Dendranthema zawadskii is a one of the popular plants as native in South Korea. In this study, linarin was isolated and purified using silica-gel, Diaion, and Sephadex LH-20 from the aerial parts of D. zawadskii. The chemical structure was completely identified through spectroscopic data including 1D, 2D nucleic magnetic resonance, and HRFABMS. Furthermore, linarin inhibited the bacterial neuraminidase (BNA) activity with 13.5 μM of IC 50 dose-dependently. Through the enzyme kinetic experiments, linarin as BNA inhibitor exhibited a typical noncompetitive inhibition mode which K m was contestant and V max decreased as the concentration of the inhibitor increased. It was further identified that the inhibition constant was 16.0 μM. Linarin was the most abundance metabolite in the aerial part of D. zawadskii extract by UHPLC-TOF/MS analysis. Therefore, D. zawadskii and its main component are expected that it can be effectively used for the infection and inflammation caused by bacteria.

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