Glucoheptonate ligand

The need to achieve high yield in one-pot synthesis, coupled to the relative kinetic inertness of rhenium complex (e.g. compared to technetium) and the mild conditions required has led to the development of useful versatile rhenium(V) intermediates that can be quickly prepared in quantitative yield, and are metastable, i.e. kinetically labile enough to react rapidly with the final chelator, again in high yield. The most widely used ligands suitable for this purpose are polydentate hydroxycarboxylic acids such as glucoheptonate [116a], citrate (47), tartrate (48), and 2-hydroxyisobutyric acid (49) [159]. Examples are discussed elsewhere in this chapter. They are typically used in the presence of Sn(II) to reduce Re(VII) to Re(V), at moderately elevated temperature (50-100 °C) at pH 2-3 (acid pH promotes reduction of perrhenate, presumably by facilitat-... 

Tc(gluconate) and Tc(glucoheptonate) have been the earliest products of Tc(V) used as radiotracers for renal imaging (De Kieviet 1981 Johannsen and Spies 1988). The compounds were shown to contain a Tc=0 core, but their structures are not completely defined, probably because of more than one stable species at carrier-added level (De Kieviet 1981). However, the x-ray structure of similar Tc complexes with similar ligands (Davison et al. 1987 DePamphilis et al. 1974 Fig. 2.1.2), indirectly supports the formulation as TcO(G1u)2, even though the structure of TcO(Ox)(OxH) demonstrates the possibility of another species with a Tc=0 core (Abrams et al. 1991). 

Initially, reduced " Tc activity and ethylenediaminetetraacetic acid (EDTA) form an intermediary complex, which is transformed slowly by ligand exchange to the Tc(V)-ECD complex, showing high in vitro stability. Originally, glucoheptonate had been used instead of EDTA (Cheesman et al. 1988). 

The only difference between the two preparations is the temperature at which the reduction is conducted at low temperatures the Tc(V) species TcOX is kinetically trapped and can be isolated, whereas at higher temperatures the Tc(V) complex suffers further reduction to yield the Tc(IV) species TcXg " (10,11). Other potential substances for radiopharmaceutical synthesis by substitution reactions include the undefined, reduced Tc-glucoheptonate complex (12) and the recently reported, lipophilic technetium(V) species Tc(HBPz Cl2 O (HBPz3 = hydrotris(l-pyra-zolyDborato ligand) (13). 

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