Amadori rearrangement

What is Amadori rearrangement?

The Amadori rearrangement was first reported by Amadori in 1925. It is the transformation of N-glycosides of aldoses into N-glycosides of corresponding ketoses under acidic condition, or more generally the conversion of aldimines into ketoamines. The reaction results in the formation of an unstable intermediate, known as an Amadori compound, which subsequently rearranges to form a more stable compound, such as a Schiff base or an Amadori product.

Amadori rearrangement - general reaction scheme - Amadori compound - Amadori product
Amadori rearrangement

The Amadori rearrangement is an important reaction in the field of food science, as it plays a crucial role in the Maillard reaction, which is responsible for the formation of flavor, aroma, and color in cooked and processed foods. The Maillard reaction is a complex series of reactions that occur between reducing sugars and amino acids when food is heated, and it is responsible for the development of the characteristic flavors and aromas of baked goods, grilled meats, and many other foods..

In addition to its importance in food science, the Amadori rearrangement also plays a key role in the formation of advanced glycation end products (AGEs) in the body. AGEs are a group of compounds that form when reducing sugars react with proteins and lipids, and they are thought to contribute to the development of chronic diseases such as diabetes and atherosclerosis..

The Amadori rearrangement is a reversible reaction, which means that the intermediate Amadori compound can be converted back into the original sugar and amino acid or protein. However, once the reaction has progressed to the formation of a Schiff base or an Amadori product, it becomes irreversible..

The rate of the Amadori rearrangement is influenced by several factors, including the concentration of the reactants, the pH of the solution, and the presence of catalysts or inhibitors. The reaction is also affected by temperature, with higher temperatures generally resulting in faster rates of reaction..

Summary

The Amadori rearrangement is a key chemical reaction in the field of food science, as well as in the formation of advanced glycation end products in the body. It plays a crucial role in the Maillard reaction, which is responsible for the development of flavor, aroma, and color in cooked and processed foods. Understanding the mechanisms of Amadori rearrangement and how it can be controlled can be important for the food industry and for understanding the pathogenesis of certain chronic diseases..

Example

One example of the Amadori rearrangement is the reaction between glucose and amino acid lysine. The initial reaction between glucose and lysine forms an unstable intermediate, the Amadori compound:

Glucose + Lysine → Amadori compound

This intermediate then rearranges to form a more stable compound, the Amadori product:

Amadori compound → Amadori product

The specific structure of the Amadori product depends on the reducing sugar and the amino acid or protein that are reacting, but the general mechanism of the reaction is the same..

Another example of the Amadori rearrangement is the reaction between fructose and the amino acid arginine.

Fructose + Arginine → Amadori compound → Amadori product

It is remarkable to note that the Amadori product that is formed in this reaction will differ from the one formed in the reaction between glucose and lysine due to the different structure of the fructose and arginine..

Mechanism of reaction

The mechanism of the Amadori rearrangement can be broken down into several steps:

  • The first step is the formation of an unstable intermediate, known as an Amadori compound. In this step, a reducing sugar, such as glucose or fructose, reacts with an amino acid or protein through a non-enzymatic process. The reaction forms a hemiacetal or hemiketal intermediate, where the aldehyde or ketone group of the sugar reacts with the amino group of the amino acid or protein..
  • In the second step, the Amadori compound rearranges to form a more stable compound, known as an Amadori product. This rearrangement is a result of the migration of an electron pair from the oxygen atom of the hemiacetal or hemiketal intermediate to the carbon atom. This creates a double bond between the carbon and oxygen atoms, resulting in a more stable compound..
  • The final step is the further reaction of the Amadori product, forming various other chemical products such as a Schiff base, which is a compound formed by the addition of an amino acid or protein to a carbonyl group..
Amadori rearrangement mechanism
Reaction mechanism of Amadori rearrangement

It’s worth noting that the specific structure of the Amadori product depends on the reducing sugar and the amino acid or protein that are reacting, and the formation of the Amadori product can also depend on the pH, temperature, and concentration of the reactants..

The Amadori rearrangement is a reversible reaction, which means that the intermediate Amadori compound can be converted back into the original sugar and amino acid or protein. However, once the reaction has progressed to the formation of a Schiff base or an Amadori product, it becomes irreversible..

References

  • Amadori, M., Atti Accad. Nazl. Lincei, 1925, 2, 337. (Chem. Abstr., 1926, 20, 902.)
  • Amadori, M., Atti Accad. Nazl. Lincei. 1929, 9, 68. (Chem. Abstr., 1929, 23, 3211.)
  • Amadori, M., Atti Accad. Nazl. Lincei., 1929, 9, 226. (Chem. Abstr., 1929, 23, 3443.)
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