Radioiodinated 1-carboxamidino-4-phenylpiperazine: a potential adrenal and myocardial imaging radiopharmaceutical.

This report describes the synthesis of radioiodinated 1-carboxamidino-4-phenylpiperazine, an aralkyl-guanidine with good adrenal and myocardial selectivity. As a tertiary aniline, the benzene portion of the molecule readily undergoes direct electrophilic radioiodination under mild reaction conditions to yield a single product with high specific activity which can be rapidly purified by anion exchange. Biodistribution studies in rats show high uptake in both the heart and the adrenals. The activity in the adrenals is retained for a prolonged period, whereas that in the heart declines with a 4-5 h half-life. The high uptake and target tissue-to-blood ratios suggest the potential use of this agent for myocardial and adrenomedullary imaging.