1. Institute of Organic Chemistry, Organic and Macromolecular Chemistry, Duesbergweg 10-14, Johannes Gutenberg-Universität Mainz, D-55099 Mainz, Germany, and Institute of Pharmacy, Department of Biopharmaceutics and Pharmaceutical Technology, Staudingerweg 5, Johannes Gutenberg-Universität Mainz, D-55099 Mainz, Germany