1. Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden
2. School of Chemistry and Chemical Biology, UCD, Dublin 4, Ireland
3. Medivir AB, P.O. Box 1086, SE-141 22 Huddinge, Sweden
4. Department of Medicinal Chemistry, BMC, Uppsala University, Box 574, SE-751 23 Uppsala, Sweden