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  1. Article: The fate of the contact ion pair determines the photochemistry of coumarin-based photocleavable protecting groups.

    Schulte, Albert Marten / Alachouzos, Georgios / Szymanski, Wiktor / Feringa, Ben L

    Chemical science

    2024  Volume 15, Issue 6, Page(s) 2062–2073

    Abstract: Photocleavable protecting groups (PPGs) enable the precise spatiotemporal control over the release of a payload of interest, in particular a bioactive substance, through light irradiation. A crucial parameter that determines the practical applicability ... ...

    Abstract Photocleavable protecting groups (PPGs) enable the precise spatiotemporal control over the release of a payload of interest, in particular a bioactive substance, through light irradiation. A crucial parameter that determines the practical applicability of PPGs is the efficiency of payload release, largely governed by the quantum yield of photolysis (QY). Understanding which parameters determine the QY will prove crucial for engineering improved PPGs and their effective future applications, especially in the emerging field of photopharmacology. The Contact Ion Pair (CIP) has been recognized as an important intermediate in the uncaging process, but the key influence of
    Language English
    Publishing date 2024-01-05
    Publishing country England
    Document type Journal Article
    ZDB-ID 2559110-1
    ISSN 2041-6539 ; 2041-6520
    ISSN (online) 2041-6539
    ISSN 2041-6520
    DOI 10.1039/d3sc05725a
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Article ; Online: Cation delocalization and photo-isomerization enhance the uncaging quantum yield of a photocleavable protecting group.

    Schulte, Albert Marten / Smid, Lianne M / Alachouzos, Georgios / Szymanski, Wiktor / Feringa, Ben L

    Chemical communications (Cambridge, England)

    2024  Volume 60, Issue 5, Page(s) 578–581

    Abstract: Photocleavable protecting groups (PPGs) enable the light-induced, spatiotemporal control over the release of a payload of interest. Two fundamental challenges in the design of new, effective PPGs are increasing the quantum yield (QY) of photolysis and ... ...

    Abstract Photocleavable protecting groups (PPGs) enable the light-induced, spatiotemporal control over the release of a payload of interest. Two fundamental challenges in the design of new, effective PPGs are increasing the quantum yield (QY) of photolysis and red-shifting the absorption spectrum. Here we describe the combination of two photochemical strategies for PPG optimization in one molecule, resulting in significant improvements in both these crucial parameters. Furthermore, we for the first time identify the process of photo-isomerization to strongly influence the QY of photolysis of a PPG and identify the
    Language English
    Publishing date 2024-01-11
    Publishing country England
    Document type Journal Article
    ZDB-ID 1472881-3
    ISSN 1364-548X ; 1359-7345 ; 0009-241X
    ISSN (online) 1364-548X
    ISSN 1359-7345 ; 0009-241X
    DOI 10.1039/d3cc05055f
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  3. Article ; Online: Strategy for Engineering High Photolysis Efficiency of Photocleavable Protecting Groups through Cation Stabilization.

    Schulte, Albert M / Alachouzos, Georgios / Szymański, Wiktor / Feringa, Ben L

    Journal of the American Chemical Society

    2022  Volume 144, Issue 27, Page(s) 12421–12430

    Abstract: Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote spatiotemporal control over the release of a molecule is needed. The design and ... ...

    Abstract Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote spatiotemporal control over the release of a molecule is needed. The design and application of PPGs in recent years have particularly focused on the development of molecules with high molar absorptivity at long irradiation wavelengths. However, a crucial parameter, which is pivotal to the efficiency of uncaging and which has until now proven highly challenging to improve, is the photolysis quantum yield (QY). Here, we describe a novel and general approach to greatly increase the photolysis QY of heterolytic PPGs through stabilization of an intermediate chromophore cation. When applied to coumarin PPGs, our strategy resulted in systems possessing an up to a 35-fold increase in QY and a convenient fluorescent readout during their uncaging, all while requiring the same number of synthetic steps for their preparation as the usual coumarin systems. We demonstrate that the same QY engineering strategy applies to different photolysis payloads and even different classes of PPGs. Furthermore, analysis of the DFT-calculated energy barriers in the first singlet excited state reveals valuable insights into the important factors that determine photolysis efficiency. The strategy reported herein will enable the development of efficient PPGs tailored for many applications.
    MeSH term(s) Cations ; Coumarins ; Photolysis
    Chemical Substances Cations ; Coumarins
    Language English
    Publishing date 2022-07-01
    Publishing country United States
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/jacs.2c04262
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  4. Article ; Online: Triplet-Triplet Energy Transfer: A Simple Strategy for an Efficient Visible Light-Induced Photoclick Reaction.

    Fu, Youxin / Alachouzos, Georgios / Simeth, Nadja A / Di Donato, Mariangela / Hilbers, Michiel F / Buma, Wybren Jan / Szymanski, Wiktor / Feringa, Ben L

    Angewandte Chemie (International ed. in English)

    2024  Volume 63, Issue 21, Page(s) e202319321

    Abstract: Photoclick reactions combine the advantages offered by light-driven processes and classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photo-crosslinking, and protein labeling. Despite these ... ...

