Isolation and structure determination of a novel glycolipid pachymoside A from marine sponge Pachymatisma johnstonia

The search for new pharmacologically active agents by screening natural sources has led to the discovery of many clinically useful drugs that play a major role in the treatment of human diseases. The goal of my thesis was to discover structurally novel type III secretion inhibitors. Active extracts from marine sponge P. johnstonia were identified via high throughput bioassays for the EPEC type III secretion inhibitors. Guided by this novel bioassay model, a new glycolipid family, the pachymosides, was fractionated and identified. To determine the structure of the pachymosides, chemical degradation was performed and the glycolipids were divided into aglycon and monosaccharide parts. Three aglycons were isolated and identified as 6, 8 and 9. [diagrams not included] Two monosaccharide residues were identified by NMR as glucose and galactose. Further chiral GC analysis determined their absolute configuration as D-glucose and D-galactose. Acetylation was performed on the pachymosides followed by 13C labelling. The structure of pachymoside A (16), a member of a novel bioactive glycolipids family, was figured out. This is the second identified structure for the type III secretion inhibitor bioassay. [diagrams not included]Science, Faculty ofChemistry, Department ofGraduat