The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Oliver Reiser - One of the best experts on this subject based on the ideXlab platform.
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bromo or Methoxy Group promoted umpolung electron transfer enabled visible light mediated synthesis of 2 substituted indole 3 glyoxylates
Organic Letters, 2018Co-Authors: Adiyala Vidyasagar, Peter Kreitmeier, Oliver ReiserAbstract:A visible-light-mediated radical tandem cyclization of ortho-isocyano-α-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C–C/C–S and C–O bonds. The reaction proceeds through a hitherto unprecedented bromine- or Methoxy-Group-promoted umpolung back electron transfer from an α-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate Group installed in the products can be utilized for several biologically relevant manipulations.
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Bromo- or Methoxy-Group-Promoted Umpolung Electron Transfer Enabled, Visible-Light-Mediated Synthesis of 2‑Substituted Indole-3-glyoxylates
2018Co-Authors: Adiyala Vidyasagar, Peter Kreitmeier, Jinwei Shi, Oliver ReiserAbstract:A visible-light-mediated radical tandem cyclization of ortho-isocyano-α-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C–C/C–S and C–O bonds. The reaction proceeds through a hitherto unprecedented bromine- or Methoxy-Group-promoted umpolung back electron transfer from an α-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate Group installed in the products can be utilized for several biologically relevant manipulations
Adiyala Vidyasagar - One of the best experts on this subject based on the ideXlab platform.
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bromo or Methoxy Group promoted umpolung electron transfer enabled visible light mediated synthesis of 2 substituted indole 3 glyoxylates
Organic Letters, 2018Co-Authors: Adiyala Vidyasagar, Peter Kreitmeier, Oliver ReiserAbstract:A visible-light-mediated radical tandem cyclization of ortho-isocyano-α-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C–C/C–S and C–O bonds. The reaction proceeds through a hitherto unprecedented bromine- or Methoxy-Group-promoted umpolung back electron transfer from an α-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate Group installed in the products can be utilized for several biologically relevant manipulations.
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Bromo- or Methoxy-Group-Promoted Umpolung Electron Transfer Enabled, Visible-Light-Mediated Synthesis of 2‑Substituted Indole-3-glyoxylates
2018Co-Authors: Adiyala Vidyasagar, Peter Kreitmeier, Jinwei Shi, Oliver ReiserAbstract:A visible-light-mediated radical tandem cyclization of ortho-isocyano-α-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C–C/C–S and C–O bonds. The reaction proceeds through a hitherto unprecedented bromine- or Methoxy-Group-promoted umpolung back electron transfer from an α-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate Group installed in the products can be utilized for several biologically relevant manipulations
Peter Kreitmeier - One of the best experts on this subject based on the ideXlab platform.
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bromo or Methoxy Group promoted umpolung electron transfer enabled visible light mediated synthesis of 2 substituted indole 3 glyoxylates
Organic Letters, 2018Co-Authors: Adiyala Vidyasagar, Peter Kreitmeier, Oliver ReiserAbstract:A visible-light-mediated radical tandem cyclization of ortho-isocyano-α-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C–C/C–S and C–O bonds. The reaction proceeds through a hitherto unprecedented bromine- or Methoxy-Group-promoted umpolung back electron transfer from an α-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate Group installed in the products can be utilized for several biologically relevant manipulations.
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Bromo- or Methoxy-Group-Promoted Umpolung Electron Transfer Enabled, Visible-Light-Mediated Synthesis of 2‑Substituted Indole-3-glyoxylates
2018Co-Authors: Adiyala Vidyasagar, Peter Kreitmeier, Jinwei Shi, Oliver ReiserAbstract:A visible-light-mediated radical tandem cyclization of ortho-isocyano-α-bromo cinnamates to 2-substituted indole-3-glyoxylates is achieved by formation of both C–C/C–S and C–O bonds. The reaction proceeds through a hitherto unprecedented bromine- or Methoxy-Group-promoted umpolung back electron transfer from an α-carbonyl radical to the photocatalyst. This method allows preparation of diverse 2-arylated or 2-thioarylated indole-3-glyoxylates. The glyoxylate Group installed in the products can be utilized for several biologically relevant manipulations
Patrick J Omalley - One of the best experts on this subject based on the ideXlab platform.
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conformational control of cofactors in nature the effect of Methoxy Group orientation on the electronic structure of ubisemiquinone
Chemical Physics Letters, 2018Co-Authors: Wagner B De Almeida, Patrick J OmalleyAbstract:Abstract Ubiquinone is the key electron and proton transfer agent in biology. Its mechanism involves the formation of its intermediate one-electron reduced form, the ubisemiquinone radical. This is formed in a protein-bound form which permits the semiquinone to vary its electronic and redox properties. This can be achieved by hydrogen bonding acceptance by one or both oxygen atoms or as we now propose by restricted orientations for the Methoxy Groups of the headGroup. We show how the orientation of the two Methoxy Groups of the quinone headGroup affects the electronic structure of the semiquinone form and demonstrate a large dependence of the ubisemiquinone spin density distribution on the orientation each Methoxy Group takes with respect to the headGroup ring plane. This is shown to significantly modify associated hyperfine couplings which in turn needs to be accounted for in interpreting experimental values in vivo. The study uncovers the key potential role the Methoxy Group orientation can play in controlling the electronic structure and spin density of ubisemiquinone and provides an electronic-level insight into the variation in electron affinity and redox potential of ubiquinone as a function of the Methoxy orientation. Taken together with the already known influence of cofactor conformation on heme and chlorophyll electronic structure, it reveals a more widespread role for cofactor conformational control of electronic structure and associated electron transfer in biology.
