Karlotoxins (KmTxs), produced by a toxic marine/estuarine phytoplankton, the dinoflagellate Karlodinium veneficum, are known to be ichthyotoxic, thus being associated with numerous fish deaths events worldwide. They have also been reported to show a variety of biological activities such as hemolytic, cytotoxic, and anti-fungal activities. Recently, the Hamann group successfully assigned the absolute configurations of KmTx2, the first complete structure elucidation among the congeners. In a structural sense, karlotoxins are a family of linear polyketides with three distinctive regions; a bis-tetrahydropyran core fragment, a long, highly oxygenated carbon chain, and a lipophilic chlorodiene unit. Such potent biological activities as well as novel molecular complexity engaged our interest in the synthesis of KmTx molecules in the purpose of supplying more samples for further biological evaluations. We have successfully established a synthetic route to access the C(40-61) B-ring fragment of the KmTx5, a congener of KmTx2, in a twelve-step reaction sequence starting from a reported tetrahydropyranyl intermediate which can be readily prepared from D-mannose in four steps following the literature precedent.
α-Boryl carbanion species are known to exhibit excellent olefinating abilities via boron-Wittig reaction. This type of reaction was first reported in the 1960’s, and actively studied mainly by Rathke, Pelter, and Matteson during the last third of the 20th century. We, however, had an impression that this area of chemistry has still been underrepresented in the literature, thus has more room to explore into. Utilizing the α-diaminobory carbanion-mediated one-pot olefination protocols we have developed, we successfully prepared a variety of substituted acrylonitriles, including tetrasubstituted alkenes, by olefinating aldehydes and ketones. We have also demonstrated a useful application of the α-boryl carbanion species for the synthesis of 2-aminoquinoline-based alkaloids.
|Advisor:||Mattern, Daniell L.|
|Commitee:||Cleland, Walter E., Hamann, Mark T., Wadkins, Randy M., Watkins, Davita L.|
|School:||The University of Mississippi|
|School Location:||United States -- Mississippi|
|Source:||DAI-B 77/06(E), Dissertation Abstracts International|
|Keywords:||Alpha-boryl carbanion, Boron-wittig olefination, Diaminoboryl acetonitrile, Karlotoxin|
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