1. Pharmaceutical Institute, Pharmaceutical Chemistry I University of Bonn An der Immenburg 4 53121 Bonn Germany
2. Clinical Pharmacology Program National Cancer Institute, NIH Bethesda MD 20892 USA
3. Molecular Pharmacology Section National Cancer Institute, NIH Bethesda MD 20892 USA
4. Institute of Inorganic Chemistry University of Bonn Gerhard-Domagk-Str. 1 53121 Bonn Germany