Organometallic radiopharmaceuticals: rhenium(I) carbonyl complexes of natural bile acids and derivatives

The precursor [Re(CO)(3)(PPh3)(2)Cl] reacts with natural bile acids to give new carboxylato-carbonyl(phosphine) rhenium(I) complexes [Re(CO)(2)(PPh3)( 2)(L)] (HL = natural bile acids). Coupling reactions between the carboxylic group of bile acids with the NH2 moiety of 2-aminothiazole, 2-(2-aminoethy l)pyridine and hydrazine form derivatives which coordinate the metal ion th rough the deprotonated amidic group. For a comparison, the carboxylato-rhen ium(I) complex [NEt4][Re(CO)(3)Cl(Ll)] (HLl = 3 alpha,7 alpha,12 alpha-trih ydroxy-5 beta-cholic acid) was synthesized starting from the [Re(CO)(3)Cl-3 ](2-) precursor. The complex [Tc(CO)(3)(PPh3)(2)Cl] reacts with HLl to form the corresponding carboxylato-carbonyl compound [Tc(CO)(2)(PPh3)(2)(LI)]. No difference in reactivity is observed with respect to the reactions carri ed out with the Re(I) starting materials. The complexes were characterized by elemental analyses, IR and NMR spectral and a few also by mass spectrome try. An octahedral geometry may be assigned to these complexes. The two pho sphine ligands are located in the axial position, and the two cis-CO groups having in trans the chelating ligand define the equatorial plane. (C) 1999 Elsevier Science S.A. All rights reserved.