1. a Laboratory of BioCatalysis , Institute of Organic Chemistry, Bulgarian Academy of Sciences , 1113, Sofia, Bulgaria
2. d Department of Chemistry , The University of Sheffield , Dainton Building, Brook Hill, Sheffield, S3 7HF, UK E-mail:
3. b Laboratory of Nuclear Magnetic Resonance , Institute of Organic Chemistry, Bulgarian Academy of Sciences , 1113, Sofia, Bulgaria
4. c Laboratory of Physical Organic Chemistry , Institute of Organic Chemistry, Bulgarian Academy of Sciences , 1113, Sofia, Bulgaria