Amylopectin methylation

A 0.2-g sample of amylopectin was analyzed to determine the fraction of the total glucose residues that are branch points in the structure. The sample was exhaustively methylated and then digested, yielding 50 /tmol of 2,3-dimethylglucose and 0.4 /tmol of 1, 2, 3, 6-tetramethylglucose. 

Table I shows the results of periodate oxidation and methylation applied to amylopectins from various sources. If the percentage of amylose in a whole starch is known, the length of unit chain of the amylopectin component can be calculated from the results of periodate oxidation of the whole starch (see Table II). The length of unit chain appears to depend on the botanical species, but not the variety, from which the starch wras isolated. In the case of tapioca and corn amylopectins, sub-fractionation of these by precipitation with methanol, followed by periodate oxidation, showed the sub-fractions had the same degree of branching as the original amylopectins.71 The action of periodate on whole starches and amylopectins is now so well established and accurate, that it may well completely supersede the methylation technique for pure starches, in view of its many advantages.

The isolation of 2,3-dimethyl-D-glucose from the hydrolysis products of certain methylated polysaccharides has been an important factor in assigning structures to these polysaccharides. From trimethyl-starch it has been recovered in about 3% yield, together with 2,3,4,6-tetra-methyl- and 2,3,6-trimethyl-D-glucopyranose, and arises from the points of linkage of the repeating chains of the amylopectin component.67,69,70 From a dimethyl-starch the yield is considerably higher (75%).71 Other sources are the methylated capsular polysaccharide of Rhizobium radici-... 

Structural analysis of isolated amylose and amylopectin components has been carried out by standard methods based on methylation, periodate oxidation, and partial acid hydrolysis studies. Methylation and periodate oxidation studies established the linkage types and frequency of... 

Problem 22.44 Amylopectin, the water insoluble fraction of starch, behaves like amylose, except that more 2,3,4,6-tetra-O-methyl-D-glucose (5%), and an equal amount of 2.3-di-O-methyl-D-glucose, is formed. Deduce the structure of amylopectin. 

On the basis of researches devoted to the products of paitial or total hydrolytic breakdown of methylated starch, the chain of a-D-anhydroglucose is thought to constitute the main element of the amylose and amylopectin molecules. These units are combined as in maltose, i.e. by means of a-glucosidic linkages formed between the carbon atoms 1 and 4 ... 

Similarly, the hydrolysis of methylated amylopectin yields small quantities of 2,3-dimethylglucose and its isomeric ether, probably 2,6-dimethylglucose. The presence of the last two compounds confirms the branching of the chains (Fig. 166) at carbon atom 6, and perhaps 3. Staudinger [31] has therefore proposed the following formula for amylopectin (reproduced according to L. F. Fieser and M. Fieser [73]) ... 

Interest in the influence of lipids on pyrazine formation has recently been generated by the identification of long-chain alkyl-substituted heterocyclic compounds in foods and in model systems. Pyrazines in this category include 2-heptylpyrazine isolated from french fried potato flavor (7), and 2-methyl-3(or 6)-pentylpyrazine and 2,5-dimethyl-3-pentylpyrazine, isolated from extruded zein/corn amylopectin/corn oil systems (8, 9). Only the involvement of lipids or lipid-decomposition products in the formation of these compounds could account for the long-chain alkyl substitution on the pyrazine ring. 

Volatile compounds generated by model systems of zeln, corn amylopectin and corn oil extruded at barrel temepratures of 120°C and 165°C were analyzed by GC and GC/MS. The largest quantities of lipid oxidation products were detected in systems containing all three components. In each system, the quantity of 2,4-deca-dienal was low relative to the quantities of hexanal, heptanal and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pentyl-pyrazine, 2-methyl-3(or 6)-hexylpyrazine and 2,5-di-methyl-3-pentylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines. 4-Methylthiazole was identified as a major decomposition product of thiamin when corn meal containing 0.5% thiamin was extruded at a final temperature of 180°C. 

Explain the basis of this procedure for determining the number of (a 1 6) branch points in amylopectin. What happens to the unbranched glucose residues in amylopectin during the methylation and hydrolysis procedure ... 

One of the more important applications of methyl sulfoxide as a sugar solvent is for n.m.r. spectral studies, where, in conjunction with acetone-de, it has been used because exchange reactions are suppressed191 (see the n.m.r. section, p. 124). Methyl sulfoxide dissolves both amylose and amylopectin,192 and these can then be separated by the judicious use of co-solvents after dissolution.193 Ultracentri-... 

Amylopectin is a polysacccharide with a very high molecular weight. The yield of tetramethyl-D-glucopyranose from the methylated polysaccharide shows that the molecules must be highly branched. 

If a polysaccharide of the amylopectin type is branched, the methylated polysaccharide must on hydrolysis yield not only tri- and tetra-methyl-D-glucose but also dimethyl-D-glucose. Freudenberg " states... 

Exhaustive methylation of 32.4 mg of amylopectin followed by acid hydrolysis yielded 10 Amoles of 2,3,4,6-tetramethylglucose. (a) What are the other products How much of each were obtained (b) What percent of the glucose residues are linked via 1-6 bonds (c) 1 the MW of the amylopectin is 1.2 X 10 , how many branch point residues does a molecule of amylopectin contain ... 

Hydrogenation of oxystarch with Eaney nickel catalyst, followed by hydrolysis, gave erythritol. Simultaneous reduction and hydrolysis gave erythritol in yields of up to 71 %. Oxyamylopectin has been reduced with sodium borohydride to the corresponding polyhydric alcohol, which has been methylated both derivatives have been hydrolyzed, to give fragments enabling the structure of amylopectin to be deduced. 

Amylopectin is hydrolyzed to the single disaccharide (+)-maltose the sequence of methylation and hydrolysis yields chiefly 2,3,6-tri-O-methyl-D-glucose. Like amylose, amylopectin is made up of chains of D-glucose units, each unit joined by an alpha glycoside linkage to C-4 of the next one. However, its structure is more complex than that of amylose. 

Molecular weights determined by physical methods show that there are up to a million D-glucose units per molecule. Yet hydrolysis of methylated amylopectin gives as high as 5% of 2,3,4,6-tetra-O-methyl-D-glucose, indicating only 20 units per chain. How can these facts be reconciled by the same structure ... 

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