Organometallic Chemistry in Water with Tc OH2 3 CO

Many attempts have been made to introduce Cp into radiopharmaceutical chemistry. The Umiting factor to overcome is surely represented by the need to synthesize the corresponding complexes from water and [ Tc04j . Cp , the classical organometaUic Hgands and water, seem to exclude each other since Cp is readily protonated and decomposes rapidly by di- or polymerization. The prohibitively high pK of about 14 efficiently prevents the presence of the deprotonated form, Cp , which is more stable than protonated HCp. Many attempts from our research to react [ Tc(OFl2)3(CO)3] in water with HCp or HCp faded and, if at all, only 

Derivatization of Cp enables the use of this classical organometallic ligand in an aqueous environment. Since many Cp derivatives have been described in the organometallic literature, many candidates are available to further explore Cp chemistry for radiopharmaceutical purposes. Considering the importance of Cp, supported by the examples that already exist, reveals its advantages and it must be emphasized that Cp merits broader and more thorough investigation than is actually the case. 

An alternative approach to the introduction of piano-stool Tc complexes into biomolecules has recently been described. Besides free Cp attached to a biomolecule one can also choose ferrocene as a Cp source as already shown by Wenzel or Katzenellenbogen and coworkers. The difficulty consists in the cleavage of the very stable [CpFe] moiety from the original ferrocene. Still, it could be shown that [RelCOjg] in hot dmso (probably present as [Re(CO)3(dmso)3] can cleave 

Despite the many advantages outlined for [ Tc(OH2)3(CO)3] for the development of radiopharmaceuticals, complexes with targeting vectors are stiU at an early stage but their utiHty is recognized [73]. Potential reasons for this have recentiy been discussed extensively [7, 74]. One of the main reasons is the newness of the approach. Reliable kits have only been available for about one year. A new method takes time for adoption and optimization. It should be emphasized at this point 

Similarly, bombesin [77-79], octreotide and derivatives [80] and surfactant proteins [81] have been investigated with theyac-[ Tc(CO)3] moiety. Beside the fact that suboptimal chelators have been chosen, stability and binding studies elucidated that the behavior of a ligand attached to a targeting vector and the free ligand respectively are comparable. This confirms that studies with model ligands are useful and relevant for extrapolation of complexation conditions to vectors. 

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