1. Faculty of Biology, University of Freiburg, Schänzlestrasse 1, 79104 Freiburg, Germany
2. Kekulé-Institute of Organic Chemistry and Biochemistry, University of Bonn, Gerhard-Domagk-Strasse 1, 53121 Bonn, Germany
3. Institute of Organic Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany