Single amino acid chelate complexes of the M(CO)₃⁺ core for correlating fluorescence and radioimaging studies (M = ^99mTc or Re)

Single amino acid chelates (SAACs) and SAAC-like bifunctional ligands can be exploited in the design of a variety of bioconjugates for facile metallation with the M(CO)₃⁺ unit with M = ^99mTc or Re. When the donor groups of the ligand are quinolone, thiazole or other similarly conjugated heterocycles, the rhenium complexes are fluorescent, affording complementary and isostructural fluorescent probes to the radioactive ^99mTc analogues. The versatility of the approach has been demonstrated by the preparation of bioconjugates incorporating peptides, biotin, folic acid, thymidine and vitamin B₁₂. In addition, the unusual photophysical properties observed for rhenium of the [bisthiazole-diamino butane-Re(CO)₃⁺] derivative [BTBA-Re(CO)₃] ⁺ are discussed.