Stereochemistry in technetium complexes

Technetium complexes have been found in which more than one stereoisomer was observed and the isomers have exhibited different biological properties. The two epimers of /sup 99m/Tc-CO2DADS and the three stereoisomers of /sup 99m/Tc-HM-PAO demonstrate different in vivo behavior. For example, the brain uptake and retention of the d-, 1- and meso- isomers of /sup 99m/Tc-HM-PAO are different. Geometric isomers have not, to date, been a major concern in technetium chemistry. Very few technetium complexes have been found in which both the cis and trans or meridinal and facial isomers have been identified. Generally only one isomer was identified when the potential for geometric isomers existed. Since one of the goals of technetium chemistry is diagnostic nuclear medicine, the findings of biological stereospecificity in a few classes of technetium complexes demonstrates the importance of stereochemical purity in potential technetium-99m diagnostic agents