Investigação química de Eugenia luschnathiana: determinação da composição volátil, isolamento e identificação de triterpenos oleananos e ursanos

Abstract

The present work had as objective to carry out the chemical investigation and of Eugenia luschnathiana, species that presents few reports in the literature. Initially the ethanol extracts of the stem, leaves, fruits and flowers were prepared. Then the extracts of the leaves and stem were partitioned using organic solvents: hexane, chloroform or dichloromethane, ethyl acetate, leaving the hydroalcoholic residue. The extracts were submitted to evaluation of their activities of free radical DPPH capture and toxicity to the microcrustacean Artemia salina. These extracts, besides the fixed oil obtained from the leaves, were saponified and esterified to investigate their chemical composition. Furthermore, the isolation, obtaining and characterization of 3 derivatives of the mevalonate route were performed: β-sitosterol and a triterpene of oleanane skeleton, arjunolic acid. By acetylation reaction the derivative 2,3,3-triacetoxyolean-12-en-28-oic acid was obtained. Eight triterpenes were identified in binary mixtures with predominance of ursane and oleanane skeletons (Δ12-13): the oleanolic and ursolic acids, very common in the Myrtaceae’s family; α-amirine and 3β, 19α-dihydroxy-urs-12-ene, the latter unheard of in the family; cyclohexane-1,9-diol, uncommon in the family and in the genus, and 4,4,8-trimethyl-13-Oxatetracyclo [6.3.1.1 1.9.02.5] tridecane, which is the first record of its spectroscopic data, and unpublished in the genus Eugenia. In addition, also unpublished in the genus, 3-p-coumaroyl-tormentic acid. The essential oil of the leaves of E. luschnathiana was obtained by means of the hydrodistillation process, in collections made at three different times of the year, in which the plant was in different stages of maturation. The samples were denominated 1 (presence of fruits), 2 (young flowers and leaves) and 3 (neither flowers or fruits), respectively. The differences in chemical compositions and their impacts on activities already reported above were evaluated, as well as antibacterial. The GC-MS analysis of the essential oil allowed the identification of 39 molecules for the different oil samples, presenting a majority composition of oxygenated and non-oxygenated sesquiterpenes, emphasizing spathulenol and caryophyllene oxide as majores compounds. The residual solution of hydrodistillation was concentrated and called decoy and also underwent the mentioned activities. The evaluation of the capture capacity of the DPPH radical of the ethanol extracts of leaves and stem and of the fractions presented good results, of which we can highlight ethyl acetate phase and hydroalcoholic residue with concentrations of IC50=59.755±0.756 and 37.451±0.001 μg/mL, respectively. From the leaves we can indicate also ethyl acetate phase fraction and the decoy with values of IC50=56.913±0.164 and 66.114±0.052 μg/mL, respectively. On the other hand, the oil samples had a low percentage of capture capacity, around 17% in the highest concentrations The toxicity test showed that all fractions are non-toxic against A. salina. However, the three samples os essential oil were highly toxic at concentrations of 72.629±3.992, 14.241±0.937 and 9.588±0.615 μg/mL. Among the different oil samples that presented the most satisfactory results were 1, which showed values of Minimum Inhibitory Concentration (MIC) of 2,5 mg/mL for gram positive bacteria Staphylococcus aureus and Staphylococcus epidermidis, and values of 5 and 10 mg/mL for gram negative Pseudomonas aeruginosa and Escherichia coli, respectively. GC-MS analysis was also applied to the saponifiable and unsaponifiable fractions and several compounds were identified, proving the lipid richness present in this species.