Estudo químico biomonitorado de extratos das folhas e do caule de Guettarda grazielae M.R.V. Barbosa (Rubiaceae)

Abstract

This work describes the isolation of some chemical constituents from the extracts of leaves and stems of Guettarda grazielae M.R.V. Barbosa, guided by larvicidal, anticholinesterase and antioxidant activities. Furthermore, a review of the biological activities of extracts and substances described in species this genus, and a compilation of triterpenes reported in the Rubiaceae species was also made. The leaves and stems, after drying and grounded, were extracted by maceration with acetone and/or ethanol. The extracts were submitted to a liquid partition between MeOH-H2O 3:2 and solvents of different polarity (hexane, chloroform and ethyl acetate). The crude extracts, as well as the fractions from this procedure, were evaluated for their potential larvicidal (larvae of the 4th stage of Aedes aegypti), antioxidant (total phenols content and DPPH) and anticholinesterase. The hexane and EtOAc fractions from ethanol extract of the leaves and stem, respectively, were the most promising in larvicidal assays, LC50 131.73 ppm and LC50 58.18 ppm. In comparison with caffeine (standard), the crude acetone extract from the leaves, as well as some of its sub-fractions from filtering into the silica gel of the fractions in hexane and chloroform, were qualitatively effective in inhibiting the action of the enzyme acetylcholinesterase. On the other hand, in the antioxidants tests, MeOH-H2O from stem (347.75 ± 0.02 GAE/g) and EtOAc fractions from the leaves (298.03 ± 0002 GAE/g) exhibit higher phenolic content. Of these, only the EtOAc fraction showed moderately active (IC50 164.85 ± 2.76 μg/mL) against DPPH. The other fractions showed weak activity or were inactive. Some of the fractions from leaves and stems that were considered promising in these assays were investigated and led to the isolation and identification structural (NMR, including DEPT) of a phytosteroid (Sitostenone) and five triterpenes (Cicloartenone, 3β,19α,23- trihydroxy-urs-12-ene, 3β,6β,19α,23-tetrahydroxy-urs-12-en-28-oic acid, 3-O-β-Dglucopyranosylquinovic acid and ursolic acid), that in general will help to expand the chemical profile of the genus Guettarda as well as of the family Rubiaceae. The review of the triterpenes that occurs in the family Rubiaceae revealed that among all species investigated, it was isolated a total of 373 triterpenes with 12 different types of skeletons and being oleanane and ursane the most representatives. Regarding the genus Guettarda, the literature records the occurrence of 44 different compounds distributed in ten species, which alkaloids and triterpenes are the most abundant compounds.