Basic aqueous chemistry of [M(OH2)(3)(CO)(3)](+) (M = Re, Tc) directed towards radiopharmaceutical application

A review on the synthesis and properties of the organometallic aqua-ion [M( OH2)(3)(CO)(3)](+) (M = Re, Tc-99, Tc-99m), as relevant for radiopharmaceut ical application, is presented. These important starting compounds can be p repared quantitatively, (a) on the no carrier added (n.c.a.) level (Tc-99m) in water, or (b) in organic solvents (Re, Tc-99) at atmospheric pressure i n a short time and from [MO4](-). The main characteristics of these carbony l complexes are the high substitution stability of the three CO ligands and the substitution lability of the coordinated water molecules. [M(OH2)(3)(C O)(3)](+) can be considered as a 'semi aquo-ion'. On the macroscopic level, upon titration with OH-, hydroxo-bridged oligomers have been isolated and characterized. The formation of hydroxo-bridged complexes is a consequence of the considerable Bronstedt acidity of [M(OH2)(3)(CO)(3)](+), whereas on the n.c.a. level no such behavior was observed. Conditions and products of the water exchange by imidazole (im) and derivatives thereof (histamine, hi stidine) will be presented. The different mononuclear complexes with these ligands are of extraordinary inertness, which is the basis for potential ap plications in biology and nuclear medicine. Finally, as a basis for bioorga nometallic chemistry, the adoption of the results from basic coordination c hemistry to the labeling of biomolecules with an organometallic moiety win be exemplified with a selected penta-peptide and a recombinant single chain fragment. (C) 1999 Elsevier Science S.A. All rights reserved.