Novel Phloroglucinol Derivatives as Neuraminidase Inhibitors Identified From Humulus lupulus L. Extract by At-Line Nanofractionation Platform

Neuraminidase inhibitors (NAIs) are a crucial therapy for combatting the influenza virus. This study employed an at-line nanofractionation technique to precisely localized potential NAIs in the extract of Humulus lupulus L. Twelve potential compounds, mainly phloroglucinol derivatives, were screened and identified. Seven of these compounds were subsequently isolated, purified, and structurally elucidated by NMR. Among them, Compound 5 showed remarkable inhibitory activity against both neuraminidase (NA, IC 50 = 0.8 µM) and the H3N2 influenza virus (EC 50 = 3.8 µM), confirming its potential as a lead compound for anti-influenza development. Compounds 4 and 8 , identified as hitherto uncharacterized phloroglucinol derivatives, also demonstrated significant inhibition against NA and the H3N2 influenza virus. Molecular docking revealed that Compounds 4 and 5 exhibited superior binding affinities compared to oseltamivir, with 4 forming critical hydrogen bonds with acidic residues (Glu119, Glu227, and Asp151) in the “150-cavity,” which significantly enhances its inhibitory potency against NAs.