The amount of branching (the number of (1-6) bonds) in amylopectin can be determ

Question

The amount of branching (the number of (1-6) bonds) in amylopectin can be determined by methylation. A sample of amylopectin is treated with a methylating agent that replaces the hydrogen of every sugar hydroxyl with a methyl group (all available -OH is converted to -OCH3). All the glycosidic bonds are then hydrolyzed with acid and the amount of 2,3-di-O-methylglucose formed is determined (the -OH at carbons 2 and 3 of glucose are -OCH3). Explain the basis of this procedure for determining the number of branch points in amylopectin. What happens to the unbranched glucose molecules in amylopectin during the methylation and hydrolysis steps? i.e. what is the product of these steps for unbranched glucoses?

Explanation / Answer

The rocedure for methylation and and hydrolysis for amylopecting would yield a derrivatised cyclic amylopectin product. On the other hand an unbranced glucose upon hydrolysis would have a ring opening reaction and would yield a linear chain methylated products along with the aldehyde transformed into dimethylacetal derrivative.

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