Methyl sugars

No molecular-ion peak is observed from either isomer. The loss of a methoxyl group to give m/e 131 is shown in Equation 16 to be from the C—1 position, on the basis of analogy to reported studies using per-O-methylated sugars with a methoxyl-d3 substituent on C-l (24). 

Methyl desoxyglycyrrhetate 61 Methyidigoxin 104 Methyl glycyrrhetate 61 Methyl iodide reagent 70 N-Methylphenylalanine 89 Methylsuccinic acid 249 Methyl sugars 188... 

Several methylated sugars have been identified in hydrolyzates of LPS, cell-wall polysaccharides, and extracellular polysaccharides. A considerable number of these have been found in the LPS from photosynthetic prokaryotes. Two polysaccharides from Mycobacterium species, a glucan" and a mannan" are remarkable in that they contain high percentages of methylated sugars. Glycolipids from Mycobacterium species are also rich in methylated sugars, some of which have not been found elsewhere, but this is beyond the scope of the present article. 

The different methylated sugars known as components of bacterial polysaccharides are summarized in Table 1. When possible, references to publications in which the methylated sugar is part of a known structure are preferred to references in which the component has merely been identified. References to sugars of undetermined configuration or absolute configuration have been omitted when there is reason to assume that they are identical to better characterized compounds from other sources. 

In the carbohydrate field, pH values outside the range 3 to 5 should be avoided whenever possible. When such factors as the presence of blocking groups render this infeasible, some reactions can still be performed at pH s of 7.5264 and 5.7.266 The partially methylated sugars,67 68 69a 60 the highly hindered glycols,261 and certain amino alcohols,9 98 100 101 l03 6 are exceptions and tend to be most readily oxidized at a pH of 7.5. 

For the preparation of partially methylated sugars direct methylation is not as a rule a suitable process, for the mixture of isomers thus produced can be fractionated only with difficulty. Instead, it is customary to introduce protecting substituents prior to methylation and to remove them afterwards. As will be seen later, this is the method used in the synthesis of mono-, di-, and tri-methylglucoses. 

IV. Degradation of the Permethylated Sample, and Analysis of the Partially Methylated Sugars... 

Separation of the partially methylated sugars by g.l.c. gives evidence on the methyl-substitution pattern complementary to that obtained from the mass spectrum. The electron-impact, mass spectra do not differentiate between the sugar isomers (such as the galactose,... 

The molar ratio of the different methylated derivatives of neutral sugars is generally calculated from the g.l.c. responses (using flame-ionization detection). In this kind of quantitation, the molar response of the different methylated sugars is assumed to be the same,7 or effective carbon-response is used.53... 

One special feature in the interpretation of the quantitative results seems not to have been exploited in practical analysis, and it certainly deserves attention. The result of the methylation analysis is sometimes complex, and can reveal the occurrence of 10 to 20 different methylated sugars. In this situation, it is not easy to decide, by simple inspection of the analytical data, whether the result could be caused by one complex, carbohydrate chain, or by a structure containing several saccharide chains bound to a common aglycon. In addition, it is not always easy to decide whether the result could fit any natural structure, or mixture of structures, or whether the complex result is attributable to undermethylation. 

Methylation of the undegraded gum by the same procedure as that used for the degraded product, namely, by treatment of the thallium salt with methyl iodide (a veiy useful method when the methyl sulfate treatment fails - ) gave the corresponding methylated gum which afforded upon hydrolysis those methylated sugars listed in the second column of... 

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