Bioactive Abietane and <i>ent</i>-Kaurane Diterpenoids from <i>Isodon tenuifolius</i>

Three new abietane diterpenoids, isoabietenins A–C (<b>1</b>–<b>3</b>), and 13 new <i>ent</i>-kauranoids, tenuifolins A–M (<b>4</b>–<b>16</b>), along with four known compounds (<b>17</b>–<b>20</b>), were isolated from the aerial parts of <i>Isodon tenuifolius</i>. The structures of the new metabolites were established on the basis of detailed spectroscopic analysis. The absolute configurations of <b>1</b>, <b>15</b>, and <b>16</b> were confirmed by single-crystal X-ray diffraction. Selected compounds were evaluated for their cytotoxicity against a small panel of human tumor cell lines, and some compounds showed inhibitory effects. Furthermore, several isolates exhibited inhibitory activity against nitric oxide production in LPS-activated RAW264.7 macrophages