Amino sugars methanol

The ions of the C series are formed from amino sugars by elimination of methanol (instead of the CH30- radical in the case of neutral hexosides). Subsequently, the fragment eliminates ketene and, at last, the CH3OCH2-radical. This sequence is not observed with the neutral hexosides, indicating the greater stability of the ammonium compared with the oxonium ion. 

Selective acetylation of the basic group in amino sugars can be achieved if silver acetate and acetic anhydride in methanol are used as the acetylating reagents. The products are the characteristically crystalline N-acetates. 

Alditols [405] and amino sugars [406] have been analysed by GC—MS as combined methyl ether—acetyl derivatives. Acetylation was performed with acetic anhydride in pyridine, as follows. A 0.15-ml volume of re-distilled dry pyridine was added to 0.5 ml of 1.5 A acidic methanolysate containing 0.025—2.5 pmol of amino sugars. The apparent pH of the methanolic pyridinium hydrochloride varied in the range 4—5. Acetic anhydride (0.1 ml) was added and the mixture was stirred thoroughly and allowed to stand at room temperature for 30 min. Evaporation to dryness was performed in vacuum over solid KOH with subsequent vacuum drying for 4 h over P20s. SE-30 was used as the stationary phase. 

Base-catalyzed reactions of amino sugars with 2,4-pentanedione in a nonaqueous solvent (piperidine-triethylamine-methanol) have also been reported. The products obtained under these conditions from 2-amino-2-deoxy-D-glucose are 3-acetyl-2-methyl-5-(D-ami)OTo-tetrahydroxybutyl)-pyrrole (2) (in about 90% yield) and 2-deoxy-2-n(4-oxopent-2-enyl)-amino]-D-glucose (28). Proofs that structure (28) is correct were (a) the ultraviolet absorption, typical of a -amino a,j3-unsaturated ketone, (b) a positive test with the ferric chloride reagent, and (c) quantitative... 

Methanolysis in anhydrous methanolic HCI, followed by N-acetylation of amino sugars and sialic acid, and derivatization of the methyl glycosides formed to volatile trimethylsilyl ethers (TMS) or trifluoracetyl derivatives are widely used (17,18). 

This reaction was first reported by MacDonald and Fischer in 1952. It is the degradation of hexoses into pentoses involving the steps of formation of dithioacetal, oxidation to unsaturated disulfone by means of perphthalic acid, hydrazine treatment, and benzalde-hyde splitting of the corresponding hydrazone. Therefore, the whole process is known as the MacDonald-Fischer degradation. In addition, when the unsaturated disulfone is dissolved in aqueous ammonia or methanol saturated with ammonia, 2-deoxy-2-amino sugar is resolved. This reaction in combination with mass spectroscopy was used to study the structure and stereochemistry of carbohydrates. ... 

Glycoproteins were hydrolysed with 2 M trifluoro-acetic acid for 6 h in bioling water bath to yield aldoses, or with 4M HCl for amino sugars. To a sample of aldoses or reducing oligosaccharides (10-500 pmol each) were added a 0.5 M methanolic solution (50 fi ) of PMP and 0.3 M sodium hydroxide (50/il). The mixture was kept for 30 min at 70 °C. After cooling and neutralization, the solution was evaporated to dryness, and the derivatives were extracted into aqueous solution with water/chloroform. 

Analytical procedures used in the routine analysis of glycoproteins often involve methanolysis and subsequent N-acetylation of the liberated amino-sugars. However, it has been demonstrated that partial 0-acetylation of alditols (commonly employed as internal standards) accompanies the N-acetylation of amino-sugars. It was also shown that a hot neutral solution of methyl chloride in methanol releases L-fucose, sialic acid, and some D-galactose residues from aj-acid... 

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