Inhibitory Potential of Quercetin Derivatives Isolated from the Aerial Parts of Siegesbeckia pubescens Makino against Bacterial Neuraminidase

This study aimed to isolate bacterial neuraminidase (BNA) inhibitory O-methylated quercetin derivatives from the aerial parts of S. pubescens. All isolated compounds were identified as (1–4), which exhibited be noncompetitive inhibitors against BNA, with IC50 ranging 14.0 84.1 μM. The responsible (1–4) showed a significant correlation between BNA effects and number O-methyl groups on quercetin; mono (1, = μM) > di (2 3, 24.3 25.8 tri (4, μM). In addition, binding affinities also examined by fluorescence quenching effect related constants (KSV, KA, n). most active inhibitor 1 possessed KSV 0.0252 × 105 L mol−1. Furthermore, relative distribution quercetins in pubescens extract was evaluated using LC-Q-TOF/MS analysis.