New fast labelling of iodinated arylcompounds with radioiodine resulting in pure radiopharmaceuticals with high specific activity

Abstract

The authors show that the methods described in literature for the labelling with I-123 or I-131 of iodinated arylcompounds, such as N-isopropyl p-iodoamphetamine (IAMP), m-iodobenzylguanidine (MIBG) and o-iodohippuric acid, yield both labelled side products and radioiodine. These methods are based on the use of Cu(II) as a catalyst, on a melt method or the use of (NH/sub 4/)/sub 2/S0/sub 4/ as a solid state transfer catalyst. This paper shows that the nucleophilic exchange reaction assisted by Cu(I) in presence of an excess reductant allows to obtain an almost quantitative labelling yield within a short reaction time without formation of radiolabelled side products or radioiodine. When high specific activities are needed, this method allows to use higher labelling temperatures (up to 150/sup 0/C) without generating degradation products. It also allows to produce pure I-123 labelled IAMP and MIBG with a specific activity of 2.5 mCi/..mu..g for an initial I-123 activity of 25 mCi. When labelling with high activities of I-131 is concerned, for the preparations of therapeutic doses of I-131 MIBG, difficulties due to the high amounts of radiolysis products generated in the I-131 solution, are ruled out by the use of an excess of reducing agent.