Definition of Amadori rearrangement
Definition of Amadori rearrangement
Amadori rearrangement is a very important mechanism in carbohydrate chemistry for the formation of osazone from glucose and fructose.
When glucose and fructose react with phenyl hydrazine the
corresponding osazone derivatives are obtained. Actually both the osazone
derivatives are identical.
In the first step of the reaction the phenylhydrazine derivative so formed in each case undergoes a very important rearrangement by which a second carbonyl function is generated in the molecule, is known as Amadori rearrangement.
In the first step of the reaction the phenylhydrazine derivative so formed in each case undergoes a very important rearrangement by which a second carbonyl function is generated in the molecule, is known as Amadori rearrangement.
Again phenyl hydrazine reacts with the newly generatedcarbonyl function and finally we get the osazone derivative in addition aniline
and ammonia are generated.
Osazone formation of glucose and fructose involve only C1 and C2 Amadori rearrangement does not occur beyond C2 .
This is due to the fact that the osazone so formed is stabilized through intra molecular hydrogen bonding and forms stable 6-membered cyclic ring. Two hydrogen bonded structures are possible which are shown below.
Why β-D –glucopyranose is oxidized 250 times faster than α-D- gluco pyranose by bromine-water?
The α and β-D gluco pyranose forms are as follows,
The bromine water oxidation of α and β-D glucopyranose form produces lactone directly. The mechanism of this oxidation is not certain but a possibility is the oxidation of the anomeric hydroxyl group.
The β-form which is more stable favors the oxidation than the α-form and occurs about 250 times faster rate.The mechanism of this reaction is shown below.
Summary
- What is Amadori rearrangement ?
- Why β-D-glucopyranose is oxidized 250 times faster than α-D-glucopyranose by bromine-water ?
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