1. Department of Life Science Informatics, B-IT, LIMES Program Unit Chemical Biology and Medicinal Chemistry, Rheinische Friedrich-Wilhelms-Universität, Dahlmannstrasse 2, D-53113 Bonn, Germany, and Department of Lead Discovery, Boehringer Ingelheim Pharma GmbH & Co. KG, D-88397 Biberach/Riss, Germany