Ch. 21 - Amino Acids, Peptides, and Proteins

Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook

Bruice 8th Edition

Ch. 21 - Amino Acids, Peptides, and Proteins

Problem 64

Chapter 22, Problem 64

Draw the product obtained when a lysine side chain in a polypeptide reacts with maleic anhydride.

Verified step by step guidance

Step 1: Identify the reactive groups in the lysine side chain and maleic anhydride. The lysine side chain contains a primary amine (-NH2) group, which is nucleophilic. Maleic anhydride contains an anhydride functional group, which is electrophilic and reactive towards nucleophiles.

Step 2: Understand the reaction mechanism. The primary amine group of lysine will attack one of the carbonyl carbons in the maleic anhydride through nucleophilic addition. This opens the anhydride ring, forming an amide bond and a carboxylic acid group.

Step 3: Consider the stereochemistry and connectivity. The reaction typically results in the formation of a single product where the lysine side chain is covalently bonded to the maleic anhydride derivative. Ensure the structure reflects the correct connectivity between the amine group and the maleic anhydride.

Step 4: Draw the product structure. The lysine side chain will now be attached to the maleic anhydride derivative via an amide bond. The remaining portion of the maleic anhydride will have a carboxylic acid group due to the ring opening.

Step 5: Verify the product. Ensure that the product structure is consistent with the reaction mechanism and that all atoms are accounted for. Double-check the functional groups and connectivity to confirm the accuracy of the drawn product.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Lysine Structure and Reactivity

Lysine is an amino acid with a side chain containing an amino group (-NH2) that is positively charged at physiological pH. This reactivity allows lysine to participate in nucleophilic reactions, where it can attack electrophilic centers in other molecules, such as maleic anhydride. Understanding lysine's structure is crucial for predicting its behavior in chemical reactions.

Maleic Anhydride Chemistry

Maleic anhydride is a cyclic anhydride that is highly reactive due to its electrophilic carbonyl groups. It can undergo nucleophilic addition reactions with amines, leading to the formation of stable adducts. Recognizing the reactivity of maleic anhydride is essential for understanding how it interacts with nucleophiles like the lysine side chain.

Nucleophilic Addition Reaction

Nucleophilic addition is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophile, resulting in the formation of a new bond. In this case, the amino group of lysine acts as the nucleophile, attacking the electrophilic carbonyl carbon of maleic anhydride. This reaction is key to forming the product of the reaction between lysine and maleic anhydride.

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Related Practice

Textbook Question

α-Amino acids can be prepared by treating an aldehyde with ammonia/trace acid, followed by hydrogen cyanide, followed by acid-catalyzed hydrolysis.

a. Draw the structures of the two intermediates formed in this reaction.

1429

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Textbook Question

Explain the difference in the pK_a values of the carboxyl groups of alanine, serine, and cysteine

1658

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Textbook Question

After the polypeptide shown below was treated with maleic anhydride, it was hydrolyzed by trypsin. (After a polypeptide is treated with maleic anhy- dride, trypsin will cleave the polypeptide only on the C-side of arginine.)

Gly-Ala-Asp-Ala-Leu-Pro-Gly-Ile-Leu-Val-Arg-Asp-Val-Gly-Lys-Val-Glu-Val-Phe-Glu-Ala-Gly- Arg-Ala-Glu-Phe-Lys-Glu-Pro-Arg-Leu-Val-Met-Lys-Val-Glu-Gly-Arg-Pro-Val-Gly-Ala-Gly-Leu-Trp

a. After a polypeptide is treated with maleic anhydride, why does trypsin no longer cleave it on the C-side of lysine?

b. How many fragments are obtained from the polypeptide?

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Textbook Question

α-Amino acids can be prepared by treating an aldehyde with ammonia/trace acid, followed by hydrogen cyanide, followed by acid-catalyzed hydrolysis.

b. What amino acid is formed when the aldehyde that is used is 3-methylbutanal?

c. What aldehyde is needed to prepare isoleucine?

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Textbook Question

Identify the location and type of charge on the hexapeptide Lys-Ser-Asp-Cys-His-Tyr at each of the following pH values:

c. pH=7

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Textbook Question

Identify the location and type of charge on the hexapeptide Lys-Ser-Asp-Cys-His-Tyr at each of the following pH values:

d. pH=12

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