Isolation of 5,7‑Dihydroxy, 6,8‑Dimethyl Flavanone from Syzygium aqueum with Its Antioxidant and Xanthine Oxidase Inhibitor Activities

Background: Syzygium aqueum Burm.f. Alston (water apple) belonging to Myrtaceae family was originated from tropical areas. It was traditionally used as a medicinal plant. Objective: The objective of the study was to isolate the active compound from the methanolic extract of S. aqueum leaves. Methods: Extraction was done using continuous extraction with methanol as a solvent. The extract was then fractionated using liquid–liquid extraction, vacuum liquid chromatography, and radial chromatography. Recrystallization was done for purification. The structure of the compound was determined by Ultraviolet‑Visible and (1D and 2D) nuclear magnetic resonance (NMR) spectrometer. Results: The isolate showed maximum wavelengths at 347 (band I) and 296 (band II) nm. After addition of NaOH and CH3COONa, the maximum wavelengths of band II moved to 340 and 339 nm, respectively. There was no change in wavelengths after addition CH3COONa/H3BO3 and AlCl3. The 1H‑NMR spectrum showed 16 protons, whereas 13C‑NMR spectrum showed 15 carbons. Based on those data, the isolate was determined as 5,7‑dihydroxy‑6,8‑dimethyl flavanone (demethoxymatteucinol). At a concentration of 100 and 50 µg/mL, it could inhibit 25.13% of xanthine oxidase (XO) activity and scavenge 11.87% of diphenyl‑picrylhydrazyl, respectively. Conclusion: Demethoxymatteucinol was isolated for the first time from S. aqueum and it had mild antioxidant and XO inhibitory activities.