The accuracy and practicality of measuring heteronuclear scalar coupling constants, nJCH, from modern NMR experimental methods is examined, based on F1 or F2 evolution of nJCH in HSQMBC (including EXSIDE) and HMBC experiments. The results from these methods are compared to both robust experimental data (derived from coupled 13C spectra), computed (Density Functional Theory) and literature values where available. We report on the accuracy, ease of use and time efficiency of these multi-dimensional methods and highlight their extent and limitations.

NOE–distance relationships are shown to be sufficiently accurate to monitor very small changes in conformer populations in response to temperature (<0.5%/10 °C) – in good agreement with Boltzmann-predictions, illustrating the effectiveness of accurate NOE–distance measurements in obtaining high quality dynamics as well as structural information for small molecules.

The easy-to-interpret and rapid SelEXSIDE NMR experiment for measuring long-range 1H–13C scalar coupling constants nJCH is improved with increased sensitivity and resolution by the incorporation of ‘pure-shift’ homonuclear decoupling and IMPRESS-Hadamard encoding, with typical increases in signal-to-noise of over 300% and 400% demonstrated for small molecule examples, and narrower linewidths enabling measurement of smaller coupling constants.

Here we report the first application of combined accurate ROE-distance analysis with DFT calculations of NMR chemical shifts to achieve the relative configuration assignment of a marine natural product, conicasterol F, a new polyhydroxylated steroid isolated from the marine sponge Theonella swinhoei. We demonstrate the substantial advantages of this combined approach as a tool for structural studies of natural products, providing a powerful alternative to, or information to underpin, total synthesis when more classical NMR data analysis fails to provide unequivocal results. In this paper, we also describe the isolation and structure elucidation of conicasterol F and its 24-ethyl derivative, theonellasterol I, and their pharmacological evaluation as human nuclear receptor modulators.

NOE–distance relationships are shown to be sufficiently accurate to monitor very small changes in conformer populations in response to temperature (<0.5%/10 °C) – in good agreement with Boltzmann-predictions, illustrating the effectiveness of accurate NOE–distance measurements in obtaining high quality dynamics as well as structural information for small molecules.