Noralashinol A, a new norlignan from stem barks of Syringa pinnatifolia

Abstract One new norlignan, namely noralashinol A (1), one known analogue (2), together with seven known lignans (3–9) were isolated from the stem barks of Syringa pinnatifolia. Their structures were elucidated extensively by spectroscopic methods, including mass spectrometry and 1D and 2D NMR spectroscopies. Compound 8 significantly inhibited NO production in LPS-induced BV-2 murine microglia cells with its IC50 value of 20.7 μM, compared to a positive control quercetin with its IC50 value of 15.3 μM.

A phytochemical investigation was performed on the peeled stem barks, hopefully to provide chemical markers for characterisation of the pharmacologically active extracts, and bring evidence for chemotaxonomic study of the genus Syringa, led to the isolation and structural identification of one new norlignan, namely noralashinol A (1), one known analogue (2), together with seven known lignans (3-9). Their structures were determined by analyses of their MS, NMR, ORD and eCD spectroscopic data, and comparison with those in literature.
All compounds were tested for their in vitro anti-inflammatory activities against NO production in lipopolysaccharide (LPS)-induced BV-2 murine microglia cells. Compound 8 showed significant inhibition with its IC 50 value of 20.7 μM, compared with a positive control quercetin with its IC 50 value of 15.3 μM, no obvious activity was observed for other compounds.

Plant material
The stem barks of S. pinnatifolia var. alashanensis Y.C. Ma & S.Q. Zhou were collected in July 2013 from Alxa League (Inner Mongolia, China) and authenticated by Prof. Suyile Chen (Alashan League Mongolian Hospital, Inner Mongolia). A voucher specimen (SP201307) was deposited at the Modern Research Center for Traditional Chinese Medicine, Beijing university of Chinese Medicine.

NO production inhibitory assay
BV-2 cells macrophages were seeded in 96-well plates (1 × 10 5 cells/well). The cells were pre-treated with compounds 1-9 for 4 h, and then incubated with LPS (1 μg/mL) for 24 h. The amount of NO was assessed by determining the nitrite concentration in the cultured BV-2 cell macrophage supernatants with Griess reagent. The absorbance was recorded on a microplate reader at a wavelength of 540 nm. Cell viability was measured by an MTT assay, and the absorbance read at 570 nm with an eLISA analyzer, and quercetin was used as positive control (Guo et al. 2015).

Supplementary material
Supplementary materials relating to this article are available online (HR-eSI-MS and 1D and 2D NMR spectra of compound 1)

Funding
This paper was financially supported by the National Natural Science Foundation of China [grant number 81473426], [grant number 81303309]. The authors expressed their thanks to Prof.
Chen-Su-Yi-Le (Alashan League Mongolian Hospital) for his help in collection of plant material and authentication.