The preparation and characterization of trans-platinum(IV) complexes with unusually high cytotoxicity

The physical and biological properties have been determined for three Pt(IV) complexes with trans amine ligands: trans,trans,trans-PtCl(2)(OH)(2)(dimethylamine)(isopropylamine)] (1(IV)), trans,trans,trans-PtCl(2)(OH)(2)(dimethylamine)(methylamine)] (2(IV)) and trans,trans,trans-PtCl(2)(OH)(2)(isopropylamine)(methylamine)] (3(IV)). The crystal structures of 2(IV) and 3(IV) reveal substantial strain resulting from repulsion between the amine ligands and the chlorido and hydroxido ligands. All three complexes have reduction potentials in the range -666 to -770 mV, values usually associated with high resistance to reduction and low cytotoxicity. However, the complexes all demonstrate surprisingly high cytotoxicity with values and trends that closely follow those seen for the Pt(II) congeners of these complexes. These results are consistent with more rapid reduction of the Pt(IV) complexes than would be expected based on the reduction potentials, perhaps associated with the trans arrangement of the chlorido ligands.