1
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He M, Piscelli BA, Cormanich RA, O’Hagan D. Conformational Analysis Explores the Role of Electrostatic Nonclassical CF···HC Hydrogen Bonding Interactions in Selectively Halogenated Cyclohexanes. J Org Chem 2024; 89:4009-4018. [PMID: 38441063 PMCID: PMC10949234 DOI: 10.1021/acs.joc.3c02868] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 02/15/2024] [Accepted: 02/21/2024] [Indexed: 03/06/2024]
Abstract
The conformational equilibria of selectively halogenated cyclohexanes are explored both experimentally (VT-NMR) for 1,1,4,-trifluorocyclohexane 7 and by computational analysis (M06-2X/aug-cc-pVTZ level), with the latter approach extending to a wider range of more highly fluorinated cyclohexanes. Perhaps unexpectedly, 7ax is preferred over the 7eq conformation by ΔG = 1.06 kcal mol-1, contradicting the accepted norm for substituents on cyclohexanes. The axial preference is stronger again in 1,1,3,3,4,5,5,-heptafluorocyclohexane 9 (ΔG = 2.73 kcal mol-1) as the CF2 groups further polarize the isolated CH2 hydrogens. Theoretical decomposition of electrostatic and hyperconjugative effects by natural bond orbital analysis indicated that nonclassical hydrogen bonding (NCHB) between the C-4 fluorine and the diaxial hydrogens at C-2 and C-6 in cyclohexane 7 and 9 largely accounts for the observed bias. The study extended to changing fluorine (F) for chlorine (Cl) and bromine (Br) at the pseudoanomeric position in the cyclohexanes. Although these halogens do not become involved in NCHBs, they polarize the geminal -CHX- hydrogen at the pseudoanomeric position to a greater extent than fluorine, and consequent electrostatic interactions influence conformer stabilities.
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Affiliation(s)
- Mengfan He
- School
of Chemistry, Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom
| | - Bruno A. Piscelli
- Instituto
de Química, Universidade Estadual
de Campinas (UNICAMP), Monteiro Lobato Street, Campinas, Sao Paulo 13083-862, Brazil
| | - Rodrigo A. Cormanich
- Instituto
de Química, Universidade Estadual
de Campinas (UNICAMP), Monteiro Lobato Street, Campinas, Sao Paulo 13083-862, Brazil
| | - David O’Hagan
- School
of Chemistry, Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews, Fife KY16 9ST, United Kingdom
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2
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Mondal R, Agbaria M, Nairoukh Z. Fluorinated Rings: Conformation and Application. Chemistry 2021; 27:7193-7213. [PMID: 33512034 DOI: 10.1002/chem.202005425] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Indexed: 12/16/2022]
Abstract
The introduction of fluorine atoms into molecules and materials across many fields of academic and industrial research is now commonplace, owing to their unique properties. A particularly interesting feature is the impact of fluorine substitution on the relative orientation of a C-F bond when incorporated into organic molecules. In this Review, we will be discussing the conformational behavior of fluorinated aliphatic carbo- and heterocyclic systems. The conformational preference of each system is associated with various interactions introduced by fluorine substitution such as charge-dipole, dipole-dipole, and hyperconjugative interactions. The contribution of each interaction on the stabilization of the fluorinated alicyclic system, which manifests itself in low conformations, will be discussed in detail. The novelty of this feature will be demonstrated by presenting the most recent applications.
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Affiliation(s)
- Rajarshi Mondal
- Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem, 9190401, Israel
| | - Mohamed Agbaria
- Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem, 9190401, Israel
| | - Zackaria Nairoukh
- Institute of Chemistry, The Hebrew University of Jerusalem, Edmond J. Safra Campus, Jerusalem, 9190401, Israel
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3
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Khani F, Atabaki H. Exploring the Origin of the Axial-Conformation Preferences in the 3-Halopiperidinium Cations: the Importance of the Coulombic Potential Energies. ACS OMEGA 2020; 5:24311-24317. [PMID: 33015447 PMCID: PMC7528170 DOI: 10.1021/acsomega.0c02506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/27/2020] [Accepted: 08/31/2020] [Indexed: 06/11/2023]
Abstract
Although there are some published conclusions in the literature concerning the origin of the axial-conformation preference in 3-fluoropiperidinium cations (charge-dipole orientation effect), the origin of the axial-conformation preferences in the 3-halopiperidinium cations [halogen = F (1), Cl (2), Br (3)] has remained an open question. To explore the origin of the axial-conformation preferences in compounds 1-3, we assessed the roles and contributions of the hyperconjugative interactions, the Coulombic electrostatic interactions, the electrostatic model associated with dipole-dipole interactions, and the steric effects associated with the Pauli exchange-type repulsions on the conformational properties of compounds 1-3 utilizing the G3MP2, LC-ωPBE, and B3LYP methods and natural bond orbital (NBO) interpretations. Natural Coulombic potential energies are in favor of the axial conformations of compounds 1-3, and justify their corresponding total energy differences. The through-space hyperconjugative interactions between the donor lone pairs of halogen atoms (LP3X) and the acceptor antibonding orbitals of H-N bonds [σ*(H-N) ⊕], LP3X → σ*(H-N) ⊕, increase from compound 1 to compound 3. The inspection of the dipole moments of the parallel C-X and H-N bonds in the axial conformations of compounds 1-3 revealed that the variations of their corresponding four-center dipole-dipole interactions correlate well with their corresponding conformational behaviors. The steric effects associated with the Pauli exchange-type repulsions are strongly in favor of the equatorial conformations of compounds 1-3. Accordingly, the charge-dipole orienting effect associated with the four-center dipole-dipole interactions is a dominant factor in the conformational behaviors of compounds 1-3.
