1. Department of Organic and Molecular Inorganic Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, Netherlands Institute for Carbohydrate Research, Rouaanstraat 27, 9723 CC Groningen, The Netherlands, and Department of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands