Isolation and characterisation of 13 pterosins and pterosides from bracken (Pteridium aquilinum (L.) Kuhn) rhizome

Rizgar Hassan Mohammad, Mohammad Nur-E-Alam, Martina Lahmann, Ifat Parveen, Graham J. Tizzard, Simon J. Coles, Mark Fowler, Alex F. Drake, Derren Heyes, Vera Thoss

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    Abstract

    Systematic phytochemical investigations of the underground rhizome of Pteridium aquilinum (L.) Kuhn (Dennstaedtiaceae) afforded thirty-five pterosins and pterosides. By detailed analysis of one- and two-dimensional nuclear magnetic resonance spectroscopy, circular dichroism (CD) and high-resolution mass spectrometric data, thirteen previously undescribed pterosins and pterosides have been identified. Interestingly, for the first time 12-O-β-D-glucopyranoside substituted pterosins, rhedynosides C and D, and the sulfate-containing pterosin, rhedynosin H, alongside the two known compounds, histiopterosin A and (2S)-pteroside A2, were isolated from the rhizomes of subsp. aquilinum of bracken. In addition, six-membered cyclic ether pterosins and pterosides, rhedynosin A and rhedynoside A, are the first examples of this type of pterosin-sesquiterpenoid. Additionally, the three previously reported compounds (rhedynosin I, (2S)-2-hydroxymethylpterosin E and (2S)-12-hydroxypterosin A) were obtained for the first time from plants as opposed to mammalian metabolic products. Single crystal X-ray diffraction analysis was applied to the previously undescribed compounds (2R)-rhedynoside B, (2R)-pteroside B and (2S)-pteroside K, yielding the first crystal structures for pterosides, and three known pterosins, (2S)-pterosin A, trans-pterosin C and cis-pterosin C. Rhedynosin C is the only example of the cyclic lactone pterosins with a keto group at position C-14. Six selected pterosins ((2S)-pterosin A, (2R)-pterosin B and trans-pterosin C) and associated glycosides ((2S)-pteroside A, (2R)-pteroside B and pteroside Z) were assessed for their anti-diabetic activity using an intestinal glucose uptake assay; all were found to be inactive at 300 μM.

    Original languageEnglish
    Pages (from-to)82-94
    Number of pages13
    JournalPhytochemistry
    Volume128
    Early online date10 May 2016
    DOIs
    Publication statusPublished - 1 Aug 2016

    Keywords

    • Bracken pterosins
    • Circular dichroism
    • Dennstaedtiaceae
    • Norsesquiterpenes
    • Pteridium aquilinum
    • Pterosides
    • Pterosins A and B
    • Sesquiterpenoids
    • SGLT1 and GLUT2 transporters

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