Inorganic Chemistry, Vol.53, No.1, 468-477, 2014
Triamidetriamine Bearing Macrobicyclic and Macrotricyclic Ligands: Potential Applications in the Development of Copper-64 Radiopharmaceuticals
A versatile and straightforward synthetic approach is described for the preparation of triamide bearing analogues of sarcophagine hexaazamacrobicyclic cage ligands without the need for a templating metal ion. Reaction of 1,1,1-tris(aminoethyl)ethane (tame) with 3 equiv of 2-chloroacetyl chloride, yields the tris(alpha-chloroamide) synthetic intermediate. 6, which when treated with either 1,1,1-tris(aminoethyl)ethane or 1,4,7-triazacyclononane furnished two novel triamidetriamine cryptand ligands (7 and 8 respectively). The Co(III) and Cu(II) complexes of cryptand 7 were prepared; however, cryptand 8 could not be metalated. The cryptands and the Co(III) complex 9 have been characterized by elemental analysis, H-1 and C-13 NMR spectroscopy, and X-ray crystallography. These studies confirm that the Co(III) complex 9 adopts an octahedral geometry. with three facial deprotonated amido-donors and three facial amine donor groups. The Cu(II) complex 10 was characterized by elemental analysis, single crystal X-ray crystallography, cyclic voltammetry, and UV-visible absorption Spectroscopy. In contrast to the Co(III) complex (9), the Cu(II) center adopts a square planar coordination geometry, with two amine and two deprotonated amido donor groups. Compound 10 exhibited a quasi-reversible, one-electron oxidation, which is assigned to the Cu2+/3+ redox couple. These cryptands represent interesting ligands for radiopharmaceutical applications, and 7 has been labeled with Cu-64 to give Cu-64-10. This complex showed good stability when subjected to L-cysteine challenge whereas low levels of decomplexation were evident in the presence of L-histidine.