1. Institute for Organic Chemistry; Saarland University; P.O. Box 151150 66123 Saarbrücken Germany
2. Department Microbial Natural Products; Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS); Helmholtz Centre for Infection Research (HZI); German Center for Infection Research (DZIF, Partner Site Hannover-Braunschweig) and Department of Pharmacy; Saarland University; Campus E8.1 66123 Saarbrücken Germany