Isolation and Identification of Constituents Exhibiting Antioxidant, Antibacterial, and Antihyperuricemia Activities in Piper methysticum Root.

The aqueous extract of kava ( Piper methysticum ) root is known as a traditional beverage for daily intake in the Western Pacific Islands, such as Fiji, Tonga, and Vanuatu, to induce relaxation and health-beneficial effects. In this study, the antioxidant, anti-hyperuricemia, and antibacterial properties of kava root were investigated through the isolation and purification of bioactive compounds in ten fractions separated by column chromatography (CC). They included six flavonoids, 5-hydroxy-4',7-dimethoxyflavanone ( C1 ), matteucinol ( C2 ), isosakuranetin ( C3 ), 5,7- dimethoxyflavanone ( C4 ), 2',4'-dihydroxy-6'-methoxydihydrochalcone (in MC5 ) and alpinetin ( C10 ), and seven kavalactones, 5,6-dehydrokawain (DK) (in MC5 and C6 ), kavain (in MC7 ), yangonin (in MC7 and C8 ), dihydro-5,6-dehydrokavain (DDK) (in MC9 ), 7,8-dihydromethysticin (in MC9 ), dihydromethysticin (in MC9 ), methysticin (in MC9 ). The chemical structures of the compounds were illustrated by the analyses of gas chromatography-mass spectrometry (GC-MS), electrospray ionization-mass spectrometry (ESI-MS), nuclear magnetic resonance ( 1 H and 13 C-NMR), and X-ray diffraction. The evaluation of the free radical scavenging activity of the isolated substances via the DPPH and ABTS assays revealed that C3 (IC 50 : ABTS = 76.5; DPPH = 74.8 µg/mL) possessed the strongest antioxidant property. In terms of anti-hyperuricemia activity evaluated via the xanthine oxidase inhibitory in vitro assay, the compound C10 was the most promising inhibitor, revealing an IC 50 of 134.52 µg/mL. The two kavalactone mixtures in MC5 and a pure compound C6 inhibited the growth of bacteria Listeria monocytogenes , while MC7 can constrain the development of Klebsiella pneumoniae. This is the first study to isolate, purify, and identify the flavonoids isosakuranetin, 2',4'-dihydroxy-6'-methoxydihydrochalcone and alpinetin in kava root and report their pharmaceutical potential. The identified bioactive compounds showed potent antioxidant, anti-hyperuricemia, and antibacterial activity and thus can enhance the value of beverages and foods derived from kava root.