1. Chemistry Department, Lomonosov Moscow State University, Vorobiovy Gory, 119899 Moscow, Russia, Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Strasse 10, 13125 Berlin, Germany, and Institute of Organic Chemistry and Organic and Macromolecular Chemistry, Johannes-Gutenberg-University Mainz, Duesbergweg 10-14, D-55128 Mainz, Germany