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Affiliation(s)
- Farnousha Khani
- Department of Chemistry, Arak Branch, Islamic Azad University, Arak, Iran
| | - Hooshang Atabaki
- Department of Chemistry, Arak Branch, Islamic Azad University, Arak, Iran
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4
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Aufiero M, Gilmour R. Informing Molecular Design by Stereoelectronic Theory: The Fluorine Gauche Effect in Catalysis. Acc Chem Res 2018; 51:1701-1710. [PMID: 29894155 DOI: 10.1021/acs.accounts.8b00192] [Citation(s) in RCA: 73] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The axioms of stereoelectronic theory constitute an atlas to navigate the contours of molecular space. All too rarely lauded, the advent and development of stereoelectronic theory has been one of organic chemistry's greatest triumphs. Inevitably, however, in the absence of a comprehensive treatise, many of the field's pioneers do not receive the veneration that they merit. Rather their legacies are the stereoelectronic pillars that persist in teaching and research. This ubiquity continues to afford practitioners of organic chemistry with an abundance of opportunities for creative endeavor in reaction design, in conceiving novel activation modes, in preorganizing intermediates, or in stabilizing productive transition states and products. Antipodal to steric governance, which mitigates destabilizing nonbonding interactions, stereoelectronic control allows well-defined, often complementary, conformations to be populated. Indeed, the prevalence of stabilizing hyperconjugative interactions in biosynthetic processes renders this approach to molecular preorganization decidedly biomimetic and, by extension, expansive. In this Account, the evolution and application of a simple donor-acceptor model based on the fluorine gauche effect is delineated. Founded on reinforcing hyperconjugative interactions involving C(sp3)-H bonding orbitals and C(sp3)-X antibonding orbitals [σC-H → σC-X*], this general stratagem has been used in conjunction with an array of secondary noncovalent interactions to achieve acyclic conformational control (ACC) in structures of interest. These secondary effects range from 1,3-allylic strain (A1,3) through to electrostatic charge-dipole and cation-π interactions. Synergy between these interactions ensures that rotation about strategic C(sp3)-C(sp3) bonds is subject to the stereoelectronic requirement for antiperiplanarity (180°). Logically, in a generic [X-CH2-CH2-Y] system (X, Y = electron withdrawing groups) conformations in which the two C(sp3)-X bonds are synclinal (i.e., gauche) are significantly populated. As such, simple donor-acceptor models are didactically and predictively powerful in achieving topological preorganization. In the case of the gauche effect, the low steric demand of fluorine ensures that the remaining substituents at the C(sp3) hybridized center are placed in a predictable area of molecular space: An exit vector analogy is thus appropriate. Furthermore, the intrinsic chemical stability of the C-F bond is advantageous, thus it may be considered as an inert conformational steering group: This juxtaposition of size and electronegativity renders fluorinated organic molecules unique among the organo-halogen series. Cognizant that the replacement of one fluorine atom in the difluoroethylene motif by another electron withdrawing group preserves the gauche conformation, it was reasoned that β-fluoroamines would be intriguing candidates for investigation. The burgeoning field of Lewis base catalysis, particularly via iminium ion activation, provided a timely platform from which to explore a postulated fluorine-iminium ion gauche effect. Necessarily, activation of this stereoelectronic effect requires a process of intramolecularization to generate the electron deficient neighboring group: Examples include protonation, condensation to generate iminium salts, or acylation. This process, akin to substrate binding, has obvious parallels with enzymatic catalysis, since it perturbs the conformational dynamics of the system [ synclinal-endo, antiperiplanar, synclinal-exo]. This Account details the development of conformationally predictable small molecules based on the [X-Cα-Cβ-F] motif through a logical process of molecular design and illustrates their synthetic value in enantioselective catalysis.
