A. Determine the structure of the disaccharide based on the following data: a. I

Question

A. Determine the structure of the disaccharide based on the following data:
a. It is a reducing sugar, and undergoes mutarotation in aqueous solution.
b. It is hydrolyzed by ?-hydrolase enzymes, but not ?-hydrolase enzymes, to form Dgalactose
and L-glucose.
c. Methylation and hydrolysis produces 2,3,4,6-tetra-O-methyl-D-galactose and 3,5,6-tri-Omethyl-
L-glucose.
d. Oxidation with bromine water followed by methylation and acidic hydrolysis produces
2,3,4,6-tetra-O-methyl-D-galactose and 3,4,5,6-tetra-O-methyl-L-gluconic acid.
Draw the structure of the disaccharide as a Haworth projection.

B. Determine the structure of an unknown sugar based on the following data:

a. It is not a reducing sugar, and does not undergo mutarotation in aqueous solution.

b. When hydrolyzed by dilute acid, it produces D-mannose, D-galactose, and 1,4-hydroquinone (4-hydroxyphenol).

c. When treated with an a-hydrolase enzyme, it produces D-galactose and a nonreducing glycoside (A), but when treated with B-hydrolase enzyme, it produces a hydroquinoneand a reducing disaccharide (B).

d. When the unknown sugar is methylated (using dimethyl sulfate and aqueous sodium hydroxide) then hydrolyzed with dilute acid, it produces 2,3,4,6-tetra-O-methyl-D-galactose, 2,3,6-tri-O-methyl-D-mannose, and 4-methoxyphenol.

e. When (A) is methylated, then hydrolyzed with dilute acid, it produces 2,3,5,6-tetra-O-methyl-D-mannose and 4-methoxyphenol.

Draw the structure of the sugar as Haworth projection.

Explanation / Answer

A. Lactose

When it is hydrolyzed,produces glucose & galactose

After methylation + hydrolysis it produces methylated glucose & galactose

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