1. Life & Medical Sciences Institute, Chemical Biology & Medicinal Chemistry Unit c/o Kekulé-Institut für Organische Chemie und Biochemie; University of Bonn; Gerhard-Domagk-Str. 1 53121 Bonn Germany
2. Institute for Physical and Theoretical Chemistry; University of Bonn; Wegelerstr. 12 53115 Bonn Germany
3. Max-Planck Fellow Group Chemical Biology, Center of Advanced European Studies and Research; Ludwig-Erhard-Allee 2 53175 Bonn Germany