Synthesis and identification of the monocation Tc(CPI)6+ in Tc(CNC(CH3)2COOCH3)6Cl and its hydrolysis products

The complex Tc(CNC(CH3)2COOCH3)6Cl (cation designated as Tc(CPI)6+) is one of a series of isonitrile-coordinated technetium complexes being investigated as a prototype radiopharmaceutical to evaluate myocardial perfusion. It has been prepared from the pertechnetate ion by aqueous Na2S2O4 reduction in the presence of the functionalized isocyanide ligand. The octahedral compound with its relatively reactive ester substituents is stable under aqueous aerobic conditions within the pH range 5-7. At high pH, however, the ester moieties undergo random, base-catalyzed hydrolysis while the six ligands remain coordinated in a fixed geometry to the central metal. The nine predicted carboxylic acid containing species were separated and identified by RP-HPLC, FAB-MS, IR, and 99Tc NMR methods. Specific k' values obtained from the RP-HPLC of these characterized compounds were used to identify technetium containing metabolites of the radiopharmaceutical. Varying rates of in vitro enzymatic hydrolysis at the terminal ester moieties of the coordinated ligands were shown to occur when this compound was incubated with blood serum from different animal species