Anti-inflammatory Labdane Diterpenoids from <i>Leonurus macranthus</i>

Twenty new polyoxygenated labdane diterpenoids (<b>1</b>–<b>20</b>) were isolated from the aerial parts of <i>Leonurus macranthus</i>. Their structures were elucidated on the basis of spectroscopic and spectrometric data (1D and 2D NMR, IR, and HRESIMS). The absolute configurations of macranthin A (<b>1</b>) and 6-<i>O</i>-deacetylmacranthin A (<b>2</b>) were determined by single-crystal X-ray crystallographic analysis and a modified Mosher’s method, respectively. Compounds <b>1</b>–<b>9</b>, <b>12</b>, <b>14</b>, and <b>19</b> showed inhibition of nitric oxide production in lipopolysaccharide-activated BV-2 microglial cells with IC₅₀ values of 10.0–63.7 μM