New method for the synthesis of radioactive 19-iodocholest-5-en-3β-ol

Abstract

In 1970, 131I-19-iodocholest-5-en-3β-ol (VIII- 131I) was synthesized and shown to concentrate in the adrenal cortex of dogs by Counsell et al . [1]. Beierwaltes and his colleagues at the university of Michigan have shown this radiopharmaceutical to be an effective adrenocortical scanning agent for the diagnosis of 5 types of adrenal disease in humans [2]. Radioactive 19-iodocholesterol is not available from commercial sources although it may be purchased from the University of Michigan Nuclear Pharmacy, Ann Arbor, as a radiochemical and converted to a radiopharmaceutical [3]. For this reason we undertook to synthesize it de novo as described by Counsell et al . [1]. We found that 19-iodocholesterol prepared by this route contained an impurity, the amount of which varied from 20% to 60% as estimated by 13C nuclear magnetic resonance spectroscopy (CMR). We now describe a modification of this synthesis to yield VIII- 131I of greater than 98% chemical purity.