Studies Toward the Synthesis of Natural Product Scaffolds Public

http://ir.library.oregonstate.edu/concern/honors_college_theses/z316q3591

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  • Part 1: A Diels-Alder Approach to the Synthesis of Novel Analogues of the Natural Product Siamenol Due to the prevalence of biaryl motifs in natural product synthesis, the Carter research group has been exploring the utility of a Diels-Alder approach to biaryl synthesis. The Diels-Alder approach involves a [4+2] cycloaddition between an acetylene dienophile and a cyclohexadiene, followed by subsequent [4+2] cycloreversion. This method of biaryl synthesis introduces numerous advantages compared to the traditional metal-mediated biaryl synthesis procedures, including a lack of environmentally hazardous transition metals. The Diels-Alder approach has been used by the Carter group to synthesize the natural product siamenol. This carbazole alkaloid, isolated from the Murraya siamensis shrub, has been found to possess moderate activity in the inhibition of the human immunodeficiency virus (HIV). Previously, synthesis of siamenol had been based on the traditional metal-mediated cross-coupling approach. Based on this initial synthesis, a series of novel analogues of siamenol have been synthesized using the Diels-Alder approach to biaryl synthesis. This project focuses on the synthesis of four such analogues of siamenol. Part 2: Advances in Proline-Based Enantioselective Organocatalysis and its Application to a Novel Synthesis of the Natural Product Aconitine Organocatalysis, while not a novel concept, has made significant strides in the last decade with the advent of improved methods of enantioselective organocatalysis. Particular advances have been made in the use of proline-based organocatalysts in catalyzing such reactions as aldol, Mannich and Michael reactions in a highly enantioselective fashion. The Carter Group has utilized Hua Cat, a proline-based sulfonamide, to catalyze a series of [2.2.2] bicyclizations based on a Mannich reactionrelated mechanism. This approach has been utilized to form a precursor to the natural product aconitine, a known analgesic and antipyretic. The key [2.2.2] bicyclization step proceeded in a high-concentration (1.0 M), room temperature reaction that produced the target [2.2.2] octane with a 57% yield and 99% e.e. Further considerations toward the synthesis of aconitine are also discussed.
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