Distahlianins A–C: Architecturally Diverse Cadinane-Type Sesquiterpenoid Dimers from Stahlianthus involucratus

Three architecturally novel cadinane sesquiterpenoid dimers, distahlianins A-C (1-3), were isolated from Stahlianthus involucratus. Compounds 1 and 2 are characterized by an unusual 5,6-spirocyclic scaffold annulated with oxygenated heterocycles to form intricate 6/6/5/6/6/6 and 6/6/5/5/6/6 hexacyclic frameworks, respectively. Compound 3 features a unique dimeric skeleton formed by two monomeric units bridged through a cyclopentane ring. Intriguingly, structural analysis revealed a unique C14 methyl migration (C-9→C-8) in the left monomer unit of 3, representing a new cadinane skeletal feature. Compound 3 exhibited potent lipid-lowering activity, with mechanistic evidence pointing to lipogenesis suppression.