1. Corporate Research and Development ASTA Medica Group, Arzneimittelwerk Dresden GmbH, P.O. Box 010131, D-01445 Radebeul, Germany, Humboldt University Berlin, Department of Chemistry, Hessische Strasse 1-2, D-10115 Berlin, Germany, and University of Leipzig, Institute of Biochemistry, Faculty of Biological Sciences, Pharmacy and Psychology, Talstrasse 33, D-04103 Leipzig, Germany