Technetium complexes chemistry

ITic intent to synthesize compounds that could be appropriate as "Tc radiophar-maccuticals for diagnosis in nuclear medicine in selective imaging of organs has predominantly stimulated investigations on technetium complex chemistry. 

Since the mid 1960s, some excellent books on technetium have appeared R. Colton The Chemistry of Rhenium and Technetium , Interscicnce (1965), R. D. Peacock The Chemistry of Technetium and Rhenium , Elsevier (1966), J. Steigman and W. C. Eckelman "The Chemistry of 4 echnetium in Medicine , Nuclear Science Series (1992), and Technetium and Rhenium. Their Chemistry and Applications , Topics in Current Chemistry (1996), edited by K. Yoshihara and T. Omori. The last book contains contributions to several aspects of technetium chemistry. However, the latest comprehensive volumes on technetium which appeared in the Gmelin Handbook of Inorganic Chemistry (8th edition. Springer) date back to 1982/83. Hie increasing flood of publications since then, particularly on technetium complex chemistry and radiopharmaccuticals, justifies this comprehensive monograph. 

Acknowledging the important part that 99mTc(V) radiopharmaceuticals are playing in nuclear medicine, advances in their coordination chemistry, as attained by new syntheses and better structural characterization, are discussed with respect to the design of Tc(V) radiotracers. In the light of current interest in making technetium complexes active in vivo, a chapter considering several aspects of reactivity is included. 

The most convenient route to organometallic technetium complexes is directly from 3, under reaction conditions which allow working in a normal laboratory. There are basically three essential compounds that fulfil these conditions and can be prepared in a one step synthesis starting from 3, and which are convenient precursors for subsequent chemistry due to their reactivity (Scheme 1). 

The radiopharmaceutical chemistry of rhenium for cancer therapy is a new and developing field. The rapid increase in the numbers of papers concerned with i86, i88Re-compiexes for nuclear medicine unquestionably shows the importance of the chemistry of rhenium complexes, as mentioned by Deutsch in his lecture at the Fourth International Symposium on Technetium in Chemistry and Nuclear Medicine held in Bressanone, Italy in 1994. 

Metal-essential radiopharmaceuticals are those whose targeting properties are inherent in the structure and chemistry of the complex itself rather than a biomolecule whose targeting ability is independent of the attachment of the metal. While this class of tracers includes many well-developed technetium complexes, it includes relatively few rhenium complexes. 

Complexes of technetium in oxidation states ranging from (-1) to (VII) have been prepared chemically and characterized. However, historically only the higher oxidation states (IV), (V) and (VII) have been of major importance in radiopharmaceutical formulations. More recently there has been increased interest in lower oxidation state technetium complexes for medical applications, and the use of ir-acceptor ligands has allowed the preparation of Tc1 complexes which are stable in vivo. The coordination chemistry of technetium has been described in Chapter 42 and recent reviews have been provided by Davison21 and by Schwochau.22 Reviews which relate to medical applications of technetium are given by Jones and Davison,549 Deutsch et al.,20 Deutsch and Barnett,550 Siedel551 and Clarke and Fackler.552 The in vivo chemistry of "mTc chelates has been described by Eckelman and Volkert,553 while the structures of technetium complexes, determined by X-ray diffraction techniques, have been reviewed by Bandoli et ai554... 

In this work, the chemistry of rhenium and technetium complexes anchored by heterofunctionalized phosphines and by scorpionates will be reviewed. Special attention will be given to those chemical aspects that, according to the authors, could enhance the ability of using these ligands in the development of target-specific radiopharmaceuticals. In this context, the chemistry of the novel fac-[M(CO)3]+ and [M(N)PXP]2+ metal fragments will also be mentioned,but to such an extent that minimizes any overlap with other reviews published in this special issue of Topics in Current Chemistry. 

There is an extensive and complex chemistry of [Re6(/A-X)D(/i,-Y)8- ] species, where X may be exclusively S or Se, or there may be a mixture of chalcogenide and halide (Y) bridges.13 There are also technetium clusters with Tc6 octahedra and allegedly only 5 face bridges, e.g., [Tc6(/u.3-Br5)Br6]1 2, but they require better characterization. 

The importance of technetium-99m radiopharmaceuticals stimulated numerous studies related to the basic chemistry of long-lived technetium Tc. A great number of technetium complexes reviewed in the preceding sections has been synthesized and characterized. Exact technetium analyses in these compounds have been needed to confirm their composition. Besides the traditional determinations of Tc by conductometric titrations of pertechnetate or by liquid scintillation counting, neutron activation of Tc has also been... 

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