The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Christian Griesinger - One of the best experts on this subject based on the ideXlab platform.
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Relative Configuration of micrograms of natural compounds using proton residual chemical shift anisotropy.
Nature communications, 2020Co-Authors: Nilamoni Nath, Juan Carlos Fuentes-monteverde, Dawrin Pech-puch, Jaime Rodríguez, Carlos Jiménez, Markus Noll, Alexander Kreiter, Michael Reggelin, Armando Navarro-vázquez, Christian GriesingerAbstract:3D molecular structure determination is a challenge for organic compounds or natural products available in minute amounts. Proton/proton and proton/carbon correlations yield the constitution. J couplings and NOEs oftentimes supported by one-bond 1H,13C residual dipolar couplings (RDCs) or by 13C residual chemical shift anisotropies (RCSAs) provide the Relative Configuration. However, these RDCs or carbon RCSAs rely on 1% natural abundance of 13C preventing their use for compounds available only in quantities of a few 10’s of µgs. By contrast, 1H RCSAs provide similar information on spatial orientation of structural moieties within a molecule, while using the abundant 1H spin. Herein, 1H RCSAs are accurately measured using constrained aligning gels or liquid crystals and applied to the 3D structural determination of molecules with varying complexities. Even more, deuterated alignment media allow the elucidation of the Relative Configuration of around 35 µg of a briarane compound isolated from Briareum asbestinum. Determination of 3D molecular structures remains challenging for natural products or organic compounds available in minute amounts. Here, the authors determine the structure of complex molecules, including few micrograms of briarane B-3 isolated from Briareum asbestinums, through measurement of 1H residual chemical shift anisotropy.
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determination of Relative Configuration from residual chemical shift anisotropy
Journal of the American Chemical Society, 2016Co-Authors: Nilamoni Nath, Armando Navarrovazquez, Thomas R Williamson, Gary E Martin, Manuel Schmidt, Christian GriesingerAbstract:Determination of Relative Configuration is frequently a rate-limiting step in the characterization of small organic molecules. Solution NMR-based nuclear Overhauser effect and scalar J-coupling constants can provide useful spatial information but often fail when stereocenters are separated by more than 4–5 A. Residual dipolar couplings (RDCs) can provide a means of assigning Relative Configuration without limits of distance between stereocenters. However, sensitivity limits their application. Chemical shift is the most readily measured NMR parameter, and partial molecular alignment can reveal the anisotropic component of the chemical shift tensor, manifested as residual chemical shift anisotropy (RCSA). Hence, 13C RCSAs provide information on the Relative orientations of specific structural moieties including nonprotonated carbons and can be used for stereochemical assignment. Herein, we present two robust and sensitive methods to accurately measure and apply 13C RCSAs for stereochemical assignment. The c...
Nilamoni Nath - One of the best experts on this subject based on the ideXlab platform.
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Relative Configuration of micrograms of natural compounds using proton residual chemical shift anisotropy.
Nature communications, 2020Co-Authors: Nilamoni Nath, Juan Carlos Fuentes-monteverde, Dawrin Pech-puch, Jaime Rodríguez, Carlos Jiménez, Markus Noll, Alexander Kreiter, Michael Reggelin, Armando Navarro-vázquez, Christian GriesingerAbstract:3D molecular structure determination is a challenge for organic compounds or natural products available in minute amounts. Proton/proton and proton/carbon correlations yield the constitution. J couplings and NOEs oftentimes supported by one-bond 1H,13C residual dipolar couplings (RDCs) or by 13C residual chemical shift anisotropies (RCSAs) provide the Relative Configuration. However, these RDCs or carbon RCSAs rely on 1% natural abundance of 13C preventing their use for compounds available only in quantities of a few 10’s of µgs. By contrast, 1H RCSAs provide similar information on spatial orientation of structural moieties within a molecule, while using the abundant 1H spin. Herein, 1H RCSAs are accurately measured using constrained aligning gels or liquid crystals and applied to the 3D structural determination of molecules with varying complexities. Even more, deuterated alignment media allow the elucidation of the Relative Configuration of around 35 µg of a briarane compound isolated from Briareum asbestinum. Determination of 3D molecular structures remains challenging for natural products or organic compounds available in minute amounts. Here, the authors determine the structure of complex molecules, including few micrograms of briarane B-3 isolated from Briareum asbestinums, through measurement of 1H residual chemical shift anisotropy.
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determination of Relative Configuration from residual chemical shift anisotropy
Journal of the American Chemical Society, 2016Co-Authors: Nilamoni Nath, Armando Navarrovazquez, Thomas R Williamson, Gary E Martin, Manuel Schmidt, Christian GriesingerAbstract:Determination of Relative Configuration is frequently a rate-limiting step in the characterization of small organic molecules. Solution NMR-based nuclear Overhauser effect and scalar J-coupling constants can provide useful spatial information but often fail when stereocenters are separated by more than 4–5 A. Residual dipolar couplings (RDCs) can provide a means of assigning Relative Configuration without limits of distance between stereocenters. However, sensitivity limits their application. Chemical shift is the most readily measured NMR parameter, and partial molecular alignment can reveal the anisotropic component of the chemical shift tensor, manifested as residual chemical shift anisotropy (RCSA). Hence, 13C RCSAs provide information on the Relative orientations of specific structural moieties including nonprotonated carbons and can be used for stereochemical assignment. Herein, we present two robust and sensitive methods to accurately measure and apply 13C RCSAs for stereochemical assignment. The c...
Andreas Goeke - One of the best experts on this subject based on the ideXlab platform.
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Sequential Diels-Alder reaction/rearrangement sequence: synthesis of functionalized bicyclo[2.2.1]heptane derivatives and revision of their Relative Configuration.
