Nitric Oxide Inhibitory Dimeric Sesquiterpenoids from <i>Artemisia rupestris</i>

Twelve new dimeric sesquiterpenoids (<b>1</b>–<b>12</b>) were isolated from the dried whole plants of <i>Artemisia rupestris</i>. Their structures were determined using MS and NMR data, and the absolute configurations were elucidated on the basis of experimental and calculated ECD spectra. Compounds <b>1</b>–<b>9</b> are presumably formed via biocatalyzed [2+2] or [4+2] cycloaddition reactions. Stereoselectivity of the [4+2] Diels–Alder reaction dictated the formation of <i>endo</i>-products. The dimeric sesquiterpenoids exhibited moderate inhibition on NO production stimulated by lipopolysaccharide in BV-2 microglial cells, with IC<sub>50</sub> values in the range 17.0–71.8 μM.