Cytotoxic Alkaloids from Australian Marine Sponges

Australia's marine environment covers extended areas, from the warm northern tropical, to the sub tropical central water, the cool temperate water of the south and the cold sub-Antarctic and Antarctic water. Australia has rich area of coral reefs. The marine biodiversity in Australia is enormous. Despite incredible biodiversity, Australian research in the marine anticancer drug discoveries is low in comparison with other countries. In this research we investigated a collection of marine sponges as a source for new anticancer leads. This thesis comprises six chapters. Chapter 1 covers the importance of natural products as a source of new drugs, and an introduction to cancer as a disease, chemotherapy in cancer treatments, and the natural products as a source for anticancer drugs. Also, the basic anticancer drug development process is highlighted. Finally, a thorough review of anticancer alkaloids isolated from marine sponges is presented. Chapter 2 presents the chemical investigation into a southern Australian marine sponge Stelletta sp., which led to the isolation and structure elucidation of bistellettazines A-C the first reported examples of terpenyl-pyrrolizidines conjugate, and bistellettazole A, a unique cyclic terpenyl-imidazole conjugate. Bistellettazines A-C and bistellettazole A feature unprecedented carbon skeletons that are proposed to share a common convergent biosynthetic origin, arising via the biogenic equivalent of a Diels-Alder addition between two hypothetical polyenyl norsesquiterpene precursors. The cytotoxic activity (in vitro) for these new alkaloids is also discussed. Chapter 3 discusses the isolation and structure elucidation of four new discorhabdins analogues namely, dihydrodiscorhabdin A, debromodiscorhabdin A, discorhabdin X and dihydrodiscorhabdin L. In addition, the known compounds discorhabdin A and discorhabdin D, were isolated from two southern Australian marine sponge specimens of the genera Higginsia and Spongosorites. The cytotoxic activity (in vitro) for these new alkaloids was also discussed. Chapter 4 discloses chemical investigation into two southern Australian marine sponge specimens of the genera Clathria and Ptilocaulis. Four new mirabilin analogues (mirabilins H-K) were isolated and characterized along with known mirabilin C, F (for the first time as TFA salt) and mirabilin G. The cytotoxic activity (in vitro) for these new alkaloids was also discussed. Chapter 5 presents the 1H NMR data for the known compounds isolated during this study, and Chapter 6 is covering the experimental part