1. Department of Organic Chemistry Arrhenius Laboratory Stockholm University 106 91 Stockholm Sweden
2. Present address: Department of Drug Design and Pharmacology University of Copenhagen Universitetsparken 2 2100 Copenhagen Denmark
3. The Skaggs Institute for Chemical Biology and Department of Chemistry The Scripps Research Institute 10550 North Torrey Pines Road La Jolla California 92037 USA
4. Center for Supramolecular Chemistry and Catalysis Shanghai University Shanghai 200444 P.R. China