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

To determine the myocardial uptake and retention properties of radioiodinated tellurium fatty acids, we prepared two new tellurium fatty acids in which iodine-125 has been chemically stabilized by attachment as a trans-vinyl iodide (I-CH = CH-R-Te-R'-COOH) and evaluated them in rats. Fabrication of 18-iodo-13-tellura-17-octadecenoic 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 = 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 (approximately 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 upon the position of the tellurium, we prepared an analogue with the same chain length, 18-[125I]iodo-7-tellura-17-octadecenoic acid, 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. Furthermore, the heart/blood ratios remained high for several hours (13:1 after 60 min; 9:1 after 4 h). Iodine-123 labeled 18-iodo-7-tellura-17-octadecenoic acid is an attractive new compound for evaluation as a myocardial imaging agent.