New cadinane sesquiterpenoids from Mikania micrantha
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Chemical investigation of the aerial parts of Mikania micrantha led to the isolation of eight sesquiterpenoids and ten diterpenoids, including five cadinane sesquiterpenoids (1−5), three bisabolene sesquiterpenoids (6 − 8), nine ent-kaurane diterpenoids (9–17), and an abietane diterpenoid (18). Among them, 1 − 3 are new and feature a rare lactone or furan ring derived from C-6 isopropyl group side chain. Compound 18 was isolated from genus Mikania for the first time, and was also the first example of abietane-type diterpenoids from this plant. Their structures were elucidated on the basis of extensive spectroscopic analyses (1D and 2D NMR, HRESIMS, and ECD). All compounds were examined for their inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 264.7 macrophage cells, and compound 18 exhibited pronounced inhibition on NO production (IC50 = 11.04 µM), being comparable to the positive control, quercetin (IC50 = 11.15 µM).