The application of NMR and LC-HRMS based prioritization strategies for the discovery of natural products by endophytic fungi from medicinal plants

Abstract

Natural products have been an abundant source of diverse and complex chemical structures and endophytic fungi have proven to be a valuable source of natural products. This thesis explores the diversity of natural products produced by fungal endophytes isolated from the leaves of medicinal plants used by the Canadian First Nations. Natural product isolation projects were selected based on three different screening strategies: The first employed antimicrobial activity as a basis for project prioritization; The second approach used nuclear magnetic resonance (NMR) metabolomics to identify extracts with atypical profiles due to the presence of structurally unique metabolites; the third approach used tandem liquid chromatography - high-resolution mass spectrometry (LC-HRMS) based metabolomic analyses to reveal extracts that contain potentially novel natural products. The bioactivity directed prioritization approach, either on its own or in combination with NMR based metabolomics, led exclusively to the isolation of known natural products, although some of the bioactivities measured for these compounds had not been previously reported. NMR based metabolomics prioritization, when used alone, also led to the isolation of known natural products or new isomers of known natural products. Finally, the third prioritization method using LC-HRMS based metabolomics led to the isolation of two new natural products. These data suggest that prioritization using LC-HRMS based metabolomics alone is the most effective method for the isolation of novel natural products. Future work should focus on extracts that are highlighted by both LC-HRMS based metabolomics as well as bioactivity screening in an effort to discover novel antimicrobial structures.