1. Department of Life Science Informatics, B-IT, LIMES Program Unit Chemical Biology and Medicinal Chemistry, Rheinische Friedrich-Wilhelms-Universität Bonn, Dahlmannstr. 2, D-53113 Bonn, Germany, and Fraunhofer Institute Intelligent Analysis and Information Systems IAIS, Schloss Birlinghoven, D-53754 Sankt Augustin, Germany