Sesquiterpenoids from Tussilago farfara: full structure elucidation, anti-diabetic and anti-inflammatory signaling pathways.

Four new sesquiterpenoids (1-4), including the first reported instance of a novel 2,3-seco oplopane carbon skeleton (1), together with 19 known analogues, were isolated from the flower buds of Tussilago farfara (coltsfoot). The challenging determination of relative and absolute configurations-particularly in flexible side chains and substituents-was achieved for the first time through an integrated approach combining spectroscopic analyses, chemical derivatization, chiral gas chromatography (GC), and quantum chemical calculations. All compounds were evaluated for anti-diabetic activity using an insulin-stimulated glucose uptake model in C2C12 myotubes and for anti-inflammatory activity via a lipopolysaccharide (LPS)-induced nitric oxide (NO) inhibition assay in RAW264.7 macrophages. Six compounds significantly enhanced glucose uptake, and mechanistic investigation of compound 3 revealed activation of the insulin receptor substrate 1 (IRS-1)/protein kinase B (Akt)/glycogen synthase kinase 3β (GSK-3β) signaling pathway. Twenty-one compounds exhibited marked inhibition of NO production; among them, compounds 2 and 6 dose-dependently suppressed inducible nitric oxide synthase (iNOS) expression and nuclear factor κB (NF-κB) phosphorylation.