A 'preformed chelate approach' model for coupling amine-modified rhenium and technetium '3+1' mixed ligand complexes to carboxylate residues - Crystal structure of ReO[CH3SCH2CH2N(CH2CH2S)(2)][p-SC6H4NH2] and ReO[CH3SCH2CH2N(CH2CH2S)(2)][p-SC6H4NHCOC6H5]

Selected '3+1' mixed ligand oxorhenium and oxotechnetium complexes containi ng the SNS/S donor atom set have been modified by introduction of a bifunct ional amine anchor on the p-position of the thiophenolato monodentate ligan d. A representative series of complexes containing several tridentate ligan ds was prepared both at macromolar (Re complexes) and nanomolar (Tc-99m com plexes) amounts. Coupling of these complexes to activated carboxylate group s was performed according to the 'preformed chelate approach' using benzoyl chloride as a model molecule. Coupling yields were high both at nanomolar and millimolar metal concentration, as revealed by high-performance liquid chromatographic analysis of Tc-99m and Re species adopting parallel radiome tric and photometric detection modes. All Re compounds have been characteri zed by classical analytical methods. In addition, the structures of represe ntative parent ReO[CH3SCH2CH2N(CH2CH2S)(2)][p-SC6H4NH2] and daughter ReO[CH 3SCH2CH2N(CH2CH2S)(2)][p-SC6H4NHCOC6H5] complexes were solved by X-ray crys tallography. Both compounds adopt a distorted trigonal bipyramidal geometry around rhenium, wherein the oxo group and the sulfur atoms of the SNS liga nd occupy the equatorial plane and the nitrogen atom and the sulfur of the monothiol are located at the apical positions trans to each other. (C) 1999 Elsevier Science ltd. All rights reserved.