Substâncias fenólicas de Helicteres eichleri K. SCHUM (Malvaceae sensu lato) e avaliação microbiológica de suas quinonas

Abstract

Natural products have been used to cure and treat various diseases since prehistoric times. These compounds have high structural diversity and arouse the interest of many researchers in the search for new bioactive molecules. Currently, microbial resistance caused by the inappropriate use of antibiotics was considered by the World Health Organization (WHO) a threat to the health of society, with a growing demand for new bioactive molecules from plants against bacterial resistance. Given the wide range of plant chemical structures, chemotaxonomic and biological knowledge of the genus Helicteres, this study sought to identify phytochemical and microbial potentials against 4 pathogenic bacterial strains, of substances isolated from Helicteres eichleri K. Schum, endemic to Brazil and popularly known as ―monkey smoke‖, family Sterculiaceae (Malvaceae sensu lato). For the phytochemical study, the crude ethanol extract was subjected to liquid-liquid chromatography, using Hex.; CH2Cl2; AcOEt; n-BuOH, obtaining their respective phases, in addition to the hydroalcoholic phase. The dichloromethane phase (20g) and the ethyl acetate phase (8g) were subjected to column chromatography using flash silica and/or C-18 cartridge and Sephadex-LH 20 as stationary phases. The antimicrobial activity of two isolated compounds (He-1 and He-2) was investigated against Staphylococcus aureus, Staphylococcus epidermidis, Klebsiella pneumoniae and Salmonella enterica typhimurium, by disk diffusion assay and by means of microdilution by determining the Minimum Inhibitory (MIC). The chromatographic process led to the isolation of four chemical constituents, whose chemical structures were defined by interpretation of 1H and 13C and two-dimensional NMR spectra, and comparisons with models in the literature. The isolated substances were two O-naphthoquinones, He-1: 4-methoxy-3,6,9-trimethyl-2,3-dihydrobenzo[de]chromene-7,8-dione (mansonone M) and He-2: 4-Hydroxy-3,6,9-trimethyl-2,3-dihydro-benzo[de]chromene-7,8-dione (mansonone H), a sulfated flavonoid, He-4: 7,4'-di -O-methyl-8-O-sulfate-isoscutellarein and a glycosylated flavonoid, He-5: kaempferol-3-O-β-D-(6‖-Ep-coumaroyl) glycopyranoside (tylyroside). The antimicrobial evaluation performed with the two sesquiterpene quinones showed that He-1 and He-2 showed antimicrobial activity against Staphylococcus aureus and Staphylococcus epidermidis, and He-1 showed low activity against Salmonella enterica typhimuriu. The four substances were isolated for the first time in the species, thus strengthening the phytochemical profile of the genus Helicteres and the O-naphthoquinones proved to be promising in terms of their antimicrobial activity.