Textbook Question
Write the mechanism for the reaction of an amino acid with di-tert-butyl dicarbonate.
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Ch. 21 - Amino Acids, Peptides, and Proteins
Bruice8th EditionOrganic ChemistryISBN: 9780135213711
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Table of contents
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 1)31
- Ch. 1 - Remembering General Chemistry: Electronic Structure and Bonding (Part 2)65
- Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry84
- Ch. 3 - An Introduction to Organic Compounds:Nomenclature, Physical Properties, and Structure183
- Ch. 4 - Isomers: The Arrangement of Atoms in Space121
- Ch. 5 - Alkenes: Structure, Nomenclature, and an Introduction to Reactivity • Thermodynamics and Kinetics83
- Ch. 6 - The Reactions of Alkenes • The Stereochemistry of Addition Reactions175
- Ch. 7 - The Reactions of Alkynes • An Introduction to Multistep Synthesis119
- Ch. 8 - Delocalized Electrons: Their Effect on Stability, pKa, and the Products of a Reaction • Aromaticity and Electronic Effects: An Introduction to the Reactions of Benzene148
- Ch. 9 - Substitution and Elimination Reactions of Alkyl Halides212
- Ch. 10 - Reactions of Alcohols, Ethers, Epoxides, Amines, and Sulfur-Containing Compounds131
- Ch. 11 - Organometallic Compounds60
- Ch. 12 - Radicals90
- Ch. 13 - Mass Spectrometry; Infrared Spectroscopy; UV/Vis Spectroscopy62
- Ch. 14 - NMR Spectroscopy95
- Ch. 15 - Reactions of Carboxylic Acids and Carboxylic Acid Derivatives123
- Ch. 16 - Reactions of Aldehydes and Ketones • More Reactions of Carboxylic Acid Derivatives141
- Ch. 17 - Reactions at the Alpha-Carbon101
- Ch. 18 - Reactions of Benzene and Substituted Benzenes144
- Ch. 19 - More About Amines • Reactions of Heterocyclic Compounds49
- Ch. 20 - The Organic Chemistry of Carbohydrates80
- Ch. 21 - Amino Acids, Peptides, and Proteins57
- Ch. 22 - Catalysis in Organic Reactions and in Enzymatic Reactions35
- Ch. 23 - The Organic Chemistry of the Coenzymes—Compounds Derived from Vitamins1
- Ch. 28 - Pericyclic Reactions58
Chapter 22, Problem 74
Dithiothreitol reacts with disulfide bridges in the same way that 2-mercaptoethanol does. With dithiothreitol, however, the equilibrium lies much more to the right. Explain.
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Dithiothreitol (DTT) contains two thiol (-SH) groups that can react with disulfide bridges (RSSR) in proteins or other molecules. The reaction involves the reduction of the disulfide bond to two thiol groups (RSH) while DTT itself forms a cyclic disulfide.
The equilibrium of this reaction lies more to the right (favoring the products) because the formation of the cyclic disulfide in DTT is highly thermodynamically favorable. This is due to the stability of the five-membered ring formed in the product.
The five-membered ring in the oxidized form of DTT is stabilized by its geometry and intramolecular interactions, which lowers the energy of the product and shifts the equilibrium toward the right.
In contrast, 2-mercaptoethanol does not form a cyclic disulfide upon oxidation. Instead, it forms a linear disulfide, which is less stable compared to the cyclic disulfide of DTT. This makes the equilibrium for 2-mercaptoethanol less favorable toward the products.
Thus, the higher thermodynamic stability of the cyclic disulfide product in DTT explains why the equilibrium lies much more to the right compared to 2-mercaptoethanol.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Disulfide Bridges
Disulfide bridges are covalent bonds formed between the sulfur atoms of two cysteine residues in proteins. These bonds play a crucial role in stabilizing the three-dimensional structure of proteins. The reduction of disulfide bridges can lead to the unfolding of proteins, affecting their function.
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Disulfide Bonds Concept 2
Reducing Agents
Reducing agents are substances that donate electrons to other compounds, thereby reducing their oxidation state. In the context of disulfide bridges, reducing agents like dithiothreitol (DTT) and 2-mercaptoethanol break these bonds by providing electrons, converting disulfides back to free thiols. The effectiveness of a reducing agent is often determined by its ability to shift the equilibrium of the reaction.
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Equilibrium in Chemical Reactions
Equilibrium in chemical reactions refers to the state where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In the case of DTT, its ability to shift the equilibrium further to the right indicates a stronger tendency to reduce disulfide bridges compared to 2-mercaptoethanol, making it a more effective reducing agent in biological systems.
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Related Practice
Textbook Question
Glycine has pKa values of 2.3 and 9.6. Do you expect the pKa values of glycylglycine to be higher or lower than these values?
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Textbook Question
Show how valine can be prepared by
d. a N-phthalimidomalonic ester synthesis.
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Textbook Question
Show how valine can be prepared by
c. a reductive amination.
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Textbook Question
Reaction of a polypeptide with carboxypeptidase A releases Met. The polypeptide undergoes partial hydrolysis to give the following peptides. What is the sequence of the polypeptide?
1. Ser, Lys, Trp
2. Gly, His, Ala
3. Glu, Val, Ser
4. Leu, Glu, Ser
5. Met, Ala, Gly
6. Ser, Lys, Val
7. Glu, His
8. Leu, Lys, Trp
9. Lys, Ser
10. Glu, His, Val
11. Trp, Leu, Glu
12. Ala, Met
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Textbook Question
Show how valine can be prepared by
a. a Hell–Volhard–Zelinski reaction.