Hakomori methylation method

The Hakomori method of methylation may be applied to mono- or poly-saccharides, and detailed procedures are available. Methylation in methyl sulfoxide appears to be similar to the method of Kuhn in that furanoside formation at the reducing group is favored, and, where this is undesirable, preliminary methylation with diazomethane is recommended. ... 

The Hakomori method has also been used extensively in the methylation of carbohydrates however, yields were typically low and non-sugar products were observed. Subsequent studies by Ciucanu and Kerek [40] led to the conclusion that OH and H were more effective bases than the methylsulfinyl carbanion. These authors developed a new method for the permethylation of carbohydrates using CH3I and solid NaOH in DMSO. This reaction is relatively clean, proceeds to completion in about 6-7 min, and gives very high yields ( 98%). The derivatization may also be performed with KOH, NaH (excess) and sodium t-butoxide. Ciucanu and Kerek have extensively reviewed the experimental parameters and have published a table of procedures, reagents, reaction times and yeilds for various other versions of Ihe permethylation reaction [40]. 

Methvlatlon. Gas-llquld Chromatography and Mass Spectrometry. The methylation of the monosaccharides, oligosaccharides and reference compounds was performed by the Hakomori method and analysis was done... 

The free polysaccharides were permethylated by the Hakomori method, hydrolyzed with 90% formic acid at 100-110°C for 8 hrs., and then with 2 M trifluoroacetic acid at 100-110°C for 3 hrs. The hydrclyzates were then reduced with sodium borohydride and acetylated wirh acetic anhydride in pyridine. The partially methylated alditol acetates thus obtained were analyzed with a Hewlett-Packard 5790 gas chromatograph. 

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. 

Methylation analysis was run by the method of Hakomori ( ), followed by hydrolysis with trifluoracetic acid, sodium borohydride reduction, and acetylation. 6LC was performed on a Hewlett-Packard 5970, used as an inlet for a mass spectrometer. Molecular weight was determined on a Sephacryl S-500 column (2.6 x 70 cm), using deionized water as solvent, upward flow, 2.75 ml/min, and detection by refractive index monitor. Model R-401 (Waters Associates). 

Methylation is the most widely used method to determine the position of the glycosyl linkages.Permethylation of glycolipids can be done according to the methods of Hakomori (32) and Ciucanu and Kerek (33). The permethylated derivatives are hydrolyzed and the products converted into partially methylated alditol acetates and identified by gas chromatography-mass spectrometry ( CG-MS) (34). 

The most important development in methylation technique is due to Hakomori, who used as the base methylsulfinyl carbanion, formed by reaction of methyl sulfoxide with sodium hydride, and thus extended to carbohydrates the reaction developed by Corey and Chaykovsky/ In certain cases, completely methylated polysaccharide may be obtained in high yield by one treatment within an hour. This method was used by Sandford and Conrad in a re-examination of the polysaccharide from Aerobacter aerogenes, and their paper should be consulted for the excellent experimental details contained therein. These authors showed that this polysaccharide has a simple, repeating structure, and previous suggestions that it is complicated and highly branched arose from interpretation based on products of incomplete methylation. 

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." ... 

ViLKAS, E., and E. Lederer N-methylation de peptides par la methode de Hakomori Structure du mycoside Cb 1. Tetrahedron Lett. 3089 (1968). 

Ltd., respectively, and recrystallized from water. TM-3 CyD was synthesized by the method of Hakomori (10) and its methylation was confirmed by elemental analysis and H-NMR. 

NH groups of the peptide bonds employing, for example, methyl iodide and silver oxide in dimethylformamide 154) or Hakomori s method using methylsulfinyl carbanion (755). Methylation of peptides not only increases their volatility, but also improves cleavage of the peptide bonds, thus giving a clearer spectrum (756). 

Substitution reactions at secondary hydroxyls are generally performed either for analysis of structure or to serve a protective function during other reactions. Etherification of the nonanomeric hydroxyls was an important structural tool in the analysis of oligosaccharide and polysaccharide structure. Methyl ethers have been employed for structural determination for more than 75 years. Thus, methyl ether formation in a polysaccharide results in substitution only at free hydroxyls. Subsequent analysis of the methylated derivatives reveals positions previously occupied in glycosidic linkage. Reagents used for this purpose have evolved from dimethylsulfate to the commonly employed method of Hakomori using sodium hydride and dimethylsulfoxide. 

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