Selecting the Most Appropriate NMR Experiment to Access Weak and/or Very Long-Range Heteronuclear Correlations

Josep Saurí, Yizhou Liu, Teodor Parella, R. Thomas Williamson, Gary E. Martin

    Research output: Contribution to journalArticleResearchpeer-review

    11 Citations (Scopus)

    Abstract

    © 2016 The American Chemical Society and American Society of Pharmacognosy. Heteronuclear long-range NMR experiments are well established as essential NMR techniques for the structure elucidation of unknown natural products and small molecules. It is generally accepted that the absence of a given nJXH correlation in an HMBC or HSQMBC spectrum would automatically place the proton at least four bonds away from the carbon in question. This assumption can, however, be misleading in the case of a mismatch between the actual coupling constant and the delay used to optimize the experiment, which can lead to structural misassignments. Another scenario arises when an investigator, for whatever reason, needs to have access to very long-range correlations to confirm or refute a structure. In such cases, a conventional HMBC experiment will most likely fail to provide the requisite correlation, regardless of the delay optimization. Two recent methods for visualizing extremely weak or very long-range connectivities are the LR-HSQMBC and the HSQMBC-TOCSY experiments. Although they are intended to provide similar structural information, they utilize different transfer mechanisms, which differentiates the experiments, making each better suited for specific classes of compounds. In this report we have sought to examine the considerations implicit in choosing the best experiment to access weak or very long-range correlations for different types of molecules.
    Original languageEnglish
    Pages (from-to)1400-1406
    JournalJournal of Natural Products
    Volume79
    Issue number5
    DOIs
    Publication statusPublished - 27 May 2016

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