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Jesani MH, Schwarz M, Kim S, Evans FL, White A, Browning A, Abrams R, Clayden J. Selective Defluorination of Trifluoromethyl Substituents by Conformationally Induced Remote Substitution. Angew Chem Int Ed Engl 2024; 63:e202403477. [PMID: 38587304 DOI: 10.1002/anie.202403477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2024] [Revised: 03/28/2024] [Accepted: 04/02/2024] [Indexed: 04/09/2024]
Abstract
The selective reduction of an aromatic trifluoromethyl substituent to a difluoromethyl substituent may be achieved by base-promoted elimination to form a difluoro-p-quinomethide which is trapped by an intramolecular nucleophile. High yields are obtained when the nucleophilic trap entails the conformationally favoured cyclisation of an aminoisobutyric acid (Aib) derivative. The resulting cyclised difluoromethyl-substituted arylimidazolidinone products are readily converted to versatile difluoromethyl-substituted aldehydes by reduction and hydrolysis. Defluorination is successful on a range of benzenoid (both para and ortho CF3-substituted) and heterocyclic substrates. Double defluorination may likewise be achieved sequentially, or in a single step, from an Aib dipeptide derivative.
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Affiliation(s)
- Mehul H Jesani
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Maria Schwarz
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Shiwhu Kim
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Finlay L Evans
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Alexander White
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Alex Browning
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Roman Abrams
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
| | - Jonathan Clayden
- School of Chemistry, University of Bristol Cantock's Close, Bristol, BS8 1TS, UK
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Lago-Silva M, Fernández-Míguez M, Rodríguez R, Quiñoá E, Freire F. Stimuli-responsive synthetic helical polymers. Chem Soc Rev 2024; 53:793-852. [PMID: 38105704 DOI: 10.1039/d3cs00952a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Synthetic dynamic helical polymers (supramolecular and covalent) and foldamers share the helix as a structural motif. Although the materials are different, these systems also share many structural properties, such as helix induction or conformational communication mechanisms. The introduction of stimuli responsive building blocks or monomer repeating units in these materials triggers conformational or structural changes, due to the presence/absence of the external stimulus, which are transmitted to the helix resulting in different effects, such as assymetry amplification, helix inversion or even changes in the helical scaffold (elongation, J/H helical aggregates). In this review, we show through selected examples how different stimuli (e.g., temperature, solvents, cations, anions, redox, chiral additives, pH or light) can alter the helical structures of dynamic helical polymers (covalent and supramolecular) and foldamers acting on the conformational composition or molecular structure of their components, which is also transmitted to the macromolecular helical structure.
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Affiliation(s)
- María Lago-Silva
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
| | - Manuel Fernández-Míguez
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
| | - Rafael Rodríguez
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
| | - Emilio Quiñoá
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
| | - Félix Freire
- Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela, E-15782 Santiago de Compostela, Spain.
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Yang Y, Xue M. Herringbone Helical Foldamers from Aromatic Ether Derived ϵ-Amino Acid Peptides. Chemistry 2023; 29:e202301832. [PMID: 37641870 DOI: 10.1002/chem.202301832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 08/28/2023] [Accepted: 08/29/2023] [Indexed: 08/31/2023]
Abstract
Oligomers based on an aromatic ether derived ϵ-amino acid peptides folded into herringbone helical structures, induced by successive NH-O-NH & O-NH-O bifurcated hydrogen bonding interactions and reinforced by π-π stacking between aryls from adjacent layers. The diaryl ether bonds -O- worked both as structural units to provide turn motifs for changing the amplitude of the slope along the axis of helix for herringbone formation, and also as acceptors for hydrogen bonding. Attachment of a single chiral carbon to the C-termini of the peptides induced excess of single-handed screw sense and amplification through the chain propagation as exemplified by chain length dependent circular dichroism (CD) investigations.
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Affiliation(s)
- Yong Yang
- School of Chemistry and Chemical Engineering, Key Laboratory of Surface & Interface Science of Polymer Materials of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
| | - Min Xue
- School of Science, Department of Physics, Key Laboratory of Optical Field Manipulation of Zhejiang Province, Zhejiang Sci-Tech University, Hangzhou, 310018, China
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Abstract
As an active branch within the field of supramolecular polymers, chiral supramolecular polymers (SPs) are an excellent benchmark to generate helical structures that can clarify the origin of homochirality in Nature or help determine new exciting functionalities of organic materials. Herein, we highlight the most utilized strategies to build up chiral SPs by using chiral monomeric units or external stimuli. Selected examples of transfer of asymmetry, in which the point or axial chirality contained by the monomeric units is efficiently transferred to the supramolecular scaffold yielding enantioenriched helical structures, will be presented. The importance of the thermodynamics and kinetics associated with those processes is stressed, especially the influence that parameters such as the helix reversal and mismatch penalties exert on the achievement of amplification of asymmetry in co-assembled systems will also be considered. Remarkable examples of breaking symmetry, in which chiral supramolecular polymers can be attained from achiral self-assembling units by applying external stimuli like stirring, solvent or light, are highlighted. Finally, the specific and promising applications of chiral supramolecular polymers are presented with recent relevant examples.
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Affiliation(s)
- Fátima García
- Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040-Madrid, Spain.
| | - Rafael Gómez
- Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040-Madrid, Spain.
| | - Luis Sánchez
- Departamento de Química Orgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria s/n, 28040-Madrid, Spain.
