2.3.4.6- Tetra-O-methyl-D-glucose

Problem 22.39 (u) Give the structure of sucrose (cane and beet sugar) from the following information (1) It is hydrolyzed by maltase or emulsin to a mixture of d-( )-glucose and D-(-)-fructose. (2) It does not reduce Fehling s solution and does not mutarotate. (3) Methylation and hydrolysis gives 2,3,4.6-tetra-O-methyl-D-glucose and a tetramethyl-D-fructose. (b) What structural features are uncertain ... 

Problom 22.43 Methylation and hydrolysis of amylose (Problem 22.42) also gives 0.2-0.4% 2,3,4.6-tetra-O-methyl-D-glucose. Explain the origin of this compound. ... 

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. 

Treatment of 15 with l,5-diazabicyclo[5.4.0]undec-5-ene (DBU) in benzene resulted in /3-elimination, but under these conditions, the liberated 2,3,4,6-tetra-O-methyl-D-glucose was further degraded, probably with formation of 3-deoxy-2,4,6-tri-0-methyl-D-erc/fhro-hex-2-enopyranose. In order to prevent this degradation, the reaction of 15 with DBU was carried out in the presence of acetic anhydride. The reaction mixture gave, after chromatography on silica gel, methyl (methyl 4-deoxy-2,3-di-0-methyl-a-L-threo-hex-4-enopyranosid)uron-ate (65) and a mixture of the 1-acetates of 2,3,4,6-tetra-O-methyl-a- and -/3-D-glucose (66). 

Oxidation of the carboxyl-reduced and acetylated Pneumococcus type 2 capsular polysaccharide revealed that only one L-rhamnose residue in the hexasaccharide repeating-unit, later demonstrated to have the structure 60, was oxidized and, consequently, /3-L-linked.156 Replacement of 2,3,6-tri-O-methyl-D-glucose in the methylation analysis of the original polysaccharide by 2,3,4,6-tetra-O-methyl-D-glucose in that of the oxidized polysaccharide established that this L-rhamnose residue is linked to 0-4 of a D-glucose residue. The analysis also showed that it was an L-rhamnose residue in the chain (and not the branching L-rhamnose residue) that was /3-linked. 

Methylation of verbascose, and hydrolysis, gave21 2,3,4,6-tetra-O-methyl-D-galactose (identified as the crystalline anilide), 2,3,4-tri-O-methyl-D-galactose (crystalline, identified by converting it into the 6-0-trityl derivative), 1,3,4,6-tetra-O-methyl-D-fructose (identified by analytical data and by its optical rotation), and a tri-O-methyl-D-glucose which, on further methylation, was converted into 2,3,4,6-tetra-O-methyl-D-glucose (identified through the crystalline anilide). 

Tetra-O-methyl-D-glucose 1 2.3.4.6- Tetra-O-methyl-D-mannose J 3... 

Early evidence that the open-chain formula is, in itself, inadequate to explain the behavior of the glycosylamines emerged from the methylation experiments of Irvine and his coworkers." iV-Phenyl-D-glucosylamine was methylated to afford a crystalline tetramethyl ether which was hydrolyzed by acid to 2,3,4,6-tetra-O-methyl-D-glucose. Condensation of the latter compound with aniline afforded the original ether, which consequently must be 2,3,4,6-tetra-O-methyl-iV-phenyl-D-glucosylamine. 

Oxidation by bromine water converts (+)-maltose into ihe monocarboxylic acid D-maltobionic acid. Treatment of this acid with methyl sulfate and sodium hydroxide yields (octa-O-methyl-D-maltobionic acid. Upon hydrolysis in acidic solution, the methylated acid yields two products, 2,3,5,6-tetra-O-methyl-o-gluconic acid and 2,3,4,6-tetra-O-methyl-D-glucose. 

Problem 35.2 The position of the free —OH group in 2,3,4,6-tetra-O-methyl-D-glucose was shown by tpc products of oxidative cleavage, as described in Sep. 34ASl What products would be expected from oxidative cleavage of 2,3,5,6-tetra-O-meihyl-D-gluconic acid ... 

Thus each molecule of completely methylated amylose that is hydrolyzed should yield one molecule of 2,3,4,6-tetra-O-methyl-D-glucose from the number of molecules of tri-O-methyl-D-glucose formed along with each molecule of the tetramethyl compound, we can calculate the length of the amylose chain. 

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