The Synthesis Of A Bis(Thiosemicarbazone) Macrocyclic Ligand And The Mn(Ii), Co(Ii), Zn(Ii) And Ga-68(Iii) Complexes

A 1,4,7,10-tetraazacyclododecane (cyclen) variant bearing two thiosemicarbazone pendant groups has been prepared. The ligand forms complexes with Mn2+, Co2+ and Zn2+. X-ray crystallography of the Mn2+, Co2+ and Zn2+ complexes showed that the ligand provides a six-coordinate environment for the metal ions. The Mn2+ and Zn2+ complexes exist in the solid state as racemic mixtures of the Delta(delta,delta,delta,delta)/?(lambda,lambda,lambda,lambda) and Delta(lambda,lambda,lambda,lambda)/?(delta,delta,delta,delta) diastereomers, and the Co2+ complex exists as the Delta(delta,delta,delta,delta)/?(lambda,lambda,lambda,lambda) and Delta(lambda,lambda,lambda,delta)/?(delta,delta,delta,lambda) diastereomers. Density functional theory calculations indicated that the relative energies of the diastereomers are within 10 kJ mol(-1). Magnetic susceptibility of the complexes indicated that both the Mn2+ and Co2+ ions are high spin. The ligand was radiolabelled with gallium-68, in the interest of developing new positron emission tomography imaging agents, which produced a single species in high radiochemical purity (>95%) at 90 degrees C for 10 min.