NMR Techniques for Structure Elucidation of Natural Products

Nuclear magnetic resonance spectroscopy has become an indispensable tool for the detailed characterisation of natural products, offering non-destructive insights into molecular connectivity, stereochemistry and dynamics. One-dimensional spectra provide chemical shift and coupling information, while a suite of two-dimensional experiments—such as COSY, HSQC, HMBC, TOCSY, NOESY and ROESY—maps proton–proton and proton–carbon correlations across varying bond lengths. Challenges presented by proton-deficient frameworks, low natural-abundance nuclei and limited sample quantities have driven the development of specialised techniques that enhance sensitivity, resolve ambiguous correlations and enable spectral editing. Recent advances include isotope-shift detection methods that unambiguously distinguish two-bond heteronuclear connectivities, modified pulse sequences that double detection sensitivity for 13C–13C correlations, and streamlined multiplicity-editing experiments for routine 13C analysis. Computational tools and automated assignment algorithms now complement experimental data, accelerating structure determination and facilitating high-throughput screening of complex extracts. Together, these innovations continue to expand the scope of NMR in natural-product discovery, underpinning global efforts in drug development, agricultural science and chemical ecology.

Research from Nature Portfolio

A new methodology applies isotope-shift detection within the HMBC framework to distinguish direct two-bond 1H–13C correlations from longer-range couplings. By exploiting subtle frequency shifts caused by isotopic substitution, this approach maintains the sensitivity and generality of conventional HMBC while delivering unambiguous assignments at sub-milligram and even nanomole scales. Demonstrated across a series of proton-deficient natural products, it enables rapid structure elucidation in cases where standard 2D NMR fails to resolve ambiguous heteronuclear pathways, thereby complementing existing correlation experiments without additional hardware requirements.

NMR Techniques for Structure Elucidation of Natural Products publication trend

The graph below shows the total number of articles in nmr techniques for structure elucidation of natural products across all publications each year (not limited to Nature Index journals).

Technical terms

HMBC: Heteronuclear multiple-bond correlation experiment revealing long-range 1H–13C connectivities across two or more bonds.

HSQC: Heteronuclear single-quantum correlation experiment mapping one-bond 1H–13C correlations for direct bond assignments.

INADEQUATE: Incredibly natural-abundance double-quantum transfer experiment correlating directly bonded 13C nuclei to elucidate carbon networks.

Isotope shift: Change in resonance frequency caused by substitution with a heavier isotope, used to differentiate coupling pathways.

Multiplicity editing: Spectral editing technique that separates NMR signals according to the number of attached protons (CH, CH2, CH3).

References

1. Unequivocal identification of two-bond heteronuclear correlations in natural products at nanomole scale by i-HMBC. Nature Communications (2023).
2. Denigrins H–L: Sulfated Derivatives of Denigrins D and E from a New Zealand Dictyodendrilla c.f. dendyi Marine Sponge. Marine Drugs (2024).
3. A Versatile Broadband Attached Proton Test Experiment for Routine 13C Nuclear Magnetic Resonance Spectroscopy. Molecules (2024).
4. More than ADEQUATE: doubling the sensitivity of 13 CH– 13 CH correlations in double-quantum NMR experiments. Chemical Communications (2022).