Abstract
Phytochemical profiling of a hybrid species of willow, Salix × alberti L. (S. integra Thunb. × Salix suchowensis W.C. Cheng ex G.Zhu) revealed four sulfated flavonoids, which were then isolated from young stem tissue. The structures of dihydroflavonols (flavanonols) taxifolin-7-sulfate (1) and dihydrokaempferol-7-sulfate (2) and flavanones, eridictyol-7-sulfate (3) and naringenin-7-sulfate (4) were elucidated through NMR spectroscopy and high-resolution mass spectrometry. The identified sulfated flavanones and dihydroflavonols have not been previously seen in plants, but the former have been partially characterised as metabolites in mammalian metabolism of dietary flavonoids. In addition to providing full spectroscopic characterisation of these metabolites for the first time, we also compared the in vitro antioxidant properties, via the DPPH radical scavenging assay, of the parent and sulfated flavanones, which showed that 7-sulfation of taxifolin and eriodictyol attenuates but does not remove anti-oxidant activity.
Highlights
Salix L. is the largest genus of Salicaceae family comprising ca. 300–450 species
In our continuing studies on novel phytochemistry in the Salicaceae, in particular those genotypes contained in the 1500+ National Willow Collection (NWC), maintained as a shortrotation coppice plantation at Rothamsted Research, we recently reported on the occurrence of salicin-7-sulfate, a new salicinoid of potential pharmacological interest (Noleto-Dias et al, 2018)
Four sulfated flavonoids were isolated from the leaves and stems of S. × alberti L
Summary
Salix L. is the largest genus of Salicaceae family comprising ca. 300–450 species. These deciduous tree and shrub species are generally native to the cooler regions of the Northern Hemisphere, but they have been introduced worldwide (Julkunen-Tiitto and Virjamo, 2016; LauronMoreau et al, 2015), due to their useful features, such as fast growth and pleasing appearance, as well as considerable value as medicines and wood products, including biomass for energy (Isebrands and Richardson, 2014). Salicinoids are signature metabolites for Salicaceae family (Boeckler et al, 2011), and are well-known for their role in the development of aspirin (Desborough and Keeling, 2017). In our continuing studies on novel phytochemistry in the Salicaceae, in particular those genotypes contained in the 1500+ National Willow Collection (NWC), maintained as a shortrotation coppice plantation at Rothamsted Research, we recently reported on the occurrence of salicin-7-sulfate, a new salicinoid of potential pharmacological interest (Noleto-Dias et al, 2018). We extend the study of sulfated metabolites in Salix and report the isolation, structure determination and radical scavenging activity of four new sulfated flavonoids from the polar extract of a willow hybrid S.
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