Natural products applied in reverse chemical proteomics

Natural products are a rich source of structurally diverse and biologically active small molecules. They constitute a useful class of compounds as leads in rational drug design and development. However, drug discovery faces a major bottleneck due to the lack of knowledge about the active compounds' cellular targets and mode of action. For this thesis, several natural products with interesting biological activity have been applied as ligands in a technique we refer to as reverse chemical proteomics. This method rapidly generates protein-ligand pairs, which will be useful for the rational design of new and more potent therapeutics, identification of druggable targets as well as for understanding the underlying biochemical pathways of these active ligands. This thesis is divided into four main chapters. Chapter 1 introduces the techniques behind reverse chemical proteomics. Chapter 2 describes the bioassay-guided fractionation of eleven marine sponges, the isolation and characterisation of two new and seven known bromotyrosines of the highly antibacterial active extract from the marine sponge Pseudoceratina purpurea, as well as isolation of bromotyrosines from the opisthobranch Tylodina corticalis, which was collected while feeding on P. purpurea. In Chapter 3, the chemical derivatisation of natural products is presented alongside the synthesis and characterisation of novel, linkers and reagents required for performing reverse chemical proteomics. Chapter 4 describes the application of T7 phage display utilising the immunosuppressant natural product FK506 as a model affinity probe. Consecutively, protein binding partners for biotinylated artesunate, daptomycin and manzamine are isolated from various T7 phage-displayed human cDNA libraries. An experimental chapter and concluding remarks follow thereafter.