1. Department of Chemistry,
2. Department of Immunology,
3. Department of Molecular and Experimental Medicine and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
4. Laboratorium für organische Chemie, Eidgenössichsche Technische Hochschule (ETH) Hönggerberg HCl-H309, Universitaetstrasse 16 CH-8093 Zürich, Switzerland.