Synthesis, structure, and antitumor properties of platinum(iv) complexes with aminonitroxyl radicals

The platinum(iv) complexes cis,trans,cis-PtIV(RNH2)(NH3)(OH)2Cl2, where R is 2,2,6,6-tetramethyl-1-oxyl-4-piperidinyl (1) or 2,2,5,5-tetramethyl-1-oxyl-3-pyrrolidinyl (2), were prepared by oxidation of the corresponding cis-PtII(RNH2)(NH3)Cl2 complexes with hydrogen peroxide. The reactions are catalyzed by tungstate salts, which makes it possible to carry out oxidation under mild conditions. The resulting complexes were characterized by elemental analysis, HPLC, and IR, UV, and ESR spectroscopy. The structure of complex 1 was established by X-ray diffraction analysis. Complex 1 exhibits the highest antitumor activity in an experimental tumor, viz., in P388 leukemia. The resistance of the tumor to this complex developed much slower than that to Cisplatin.