Estudo fitoquímico do resíduo madeireiro de Sextonia rubra (Lauraceae) e investigação do potencial antioxidante

Abstract

Sextonia rubra (Mez.) van der Werff (LAURACEAE), is the only representative its genus in Brazilian Amazon, known for Louro Gamela and exploited by the timber industry. The aim of this research was to study the chemical profile of S. rubra’s barks and antioxidant activity of extracts and isolated compounds. The barks were extracted with 70% of ethanol v/v. The extract obtained was partitioned by hexane, chloroform, ethyl acetate and butanol solvents, in this order. Afterwards, the crude extract and fractions were analyzed by phytochemical assays by tubes test and thin layer chromatography (TLC); certain levels of total phenols and antioxidant activity against DPPH• and ABTS•+ radicals The isolation of active compounds was made by high performance countercurrent chromatography (HPCCC), using the normal and reversal phases, step gradient with different proportions of hexane, ethyl acetate, methanol, n- butanol and water. LLG03 extract (ethyl acetate) (11,64 g) showed the highest amount of stains with antioxidant potential on CCDs developed with DPPH•, so it was chosen for fractionation. The chemical profile of the extracts indicated condensed tannins, phenolics, terpenes, saponins and alkaloids. The extracts showed the following efficient concentrations (EC50, µg/mL) to scavenging DPPH and ABTS free radicals: LLG (crude): 10,67 and 17,67; LLG03 (ethyl acetate): 19,27 and 8,99; LLG04 (n-butanol): 17,77 and 8,25 and LLG05 (hydroalcoholic residue): 18,37 and 8,00. The fractionation of LLG03 by CCC provid the substances: Epicatechin (SF13-26, 21,7 mg), Vanillic Acid (SF14-11, 10,0 mg, AVA), Protocatechuic Acid (SF14-16, 18,4 mg, APR), Proanthocyanidin A2 (SF14-24, 3,2 mg, POA A2), Rubrenolide (SF16-26, 22,8 mg) and Rubrinolide (SF16-28, 34,5 mg). EC50 values (µg/mL) against ABTS were: epicatechin (1,93); AVA (2,16); POA A2 (7,22); APR (9,96) and rubrenolide (18,46). The EC50 against DPPH radical were: epicatechin (13,91); AVA (39,27) and POA A2 (58,17). Among the activities observed, the antioxidant potential of epicatechin (more active) stands out: AVA, APR, POA A2 and the unprecedented antioxidant anticity of rubrinolide against ABTS. This research was unprecedented for S. rubra, presenting another option for using this residue, for the discovery of new natural products with biological potential.