Cobalt(III)-py₂en systems as potential carriers of β-ketoester-based ligands

Two cobalt(III) complexes containing different β-ketoesters, namely [Co^III(L1)(py₂en)](ClO₄)₂·H₂O (1) and [Co^III(L2)(py₂en)](ClO₄)₂ (2) (py₂en = N,N'-bis(pyridin-2-ylmethyl)ethylenediamine; L1^- = methylacetoacetate; L2^- = ethyl 4-chloroacetoacetate) have been prepared and investigated as prototypes of bioreductive prodrugs. The presence of β-ketoester and py₂en ligands in 1 and 2, as well as the perchlorate counterions, was supported by IR spectroscopy and CHN elemental analysis. The composition molecular structure of both complexes was confirmed by NMR spectroscopy and ESI mass spectrometry. Structural information was also obtained for 2via X-ray diffraction analysis. The redox properties indicate that 1 and 2 are suitable for reduction under biological conditions. Investigation of DNA-interacting suggest that 1 and 2 bind DNA via electrostatic forces. Both complexes may be employed as possible platforms for the delivery of biologically active compounds, since their reaction with ascorbic acid in PBS at pH 6.2 and 7.4 at 37°C results in the release of the β-ketoester ligands upon Co(III)/Co(II) reduction.