Antioxidant Lignans and Chromone Glycosides from <i>Eurya japonica</i>

Four new 8,8′,7,2′-lignans, (+)-ovafolinin B-9′-<i>O</i>-β-d-glucopyranoside (<b>1</b>), (−)-ovafolinin B-9′-<i>O</i>-β-d-glucopyranoside (<b>2</b>), (+)-ovafolinin E-9′-<i>O</i>-β-d-glucopyranoside (<b>3</b>), and (−)-ovafolinin E-9′-<i>O</i>-β-d-glucopyranoside (<b>4</b>), two neolignans, eusiderin N (<b>5</b>) and (7<i>S</i>,8<i>R</i>)-3,5,5′-trimethoxy-4′,7-epoxy-8,3′-neolignan-9,9′-diol-4-<i>O</i>-β-d-xylopyranoside (<b>6</b>), and two new chromone glycosides, 5,7-dihydroxy-4<i>H</i>-chromen-4-one-3-<i>O</i>-β-d-glucopyranoside (<b>7</b>) and 5,7-dihydroxy-4<i>H</i>-chromen-4-one-3-<i>O</i>-β-d-xylopyranoside (<b>8</b>), together with 25 known compounds, were isolated from the stems of <i>Eurya japonica</i>. Structural elucidation of compounds <b>1</b>–<b>8</b> was established by spectroscopic methods, especially 2D NMR techniques, electronic circular dichroism data, and comparison with reported data. The isolates were evaluated for antioxidant and anti-NO production activities. Compounds <b>1</b>, <b>2</b>, <b>12</b>–<b>20</b>, and <b>29</b> (ED₅₀ 23.40 μM for <b>1</b>) demonstrated potent antioxidant activity compared to the positive control α-tocopherol (ED₅₀ 27.21 μM). On the other hand, compounds <b>1</b>, <b>2</b>, <b>7</b>–<b>9</b>, <b>12</b>–<b>20</b>, and <b>32</b> showed only weak anti-NO production activity when compared to the positive control quercetin