Antioxidant compounds produced by Pseudocercospora sp. ESL 02, an endophytic fungus isolated from Elaeocarpus sylvestris

Objective: To isolate endophytic fungi from Elaeocarpus sylvestris (E. sylvestris) and to isolate antioxidant compounds from a potential source fungus. Methods: Endophytic fungi were isolated from fresh leaves and stems of E. sylvestris and identified based on DNA analysis. 1,1-Diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity was used to evaluate the antioxidant activity of the fungi. The po-tential antioxidant fungus was further studied to isolate antioxidant compounds. The isolated compounds were identified by melting point analysis, optical rotation, spectral analysis using a UV spectrophotometer, high resolution fast atom bombardment mass spectrometry, X-ray crystallography analysis, 1H nuclear magnetic resonance analysis and 13C nuclear magnetic resonance analysis. The isolated compounds were evaluated with DPPH radical scavenging, reducing power, and b-carotene bleaching assays. Results: Seven endophytic fungi were successfully isolated from E. sylvestris and identified as Pestalotiopsis sp. EST 01, Pestalotiopsis sp. EST 02, Diaporthales sp. EST 03, Meyerozyma sp. EST 04, Diaporthales sp. EST 05, Pestalotiopsis sp. ESL 01, and Pseudocercospora sp. ESL 02. Of the seven fungi, Pseudocercospora sp. ESL 02 had the highest antioxidant activity [IC50 = (30.54 ± 0.88) mg/mL]. From that fungus, two compounds identified as terreic acid (1) and 6-methylsalicylic acid (2) were isolated with an IC50 of DPPH radical scavenging activity of (0.22 ± 0.02) mmol/L and (3.87 ± 0.27) mmol/L, respectively. The compounds also had good activities from the reducing power and b-carotene bleaching assays. Conclusions: The Pseudocercospora sp. ESL 02 fungus isolated from E. sylvestris looks promising as a novel source of terreic acid.

Antioxidant and α-glucosidase inhibitor activities of natural compounds isolated from Quercus gilva Blume leaves

To isolate and investigate antioxidant and α-glucosidase inhibitor compounds in the leaves of Quercus gilva Blume (Q. gilva). Methods: Dry leaves of Q. gilva were extracted with methanol and the methanolic extract was further separated by silica gel column chromatography using several solvents with increasing polarity. The antioxidant activities of the isolated compounds were evaluated using various in vitro assays: 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity, hydrogen peroxide radical scavenging activity, β-carotene bleaching assay, and reducing power assay. The α-glucosidase inhibitory assay was conducted against α-glucosidase from Saccharomyces cerevisiae. Results: Three compounds were isolated and their structures were identified as catechin (1), epicatechin (2), and tiliroside (3) using an instrumental analysis. Compound 2 had higher antioxidant activity with inhibitory concentrations (IC50) of (22.55 ± 2.23) μmol/L than that of quercetin, which was used as the standard, with an IC50 of (28.08 ± 2.39) μmol/L, followed by compound 1 with IC50 of (40.86 ± 3.45) μmol/L. On the other hand, compound 3 had the lowest antioxidant activity with an IC50 of (160.24 ± 8.15) μmol/L. However, compound 3 had the highest α-glucosidase inhibitory activity with an IC50 of (28.36 ± 0.11) μmol/L, followed by compounds 1 and 2 with (168.60 ± 5.15) and (920.60 ± 10.10) μmol/L, respectively. Conclusions: The results obtained for the antioxidant activities and α-glucosidase inhibitory activities in a methanolic extract from the leaves of Q. gilva confirmed the potential of this plant as a source of natural antioxidants and antidiabetic medicine.