed generic name, [I23I]epidepride) is the iodine-123 substituted analogue of isoremoxipride (FLB 457). both of which are very potent dopamine D-2 antagonists (epidepnde KD 0.024 nM). [ 12311Epidepride was radioiodinated in 60-70% radiochemical yields i n 35 min from the corresponding 5-(mbutyltin) derivative using NaI23I with a specific radioactivity of 3000 Wmmol, and oxidized in situ with chloramine-T. The aryltin precursor was prepared from non-labelled epidepride by palladium-catalyzed stannylation using bis(m-n-butyltin) in tnethylamine. Alternatively, using no carrier-added Na 1251 as the radioisotope, [ 125Ilepidepride at 2000 Ci/mmol specific radioactivity was prepared in 86% radiochemical yield and 99% radiochemical purity after purification by reverse phase HPLC in ethanolic phosphate buffer.