1. Pharmaceutical Institute Pharmaceutical & Medicinal Chemistry University of Bonn An der Immenburg 4 53121 Bonn Germany), E-mails
2. Present address: Pharmaceutical Institute Pharmaceutical Chemistry Eberhard-Karls-University Tübingen Auf der Morgenstelle 8 72076 Tübingen Germany
3. Institute for Virology and Immunobiology Julius-Maximilians-University Würzburg Versbacher Strasse 7 97078 Würzburg Germany