1. Department of Organic Pharmaceutical Chemistry, Biomedical Centre, Uppsala University, Box 574, S-751 23 Uppsala, Sweden, Medicinal and Computational Chemistry Section, Karo Bio AB, Novum, S-141 57 Huddinge, Sweden, Department of Medicinal Chemistry, Preclinical R&D, Astra Arcus AB, S-151 85 Södertälje, Sweden, and Chemistry Department, Emory University, 1515 Pierce Drive, Atlanta, Georgia 30322