| Part I. Blooms of the "red tide" dinoflagellate Ptychodiscus brevis Davis (formerly Gymnodinium breve, Davis) cause massive fish kills, mollusk poisoning, and human food poisoning along the Florida coast and in the Gulf of Mexico. An investigation into the nature of the toxins produced by this alga was begun.;The structure of a second toxin, brevetoxin C (BTX-C), was determined by analysis of its J-modulated spin echo ('13)C-NMR, ('1)H-NMR, and Desorption/Chemical Ionization mass spectral data.;Part II. Studies of bioactive compounds from East African medicinal plants were undertaken. (1) The ether extract from the root bark of Trichilia roka showed strong insect antifeedant activity against the North American pest insects, the Southern army worm (Spodoptera eridania) and the Mexican bean beetle (Epilachan varivestis). Several active liminoids were isolated including the major compound trichilin A. Structures were elucidated from combined spectral data including the use of two-dimensional ('1)H-NMR spectroscopy. (2) The methanol extract from the roots of Ajuga remota caused disruption of the normal molting cycle when fed in an artificial diet to several species of Lepidoptera caterpillars. The previously known phytoecdysones-ecdysone, ajugasterone C and cyasterone were separated directly from the crude extract by droplet countercurrent chromatography (DCCC) and proved responsible for the observed bioactivity. (3) During our isolation studies on insect antifeedants from plants collected in East Africa, we found that several of the crude extracts exhibited mutagenic activity according to the Ames' method. Structural elucidation of several of these mutagens shows that they all possess skeletons which are quite common and have a wide distribution. (4) Finally, structural features of the insect antifeedant azadirachtin were investigated by using long-range selective proton decoupling (LSPD).;The major toxin, brevetoxin B (BTX-B), was carefully isolated from a diethyl ether extract of P. brevis; structure determination (relative stereochemistry) was accomplished by X-ray analysis. A 1,2 dibenzoate system was introduced into ring-H of BTX-B through a five-step reaction sequence and the absolute stereochemistry was then determined by circular dichroism (CD) using the nonempirical dibenzoate chirality method. |
