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Total Synthesis of Kopsinitarine E.

Karre Nagaraju1, Dongshun Ni1, Dawei Ma1

  • 1State Key Laboratory of Bioorganic & Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, 345 Lingling Lu, Shanghai, 200032, China.

Angewandte Chemie (International Ed. in English)
|August 25, 2020
PubMed
Summary

Researchers achieved the first total synthesis of kopsinitarine E, a complex Kopsia alkaloid. Key steps included radical cascade cyclization and Mannich reactions to build its strained cage structure.

Keywords:
Mannich reactioncyclizationindole alkaloidssemi-pinacol rearrangementtotal synthesis

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Area of Science:

  • Organic Chemistry
  • Natural Product Synthesis

Background:

  • Kopsinitarines A-E are complex octacyclic Kopsia alkaloids.
  • These alkaloids possess strained cage skeletons and a unique cyclic hemiaminal bridge.
  • Their complex structures present significant challenges for total synthesis.

Purpose of the Study:

  • To report the first total synthesis of kopsinitarine E.
  • To develop novel synthetic strategies for constructing complex alkaloid frameworks.

Main Methods:

  • Samarium(II) iodide (SmI2)-mediated radical cascade cyclization to form the carbocyclic skeleton.
  • Semi-pinacol rearrangement for key skeletal construction.
  • Chemoselective hydrosilyl amide reduction to form the hemiaminal ether bridge.
  • Intramolecular Mannich reaction to establish the strained cage system.

Main Results:

  • Successful total synthesis of kopsinitarine E.
  • Demonstration of key synthetic transformations for constructing complex alkaloid architectures.
  • Establishment of the highly strained cage system characteristic of kopsinitarine E.

Conclusions:

  • The developed synthetic route provides access to kopsinitarine E.
  • This work highlights the utility of radical cascade cyclizations and Mannich reactions in natural product synthesis.
  • The synthesis provides a platform for further exploration of Kopsia alkaloids.