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Affiliation(s)
- Marialuisa Aufiero
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
| | - Ryan Gilmour
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
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5
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Martins FA, Silla JM, Freitas MP. Conformational impact of structural modifications in 2-fluorocyclohexanone. Beilstein J Org Chem 2017; 13:1781-1787. [PMID: 28904621 PMCID: PMC5588668 DOI: 10.3762/bjoc.13.172] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 08/10/2017] [Indexed: 11/23/2022] Open
Abstract
2-Haloketones are building blocks that combine physical, chemical and biological features of materials and bioactive compounds, while organic fluorine plays a fundamental role in the design of performance organic molecules. Since these features are dependent on the three-dimensional chemical structure of a molecule, simple structural modifications can affect its conformational stability and, consequently, the corresponding physicochemical/biological property of interest. In this work, structural changes in 2-fluorocyclohexanone were theoretically studied with the aim at finding intramolecular interactions that induce the conformational equilibrium towards the axial or equatorial conformer. The interactions evaluated were hydrogen bonding, hyperconjugation, electrostatic and steric effects. While the gauche effect, originated from hyperconjugative interactions, does not appear to cause some preferences for the axial conformation of organofluorine heterocycles, more classical effects indeed rule the conformational equilibrium of the compounds. Spectroscopic parameters (NMR chemical shifts and coupling constants), which can be useful to determine the stereochemistry and the interactions operating in the series of 2-fluorocyclohexanone derivatives, were also calculated.
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Affiliation(s)
- Francisco A Martins
- Department of Chemistry, Federal University of Lavras, 37200-000, Lavras, MG, Brazil
| | - Josué M Silla
- Department of Chemistry, Federal University of Lavras, 37200-000, Lavras, MG, Brazil
| | - Matheus P Freitas
- Department of Chemistry, Federal University of Lavras, 37200-000, Lavras, MG, Brazil
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6
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Baranac-Stojanović M, Stojanović M, Aleksić J. Theoretical study of azido gauche effect and its origin. NEW J CHEM 2017. [DOI: 10.1039/c7nj00369b] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
The strength and origin of the azido gauche effect were studied by ab initio calculations and compared with the well-known fluorine gauche effect.
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Affiliation(s)
| | | | - Jovana Aleksić
- Center for Chemistry ICTM
- University of Belgrade
- 11000 Belgrade
- Serbia
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7
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Affiliation(s)
- Christian Thiehoff
- Institute for Organic Chemistry; Westfälische Wilhelms-Universität Münster; Corrensstr. 40 48149 Münster Germany
| | - Yannick P. Rey
- Institute for Organic Chemistry; Westfälische Wilhelms-Universität Münster; Corrensstr. 40 48149 Münster Germany
| | - Ryan Gilmour
- Institute for Organic Chemistry; Westfälische Wilhelms-Universität Münster; Corrensstr. 40 48149 Münster Germany
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8
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Intramolecular interactions contributing for the conformational preference of bioactive diphenhydramine: Manifestation of the gauche effect. J Mol Struct 2015. [DOI: 10.1016/j.molstruc.2015.03.033] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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9
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Baranac-Stojanović M, Aleksić J, Stojanović M. Energy decomposition analysis of gauche preference in 2-haloethanol, 2-haloethylamine (halogen = F, Cl), their protonated forms and anti preference in 1-chloro-2-fluoroethane. RSC Adv 2015. [DOI: 10.1039/c5ra01164g] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Small, electronegative elements contribute more electrostatic and orbital stabilization to the anti → gauche isomerization, and greater steric repulsion. The first and the latter actually oppose our traditional view of conformational equilibria.
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Affiliation(s)
| | - Jovana Aleksić
- Center for Chemistry ICTM
- University of Belgrade
- 11000 Belgrade
- Serbia
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10
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Silla JM, Duarte CJ, Cormanich RA, Rittner R, Freitas MP. Conformational analysis of 2,2-difluoroethylamine hydrochloride: double gauche effect. Beilstein J Org Chem 2014; 10:877-82. [PMID: 24778743 PMCID: PMC3999868 DOI: 10.3762/bjoc.10.84] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 03/23/2014] [Indexed: 11/23/2022] Open
Abstract
The gauche effect in fluorinated alkylammonium salts is well known and attributed either to an intramolecular hydrogen bond or to an electrostatic attraction between the positively charged nitrogen and the vicinal electronegative fluorine atom. This work reports the effect of adding a fluorine atom in 2-fluoroethylamine hydrochloride on the conformational isomerism of the resulting 2,2-difluoroethylamine chloride (2). The analysis was carried out using NMR coupling constants in D2O solution, in order to mimic the equilibrium conditions in a physiological medium, in the gas phase and in implicit water through theoretical calculations. Despite the presence of σCH→σ*CF and σCH→σ*CN interactions, which usually rule the hyperconjugative gauche effect in 1,2-disubstituted ethanes, the most important forces leading to the double gauche effect ((+)NH3 in the gauche relationship with both fluorine atoms) in 2 are the Lewis-type ones. Particularly, electrostatic interactions are operative even in water solution, where they should be significantly attenuated, whereas hyperconjugation and hydrogen bond have secondary importance.
