Seco- and isopimarane diterpenoids from Kaempferia marginata rhizomes and their NO inhibition activities

Three undescribed 9,10-seco-isopimarane diterpenoids, marginols I–K, and an unprecedent isopimara-8(9),15-diene diterpene, 14-epi-boesenberol F, together with a known 9,10-seco-isopimarane diterpenoid, kaemgalangol A, were isolated from the rhizomes of Vietnamese Kaempferia marginata. Marginols I and J contained a naturally very rare 6-oxabicyclo[3.2.1]octane-5-ol ring, while marginol K had a naturally rare oxepan-2-one ring in its structure. The unprecedented structures were elucidated by spectroscopic techniques, including HR-ESI-TOF-MS, UV, IR, and 1D and 2D NMR. The absolute configurations of marginols I–K and 14-epi-boesenberol F were determined by ECD calculations. The NO production inhibitory assay revealed that the isolated compounds, except marginol J, exhibited NO inhibitory activities with IC₅₀ values ranging from 65.06 to 87.70 μM against lipopolysaccharide (LPS)-induced RAW264.7 cells.