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The effect of tellurium (Te) position on myocardial specificity and retention of fatty acids in which radioiodide is stabilized as a trans-(E)-vinyl iodide has been evaluated in rats. Five analogues of 18-iodo-17-octadecenoic acid (ICH = CH-R-Te-R'-COOH) with Te at positions 5, 7, 9, 11, and 13 were prepared by coupling of a trans-diiodoalkene (ICH = CH-R-I) with the requisite sodium [(alkoxycarbonyl)alkyl]telluride substrate (NaTe-R'-COOR"; R" = Me or Et), followed by basic hydrolysis. By varying R and R', a series of analogues with a chain length of 18 carbon atoms was prepared. The telluride substrates were generated in situ by NaBH4 reduction of the corresponding ditellurides, and the diiodoalkenes were prepared by sodium iodide-chloramine-T treatment of the corresponding vinylboronic acids [(HO)2BCH = CH-R-I)]. The vinylboronic acids were prepared by treatment of the terminal acetylenes (HC identical to C-R-I), synthesized from commercially available materials, with catecholborane. All new compounds were analyzed by TLC, NMR, MS, and elemental analyses. The 125I analogues [(E)-125ICH = CH-R-Te-R'-COOH] were prepared in the same manner and evaluated in rats (four per group). Heart uptake and retention were dependent upon the Te position. The analogue with Te at position 5 showed the most pronounced (5-min values) heart uptake (3.7-4.1 dose/g), myocardial retention, and heart/blood ratios (37:1) and is a candidate for radiolabeling with 123I and further evaluation as a myocardial imaging agent.

A method has been developed for the preparation of terminal halogenated tellurium fatty acids (X-R-Te-R'-COOH). The synthesis and physical properties of 17-bromo- and 17-iodo-9-telluraheptadecanoic acid (17-iodo-9-THDA) are described. The radiohalogenated agents are of interest as a result of their expected pronounced and prolonged heart uptake and potential use for evaluation of regional myocardial fatty acid metabolism. Evaluation in rats indicates that the myocardial uptake of 17-[131I]iodo-9-telluraheptadecanoic acid (17-[131I]iodo-9-THDA) is accompanied by significant in vivo deiodination. A comparison of the heart uptake and deiodination of 17-[131I]iodo-9-THDA and 16-[131I]iodopalmitic acid has demonstrated a close similarity in blood levels of radioactivity and thyroid uptake of radioiodide after administration of these agents to rats. These data suggest that the mechanism of deiodination of terminal radioiodinated alkanoic acids primarily results from direct cleavage of the carbon-iodine bond and not from loss of radioiodine from the final catabolite.

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