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Affiliation(s)
- Josué M Silla
- Department of Chemistry, Federal University of Lavras, P. O. Box 3037, 37200-000, Lavras, MG, Brazil
| | - Claudimar J Duarte
- Chemistry Institute, State University of Campinas, P. O. Box 6154, 13084-971, Campinas, SP, Brazil
| | - Rodrigo A Cormanich
- Chemistry Institute, State University of Campinas, P. O. Box 6154, 13084-971, Campinas, SP, Brazil
| | - Roberto Rittner
- Chemistry Institute, State University of Campinas, P. O. Box 6154, 13084-971, Campinas, SP, Brazil
| | - Matheus P Freitas
- Department of Chemistry, Federal University of Lavras, P. O. Box 3037, 37200-000, Lavras, MG, Brazil
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11
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Compain G, Bonneau C, Martin-Mingot A, Thibaudeau S. Selective Anti-Markovnikov Cyclization and Hydrofluorination Reaction in Superacid HF/SbF5: A Tool in the Design of Nitrogen-Containing (Fluorinated) Polycyclic Systems. J Org Chem 2013; 78:4463-72. [DOI: 10.1021/jo400398y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Guillaume Compain
- Superacid group in
“Organic Synthesis”
team, Université de Poitiers, CNRS
UMR 7285 IC2MP, 4, avenue Michel Brunet, F-86022 Poitiers Cedex, France
| | - Céline Bonneau
- Superacid group in
“Organic Synthesis”
team, Université de Poitiers, CNRS
UMR 7285 IC2MP, 4, avenue Michel Brunet, F-86022 Poitiers Cedex, France
| | - Agnès Martin-Mingot
- Superacid group in
“Organic Synthesis”
team, Université de Poitiers, CNRS
UMR 7285 IC2MP, 4, avenue Michel Brunet, F-86022 Poitiers Cedex, France
| | - Sébastien Thibaudeau
- Superacid group in
“Organic Synthesis”
team, Université de Poitiers, CNRS
UMR 7285 IC2MP, 4, avenue Michel Brunet, F-86022 Poitiers Cedex, France
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12
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Mooring SR, Liu J, Liang Z, Ahn J, Hong S, Yoon Y, Snyder JP, Shim H. Benzenesulfonamides: a unique class of chemokine receptor type 4 inhibitors. ChemMedChem 2013; 8:622-32. [PMID: 23468189 PMCID: PMC3752296 DOI: 10.1002/cmdc.201200582] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2012] [Revised: 01/03/2013] [Indexed: 11/08/2022]
Abstract
The interaction of CXCR4 with CXCL12 (SDF-1) plays a critical role in cancer metastasis by facilitating the homing of tumor cells to metastatic sites. Based on our previously published work on CXCR4 antagonists, we have synthesized a series of aryl sulfonamides that inhibit the CXCR4/CXCL12 interaction. Analogue bioactivities were assessed with binding affinity and Matrigel invasion assays. Computer modeling was employed to evaluate a selection of the new analogues docked into the CXCR4 X-ray structure and to rationalize discrepancies between the affinity and Matrigel in vitro assays. A lead compound displays nanomolar potency in the binding affinity assay (IC(50)=8.0 nM) and the Matrigel invasion assay (100 % blockade of invasion at 10 nM). These data demonstrate that benzenesulfonamides are a unique class of CXCR4 inhibitors with high potency.
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Affiliation(s)
- Suazette Reid Mooring
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, Fax: 1-404-778-5550
| | - Jin Liu
- Department of Chemistry and Emory Institute for Drug Discovery, Emory University, Atlanta, GA
| | - Zhongxing Liang
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, Fax: 1-404-778-5550
- Winship Cancer Institute, Emory University, Atlanta, GA
| | - Jeffrey Ahn
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, Fax: 1-404-778-5550
| | - Samuel Hong
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, Fax: 1-404-778-5550
| | - Younghyoun Yoon
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, Fax: 1-404-778-5550
| | - James P. Snyder
- Department of Chemistry and Emory Institute for Drug Discovery, Emory University, Atlanta, GA
| | - Hyunsuk Shim
- Department of Radiology and Imaging Sciences, Emory University, Atlanta, GA, Fax: 1-404-778-5550
- Winship Cancer Institute, Emory University, Atlanta, GA
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13
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Compain G, Martin-Mingot A, Maresca A, Thibaudeau S, Supuran CT. Superacid synthesis of halogen containing N-substituted-4-aminobenzene sulfonamides: New selective tumor-associated carbonic anhydrase inhibitors. Bioorg Med Chem 2013; 21:1555-63. [DOI: 10.1016/j.bmc.2012.05.037] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2012] [Revised: 05/09/2012] [Accepted: 05/15/2012] [Indexed: 01/07/2023]
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14
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Durantie E, Bucher C, Gilmour R. Fluorine-directed β-galactosylation: chemical glycosylation development by molecular editing. Chemistry 2012; 18:8208-15. [PMID: 22592962 DOI: 10.1002/chem.201200468] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2012] [Indexed: 11/10/2022]
Abstract
Validation of the 2-fluoro substituent as an inert steering group to control chemical glycosylation is presented. A molecular editing study has revealed that the exceptional levels of diastereocontrol in glycosylation processes by using 2-fluoro-3,4,6-tri-O-benzyl glucopyranosyl trichloroacetimidate (TCA) scaffolds are a consequence of the 2R,3S,4S stereotriad. This study has also revealed that epimerization at C4, results in a substantial enhancement in β-selectivity (up to β/α 300:1).
