Textbook Question
Show the steps in the synthesis of the tetrapeptide in Problem 34, using Merrifield's method.
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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 37
Write the mechanism for the reaction of a cysteine side chain with iodoacetic acid.
Verified step by step guidance1
Step 1: Identify the reactive groups in the cysteine side chain and iodoacetic acid. The cysteine side chain contains a thiol (-SH) group, which is nucleophilic. Iodoacetic acid contains an electrophilic carbon attached to iodine, making it susceptible to nucleophilic attack.
Step 2: The thiol group of cysteine performs a nucleophilic attack on the electrophilic carbon of iodoacetic acid. This occurs as the sulfur atom donates a pair of electrons to the carbon, displacing the iodine atom as a leaving group.
Step 3: The displacement of iodine results in the formation of a thioether bond between the sulfur atom of cysteine and the carbon of iodoacetic acid. This is a substitution reaction (SN2 mechanism).
Step 4: The product formed is a modified cysteine residue where the thiol group is now alkylated with the carboxymethyl group from iodoacetic acid. This modification is often used in biochemistry to block the thiol group or to introduce a functional group.
Step 5: Ensure the reaction conditions are suitable for the mechanism to proceed, such as maintaining a neutral or slightly basic pH to keep the thiol group deprotonated and nucleophilic.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Cysteine Structure and Reactivity
Cysteine is an amino acid containing a thiol (-SH) group in its side chain, which makes it nucleophilic. This thiol group can participate in various chemical reactions, including nucleophilic substitutions. Understanding the structure of cysteine is crucial for predicting its reactivity with electrophiles like iodoacetic acid.
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Isoelectric Point of Cysteine
Nucleophilic Substitution Mechanism (SN2)
The SN2 mechanism involves a nucleophile attacking an electrophile, resulting in the simultaneous displacement of a leaving group. In this case, the thiol group of cysteine acts as the nucleophile, attacking the carbon atom of iodoacetic acid that is bonded to iodine, leading to the formation of a thioester. This mechanism is characterized by a single concerted step and is essential for understanding the reaction pathway.
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01:47Nucleophiles and Electrophiles can react in Substitution Reactions.
Electrophiles and Leaving Groups
Electrophiles are species that accept electron pairs from nucleophiles during chemical reactions. In this reaction, iodoacetic acid serves as the electrophile, with the iodine atom acting as a good leaving group due to its ability to stabilize the negative charge after departure. Recognizing the roles of electrophiles and leaving groups is vital for analyzing reaction mechanisms in organic chemistry.
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07:22The 3 important leaving groups to know.
Related Practice
Textbook Question
Show the steps in the synthesis of the tetrapeptide Leu-Phe-Ala-Val.
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Textbook Question
Three peptides were obtained from a trypsin digestion of two different polypeptides. In each case, indicate the possible sequences from the given data and tell what further experiment should be carried out in order to determine the primary structure of the polypeptide.
a. polypeptide I:
1. Val-Gly-Asp-Lys
2. Leu-Glu-Pro-Ala-Arg
3. Ala-Leu-Gly-Asp
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Textbook Question
A decapeptide undergoes partial hydrolysis to give peptides whose amino acid compositions are shown. Reaction of the intact decapeptide with Edman's reagent releases PTH-Gly. What is the sequence of the decapeptide?
1. Ala, Trp
2. Val, Pro, Asp
3. Pro, Val
4. Ala, Glu
5. Trp, Ala, Arg
6. Arg, Gly
7. Glu, Ala, Leu
8. Met, Pro, Leu, Glu
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Textbook Question
a. Calculate the overall yield of bradykinin when the yield for the addition of each amino acid to the chain is 70%.
b. What would be the overall yield of a peptide containing 15 amino acids if the yield for the incorporation of each is 80%
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Textbook Question
Indicate the peptides produced from cleavage by the indicated reagent:
a. His-Lys-Leu-Val-Glu-Pro-Arg-Ala-Gly-Ala by trypsin
b. Leu-Gly-Ser-Met-Phe-Pro-Tyr-Gly-Val by chymotrypsin
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