1. Department Microbial Natural Products, Helmholtz Institute for Pharmaceutical Research Saarland (HIPS), Helmholtz Centre for Infection Research (HZI), Saarland University, Campus E8 1, 66123 Saarbrücken, 66123 Saarbrücken, Germany
2. German Center for Infection Research (DZIF), Partner Site Hannover-Braunschweig Inhoffenstraße 7, 38124 Braunschweig, Germany
3. Department of Organic Chemistry, University of Debrecen, P. O. Box 400, 4002 Debrecen, Hungary