1. Vrije Universiteit Brussel, High Resolution NMR Centre
(HNMR), Department of Materials and Chemistry (MACH), Pleinlaan 2,
B-1050 Brussels, Belgium, and NMR Laboratory, Institute of Organic
Chemistry with Centre of Phytochemistry, Bulgarian Academy of Sciences,
Acad. G. Bontchev Str., Bl.9, 1113 Sofia, Bulgaria