1. PharmaCenter Bonn, Pharmaceutical Chemistry I, University of Bonn, An der Immenburg 4, 53121 Bonn, Germany, Department of Pharmacy, University of Düsseldorf, Universitätsstrasse 1, 40225 Düsseldorf, Germany, Institute for Pharmaceutical Biology, University of Bonn, Nussallee 6, 53115 Bonn, Germany, Department of Pharmacology, University of Bonn, Reuterstrasse 2b, 53113 Bonn, Germany, and Department of Pharmacology, The University of North Carolina at Chapel Hill, North Carolina 27599-7365