| Summary: | To identify new potential anti-influenza compounds, we isolated six flavonoids, 2′-hydroxyl yokovanol (<b>1</b>), 2′-hydroxyl neophellamuretin (<b>2</b>), yokovanol (<b>3</b>), swertisin (<b>4</b>), spinosin (<b>5</b>), and 7-methyl-apigenin-6-C-β-glucopyranosyl 2″-<i>O</i>-β-<span style="font-variant: small-caps;">d</span>-xylopyranoside (<b>6</b>) from MeOH extractions of <i>Ohwia caudata</i>. We screened these compounds for antiviral activity using green fluorescent protein (GFP)-expressing H1N1 (A/PR/8/34) influenza A-infected RAW 264.7 cells. Compounds <b>1</b> and <b>3</b> exhibited significant inhibitory effects against influenza A viral infection in co-treatment conditions. In addition, compounds <b>1</b> and <b>3</b> reduced viral protein levels, including M1, M2, HA, and neuraminidase (NA), and suppressed neuraminidase (NA) activity in RAW 264.7 cells. These findings demonstrated that 2′-hydroxyl yokovanol and yokovanol, isolated from <i>O. caudate</i>, inhibit influenza A virus by suppressing NA activity. The moderate inhibitory activities of these flavonoids against influenza A virus suggest that they may be developed as novel anti-influenza drugs in the future.
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