1. Welsh School of Pharmacy, Cardiff University, King Edward VII Avenue, Cardiff CF10 3XF, U.K., Medicinal Chemistry, Drug Metabolism and Pharmacokinetics, and Virology Departments, GlaxoSmithKline, Research Triangle Park, North Carolina, 27709, and Rega Institute for Medical Research, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium