1. Departments of Medicinal Chemistry and Pharmacology, Istituto di Ricerche di Biologia Molecolare, P. Angeletti S.p.A. (IRBM-MRL Rome), Via Pontina Km 30,600, 00040 Pomezia, Italy
2. Department of Medicinal Chemistry, Merck Research Laboratories, Rahway, New Jersey 07065
3. Department of Antiviral Research, Merck Research Laboratories, West Point, Pennsylvania 19486