Dibenzocyclooctadiene Lignans from Artemisia sieversiana and Their Nitric Oxide Inhibitory Effects

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Introduction
Artemisia sieversiana Ehrhart ex Willd, also known as 'Da-Zi-Hao', 'Bai-Hao', 'Bai-Ai-Hao' and 'You-Hu' in Chinese, is an annual or biennial herb of the Compositae and widespread in China, Pakistan, Mongolia and Central Asia. In China, it has a long medicinal history in traditional Chinese medicine and Mongolian medicine, which has been used to treat diarrhea and jaundice [1]. Encouraged by the chemical diversity and notable biological activities of A. sieversiana [2][3][4][5][6], we have re-investigated the ingredients of the aerial parts of this plant, which led to the identification of three previously undescribed dibenzocyclooctadiene lignans and eight known compounds.
Herein, we have described their isolation and structural elucidation of these compounds together with their anti-neuroinflammatory effects on the lipopolysaccharides (LPS)induced nitric oxide production in BV-2 murine microglial cells.
The  negative Cotton effect 220 nm, indicating that 2 had a R-biphenyl configuration [16].
All the isolated compounds were for their anti-neuroinflammatory effects on the lipopolysaccharides (LPS)-induced nitric oxide production in BV-2 murine microglial cells by using the method previously reported (Table 2) [17]. The known compound quercetin (IC50 = 16.0 μM) were used as positive control in the bioassay. Compounds

Conclusion
In conclusion, this study investigated chemically the aerial parts of Artemisia sieversiana, which resulted in ten dibenzocyclooctadiene lignans (1-10), including two unknown ones (1-2). Their structures were elucidated from extensive spectroscopic analysis, including MS, NMR and circular dichroism experiments. To our knowledge, this study is the first to report dibenzocyclooctadiene lignans in the genus Artemisia and this plant. Lignans can be considered as one of its main and characteristic components in Artemisia genus, but tetrahydrofuran lignans are the most common and related references on dibenzocyclooctadiene lignans in this genus are scarcely.
Therefore these ingredients can be interesting for chemotaxonomic significance of

NO production inhibitory assay
The production of NO in the medium was assessed by determining the nitrite concentration with Griess reagent (1% sulfanilamide and 0.1% naphthylenediamine in 5% phosphoric acid). BV-2 cells macrophages were seeded in 96-well plates (1×10 5 cells/well). The cells were pre-treated with compounds 1-10 for 4 h, and then incubated absorbance was recorded on a microplate reader at a wavelength of 540 nm. The IC50 value was generated by GraphPad Prism 5 software. Cell viability was measured by an MTT assay and the absorbance read at 570 nm with an ELISA analyzer. Quercetin was employed as a positive control.