Dipolare Restkopplungen als effektives Instrument der Konstitutionsanalyse: die unerwartete Bildung tricyclischer Verbindungen

Kummerlöwe, Grit; Crone, Benedikt; Kretschmer, Manuel; Kirsch, Stefan F.; Luy, Burkhard

doi:10.1002/ange.201007305

Cited by 25 publications

(8 citation statements)

References 40 publications

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During the last decade anisotropic nuclear magnetic resonance (NMR) parameters measured in weakly aligned samples have had a profound impact on the structure determination of bio-macromolecules [1] and small-tomedium-sized organic molecules. [2] Almost exclusively, residual dipolar couplings (RDCs) have been used for the analysis of the conformation, [3] configuration, [4] and constitution, [5] while residual chemical shift anisotropies (RCSAs) as additional parameters have only been used with proteins and nucleic acids. [6] The development of the field has mainly been determined by the availability of suitable, very weakly aligning media.

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Residual Chemical Shift Anisotropy (RCSA): A Tool for the Analysis of the Configuration of Small Molecules

et al. 2011

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Together we are strong: A new, robust method allows the measurement of residual chemical shift anisotropies for the determination of conformation and configuration of molecules in organic solvents. The power of the method is shown by the example of estrone and 13‐epi‐estrone (see structures), where only the combined use of residual chemical shift anisotropies and residual dipolar couplings leads to the distinction of the two diastereomers.

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Residual Chemical Shift Anisotropy (RCSA): A Tool for the Analysis of the Configuration of Small Molecules

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“…Recently, Luy, Kirsch, and co‐workers proposed the very elegant and original idea of expanding the use of RDCs to determine the constitution of a small organic molecule whose structure could not be determined by using a combination of conventional spectroscopic methods 13. The electrophilic cyclization of azide‐containing 1,5‐enynes 1 was known to selectively produce either the corresponding arene 2 or cyclohexadiene 3 .…”

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“…b) The 3D structure of compound 4 with RDCs color‐coded in the bonds (red: negative, blue: positive). c) Axis of the calculated alignment tensor 13…”

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Constitutional, Configurational, and Conformational Analysis of Small Organic Molecules on the Basis of NMR Residual Dipolar Couplings

Gil

2011

Angew Chem Int Ed

109

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Dedicated to Professor Aksel BothnerBy on the occasion of his 90th birthday configuration determination · conformation analysis · NMR spectroscopy · residual dipolar couplings · structure elucidation NMR spectroscopy is arguably one of the most powerful tools available to chemists for the structural analysis of molecules. NMR experiments based on the nuclear Overhauser enhancement (NOE) [1] and on the analysis of 3 J coupling constants [2] have been used intensively in the configurational and conformational analysis of small organic molecules. However, as these two NMR parameters provide only localized structural information, they fail to provide information on the relative configuration of remotely located molecular fragments.Unlike NOEs and 3 J coupling constants, the direct spinspin interaction known as dipolar coupling (D ij ; Figure 1) can provide very powerful structural information of a nonlocal character.[3] The value of D ij between two nuclei i and j (which can either be bonded to one another or not directly connected) depends not only on the distance between them (r), but also on the angle of the internuclear vector (r ij ) with respect to the direction of the magnetic field (B 0 ), which acts as a global axis of reference. Hence, from the equation in Figure 1, it can be inferred that a unique combination of dipolar-coupled pairs of spins can produce a unique set of dipolar couplings, which in turn can enable unambiguous determination of the relative spatial arrangement of atoms in a molecule. This spatial arrangement reflects the constitution, configuration, and preferred conformation of the molecule.When the concept is explained in this way, the use of dipolar couplings for the analysis of small molecules sounds very simple and straightforward. However, the size of dipolar couplings is on the order of kilohertz. In solid-state powders, all possible spatial orientations adopted by molecules lead to extremely broad lines in the NMR spectrum, which makes the extraction of individual dipolar couplings impossible. In solution, dipolar couplings average out as a result of isotropic molecular tumbling and are not observable in the NMR spectrum (isotropic conditions). However, if molecules are forced to adopt a minor degree of alignment in solution, a measurable fraction of the original dipolar coupling, known as residual dipolar coupling (RDC), is observed in the NMR spectrum. RDCs conserve the same structural information provided by the original dipolar couplings, since they are scaled down proportionally. From a practical standpoint, RDCs can be measured relatively easily provided that the degree of alignment is weak (0.01-0

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“…[2] Bislang wurden zur Konformations-, [3] Konfigurations- [4] und auch Konstitutionsaufklärung [5] fast ausschließlich dipolare Restkopplungen (RDCs) genutzt, während bei Proteinen und Nucleinsäuren auch schon die residuale chemische Verschiebungsanisotropie (RCSA) als zusätzlicher Parameter zum Einsatz kam. [6] Die Entwicklung in dem Feld wurde hauptsächlich durch die Verfügbarkeit von geeigneten, sehr schwach orientierenden Medien bestimmt.…”

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“…Während des letzten Jahrzehnts gewannen anisotrope NMRspektroskopische Parameter, gemessen in schwach orientierten Proben, immer mehr an Bedeutung für die Strukturaufklärung sowohl von großen Biomolekülen [1] als auch von kleinen bis mittelgroßen organischen Molekülen. [2] Bislang wurden zur Konformations-, [3] Konfigurations- [4] und auch Konstitutionsaufklärung [5] fast ausschließlich dipolare Restkopplungen (RDCs) genutzt, während bei Proteinen und Nucleinsäuren auch schon die residuale chemische Verschiebungsanisotropie (RCSA) als zusätzlicher Parameter zum Einsatz kam. [6] Die Entwicklung in dem Feld wurde hauptsächlich durch die Verfügbarkeit von geeigneten, sehr schwach orientierenden Medien bestimmt.…”

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Residuale chemische Verschiebungsanisotropie (RCSAs) – ein Parameter zur Konfigurationsanalyse kleiner Moleküle

et al. 2011

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Gemeinsam stark: Eine neue Methode ermöglicht die zuverlässige Messung residualer chemischer Verschiebungsanisotropien (RCSAs) als zusätzliche NMR‐spektroskopische Parameter für die Konformations‐ und Konfigurationsbestimmung kleiner Moleküle. Am Beispiel von Estron und 13‐epi‐Estron (siehe Strukturen) wird gezeigt, dass nur die gemeinsame Nutzung von RCSAs und dipolaren Restkopplungen zur eindeutigen Unterscheidung der beiden Diastereomere führt.

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Dipolare Restkopplungen als effektives Instrument der Konstitutionsanalyse: die unerwartete Bildung tricyclischer Verbindungen

Cited by 25 publications

References 40 publications

Residual Chemical Shift Anisotropy (RCSA): A Tool for the Analysis of the Configuration of Small Molecules

Residual Chemical Shift Anisotropy (RCSA): A Tool for the Analysis of the Configuration of Small Molecules

Constitutional, Configurational, and Conformational Analysis of Small Organic Molecules on the Basis of NMR Residual Dipolar Couplings

Residuale chemische Verschiebungsanisotropie (RCSAs) – ein Parameter zur Konfigurationsanalyse kleiner Moleküle

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