1. Pharmaceutical and Medicinal Chemistry, Saarland University, P.O. Box 151150, D-66041 Saarbrücken, Germany, Max Planck Institute for Informatics, Stuhlsatzenhausweg 85, D-66123 Saarbrücken, Germany, Department of Pharmaceutical Sciences, University of Bologna, Via Belmeloro 6, I-40126 Bologna, Italy