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Rhododendron micranthum is used traditionally as a remedy for the treatment of chronic bronchitis in China. To clarify the chemical basis and provide a reference for the rational use of this medicinal plant, a phytochemical study was carried out on the twigs and leaves of R. micranthum, which afforded eight new compounds (1-8) and eight known compounds (9-16). Their structures were rigorously determined by comprehensive HRESIMS, NMR and electronic circular dichroism (ECD) analyses. The anti-inflammatory activities of these compounds were evaluated. Compounds 3, 13, and 14 suppressed the transcription of the NF-κB-dependent reporter gene in LPS-induced 293T/NF-κB-luc cells at 10 μM, while no effect on cell viability was observed., (Copyright © 2019 Elsevier B.V. All rights reserved.)

[Display omitted] • Fifteen undescribed triterpene spiroketal lactones were isolated from Pseudolarix amabilis. • Six compounds exhibited significant NF-κB pathway inhibition activities (IC 50 : 0.09 to 0.49 μM). • Compound 16 showed anti-inflammatory activity against xylene-induced ear swelling and improved the disease activity index (DAI) of ulcerative colitis. Fifteen new triterpenoids (1 – 15), along with twenty known ones (16 – 35), were isolated from Pseudolarix amabilis. The triterpenoid structures include multiple skeleton types, such as 2,3-seco-cycloartane, 3,4-seco-cycloartane, 3,4:9,10-diseco-cycloartane, and 3,4:8,9:9,10-triseco-cycloartane, as elucidated by extensive spectroscopy (1D NMR, 2D NMR, HRESIMS, and IR) and single-crystal X-ray diffraction. The anti-inflammatory activities of compounds 1 – 35 were evaluated. Compounds 3 , 11 , 16 , 24 , 25 , and 26 suppressed the transcription of the NF-κB-dependent reporter gene in LPS-induced 293T/NF-κB-Luc cells with IC 50 values of 0.12, 0.10, 0.30, 0.09, 0.49, and 0.35 μ M, respectively. In addition, compound 16 showed anti-inflammatory activity against xylene-induced ear swelling in vivo with an inhibition rate of 44.7 % (30 mg/kg). Compound 16 significantly improved the disease activity index (DAI) of ulcerative colitis at a dose of 400 mg/kg in a dextran sodium sulfate (DSS)-induced mouse model of experimental ulcerative colitis (P < 0.01). [ABSTRACT FROM AUTHOR]