Integration of diffusion NMR spectroscopy in the natural products research workflow
Drug discovery using synthetic chemistry techniques is often preferred over natural products research. Issues with efficiency of source selection, screening, dereplication, isolation and structure elucidation processes frequently hinder the research and commercialisation potential of natural products. New nuclear magnetic resonance (NMR) approaches have been developed that could provide spectroscopic information without the need for separating the components in a mixture. Scientists on the DOSYMNPS (Novel applications of diffusion NMR spectroscopy in microbial natural products research) project developed methodologies to process and use diffusion NMR spectroscopy data for characterisation of crude and prefractionated microbial extracts. Scientists were able to reconstruct each component in their carefully designed artificial mixtures of secondary metabolites. Using a novel protocol, they extracted synthetic component spectra that closely resembled the actual pure compound spectra. Though not applicable to crude microbial extracts due to their complex nature, the NMR-based tools developed by project members are useful with simpler mixtures such as those obtained by semipreparative high-performance liquid chromatography (HPLC) fractionation of crude extracts. Using diffusion NMR spectroscopy, researchers worked to improve the identification of already known compounds, a process referred to as dereplication. Researchers tested their NMR-based dereplication approach in different databases containing experimental NMR spectra or experimental and calculated chemical shift assignments of natural products. To enhance accuracy, they developed a protocol to correlate actual mass with the estimated molecular weight of the mixture components retrieved from the diffusion NMR experiments. Researchers also proved the feasibility of direct structural elucidation of novel secondary metabolites in simple mixtures using standard 1D and 2D NMR data combined with diffusion experiments. Research outcomes have significantly enhanced the competitiveness of natural products research through an expanded arsenal of NMR-based tools. These tools are currently being used at the host institution's chemistry department for research in natural products chemistry.
Keywords
Secondary metabolite, NMR spectra, natural products, diffusion NMR, DOSY, dereplication, structure elucidation
