TY - JOUR
T1 - Selecting the Most Appropriate NMR Experiment to Access Weak and/or Very Long-Range Heteronuclear Correlations
AU - Sauri, Josep
AU - Liu, Yizhou
AU - Parella, Teodor
AU - Williamson, R. Thomas
AU - Martin, Gary E.
PY - 2016/5/27
Y1 - 2016/5/27
N2 - 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 uhrn 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.
AB - 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 uhrn 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.
KW - Structure elucidation
KW - Coupling-constants
KW - Pulse sequences
KW - Lr-hsqmbc
KW - Hmbc
KW - Sensitivity
UR - https://www.webofscience.com/api/gateway?GWVersion=2&SrcApp=pure_univeritat_ramon_llull&SrcAuth=WosAPI&KeyUT=WOS:000377150900022&DestLinkType=FullRecord&DestApp=WOS_CPL
U2 - 10.1021/acs.jnatprod.6b00139
DO - 10.1021/acs.jnatprod.6b00139
M3 - Article
C2 - 27136955
SN - 0163-3864
VL - 79
SP - 1400
EP - 1406
JO - Journal of Natural Products
JF - Journal of Natural Products
IS - 5
ER -