Walrobsins A and B, Two Anti-inflammatory Limonoids from Root Barks of Walsura robusta

Walrobsins A (1) and B (2), two limonoids featuring an unprecedented 5-oxatri­cyclo­[5.4.1^1,4]­hendecane ring system, were isolated from the root barks of Walsura robusta. Their structures, including their absolute configurations, were determined by analyses of HR-ESIMS, 1D/2D NMR, and X-ray crystallography. Compounds 1 and 2 possessed a stable hemiketal structure formed between the OH-11 and 3-carbonyl group in the hexatomic oxoheterocyclic ring. Compound 1 showed significant anti-inflammatory activity with an IC₅₀ value of 7.8 μM and inhibited the expression of iNOS and IL-1β in a dose-dependent manner.