1. Chemistry Department, University of Coimbra, 3049 Coimbra, Portugal; Dipartamento di Chimica, Universita di Perugia, Perugia, Italy; Department of Medicinal Chemistry, University of Washington, Seattle, Washington; Instituto de Tecnologia Química e Biológica, Rua da Quinta Grande, 2780 Oeiras, Portugal; and Department of Chemistry, University of Arkansas, Fayetteville, Arkansas 72701