1. Laboratory for Chemometrics and Cheminformatics, Chemistry Department, University of Perugia, Via Elce di Sotto, 10, I-06123 Perugia, Italy, Molecular Discovery Ltd., 215 Marsh Road, HA5 5NE, Pinner, Middlesex, UK, and Department of Laser Medicine, Molecular Drug Research Group, Heinrich-Heine-Universität, Universitätsstr.1, D-40 225 Düsseldorf, Germany