Methylation-GC-MS analysis of arabinofuranose- and galactofuranose-containing structures: rapid synthesis of partially O-methylated alditol acetate standards

Guilherme L Sassaki,Marcello Iacomini,Philip A.J Gorin

doi:10.1590/s0001-37652005000200003

Guilherme L Sassaki, Marcello Iacomini + Show 1 more

Open Access

https://doi.org/10.1590/s0001-37652005000200003

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Abstract

Arabinose and galactose were treated with MeOH containing traces of H2SO4 or HCl at 25ºC to give mixtures of their methyl alpha- and beta-furanosides, as shown by 1D and 2D nuclear magnetic resonance (NMR). Oxidation of the Me alpha,beta-Araf mixture with NaIO4 preferentially oxidised the beta-isomer, to give pure Me alpha-Araf . Each product was progressively O-methylated using the Purdie reagent (MeI/Ag2O) at 25ºC 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 were HO-2 > HO-3 > HO-6 > HO-5, that of Me alpha and Me beta-Araf HO-2 > HO-3 > HO-5, and that of Me alpha-Araf HO-2 > HO-3 > HO-5.

Highlights

Arabinose and galactose are widely found in complex carbohydrates and are present in pyranosyl and furanosyl rings in molecules encompassing a great variety of glycosidic linkages with α- and βanomeric configurations
The products can be converted by successive hydrolysis to give partially O-methylated aldoses, which are reduced with NaBH4, followed by acetylation to provide partially O-methylated alditol acetates (PMAAs), which on gas chromatography-mass spectrometry (GC-MS), have typical retention times (Rt ) and electron impact (e.i.) spectra (Jansson et al 1970)
A similar procedure was used for preparation of 15 O-methyl alditol acetates starting from methyl α-galactopyranoside (Fournet et al 1978) and the MS data were presented in a tabular form

Summary

INTRODUCTION

Arabinose and galactose are widely found in complex carbohydrates and are present in pyranosyl and furanosyl rings in molecules encompassing a great variety of glycosidic linkages with α- and βanomeric configurations. A similar procedure was used for preparation of 15 O-methyl alditol acetates starting from methyl α-galactopyranoside (Fournet et al 1978) and the MS data were presented in a tabular form Another of the early investigations directed to the preparation of methylation standards for carbohydrate analysis was by Elkin et al (1975), who partially and fully O-methylated the methyl pyranosides of Rha, Fuc, Ara, Xyl, Man, Gal, and Glc, among others with the Purdie reagent (Purdie and Irvine 1903), but the resulting O-methyl derivatives were only poorly resolved by GLC and MS and not employed.

MATERIALS AND METHODS

RESULTS AND DISCUSSION

74 HC OAc 146 HC OAc 333 218 HC OAc 261 290 HC OAc 189 362 HC OAc 117