New myocardial imaging agents: stabilization of radioiodine as a terminal vinyl iodide moiety on tellurium fatty acids

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Abstract
To determine the myocardial uptake and retention properties of radioiodinated tellurium fatty acids, 2 new tellurium fatty acids in which 125I was chemically stabilized by attachment as a trans-vinyl iodide (I.sbd.CH.dbd.CH.sbd.R.sbd.Te.sbd.R''.sbd.COOH) were prepared and evaluated in rats. Fabrication of 18-iodo-13-tellura-170-ctadecenoic acid was accomplished by coupling 1,5-diiodo-1-pentene with sodium 12-(methoxycarbonyl)-n-dodecan-1-yl telluride. The [5-125I]-1,5-diiodo-1-pentene was prepared by an organoborane technique involving 125I+ treatment of 5-iodo-1-penten-1-ylboronic acid [I(CH2)3CH.dbd.CHB(OH)2]. The absolute heart uptake of this agent was moderate (1.47-2.52% dose/g after 60 min), but the heart/blood ratios were low (.apprx. 2.6:1). Only marginal in vivo deiodination occurred, since the thyroid uptake was low (15-18% dose/g after 60 min). The effect of tellurium in position 13 was unexpected. To determine if the low heart specificity and low heart/blood ratios were dependent on the position of the tellurium, an analog with the same chain length, 18-[125I]iodo-7-tellura-17-octadecenoic acid, was prepared in the same manner by reaction of [11-125I]-1,11-diiodo-1-undecene with sodium 6-(methoxycarbonyl)-n-hexan-1-yl telluride. This agent showed pronounced heart uptake (2.47-3.94% dose/g after 60 min) and prolonged retention (1.76-3.14% dose/g after 4 h) in rats. The heart/blood ratios remained high for several hours (13:1 after 60 min; 9:1 after 4 h). 123I labeled 18-iodo-7-tellura-17-octadecenoic acid is an attractive new compound for evaluation as a myocardial imaging agent.

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