1. Institute for Molecular Biosciences, Goethe-University Frankfurt , Max-von-Laue-Strasse 9 , 60438 Frankfurt/M. , Germany
2. Center for Biomolecular Magnetic Resonance (BMRZ), Goethe-University Frankfurt , Max-von-Laue-Strasse 7 , 60438 Frankfurt/M. , Germany
3. Institute for Organic Chemistry and Chemical Biology, Goethe-University Frankfurt , Max-von-Laue-Strasse 7 , 60438 Frankfurt/M. , Germany
4. Department of Chemistry, Duke University , Durham , NC 27708, USA
5. Philipps-University Marburg, Department of Pharmacy, Institute of Pharmaceutical Chemistry , Marbacher Weg 6 , 35037 Marburg , Germany