| Summary: | With the aim of developing <sup>99m</sup>Tc-labeled fatty acids intended for myocardial metabolism imaging we report herein the synthesis and characterization of two novel derivatives of undecanonoic and hexadecanonoic acid that have been functionalized at the ω-site by cysteine through the formation of a thioether bond (<b>Cys−FA11</b> and <b>Cys−FA16</b>). Equimolar amounts of each ligand and the [NEt<sub>4</sub>]<sub>2</sub>[Re(CO)<sub>3</sub>Br<sub>3</sub>] precursor generated the respective hexacoordinated neutral complexes in which the ligand coordinated to the metal through the SNO donor system of cysteine. The rhenium complexes were characterized by elemental analysis, IR and NMR spectroscopies. The analogous technetium-99m complexes, <b><sup>99m</sup>Tc−Cys−FA11</b> and <b><sup>99m</sup>Tc−Cys−FA16</b> were prepared by incubation of the ligand with the precursor [<sup>99m</sup>Tc(CO)<sub>3</sub>(H<sub>2</sub>O)<sub>3</sub>]<sup>+</sup> (radiochemical yield ≥98%). Their structure was established by comparative HPLC techniques. In vivo studies in mice showed high initial heart uptake for both <sup>99m</sup>Tc complexes (7.4 ± 0.53 and 7.07 ± 0.73 percentage of injected dose (%ID)/g at 1 min post injection. Rapid clearance (0.60 ± 0.02 %ID/g) was observed for <b><sup>99m</sup>Tc−Cys−FA11</b> while the clearance of the longer fatty acid <b><sup>99m</sup>Tc−Cys−FA16</b> was slower (2.31 ± 0.09 %ID/g at 15 min p.i.). Metabolite analysis study indicated that complexes were catabolized through the β-oxidation process.
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