Abstract
The knowledge on element 43 (Tc) of the periodic table, built over the years through the contributions given by the close relationship between chemistry and nuclear medicine, allowed the development of new and increasingly effective radiopharmaceuticals useful both as perfusion and target specific imaging agents for SPECT (single photon emission tomography). Among the manifold Tc-compounds, Tc(V) nitrido complexes played a relevant role in the search for new technetium-99m radiopharmaceuticals, providing efficient labeling procedures that can be conveniently exploited for the design and synthesis of agents, also incorporating small organic molecules or peptides having defined structural features. With this work, we present an overview of four decades of research on the chemistry and on the nuclear medicine applications of Tc(V) nitrido complexes.
Highlights
The chemistry of technetium nitrido complexes has been actively explored and a variety of [99m Tc]Tc≡N species have been prepared at tracer level (Tc concentration 10−7 –10−9 M) and investigated as potential radiopharmaceuticals (RPs)
A remarkably high in vitro and in vivo stability and negligible interaction with serum proteins were proved for a number of different [99m Tc]TcN complexes comprising those with intermediate coordination number
Homoleptic [99m Tc][TcN(S2 CNR2 )2 ] complexes where the S2 CNR2 group is derived from primary amines as well as few secondary amines carrying alkyl and ester groups, showed to cross the blood–brain barrier, suggesting a possible application in brain perfusion imaging [96]
Summary
2 ) , TcN(tcbatsc), they usually exhibit sp geometry with an apical nitrido nitrogen atom and 2the. In LS molecules, this position is taken either by an amine nitrogen or a chloride, except for TcN(NCS) (PPh3 ) (CH3 CN) [57], ligands having narrower “bite” angles, like diethyldithiocarbamate, phenanthroline, and bipyridine In these complexes, an entire face of the octahedron is taken by identical donor atoms, so that facisomers are generated. A remarkably high in vitro and in vivo stability and negligible interaction with serum proteins were proved for a number of different [99m Tc]TcN complexes comprising those with intermediate coordination number (5, 6) such as [TcN(L)(PN(R)P)]0/+ (vide infra) This information to the RP domain, the common feature is that the position trans to nitride is poorly exposed to the risk of exchanging with competing ligands in vitro and in vivo. The Tc≡N bond length widens to 1.669 Å which is the third longest value found in the complexes investigated in this work
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