Diffusion-ordered Spectroscopy of Flavonol Mixture from Mesembryanthemum forsskaolii (Aizoaceae)

Aims: Phytochemical investigation of phenolic content in Mesembryanthemum forsskaolii Hochst. Ex. Boiss (family Aizoaceae).

Methodology: Chromatographic isolation of the total alcohol extract of the herb followed by the spectroscopic identification of the isolated compounds was performed adopting 1D, 2D NMR techniques including Diffusion-Ordered Spectroscopy (DOSY). Quantification of the phenolic content and evaluation of the antioxidant potential of M. forsskaolii was also performed. The total phenolic content (TPC) was determined using the Folin-Ciocalteu method and the total flavonoids content (TFC) was measured via complexation with aluminum chloride and the antioxidant activity was evaluated with DPPH (2.2-diphenyl-1-picrylhydrazyl) assay.

Results: Apigenin (1), kaempferol-3-O-glucoside (2), isorhamnetin-3-O-glucoside (3), apigenin-7-O-glucoside (4) and rutin (5) were isolated and identified. A mixture of isorhamnetin-3-O-rutinoside (6) and kaempferol-3-O-rutinoside (7) was obtained and its composition was identified without the need for further separation. 2D-DOSY experiment was performed, however very poor separation of peaks was obtained, and that may be attributable to close molecular weights of the mixture components and their structure similarity. It is noteworthy that, all the isolated compounds are reported for the first time from this plant. The TPC was 0.090±0.001 gallic acid equivalents in mg/g plant material. The TFC was 0.033±0.006 rutin equivalent in mg/ g plant material. The plant exhibited a very low antioxidant property as DPPH scavenging activity was 0.085±0.002 mg ascorbic acid equivalent antioxidant capacity in 1 g plant material.

Conclusion: Results provide a new addition to the chemical literature of M. forsskaolii, in addition it increases the importance of NMR techniques in flavonoids structure elucidation.