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

L and D Amino Acids

Organic Chemistry

29. Amino Acids

L and D Amino Acids

Previous problemNext problem

5:21 minutes

Problem 46

Textbook Question

Sometimes chemists need the unnatural D enantiomer of an amino acid, often as part of a drug or an insecticide. Most L-amino acids are isolated from proteins, but the D-amino acids are rarely found in natural proteins. D-amino acids can be synthesized from the corresponding L-amino acids. The following synthetic scheme is one of the possible methods.

(a) Draw the structures of intermediates 1 and 2 in this scheme.
(b) How do we know that the product is entirely the unnatural D configuration?

Verified step by step guidance

Step 1: Analyze the reaction scheme provided. The starting material is an L-amino acid with the general structure NH₂-CHR-COOH, where the amino group is in the L-configuration. The first reaction involves NaNO₂ and HCl, which converts the amino group into a diazonium salt intermediate (Intermediate 1). This step replaces the NH₂ group with a diazonium group (-N₂⁺).

Step 2: The second reaction involves NaN₃ (sodium azide), which reacts with the diazonium salt (Intermediate 1) to form Intermediate 2. In this step, the diazonium group (-N₂⁺) is replaced by an azide group (-N₃). This intermediate is crucial for the stereochemical inversion in the next step.

Step 3: The final reaction involves hydrogenation (H₂/Pd catalyst), which reduces the azide group (-N₃) in Intermediate 2 to an amino group (-NH₂). During this reduction, the stereochemistry at the chiral center is inverted, resulting in the D-configuration of the amino acid.

Step 4: To confirm that the product is entirely in the unnatural D-configuration, the stereochemical inversion during the hydrogenation step is key. The inversion occurs because the azide intermediate allows for a backside attack during the reduction process, flipping the configuration from L to D.

Step 5: The synthetic scheme ensures that the product is entirely in the D-configuration due to the stereochemical control in the reduction step. This is verified by analyzing the stereochemistry of the final product using techniques such as optical rotation or chiral chromatography.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Enantiomers and Chirality

Enantiomers are a pair of molecules that are non-superimposable mirror images of each other, often due to the presence of a chiral center, typically a carbon atom bonded to four different groups. Chirality is a fundamental concept in organic chemistry, particularly in the study of amino acids and pharmaceuticals, as the biological activity of molecules can differ significantly between enantiomers.

Synthesis of D-amino Acids

D-amino acids can be synthesized from their corresponding L-amino acids through various chemical reactions, such as racemization or specific enzymatic processes. Understanding the synthetic pathways and mechanisms involved is crucial for chemists to produce the desired enantiomer for applications in drug development and other fields.

Determining Configuration

To confirm that a product is entirely in the unnatural D configuration, chemists often use techniques such as optical rotation measurements or chiral chromatography. These methods allow for the analysis of the optical activity of the compound, which is directly related to its stereochemistry, thus providing evidence of the enantiomeric purity of the synthesized product.

Watch next

Master Representations of L-Configuration with a bite sized video explanation from Johnny

Start learning

Related Videos

Related Practice

Textbook Question

Draw three-dimensional representations of the following amino acids.

(a) L-phenylalanine

Textbook Question

Most naturally occurring amino acids have chiral centers (the asymmetric α carbon atoms) that are named (S) by the Cahn–Ingold–Prelog convention (Section 5-3). The common naturally occurring form of cysteine has a chiral center that is named (R), however.

(a) What is the relationship between (R)-cysteine and (S)-alanine? Do they have the opposite three-dimensional configuration (as the names might suggest) or the same configuration?

Textbook Question

Esterase is an enzyme that catalyzes the hydrolysis of esters. It hydrolyzes esters of l-amino acids more rapidly than esters of D-amino acids. How can this enzyme be used to separate a racemic mixture of amino acids?

Textbook Question

Draw the structure of the phenylthiohydantoin derivatives of

Textbook Question

Suggest how you would separate the free L-amino acid from its acylated D enantiomer in Figure 24-5.

Open Question

Provide the Fischer Projection representation of D-Aspartic Acid. Indicate if the chiral center is R or S.

Open Question

Convert the following Fischer Projection of L-Proline into a bondline structure.

Textbook Question

An opioid pentapeptide has the following structure: Tyr-Cys-Gly-Phe-Cys

a. Draw the structure of the pentapeptide including all the side chains.

b. Write its structure following mild oxidation.