1. Faculty of Food Technology and Biotechnology, University of Zagreb, Pierottijeva 6, 10000 Zagreb, Croatia
2. Institut für Pharmazie und Molekulare Biotechnologie, Universität Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany
3. New address: Department of Chemistry, Umiversity of Bochum, Universitätsstraße 150, 44801 Bochum, Germany, Fax: +49‐234‐14378