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Affiliation(s)
- Estelle Durantie
- Laboratory for Organic Chemistry, Swiss Federal Institute of Technology (ETH) Zürich, 8093 Zürich, Switzerland
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15
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Zimmer LE, Sparr C, Gilmour R. Konformative Fluoreffekte in der Organokatalyse: eine neuartige Strategie zum molekularen Design. Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201102027] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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16
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Zimmer LE, Sparr C, Gilmour R. Fluorine conformational effects in organocatalysis: an emerging strategy for molecular design. Angew Chem Int Ed Engl 2011; 50:11860-71. [PMID: 21953782 DOI: 10.1002/anie.201102027] [Citation(s) in RCA: 239] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Indexed: 11/12/2022]
Abstract
Molecular design strategies that profit from the intrinsic stereoelectronic and electrostatic effects of fluorinated organic molecules have mainly been restricted to bio-organic chemistry. Indeed, many fluorine conformational effects remain academic curiosities with no immediate application. However, the renaissance of organocatalysis offers the possibility to exploit many of these well-described phenomena for molecular preorganization. In this minireview, we highlight examples of catalyst refinement by introduction of an aliphatic C-F bond which functions as a chemically inert steering group for conformational control.
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Affiliation(s)
- Lucie E Zimmer
- ETH Zürich, Laboratorium für Organische Chemie, Departement Chemie und Angewandte Biowissenschaften, Wolfgang-Pauli-Str. 10, CH-8093 Zürich, Switzerland
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18
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19
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Bridger GJ, Skerlj RT, Hernandez-Abad PE, Bogucki DE, Wang Z, Zhou Y, Nan S, Boehringer EM, Wilson T, Crawford J, Metz M, Hatse S, Princen K, De Clercq E, Schols D. Synthesis and structure-activity relationships of azamacrocyclic C-X-C chemokine receptor 4 antagonists: analogues containing a single azamacrocyclic ring are potent inhibitors of T-cell tropic (X4) HIV-1 replication. J Med Chem 2010; 53:1250-60. [PMID: 20043638 DOI: 10.1021/jm901530b] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Bis-tetraazamacrocycles such as the bicyclam AMD3100 (1) are a class of potent and selective anti-HIV-1 agents that inhibit virus replication by binding to the chemokine receptor CXCR4, the coreceptor for entry of X4 viruses. By sequential replacement and/or deletion of the amino groups within the azamacrocyclic ring systems, we have determined the minimum structural features required for potent antiviral activity in this class of compounds. All eight amino groups are not required for activity, the critical amino groups on a per ring basis are nonidentical, and the overall charge at physiological pH can be reduced without compromising potency. This approach led to the identification of several single ring azamacrocyclic analogues such as AMD3465 (3d), 36, and 40, which exhibit EC(50)'s against the cytopathic effects of HIV-1 of 9.0, 1.0, and 4.0 nM, respectively, antiviral potencies that are comparable to 1 (EC(50) against HIV-1 of 4.0 nM). More importantly, however, the key structural elements of 1 required for antiviral activity may facilitate the design of nonmacrocyclic CXCR4 antagonists suitable for HIV treatment via oral administration.
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Affiliation(s)
- Gary J Bridger
- AnorMED Inc. now Genzyme Corporation, 500 Kendall Street, Cambridge, Massachusetts 02142, USA.
