Uronic acids methanolysis

De Ruiter, G. A., Schols, H. A., Voragen, A. G. J., and Rombouts, F. M., Carbohydrate analysis of water-soluble uronic acid-containing polysaccharides with high-performance anion-exchange chromatography using methanolysis combined with TFA hydrolysis is superior to four other methods, Anal. Biochem., 207, 176, 1992. 

Methanolysis of standard uronic acids has been studied by Inoue and Miyawaki in regard to the depolymerization of chondroitin sulfate and dermatan sulfate. These workers found the glucosiduronic linkage to ga-lactosamine to be rather resistant to methanolysis, but that it is more efficiently cleaved after deamination of the amino galactoside, with its conversion into 2,5-anhydrotalose. For iduronic, glucuronic, and man-nuronic acids released from a polymer, it was found that the peaks monitored for these acids, relative to an internal standard, increase during the first 8 h of methanolysis (M hydrogen chloride, 100°) and remain constant for up to 20 h of methanolysis. This indicated that 8 h is required for complete methanolysis, and that the monosaccharides liberated are stable to the conditions of methanolysis. 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

Many authors have commented upon the problems associated with the hydrolytic step, which has been considered to be the main source of loss in carbohydrate analysis.19 The fact that, in determining uronic acids, differing results were obtained, depending on whether hydrolysis or methanolysis was employed, led others20 to conclude that... 

Cellulose may also serve as the starting material for the preparation of D-glucurono-6,3-lactone. However, the methanolysis of cellulose to methyl a,/3-D-glucopyranoside (66) has thus far been reported to proceed in only low yield. Whereas the oxidation of cellulose to cell-uronic acid (65) proceeds in high yield,344 the hydrolysis of this material to 63 has not yet been efficiently achieved. The preparation of 63 has been reviewed in detail,345-349 as have its subsequent reactions.350... 

The characterization and quantitative determination of uronic acid components in polysaccharides faces the problem of complete release of the uronic acids without accompanying decomposition. This is a difficult task because of the acid resistance of the glycosiduronic bond. From a comparison of several methods, it was shown that methanolysis combined with trifluoroacetic acid hydrolysis is the best for the liberation of uronic acids.204 The identification can be performed by gas chromatography of the trimethylsilyl derivatives.205... 

Proof of the structure of the uronic acid was obtained by Hirst, Jones and Jones,46 who isolated the methyl glycoside methyl ester by methyla-tion of the products from the graded methanolysis of alginic acid. The tri-O-methyl-D-mannuronic acid was converted to the diamide of 2,3,4-tri-O-methyl-D-mannaric acid, which had previously been prepared from... 

Bleton J, Mejanelle P, Sansoulet J, Goursaud S, and Tchapla A (1996) Characterization of neutral sugars and uronic acids after methanolysis and trimethylsilylat-ion for recognition of plant gums. Journal of Chromatography A 720 27-49. 

These derivatives of the monosaccharide structural units are then qualitatively and quantitatively analyzed by gas chromatography on capillary columns. In more difficult cases, a preliminary separation of acidic and neutral polysaccharides on an ion exchanger is recommended. Methanolysis or hydrolysis of polysaccharides containing uronic acids and anhydro sugars are critical due to losses of these labile building blocks. 

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