1. Katholieke Universiteit Leuven, Department of Chemistry, Biomolecular Architecture and BioMacS, Celestijnenlaan 200F, B-3001 Leuven, Belgium, and Katholieke Universiteit Leuven, Laboratory of Medicinal Chemistry, Rega Institute for Medical Research and BioMacS, Minderbroedersstraat 10, B-3000 Leuven, Belgium