19- nor -Clerodane Diterpenoid Dimers from Croton euryphyllus and Their NLRP3 Inflammasome Inhibitory Activity

Guided by LC-MS profiling and polarity-based fractionation, four novel 19- nor -clerodane diterpenoid dimers, euryproids A–D ( 1 – 4 ), were isolated from Croton euryphyllus, employing crotoeurin A ( 5 ) as a reference. Compound 1 possesses an architecturally novel 6/6/6/6/6 carbocyclic framework through an intermolecular Diels–Alder cycloaddition, while 2 – 4 feature a rare cyclobutane-bridged skeleton constructed via a [2 + 2] cycloaddition. Compound 4 exhibited potent NLRP3 inflammasome inhibition, significantly suppressing LDH release, IL-1 β secretion, and ASC speck formation with minimal cytotoxicity.