Methyl glycosides analysis

Glycosyl-residue compositions were determined by GC-CIMS analysis of the per-O-trimethylsilylated methyl glycosides [23] separated on a fused-silicaDB-1 capillary column. The identity of each peak was confirmed by CIMS on a HP-5989 MS Engine (Hewlett-Packard). 

The monosaccharide composition of all the samples was determined by GLC analysis of the trimethylsilyl methyl glycoside derivatives [1]. 

With the development of new liquid phases, interest in the separation of alditol acetates has revived, and this now may be considered the most widely used method for analyzing carbohydrate mixtures, provided that reduction does not introduce an ambiguity into the analysis also, it must be borne in mind that the multiplicity of peaks obtained by trimethylsilylation of a free sugar or of its methyl glycosides may serve a useful purpose in characterization. 

After their isolation by chromatographic techniques (anion-exchange chromatography, size exclusion, etc.), different analytical methodologies have been used to identify and quantify the polysaccharides in wine the most commonly used being the traditional methylation analysis followed by GC-MS (Doco and Bril-louet 1993). Polysaccharides have also been determined after solvolysis with anhydrous methanol containing HCl by GC-MS of their per-G-trimethylsilylated methyl glycosides (Vidal et al. 2003). Other techniques such as Fourier transform infrared spectroscopy (FTIR) have been more recently proposed (Coimbra et al. 2002,2005 Boulet et al. 2007). 

As all acyl-neuraminic acids, it occurs in the pyranose form. The absolute conformation of NeuSAc 1 has been determined by NMR studies on the methyl ester of sialic acid [2] and by X-ray analysis of crystals of neuraminic acid P-methyl glycoside [3]. According to these investigations, the anomeric hydroxyl group of the non-glycosidally bound neuraminic acid is arranged axially on C-2. 

The model monosaccharides just listed were prepared from common precursor IV.l (Scheme 39), which was readily obtained by azidonitration of 3,4,6-tri-O-acetyl-D-galactal followed by deacetylation with sodium methoxide. Treatment of IV.l with acetone and toluene p-sulfonic acid monohydrate at room temperature led to predominant formation of the thermodynamically favored 3,4-O-isopropylidene (IV.2) in 61% yield while also producing 27% of the 4,6-O-isopropylidene derivative IV.3. The position of the isopropylidene IV.2 was verified by the use of NMR chemical shift analysis to confirm the position of the acetate group in the resultant acetylated adduct IV.4. Synthesis of the 4-O-sulfate derivative (IV.7) from IV.2 utilized a step that differentiated the 3-OH and 4-OH positions after benzylation and de-isopro-pylidination of IV.2, a selective methylation at the 3-OH of diol IV.5 was achieved via a tin procedure [91] to give methyl glycoside IV.6. Conversion of the azide into... 

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