28. Carbohydrates

Which of the following are reducing sugars? Comment on the common name sucrose for table sugar.

(c) a-D-allopyranose

(d) ethyl b-D-ribofuranoside

Which of the following are reducing sugars? Comment on the common name sucrose for table sugar.

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(f) <IMAGE>

Name the following compounds and indicate whether or not each is a reducing sugar:

b. <IMAGE>

Name the following compounds and indicate whether or not each is a reducing sugar:

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A hexose is obtained when the residue of a shrub Sterculia setigeria undergoes acid-catalyzed hydrolysis. Identify the hexose from the following experimental information: it undergoes mutarotation; it does not react with Br2; and d-galactonic acid and d-talonic acid are formed when it reacts with Tollens’ reagent.

When the gum of the shrub Sterculia setigera is subjected to acidic hydrolysis, one of the water-soluble components of the

hydrolysate is found to be tagatose. The following information is known about tagatose:

(1) Molecular formula C6H12O6

(2) Undergoes mutarotation.

(3) Does not react with bromine water.

(4) Reduces Tollens reagent to give d-galactonic acid and d-talonic acid.

(5) Methylation of tagatose (using excess CH3 I and Ag2O) followed by acidic hydrolysis gives

1,3,4,5-tetra-O-methyltagatose.

(a) Draw a Fischer projection structure for the open-chain form of tagatose.

Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?

(a) 4-O-(a-D-glucopyranosyl)-D-galactopyranose

Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?

(b) a-D-fructofuranosyl-b-D-mannopyranoside

Which of the following sugars are reducing sugars? Which ones would undergo mutarotation?

(c) 6-O-(b-D-galactopyranosyl)-D-glucopyranose