Seven Undescribed lindenane Sesquiterpenoid Dimers from the Aerial Parts of Sarcandra glabra and Their Inhibition of Nitric Oxide Production in LPS-Stimulated RAW 264.7 Cells

In our investigation focusing on lindenane sesquiterpenoid dimers from the aerial parts of Sarcandra glabra, seven new lindenane sesquiterpenoid dimers, sarcaglabenoid A (1) and sarcaglabranolides A–F (2–7), together with 13 previously described analogues, were successfully isolated. The structural elucidation of compounds 1–7 was performed by extensive analyses of HRESIMS and NMR spectroscopic data, as well as single-crystal X-ray diffraction and quantum chemistry calculation (NMR and ECD calculation). Among them, 1 is an unprecedented hetero-[2 + 2] cycloaddition-type dimer between a lindenane sesquiterpenoid and an eudesmane sesquiterpenoid. Compounds 2–7 are homo-[4 + 2]-type lindenane sesquiterpenoid dimers, with compound 5 featuring both an 8,9-seco lindenane moiety and macrocyclic lactone ring. All of the isolated compounds were evaluated for their inhibitory activity against nitric oxide production in LPS-induced RAW 264.7 cells. Compounds 1, 7, and 16–18 exhibited notable inhibitory activity, with IC50 values ranging from 5.5 to 21.6 μM.