* Corresponding authors

^a Drug Research Program, Division of Pharmaceutical Chemistry and Technology, Faculty of Pharmacy, University of Helsinki, P. O. Box 56 (Viikinkaari 5 E), Finland

^b Bioorganic & Biophysical Chemistry Laboratory, Linnaeus University Centre for Biomaterials Chemistry, Linnaeus University, SE-39182 Kalmar, Sweden
E-mail: ian.nicholls@lnu.se

^c Department of Chemistry, Faculty of Science, University of Helsinki, P. O. Box 55 (A. I. Virtasen aukio 1), Finland