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UBC Theses and Dissertations

Methodology for natural product synthesis : sordarin, himandrine and lepadiformine Liang, Huan


Fungal infection, of small concern in healthy individuals, can become problematic in immunosuppressed patients with illnesses such as AIDS, and the search for substances that exert antifungal action by new mechanisms continues. A noteworthy group of potent antimycotic natural products known as the sordarins meet this criterion. In order to investigate the effect of various functional and skeletal changes to sordarin on anti-pathogenic activity, we have devised practical, expeditious, and efficient routes to analogs of the natural product. The bioactivity of the new compounds against various pathogenic fungi was evaluated. This research constitutes the first half of my doctoral dissertation. The second half of my work centers on the development of a practical method for the oxidative amidation of phenols. This reaction achieves the conversion of phenols into spirocyclic (sulfon)amido-dienones. The new methodology forms the centerpiece of envisioned syntheses of (±)-himandrine and (-)-lepadiformines. Himandrine, isolated from the bark of Galbulimima belgraveana, displays anticholinergic activity and is thus of potential interest for the treatment of a number of human ailments. Our himandrine skeleton synthesis centered on a tandem oxidative amidation and Diels-Alder reaction, using three different approaches. The alkaloid (-)-lepadiformines displays potency as a potassium channel blocker. Our synthetic study towards this substance utilizes the oxidative cyclization of a phenolic sulfonamide as the key step. The resulting dienone is then desymmetrized through a stereoselective Michael addition leading to an enantiopure tricyclic intermediate, to which hydrocarbon side chain was appended in high yield. Further elaboration will lead to the natural product.

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