A proton nuclear magnetic resonance study of the interaction of zinc(II) with the antitumour drug streptonigrin

Abstract

The interaction of zinc(II) with the antitumour drug streptonigrin in [2H8]tetrahydrofuran has been studied by 400 MHz variable-temperature 1H NMR spectroscopy. At 190 K, and in the presence of an excess of zinc(II) trifluoromethanesulfonate (triflate) (10-15 equivalents), streptonigrin forms a 1:1 complex 1a (6%) and two diastereomeric 2:1 complexes, 1b (15%) and 1c (79%). The relative concentrations of these complexes are highly temperature dependent and at room temperature only 1a is detected. A fourth minor complex 1d was detected (< 5%) in the range 240-260 K. In CD3CN and less than 5 equivalents of zinc(II) triflate, 1a-1d are detected, but in the presence of 10-15 equivalents of zinc(II) triflate 1a is the predominant complex (> 93%) in the range 235-300 K. Implications for the role of metal ions in the mechanism of the antitumour action of streptonigrin are discussed. Show more