1. Department of Chemistry; Indiana University; Bloomington IN 47405 USA
2. Novo Nordisk Research Center Indianapolis; Indianapolis IN 46241 USA
3. Institute for Diabetes and Obesity, Helmholtz Diabetes Center; Helmholtz Zentrum München; 85764 Neuherberg Germany
4. Division of Metabolic Diseases, Department of Medicine; Technische Universität München; 80333 Munich Germany