1. Medical Department, Pharmachemie BV, PO Box 552, Haarlem NL-003 RN, The Netherlands
2. Free University of Brussels VUB, Pleinlaan 2, Department of General and Organic Chemistry, Faculty of Engineering, Brussels B-1050, Belgium
3. Free University of Brussels VUB, Pleinlaan 2, High Resolution NMR Centre HNMR, Brussels B-1050, Belgium
4. Laboratory for Tumor Biology and Pharmacology, Academic Hospital Rotterdam, PO Box 2040, Rotterdam NL-3000 CA, The Netherlands