A new, well-retained myocardial imaging agent: radioiodinated 15-(p-lodophenyl)-6-tellurapentadecanoic acid.

A method involving the acid-catalyzed decomposition of a piperidyltriazene intermediate in the presence of radioiodide has been developed for the synthesis of radioiodinated 15-(p-iodophenyl)-6-tellurapentadecanoic acid. The iodine-125-labeled agent shows rapid, pronounced myocardial uptake in rats (5.30-6.45% injected dose/g after 5 min) and also exhibits the prolonged retention previously observed with 9-[123mTe]telluraheptadecanoic acid (9-123mTe]HDA). After 6 hr, the heart uptake remained high (3.89-5.33%) dose/g) and decreased only to 3.02-3.41% dose/g after 24 hr. Very low blood activity was detected (0.24-0.27% dose/g at 5 min; 0.29-0.32% dose/g at 6 hr) and the heart-to-blood ratios were high (22:1 at 5 min; 15:1 at 6 hr). Minimal deiodination was demonstrated by the low thyroid uptake (1.41-1.63% dose/g at 5 min; 5.33-7.08% dose/g at 6 hr). The rapid and pronounced uptake, prolonged myocardial retention, and low in vivo deiodination make this agent attractive for further evaluation.