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Four pairs of undescribed chromane and chromene meroterpenoid scalemic mixtures (1a/1b - 4a/4b), together with three pairs of known chromane meroterpenoid ones (5a/5b - 7a/7b) were isolated from the twigs and leaves of Rhododendron dauricum L. Among them, 1a/1b - 3a/3b and 5a/5b - 7a/7b were the chromane ones derived from an intramolecular [2 + 2] cyclic addition of their respective chromene precursors, forming a 6/6/6/4 and 6/6/5/4 ring fused scaffold. The absolute configurations of the chiral center at C-15 of 2a / 2b were determined by Snatzke's method, and comparing the experimental and calculated electronic circular dichroism (ECD) data. The inhibitory effects of the isolated compounds were tested against lipopolysaccharide (LPS)-induced nitric oxide production in RAW264.7 macrophage cells to evaluate their anti-inflammatory activity. Compounds 4a , 4b and 6a displayed inhibitory effects on nitric oxide (NO) production, and compound 4b exhibited the obvious anti-inflammatory activity, with an IC 50 value of 6.91 ± 0.97 μM, by downregulating nuclear factor kappa B (NF-κB) and reducing the expression of inducible nitric oxide synthase (iNOS) in LPS-induced RAW264.7 cells. These results intimated that 4b could be used as a leading compound to develop anti-inflammatory drugs and is worthy of further investigated. • Eight undescribed meroterpenoid scalemic mixtures were isolated from R dauricum L. • The new structures were elucidated by extensive analysis of spectroscopic data. • The absolute configuration of 2 was determined by Mo 2 -induced CD analyses. • Compound 4b exhibited the obvious anti-inflammatory activity. [ABSTRACT FROM AUTHOR]

The ent-kaurane diterpenoid enriched fraction (EDEF) of maize root was isolated and purified, and 10 compounds, including 4 ent-kaurane diterpenoids, were isolated and identified. We evaluated their neuroprotective properties in vitro for the first time using an H 2 O 2 -induced oxidative damage model in SH-SY5Y cells. The results showed that pretreatment with maizediterpene D, a new ent-kaurane diterpenoid isolated from the EDEF, significantly attenuated H 2 O 2 -induced apoptosis by improving cell survival, reducing ROS production and increasing mitochondrial membrane potential. Mechanistically, the neuroprotective effect of maizediterpene D was confirmed to be related to the dual activation of IGF-1R and BDNF/TrkB crosstalk pathways. Our findings suggest that the EDEF and its active constituent maizediterpene D had good neuroprotective properties and could serve as potential candidates for the development of therapeutic drugs for oxidative stress-related diseases. [Display omitted] • EDEF and Maizediterpene D were isolated from maize roots. • EDEF showed good antioxidant activity against H 2 O 2 induced oxidative stress. • D showed better cytoprotective activity against H 2 O 2 triggered oxidative stress. • M-D attenuated H 2 O 2 induced oxidative stress by BDNF/TrkB and BDNF/TrkB crosstalk pathways [ABSTRACT FROM AUTHOR]