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Arabinose and galactose were treated with MeOH containing traces of H2SO4 or HCl at 25◦C to give mixtures of their methyl alpha-andbeta-furanosides, as shown by 1D and 2D nuclear magnetic resonance (NMR). Oxidation of the Me alpha, beta-Ara f mixture with NaIO4 preferentially oxidized the beta-isomer, to give pure Me alpha-Ara f. Each product was progressively O-methylated using the Purdie reagent (MeI/Ag2O) at 25◦C and resulting mixtures of partially methylated glycosides (PMGs) were rapidly assayed by thin layer chromatography (TLC) first to favour higher yields of mono-O-methyl derivatives and later for products with higher degrees of methylation. The products were converted to complex mixtures of partially O-methylated alditol acetate derivatives (PMAAs) by successive hydrolysis, reduction with NaBD4, and acetylation. These can be used as gas chromatography-mass spectrometry (GC-MS) standards in methylation analysis of complex carbohydrates containing arabinofuranosyl and galactofuranosyl units. Of particular interest were the retention times and electron impact MS of the difficult to prepare alditol acetates of 5,6-Me2Gal,2,5-Me2Gal,2,5,6-Me3Gal,3,5,6-Me3Gal,5-MeAra,2,5-Me2Ara, and 3,5-Me2Ara. The relative reactivities of hydroxyl groups for mixtures of Me alpha- and Me beta-Galf wereHO-2>HO-3>HO-6>HO-5,that of Me alpha-and Me beta-Ara f HO-2>HO-3>HO-5,and that of Me alpha-Ara f HO-2>HO-3≥HO-5. Partially O-methylated alditol acetates, GC-MS standards, Purdie methylation, OH reactivity, NMR.

Palabras clave: partially O-methylated alditol acetates,GC-MS standards, Purdie methylation, OH reactivity, NMR.
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Universidad Autónoma del Estado de México
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Versión 3.0 | 2017
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