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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Studies toward the total synthesis of swerilactones A and B

Hamann, Diane 07 December 2016 (has links)
Swerilactones and related natural products were isolated from the plant Swertia mileensis and related species from the Gentianacea family. All members have shown moderate bioactivity in a hepatitis B virus assay. Despite their appealing framework and bioactivity, to date no syntheses of these compounds have been reported in the literature. All members of the natural products family display a polycyclic framework, containing lactone-pyran fused bicyclic subunits, and are heavily oxygenated. En route to swerilactones A and B, featuring a complex pentacyclic (6/6/6/6) ring system, the successful syntheses of two key building blocks for studies of a biomimetic [4+2] cycloaddition have been accomplished. The challenges associated with the design of a novel synthesis of a 2H-pyran diene are presented and ultimately relied on a Saucy-Marbet rearrangement of a propargyl vinyl ether. Reactivity studies for the 2H-pyran have shown thermal normal demand and photoinduced, radical cation [4+2] cycloadditions are Diels-Alder modes of choice, whereas inverse demand pathways were unproductive. Synthetic routes to obtain carboxylate and various enol ether substituted dienophilic lactones are also outlined. They relied on a unified strategy, comprised of the rapid assembly of a β-brominated sorbate derivative via cross-couplings and final oxa-6π electrocyclization as an original ring closure strategy. Our attempts at coupling the 2H-pyran intermediate with the dienophilic lactones to access the core structure of swerilactones A and B, leveraging our preliminary reactivity studies are presented in detail. In addition, alternatives strategies to assemble the core structures of swerilactones A and B are described, along with our efforts (and potential routes) toward related members of this family of natural products.

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