1. Contribution from the Institute of Organic Chemistry of the Polish Academy of Sciences, PL-01-224 Warszawa, Kasprzaka 44, Poland, Pharmaceutical Research Institute, PL-01-793 Warszawa, Rydygiera 8, Poland, Department of Chemistry, Ruhr-University Bochum, D-44780 Bochum, Universitätstrasse 150, and Department of Chemistry, University of Kaiserslautern, D-67663 Kaiserslautern, Erwin-Schrödinger-Strasse, Germany