Chemical constituents of the seeds of <i>Citrus reticulata</i> and their bioactivity

Four new limonoids (<b>1-4</b>), reticulactone A <b>(1)</b>, 21,23-dihydro-23-ethoxy-21-oxolimonin <b>(2)</b>, tetrahydro-20,22-dihydroxy-21,23-diethoxy-nomilin <b>(3)</b>, and dasycarinone B <b>(4)</b>, as well as 11 known limonoids and one known carbolic acid, were isolated from the EtOH extract of the seeds of <i>Citrus reticulata</i> Blanco. The inhibitory effects of 15 limonoids (<b>1</b>-<b>15</b>) on the proliferation of HepG2 liver cancer cells were evaluated using the CCK-8 assay. Based on their structural characteristics, the results revealed that the typical limonoid compounds <b>2</b>, <b>5</b>, <b>10</b>, and <b>12</b> exhibited stronger cytotoxicity compared to other limonoid compounds. Notably, the novel compound <b>2</b> demonstrated the strongest cytotoxic activity (IC₅₀ = 18.24 ± 2.78 μM).