A student is attempting to add asparagine to a methionine that is connected to a solid polystyrene bead. They mix together the two components below with DCC, and some of the indicated product is generated. However, more happens in this mixture, resulting in multiple products. What reactivity is happening, and how can it be avoided (to give the indicated product in high yield)?
A student is attempting to add asparagine to a methionine that is connected to a solid polystyrene bead. They mix together the two components below with DCC, and some of the indicated product is generated. However, more happens in this mixture, resulting in multiple products. What reactivity is happening, and how can it be avoided (to give the indicated product in high yield)?
Biochemistry
9th Edition
ISBN:9781319114671
Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.
Chapter1: Biochemistry: An Evolving Science
Section: Chapter Questions
Problem 1P
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Question
A student is attempting to add asparagine to a methionine that is connected to a solid polystyrene bead. They mix together the two components below with DCC, and some of the indicated product is generated. However, more happens in this mixture, resulting in multiple products. What reactivity is happening, and how can it be avoided (to give the indicated product in high yield)?
![**Peptide Bond Formation Reaction**
**Reaction Scheme:**
--O S-
| |
H₂N—C—NH₂ + H₂N—C—CO—Ph → [With DCC] → H₂N—C—NH—C—NH₂
| | | | | |
H—C—OH H—H
**Explanation of the Reaction:**
In this reaction, a peptide bond is formed between two amino acids using dicyclohexylcarbodiimide (DCC) as a coupling reagent.
**Reactants:**
1. The left reactant is a protected amino acid, specifically with an amide group (NH₂) and a carboxylic acid group (OH) adjacent to it.
2. The right reactant is another amino acid but with a protecting group on the amine side chain, specifically a benzyloxycarbonyl (Cbz) group (C₆H₅-CH₂-O-C(=O)-).
**Product:**
The reaction yields a dipeptide, where a peptide bond (C—NH) forms between the amino group of the left reactant and the carboxyl group of the right reactant.
**Mechanism:**
1. The DCC activates the carboxyl group of the right reactant, making it more electrophilic.
2. The amine group from the left reactant then attacks the activated electrophilic carbon to form an amide bond, releasing a molecule of dicyclohexylurea as a byproduct.
This reaction is essential in organic chemistry and biochemistry for synthesizing peptides and proteins, wherein long chains of amino acids are linked via peptide bonds.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fbc4fc54f-d9be-4a25-ba56-f776739e96ca%2Fc614dd63-9b6d-4200-b1ca-a717a5a2253e%2Fxf1vb8c_processed.jpeg&w=3840&q=75)
Transcribed Image Text:**Peptide Bond Formation Reaction**
**Reaction Scheme:**
--O S-
| |
H₂N—C—NH₂ + H₂N—C—CO—Ph → [With DCC] → H₂N—C—NH—C—NH₂
| | | | | |
H—C—OH H—H
**Explanation of the Reaction:**
In this reaction, a peptide bond is formed between two amino acids using dicyclohexylcarbodiimide (DCC) as a coupling reagent.
**Reactants:**
1. The left reactant is a protected amino acid, specifically with an amide group (NH₂) and a carboxylic acid group (OH) adjacent to it.
2. The right reactant is another amino acid but with a protecting group on the amine side chain, specifically a benzyloxycarbonyl (Cbz) group (C₆H₅-CH₂-O-C(=O)-).
**Product:**
The reaction yields a dipeptide, where a peptide bond (C—NH) forms between the amino group of the left reactant and the carboxyl group of the right reactant.
**Mechanism:**
1. The DCC activates the carboxyl group of the right reactant, making it more electrophilic.
2. The amine group from the left reactant then attacks the activated electrophilic carbon to form an amide bond, releasing a molecule of dicyclohexylurea as a byproduct.
This reaction is essential in organic chemistry and biochemistry for synthesizing peptides and proteins, wherein long chains of amino acids are linked via peptide bonds.
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