Reactivity of the [M(PS)<sub>2</sub>]<sup>+</sup> Building
Block (M = Re<sup>III</sup> and <sup>99m</sup>Tc<sup>III</sup>; PS
= Phosphinothiolate) toward Isopropylxanthate and Pyridine-2-thiolate
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Abstract
The coordination properties of isopropylxanthate
(<i>i</i>-Pr-Tiox) and pyridine-2-thiolate (PyS) toward
the [M(PS)<sub>2</sub>]<sup>+</sup> moiety (M = Re and <sup>99m</sup>Tc; PS = phosphinothiolate)
were investigated. Synthesis and full characterization of [Re(PS2)<sub>2</sub>(<i>i</i>-Pr-Tiox)] (<b>Re1</b>), [Re(PSiso)<sub>2</sub>(<i>i</i>-Pr-Tiox)] (<b>Re2</b>), [Re(PS2)<sub>2</sub>(PyS)] (<b>Re3</b>), and [Re(PSiso)<sub>2</sub>(PyS)]
(<b>Re4</b>), where PS2 = 2-(diphenylphosphino)ethanethiolate
and PSiso = 2-(diisopropylphosphino)ethanethiolate,
and the structural X-ray analysis of complex <b>Re3</b> were
carried out. <sup>99m</sup>Tc analogues of complexes <b>Re2</b> (<sup><b>99m</b></sup><b>Tc2</b>) and <b>Re4</b> (<sup><b>99m</b></sup><b>Tc4</b>) were obtained in high
radiochemical yield following a simple one-pot procedure. The chemical
identity of the radiolabeled compounds was confirmed by chromatographic
comparison with the corresponding rhenium complexes and by dual radio/UV
HPLC analysis combined with ESI(+)-MS of <sup>99g/99m</sup>Tc complexes
prepared in carrier-added conditions. The two radiolabeled complexes
were stable with regard to trans chelation with cysteine, glutathione,
and ethylenediaminotetraacetic acid and in rat and
human sera. This study highlights the substitution-inert metal-fragment
behavior of the [M(PS)<sub>2</sub>]<sup>+</sup> framework, which reacts
with suitable bidentate coligands to form stable hexacoordinated asymmetrical
complexes. This feature makes it a promising platform on which to
develop a new class of Re/Tc complexes that are potentially useful
in radiopharmaceutical applications