Novel Polyketides with Agricultural Bioactivity Produced by <i>Phomopsis</i> sp. HDSJ-28, an Endophytic Fungus Derived from <i>Taxus yunnanensis</i>

Phomopsisols A and B (<b>1</b> and <b>2</b>), possessing an unprecedented highly oxygenated isobenzofuran dimer core, along with one new tenellone derivative (<b>3</b>), and two new polyketides (<b>13</b> and <b>14</b>), as well as 11 known compounds, were isolated from the endophytic <i>Phomopsis</i> sp. associated with <i>Taxus yunnanensis</i>. The structures were determined mainly by the NMR, MS, ECD, and optical rotation calculations and single-crystal X-ray diffraction analyses. Most compounds demonstrated selective antifungal activity against the phytopathogens <i>Colletotrichum karsti</i> and <i>Colletotrichum gloeosporioides</i>, rather than against the biocontrol fungus <i>Clonostachys rosea</i>. Compounds <b>1</b>-<b>6</b> and <b>9</b>-<b>12</b> exhibited attractive feeding activities toward silkworms with attraction rates of 33-65%. Compounds <b>1</b>, <b>9</b>, <b>10</b>, <b>15</b>, and <b>16</b> promoted the growth of <i>Oryza sativa</i> seedlings. In contrast, compounds <b>3</b>-<b>6</b> completely inhibited both shoot and root growths of rice at a concentration of 20 μg/mL. Notably, compound <b>3</b> demonstrated significant multiple agricultural activities, including antifungal activity, feeding attraction, and phytotoxicity.