Isolation of jacaranone, a sedative constituent extracted from the flowers of the Mexican tree Ternstroemia pringlei

Ethnopharmacological relevanceTernstroemia pringlei represents one of the most widely employed and commercially exploited medicinal plant in Mexico, used popularly as a tranquilizer and for the treatment of insomnia.Aim of the studyTo investigate the sedative constituents of the plant through a bio-guided fractionation of extracts derived from calyx and fruits.Materials and methodsCrude extracts with different polarities (CHCl3, AcOEt, MeOH, aqueous) were prepared and subjected to chromatographic fractionation, leading to the isolation of the sedative compound (1) from the MeOH crude extract. The identity of 1 was unequivocally established by means of 1D and 2D NMR spectroscopic analysis. The sleeping time induced by sodium pentobarbital and the elevated plus-maze models were performed on mice to determine the sedative and anxiolytic activities, respectively. Bioactivity was also investigated though in vitro GABA release experiments using mice brain slices.ResultsThe sedative compound was established as jacaranone (1), and its effect was clearly demonstrated through a dose-dependent response analysis (ED50 = 25 mg/kg mouse weight). When tested in the elevated plus-maze model, none of the extracts from Ternstroemia pringlei displayed anxiolytic activity. GABA release experiments showed that the MeOH and aqueous crude extracts released this neurotransmitter at a ratio of 217 and 179 pmol/g protein, respectively, evidencing the presence of other bioactive constituents in the extracts apart of 1, whose activity was absent in this model.ConclusionsAlthough 1 has been isolated and identified in a number of plant species, this is the first time that its sedative effect has been demonstrated. No previous record exists of other sedative compounds having been isolated from Ternstroemia pringlei.