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

25. Condensation Chemistry

Condensation Reactions

Organic Chemistry

25. Condensation Chemistry

Condensation Reactions

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Problem 78

Textbook Question

Propose a mechanism for the rearrangement of the thiazoline obtained from the reaction of Edman's reagent with a peptide to a PTH-amino acid. (Hint: Thioesters are very reactive toward nucleophiles.)

Verified step by step guidance

Identify the starting material: The thiazoline is formed from the reaction of Edman’s reagent (phenyl isothiocyanate, Ph-N=C=S) with the N-terminal amino group of the peptide. This forms a cyclic intermediate known as thiazoline.

Recognize the reactivity of thioesters: Thioesters are highly reactive toward nucleophiles due to the poor overlap between the sulfur atom's orbitals and the carbonyl carbon, making the carbonyl carbon more electrophilic.

Propose the nucleophilic attack: A water molecule (acting as a nucleophile) attacks the electrophilic carbonyl carbon of the thioester in the thiazoline ring. This leads to the opening of the thiazoline ring and the formation of a tetrahedral intermediate.

Facilitate the rearrangement: The tetrahedral intermediate collapses, expelling the sulfur-containing group and forming a new carbonyl group. This results in the formation of the phenylthiohydantoin (PTH) derivative of the amino acid.

Conclude the mechanism: The final product is the PTH-amino acid, which is stable and can be identified to determine the N-terminal amino acid of the peptide.

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Key Concepts

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

Thiazoline Chemistry

Thiazolines are five-membered heterocycles containing both sulfur and nitrogen. In the context of Edman's reagent, thiazolines are formed when the reagent reacts with the amino group of a peptide. Understanding the structure and reactivity of thiazolines is crucial for proposing a rearrangement mechanism, as their unique properties influence how they interact with other molecules.

PTH-Amino Acid Formation

Phenylthiohydantoin (PTH) amino acids are derivatives formed during the Edman degradation process, which is used for sequencing peptides. The conversion of thiazoline to PTH-amino acids involves a series of nucleophilic attacks and rearrangements. Recognizing the steps involved in this transformation is essential for accurately proposing the mechanism of rearrangement.

Reactivity of Thioesters

Thioesters are highly reactive compounds that can undergo nucleophilic attack due to the electrophilic nature of the carbonyl carbon. In the context of the rearrangement mechanism, the hint suggests that thioesters formed during the reaction can react with nucleophiles, facilitating the conversion of thiazoline to PTH-amino acids. Understanding this reactivity is key to predicting the pathway of the rearrangement.

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