1. Department of Chemistry, Organic Chemistry, Royal Institute of Technology, S-100 44 Stockholm, Sweden, Department of Medicinal Chemistry, Royal Danish School of Pharmacy, Universitetsparken 2, DK-2100 Copenhagen, Denmark, Department of Bioorganic Chemistry, Institute of Chemistry, Akadeemia tee 15, EE 0026 Tallinn, Estonia, and Department of Organic Chemistry, Technical University of Denmark, DK-2800, Lyngby, Denmark