1. Department of Organic Chemistry, University of Chemical Technology and Metallurgy, 8 St. Kliment Ohridski blvd, 1756 Sofia, Bulgaria
2. Institute of Organic Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences, Acad. G. Bonchev avenue, bldg. 9, 1113 Sofia, Bulgaria
3. Faculty of Chemistry, Brno University of Technology, Materials Research Centre, Purkyňova 464/118, 612 00 Brno, Czech Republic
4. Department of Pharmaceutical Chemistry, Tokyo University of Pharmacy and Life Sciences, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan