Analysis of natural occurring arsenic-containing riboside by HPLC-ICPMS - use of zirconium anion exchange chromatography and synthesis of chiral arsenoribose standards

  • Eman Alkasasbeh

    Student thesis: Doctoral Thesis

    Abstract

    The metalloid arsenic is a toxic element and a potential environmental health issue as it is
    naturally found in the diet, particularly seafood, as well as drinking water. Arsenic-containing
    ribosides constitute an important class of natural arsenic species that are biosynthesised by marine
    macroalgae. Their importance emerges from being part of the transformation and cycling of
    arsenic species in the marine environment.
    Because of the drawbacks related to current analytical methods for arsenoriboses, this research
    project aims to [1] improve speciation methods for arsenoriboses currently performed using highperformance
    liquid chromatography – inductively coupled plasma mass spectrometry (HPLCICPMS)
    with a silica-based anion-exchange column by using a zirconium-based anion-exchange
    column, and [2] analyse and synthesis the chiral arsenoribose standards.
    Chapter 2 investigates a new and fast method for arsenoribose analysis. HPLC-ICPMS utilising
    a ZirChrom®-SAX column with an aqueous 10 mM ammonium dihydrogen phosphate mobile
    phase at pH 7.5 (adjusted with aqueous ammonia) was evaluated for measuring glycerol
    arsenoriboside (OH-ribose), phosphate arsenoriboside (PO4-ribose), sulfonate arsenoriboside
    (SO3-ribose) and sulfate arsenoriboside (OSO3-ribose) in marine macroalgae and animals by
    analysis of seven reference materials. The results obtained were compared with those obtained
    using PRP-X100 anion-exchange chromatography. Inorganic arsenic species were not eluted
    from the zirconium column because of the strong interaction with the zirconia stationary phase.
    Measurements of SO3-ribose and OSO3-ribose concentrations were in close agreement with those
    obtained using the PRP-X100 column. Peak shapes of these arsenoriboses were improved,
    allowing lower amounts to be quantified. The quantification of OH-ribose and PO4-ribose, however, was sample dependent and not possible if arsenobetaine (AB) and dimethylarsinic acid
    (DMA) were present at large concentrations because of coelution of these species with OH-ribose
    and PO4-ribose respectively. In the absence of OH-ribose, AB can be determined using the
    zirconium column, while AB coeluted with arsenic cations on the PRP-X100 column.
    Identifying the stereochemistry of natural arsenoriboses that are found in marine algae is crucial
    as they play an essential role in arsenic metabolism, which may lead to various biological effects.
    To detect and identify these arsenic species, Chapter 3 describes development of a technique to
    separate diastereomeric isomers of the major arsenoribose species that have been found in marine
    algae. The racemic mixture of isolated SO3-ribose standards was analysed by HPLC-ICPMS. The
    separation was achieved using a C18 reversed-phase column with 20 mM ammonium formate
    buffer, pH 3.2, at room temperature and a flow rate of 1 mL min-1. More work, however, is needed
    to confirm the isomers by synthesis of each isomer separately.
    Chapter 4 presents the first synthesis of (S)-2′,3′-di-O-benzylpropyl 2,3,5-tri-O-acetyl-β-Driboside,
    a key precursor for preparing naturally occurring optically active arsenic-containing
    ribosides, starting from (R)-2,3-di-O-benzylglycerol. Key steps in the synthesis are glycosidation
    and selective protection/deprotection of hydroxy groups to obtain the desired product at 83%
    yield.
    Date of Award2020
    Original languageEnglish
    SupervisorAshraf GHANEM (Supervisor), Bill Maher (Supervisor) & Simon FOSTER (Supervisor)

    Cite this

    '