The exocyclic functionalisation of bis(thiosemicarbazonate) complexes of zinc and copper: the synthesis of monomeric and dimeric species

This paper reports the synthesis of bimetallic zinc thiosemicarbazone complexes with rigid aromatic linkers, using either 1,3- or 1,4- benzenediamines or 1,3- or 1,4- benzenedialdehydes as the basis of the linking groups. Non-rigid aliphatic diamines and dialdehydes were also used to link the zinc chelating units. Reaction of a bis(thiosemicarbazone) with a pendant NHNH₂ group with monoaldehydes or ketones gives a range of monomeric complexes with exocylic imine groups bearing a range of substituents. The zinc complexes can be quantitatively and rapidly transmetallated to the corresponding copper complexes and this route or direct reaction with the free ligand can be used to radiolabel the monomeric species with ⁶⁴Cu. In vivo and in vitro studies of one of the ⁶⁴Cu imine complexes shows substantial hypoxic selectivity and high tumour uptake in a murine model.