1. Consiglio per la Ricerca e la Sperimentazione in Agricoltura (C.R.A.), Istituto Sperimentale per le Colture Industriali, Via di Corticella 133, I-40129 Bologna, Italy, Department of Pharmacology, Biochemical Toxicology Unit, University of Bologna, Via Irnerio 48, 40126 Bologna, Italy, and Department of Organic Chemistry “A. Mangini”, University of Bologna, Via San Giacomo 11, I-40126, Bologna, Italy