What is the Difference Between Reductive Amination and Transamination

An amino group is a functional group in organic chemistry that consists of a nitrogen atom bonded to two hydrogen atoms. Reductive amination and transamination are both reactions involving amino groups.

What is the difference between reductive amination and transamination? Reductive amination uses aldehydes and ketones as substrates, while transamination uses amino acids and keto acids as substrates.

Key Areas Covered

1. What is Reductive Amination 
      – Definition, Features
2. What is Transamination
      – Definition, Features
3. Similarities Between Reductive Amination and Transamination
      – Outline of Common Features
4. Difference Between Reductive Amination and Transamination 
      – Comparison of Key Differences
5. FAQ: Reductive Amination and Transamination
      – Answers to Frequently Asked Questions

Key Terms

Reductive Amination, Transamination

What is Reductive Amination

Reductive amination is a chemical reaction that involves the conversion of a carbonyl compound (such as an aldehyde or a ketone) into an amine. The reaction occurs in two steps, as follows.

1. Imine formation – an imine intermediate is formed between the reaction of amine and a carbonyl compound. This is a reversible reaction, and it can be catalyzed with the help of an acid or a base.
2. Reduction – imine, thus formed, is reduced to amine. The reducing agent used here is usually sodium borohydride or lithium aluminum hydride.

The mechanism for reductive amination could be simplified into a few steps: nucleophilic attack, proton transfer, dehydration, and reduction. Furthermore, synthesis of benzylamine and amphetamine are good examples of reductive amination.

There are many applications of reductive amination. It is used in the production of primary, secondary, and tertiary amines. It is also used in the solid-phase synthesis of peptides and proteins and in the production of chemicals such as certain agrochemicals, pharmaceuticals, and dyes.

What is Transamination

Transamination involves the transfer of an amino group from an amino acid to a keto acid. This results in the formation of a new amino acid and a keto acid. This process helps to remove excess amino acids. Moreover, some examples of transamination are alanine-pyruvate transaminase (ALT), aspartate-oxaloacetate transaminase, and glutamate dehydrogenase.

The transamination reaction is catalyzed by enzymes called aminotransferases or transaminases. The mechanism of transamination is simplified as follows.

1. Formation of a Schiff base – a Schiff base intermediate is formed when an amino acid donates its amino group to pyridoxal phosphate (PLP).
2. Proton transfer – A proton is transferred from the alpha carbon of the amino acid to PLP. This results in the formation of a pyridoxal monophosphate (PMP) intermediate and a keto acid.  
3. Transfer of the amino group – PMP donates its amino group to the keto acid acceptor.

Similarities Between Reductive Amination and Transamination

1. Both reactions deal with the transfer or addition of amino groups.
2. Moreover, these reactions involve carbonyl groups.
3. In addition, both reactions are catalyzed by specific enzymes.

Difference Between Reductive Amination and Transamination

Definition

• Transamination involves the transfer of an amino group from one amino acid to a keto acid while reductive amination directly adds an amino group to a keto acid using ammonia.

Nature

• Transamination requires a pyridoxal phosphate (PLP) cofactor, whereas reductive amination often uses NADH or NADPH as a reducing agent.

Substrates

• Reductive amination uses aldehydes and ketones as substrates, while transamination uses amino acids and keto acids as substrates.

Result

• While transamination produces a new amino acid and a keto acid, reductive amination produces a new amino acid and water.

Reversibility

• Transamination can be reversible, but reductive amination is generally irreversible.

Catalysis

• Transamination is catalyzed by transaminases (aminotransferases), while reductive amination is catalyzed by amino acid dehydrogenases.

Conclusion

Reductive amination and transamination are both reactions involving amino groups. Reductive amination creates a new amino acid from an aldehyde or ketone, while transamination transfers an amino group from one amino acid to another. Thus, this is the main difference between reductive amination and transamination.

FAQ: Reductive Amination and Transamination

1. What is a reductive amination?

Reductive amination is a chemical reaction that converts a carbonyl group (aldehyde or ketone) into an amine. It involves the formation of an intermediate imine, followed by reduction using a reducing agent.

2. Why is it called reductive amination?

Reductive amination is called that because it involves two key steps: reduction of an imine or enamine intermediate to an amine and amination of a carbonyl compound to form the imine or enamine.

3. What is the difference between transamination and oxidative deamination?

The basic difference between transamination and oxidative deamination is that transamination transfers an amino group between molecules, while oxidative deamination removes an amino group, releasing ammonia.

4. What is the disadvantage of reductive amination?

A disadvantage of reductive amination is the potential for over-reduction. This can lead to the formation of secondary or tertiary amines. The reaction can sometimes be slow or require harsh conditions.

5. What is the best reducing agent for reductive amination?

Sodium cyanoborohydride is often considered the best reducing agent for reductive amination. This is because of its selectivity for imines over carbonyl compounds.

Reference:

1. “Reductive Amination.” Science Direct.
2. “Transamination.” Science Direct.

Image Courtesy:

1. “RedveAm” By Smokefoot – Own work (CC BY 4.0) via Commons Wikimedia
2. “Transaminierung” By Alcibiades – Own work (Public Domain) via Commons Wikimedia