A comparison between the application of NMR and LC-HRMS based metabolomics on the discovery of natural products from endophytic fungi

Natural products have been an excellent source of diverse and complex chemical structures. However, as we isolate more natural products it becomes increasingly difficult to discover novel chemical entities. Screening strategies that rely solely on evaluation of biological activity are becoming redundant, and metabolomic approaches are being increasingly used to avoid the isolation of known natural products [1]. In this project, we employed nuclear magnetic resonance (NMR) [2] as well as liquid chromatography tandem high resolution mass spectrometry (LC-HRMS)-based [3] metabolomics screens in an effort to more effectively prioritise endophyte extracts for natural product discovery. Fungi used in this project were isolated from the leaves of medicinal plants used by the Canadian First Nations.4 Independent principal component analysis of the NMR and LC-HRMS metabolomics data identified extracts possessing unique metabolic profiles from the two screening methods and these extracts were selected for further investigation. The NMR metabolomic screening prioritised five extracts that contained a high abundance of structurally similar natural products, particularly those showing an abundance of peaks between 1.0 – 2.0 ppm and 6.0 – 6.4 ppm, and ultimately led to the isolation of only known compounds. Advantages gained through the increased sensitivity and accuracy of LC-HRMS make the mass spectrometric based method greatly superior as a screening and prioritization tool. LC-HRMS based metabolomics strength lies within the completeness of the chemical database that is being used as a dereplication step. Prioritized extracts can be removed from further study if the target m/z chosen by PCA has a known natural product structure within 5ppm. This strategy of prioritization has highlighted seven endophytic extracts containing an m/z without a match in our database allowing for the discovery of new natural products from our fungal library in the future.