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Dennis G. Hall - One of the best experts on this subject based on the ideXlab platform.

  • Boronic Acid catalysis.
    Chemical Society reviews, 2019
    Co-Authors: Dennis G. Hall
    Abstract:

    Although Boronic Acids are recognized primarily for their utility as reagents in transition metal-catalyzed transformations, other applications are emerging, including their use as reaction catalysts. Few methods are available for the catalytic activation of hydroxy functional groups as a way to promote their direct transformation into useful products under mild conditions. To this end, the ability of Boronic Acids to form reversible covalent bonds with hydroxy groups can be exploited to enable both electrophilic and nucleophilic modes of activation in various organic reactions. Using the concept of Boronic Acid catalysis (BAC), electrophilic activation of carboxylic Acids leads to the formation of amides from amines, as well as cycloadditions and conjugate additions with unsaturated carboxylic Acids. Alcohols can also be activated with Boronic Acid catalysts to form carbocation intermediates that can be trapped in selective Friedel–Crafts-type reactions with arenes and other nucleophiles. On the other hand, diols and saccharides can form tetrahedral adducts with Boronic Acids, which increases their nucleophilic character towards electrophiles. Altogether, BAC imparts mild and selective reaction conditions that display high atom-economy by circumventing the need for wasteful stoichiometric activation of hydroxy groups into halides or sulfonates.

  • mild Boronic Acid catalyzed nazarov cyclization of divinyl alcohols in tandem with diels alder cycloaddition
    ChemInform, 2013
    Co-Authors: Hongchao Zheng, Michal Lejkowski, Dennis G. Hall
    Abstract:

    A convenient one-pot method is presented for the stereoselective synthesis of highly functionalized bicyclic compounds (III) via Boronic Acid catalyzed Nazarov cyclization of divinyl alcohols and subsequent Diels—Alder reaction with maleic anhydride or phenylmaleimide.

  • mild Boronic Acid catalyzed nazarov cyclization of divinyl alcohols in tandem with diels alder cycloaddition
    Tetrahedron Letters, 2013
    Co-Authors: Hongchao Zheng, Michal Lejkowski, Dennis G. Hall
    Abstract:

    Abstract Boronic Acid catalysis (BAC) was applied to a sequential Nazarov cyclization of divinyl alcohols/Diels–Alder cycloadditions leading to the preparation of highly functionalized bicyclic compounds in a highly diastereoselective fashion. In these one-pot transformations, highly functionalized dienes were generated in situ through Boronic Acid catalyzed Nazarov cyclizations of divinyl alcohols and were subsequently trapped with different dienophiles such as maleic anhydride and phenylmaleimide. The tandem reactions proceed directly from divinyl alcohols under very mild reaction conditions using air-stable catalysts, and as such this methodology represents a greener alternative to existing methods employing strong Lewis and Bronsted Acids.

  • Boronic Acid catalysis for mild and selective 3 2 dipolar cycloadditions to unsaturated carboxylic Acids
    ChemInform, 2010
    Co-Authors: Hongchao Zheng, Robert Mcdonald, Dennis G. Hall
    Abstract:

    Free, unsaturated carboxylic Acids can participate directly in dipolar cycloadditions with azides, nitrile oxides, and nitrones by using mild Boronic Acid catalysis at room temperature to give readily isolated heterocyclic products.

  • Boronic Acid catalysis for mild and selective 3 2 dipolar cycloadditions to unsaturated carboxylic Acids
    Chemistry: A European Journal, 2010
    Co-Authors: Hongchao Zheng, Robert Mcdonald, Dennis G. Hall
    Abstract:

    Herein, the concept of Boronic Acid catalysis (BAC) for the activation of unsaturated carboxylic Acids is applied in several classic dipolar [3+2] cycloadditions involving azides, nitrile oxides, and nitrones as partners. These cycloadditions can be used to produce pharmaceutically interesting, small heterocyclic products, such as triazoles, isoxazoles, and isoxazolidines. These cycloadducts are formed directly and include a free carboxylic Acid functionality that can be employed for further transformations, thereby avoiding prior masking or functionalization. In all cases, BAC provides faster reactions, under milder conditions, with much improved product yields and regioselectivities. In some instances, such as triazole formation from the reaction of azides with 2-alkynoic Acids, catalysis with ortho-nitrophenylBoronic Acid circumvents the undesirable product decarboxylation observed when using thermal activation. By using NMR spectroscopic studies, the Boronic Acid catalyst was shown to provide activation by a LUMO-lowering effect in the unsaturated carboxylic Acid, likely via a monoacylated hemiBoronic ester intermediate.

Hongchao Zheng - One of the best experts on this subject based on the ideXlab platform.

Seiji Shinkai - One of the best experts on this subject based on the ideXlab platform.

  • fluorescent sensing of uronic Acids based on a cooperative action of Boronic Acid and metal chelate
    Chemical Communications, 1997
    Co-Authors: Masayuki Takeuchi, Masashi Yamamoto, Seiji Shinkai
    Abstract:

    A new fluorescent molecular sensor for uronic Acids is designed, which features two-point interactions of Boronic Acid–diol complexation and zinc(II)–carboxylate coordination.

  • Discrimination between glucose-1-phosphate and glucose-6-phosphate with a Boronic-Acid-appended metalloporphyrin
    Tetrahedron Letters, 1995
    Co-Authors: Tomoyuki Imada, Hideomi Kijima, Masayuki Takeuchi, Seiji Shinkai
    Abstract:

    Abstract When D-glucose-6-phosphate (G-6-P) is bound to Boronic-Acid-appended zinc(II) porphyrin ( 2 ), the δp value in 31 P NMR spectroscopy markedly shifts to higher magnetic field and a strong exciton-coupling band appears in CD spectroscopy. Such large changes are not observable for 2 plus D-glucose, 2 plus α-D-glucose-1-phosphate (G-1-P), and for Boronic-Acid-appended porphyrin (free base: 1 ) plus these glucose derivatives. This is first example that G-1-P and G-6-P are successfully discriminated by an artificial receptor.

