Estudo químico, atividade antioxidante, atividade antimicrobiana e análise do óleo essencial da espécie kielmeyera coriacea mart. & zucc (pau-santo) do cerrado

Abstract

Kielmeyera coriacea Mart. & Zucc, known as pau-santo , belongs to the family Clusiaceae. This plant is rich in xanthones, substances that exhibit various pharmacological properties. The objective of this study was to analyze and quantify the chemical constituents of the aerial parts, evaluate the antimicrobial and antioxidant activity of extracts and partitions of Kielmeyera coriacea. The percentages obtained for the macromolecular constituents of barks and wood are within the acceptable range for hardwood trees. The Klason lignin content found, was 14.7, 57.3 and 28.0 % and holocellulose was 30.0, 5.5 and 71.7 % for inner bark, outer bark and wood, respectively. The essential oils from different parts of Kielmeyera coriacea was analyzed for the first time in this work. The main identified compounds in the essential oil of leaf were sesquiterpenes, 51.3% of the oil consists of D-germacrene, trans-caryophyllene and bicyclogermacrene. In the flower, eugenol represents about 44.0 % of the essential oil, being the major constituent. Compared with essential oils of Kielmeyera rugosa, there were differences in the concentration of the components found in leaves and flowers of both species. In the inner bark, the most components are sesquiterpenes and constituents in higher concentrations were alpha-copaene (14.9 %), alpha-trans-bergamotene (13.0 %) and beta-bisabolene (9.4 %). In the outer bark, alkanes and sesquiterpenes are present in higher concentration. In the oil of wood, palmitic acid is the major component (16.2 %) and the alkanes are present in high concentration, together represent 51.3 % of essential oil. This essential oil can be considered an alternative source for 2-ethylhexyl-3-(4-methoxyphenyl)-2-propenoate (known as Parsol MCX, found in formulations of sunscreens). The levels of total phenols determined by Folin-Ciocalteau method, were 309, 346 and 372 expressed in Galic acid equivalents (GAC) per gram of sample, for ethanol extracts of leaves and inner bark and methanol-water partition of the inner bark, respectively. The inner bark was the sample that showed the highest content of proanthocyanidins with values of 328, 253 and 410 in catechin equivalents per gram of sample, for the ethanol extract, dichloromethane and methanol-water partitions, respectively. The inner bark was also the sample that showed the greatest antioxidant activity, with EC50 values of 5.9, 6.6 and 4.3 ppm for ethanol extract, dichloromethane and methanol-water partitions, respectively. The fractions 4, 5 and 6 of methanol-water partition from the inner bark presented good antioxidant activity with EC50 values of 4.7, 4.8 and 4.3 ppm, respectively. The analysis of fractions 5 and 6, obtained from the fractionation column of dichloromethane partition of the inner bark, which had high EC50 values, by HPLC, showed the presence of a few compounds, not yet identified in this study. The analysis of IV in extracts and fractions showed that the main functional groups present in the extracts were hydroxyl, carbonyl, presence of alkanes and C-O bond. The infrared analysis not allowed identify differences in the structure of phenolic compounds and presented global functionality very similar. The results of MIC against oral microorganisms showed that, the inner bark was the sample with higher activity and cyclohexane partition was most active, inhibiting bacterial growth for three oral microorganisms (S. mutans, S. sanguinis, A. naeslundii) at a concentration of 6,2 μg mL-1.