Estudo fitoquímico da espécie Pavonia malacophylla (Link & Otto) Garcke (Malvaceae sensu lato) e avaliação microbiológica dos seus compostos fenólicos

Abstract

Medicinal plants act as alternative sources or complements in allopathic drug therapy. The family Malvaceae sensu lato stands out for presenting numerous compounds described in the literature with pharmacological properties acting as anticancer, anti-inflammatory, antioxidant, antimicrobial and antiviral. Pavonia malacophylla is popularly known as ‘malva-rosa’, distributed over much of the Brazilian territory. This research aimed to isolate phytoconstituents from P. malacophylla and evaluate the antimicrobial potential of their phenolic compounds against the bacterial strains Staphylococcus aureus MRSA, Staphylococcus epidermidis, Salmonella enterica Typhimurium and Klebsiella pneumoniae. The phytochemical study was carried out with aerial parts of P. malacophylla that were dehydrated, crushed and subjected to maceration with 95% EtOH. The Crude Ethanol Extract (CEE) by rapid filtration using silica gel as stationary phase and hexane, ethyl acetate and methanol as pure mobile phases or in binary mixtures, provided the AcOEt:MeOH fraction (1:1) which was subjected to chromatography using as stationary phase Amberlite XAD-2 and mobile phases water, methanol, hexane, acetone and ethyl acetate. The 100% MeOH fraction was subjected to successive chromatographic columns using Sephadex LH-20 as stationary phase and MeOH and MeOH:CHCl3 as eluents in proportions (7:3) and (1:1). Fractions were compared by TLC and pooled according to elution profile similarity. From these processes, substances coded as Pm-1 (15.0 mg), Pm-2 (3.0 mg), Pm-3 (20.0 mg), Pm-6 (18.0 mg) and Pm-7 (10.0 mg). Subsequently, a liquid-liquid chromatography was performed with CEE using hexane, chloroform and ethyl acetate as mobile phases, obtaining their respective phases, in addition to the hydroalcoholic phase. The chloroform phase was subjected to a chromatographic column using flash silica as stationary phase and hexane, ethyl acetate and methanol as eluents, pure or in binary mixtures. Fractions were compared by TLC and pooled according to elution profile similarity. From this chromatographic process, substances coded as Pm-4 (10.0 mg) and Pm-5 (12.0 mg) were obtained. Seven substances were isolated and characterized by one and two-dimensional 1H and 13C NMR spectroscopy and through comparisons with literature data it was possible to identify them as sitosterol-3-O-β-D-glucopyranoside (Pm-1), 3,5,7,4'-tetrahydroxy flavone (kaempferol) (Pm-2), kaempferol-3-O-β-D-(6''-E-p-coumaroyl) glycoside (tiliroside) (Pm-3), decanol (Pm-4), 5,7-dihydroxy-3,8,4'-trimethoxy flavone (Pm-5), kaempferol-3-β-D-glucopyranoside (astragalin) (Pm-6) and methyl-4-hydroxy-cinnamate (Pm-7). The antimicrobial evaluation resulted in growth inhibition of S. aureus MRSA, S. epidermidis and S. enterica Typhimurium strains against Pm-5, Pm-6 and Pm-7 at a concentration ≥ 512 μg/mL. All compounds were isolated for the first time in the species, three of which were re-isolated (Pm-1, Pm-2 and Pm-3) and one isolated for the first time in the genus Pavonia (Pm-7), contributing to the chemotaxonomic knowledge and ethnopharmacological from the family Malvaceae sensu lato.