| This dissertation focuses on the investigation of the chemistry of four marine organisms: an unidentified sponge from Nauru, a sponge (a Plakortis sp.) and a tunicate (tentatively identified as a Leptoclinides sp.) from Truk Lagoon, and another tunicate Amphicarpa meridiana, from South Australia.;Three symmetrical tetraenes, naurol A, naurol B and naurol C, were isolated from an unidentified sponge from Nauru. These compounds exhibit a unique carbon skeleton found only in one other natural product, limatulone, which was isolated from a limpet, Collisella limatula. Two of these tetraenes, naurol A and naurol B, were found to be toxic to lymphocytic leukemia (PS cell line). The known compound, ergosterol peroxide, was also isolated from this sponge.;A study on the chemistry of a sponge from Truk Lagoon, identified as a Plakortis sp., showed the presence of five new peroxy derivatives of straight-chain fatty acid methyl esters. Four new butenolides, related in structure to these peroxy compounds, were also isolated.;An investigation of the chemistry of an ascidian from South Australia, Amphicarpa meridiana, led to the isolation of a new cytotoxic pentacyclic aromatic alkaloid, meridine, while a reinvestigation of the chemistry of an ascidian, tentatively identified as a Leptoclinides sp., from Truk Lagoon, resulted in the isolation of another pentacyclic aromatic alkaloid, 11-hydroxyascididemin. 2-Bromoleptoclinidinone was also isolated from this tunicate and its structure was revised based on the results from INAPT experiments and chemical correlation with ascididemin by hydrogenolysis of the former using Pd/C in methanol. |
