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Huang L, Ye L, Li XH, Li ZL, Lin JS, Liu XY. Stereoselective Radical Cyclization Cascades Triggered by Addition of Diverse Radicals to Alkynes To Construct 6(5)–6–5 Fused Rings. Org Lett 2016; 18:5284-5287. [DOI: 10.1021/acs.orglett.6b02599] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Lin Huang
- Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China
| | - Liu Ye
- Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China
| | - Xiao-Hua Li
- Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China
| | - Zhong-Liang Li
- Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China
| | - Jin-Shun Lin
- Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China
| | - Xin-Yuan Liu
- Department of Chemistry, South University of Science and Technology of China, Shenzhen 518055, China
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Wille U. ‘Self-terminating radical cyclizations’ - new insight into the mechanism of the termination step from computational studies. J PHYS ORG CHEM 2010. [DOI: 10.1002/poc.1808] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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Tan KJ, White JM, Wille U. Self-Terminating Radical Cyclizations: How Are Thiyl Radicals Performing? European J Org Chem 2010. [DOI: 10.1002/ejoc.201000655] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Rabotyagova OS, Cebe P, Kaplan DL. Collagen Structural Hierarchy and Susceptibility to Degradation by Ultraviolet Radiation. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2008; 28:1420-1429. [PMID: 22199459 PMCID: PMC3244270 DOI: 10.1016/j.msec.2008.03.012] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Collagen type I is the most abundant extracellular matrix protein in the human body, providing the basis for tissue structure and directing cellular functions. Collagen has complex structural hierarchy, organized at different length scales, including the characteristic triple helical feature. In the present study, the relationship between collagen structure (native vs. denatured) and sensitivity to UV radiation was assessed, with a focus on changes in primary structure, changes in conformation, microstructure and material properties. A brief review of free radical reactions involved in collagen degradation is also provided as a mechanistic basis for the changes observed in the study. Structural and functional changes in the collagens were related to the initial conformation (native vs. denatured) and the energy of irradiation. These changes were tracked using SDS-PAGE to assess molecular weight, Fourier transform infrared (FTIR) spectroscopy to study changes in the secondary structure, and atomic force microscopy (AFM) to characterize changes in mechanical properties. The results correlate differences in sensitivity to irradiation with initial collagen structural state: collagen in native conformation vs. heat-treated (denatured) collagen. Changes in collagen were found at all levels of the hierarchical structural organization. In general, the native collagen triple helix is most sensitive to UV-254nm radiation. The triple helix delays single chain degradation. The loss of the triple helix in collagen is accompanied by hydrogen abstraction through free radical mechanisms. The results received suggest that the effects of electromagnetic radiation on biologically relevant extracellular matrices (collagen in the present study) are important to assess in the context of the state of collagen structure. The results have implications in tissue remodeling, wound repair and disease progression.
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Affiliation(s)
- Olena S. Rabotyagova
- Departments of Chemistry, Biomedical Engineering and Physics, Tufts University, Medford, Massachusetts 02155 USA
| | - Peggy Cebe
- Departments of Chemistry, Biomedical Engineering and Physics, Tufts University, Medford, Massachusetts 02155 USA
| | - David L. Kaplan
- Departments of Chemistry, Biomedical Engineering and Physics, Tufts University, Medford, Massachusetts 02155 USA
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Wille U, Heuger G, Jargstorff C. N-Centered Radicals in Self-Terminating Radical Cyclizations: Experimental and Computational Studies. J Org Chem 2008; 73:1413-21. [DOI: 10.1021/jo702261u] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Uta Wille
- School of Chemistry/BIO21 Molecular Science and Biotechnology Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia, ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Otto-Diels Institut für Organische Chemie, Christian-Albrechts Universität Kiel, Olshausenstrasse 40, 24098 Kiel, Germany
| | - Gerold Heuger
- School of Chemistry/BIO21 Molecular Science and Biotechnology Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia, ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Otto-Diels Institut für Organische Chemie, Christian-Albrechts Universität Kiel, Olshausenstrasse 40, 24098 Kiel, Germany
| | - Christian Jargstorff
- School of Chemistry/BIO21 Molecular Science and Biotechnology Institute, The University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia, ARC Centre of Excellence for Free Radical Chemistry and Biotechnology, Otto-Diels Institut für Organische Chemie, Christian-Albrechts Universität Kiel, Olshausenstrasse 40, 24098 Kiel, Germany
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Majumdar KC, Basu PK, Chattopadhyay SK. Formation of five- and six-membered heterocyclic rings under radical cyclisation conditions. Tetrahedron 2007. [DOI: 10.1016/j.tet.2006.09.049] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Abstract
Cyclization of an aryl radical at the ipso position of a p-O-aryl-substituted acetamide or benzamide generates oxindoles or quinolones bearing spirocyclohexadienone rings. This versatile reaction is applied to formal syntheses of the vasopressin inhibitor SR121463A and aza-galanthamine.
