Arsenosugar

Currently available CRMs Presently available are CRM matrices (fish) with certified values for arsenobetaine and DMA, and caUbrants for those compounds. The offer is, however, very limited. Future needs include CRMs certified for arsenosugars and calibrants for those compounds. 

Andrewes, P., Demarini, D.M., Funasaka, K., Wallace, K., I ai, V.W.M., Sun, H., Cullen, W.R., Kitchin. K.T. 2004. Do arsenosugars pose a risk to human health The comparative toxicities of a trivalent and pentavalent arsenosugar. Environmental Science and Technology, 38, 4140-4148. Henderson, P.J., Knight, R.D., Mcmartin, I. 2002. Geochemistry of soils within a 100 km radius of the Horne Cu smelter, Rouyn-Noranda, Quebec. Geological Survey of Canada Open File 4169. 

Besides the applications of the electrophilicity index mentioned in the review article [40], following recent applications and developments have been observed, including relationship between basicity and nucleophilicity [64], 3D-quantitative structure activity analysis [65], Quantitative Structure-Toxicity Relationship (QSTR) [66], redox potential [67,68], Woodward-Hoffmann rules [69], Michael-type reactions [70], Sn2 reactions [71], multiphilic descriptions [72], etc. Molecular systems include silylenes [73], heterocyclohexanones [74], pyrido-di-indoles [65], bipyridine [75], aromatic and heterocyclic sulfonamides [76], substituted nitrenes and phosphi-nidenes [77], first-row transition metal ions [67], triruthenium ring core structures [78], benzhydryl derivatives [79], multivalent superatoms [80], nitrobenzodifuroxan [70], dialkylpyridinium ions [81], dioxins [82], arsenosugars and thioarsenicals [83], dynamic properties of clusters and nanostructures [84], porphyrin compounds [85-87], and so on. 

One factor has been overlooked in this reversion to seaweed use. Seaweed naturally contains high levels of arsenic, typically between 20 and 100 mg kg" dry weight (dw). Thus, sustained use of seaweed may lead to the buildup of arsenic in soils. The dominant species of arsenic in these seaweeds are in the form of arsenoribofuranosides (arsenosugars). These are assumed to be relatively nontoxic to humans and animals as compared to inorganic species. The arsenosugars are metabolized to different organo-arsenic species but mainly to DMA(V) (dimethylarsinic acid) when consumed as a food source. (Adapted from Castlehouse et ah, 2003)... 

Almela, C. Laparra, J. M. Velez, D. Barbera, R. Farre, R. Montoro, R. Arsenosugars in Raw and Cooked Edible Seaweed Characterization and Bioaccessibility. J. Agric. Food Chem. 2003, 53, 7344-7351. 

A number of arsenic-containing ribosides, also referred to here simply as arsenosugars, occur in marine samples. Most of the arsenosugars are dimethylarsinoylribosides (Fig. 2, compounds 9 to 25). This group of compounds was unknown prior to 1981, when 9 and 12 were isolated from a brown alga (55). Structures for the two compounds were origi-... 

Compound 13 was the first arsenosugar to be synthesized (Fig. 4) (56). The orthoester 26 was transesterified with the alcohol 27 to give an intermediate orthoester, which rearranged on treatment with mer-cury(II) bromide to the riboside 28. Removal of the ester protecting groups yielded the triol 29, which was converted to the isopropylidene derivative and then the chloride 30. The key intermediate 31 was then prepared by treating the chloride 30 with dimethylarsinosodium after the method of Feltham et al. (62). Attempts to purify this arsine proved difficult. Instead, it was oxidized without purification, giving 32, which... 

Fig. 3. Typical separation of four arsenosugars and DMA by HPLC/ICP-MS using an ODS reversed-phase column at pH 3.2 under conditions described in Ref. 60. The sensitivity and specificity of the detector allows the determination of arsenosugars and other arsenic compounds to be conducted on dilute aqueous extracts of the marine samples.

The total dissolved arsenic concentrations for the stations off British Columbia were 3-52 /u.g/liter (41), consistent with results for fjord porewaters (42) and estuarine porewaters (84). These results, however, rely on analytical techniques that would not detect the hidden or refractory arsenic levels reported earlier as occurring in seawater, and the true values may be slightly higher than those reported. The identity of the hidden and refractory arsenic remains unknown possible candidates include arsenosugars, TeMA, arsenobetaine, and arsenocholine. 

Fig. 9. Proposed pathway for the biogenesis of arsenosugars from arsenate (1). All...

In these experiments, 74As-arsenobetaine was similarly not detected, again showing that conversion of arsenosugars to arsenobetaine was not taking place within the animals. Unlike the study with Homarus, however, a single unknown transformation product was observed in the gastropods. 

Preliminary experiments in which HPLC/ICP-MS techniques have been used to monitor arsenic transformations within planktonic crustaceans feeding on a cultured unicellular alga containing arsenosugars at high concentrations have also been unable to demonstrate the production of arsenobetaine (98). Clearly there is much scope for work in this area. 

Fig. 10. Possible pathways for the biogenesis of arsenobetaine (7) from arsenosugars.

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