1
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O'Hagan D. The Emergence and Properties of Selectively Fluorinated 'Janus' Cyclohexanes. CHEM REC 2023; 23:e202300027. [PMID: 37016509 DOI: 10.1002/tcr.202300027] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/14/2023] [Indexed: 04/06/2023]
Abstract
This account describes the evolution of a research programme that started by linking fluoromethylene (-CHF-) groups along aliphatic chains and then progressing to alicyclic rings with contiguous fluorine atoms. Different stereoisomers of aliphatic chains tend to adopt low polarity conformations. In order to force polar conformations, the programme began to address ring systems and in particular cyclohexanes, to restrain conformational freedom and co-aligned C-F bonds. The flagship molecule, all-cis-1,2,3,4,5,6-hexafluorocyclohexane 7, emerged to be the most polar aliphatic compound recorded. The polarity arises because there are three co-aligned triaxial C-F bonds and the six fluorines occupy one face of the ring. Conversely the electropositive hydrogens occupy the other face. These have been termed Janus face cyclohexanes after the Roman god with two faces. The review outlines progress by our group and others in preparing derivatives of the parent cyclohexane 7, in order to explore properties and potential applications of these Janus cyclohexanes.
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Affiliation(s)
- David O'Hagan
- University of St Andrews, St. Andrews, United Kingdom
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2
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Burrows J, Kamo S, Koide K. Scalable Birch reduction with lithium and ethylenediamine in tetrahydrofuran. Science 2021; 374:741-746. [PMID: 34735232 DOI: 10.1126/science.abk3099] [Citation(s) in RCA: 40] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
[Figure: see text].
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Affiliation(s)
- James Burrows
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Shogo Kamo
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
| | - Kazunori Koide
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA 15260, USA
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Clark JL, Neyyappadath RM, Yu C, Slawin AMZ, Cordes DB, O'Hagan D. Janus All-Cis 2,3,4,5,6-Pentafluorocyclohexyl Building Blocks Applied to Medicinal Chemistry and Bioactives Discovery Chemistry. Chemistry 2021; 27:16000-16005. [PMID: 34486192 PMCID: PMC9292521 DOI: 10.1002/chem.202102819] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2021] [Indexed: 12/24/2022]
Abstract
Monoalkylated derivatives of the unusually polar all‐cis 2,3,4,5,6‐ pentafluorocyclohexyl (Janus face) motif are prepared starting from an aryl hydrogenation of 2,3,4,5,6‐ pentafluorophenylacetate methyl ester 15. The method used Zeng's Rh(CAAC) carbene catalyst 4 in the hydrogenation following the protocol developed by Glorius. The resultant Janus pentafluorocyclohexylacetate methyl ester 16 was converted to the corresponding alcohol 18, aldehyde 13, bromide 29 and azide 14 through functional group manipulations, and some of these building blocks were used in Ugi‐multicomponent and Cu‐catalysed click reactions. NBoc protected pentafluoroarylphenylalanine methyl ester 35 was also subject to an aryl hydrogenation, and then deprotection to generate the Janus face β‐pentafluorocyclohexyl‐alanine amino acid 15, which was incorporated into representative members of an emerging class of candidate antiviral compounds. Log P measurements demonstrate that the all‐cis 2,3,4,5,6‐pentafluorocyclohexyl ring system is more polar than a phenyl ring. In overview the paper introduces new building blocks containing this Janus ring and demonstrates their progression to molecules typically used in bioactives discovery programmes.
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Affiliation(s)
- Joshua L Clark
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
| | | | - Cihang Yu
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
| | - Alexandra M Z Slawin
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
| | - David B Cordes
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
| | - David O'Hagan
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, Fife, KY16 9ST, UK
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4
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Vulpetti A, Dalvit C. Hydrogen Bond Acceptor Propensity of Different Fluorine Atom Types: An Analysis of Experimentally and Computationally Derived Parameters. Chemistry 2021; 27:8764-8773. [PMID: 33949737 DOI: 10.1002/chem.202100301] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Indexed: 12/29/2022]
Abstract
The propensity of organic fluorine acting as a weak hydrogen bond acceptor (HBA) in intermolecular and intramolecular interactions has been the subject of many experimental and theoretical studies often reaching different conclusions. Over the last few years, new and stronger evidences have emerged for the direct involvement of fluorine in weak hydrogen bond (HB) formation. However, not all the fluorine atom types can act as weak HBA. In this work, the differential HBA propensity of various types of fluorine atoms was analyzed with a particular emphasis for the different types of alkyl fluorides. This was carried out by evaluating ab initio computed parameters, experimental 19 F NMR chemical shifts and small molecule crystallographic structures (extracted from the CSD database). According to this analysis, shielded (with reference to the 19 F NMR chemical shift) alkyl mono-fluorinated motifs display the highest HBA propensity in agreement with solution studies. Although much weaker than other well-characterized HB complexes, the fragile HBs formed by these fluorinated motifs have important implications for the chemical-physical and structural properties of the molecules, chemical reactions, and protein-ligand recognition.