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Curran DP, Turner TR. Do alpha-acyloxy and alpha-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals? Beilstein J Org Chem 2006; 2:10. [PMID: 16725051 PMCID: PMC1524793 DOI: 10.1186/1860-5397-2-10] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2006] [Accepted: 05/25/2006] [Indexed: 12/02/2022] Open
Abstract
The generation of α-acyloxy and α-alkoxycarbonyloxy radicals under reductive conditions in fragmentable probe experiments does not provide unequivocal evidence for the fragmentation of such radicals to give ketones and acyl or alkoxycarbonyl radicals. Instead, standard reduction predominates, even at low tin hydride concentrations. Some ketone product is formed in the α-acyloxy substrate at low concentrations, but it is unclear whether this product arises through a slow radical fragmentation process or an inefficient, chain-breaking oxidative process.
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Affiliation(s)
- Dennis P Curran
- Department of Chemistry, University of Pittsburgh, 219 Parkman Ave., Pittsburgh, PA 15260 USA
| | - Tiffany R Turner
- Department of Chemistry, University of Pittsburgh, 219 Parkman Ave., Pittsburgh, PA 15260 USA
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Wille U. Computational Study on the 1,2-Rearrangement in β-(Nitroxy)vinyl and β-(Acetoxy)vinyl Radicals. J Org Chem 2006; 71:4040-8. [PMID: 16709042 DOI: 10.1021/jo0520543] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The 1,2-nitroxyl and 1,2-acetoxyl rearrangement in beta-(nitroxy)vinyl and beta-(acetoxy)vinyl radicals 13a and 13b, respectively, has been studied for the gas phase with various ab initio and density functional methods. The energetically most favorable pathway for 13a is calculated to proceed via reversible fragmentation/radical addition through transition state I-19a. In the case of 13b, rearrangement through a five-membered ring transition state III-16b and the fragmentation/radical addition pathway via transition state I-19b are competing processes. Mulliken and natural population analysis reveal a certain degree of charge separation in III-16a/b that may indicate a potential solvent effect on the rearrangement rate. A stepwise group migration through a cyclic radical intermediate V-18a/b or rearrangement through a three-membered ring transition state II-15a/b can be ruled out for both vinyl radicals. A comparison of the results of the calculations with experimental findings provides important insights into the kinetics of "self-terminating radical oxygenations". A significant method dependence on the outcome of the calculations was observed, which revealed the unsuitability of the UHF, MP2, B3LYP, and mPW1PW91 methods for computing these radical rearrangement processes. The results from BHandHLYP/cc-pVDZ calculations showed the best agreement with single-point energy calculations performed at the QCISD and CCSD(T) levels of theory.
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Affiliation(s)
- Uta Wille
- ARC Centre of Excellence in Free Radical Chemistry and Biochemistry, University of Melbourne, VIC 3010, Australia.
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Wille U, Dreessen T. Mechanistic Insights into NO3• Induced Self-Terminating Radical Oxygenations, Part 1: A Computational Study on NO3• and Its Addition to Alkynes. J Phys Chem A 2006; 110:2195-203. [PMID: 16466256 DOI: 10.1021/jp0454772] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The geometry of the nitrate radical, NO3*, for which unrestricted Hartree-Fock (HF) breaks spatial symmetry of the wave function, was optimized using hybrid density functionals that include varying fractions of Hartree-Fock exchange. Although symmetry breaking was not observed even when the functional with the highest HF exchange (BHandHLYP) was used, only B3LYP correctly describes the D(3h) symmetry of NO3* as ground-state structure with the lowest energy. Further, geometries and energies of the stationary points in the addition of NO3* to ethyne, propyne, and 2-butyne were calculated using ab initio and density functional methods. The reactions proceed through Z-configurated transition states leading to Z-configurated vinyl radicals with the activation barrier decreasing with increasing methyl substitution at the C[triple bond]C by ca. 11 kJ mol(-1) per methyl group. It was found that the results obtained at the BHandHLYP/cc-pVDZ level of theory are in good agreement with the data from single-point QCISD and CCSD(T) calculations.
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Affiliation(s)
- Uta Wille
- School of Chemistry, The University of Melbourne, Victoria 3010, Australia.
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