Cyclopentadienyl Chemistry in Water: Synthesis and Properties of Bifunctionalized [(η<sup>5</sup>-C<sub>5</sub>H<sub>3</sub>{COOR}<sub>2</sub>)M(CO)<sub>3</sub>] (M = Re and<sup>99m</sup>Tc) Complexes
作者:Samer Ursillo、Daniel Can、Harmel W. Peindy N’Dongo、Paul Schmutz、Bernhard Spingler、Roger Alberto
DOI:10.1021/om501029e
日期:2014.12.8
Complexes of the [(eta(5)-C5H4COOR)M(CO)(3)] type (M = (99)mTc, Re; R = targeting function) are basic bioorganometallic structures with the potential of combining molecular imaging ((99)mTc) with therapy (cold Re or (186)/Re-188). So far, the single carboxylate group on the cyclopentadienyl ring (C-p(-)) limited targeting to one function. The concept of C-p(-) as a scaffold for attaching biological molecules could be extended substantially with two or more functionalities bound to the C-p(-) ligand. Accordingly, the rarely studied bis-substituted cyclopentadienyl ligands [C5H3(1,2-COOMe)(2)](-) and [C5H3(1,3-COOMe)(2)](-) were synthesized and their coordination to the fac-M(CO)(3)}(+) moiety was studied in water. Both ligands are deprotonated at physiological pH and do not undergo Diels-Alder reactions. In water, they react directly with [Re(OH2)(3)(CO)(3)](+) to form [(eta(5)-C5H31,2-COOMe}(2))Re(CO)(3)] and [(eta(5)-C5H31,3-COOMe}(2))Re(CO)(3)]. Controlled hydrolysis at neutral to alkaline pH gives the monoesters and fully hydrolyzed [(eta(5)-C5H31,2-COOH}(2))Re(CO)(3)] and [(eta(5)-C5H31,3-COOH}(2))Re(CO)(3)]. Thermal treatment leads to decarboxylation and formation of [(eta(5)-C5H4COOH)Re(CO)(3)]. The corresponding 99mTc homologues are directly accessible under slightly acidic conditions from [(99)mTcO(4)](-) in high yields. In the presented strategy, the C-p(-) ring acts as a scaffold for attaching multiple targeting agents or pharmacophores at the same time.