## 3 Results
### Discovery of Bioactive Compounds from Xylaria sp. KET18  
A total of five organic compounds were purified from the KET18 extract through CC and HPLC analyses (Figure 4). Compound **1** was described as an oily, colorless substance. On the \({}^{1}\)H, \({}^{13}\)C NMR spectrum, signals of two carbonyl carbons appeared at 8C 181.6 and 174.5, two methylene groups at [8C 25.8 (C-3)/8H 2.52 and 2.39 (m), and 8C 30.3 (C-4)/8H 2.39 and 2.20 (m)], a nitrogen-bonded methine group at 8C 57.0 (C-2)/8H 4.33 (dd, \(J\) = 4.2, 9.0 Hz), and a methoxy group at 8C 52.9/8H 3.78 (s). Compound **2** was an oily, colorless substance with an aromatic ring added by two substituents in the para position. The structure was observed from signals at \(\updelta\)C 130.9 (C-2 and C-6)/8\({}_{\mathrm{H}}\) 7.05 (2H, d, \(J\) = 8.4 Hz, H-2 and H-6) va \(\updelta\)C 116.1 (C-3 and C-5)/8\({}_{\mathrm{H}}\) 6.72 (2H, d, \(J\) = 8.4 Hz, H-3 and H-5). In addition, the \({}^{1}\)H and \({}^{13}\)C NMR spectra also displayed an oxymethylene group at 8C 64.6 (C-8)/8H 3.70 (2H, t, \(J\) = 7.2 Hz) along with a methylene group at 8C 39.4 (C-7)/8H 2.73 (2H, t, \(J\) = 7.2 Hz). Compounds **3** and **4** were both detected as powdery white substances. The \({}^{1}\)H NMR spectrum of **3** indicated six double bonds with the appearance of 12 olefin protons and four double bonds in trans and two double bonds in cis configuration. In addition, the \({}^{1}\)H NMR spectrum also recorded signals of four oxymethine groups [8H 4.35 (m, H-7), 3.98 (m, H-8), 4.52 (m, H-15), 5.04 (m, H-23)] and a methyl group at 8H 1.28 (d, \(J\) = 6.6 Hz, H-24). On the \({}^{1}\)H NMR spectrum of **4**, signals of six double bonds were recorded, with the appearance of 10 olefin protons at 8H 5.60. Moreover, \({}^{13}\)C NMR and heteronuclear single quantum coherence (HSQC) spectra showed signals of 24 carbons, including two carbonyl carbons at 8C 166.3 (C-1) and 211.9 (C-15), five double bonds, three oxymethine groups, seven methylene groups, and one methyl group. These data supported the fact that both **3** and **4** had a macrolide frame. Compound **5** was described as a powdery yellow substance. The \({}^{1}\)H NMR spectrum displayed seven aromatic protons, including an A2B2 aromatic ring system at 8H 7.35 (2H, d, \(J\) = 8.4 Hz, H-2\({}^{\prime}\), H-6\({}^{\prime}\)) and 6.85 (2H, d, \(J\) = 8.4 Hz, H-3\({}^{\prime}\) and H-5\({}^{\prime}\)), an AX system at 8H 6.44 (1H, br d, \(J\) = 2.4 Hz, H-6) and 6.45 (1H, br d, \(J\) = 1.8 Hz, H-8), and a singlet proton at 8H 7.96 (1H, s, H-2). The \({}^{13}\)C NMR spectrum of **5** revealed signals of 15 carbon atoms, including a carbonyl group at 8C 177.8. The results from the \({}^{1}\)H and \({}^{13}\)C NMR spectrum confirmed that **5** was an isoflavenoid. Combining the analytical data with previous references, the five pure compounds were, respectively, identified as methyl pyroglutamate (**1**) [21], 2-(4-hydroxyphenyl)ethanol (**2**) [22], macrolactin A (**3**) [23], macrolactin F (**4**) [24], and prunetin (**5**) [25].  
Figure 3: Scavenging activity of the KET18 extract against hydroxyl (**a**) and DPPH (**b**) radicals with ascorbic acid as the positive control.