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Unusually large flavonoids found in a candytuft

Kew scientists have discovered some of the largest known flavonoid glycosides in a species of Iberis growing in Kew’s rock garden.

Image of Iberis saxatilis and the structure of one of the large flavonoid glycosides

While working on a project studying the medicinal properties of plants, researchers at Kew noticed unusually large flavonoid glycosides in an extract of Iberis saxatilis (a species of candytuft). The compounds were revealed using analysis by liquid chromatography-mass spectrometry, which can be used to separate the chemicals in a plant extract and determine their molecular masses. The largest had a molecular mass of 1300 Da, making it the seventh largest flavonoid glycoside (excluding anthocyanin pigments) currently reported on databases of natural compounds. The majority of flavonoid glycosides produced by plants are much smaller.

After purifying the compounds and determining their chemical structures by nuclear magnetic resonance spectroscopy, the Kew researcher realised it was not just their size that made the Iberis compounds unusual.  They had the largest number of sugars (five) forming a single chain attached at one point on the flavonoid. In other rare examples of flavonoids bearing five or more sugars, the sugars form two or more chains attached to the flavonoid at multiple points. Why this species of candytuft has evolved these unusual flavonoid glycosides is not clear.

Reference

Prescott, T.A.K., Kite, G.C., Porter, E.A. & Veitch, N.C. (2013). Highly glycosylated flavonols with an O-linked branched pentasaccharide from Iberis saxatilis ( Brassicaceae ). Phytochemistry 88, 85–91.

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