1. Institute of Organic Chemistry with Center of Phytochemistry, Bulgarian Academy of Sciences, G. Bonchev 9, Sofia 1113, Bulgaria
2. Institute of Microbiology, Bulgarian Academy of Sciences, G. Bonchev 26, Sofia 1113, Bulgaria
3. Interfacultary Institute of Biochemistry, University of Tübingen, Hoppe-Seyler-Straße 4, D-72076 Tübingen, Germany
4. Institute of Organic Chemistry with Center of Phytochemistry, Bulgarian Academy of Sciences, G. Bonchev 9, Sofi a 1113, Bulgaria