Bacterial neuraminidase inhibition by phenolic compounds from Usnea longissima

Abstract

Activity-guided phytochemical investigation of the methanol extract of Usnea longissima led to the isolation of nine (1-9) phenolic metabolites, including compounds 6 and 7, which were reported for the first time from this species. All isolated compounds were completely characterized through spectroscopic analysis, including 2D NMR and HREIMS data. Individually, the activity of each purified compound was assessed against bacterial neuraminidase (BNA), and most of them displayed dose-dependent inhibition. Among the purified compounds, compounds 2 and 3 exhibited significant inhibitory activities, with IC50 values of 7.8 and 8.2 mu M, respectively, and had three-fold greater potency than the reference compound quercetin (IC50=21.4 mu M). Furthermore, enzyme kinetics revealed that compounds 2 and 3 exhibited reversible and mixed type-I inhibitory behaviors, with inhibitory constant (K-i) values of 6.8 and 7.2 mu M, respectively. Our results revealed the potential of U. longissima in inhibiting the enzyme BNA and highlighted its additional medicinal properties. (c) 2018 SAAB. Published by Elsevier B.V. All rights reserved.