Expedited NMR Assignment of Small- to Medium-Sized Molecules with Improved HSQC−CLIP−COSY Experiments

• Published in: Analytical chemistry (Washington) 2021-02, Vol.93 (6), p.3096-3102
• Main Authors: Gyöngyösi, Tamás, Timári, István, Sinnaeve, Davy, Luy, Burkhard, Kövér, Katalin E.
• Format: Article
• Language: English
• Subjects: Analytical chemistry; Chemical Sciences
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/acs.analchem.0c04124

Resonance assignment is a pivotal step for any nuclear magnetic resonance (NMR) analysis, such as structure elucidation or the investigation of protein–ligand interactions. Both 1H-13C heteronuclear single quantum correlation (HSQC) and 1H-1H correlation spectroscopy (COSY) two-dimensional (2D) experiments are invaluable for 1H NMR assignment, by extending the high signal dispersion of 13C chemical shifts onto 1H resonances and by providing a high amount of through-bond 1H-1H connectivity information, respectively. The recently introduced HSQC−CLIP(Clean In-Phase)−COSY method combines these two experiments, providing COSY correlations along the high-resolution 13C dimension with clean in-phase multiplets. However, two experiments need to be recorded to unambiguously identify COSY cross-peaks. Here, we propose novel variants of the HSQC–CLIP–COSY pulse sequence that edit cross-peak signs so that direct HSQC responses can be distinguished from COSY relay peaks, and/or the multiplicities of the 13C nuclei are reflected, allowing the assignment of all the peaks in a single experiment. The advanced HSQC–CLIP–COSY variants have the potential to accelerate and simplify the NMR structure-elucidation process of both synthetic and natural products and to become valuable tools for high-throughput computer-assisted structure determination.