Demethylation of methylated sugars

Demethylation of methylated sugars by means of hydrogen peroxide in the presence of ferrous ions (the Fenton reagent) has been re-... 

Column and paper-chromatographic methods for the separation, identification, and estimation of methylated monosaccharides have been developed, and are satisfactory, provided that the appropriate reference compounds are available. Recent developments in this field are the ready demethylation of methylated sugars with boron trichloride and the use of gas-liquid partition chromatography for the analysis of mixtures of methylated sugars. ... 

Quebrachitol, 2-0-methyl-L-inositol, occurs in many plants and can be readily recovered from the latex of Hevea brasiliensis, the common Malayan rubber tree. (-(-)-Pinitol, 3-O-methyl-D-inositol, is a common constituent of many plants, particularly conifers, and can be readily isolated from the heartwood of the sugar pine, Pinus lambertiana. The enantiomorph, (—)-pinitol, has also been found in Nature. All these methyl ethers are demethylated to the parent inositols by boiling hydriodic acid. 

Reduction of the nitro group of 545-547 in the presence of Raney nickel catalyst respectively afforded the corresponding 4-amino-pento-, -hexo-, and -hepto-pyranosides 548-550. Methyl 4-amino-2,3,4,6-tetradeoxy-a- and -/3-DL-en/t/iro-hexopyranoside (549), characterized as the A -benzoyl derivative, was identical in its H-n.m.r.-speetral data with the analogous derivative of the natural, antibiotic sugar tolyposamine. On the other hand, reductive demethyl-ation of 549 with formaldehyde-Raney nickel (under 3.5 kg/cm2 pressure of hydrogen) was effected, to yield another antibiotic sugar, methyl DL-forosaminide (551). 

Sugar methylation is the last step during REB biosynthesis (Scheme 20.2). A rebM-disrupted mutant of Lech, aerocolonigenes accumulated 4 -0-demethyl-REB (17),... 

Evidence that the n-glucosidic interchain linkages in starch are, in fact, (l->6)-a-n in nature came originally from the isolation of small proportions of 2,3-di-O-methyl-n-glucose after methylation and hydrolysis. This evidence was, however, hardly definitive, as the small amounts of this dimethyl sugar obtained could equally well have arisen as a result of undermethylation or demethylation. The isolation of isomaltose after the action of crude, bacterial alpha-amylase on the polysaccharides is equally equivocal. No pure alpha-amylase is known that gives isomaltose as a product of its action on starch, and it is likely that this product was formed by a contaminating enzyme in the crude preparation of olpho-amylase used. 

Contrary to previous reports Caroff and Szabo have shown that cleavage of permethylated oligo- and poly-saccharides containing amino-sugars, by either acid hydrolysis, acetolysis, or methanolysis, does not cause cleavage of A -methyl groups, but may result in some 0-demethylation. ... 

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