Synthesis and biodistribution of 99mTc-labeled piperidinyl bis(aminoethanethiol) complexes: potential brain perfusion imaging agents for single photon emission computed tomography

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Abstract
In developing clinically useful 99mTc-labeled radiopharmaceuticals for the evaluation of regional cerebral perfusion with single photon emission computed tomography (SPECT), a number of substituted alkyl(aryl)piperidinyl bis(aminoethanethiol) ligands for chelating [99mTc]TcO(III) were synthesized. Each ligand forms two diastereomers, syn and anti, after reacting with a racemic mixture of the ligand. The diastereomers were separated by high-pressure liquid chromatography. In biodistribution studies conducted in rats, the diastereomers exhibit widely disparate brain uptake values; however, this disparity seems to diminish as the steric bulk of the substituent at the C-4 position of the piperidinyl moiety increases. Furthermore, all the complexes evaluated failed to show a prolonged retention in the rat brain, suggesting that further structural modification may be necessary to obtain clinically useful complexes from this class of compounds.