The Journal of organic chemistry, 2014Co-Authors: Demin Liang, Yue Zou, Quanrui Wang, Andreas GoekeAbstract:A sequential Diels–Alder reaction/rearrangement sequence was developed for the synthesis of diverse functionalized bicyclo[2.2.1]heptanes as novel floral and woody odorants. The outcome of the rearrangement depended on the substitution pattern of the dienes. 2D NMR analysis has established the correct Relative Configuration of the bicyclo[2.2.1]heptanone, which was originally misassigned. Furthermore, when the initiating DA reaction was catalyzed by a chiral Lewis acid, the bicyclo[2.2.1]heptane derivatives including (+)-herbanone can be obtained in an enantiomeric ratio (er) up to 96.5:3.5.
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sequential diels alder reaction rearrangement sequence synthesis of functionalized bicyclo 2 2 1 heptane derivatives and revision of their Relative Configuration
Journal of Organic Chemistry, 2014Co-Authors: Demin Liang, Quanrui Wang, Andreas GoekeAbstract:A sequential Diels–Alder reaction/rearrangement sequence was developed for the synthesis of diverse functionalized bicyclo[2.2.1]heptanes as novel floral and woody odorants. The outcome of the rearrangement depended on the substitution pattern of the dienes. 2D NMR analysis has established the correct Relative Configuration of the bicyclo[2.2.1]heptanone, which was originally misassigned. Furthermore, when the initiating DA reaction was catalyzed by a chiral Lewis acid, the bicyclo[2.2.1]heptane derivatives including (+)-herbanone can be obtained in an enantiomeric ratio (er) up to 96.5:3.5.
Susumi Hatakeyama - One of the best experts on this subject based on the ideXlab platform.
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Total synthesis of (+/-)-trachyspic acid and determination of the Relative Configuration.
Organic letters, 2003Co-Authors: Kanako Hirai, Hidenori Ooi, Tomoyuki Esumi, Yoshiharu Iwabuchi, Susumi HatakeyamaAbstract:[reaction: see text] The first total synthesis of (+/-)-trachyspic acid, a tumor cell heparanase inhibitor, was accomplished based on Cr(II)/Ni(II)-mediated reaction of the aldehyde containing the citric acid moiety and the long-chain triflate, and the Relative Configuration of this natural product was determined.
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total synthesis of trachyspic acid and determination of the Relative Configuration
Organic Letters, 2003Co-Authors: Kanako Hirai, Hidenori Ooi, Tomoyuki Esumi, Yoshiharu Iwabuchi, Susumi HatakeyamaAbstract:[reaction: see text] The first total synthesis of (+/-)-trachyspic acid, a tumor cell heparanase inhibitor, was accomplished based on Cr(II)/Ni(II)-mediated reaction of the aldehyde containing the citric acid moiety and the long-chain triflate, and the Relative Configuration of this natural product was determined.
Janine Cossy - One of the best experts on this subject based on the ideXlab platform.
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Synthetic Studies toward the C32–C46 Segment of Hemicalide. Assignment of the Relative Configuration of the C36–C42 Subunit
Organic Letters, 2015Co-Authors: Simon Specklin, Camille Lecourt, Guillaume Boissonnat, Geoffroy Sorin, Marie-isabelle Lannou, Janick Ardisson, François Sautel, Georges Massiot, Christophe Meyer, Janine CossyAbstract:The synthesis of five diastereomeric model compounds incorporating the C32–C46 segment of the antitumor marine natural product hemicalide has been achieved through a convergent approach relying on the 1,4-addition of an alkenyl boronate to an α,β-unsaturated δ-lactone followed by α-hydroxylation of an enolate and a Julia–Kocienski olefination. Comparison of the 1H and 13C NMR data of the model compounds with those of hemicalide enabled the assignment of the Relative Configuration of the C36–C42 subunit.
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synthetic studies toward the c32 c46 segment of hemicalide assignment of the Relative Configuration of the c36 c42 subunit
Organic Letters, 2015Co-Authors: Simon Specklin, Camille Lecourt, Guillaume Boissonnat, Geoffroy Sorin, Marie-isabelle Lannou, Janick Ardisson, François Sautel, Georges Massiot, Christophe Meyer, Janine CossyAbstract:The synthesis of five diastereomeric model compounds incorporating the C32-C46 segment of the antitumor marine natural product hemicalide has been achieved through a convergent approach relying on the 1,4-addition of an alkenyl boronate to an α,β-unsaturated δ-lactone followed by α-hydroxylation of an enolate and a Julia-Kocienski olefination. Comparison of the (1)H and (13)C NMR data of the model compounds with those of hemicalide enabled the assignment of the Relative Configuration of the C36-C42 subunit.
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Strength by joining methods: combining synthesis with NMR, IR, and vibrational circular dichroism spectroscopy for the determination of the Relative Configuration in hemicalide.
Chemistry (Weinheim an der Bergstrasse Germany), 2014Co-Authors: Ewoud De Gussem, Simon Specklin, Christophe Meyer, Janine Cossy, Wouter A. Herrebout, Patrick BultinckAbstract:The Relative Configuration of a key subunit of hemicalide, a recently isolated, highly bioactive marine natural product having potent antiproliferative activity against a panel of human cancer cell lines, was assigned by combining stereocontrolled synthesis of model substrates with NMR, IR, and vibrational circular dichroism (VCD) spectroscopy. The assignment of the absolute Configuration of asymmetric carbon center C42 in two structurally complex epimeric substructures containing six stereocenters by VCD analysis illustrates the power and reliability of combining methods.
