1. a Acad. R. Tsanev Institute of Molecular Biology, Bulgarian Academy of Sciences , Acad. G. Bonchev Street, Block 21, 1113 Sofia , Bulgaria
2. b Department of Chemistry, Faculty of Sciences , Aristotle University of Thessaloniki , P.O. Box 135, 54124 Thessaloniki , Greece
3. c Faculty of Chemistry , Adam Mickiewicz University , ul. Grunwaldzka 6, 60780 Poznań , Poland
4. d Institute of Organic Chemistry with Center of Phytochemistry, Bulgarian Academy of Sciences , Acad. G. Bonchev Street, Block 9, 1113 Sofia , Bulgaria