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Nucleophilic radioiodination of 6-bromocholesterol via non-isotopic exchange reaction in molten state

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Abstract

A synthetic method for preparing radioiodinated 6-[125 I]iodocholesterol[CL-6-125 I] for adrenal evaluation is described. The radioiodine atom wasincorporated onto the cholesterol molecule via non-isotopic exchange between6-bromocholesterol [CL-6-Br] and radioiodine as iodide ion [ 125 I –]in a molten state. The different parameters affecting the yield of exchange were investigated using 125 I (T 1/2 .60 d) to centralize the different physical and chemical reaction conditions and purification of the final product as pure as 6-[125 I]iodocholesterol. The method was suitable to either 131 I (T 1/2 .8 d) nucleophilic radioiodination which facilitates the scanning of the adrenal for a few days after administration or the use of 124 I (T 1/2 .4.16 d) nucleophilic radioiodination for PET evaluation of the adrenal. TLC as well as HPLC chromatographic analysis is used to determine the efficiency of the exchange reactions under different chemical reaction conditions and to monitor the stability of the final product as pure as CL-6-125 I with radiochemical purity of .99%. This no-carrier-added method improved the speed of the reaction and affords high radiochemical yield of 90 % and suitable specific activity due to the use of CL-6-Br rather than CL-6-I as substrate. Kinetic studies revealed second order iodine-bromine exchange reaction. The activation energy for the exchange reaction in ammonium acetate (m.p. 114 °C) was calculated to be 4.576 kcal/mole.

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Authors and Affiliations

  1. Labelled Compounds Department, Radioisotope Production Division, Hot Labs. Centre, Atomic Energy Authority, P.O. Box 13759, Cairo, Egypt

    M. El-Tawoosy

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  1. M. El-Tawoosy
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El-Tawoosy, M. Nucleophilic radioiodination of 6-bromocholesterol via non-isotopic exchange reaction in molten state. Journal of Radioanalytical and Nuclear Chemistry 249, 535–540 (2001). https://doi.org/10.1023/A:1013229827935

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