1. Institute of Medicinal and Pharmaceutical Chemistry; Technische Universität Braunschweig; Beethovenstrasse 55 38106 Braunschweig Germany
2. Department of Chemical Biology; Helmholtz Centre for Infection Research GmbH; Inhoffenstrasse 7 38124 Braunschweig Germany
3. Department of Paedriatric Oncology; Children's Hospital Cologne; Amsterdamer Strasse 59 50735 Cologne Germany