    Abstract Photoclick reactions combine the advantages offered by light-driven processes and classical click chemistry and have found applications ranging from surface functionalization, polymer conjugation, photo-crosslinking, and protein labeling. Despite these advances, the dependency of most of the photoclick reactions on UV light poses a severe obstacle for their general implementation, as this light can be absorbed by other molecules in the system resulting in their degradation or unwanted reactivity. However, the development of a simple and efficient system to achieve bathochromically shifted photoclick transformations remains challenging. Here, we introduce triplet-triplet energy transfer as a fast and selective way to enable visible light-induced photoclick reactions. Specifically, we show that 9,10-phenanthrenequinones (PQs) can efficiently react with electron-rich alkenes (ERAs) in the presence of a catalytic amount (as little as 5 mol %) of photosensitizers. The photocycloaddition reaction can be achieved under green (530 nm) or orange (590 nm) light irradiation, representing a bathochromic shift of over 100 nm as compared to the classical PQ-ERAs system. Furthermore, by combining appropriate reactants, we establish an orthogonal, blue and green light-induced photoclick reaction system in which the product distribution can be precisely controlled by the choice of the color of light.
    Language English
    Publishing date 2024-04-12
    Publishing country Germany
    Document type Journal Article
    ZDB-ID 2011836-3
    ISSN 1521-3773 ; 1433-7851
    ISSN (online) 1521-3773
    ISSN 1433-7851
    DOI 10.1002/anie.202319321
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  5. Article: Strategy for Engineering High Photolysis Efficiency of Photocleavable Protecting Groups through Cation Stabilization

    Schulte, Albert M. / Alachouzos, Georgios / Szymański, Wiktor / Feringa, Ben L.

    Journal of the American Chemical Society. 2022 July 01, v. 144, no. 27

    2022  

    Abstract: Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote spatiotemporal control over the release of a molecule is needed. The design and ... ...

    Abstract Photolabile protecting groups (PPGs) enable the precise activation of molecular function with light in many research areas, such as photopharmacology, where remote spatiotemporal control over the release of a molecule is needed. The design and application of PPGs in recent years have particularly focused on the development of molecules with high molar absorptivity at long irradiation wavelengths. However, a crucial parameter, which is pivotal to the efficiency of uncaging and which has until now proven highly challenging to improve, is the photolysis quantum yield (QY). Here, we describe a novel and general approach to greatly increase the photolysis QY of heterolytic PPGs through stabilization of an intermediate chromophore cation. When applied to coumarin PPGs, our strategy resulted in systems possessing an up to a 35-fold increase in QY and a convenient fluorescent readout during their uncaging, all while requiring the same number of synthetic steps for their preparation as the usual coumarin systems. We demonstrate that the same QY engineering strategy applies to different photolysis payloads and even different classes of PPGs. Furthermore, analysis of the DFT-calculated energy barriers in the first singlet excited state reveals valuable insights into the important factors that determine photolysis efficiency. The strategy reported herein will enable the development of efficient PPGs tailored for many applications.
    Keywords absorptivity ; cations ; coumarin ; energy ; fluorescence ; heterolytic cleavage ; irradiation ; photolysis
    Language English
    Dates of publication 2022-0701
    Size p. 12421-12430.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/jacs.2c04262
    Database NAL-Catalogue (AGRICOLA)

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  6. Article: Stereochemical Relay through a Cationic Intermediate: Helical Preorganization Dictates Direction of Conrotation in the halo-Nazarov Cyclization

    Alachouzos, Georgios / Holt, Connor / Frontier, Alison J

    Organic letters. 2020 Apr. 30, v. 22, no. 10

    2020  

    Abstract: A stereocontrolled halo-Prins/halo-Nazarov cyclization protocol is reported, where chiral information from a secondary alcohol is relayed through several intermediates yielding halocyclopentene products diastereoselectively. An enantiopure product is ... ...

    Abstract A stereocontrolled halo-Prins/halo-Nazarov cyclization protocol is reported, where chiral information from a secondary alcohol is relayed through several intermediates yielding halocyclopentene products diastereoselectively. An enantiopure product is obtained when a nonracemic secondary alcohol is used. Experimental and computational studies are described, enabling the design and synthesis of systems that ionize and cyclize with >95% chirality transfer through a mechanism involving the creation and preservation of transient helical chirality in a pentadienyl cation intermediate. First, a diastereoselective alkynyl Prins cyclization is executed to synthesize a conformationally distorted dihydropyran intermediate with a curved backbone and high reactivity. This chiral precursor adopts a specific helical alignment early in the subsequent cationic ionization/halo-Nazarov cyclization process, dictating the direction of conrotation in the electrocyclization. Notably, despite the ablation of an sp³ stereogenic center during ionization, the low halo-Nazarov barrier enables efficient capture of a cationic intermediate with dynamic conformational chirality. The ionization and electrocyclization thus occur with “memory of chirality”.
    Keywords alcohols ; cations ; diastereoselectivity ; enantiomers ; ionization ; optical isomerism ; stereochemistry
    Language English
    Dates of publication 2020-0430
    Size p. 4010-4015.
    Publishing place American Chemical Society
    Document type Article
    Note NAL-AP-2-clean
    ISSN 1523-7052
    DOI 10.1021/acs.orglett.0c01330
    Database NAL-Catalogue (AGRICOLA)

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  7. Article ; Online: Cationic Cascade for Building Complex Polycyclic Molecules from Simple Precursors: Diastereoselective Installation of Three Contiguous Stereogenic Centers in a One-Pot Process.

