First insight into the phenolic content of Spartina maritima: isolation, characterization and quantification of four C-glycosidic flavonoids

The phenolic content of Spartina maritima was investigated using chromatographic and spectroscopic techniques. Aqueous methanolic extracts were prepared from plant collected in different seasons in the Bay of Arcachon (French Atlantic coast). High performance liquid chromatography (HPLC) with diode array detection (DAD) coupled with mass spectrometry allowed identification of four major phenolics in the aerial tissue, all belonging to the C-glycosidic-flavonoid class. They were isolated from the crude extracts, and their structures were assigned to isovitexin, isoscoparin and their respective 2″-O-glucosides on the basis of NMR, mass and UV spectroscopies. The seasonal variation of the flavonoid content was quantified over the period January 2013 to May 2015. The total concentration found ranged from 1.73 to 4.60 mg g⁻¹ dry wt for isovitexin derivatives, and 0.88–2.66 mg g⁻¹ dry wt for isoscoparin derivatives. The phenolic content of the rhizomes was very low and mainly dominated by coumaric acid (0.03–0.08 mg g⁻¹), along with ferulic acid (≤0.06 mg g⁻¹). The lack of significant concentrations of flavonoids in the rhizome contrasts with the aerial tissue. This work constitutes the first phenolic profiling of S. maritima and should provide a foundation for further studies, considering the reported biological activities of C-glycosidic flavonoids, and the lack of knowledge of the phenolic chemistry of the genus Spartina.