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the effect of Methoxy Group rotation and hydrogen bonding on the redox properties of ubiquinone
Computational and Theoretical Chemistry, 2015Co-Authors: Wagner B De Almeida, Patrick J OmalleyAbstract:Abstract Two critical factors influencing the electron affinity and associated redox potential of ubiqiuinone – the orientation relative to the ring plane of the Methoxy Groups and the number of hydrogen bond donors to the oxygen atoms are investigated using Density Functional Theory calculations. Increasing the number of hydrogen bond donors to the oxygen atoms leads to an increase of approximately 350 meV for each hydrogen bond donor. The profile for the Methoxy Group rotation shows that the electron affinity is at a minimum for in plane orientations whereas maximum values of electron affinity are found for orientations nearly perpendicular to the ring plane. Maximum variation in electron affinity values using the Methoxy Group is around 200 meV. The theoretical dependence of ubiquinone electron affinity values, as a function of variation of Methoxy dihedral angles and hydrogen bond donation demonstrates the two principal mechanisms available to the ubiquinone molecule in vivo to adapt its redox potential value to perform efficient electron transfer.
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the 2 Methoxy Group orientation regulates the redox potential difference between the primary qa and secondary qb quinones of type ii bacterial photosynthetic reaction centers
Journal of Physical Chemistry Letters, 2014Co-Authors: Wagner B De Almeida, Alexander T Taguchi, Sergei A Dikanov, Colin A Wraight, Patrick J OmalleyAbstract:Recent studies have shown that only quinones with a 2-Methoxy Group can act simultaneously as the primary (QA) and secondary (QB) electron acceptors in photosynthetic reaction centers from purple bacteria such as Rb. sphaeroides. 13C HYSCORE measurements of the 2-Methoxy Group in the semiquinone states, SQA and SQB, were compared with DFT calculations of the 13C hyperfine couplings as a function of the 2-Methoxy dihedral angle. X-ray structure comparisons support 2-Methoxy dihedral angle assignments corresponding to a redox potential gap (ΔEm) between QA and QB of 175–193 mV. A model having a methyl Group substituted for the 2-Methoxy Group exhibits no electron affinity difference. This is consistent with the failure of a 2-methyl ubiquinone analogue to function as QB in mutant reaction centers with a ΔEm of ∼160–195 mV. The conclusion reached is that the 2-Methoxy Group is the principal determinant of electron transfer from QA to QB in type II photosynthetic reaction centers with ubiquinone serving as bo...
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conformational differences between the Methoxy Groups of qa and qb site ubisemiquinones in bacterial reaction centers a key role for Methoxy Group orientation in modulating ubiquinone redox potential
Biochemistry, 2013Co-Authors: Alexander T Taguchi, Patrick J Omalley, Colin A Wraight, Sergei A DikanovAbstract:Ubiquinone is an almost universal, membrane-associated redox mediator. Its ability to accept either one or two electrons allows it to function in critical roles in biological electron transport. The redox properties of ubiquinone in vivo are determined by its environment in the binding sites of proteins and by the dihedral angle of each Methoxy Group relative to the ring plane. This is an attribute unique to ubiquinone among natural quinones and could account for its widespread function with many different re ox complexes. In this work, we use the photosynthetic reaction center as a model system for Understanding the role of Methoxy conformations in determining the redox potential of the ubiquinone/semiquinone couple. Despite the abundance of X-ray crystal structures for the reaction center, quinone site resolution has thus far been too low to provide a reliable measure of the Methoxy dihedral angles of the primary and secondary quinones, Q(A) and Q(B). We performed 2D ESEEM (HYSCORE) on isolated reaction centers with ubiquinones C-13-labeled at the headGroup methyl and Methoxy substituents, and have measured the C-13 isotropic and anisotropic components of the hyperfine tensors. Hyperfine couplings were compared to those derived by DFT calculations as a function of Methoxy torsional angle allowing estimation of the Methoxy dihedral angles for the semiquinones in the Q(A) and Q(B) sites. Based on this analysis, the orientation of the 2-Methoxy Groups are distinct in the two sites, with Q(B) more out of plane by 20-25. This corresponds to an approximate to 50 meV larger electron affinity for the Q(B) quinone, indicating a substantial contribution to the experimental difference in redox potentials (60-75 mV) of the two quinones. The methods developed here can be readily extended to ubiquinone-binding sites in other protein complexes.
Hisashi Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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chiral phosphoric acid catalyzed kinetic resolution via amide bond formation
Journal of the American Chemical Society, 2017Co-Authors: Yasushi Shimoda, Hisashi YamamotoAbstract:We describe the kinetic resolution of a readily available 2-pyridyl ester via an amide bond formation catalyzed by a chiral Bronsted acid. A chiral phosphoric acid bearing a 2,4,6-trimethyl-3,5-dinitrophenyl Group at the 3,3′-position enabled this transformation with high selectivities. We also found that the addition of Lewis acid increased both the reactivity and selectivity in the substrate with a Methoxy Group.
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Chiral Phosphoric Acid-Catalyzed Kinetic Resolution via Amide Bond Formation
2017Co-Authors: Yasushi Shimoda, Hisashi YamamotoAbstract:We describe the kinetic resolution of a readily available 2-pyridyl ester via an amide bond formation catalyzed by a chiral Brønsted acid. A chiral phosphoric acid bearing a 2,4,6-trimethyl-3,5-dinitrophenyl Group at the 3,3′-position enabled this transformation with high selectivities. We also found that the addition of Lewis acid increased both the reactivity and selectivity in the substrate with a Methoxy Group
