Phenylpropenoids from <i>Bupleurum fruticosum</i> as Anti-Human Rhinovirus Species A Selective Capsid Binders

The dichloromethane extract of the leaves of <i>Bupleurum fruticosum</i> was found to inhibit the replication of human rhinovirus (HRV) serotypes 14 and 39. Bioassay-guided fractionation led to the isolation of seven phenylpropenol derivatives (<b>3</b>–<b>9</b>), two polyacetylenes (<b>1</b> and <b>2</b>), and one monoterpene (<b>10</b>). Compounds <b>1</b> and <b>10</b> were identified as previously undescribed secondary metabolites after extensive 1D and 2D NMR experiments as well as high-resolution mass spectrometry. Compounds <b>2</b>, <b>4</b>, and <b>5</b> showed a selective inhibition of viral replication against HRV39 serotype, with <b>2</b> and <b>4</b> being the most active, with EC₅₀ values of 1.8 ± 0.02 and 2.4 ± 0.04 μM. Mechanism of action studies indicated that <b>4</b> behaves not only as a capsid binder, interfering with the early phases of virus replication, but also as a late-phase replication inhibitor. Docking experiments were performed to confirm the ability of the antiviral phenylpropenoids to selectively fit into the hydrophobic pocket of VP1-HRV39