1. Department of Chemistry University of Fribourg Chemin du Musée 9 1700 Fribourg Switzerland
2. NuChem Sciences Inc. 2350 Rue Cohen, Suite 201 Saint-Laurent Quebec H4R 2N6 Canada
3. Present address: Valence Discovery Inc. 6666 Rue St-Urbain, Suite 200 Montreal Quebec H2S 3H1 Canada
4. Department of Chemistry and Applied Biosciences Swiss Federal Institute of Technology, ETH Zürich Vladimir-Prelog-Weg 8093 Zürich Switzerland