Xu, Wei



Faculty of Pharmacy, Department of Pharmaceutical Sciences 分子創成化学講座 (Shiba-Kyoritsu)


Research Associate/Assistant Professor/Instructor


Papers 【 Display / hide

  • A brief introduction to highly symmetric N-heteroarene-based macrocycles

    Xu W., Kumagai N.

    Tetrahedron (Tetrahedron)  141 2023.07

    ISSN  00404020

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    Nitrogen-containing macrocycles have attracted sustained attention because of their fascinating structures and extensive applications in organic chemistry, therapeutic developments, and materials science. The nitrogen atoms in the macrocycles play important roles in the interaction with metal cations or small molecules, endowing their potential in catalysis, fluorescent sensors, and host–guest chemistry. In this context, herein we summarize highly symmetric nitrogen-containing N3/N4/N6 macrocycles comprising pyrroles, pyridines, quinolines, and (iso)indoles as key N-heteroarenes. The direct and indirect connectivity of N-heteroarene subunits allows for the construction of both flat and non-flat cyclic architectures. The synthesis, structure, and properties of these macrocycles are highlighted.

  • TEtraQuinolines: A Missing Link in the Family of Porphyrinoid Macrocycles

    Xu W., Nagata Y., Kumagai N.

    Journal of the American Chemical Society (Journal of the American Chemical Society)  145 ( 4 ) 2609 - 2618 2023.02

    ISSN  00027863

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    Porphyrin contains four inwardly oriented nitrogen atoms. It is arguably the most ubiquitous multifunctional naturally occurring macrocycle that has inspired the design of novel nitrogen-containing heterocycles for decades. While cyclic tetramers of pyrrole, indole, and pyridine have been exploited as macrocycles in this category, quinoline has been largely neglected as a synthon. Herein, we report the synthesis of TEtraQuinoline (TEQ) as a ‘missing link’ in this N4 macrocycle family. In TEQs, four quinoline units are concatenated to produce an S4-symmetric architecture. TEQs are characterized by a highly rigid saddle shape, wherein the lone-pair orbitals of the four nitrogen atoms are not aligned in a planar fashion. Nevertheless, TEQs can coordinate a series of transition-metal cations (Fe2+, Co2+, Ni2+, Cu2+, Zn2+, and Pd2+). TEQs are inherently fluorescence-silent but become strongly emissive upon protonation or complexation of Zn(II) cations (ϕ = 0.71). TEQ/Fe(II) complexes can catalyze dehydrogenation and oxygenation reactions with catalyst loadings as low as 0.1 mol %.

  • Azo-tagged C4N4 fluorophores: unusual overcrowded structures and their application to fluorescent imaging

    Kohei M., Takizawa N., Tsutsumi R., Xu W., Kumagai N.

    Organic and Biomolecular Chemistry (Organic and Biomolecular Chemistry)  21 ( 14 ) 2889 - 2893 2023.01

    ISSN  14770520

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    The C4N4 fluorophore is an intense fluorescence emitter featuring a 2,5-diaminopyrimidine core comprising four carbon and four nitrogen atoms. A series of C4N4 derivatives was photochemically dimerized at the 5-amino group, furnishing overcrowded orthotetraaryl-substituted diaryl azo compounds with a characteristic skewed structure revealed by X-ray crystallography. The photo-quenched azo-C4N4s are useful for fluorescently visualizing cells under hypoxic conditions.

  • Chemoselective Catalytic Dehydrogenation of Benzylic Amines Driven by the TEtraQuinoline/FeCl<inf>2</inf> Complex

    Nishiwaki M., Xu W., Kumagai N.

    Asian Journal of Organic Chemistry (Asian Journal of Organic Chemistry)  12 ( 9 )  2023

    ISSN  21935807

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    A chemoselective dehydrogenation protocol for benzylic amines catalyzed by the TEtraQuinoline (TEQ)/FeCl2 complex is described. In combination with 2 equiv of tert-butyl hydroperoxide, as little as 0.1 mol% of catalyst loading was sufficient to convert primary and secondary benzylic amines to the corresponding imines and dimerized imines, respectively. Subsequent hydrolysis of the imines allowed for removal of the benzyl group on the nitrogen atom. Nonaromatic carbon-carbon multiple bonds and the O-Bn group remained intact in the present protocol, providing a complementary deprotection procedure to reductive removal conditions exerted by Pd catalysis.

  • Strategic Synthesis of Asymmetrically Substituted C4N4 Fluorophores

    Xu W., Kohei M., Shibasaki M., Kumagai N.

    Synthesis (Germany) (Synthesis (Germany))  53 ( 18 ) 3355 - 3360 2021.09

    ISSN  00397881

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    C4N4 fluorophores comprise a recently disclosed new class of emissive organic molecules with modular synthetic capabilities. Herein, we report a new synthetic protocol toward asymmetrically di arylated C4N4 fluorescent materials. Direct monoarylation of 1-naphthol is exploited to suppress undesired diarylation and to provide a free phenolic hydroxy group for prospective linking to a molecule of interest. Installation of the second aromatic unit in order to acquire fluorescent properties is achieved by Suzuki-Miyaura cross-coupling.

Research Projects of Competitive Funds, etc. 【 Display / hide

  • Strategic Exploration of Quinoline-Based Materials


    MEXT,JSPS, Grant-in-Aid for Scientific Research, 若手研究, Principal investigator


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