Dehydro-L-Proline
Chapter 2
21. An amino acid having the constitution shown has been isolated from horse chestnuts. It is configurationally related to L-proline and has the R configuration at C-3. Write a stereochemically correct representation for this compound.
The addition of carbene by the cuprous chloride catalyzed the decomposition of diazomethane to 3,4-dehydro-l-proline, which led to a combination of cis-3,4-methylene-l-proline and trans-3,4-methylene-l-proline in a proportion of 1:3.5. In addition, the cis amino acid was the same as the natural amino acid secluded from seeds of ‘Aesculus parviflora’ by a modified technique. Furthermore, detailed X-ray analysis of the hydrochloride of the cis amino acid and of the trans amino acid gave complete bond angles, distances, and computer stereograms. Afterwards, both the cis and the trans amino acids approached a boat conformation through bicyclic scheme; which proves the evaluation of the nuclear magnetic resonance (NMR) data. The pyrrolidine ring of both the acids has all four carbons in a plane, whereas the nitrogen atom and the cyclopropyl carbon are relocated to the same side of the plane. In this matter, the …show more content…
conformation of the hetero ring varies significantly from all other natural pyrrolidine amino acids. The synthesized horse-chestnut amino acid has a nomenclature of cis-3,4-methylene-l-proline, which proves that it is configurationally related to l-proline. Furthermore, at C-3, the priority of the substituents decreases in clockwise direction, thus, it is R configuration. In conclusion, the stereochemically correct representation for this compound is:
Chapter 3
12. trans-3-Alkyl-2-chlorocyclohexanones (alkyl = methyl, ethyl, 2-propyl) exist in the diequatorial conformation. In contrast, the corresponding O-methyl oximes exist as diaxial conformers. Explain the preference for the diaxial conformation of the oxime ethers. A sequence of trans-3-alkyl-2-chlorocyclohexanones was formulated and revealed to exist primarily in the diequatorial chair conformation.
However, the formation of the oximes and various oxime products resulted in an incredible conformational inversion for the ethyl, isopropyl, and methyl systems. Furthermore, through the analysis of vicinal interproton coupling constants, it is believed that these compounds exist mainly in the diaxial chair conformation. To verify this, an X-ray crystallography was carried out, and the result undeniably shows that the configuration of chair with diaxial substituents is favored in the solid state. It is presumed that the origin of this preference is the result of a strong hyperconjugative stabilization of the axial conformation; also known as the ‘vinylogous anomeric
effect”.
The reason why the oxime ethers prefer the diaxial conformation appears to be because of the π → σ* and σ → π* hyperconjugation between the oximino and chloro substituents. To define, hyperconjugation is the weak interaction between sigma bonds with p orbitals; it explains why alkyl substituents stabilize carbocations. In addition, as hyperconjugation also exists in the ketone, the question that is raised is why the oximino ethers are more disposed to the diaxial conformation. The information that the oximino ethers assume the diaxial conformation designates that the hyperconjugative stabilization is larger for the oximes than the ketones. To sum up, this indicates that the π → σ* component must be major, as a larger donor ability is expected for the oxime ethers.
21. An amino acid having the constitution shown has been isolated from horse chestnuts. It is configurationally related to L-proline and has the R configuration at C-3. Write a stereochemically correct representation for this compound.
The addition of carbene by the cuprous chloride catalyzed the decomposition of diazomethane to 3,4-dehydro-l-proline, which led to a combination of cis-3,4-methylene-l-proline and trans-3,4-methylene-l-proline in a proportion of 1:3.5. In addition, the cis amino acid was the same as the natural amino acid secluded from seeds of ‘Aesculus parviflora’ by a modified technique. Furthermore, detailed X-ray analysis of the hydrochloride of the cis amino acid and of the trans amino acid gave complete bond angles, distances, and computer stereograms. Afterwards, both the cis and the trans amino acids approached a boat conformation through bicyclic scheme; which proves the evaluation of the nuclear magnetic resonance (NMR) data. The pyrrolidine ring of both the acids has all four carbons in a plane, whereas the nitrogen atom and the cyclopropyl carbon are relocated to the same side of the plane. In this matter, the …show more content…
conformation of the hetero ring varies significantly from all other natural pyrrolidine amino acids. The synthesized horse-chestnut amino acid has a nomenclature of cis-3,4-methylene-l-proline, which proves that it is configurationally related to l-proline. Furthermore, at C-3, the priority of the substituents decreases in clockwise direction, thus, it is R configuration. In conclusion, the stereochemically correct representation for this compound is:
Chapter 3
12. trans-3-Alkyl-2-chlorocyclohexanones (alkyl = methyl, ethyl, 2-propyl) exist in the diequatorial conformation. In contrast, the corresponding O-methyl oximes exist as diaxial conformers. Explain the preference for the diaxial conformation of the oxime ethers. A sequence of trans-3-alkyl-2-chlorocyclohexanones was formulated and revealed to exist primarily in the diequatorial chair conformation.
However, the formation of the oximes and various oxime products resulted in an incredible conformational inversion for the ethyl, isopropyl, and methyl systems. Furthermore, through the analysis of vicinal interproton coupling constants, it is believed that these compounds exist mainly in the diaxial chair conformation. To verify this, an X-ray crystallography was carried out, and the result undeniably shows that the configuration of chair with diaxial substituents is favored in the solid state. It is presumed that the origin of this preference is the result of a strong hyperconjugative stabilization of the axial conformation; also known as the ‘vinylogous anomeric
effect”.
The reason why the oxime ethers prefer the diaxial conformation appears to be because of the π → σ* and σ → π* hyperconjugation between the oximino and chloro substituents. To define, hyperconjugation is the weak interaction between sigma bonds with p orbitals; it explains why alkyl substituents stabilize carbocations. In addition, as hyperconjugation also exists in the ketone, the question that is raised is why the oximino ethers are more disposed to the diaxial conformation. The information that the oximino ethers assume the diaxial conformation designates that the hyperconjugative stabilization is larger for the oximes than the ketones. To sum up, this indicates that the π → σ* component must be major, as a larger donor ability is expected for the oxime ethers.