1. Department of Organic and Biomolecular Chemistry, University of Göttingen, Tammannstrasse 2, D-37077 Göttingen, Germany, Labor Grün-Wollny, Versaillerstrasse 1, D-35394 Giessen, Germany, and Oncotest GmbH, Am Flughafen 12-14, D-79108 Freiburg, Germany