1. Departments of Medicinal Chemistry and Molecular Virology and Host Defense, SmithKline Beecham Pharmaceuticals, King of Prussia, Pennsylvania 19406, Nycomed Pharma As, Gaustadalléene 21, Oslo, Norway, and Hafslund Nycomed Pharma, St. Peter-Strasse 25, P.O. Box 120, A-4021 Linz, Austria