2.3- Di-O-methyl-D-glucose

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. 

The answer is found in the following fact along with the trimethyl and tetra-methyl compounds, hydrolysis yields 2,3-di-O-methyl-D-glucose and in an amount nearly equal to that of the tetramethyl derivative. 

The preceding explanation of the failure of a 2-0-substituted aldose to form saccharinic acids (on treatment with alkali) finds substantiation in the results of a study of the action of lime-water, at room temperature, on 2,3-di-O-methyl-D-glucose. The presence, in this latter reaction mixture, of an fl[,/3-unsaturated aldehyde(IV, R = CH3) was established by its further, facile conversion to 5-(hydroxymethyl)-2-furaldehyde upon acidification. 

Neither are saccharinates formed from 2,3-di-O-methyl-D-glucose (XIII) which, in alkaline solution, has an absorption band corresponding to that of an a,(3-unsaturated carbonyl derivative (XIV). The trisaccharide, a-L-fucopyranosyl-(l— 2)- 8-D-galactopyranosyl-(l— 4)-D-glucose,... 

Di-O-Methyl-D- glucose (23) asperoside, krisbnoside 56 Streblus asper ... 

The enol ether (23) has been obtained from 2-0-methyl-D-glucose and from 2,3-di-O-methyl-D-glucose. Klemer, Lukowski, and Zerhusen isolated a crystalline form of (23) with C ]d + 16° no mutarotation was mentioned. They assumed their compound to be pyranoid by analogy with (24). The nuclear magnetic resonance spectrum of the reaction mixture from 2,3-di-O-methyl-D-glucose showed the presence of equimolar amounts... 

Hydrolysis of methylated amylopectin yielded 2,3,6-tri-O-methyl-D-glucose, 2,3,4,6-tetra-O-methyl-D-glucose and 2,3-Di-O-methyl-D-glucose in the approximate respective ratio of 90 5 5. Following the approach in the analysis of amylose, amylopectin can be depicted as ... 

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