1. Department of Chemical Sciences; University of Naples Federico II, Complesso Universitario di Monte Sant'Angelo; via Cinthia 21 80126 Naples Italy
2. EMBL, CS 90181; 71 AV des Martyrs 38009 Grenoble (38) France
3. Department of Chemistry and Biochemistry; University of Bern; Freiestrasse 3 3012 Bern Switzerland
4. Department of Organic Chemistry; Faculty of Chemistry; University of Łódź; Tamka 12 91-403 Poland