A new [2 + 1] mixed ligand concept based on [99(m)Tc(OH2)3(CO)3]+: a basic study

Abstract

Mixed ligand fac-tricarbonyl complexes of the general formula [M(L¹)(L²)(CO)₃] (M = Re, ^99(m)Tc, L¹ = imidazole, benzyl isocyanide, L² = 1H-imidazole-4-carboxylic acid, pyridine-2,4-dicarboxylic acid, pyridine-2,5-dicarboxylic acid) have been prepared starting from the precursors [M(OH₂)₃(CO)₃]⁺. The complexes can be obtained in good yield and purity in a two-step procedure by first attaching the bidentate ligand followed by addition of the monodentate. ^99mTc compounds can also be prepared at the tracer level in one-pot procedures with L¹ and L² being concomitantly present. This [2 + 1] approach allows the labeling of bioactive molecules containing a monodentate or a bidentate donor site. Examples given in here are N-(tert-butoxycarbonyl)glycyl-N-(3-(imidazol-1-yl)propyl)phenylalaninamide, 5-((3-(imidazol-1-yl)propyl)aminomethyl)-2′-deoxyuridine and 4-(5-isonitrilpentyl)-1-(2-methoxyphenyl)-piperazine as L¹ and N-((6-carboxypyridine-3-yl)methyl)glycylphenylalanine as L². The corresponding second ligand can be used to influence the physico-chemical properties of the conjugate. The crystal structures of [⁹⁹Tc(OH₂)(imc)(CO)₃], [Re(OH₂)(2,4-dipic)(CO)₃], [Re(bic)(2,4-dipic)(CO)₃] and [Re(im)(2,5-dipic)(CO)₃] are reported.