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21
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Sun A, Yoon JJ, Yin Y, Prussia A, Yang Y, Min J, Plemper RK, Snyder JP. Potent non-nucleoside inhibitors of the measles virus RNA-dependent RNA polymerase complex. J Med Chem 2008; 51:3731-41. [PMID: 18529043 PMCID: PMC2587337 DOI: 10.1021/jm701239a] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Measles virus (MV) is one of the most infectious pathogens known. In spite of the existence of a vaccine, approximately 350000 deaths/year result from MV or associated complications. Antimeasles compounds could conceivably diminish these statistics and provide a therapy that complements vaccine treatment. We recently described a high-throughput screening hit compound 1 (16677) against MV-infected cells with the capacity to eliminate viral reproduction at 250 nM by inhibiting the action of the virus's RNA-dependent RNA polymerase complex (RdRp). The compound, 1-methyl-3-(trifluoromethyl)- N-[4-sulfonylphenyl]-1 H-pyrazole-5-carboxamide, 1 carries a critical CF 3 moiety on the 1,2-pyrazole ring. Elaborating on the preliminary structure-activity (SAR) study, the present work presents the synthesis and SAR of a much broader range of low nanomolar nonpeptidic MV inhibitors and speculates on the role of the CF 3 functionality.
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Affiliation(s)
- Aiming Sun
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, USA.
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22
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Hyla-Kryspin I, Haufe G, Grimme S. MP2 and QCISD(T) study on the convergence of interaction energies of weak O–H⋯F–C, C–H⋯O, and C–H⋯F–C hydrogen bridges. Chem Phys 2008. [DOI: 10.1016/j.chemphys.2008.02.023] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Clift MD, Ji H, Deniau GP, O'Hagan D, Silverman RB. Enantiomers of 4-amino-3-fluorobutanoic acid as substrates for gamma-aminobutyric acid aminotransferase. Conformational probes for GABA binding. Biochemistry 2007; 46:13819-28. [PMID: 17988152 DOI: 10.1021/bi701249q] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gamma-aminobutyric acid aminotransferase (GABA-AT), a pyridoxal 5'-phosphate dependent enzyme, catalyzes the degradation of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) to succinic semialdehyde with concomitant conversion of pyridoxal 5'-phosphate (PLP) to pyridoxamine 5'-phosphate (PMP). The enzyme then catalyzes the conversion of alpha-ketoglutarate to the excitatory neurotransmitter L-glutamate. Racemic 4-amino-3-fluorobutanoic acid (3-F-GABA) was shown previously to act as a substrate for GABA-AT, not for transamination, but for HF elimination. Here we report studies of the reaction catalyzed by GABA-AT on (R)- and (S)-3-F-GABA. Neither enantiomer is a substrate for transamination. Very little elimination from the (S)-enantiomer was detected using a coupled enzyme assay; The rate of elimination of HF from the (R)-enantiomer is at least 10 times greater than that for the (S)-enantiomer. The (R)-enantiomer is about 20 times more efficient as a substrate for GABA-AT catalyzed HF elimination than GABA is a substrate for transamination. The (R)-enantiomer also inhibits the transamination of GABA 10 times more effectively than the (S)-enantiomer. Using a combination of computer modeling and the knowledge that vicinal C-F and C-NH3+ bonds have a strong preference to align gauche rather than anti to each other, it is concluded that on binding of free 3-F-GABA to GABA-AT the optimal conformation places the C-NH3+ and C-F bonds gauche in the (R)-enantiomer but anti in the (S)-enantiomer. Furthermore, the dynamic binding process and the bioactive conformation of GABA bound to GABA-AT have been inferred on the basis of the different biological behavior of the two enantiomers of 3-F-GABA when they bind to the enzyme. The present study suggests that the C-F bond can be utilized as a conformational probe to explore the dynamic binding process and provide insight into the bioactive conformation of substrates, which cannot be easily determined by other biophysical approaches.
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Affiliation(s)
- Michael D Clift
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, USA
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24
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Gooseman N, O'Hagan D, Peach M, Slawin A, Tozer D, Young R. An ElectrostaticGauche Effect in β-Fluoro- and β-Hydroxy-N-ethylpyridinium Cations. Angew Chem Int Ed Engl 2007. [DOI: 10.1002/ange.200700714] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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25
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Gooseman NEJ, O'Hagan D, Peach MJG, Slawin AMZ, Tozer DJ, Young RJ. An ElectrostaticGauche Effect in β-Fluoro- and β-Hydroxy-N-ethylpyridinium Cations. Angew Chem Int Ed Engl 2007; 46:5904-8. [PMID: 17610229 DOI: 10.1002/anie.200700714] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Natalie E J Gooseman
- School of Chemistry and Centre for Biomolecular Sciences, University of St. Andrews, North Haugh, St. Andrews, Fife, KY16 9ST, UK
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26
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27
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Smith DM, Woerpel KA. Electrostatic interactions in cations and their importance in biology and chemistry. Org Biomol Chem 2006; 4:1195-201. [PMID: 16557303 DOI: 10.1039/b600056h] [Citation(s) in RCA: 127] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electrostatic effects exert strongly stabilizing influences on cations, in many cases controlling the conformational preferences of these cations. The lowest energy conformers are ones where the positive charge is brought closest to substituents bearing partial negative charges. These conformational biases, along with stereoelectronic effects, can control the stereoselectivity of reactions involving carbocationic intermediates.