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Affiliation(s)
- Anna Vulpetti
- Global Discovery Chemistry, Novartis Institutes for Biomedical Research, 4002, Basel, Switzerland
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5
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McDaniel KA, Blood AR, Smith GC, Jui NT. Dearomatization of Unactivated Arenes via Catalytic Hydroalkylation. ACS Catal 2021; 11:4968-4972. [PMID: 34367722 PMCID: PMC8346228 DOI: 10.1021/acscatal.1c00732] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The dearomative cyclization of linear amides to complex spirocyclic butyrolactams has been enabled by photoredox catalysis through a reductive radical-polar crossover mechanism. This mechanism operates with precision on unactivated aromatic substrates to give a wide range of 1,4-hydroalkylation products. This method utilizes a simple organic catalyst/reductant pair to deliver products in a highly flexible manner with respect to substitution, and the products can be further functionalized under simple conditions to afford a collection of motifs. The mechanistic analysis performed here outlines the salient features of this strategy, which were applied to prepare a collection of complex scaffolds including the anticonvulsive agent gabapentin.
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Affiliation(s)
- Kelly A. McDaniel
- Department of Chemistry and Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, United States
| | - Anna R. Blood
- Department of Chemistry and Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, United States
| | - Gavin C. Smith
- Department of Chemistry and Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, United States
| | - Nathan T. Jui
- Department of Chemistry and Winship Cancer Institute, Emory University, Atlanta, Georgia 30322, United States
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O'Hagan D. Polar Organofluorine Substituents: Multivicinal Fluorines on Alkyl Chains and Alicyclic Rings. Chemistry 2020; 26:7981-7997. [PMID: 32083392 DOI: 10.1002/chem.202000178] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 02/20/2020] [Indexed: 12/12/2022]
Abstract
This Review outlines the progression, primarily of our own work, but with important contributions from other labs, on the synthesis and properties of multiple vicinally fluorinated alkyl chains and rings. Chain conformations of individual diastereoisomers with -CHF- at adjacent carbons are influenced by stereoelectronic factors associated with the polar C-F bond and the polarised geminal hydrogens. Generally, the chain will prefer a conformation which acts to minimise overall molecular polarity, and where the C-F bonds orient away from each other. However, when vicinal fluorine atoms are positioned on a ring then conformations are more constrained. The ring will adopt optimal conformations such as a chair in cyclohexane and then C-F bonds can be introduced with a stereochemistry that forces parallel (axial) orientations. In the case of cyclohexane, 1,3-diaxial arrangements of C-F bonds impart considerable polarity to the ring, resulting in an electronegative 'fluorine face' and an electropositive 'hydrogen face'. For all-syn 1,2,3,4,5,6-hexafluorocyclohexane, this arrangement generates an unusually polar aliphatic ring system. Most recently the concept has been extended to the preparation of all-syn 1,2,3-trifluorocyclopropanes, a rigid ring system with fluorine atoms on one face and hydrogens on the other. Lipophilicity Log P values of such compounds indicate that they are significantly more polar than their parent alicyclic hydrocarbons and give some positive indication for a future role of such substituents in medicinal chemistry. Expanding to such a role will require access to improved synthesis methods to these motifs and consequently access to a broader a range of building blocks, however some exciting new methods have emerged recently and these are briefly reviewed.
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Affiliation(s)
- David O'Hagan
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK
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7
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Bykova T, Al-Maharik N, Slawin AMZ, Bühl M, Lebl T, O'Hagan D. Benzylic Functionalisation of Phenyl all-cis-2,3,5,6-Tetrafluorocyclohexane Provides Access to New Organofluorine Building Blocks. Chemistry 2018; 24:13290-13296. [PMID: 29882357 DOI: 10.1002/chem.201802166] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2018] [Revised: 06/04/2018] [Indexed: 11/07/2022]
Abstract
Selectively fluorinated hydrocarbons continue to attract attention for tuning pharmacokinetic properties in agrochemical and pharmaceutical discovery programmes. This study identifies benzylic bromination of phenyl all-cis-2,3,5,6-tetrafluorocyclohexane 2 as a key reaction for accessing building blocks containing the all-cis-2,3,5,6-tetrafluorocyclohexane ring system. These cyclohexanes are of interest as the fluorines are only on one face of the cyclohexane, and this imparts an unusual polar aspect, very different to an otherwise hydrophobic cyclohexane. Ritter type reactions of benzyl bromide 4 with DMF and acetonitrile generated the corresponding benzyl alcohol 6 and benzylacetamide 7 respectively. Benzylacetamide 7 was hydrolysed to benzyl amine 8 and syn-amino-alcohol 9, and separately the phenyl ring was oxidatively cleaved to furnish carboxylic acid acetamide 10, which after hydrolysis gave the tetrafluorocyclohexyl amino acid 11. A trans-halogenation of benzylbromide 4 with AgF2 gave benzyl fluoride 13. Oxidative cleavage of the aryl ring then gave pentafluorocyclohexyl carboxylic acid 14. This carboxylic acid was readily converted to amides 23-26 and the preferred conformations of these α-fluoroamides were explored by DFT, X-ray structure and 1 H-19 F HOESY NMR analysis.
