Synthesis of radioiodinated metyrapone--a potential adrenal imaging agent

Metyrapone has been labelled with radioiodine selectively in the 4'-position of ring B. The synthesis of 123I-(131)-metyrapone involves four intermediate compounds. 4'-Bromo-metyrapone serves as a stable precursor that is labelled before use. Studies of the biodistribution of [131I]metyrapone in rats indicate the highest concentration in the adrenal gland 10 min after the injection with a fast elimination of the radioactivity. However, the absolute uptake in the normal adrenal is low. When [123I]metyrapone was used in a patient with bilateral hyperplasia, faint adrenal images were obtained.