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Affiliation(s)
- Deborah M Smith
- Department of Chemistry, University of California, Irvine, California 92697-2025, USA
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28
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Kim W, McMillan RA, Snyder JP, Conticello VP. A Stereoelectronic Effect on Turn Formation Due to Proline Substitution in Elastin-Mimetic Polypeptides. J Am Chem Soc 2005; 127:18121-32. [PMID: 16366565 DOI: 10.1021/ja054105j] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Stereoelectronic effects have been identified as contributing factors to the conformational stability of collagen-mimetic peptide sequences. To assess the relevance of these factors within other protein structural contexts, three polypeptide sequences were prepared in which the sequences were derived from the canonical repeat unit (Val-Pro-Gly-Val-Gly) of the protein material elastin. These elastin-mimetic polypeptides, elastin-1, elastin-2, and elastin-3, incorporate (2S)-proline, (2S,4S)-4-fluoroproline, and (2S,4R)-4-fluoroproline, respectively, at the second position of the elastin repeat. Calorimetric and spectroscopic investigations of these three polypeptides indicate that the incorporation of the substituted proline residues had a dramatic effect upon the self-assembly of the corresponding elastin peptide. The presence of (2S,4R)-4-fluoroproline in elastin-3 lowered the temperature of the phase transition and increased the type II beta-turn population with respect to the parent polypeptide, while the presence of (2S,4S)-4-fluoroproline in elastin-2 had the opposite effect. These results suggest that stereoelectronic effects could either enhance or hinder the self-assembly of elastin-mimetic polypeptides, depending on the influence of the proline analogue on the energetics of the beta-turn conformation that develops within the pentapeptide structural repeats above the phase transition. Density functional theory (DFT) was employed to model three possible turn types (betaI-, betaII-, and inverse gamma-turns) derived from model peptide segments (MeCO-Xaa-Gly-NHMe) (Xaa = Pro, 4S-F-Pro, or 4R-F-Pro) corresponding to the turn-forming residues of the elastin repeat unit (Val-Pro-Gly-Val-Gly). The results of the these calculations suggested a similar outcome to the experimental data for the elastin-mimetic polypeptides, in that type II beta-turn structures were stabilized for peptide segments containing (2S,4R)-fluoroproline and destabilized for segments containing (2S,4S)-fluoroproline relative to the canonical proline residue.
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Affiliation(s)
- Wookhyun Kim
- Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, USA
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29
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Tenza K, Northen JS, O'Hagan D, Slawin AMZ. Stereoselective alpha-fluoroamide and alpha-fluoro-gamma-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement. Beilstein J Org Chem 2005; 1:13. [PMID: 16542024 PMCID: PMC1399461 DOI: 10.1186/1860-5397-1-13] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2005] [Accepted: 10/17/2005] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Asymmetric introduction of fluorine alpha-to a carbonyl has become popular recently, largely because the direct fluorination of enolates by asymmetric electrophilic fluorinating reagents has improved, and as a result such compounds are becoming attractive synthons. We have sought an alternative but straightforward asymmetric method to this class of compounds, utilising the zwitterionic aza-Claisen rearrangement by reacting alpha-fluoroacid chlorides and homochiral N-allylpyrrolidines as starting materials. RESULTS Treatment of N-allylmorpholine with 2-fluoropropionyl chloride under Yb(OTf)3 catalysis generated the zwitterionic aza-Claisen rearrangement product in good yield and demonstrated the chemical feasibility of the approach. For the asymmetric reaction, N-allyl-(S)-2-(methoxymethyl)pyrrolidine was treated with either 2-fluoropropionyl chloride or 2-fluorophenylacetic acid chloride under similar conditions and resulted in N-(alpha-fluoro-gamma-vinylamide)pyrrolidine products as homochiral materials in 99% de. These products were readily converted to their corresponding alpha-fluoro-gamma-lactones by iodolactonisation and in good diastereoselectivity. CONCLUSION Molecules which have fluorine at a stereogeneic centre are finding increasing utility in pharmaceutical, fine chemicals and materials research. The zwitterionic aza-Claisen rearrangement proved to be an effective and competitive complement to asymmetric electrophilic fluorination strategies and provides access to versatile synthetic intermediates with fluorine at the stereogenic centre.
