Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

29. Amino Acids

Proteins and Amino Acids

Organic Chemistry

29. Amino Acids

Proteins and Amino Acids

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3:48 minutes

Problem 16

Textbook Question

Give equations for the formation and hydrogenolysis of N-benzyloxycarbonyl methionine.

Verified step by step guidance

Identify the structure of N-benzyloxycarbonyl methionine. This compound is a derivative of methionine where the amino group (-NH2) is protected by a benzyloxycarbonyl (Cbz) group. The general structure of the Cbz group is C6H5CH2OCO-.

Write the reaction for the formation of N-benzyloxycarbonyl methionine. This typically involves reacting methionine with benzyl chloroformate (C6H5CH2OCOCl) in the presence of a base (e.g., NaOH or NaHCO3) to neutralize the HCl byproduct. The reaction can be represented as: \( \text{H2N-CH(CH2CH2SCH3)-COOH} + \text{C6H5CH2OCOCl} \rightarrow \text{C6H5CH2OCO-NH-CH(CH2CH2SCH3)-COOH} + \text{HCl} \).

Explain the purpose of the benzyloxycarbonyl (Cbz) group. It is a protecting group used to temporarily block the amino group (-NH2) during chemical reactions to prevent unwanted side reactions. This is particularly useful in peptide synthesis.

Write the reaction for the hydrogenolysis of N-benzyloxycarbonyl methionine. Hydrogenolysis involves the removal of the Cbz group using hydrogen gas (H2) in the presence of a palladium catalyst (e.g., Pd/C). The reaction can be represented as: \( \text{C6H5CH2OCO-NH-CH(CH2CH2SCH3)-COOH} + \text{H2} \xrightarrow{\text{Pd/C}} \text{H2N-CH(CH2CH2SCH3)-COOH} + \text{C6H5CH3} + \text{CO2} \).

Summarize the overall process. The formation of N-benzyloxycarbonyl methionine involves protecting the amino group of methionine with a Cbz group using benzyl chloroformate. The hydrogenolysis step removes the Cbz group, regenerating the free amino group and producing toluene (C6H5CH3) and carbon dioxide (CO2) as byproducts.

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Key Concepts

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

N-benzyloxycarbonyl (Z) Group

The N-benzyloxycarbonyl (Z) group is a protective group used in organic synthesis, particularly in peptide chemistry. It protects the amine group of amino acids during reactions, preventing unwanted side reactions. The Z group can be removed under specific conditions, allowing for the subsequent functionalization of the amino acid.

Hydrogenolysis

Hydrogenolysis is a chemical reaction that involves the cleavage of a bond by hydrogen in the presence of a catalyst, typically resulting in the removal of a protecting group. In the context of N-benzyloxycarbonyl methionine, hydrogenolysis would involve the reduction of the Z group to yield the free amino acid. This reaction is crucial for the synthesis of peptides and proteins.

Formation of N-benzyloxycarbonyl Methionine

The formation of N-benzyloxycarbonyl methionine involves the reaction of methionine with benzyloxycarbonyl chloride (Z-Cl) in the presence of a base. This reaction results in the attachment of the Z group to the amino group of methionine, creating a protected amino acid that can be used in peptide synthesis without interference from the amine.

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Related Practice

Textbook Question

Show how the following amino acids might be formed in the laboratory by reductive amination of the appropriate α-ketoacid.

(a) alanine

Textbook Question

Show how you would synthesize any of the standard amino acids from each starting material. You may use any necessary reagents.

(b)

Textbook Question

Show how you would use bromination followed by amination to synthesize the following amino acids.

(b) leucine

Textbook Question

The herbicide glyphosate (Roundup®) kills plants by inhibiting an enzyme needed for synthesis of phenylalanine. Deprived of phenylalanine, the plant cannot make the proteins it needs, and it gradually weakens and dies. Although a small amount of glyphosate is deadly to a plant, its human toxicity is quite low. Suggest why this powerful herbicide has little effect on humans.

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

Textbook Question

Show the peptides that would result from cleavage by the indicated reagent:

a. Val-Arg-Gly-Met-Arg-Ala-Ser by carboxypeptidase A

b. Ser-Phe-Lys-Met-Pro-Ser-Ala-Asp by cyanogen bromide

c. Arg-Ser-Pro-Lys-Lys-Ser-Glu-Gly by trypsin

Textbook Question

Show how valine can be prepared by

d. a N-phthalimidomalonic ester synthesis.