This project seeks to develop and implement new tactics for the total synthesis of complex natural products that exhibit promising biological activities. Targeted structures that will be synthesized under the aegis of this grant are: 1) zaragozic acid C, a squalene synthase inhibitor;2) pactamycin, an antibiotic;3) leustroducsin B, a colony-stimulating factor inducer. These three structurally unique natural products share a high level of functional group and stereochemical complexity that renders them attractive platforms for new reaction discovery. An underlying principle of the proposed research is that buildup of the carbon skeleton must coincide with introduction of stereochemical information for maximum efficiency;therefore, cascade reactions are a staple of the projected synthetic routes. The strategies in particular seek to harness the unique reactivity of a newly developed reagent: tert-butyl tert-butyldimethylsilyl glyoxylate. This is a coupling reagent that conjoins complementary nucleophilic and electrophilic reaction partners, often with high levels of stereocontrol for the stereogenic centers that are concomitantly built up with the carbon skeleton. In each proposed synthesis, the key step is a new, mechanistically guided poly-addition reaction that introduces a significant fraction of the molecular complexity in a single operation. The reactions are configured such that the key functional groups are introduced in the proper oxidation state, minimizing wasteful downstream operations.
The molecules that are targeted for synthesis in this study all exhibit potent biological activities that could hold significance in the development of small molecule therapeutics. The efficient preparation of these compounds is a necessary precondition for any future biomedical applications.
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