1. DISCAFF, Università del Piemonte Orientale, Viale Ferrucci 33, 28100 Novara, Italy, Department of Organic and Bioorganic Chemistry, Lund University, P.O.B. 124, 221 00 Lund, Sweden, Dipartimento di Scienze Botaniche, Universitá degli Studi di Cagliari, Viale San Ignazio 13, 09123 Cagliari, Italy, and Centre for Pharmacognosy and Phytotherapy, The School of Pharmacy, University of London, London, WC1N 1AX England