    Alachouzos, Georgios / Frontier, Alison J

    Journal of the American Chemical Society

    2018  Volume 141, Issue 1, Page(s) 118–122

    Abstract: An expedient strategy for the synthesis of polycyclic small molecules is described. The method first joins together two achiral building blocks (an enyne and an aldehyde or a ketone) using an alkynyl halo-Prins protocol. Then, in the same reaction vessel, ...

    Abstract An expedient strategy for the synthesis of polycyclic small molecules is described. The method first joins together two achiral building blocks (an enyne and an aldehyde or a ketone) using an alkynyl halo-Prins protocol. Then, in the same reaction vessel, acidic conditions initiate a cationic cascade that includes a stereospecific halo-Nazarov electrocyclization and a diastereoselective Friedel-Crafts allylation. The entire sequence forms three carbon-carbon bonds and a carbon-halogen bond, generating halocyclopentene adducts in one pot from simple precursors. The process occurs with excellent diastereocontrol, providing highly functionalized polycycles containing three tertiary or quaternary stereogenic centers in a linear array. It is even possible to install three contiguous all-carbon quaternary centers using this method.
    Language English
    Publishing date 2018-12-20
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/jacs.8b11713
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  8. Article: Cationic Cascade for Building Complex Polycyclic Molecules from Simple Precursors: Diastereoselective Installation of Three Contiguous Stereogenic Centers in a One-Pot Process

    Alachouzos, Georgios / Alison J. Frontier

    Journal of the American Chemical Society. 2018 Dec. 20, v. 141, no. 1

    2018  

    Abstract: An expedient strategy for the synthesis of polycyclic small molecules is described. The method first joins together two achiral building blocks (an enyne and an aldehyde or a ketone) using an alkynyl halo-Prins protocol. Then, in the same reaction vessel, ...

    Abstract An expedient strategy for the synthesis of polycyclic small molecules is described. The method first joins together two achiral building blocks (an enyne and an aldehyde or a ketone) using an alkynyl halo-Prins protocol. Then, in the same reaction vessel, acidic conditions initiate a cationic cascade that includes a stereospecific halo-Nazarov electrocyclization and a diastereoselective Friedel–Crafts allylation. The entire sequence forms three carbon–carbon bonds and a carbon–halogen bond, generating halocyclopentene adducts in one pot from simple precursors. The process occurs with excellent diastereocontrol, providing highly functionalized polycycles containing three tertiary or quaternary stereogenic centers in a linear array. It is even possible to install three contiguous all-carbon quaternary centers using this method.
    Keywords aldehydes ; allylation ; chemical bonding ; diastereoselectivity
    Language English
    Dates of publication 2018-1220
    Size p. 118-122.
    Publishing place American Chemical Society
    Document type Article
    ZDB-ID 3155-0
    ISSN 1520-5126 ; 0002-7863
    ISSN (online) 1520-5126
    ISSN 0002-7863
    DOI 10.1021/jacs.8b11713
    Database NAL-Catalogue (AGRICOLA)

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  9. Article ; Online: Stereochemical Relay through a Cationic Intermediate: Helical Preorganization Dictates Direction of Conrotation in the

    Alachouzos, Georgios / Holt, Connor / Frontier, Alison J

    Organic letters

    2020  Volume 22, Issue 10, Page(s) 4010–4015

    Abstract: ... A ... ...

    Abstract A stereocontrolled
    Language English
    Publishing date 2020-04-30
    Publishing country United States
    Document type Journal Article ; Research Support, U.S. Gov't, Non-P.H.S.
    ISSN 1523-7052
    ISSN (online) 1523-7052
    DOI 10.1021/acs.orglett.0c01330
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article ; Online: Correction to "Stereochemical Relay through a Cationic Intermediate: Helical Preorganization Dictates Direction of Conrotation in the

    Alachouzos, Georgios / Holt, Connor / Frontier, Alison J

    Organic letters

    2020  Volume 22, Issue 14, Page(s) 5713

    Language English
    Publishing date 2020-07-07
    Publishing country United States
    Document type Published Erratum
    ISSN 1523-7052
    ISSN (online) 1523-7052
    DOI 10.1021/acs.orglett.0c02062
    Database MEDical Literature Analysis and Retrieval System OnLINE

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