Structurally Diverse Diterpenoids from <i>Isodon scoparius</i> and Their Bioactivity

Fourteen new diterpenoids (<b>1</b>–<b>14</b>) based on four skeletal types and two known analogues (<b>15</b> and <b>16</b>) were isolated from the aerial parts of <i>Isodon scoparius</i>. Compound <b>2</b> is the first <i>ent</i>-kaurane diterpenoid featuring a 1,11-ether bridge, and the structures of these new compounds were established mainly by NMR and MS methods. The absolute configurations of <b>1</b> and <b>5</b> and the relative configuration of <b>3</b> were determined using single-crystal X-ray diffraction. The absolute configuration of <b>14</b> was determined by comparison of the experimental and calculated electronic circular dichroism spectra. Compounds <b>1</b>, <b>4</b>, and <b>15</b> were active against five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480), and they also inhibited NO production in LPS-stimulated RAW264.7 cells, with IC₅₀ values of 1.0, 3.1, and 1.8 μM, respectively