^99mTc(CO)₃-15-[N-(acetyloxy)-2-picolylamino] pentadecanoic acid: A potential radiotracer for evaluation of fatty acid metabolism

^99mTc(CO)₃-15-[N-(Acetyloxy)-2-picolylamino] pentadecanoic acid (1a) was prepared by incorporating [^99mTc-(CO) ₃]⁺ into 15-[N-(hydroxycarbonylmethyl)-2-picolylamino] pentadecanoic acid (2a). The overall radiochemical yield of 1a after HPLC purification was 60-63%. Radiotracer 1a was found to be chemically stable when incubated in human plasma for 4 h at 37°C. Tissue distribution studies showed that high radioactivity accumulated in the heart with rapid clearance. The maximum heart-to-blood uptake ratio was 1.87 at 5 min after a tail-vein injection. Radioactive metabolites were analyzed in urine samples of mice and corresponded to a 9.3:1 ratio of ^99mTc-(CO)₃-5-[N- (acetyloxy)-2-picolylamino]pentanoic acid (1b) to ^99mTc(CO) ₃-3-[N-(acetyloxy)-2-picolylamino]-propionic acid (1c), indicating that 1a is mainly metabolized to 1b via β-oxidation in the body. These results suggest that 1a is a promising radiotracer for evaluation of fatty acid metabolism in myocardium.