Diferenciação química e determinação das atividades antioxidantes de duas espécies botânicas semelhantes: Eugenia adenocalyx e Eugenia lisboae (Myrtaceae)

Abstract

The Eugenia genus belongs to the Myrtaceae family and comprises approximately 1038 species with wide distribution in the Amazônia biome. In the Adolpho Ducke Forest Reserve (RFAD), a representative sample of the Terra-Firme ecosystem of Amazônia located in the Amazonas State, it is possible to find species of this genus, such as Eugenia adenocalyx and Eugenia lisboae. The Eugenia presents a botanical complexity and morphological similarity. This work has aimed to characterize the chemical composition and evaluate the antioxidant activities of Eugenia adenocalyx and E. lisboae in order to discriminate the chemical composition and corroborate with morphological studies of these species. The extracts obtained from these two Eugenia were analyzed using spectrometric methods assisted by chemometric tools. This methodology has proved to be efficient in chemical differentiation of these species, since it directs to isolation of the substances responsible for the chemical differentiation. The use of chromatographic and spectrometric techniques has resulted in the isolation and identification of rotundioic acid (1), di-hydro-kaempferol (2) and of di-hydro-kaempferol-3-O-[-xylopyranosyl-(12)]--rhamnopyranoside (3) and from the ethanolic leaves extract of E. lisboae, besides five alkylresorcinols glycosides, 3-O-methyl-5-(1’-hydroxypentyl)-resorcinol-4-O--glucopyranoside (4), 3-O-methyl-5-(1’-hydroxypentyl)-resorcinol-4-O-’’-galloyl)-glucopyranoside (5), 3-O-methyl-5-(1’-hydroxypentyl)-resorcinol-4-O--’’, 6’’-di-galloyl)-glucopyranoside (6), 4-hydroxy-3-O-methyl-5-pentylresorcinol-1-O-[-xylopyranosyl-(16)]--glucopyranoside (7), 4-hydroxy-3-O-methyl-5-pentyl-resorcinol-1-O-[-xylopyranosyl-(16)]--(4’’-galloyl)-glucopyranoside (8) and from the ethanolic leaves extract of E. adenocalyx. Among eight substances described, (3-5) and (8) have not yet been described in the literature. The identification of these substances permitted to verify which chemical composition is related to each species. The statistical analysis of the results from DPPH and ABTS methods have demonstrated that the ethanolic extracts of E. adenocalyx (EF4-3, IC50 = 90.4 g.mL1, EC4-3, mEqT = 1,914.7 g.mL1) have showed the best antioxidant activities. Being this extract slightly rich in alkylresorcinols derivative in their composition. The alkylresorcinol (5) presents range of values of IC50 = 59.37 g.mL1 and mEqT = 1,879.0 g.mL1, and (8) indicates range of IC50 = 59.33 g.mL1 and mEqT = 1,802.3 g.mL1. Therefore, this chemical study has contributed with the chemical knowledge about the Eugenia genus, as well as corroborated with the taxonomic studies of both two similar Amazon species.