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Affiliation(s)
- Tetiana Bykova
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY15 5EA, UK
| | - Nawaf Al-Maharik
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY15 5EA, UK
- Current address: Alistiqlal University, Jericho, Palestine
| | - Alexandra M Z Slawin
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY15 5EA, UK
| | - Michael Bühl
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY15 5EA, UK
| | - Tomas Lebl
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY15 5EA, UK
| | - David O'Hagan
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY15 5EA, UK
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Rodil A, Bosisio S, Ayoup MS, Quinn L, Cordes DB, Slawin AMZ, Murphy CD, Michel J, O'Hagan D. Metabolism and hydrophilicity of the polarised 'Janus face' all- cis tetrafluorocyclohexyl ring, a candidate motif for drug discovery. Chem Sci 2018; 9:3023-3028. [PMID: 29732086 PMCID: PMC5916015 DOI: 10.1039/c8sc00299a] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 02/17/2018] [Indexed: 01/07/2023] Open
Abstract
The metabolism and polarity of the all-cis tetra-fluorocyclohexane motif is explored in the context of its potential as a motif for inclusion in drug discovery programmes. Biotransformations of phenyl all-cis tetra-, tri- and di- fluoro cyclohexanes with the human metabolism model organism Cunninghamella elegans illustrates various hydroxylated products, but limited to benzylic hydroxylation for the phenyl all-cis tetrafluorocyclohexyl ring system. Evaluation of the lipophilicities (log P) indicates a significant and progressive increase in polarity with increasing fluorination on the cyclohexane ring system. Molecular dynamics simulations indicate that water associates much more closely with the hydrogen face of these Janus face cyclohexyl rings than the fluorine face owing to enhanced hydrogen bonding interactions with the polarised hydrogens and water.
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Affiliation(s)
- Andrea Rodil
- EaStChem School of Chemistry , University of St Andrews , North Haugh, St Andrews, Fife KY16 9ST , UK .
| | - Stefano Bosisio
- EaStChem School of Chemistry , University of Edinburgh , Joseph Black Building, David Brewster Road , Edinburgh , EH9 3FJ , UK .
| | - Mohammed Salah Ayoup
- EaStChem School of Chemistry , University of St Andrews , North Haugh, St Andrews, Fife KY16 9ST , UK . .,Department of Chemistry , Faculty of Science , Alexandria University , P.B. 426 Ibrahimia , Egypt
| | - Laura Quinn
- UCD School of Biomolecular and Biomedical Sciences , University College Dublin , Belfield , Dublin , Ireland .
| | - David B Cordes
- EaStChem School of Chemistry , University of St Andrews , North Haugh, St Andrews, Fife KY16 9ST , UK .
| | - Alexandra M Z Slawin
- EaStChem School of Chemistry , University of St Andrews , North Haugh, St Andrews, Fife KY16 9ST , UK .
| | - Cormac D Murphy
- UCD School of Biomolecular and Biomedical Sciences , University College Dublin , Belfield , Dublin , Ireland .
| | - Julien Michel
- EaStChem School of Chemistry , University of Edinburgh , Joseph Black Building, David Brewster Road , Edinburgh , EH9 3FJ , UK .
| | - David O'Hagan
- EaStChem School of Chemistry , University of St Andrews , North Haugh, St Andrews, Fife KY16 9ST , UK .
