METHODS AND RESULTS

General All reagents were of analytical grade. For methylation reactions, an ethereal solution of diazomethane (30 ml) was prepared by dissolving 2.14 g of N-methyl-N-nitroso-p-toluenesulphonamide (Diazald; Aldrich, Steinheim, Germany) in 10.0 ml of ethanol containing 4.0% potassium hydroxide. 6) Hydrogenation reactions were carried out under an atmosphere of hydrogen in the presence of palladium (3.0 or 10.0%) on activated charcoal (Acros Organics, New Jersey, USA) as catalyst. 7) The acetylated chromene was prepared by treatment with acetic anhydride (20.0 ml) and pyridine (20.0 ml) overnight. 8) Benznidazole, employed as positive control in the assays of trypanocidal activity, was obtained from Roche (Rio de Janeiro, Brazil). Plant Material Specimens of P. gaudichaudianum and P. aduncum were cultivated from seed under greenhouse conditions at the Institute of Chemistry, UNESP, Araraquara-SP, Brazil. Plant material was authenticated by Dr. Guillermo E. D. Paredes (Universidad Pedro Ruiz Gallo, Lambayeque, Peru) and voucher specimens (with codes Kato 0093 and 0057, respectively) were deposited at the Herbarium of the