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Chapter 31: Problem 725

D-Raffinose is a trisaccharide that does not react with Fehling's solution. Upon hydrolysis it produces \(\mathrm{D}\) - glucose, D-galactose, and D-fructose. Completely methylated raffinose is hydrolyzed to \(2,3,4-\) tri- O -methylglucose, \(1,3,4,6-\) tetra-O-methylfrueto se, and \(2,3,4,6-\) tetra- \(\mathrm{O}-\) methylgalactose. What structures for raffinose are consistent with these data? What further information, if any, is required to identify completely the structure of raffinose?

Short Answer

Expert verified
D-Raffinose is a trisaccharide consisting of D-glucose, D-fructose, and D-galactose monosaccharides linked together. Based on the methylation pattern of the hydrolyzed products, D-raffinose has D-glucose connected at its first carbon atom to the second carbon atom of D-fructose, which in turn is connected at its first carbon atom to the first carbon atom of D-galactose. Thus, the structure can be represented as D-glucose (1→2) D-fructose (1→1) D-galactose. However, to completely identify the structure, additional information is needed about the type of glycosidic bonds (α or β) between the monosaccharides.

Step by step solution

01

Analyze the given information for D-raffinose hydrolysis

D-raffinose is a trisaccharide that hydrolyzes to D-glucose, D-galactose, and D-fructose. This means that it consists of these three monosaccharides linked together in some configuration.
02

Analyze the given information for completely methylated D-raffinose hydrolysis

When completely methylated D-raffinose is hydrolyzed, it produces 2,3,4-tri-O-methylglucose, 1,3,4,6-tetra-O-methylfructose, and 2,3,4,6-tetra-O-methylgalactose. This information will help us in finding the possible linkage points in D-raffinose.
03

Determine monosaccharide connections

Based on the methylation pattern of the hydrolyzed products, the connection points on the monosaccharides can be inferred: - In D-glucose, the 2,3,4 positions are methylated, meaning the original connection point must be at the 1 position. - In D-fructose, the 1,3,4,6 positions are methylated, meaning the original connection point must be at the 2 position. - In D-galactose, the 2,3,4,6 positions are methylated, meaning the original connection point must be at the 1 position.
04

Propose a structure for D-raffinose

Given the connection points determined in Step 3, D-raffinose has D-glucose connected at its first carbon atom to the second carbon atom of D-fructose, which in turn is connected at its first carbon atom to the first carbon atom of D-galactose. Therefore, the structure can be represented as: D-glucose (1→2) D-fructose (1→1) D-galactose.
05

Determine if further information is needed

To completely identify the structure of D-raffinose, we need information about the type of glycosidic bonds (α or β) between the monosaccharides. Since this information is not given, additional information is required to fully identify the structure.

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Most popular questions from this chapter

Show how the structure of maltose can be deduced from the following evidence: (a) The sugar is hydrolyzed by yeast \(\alpha\) -D-glucosidase to \(\mathrm{D}\) glucose. (b) Maltose mutarotates and forms a phenylosazone. Methylation with dimethyl sulfate in basic solution followed by acid hydrolysis gives \(2,3,4,6\) -tetra- \(\mathrm{O}\) -methyl-Dglucopyranose and \(2,3,6-\) tri-O-methyl- D-glucose. (c) Bromine oxidation of maltose followed by methylation and hydrolysis gives \(2,3,4,6\) -tetra-O-methyl-D- glucopyranose and a tetramethyl-D-gluconic acid which readily forms a \(\gamma\) -lactone.

How can the D-glucoside units of cellulose produce a polymer with a stronger, more compact physical structure than the D-glucose units of starch?

Will 2-deoxyribose form an osazone? Why?

(a) A certain sugar and its methyl glycoside can be isolated in both \(\alpha-\) and \(\beta\) -anomeric forms. Also, the ring structure of the glycoside is known to be present in the pyranose form. How could you ascertain from rotation data whether or not the parent sugar also exists in the pyranose form? (b) A D-glucose derivative with a 1,2 -epoxide ring gives a methy, \(\beta\) -D-glucoside on solvolysis with methanol. Explain how this reaction helps to establish the configuration of the \(\alpha-\) and \(\beta\) -anomers of D-glucose.

When methyl \(\alpha-\mathrm{D}-\) glucoside was treated with \(\mathrm{HIO}_{4}\), it yielded 1 mole of formic acid, plus a product (A). Write the structure of \(\mathrm{A}\). When a methyl glycoside of unknown structure (B) was similarly treated with \(\mathrm{HIO}_{4}\), only 1 mole of \(\mathrm{HIO}_{4}\), was consumed, and no formic acid was produced, but the same product (A) was obtained. Draw the configurational structure of \(\mathrm{B}\).
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