Discovery of bioactive secondary metabolites from benthic filamentous marine cyanobacteria

Abstract

The main objective of this MSc research was to discover marine natural products from filamentous marine cyanobacteria. These marine cyanobacteria samples were collected from various islands around Singapore such as Pulau Hantu Kechil, Lazarus and St. John’s Islands. The preliminary analysis of the extracts from these samples indicated interesting chemistry based on NMR and preliminary cytotoxicity assays. Henceforth, the chemistry and biological activities of the compounds isolated from these samples will be further discussed in the following chapters. In Chapters 1 to 3, it covers an introduction on the importance of marine natural products, filamentous marine cyanobacteria, and molecular networking in a natural product research. These chapters would support the purpose of conducting investigations on marine natural products coming from filamentous marine cyanobacteria. Chapter 4 covers the marine natural products that have been isolated from Pulau Hantu Kechil, which are known compounds, lyngbyatoxin A (1), majusculamides A (2) and B (3) from the filamentous marine cyanobacteria Lyngbya majuscula. These compounds were then further investigated for its biological activities to determine if it supports literature. Further investigations by molecular networking were then conducted to determine if potential analogues of these compounds are present. Chapter 5 describes the discovery and structural elucidation of lazarusamate (4), which is a linear lipopeptide isolated from the filamentous marine cyanobacteria Symploca sp. collected from Lazarus Island. Biological activities of the compound are also reported in this chapter. Molecular networking analysis was also conducted for this compound to determine presence of potential analogues. The last working chapter, Chapter 6, then describes the discovery and structural elucidation of benderadiene (5), which is a cyclopropyl containing compound isolated from the filamentous marine cyanobacteria Lyngbya majuscula cf., collected from St John’s Island. Biological activities of this compound were also reported and discussed, and a preliminary molecular docking experiment was conducted on Swissdock to further support the biological activity which the compound exhibited. Last but not least, the final chapter concludes the thesis which summarises the discovery of filamentous marine cyanobacterial compounds and potential future works.