  • novel saccharide photoinduced electron transfer sensors based on the interaction of Boronic Acid and amine
    Journal of the American Chemical Society, 1995
    Co-Authors: Tony D. James, K Samankumara R A Sandanayake, Ritsuko Iguchi, Seiji Shinkai
    Abstract:

    Two Boronic Acid systems, monoBoronic Acid 3 and diBoronic Acid 8, were synthesized. When saccharides form cyclic boronate esters with these Boronic Acids, the Lewis Acid-base interaction between the Boronic Acid moiety and tertiary amine is strengthened; when saccharides form cyclic boronate esters with Boronic Acids the Acidity of the Boronic Acid is enhanced. The strength of this Acid-base interaction modulates the photoinduced electron transfer (PET) from the amine to anthracene. Both of these compounds show increased fluoresecence at pH 7.77 through supression of the photoinduced electron transfer from nitrogen to anthracene on saccharide binding, a direct result of the stronger boron-nitrogen bond. Compound 3 shows the typical selectivity of monoBoronic Acids towards saccharides. Compound 8 which has a cleftlike structure is particularly selective and sensitive for, glucose due to the formation of an intramolecular 1:1 complex between the two Boronic Acids and the 1,2- and 4,6-hydroxyls of glucose. This is the first example in which ditopic recognition of monosaccharides is achieved in a PET sensor system.

Binghe Wang - One of the best experts on this subject based on the ideXlab platform.

  • selecting aptamers for a glycoprotein through the incorporation of the Boronic Acid moiety
    Journal of the American Chemical Society, 2008
    Co-Authors: Na Lin, Zhen Huang, Craig Altier, Hao Fang, Binghe Wang
    Abstract:

    The first general method for the selection of Boronic Acid−based aptamers (boronolectins) that allows for glycan substructure focusing is described. Using fibrinogen as a model glycoprotein, we have selected Boronic Acid-modified DNA aptamers that have high affinities (low nM Kd) and the ability to recognize changes in the glycosylation site. The method developed should also be applicable to the development of aptamers for other glycoproducts, such as glycolipids and glycopeptides.

  • regulating the fluorescence intensity of an anthracene Boronic Acid system a b n bond or a hydrolysis mechanism
    Bioorganic Chemistry, 2004
    Co-Authors: Gurpreet Kaur, Binghe Wang, Greg Springsteen, Stefan Franzen
    Abstract:

    An anthracene-based fluorescent Boronic Acid system developed by the Shinkai group has been widely used for the preparation of fluorescent sensors for carbohydrates. Such application is based on the significant fluorescence intensity increase of this system upon binding with a carbohydrate. The mechanism through which this fluorescence intensity change happens was originally proposed to go through a B-N bond formation mechanism, which masks the nitrogen lone pair electrons. However, our own fluorescence studies suggest a possible alternative mechanism for the fluorescence change upon the formation of a Boronic Acid (1a) complex with diols. In this new proposed mechanism, complex formation induces solvolysis, which results in the protonation of the amine nitrogen if the reactions are carried out in a protic solvent such as water. This protonation prevents the photoinduced electron transfer, resulting in reduced quenching of the anthracene fluorescence. Such a solvolysis mechanism is supported by evidence from various types of experiments and theoretical calculations.

  • Progress in Boronic Acid-Based Fluorescent Glucose Sensors
    Journal of Fluorescence, 2004
    Co-Authors: Hao Fang, Gurpreet Kaur, Binghe Wang
    Abstract:

    Effective management of diabetes relies on the frequent monitoring of blood glucose concentrations. The current approach of blood sampling and glucose concentration determination in vitro presents many problems. Therefore, there is a drive for the development of non-invasive and continuous monitoring of glucose concentrations. The use of implanted glucose fluorescent sensors represents a promising approach. Due to its strong interaction with diol moieties, the Boronic Acid group often plays a critical role in the design of such glucose sensors. This paper reviews the progress in this area during the last ten years.

  • Boronic Acid compounds as potential pharmaceutical agents.
    Medicinal research reviews, 2003
    Co-Authors: Wenqian Yang, Xingming Gao, Binghe Wang
    Abstract:

    Boronic Acid compounds have been used, because of their unique structural features, for the development of potent enzyme inhibitors, boron neutron capture agents for cancer therapy, and as antibody mimics that recognize biologically important saccharides. Consequently, there has been a surge of interests in Boronic Acid compounds. This study reviews the recent development in this area during the last six years.

  • a detailed examination of Boronic Acid diol complexation
    Tetrahedron, 2002
    Co-Authors: Greg Springsteen, Binghe Wang
    Abstract:

    Abstract Boronic Acids bind with compounds containing diol moieties with high affinity through reversible boronate formation. However, the conditions that foster tight binding between the diol and the Boronic Acid are not well understood. Also, due to the multiple ionic states of both the Boronic Acid and boronate ester, the equilibrium constants reported in the literature have not always been strictly defined, and therefore there is a lack of ‘comparability’ between the reported values. To address these issues, we have developed a method for examining boronate ester stability using the fluorescent reporter Alizarin Red S. We have used this system to determine the binding constants of a series of diols, and as a basis from which to derive a number of relationships that correlate the various equilibrium constants in the literature.

Mark S Taylor - One of the best experts on this subject based on the ideXlab platform.