1. Pharmaceutical Chemistry, Institute of Pharmacy, University of Leipzig, Brüderstrasse 34, D-04103 Leipzig, Germany, Institute of Pharmacy and Food Chemistry, Julius-Maximilians-Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany, Institute of Pharmacology and Toxicology, Julius-Maximilians-Universität Würzburg, Versbacher Strasse 9, D-97078 Würzburg, Germany, and Pharmaceutical Institute, University of Bonn, Kreuzbergweg 26, D-53115 Bonn, Germany