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Cα-Cβ and Cα-N bond cleavage in the dissociation of protonated N-benzyllactams: dissociative proton transfer and intramolecular proton-transport catalysis.
Org Biomol Chem. 2012 Jan 28; 10(4):791-7.OB

Abstract

In mass spectrometry of protonated N-benzylbutyrolactams, the added proton is initially localized on the carbonyl oxygen, which is the thermodynamically preferred protonation site. Upon collisional activation, dissociative proton transfer takes place leading to the occurrence of fragmentation reactions. The major fragmentations observed are the cleavages of C(α)-C(β) and C(α)-N bonds on the two sides of the methylene linker, which is different to the cleavage of the amide bond itself seen in most amide cases. Theoretical calculations and isotopic labeling experiments demonstrate that the phenyl ring regulates the proton transfer reactions. The proton directly migrates to the C(β) position via a 1,5-H shift leading to the efficient loss of benzene, while it stepwise migrates to the amide nitrogen resulting in the formation of a benzyl cation. The stepwise proton transfer is achieved via intramolecular proton-transport catalysis. The C(γ) position accepts the proton from the carbonyl oxygen via a 1,6-H shift, and then donates it to the amide nitrogen via a 1,4-H shift. The general 1,3-H shift from the carbonyl oxygen to the amide nitrogen can be excluded in this case due to its significant energy barrier. The substituent effects are also applied to explore the reaction mechanism, and it proves that both C(β) and C(γ) are involved in the dissociative proton transfer processes. For monosubstituted N-benzylbutyrolactams, the abundance ratios of the two competing product ions are well correlated with the nature of the substituents.

Authors+Show Affiliations

Department of Chemistry, Zhejiang University, Hangzhou, China.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

22120184

Citation

Chai, Yunfeng, et al. "Cα-Cβ and Cα-N Bond Cleavage in the Dissociation of Protonated N-benzyllactams: Dissociative Proton Transfer and Intramolecular Proton-transport Catalysis." Organic & Biomolecular Chemistry, vol. 10, no. 4, 2012, pp. 791-7.
Chai Y, Guo C, Jiang K, et al. Cα-Cβ and Cα-N bond cleavage in the dissociation of protonated N-benzyllactams: dissociative proton transfer and intramolecular proton-transport catalysis. Org Biomol Chem. 2012;10(4):791-7.
Chai, Y., Guo, C., Jiang, K., Pan, Y., & Sun, C. (2012). Cα-Cβ and Cα-N bond cleavage in the dissociation of protonated N-benzyllactams: dissociative proton transfer and intramolecular proton-transport catalysis. Organic & Biomolecular Chemistry, 10(4), 791-7. https://doi.org/10.1039/c1ob06020a
Chai Y, et al. Cα-Cβ and Cα-N Bond Cleavage in the Dissociation of Protonated N-benzyllactams: Dissociative Proton Transfer and Intramolecular Proton-transport Catalysis. Org Biomol Chem. 2012 Jan 28;10(4):791-7. PubMed PMID: 22120184.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Cα-Cβ and Cα-N bond cleavage in the dissociation of protonated N-benzyllactams: dissociative proton transfer and intramolecular proton-transport catalysis. AU - Chai,Yunfeng, AU - Guo,Cheng, AU - Jiang,Kezhi, AU - Pan,Yuanjiang, AU - Sun,Cuirong, Y1 - 2011/11/28/ PY - 2011/11/29/entrez PY - 2011/11/29/pubmed PY - 2012/4/14/medline SP - 791 EP - 7 JF - Organic & biomolecular chemistry JO - Org Biomol Chem VL - 10 IS - 4 N2 - In mass spectrometry of protonated N-benzylbutyrolactams, the added proton is initially localized on the carbonyl oxygen, which is the thermodynamically preferred protonation site. Upon collisional activation, dissociative proton transfer takes place leading to the occurrence of fragmentation reactions. The major fragmentations observed are the cleavages of C(α)-C(β) and C(α)-N bonds on the two sides of the methylene linker, which is different to the cleavage of the amide bond itself seen in most amide cases. Theoretical calculations and isotopic labeling experiments demonstrate that the phenyl ring regulates the proton transfer reactions. The proton directly migrates to the C(β) position via a 1,5-H shift leading to the efficient loss of benzene, while it stepwise migrates to the amide nitrogen resulting in the formation of a benzyl cation. The stepwise proton transfer is achieved via intramolecular proton-transport catalysis. The C(γ) position accepts the proton from the carbonyl oxygen via a 1,6-H shift, and then donates it to the amide nitrogen via a 1,4-H shift. The general 1,3-H shift from the carbonyl oxygen to the amide nitrogen can be excluded in this case due to its significant energy barrier. The substituent effects are also applied to explore the reaction mechanism, and it proves that both C(β) and C(γ) are involved in the dissociative proton transfer processes. For monosubstituted N-benzylbutyrolactams, the abundance ratios of the two competing product ions are well correlated with the nature of the substituents. SN - 1477-0539 UR - https://www.unboundmedicine.com/medline/citation/22120184/Cα_Cβ_and_Cα_N_bond_cleavage_in_the_dissociation_of_protonated_N_benzyllactams:_dissociative_proton_transfer_and_intramolecular_proton_transport_catalysis_ L2 - https://doi.org/10.1039/c1ob06020a DB - PRIME DP - Unbound Medicine ER -