1. Department of Biochemistry; Academic Medical Center; University of Amsterdam; Meibergdreef 15 1105 AZ Amsterdam The Netherlands
2. Present address: Institute of Biochemistry; Christian-Albrechts-University of Kiel; Otto-Hahn-Platz 9 24098 Kiel Germany
3. Department of Bio-organic Synthesis; Leiden Institute of Chemistry; Leiden University; Einsteeinweg 55 2300 RA Leiden The Netherlands
4. Present address: Department of Chemistry; Simon Fraser University; 8888 University Drive Burnaby V5A 1S6 BC Canada
5. Department of Biochemistry; Leiden Institute of Chemistry; Leiden University; Einsteinweg 55 2300 RA Leiden The Netherlands
6. Institute of Organic and Analytical Chemistry; Université D'Orléans; Rue de Chartres B. P. 6759 45100 Orléans France
7. Department of Medicine; University of Cambridge; Addenbrooke's Hospital; Hills Road Cambridge CB2 2QQ UK