1. Department of Pharmacochemistry, Faculty of Exact Sciences, Leiden/Amsterdam Center for Drug Research (LACDR), Division of Medicinal Chemistry, Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands, Department of Medicinal Chemistry, Boehringer Ingelheim RCV GmbH & Co. KG, Dr. Boehringergasse 5-11, Vienna, Austria, and Department of Human Anatomy, Pharmacology and Forensic Medicine, Section of Pharmacology, University of Parma, Via Volturno 39, 43100 Parma, Italy