1. Centre
of Biomolecular Drug Research and Institute of Organic Chemistry, Leibniz Universität Hannover, Schneiderberg 38, D-30167 Hannover, Germany
2. European Molecular Biology Laboratory, Meyerhofstr. 1, 69117 Heidelberg, Germany
3. Group
of Structural Chemistry, Helmholtz Centre for Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany