1. Department of Biochemistry, Center for Biomedical Mass Spectrometry, Boston University School of Medicine, Boston, MA 02118, USA
2. Complex Carbohydrate Research Center, University of Georgia, Athens, GE 30602, USA
3. Department of Chemistry, University of Georgia, Athens, GE 30602, USA
4. Department of Chemical Biology and Drug Discovery, Utrecht Institute for Pharmaceutical Sciences and Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht 3584, The Netherlands