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Ousaka N, MacLachlan MJ, Akine S. Stapling strategy for slowing helicity interconversion of α-helical peptides and isolating chiral auxiliary-free one-handed forms. Nat Commun 2023; 14:6834. [PMID: 37884515 PMCID: PMC10603036 DOI: 10.1038/s41467-023-42493-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 10/12/2023] [Indexed: 10/28/2023] Open
Abstract
In nature, α-helical peptides adopt right-handed conformations that are dictated by L-amino acids. Isolating one-handed α-helical peptides composed of only achiral components remains a significant challenge. Here, this goal is achieved by optical resolution of the corresponding racemic (quasi-)static α-helical peptide with double stapling, which effectively freezes the interconversion between the right-handed (P)- and left-handed (M)-α-helices. An as-obtained doubly stapled analogue having an unprotected L-valine residue at the C-terminus transforms from a kinetically trapped (M)-α-helix to a thermodynamically stable (P)-α-helix upon heating. In contrast, the corresponding singly stapled α-helical peptide undergoes an acid/base-triggered and solvent-induced reversible inversion of its preferred helicity within minutes. The interconversion rates of the singly and doubly stapled α-helical peptide foldamers are approximately 106 and 1012 times slower, respectively, than that of a non-stapled dynamic helical peptide. Therefore, the enantiopure doubly-stapled (quasi-)static α-helical peptide would retain its optical activity for several years at 25 °C.
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Affiliation(s)
- Naoki Ousaka
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.
| | - Mark J MacLachlan
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.
- Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, V6T 1Z1, Canada.
- Quantum Matter Institute, University of British Columbia, 2355 East Mall, Vancouver, BC, V6T 1Z4, Canada.
| | - Shigehisa Akine
- Nano Life Science Institute (WPI-NanoLSI), Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan.
- Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, 920-1192, Japan.
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Morris DJ, Wales SM, Echavarren J, Žabka M, Marsico G, Ward JW, Pridmore NE, Clayden J. Dynamic and Persistent Cyclochirality in Hydrogen-Bonded Derivatives of Medium-Ring Triamines. J Am Chem Soc 2023; 145:19030-19041. [PMID: 37594473 PMCID: PMC10472504 DOI: 10.1021/jacs.3c06570] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Indexed: 08/19/2023]
Abstract
Cyclic triureas derived from 1,4,7-triazacyclononane (TACN) were synthesized; X-ray crystallography showed a chiral bowl-like conformation with each urea hydrogen-bonded to its neighbor with uniform directionality, forming a "cyclochiral" closed loop of hydrogen bonds. Variable-temperature 1H NMR, 1H-1H exchange spectroscopy, Eyring analysis, computational modeling, and studies in various solvents revealed that cyclochirality is dynamic (ΔG‡25°C = 63-71 kJ mol-1 in noncoordinating solvents), exchanging between enantiomers by two mechanisms: bowl inversion and directionality reversal, with the former subject to a slightly smaller enantiomerization barrier. The enantiomerization rate substantially increased in the presence of hydrogen-bonding solvents. Population of only one of the two cyclochiral hydrogen-bond directionalities could be induced by annulating one ethylene bridge with a trans-cyclohexane. Alternatively, enantiomerization could be inhibited by annulating one ethylene bridge with a cis-cyclohexane (preventing bowl inversion) and replacing one urea function with a formamide (preventing directionality reversal). Combining these structural modifications resulted in an enantiomerization barrier of ΔG‡25°C = 93 kJ mol-1, furnishing a planar-chiral, atropisomeric bowl-shaped structure whose stereochemical stability arises solely from its hydrogen-bonding network.
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Affiliation(s)
| | | | - Javier Echavarren
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - Matej Žabka
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - Giulia Marsico
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - John W. Ward
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - Natalie E. Pridmore
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
| | - Jonathan Clayden
- School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, U.K.
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McCann S, Roe WE, Agnew HE, Knipe PC. Non-Covalent Interactions Enforce Conformation in Switchable and Water-Soluble Diketopiperazine-Pyridine Foldamers. Angew Chem Int Ed Engl 2023; 62:e202307180. [PMID: 37414732 PMCID: PMC10952507 DOI: 10.1002/anie.202307180] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2023] [Revised: 07/05/2023] [Accepted: 07/06/2023] [Indexed: 07/08/2023]
Abstract
To reach their potential as mimics of the dynamic molecules present in biological systems, foldamers must be designed to display stimulus-responsive behavior. Here we report such a foldamer architecture based on alternating pyridine-diketopiperazine linkers. Epimerization is conveniently prevented through a copper-catalyzed coupling protocol. The compounds' native unswitched conformation is first discovered in the solid and solution state. The foldamers can be solubilized in DMSO and pH 9.5 buffer, retaining conformational control to a large degree. Lastly, dynamic switching is demonstrated through treatment with acid, leading to behaviour we describe as stimulus-responsive sidechain reconfiguration.
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Affiliation(s)
- Sinead McCann
- School of Chemistry and Chemical EngineeringQueen's University BelfastDavid Keir Building, Stranmillis RoadBelfastBT9 5AGUK
| | - William E. Roe
- School of Chemistry and Chemical EngineeringQueen's University BelfastDavid Keir Building, Stranmillis RoadBelfastBT9 5AGUK
| | - Hannah E. Agnew
- School of Chemistry and Chemical EngineeringQueen's University BelfastDavid Keir Building, Stranmillis RoadBelfastBT9 5AGUK
| | - Peter C. Knipe
- School of Chemistry and Chemical EngineeringQueen's University BelfastDavid Keir Building, Stranmillis RoadBelfastBT9 5AGUK
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