Polysaccharides partially methylated, preparation

The importance of the methyl ethers of D-mannose lies largely in their occurrence in structural studies in the polysaccharide field. Since previous articles in this series14 have discussed the basic principles involved in the preparation and elucidation of the structure of partially methylated aldoses, it is not intended to give unnecessary details in cases where general procedures are already familiar. 

Of the numerous alkyl protecting groups known [8, 9], only those widely used in synthetic chemistry of carbohydrates will be discussed. Methyl ethers — with hundreds of selective methylations far exceeding the scope of the review — were excluded for their unimportant role as synthetic intermediates (great majority of partial methylations are carried out to complete the list of reference compounds for the methylation analysis of polysaccharides, or simply to prepare ethers widely occurring in biologically important molecules). 

Earlier attempts by Elarreri and by Macbeth and Mackay to prepare tri-O-inethylglyeogen (OMe, 45.6%) by direct methylation of the polysaccharide had not been successful, but gave partially methylated products of OMe 32-37 %. Haworth and coworkers found, however, that by simultaneous deacetylation and methylation of glycogen triacetate, followed by five or six further methylations, a trimethyl ether (OMe, 43.7) could be isolated in 90 % yield. The preliminary acetylation, during which degrada-... 

In connection with the analysis of ollgo- and polysaccharides by the permethylation - "ionic hydrogenation" procedure, a series of partially methylated anhydro-D-alditol acetates has been prepared by reductive cleavage of permethyl and partially methylated methyl glycosides and a library of capillary g.c. retention times and e.l.- and c.i.-m.s. data compiled. The usefulness of this data was demonstrated in the analysis of a microgram quantity of a... 

Mixtures containing nearly all possible partially methylated alditol acetates have been prepared as standards for the methylation analysis of cell-wall polysaccharides. Incomplete Hakamori methylation (1.e. limiting amounts of potassium dimsyl) of neutral monosaccharides with purification of the derivatives on a C g reversed-phase column was followed by standard hydrolysis, reduction, and acetylation. Relative capillary g.c. retention data was... 

However, one of the first matrices used for insolubilization of the aflBnant was cellulose that had been partially etherified with 3-hydroxy-phenoxy or 4-diazobenzyl groups (which react with diazotized protein or protein, respectively). Amino compounds may also be attached to the acid chlorides of carboxy polysaccharides.0-(3-Allyloxy-2-hydroxy-propyl)-cellulose and -Sephadex can be mercuriated and, in this form, used for isolation of thiolated antibodies and fractionation of mononucleotides according to their aflBnity for an organomercurial. Another mercurial, prepared by treatment of 0-(2-aminoethyl)Sephadex with IV-acetylhomocysteine thiolactone to give a thiol (49) which, on treatment with 2,5-bis[(acetoxymercuri) methyl]-1,4-dioxane, gives 50, can also be used in aflSnity chromatography of thiolated proteins. 

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