1. Current address: Bayer Pharma AG; Aprather Weg 18a 42096 Wuppertal Germany
2. University of Duisburg-Essen; Organic Chemistry; Universitätsstrasse 2-5 45144 Essen Germany
3. University of Duisburg-Essen; Structural and Medicinal Biochemistry; Universitätsstrasse 2-5, 45144 Essen Germany