1. Dipartimento Farmaco-Chimico, University of Bari, via Orabona 4, I-70125 Bari, Italy, Dipartimento Farmaco-Chimico, University of Messina, viale Annunziata, 98168 Messina, Italy, and Pharmaceutical and Medicinal Chemistry Department, Saarland University, P.O. Box 15 11 50, D-66041 Saarbrücken, Germany