Servei de Ressonància Magnètica Nuclear, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Barcelona, Catalonia, Spain.
Structure Elucidation Group, Analytical Research & Development, Merck & Co., Inc., 33 Avenue Louis Pasteur, Boston, Massachusetts 02115, United States.
J Nat Prod. 2020 Apr 24;83(4):1275-1282. doi: 10.1021/acs.jnatprod.0c00058. Epub 2020 Mar 10.
The detection of ultra-long-range ( and higher) heteronuclear connectivities can complement the conventional use of HMBC/HSQMBC data in structure elucidation NMR studies of proton-deficient natural products, where two-bond and three-bond correlations are usually observed. The performance of the selHSQMBC experiment with respect to its broadband HSQMBC counterpart is evaluated. Despite its frequency-selectivity nature, selHSQMBC efficiently prevents any unwanted signal phase and intensity modulations due to passive proton-proton coupling constants typically involved in HSQMBC. As a result, selHSQMBC offers a significant sensitivity enhancement and provides pure in-phase multiplets, improving the detection levels for short- and long-range cross-peaks corresponding to small heteronuclear coupling values. This is particularly relevant for experiments optimized to small values (2-3 Hz), referred to as LR-selHSQMBC, where key cross-peaks that are not visible in the equivalent broadband LR-HSQMBC spectrum can become observable in optimum conditions.
超远距离（及更高距离）异核连接的检测可以补充质子缺乏天然产物结构阐明 NMR 研究中常规使用的 HMBC/HSQMBC 数据，其中通常观察到两键和三键相关。评估了 selHSQMBC 实验相对于其宽带 HSQMBC 对应物的性能。尽管 selHSQMBC 具有频率选择性，但它有效地防止了由于 HSQMBC 中通常涉及的被动质子-质子耦合常数引起的任何不需要的信号相位和强度调制。因此，selHSQMBC 提供了显著的灵敏度增强，并提供了纯同相多重峰，提高了对应于小异核耦合值的短程和远程交叉峰的检测水平。对于优化为小值（2-3 Hz）的实验（称为 LR-selHSQMBC），这尤其重要，其中在等效宽带 LR-HSQMBC 谱中不可见的关键交叉峰在最佳条件下可以变得可观察到。
