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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2:18 minutes

Problem 10b

Textbook Question

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

Verified step by step guidance

Identify the starting material: Leucine is a branched-chain amino acid. To synthesize leucine, we need to start with a suitable alkane or alkyl group that can be functionalized to introduce both the amino group (-NH2) and the carboxylic acid group (-COOH). A good starting material could be isocaproic acid (a branched alkane with a carboxylic acid group).

Perform bromination: Bromination is typically carried out using Br2 in the presence of light or a radical initiator. This step introduces a bromine atom to the alkane chain via a free radical halogenation mechanism. For example, brominate the isocaproic acid at the appropriate carbon to create a bromo intermediate.

Prepare for amination: The brominated intermediate can now undergo nucleophilic substitution. The bromine atom is a good leaving group, and it can be replaced by an amino group (-NH2) using an excess of ammonia (NH3) in a solvent like ethanol. This step introduces the amino group to the molecule.

Adjust the stereochemistry: If the synthesis requires a specific stereochemistry (e.g., the L-isomer of leucine), you may need to use a chiral auxiliary or resolve the racemic mixture formed during the amination step.

Finalize the structure: Ensure that the molecule has both the amino group (-NH2) and the carboxylic acid group (-COOH) in the correct positions to match the structure of leucine. If necessary, perform any additional functional group modifications or purifications to obtain the desired amino acid.

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Key Concepts

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

Bromination

Bromination is a chemical reaction that involves the addition of bromine to a compound, typically an alkene or an aromatic ring. This process can introduce bromine atoms into organic molecules, which can later be substituted or transformed into other functional groups. In the context of amino acid synthesis, bromination can serve as a key step to modify a precursor compound, making it more reactive for subsequent reactions.

Amination

Amination refers to the process of introducing an amino group (-NH2) into a molecule. This reaction is crucial in organic synthesis, particularly for the formation of amino acids, as it allows for the conversion of halogenated compounds (like those produced by bromination) into amines. The choice of amination method can influence the final structure and properties of the synthesized amino acid, such as leucine.

Synthesis of Amino Acids

The synthesis of amino acids involves a series of chemical reactions that transform simple organic compounds into more complex structures containing both amine and carboxylic acid functional groups. Understanding the specific pathways and reactions, such as bromination followed by amination, is essential for creating amino acids like leucine. This process often requires knowledge of stereochemistry and functional group transformations to ensure the correct amino acid is produced.

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Textbook Question

Which of the following C-terminal peptide bonds is more readily cleaved by carboxypeptidase A? Explain your choice.

Ser-Ala-Leu or Ser-Ala-Asp

Textbook Question

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

(a)

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

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

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

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

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