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 Award | 2020 |
|---|---|
| Original language | English |
| Supervisor | Ashraf GHANEM (Supervisor), Bill Maher (Supervisor) & Simon FOSTER (Supervisor) |