Methylation Haworth method

NRRL B-742 dextran may be artifactual structures, resulting from incomplete methylation of this highly branched polysaccharide. Dextrans have been methylated most frequently by the Haworth method, " and by procedures that employ sodium and methyl iodide in liquid ammonia. " " Rapid methylation of dextrans has been achieved " through the use of the Hakomori procedure, which utilizes methyl sulfoxide as solvent for the dextran. Careful control of the reaction temperature would, however, appear to be essential when a dextran is methylated in this solvent, as hot methyl sulfoxide has been reported to depolymerize native dextrans." ... 

Haworth Methylation Haworth Phenanthrene Synthesis Hayashi Rearrangement Heck Reaction Helferich Method Hell-Volhard-Zelinsky Reaction Henkel Process Henkel Reaction Henry Reaction... 

Total methylation of all available hydroxyl groups in a polysaccharide generally requires initial methylation by the Haworth method (dimethyl sulfate and aqueous sodium hydroxide) to introduce sufficient lipophilic... 

Both methods of approach moreover proved that a series of methylated derivatives of D-glucosamine described by Cutler, Haworth and Peat,14 and most useful as reference compounds in this field, were all of the pyranose configuration. Further proof of the pyranose structure of methyl D-glucosaminide and methyl N-acetyl-D-glucosaminide was pro-... 

Methylgraminin was obtained as a colorless sirup by the method of Haworth and Streight.24 Hydrolysis of the methyl derivative gave a mixture of di-, tri-, and tetramethyl-D-fructoses that were separated after conversion to benzoyl derivatives. The authors conclude that these partially methylated D-fructoses are present in the ratios 1 1 1 or 1 2 1. 

For the methylation of the free hydroxyl groups of a partially esterified carbohydrate, e.g., of a partially acetylated compound, only the Purdie method is available. Although liquid ammonia does not react with esters at — 70°C., there is a danger of saponification if the temperature of the reaction mixture is allowed to rise before all the ammonia has been removed. The aqueous alkali employed in the methods of Haworth or Menzies will, of course, remove ester groups by hydrolysis. 

Methods of Formation.—The first sample of 4,6-dimethyl-D-glucose, prepared by Haworth and Sedgwick97 in 1926, came, together with tri-and tetramethylglucoses, from the incomplete methylation of glucose with methyl sulfate and sodium hydroxide. It was not characterized until about a decade later, when it was isolated by Bell and Synge98 from another source. 

Methylation of a carbohydrate is most practically achieved by using the Hakomori procedure,9 which has largely replaced the Purdie, Haworth, and Kuhn methylation methods. 

Since the methylation analysis of raffinose by Haworth and coworkers,114 the structure assigned (4) has been confirmed by chemical and enzymic methods.115... 

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