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Al-Maharik N, Kirsch P, Slawin AMZ, Cordes DB, O'Hagan D. Fluorinated liquid crystals: evaluation of selectively fluorinated facially polarised cyclohexyl motifs for liquid crystal applications. Org Biomol Chem 2018; 14:9974-9980. [PMID: 27722421 DOI: 10.1039/c6ob01986b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This paper explores the synthesis of a series of prototype negative dielectric liquid crystalline (LC) compounds which contain fluorinated cyclohexane motifs. The series are analogues and differ only in that they contain between one to four fluorine atoms. The stereochemistry is such that all of the fluorines/C-F bonds are on one face of the cyclohexane ring. This follows from the recent recognition that cyclohexanes with fluorines orientated in one direction, perpendicular to the ring have a strong molecular dipole, a characteristic that might be an advantage in the design of negative dielectric materials. However it is found that the increased polarity, particularly with two or more oriented C-F bonds, leads to higher melting points and poorer solubility in test matrix formulations, relative to hydrocarbon liquid crystals. This arises due to electrostatic intermolecular interactions between the polarised cyclohexyl and aryl rings. The study highlights that in order to take advantage of these polar cyclohexane motifs for liquid crystal design, appropriate scaffolds are required which are free of aromatic rings and contain peripheral solubilising motifs.
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Affiliation(s)
- Nawaf Al-Maharik
- EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK.
| | - Peer Kirsch
- Merck KGaA, Liquid Crystals R&D Chemistry, Frankfurter Str. 250, D-64293 Darmstadt, Germany.
| | - Alexandra M Z Slawin
- EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK.
| | - David B Cordes
- EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK.
| | - David O'Hagan
- EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews, Fife KY16 9ST, UK.
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10
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Bykova T, Al-Maharik N, Slawin AMZ, O'Hagan D. Fluorinated cyclohexanes: Synthesis of amine building blocks of the all- cis 2,3,5,6-tetrafluorocyclohexylamine motif. Beilstein J Org Chem 2017; 13:728-733. [PMID: 28503208 PMCID: PMC5405691 DOI: 10.3762/bjoc.13.72] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 03/28/2017] [Indexed: 01/07/2023] Open
Abstract
This paper reports the synthesis of three amine stereoisomers 5a–c of the tetrafluorocyclohexyl ring system, as building blocks for discovery chemistry programmes. The synthesis starts from a Birch reduction of benzonitrile, followed by an in situ methyl iodide quench. The resultant 2,5-cyclohexadiene was progressed via double epoxidations and then hydrofluorination ring opening reactions. The resultant fluorohydrin moieties were then converted to different stereoisomers of the tetrafluorocyclohexyl ring system, and then reductive hydrogenation of the nitrile delivered three amine stereoisomers. It proved necessary to place a methyl group on the cyclohexane ring in order to stabilise the compound against subsequent HF elimination. The two all-cis tetrafluorocyclohexyl isomers 5a and 5b constitute facially polarized cyclohexane rings, with fluorines on the electronegative face and hydrogens on the electropositive face.
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Affiliation(s)
- Tetiana Bykova
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK
| | - Nawaf Al-Maharik
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK
| | - Alexandra M Z Slawin
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK
| | - David O'Hagan
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK
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11
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Remete AM, Nonn M, Fustero S, Fülöp F, Kiss L. A Stereocontrolled Protocol to Highly Functionalized Fluorinated Scaffolds through a Fluoride Opening of Oxiranes. Molecules 2016; 21:molecules21111493. [PMID: 27869692 PMCID: PMC6274065 DOI: 10.3390/molecules21111493] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2016] [Revised: 09/19/2016] [Accepted: 11/04/2016] [Indexed: 11/18/2022] Open
Abstract
A novel selective and substrate-dependent synthetic protocol has been developed towards the synthesis of various fluorine-containing, highly functionalized cycloalkane derivatives. The method involves the stereoselective epoxidation of some unsaturated cyclic β-amino acid derivatives as model compounds, followed by a regioselective fluoride opening of oxiranes under various conditions with Deoxofluor and XtalFluor-E reagents, thereby offering an insight into this new epoxide opening methodology with fluoride.
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Affiliation(s)
- Attila Márió Remete
- Institute of Pharmaceutical Chemistry, University of Szeged, Eötvös u. 6, H-6720 Szeged, Hungary.
| | - Melinda Nonn
- MTA-SZTE Stereochemistry Research Group, Hungarian Academy of Sciences, Eötvös u. 6, H-6720 Szeged, Hungary.
| | - Santos Fustero
- Departamento de Química Orgánica, Facultad de Farmacia, Universidad de Valencia, Av. Vicente Andrés Estellés, s/n 46100 Valencia, Spain.
| | - Ferenc Fülöp
- Institute of Pharmaceutical Chemistry, University of Szeged, Eötvös u. 6, H-6720 Szeged, Hungary.
- MTA-SZTE Stereochemistry Research Group, Hungarian Academy of Sciences, Eötvös u. 6, H-6720 Szeged, Hungary.
| | - Loránd Kiss
- Institute of Pharmaceutical Chemistry, University of Szeged, Eötvös u. 6, H-6720 Szeged, Hungary.
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