No abstract

A procedure is described for the fractionation of selenium species in oyster samples by aqueous extraction. Several parameters were tested in order to evaluate the efficiency of the aqueous extraction: nature, concentration, pH and temperature of the solvent used. The soluble fraction in the aqueous solvent contains 35¡3% of the total selenium content (1.22¡0.03 mg g 21 ). The subsequent enzymatic hydrolysis of both the liquid extract and the solid residue allows the determination of selenium species by high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry. The chromatographic analyses were carried out in two chromatographic modes (anionic and cationic exchange) for the identification of selenium species in the samples. The species found in oyster tissues under the proposed treatment were trimethylselenonium ion (9.8¡0.8%) and selenomethionine (46¡6%). By using mass cut-off filters it was possible to determine the percentage of selenium remaining in chemical forms with a molecular weight higher than 10 kDa, and therefore to conclude that enzymatic hydrolysis is more efficient in the soluble fraction than in the non-soluble one.

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The synthesis of highly functionalized nitriles by an alkoxyl radical fragmentation of cyclic beta-hydroxy azides is described. The alkoxyl radicals were generated by reaction of the alcohols with (diacetoxyiodo)benzene and iodine under mild conditions compatible with the presence of sensitive substituents and the protective groups most frequently used in carbohydrate chemistry. To explore the scope and limitations of this methodology, experiments were carried out using a variety of beta-hydroxy azides of the carbohydrate (1-6, 33, and 41), monoterpenoid (21 and 22), and steroid (23-25) families of natural products. Of special interest are the aldopentonitriles (15-18, 34, and 42) and aldotetrononitriles (19 and 20) synthesized from the corresponding 2-azido-2-deoxycarbohydrates. To demonstrate the versatility of these aldononitriles as chiral synthons, 1,4-imino-1-deoxysugar (37) and 1,5-imino-1-deoxysugar (43) analogues of the polyhydroxypyrrolidine and -piperidine types were prepared.

A procedure is described for the enzymatic digestion of tuna and mussel samples that allows the determination of selenium species by high-performance liquid chromatography in conjunction with inductively coupled plasma mass spectrometry. The species were extracted by two-step enzymatic hydrolysis with a non-specific protease (subtilisin). The selenium species were separated on a Spherisorb 5 ODS/AMINO column using two different chromatographic conditions, namely phosphate buffers at pH 2.8 and pH 6.0 as mobile phases. The method determines organic (trimethylselenonium, selenocystine, selenomethionine and selenoethionine) and inorganic selenium species (selenite and selenate), but only organic selenium species were found in the samples. The sum of identified selenium species in the sample was about 30% of the total selenium present in the enzymatic extract despite the fact that recoveries of total hydrolysed selenium were 93-102%. Trimethylselenonium ion and selenomethionine were found in both tuna and mussel samples and an unknown selenium species was also found in tuna samples.