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Affiliation(s)
- Kenny Tenza
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, UK KY16 9ST
| | - Julian S Northen
- Onyx Scientific Ltd., Units 97/98 Silverbriar, Sunderland Enterprise Park East, Sunderland UK, SR5 2TQ
| | - David O'Hagan
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, UK KY16 9ST
| | - Alexandra M Z Slawin
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, UK KY16 9ST
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Sun A, Lankin DC, Hardcastle K, Snyder JP. 3-Fluoropiperidines andN-Methyl-3-fluoropiperidinium Salts: The Persistence of Axial Fluorine. Chemistry 2005; 11:1579-91. [PMID: 15662680 DOI: 10.1002/chem.200400835] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
It has previously been shown that the fluorine atom in N-protonated 3-fluoropiperidine salts in water strongly prefers the axial orientation in the six-membered ring chairs. In the present work we examine the proposition that the N-methyl salts are equally disposed to present axial fluorine. Initially, we explored this point by comparing the structures of the corresponding NH2+, NHMe+, and NMe2+ salts by means of density functional theory (DFT), ab initio, and MMFF force field calculations with and without aqueous solvation models. The predictions unambiguously pointed to axial fluorine for all salts investigated, including those with simultaneous axial F and (N)Me. The calculations were followed by synthesis of the corresponding series of 4,4-diphenylpiperidinium salts. These were evaluated by one- and two-dimensional NMR spectroscopy in [D6]DMSO to fully corroborate the axial disposition of the fluorine in each of the compounds. X-ray crystal structure determinations were likewise performed for the diphenyl-3-fluoro NH2+ and NMe2+ systems to substantiate axial-F. Comparison of the X-ray structures of the fluorinated and unfluorinated NMe2+ salts reveals that the fluorine resides axial in spite of substantial steric compression. While the charge-dipole phenomenon responsible for the axial-F conformation in the parent protonated fluoropiperidinium compounds carries over to doubly alkylated salts, we show that it extends to molecular orientation in the packing of the unit cells in the solid state as well. Finally, using the computational methods that successfully motivated our synthesis and structural work, we have made predictions for a number of new structures and re-examined some parallel results reported by the Eliel group in the early 1970s. Although C-F...H-N hydrogen bonds are reported to be weak and few in number, the CF...HN charge-dipole orienting effect is a powerful directing force that matches the hydrogen-bond in both its energetic contribution and conformational consequences.
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Affiliation(s)
- Aiming Sun
- Department of Chemistry, Emory University, Atlanta, GA 30322, USA
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31
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McDonnell C, López O, Murphy P, Fernández Bolaños JG, Hazell R, Bols M. Conformational Effects on Glycoside Reactivity: Study of the High Reactive Conformer of Glucose. J Am Chem Soc 2004; 126:12374-85. [PMID: 15453771 DOI: 10.1021/ja047476t] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The effect of conformation on glycoside reactivity was investigated by studying the hydrolysis of a selection of 3,6-anhydroglucosides as models for glucose in the highly reactive (1)C(4) conformation. Methyl 3,6-anhydro-beta-D-glucopyranoside was found to hydrolyze 200-400 times faster than methyl glucosides in the (4)C(1) conformation, while methyl 3,6-anhydro-beta-D-galactopyranoside, which is in the B(1,4) conformation, was less reactive than methyl beta-D-galactopyranoside. Methyl (3,6-anhydro-beta-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranoside, methyl (3,6-anhydro-alpha-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranosyl-(1 --> 6)-alpha-D-glucopyranoside, and methyl (3,6-anhydro-beta-D-glucopyranosyl)-(1 --> 6)-alpha-D-glucopyranosyl-(1 --> 6)-alpha-D-glucopyranoside were prepared and found to react selectively at the anhydro residue. The finding that (1)C(4) conformers of glucosides are highly reactive species is in accordance with and supports previous results showing that axial OH groups are less electron withdrawing than equatorial OH groups.
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Grunewald GL, Romero FA, Criscione KR. Nanomolar Inhibitors of CNS Epinephrine Biosynthesis: (R)-(+)-3-Fluoromethyl-7-(N-substituted aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines as Potent and Highly Selective Inhibitors of Phenylethanolamine N-Methyltransferase. J Med Chem 2004; 48:1806-12. [PMID: 15771426 DOI: 10.1021/jm049594x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A series of (R)-(+)-3-fluoromethyl-7-(N-substituted aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines has been synthesized and evaluated as inhibitors of PNMT and for their affinity for the alpha(2)-adrenoceptor. Compounds (R)-8 and (R)-9 are remarkably potent and selective inhibitors of PNMT and are predicted to penetrate the blood-brain barrier on the basis of their calculated log P values. Conformational analysis and docking studies were performed in order to examine why the (R)-enantiomer of these 3-fluoromethyl-7-(N-substituted aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines is more potent than the (S)-enantiomer and to determine the likely bound ring conformer of the (R)-enantiomer. It appears that the (R)-enantiomer participates in a water-mediated hydrogen bond in which the (S)-enantiomer cannot. The likely favored ring conformation for (R)-3-fluoromethyl-7-(N-substituted aminosulfonyl)-1,2,3,4-tetrahydroisoquinolines in the PNMT active site is similar to the ring conformation of (R)-5a as determined by gas-phase ab initio calculations.
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Affiliation(s)
- Gary L Grunewald
- Department of Medicinal Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, USA.
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