1. Chemical Synthesis Laboratory, Swiss Federal Institute of Technology (EPFL), SB-ISIC-LSYNC, CH-1015 Lausanne, Switzerland, Laboratorium für Organische Chemie, Swiss Federal Institute of Technology (ETH), CH-8093 Zürich, Switzerland, and Actelion Pharmaceuticals, Gewerbestrasse 16, CH-4123 Allschwil, Switzerland