Tricarbonyltechnetium(i) and tricarbonylrhenium(i) complexes of amino acids: Crystal and molecular structure of a novel cyclic dimeric Re(CO) ₃-amino acid complex comprised of the OON donor atom set of the tridentate ligand

Radiolabeled complexes of monoamino polycarboxylic, polyamino monocarboxylic and thiol containing amino acid ligands were prepared from a fac-[^99mTc(CO)₃(H₂O)₃]⁺ precursor.The overall radiochemical yield was 94-98%. The complexes exhibited substantial in vitro and in vivo stability. The corresponding Re(i) complexes of the ligands DAPA, Asp and CysH were prepared and characterized by means of IR, NMR, and MS spectroscopic studies, as well as X-ray crystallography (for those containing d,l-DAPA and d,l-Asp). The rhenium complexes have been structurally correlated with the technetium complexes by means of HPLC studies. The reaction of Re(CO)₅Cl with d,l-Asp in presence of triethylamine led to the formation of a new class of cyclic dimeric complexes formed by the OON donor atom set of the tridentate ligands. The amino carboxylate ligand system formed well defined complexes with a fac-[M(CO)₃(H₂O) ₃]⁺ core and shows good promise in ^99mTc(CO) ₃ tracer development.