Structurally diverse sesquiterpenoids from Sarcandra glabra and their anti-inflammatory activities

Fifteen sesquiterpenoids, including five previously undescribed monomers with oxidative rearranged skeletons (sarglabenoids A–E, 1–5) and three previously unreported lindenane [2 + 2] dimers (sarglabenoids F–H, 6–8), alongside seven related precursors (9–15), were isolated from the root of Sarcandra glabra. The structures of these compounds were elucidated using a combination of high-resolution electrospray ionization mass spectrometry, one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy, the circular dichroism exciton chirality method, electronic circular dichroism, and nuclear magnetic resonance calculations integrated with DP4+ analysis. Compounds 1 and 2 feature an unique 5/5 spiro ring system, which is likely derived from a pinacol rearrangement of precursor 14. Compounds 3 and 4 are seco-C8/9 derivatives formed via Baeyer-Villiger oxidation of precursors 14 and 15, while compounds 6–8 represent the [2 + 2] dimers of various lindenane monomers (9–13). Notably, compounds 4 and 5 exhibited moderate inhibition of Interleukin-1β production in non-cytotoxic concentration in lipopolysaccharide-induced Tohoku Hospital Pediatrics-1 cells, with IC₅₀ values of 16.28 ± 0.76 μM and 11.32 ± 0.77 μM respectively.