Diterpenoids and\nTriterpenoids from the Aerial Parts\nof Isodon serra and Their Biological\nActivities

Five undescribed diterpenoids, serranins A–E (<b>1</b>–<b>5</b>), and four novel triterpenoids, serratic\nacids\nA–D (<b>6</b>–<b>9</b>), along with 32 known\nterpenoids (<b>10</b>–<b>41</b>) were isolated\nfrom the aerial parts of Isodon serra. The planar structures of <b>1</b>–<b>9</b> and\ntheir relative configurations were established on the basis of extensive\nspectroscopic analysis. Structurally, compounds <b>6</b>–<b>9</b> are the first examples of 18,19-<i>seco</i>-ursane <i>p</i>-coumaric or ferulic esters, while compounds <b>1</b>–<b>5</b> further enriched the plant’s diterpene\nprofile. Bioactivity evaluation revealed that four diterpenoids (<b>2</b>, <b>10</b>, <b>12</b>, and <b>13</b>)\nexhibited potent cytotoxic activity against four cancer cell lines\n(B16–F10, A375, A549, and MDA-MB-231) with IC<sub>50</sub> values\nbelow 10 μM. Remarkably, <b>7</b> and <b>38</b> exhibited\na comparable antimelanogenesis effect to that of positive control\n(kojic acid) in B16–F10 cells.