[1] Med Univ Sofia, Dept Chem, Fac Pharm, 2 Dunav St, Sofia 1000, Bulgaria
[2] Bulgarian Acad Sci, Inst Microbiol, 26 Acad G Bonchev St, BU-1113 Sofia, Bulgaria
[3] Bulgarian Acad Sci, Ctr Phytochem, Inst Organ Chem, Lab Nucl Magnet Resonance, 9 Acad G Bonchev St, BU-1113 Sofia, Bulgaria
[4] Med Univ Sofia, Lab Expt Chemotherapy, Dept Pharmacol Pharmacotherapy & Toxicol, Fac Pharm, 2 Dunav St, Sofia 1000, Bulgaria
[5] Sapienza Univ, Dept Physiol & Pharmacol Vittorio Erspamer, Ple Aldo Moro 5, I-00185 Rome, Italy
[6] Univ Belgrade, Dept Toxicol, Fac Pharm, 450 Vojvode Stepe St, Belgrade 11221, Serbia
[7] Bulgarian Acad Sci, Inst Mineral & Crystallog, 107 Acad G Bonchev St, Sofia 1113, Bulgaria