1. Institute for Research in Biomedicine, Barcelona Science Park, University of Barcelona, Josep Samitier 1-5, E-08028 Barcelona, Spain, Laboratory of Organic Chemistry, Faculty of Pharmacy, University of Barcelona, 08028-Barcelona, Spain, Department of Organic Chemistry, University Leipzig, Johannisallee 29, D-04103 Leipzig, Germany, and Department of Organic Chemistry, University of Barcelona, 08028-Barcelona, Spain