Measuring Long-Range Heteronuclear NMR Correlations in Natural Products

LR-HSQMBC versus LR-selHSQMBC: Enhancing the Observation ofTiny Long-Range Heteronuclear NMR Correlations

Kumar Motiram-Corral, Pau Nolis, Josep Saurí, and Teodor Parella


ABSTRACT:The detection of ultra-long-range (4JCHand higher) heteronuclear connectivities can complement the conventionaluse of HMBC/HSQMBC data in structure elucidation NMR studies of proton-deficient natural products, where two-bond andthree-bond correlations are usually observed. The performance of the selHSQMBC experiment with respect to its broadbandHSQMBC counterpart is evaluated. Despite its frequency-selectivity nature, selHSQMBC efficiently prevents any unwanted signalphase 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 forshort- and long-range cross-peaks corresponding to small heteronuclear coupling values. This is particularly relevant for experimentsoptimized to smallnJCHvalues (2−3 Hz), referred to as LR-selHSQMBC, where key cross-peaks that are not visible in the equivalentbroadband LR-HSQMBC spectrum can become observable in optimum conditions.


© 2020, Pau. All rights reserved by the author(s) and Universitat Autonoma de Barcelona except for texts and images already copyrighted by third parties (e.g. journal publishers) and used here under the fair use provision.