1. Research Group Bioorganic Chemistry Leibniz Institute for Plant Biochemistry Weinberg 3 06120 Halle (Saale) Germany
2. Present address: Molecular Design and Engineering Bayer AG Aprather Weg 18 A 42113 Wuppertal Germany
3. Institute of Chemistry Martin-Luther-University Halle-Wittenberg Weinbergweg 22 06120 Halle (Saale) Germany
4. Institute for Organic Chemistry University of Regensburg Universitätstr. 31 93053 Regensburg Germany