Estudo químico e isolamento de flavonoides Myrcia spp. ocorrentes em Amazônia de terra firme

Abstract

Myrtaceae constitutes one of the largest and most important Angiosperm families of the Brazil flora and is concentrated in a single tribe: Myrteae (three sub-tribes: Myrciinae, Eugeniinae, and Myrtinae). Species of this family have been distributed in almost all brazilian biomes. The Myrcia spp. constitutes one of the largest genus belonging to Myrtaceae in number species and chemical and biological studies. These chemical studies of Myrcia spp. have revealed the presence of terpenes, phenolics, and flavonoids, which are responsible for several chemical and biological activities. This dissertation describe the chemical study of Myrcia bracteata, M. citrifolia, and M. fenestrata collected in the Reserva Florestal Adopho Ducke, Manaus (AM), as well as evaluates the antioxidant and hypoglycemic potentials of the extracts, fractions, and isolated compounds. The HPLC fractionation of the stems and leaves ethyl acetate extract from Myrcia bracteata had resulted in the isolation of four glycosylated flavonoids. These were characterized, particularly by NMR and MS, as two dihydroflavones (naringenin-7-O-glucoside and eriodictyol-7-O-glucoside), one dihydroflavonol (astilbin) and one flavanol (quercitrin). The ANOVA of the results sequestering ability of free radical DPPH• has revealed that the non-aqueous extracts of three species of Myrcia (except the leaves aqueous extract of M. fenestrata) have the lowest values of CS50 (between 37-51%). Among these extracts, the leaves and stems ethanol extracts of M. bracteata have shown signs of the flavonoid hydrogens type in the 1H NMR spectra. The sequential aqueous extract of M. bracteata and naringenin-7-O-glucoside have exhibit inhibitory effects of a-glucosidase enzyme activity by Saccharomyces cerevisiae of 20.60 ± 0.08 and 23.27 ± 1.86%, respectively. The leaves aqueous direct extract from Myrcia fenestrata was the only sample that showed inhibitory response against the a-glucosidase enzyme of the intestine of rats, whose value is 55 ± 3%. Therefore, the species M. bracteata shows a source of the antioxidant and hypoglycemic flavonoids, among which three were not yet described on genus and family. Therefore, this work has contributed to the knowledge of the Chemistry of Natural Products from plants of the Amazônia bioma.