1. Institute II of Pharmacology, Center of Pharmacology, Medical Faculty; University of Cologne; Gleueler Strasse 24 50931 Cologne Germany
2. Institute of Organic Chemistry, Department of Chemistry; University of Cologne; Greinstrasse 4 50939 Cologne Germany
3. Pharmaceutical Institute, Pharmaceutical Chemistry I; University of Bonn; An der Immenburg 4 53121 Bonn Germany