Enantioselective Total Syntheses of Methanoquinolizidine-Containing Akuammiline Alkaloids and Related Studies

J Am Chem Soc. 2018 May 23;140(20):6483-6492. doi: 10.1021/jacs.8b03404. Epub 2018 May 15.

Abstract

The akuammiline alkaloids are a structurally diverse class of bioactive natural products isolated from plants found in various parts of the world. A particularly challenging subset of akuammiline alkaloids are those that contain a methanoquinolizidine core. We describe a synthetic approach to these compounds that has enabled the first total syntheses of (+)-strictamine, (-)-2( S)-cathafoline, (+)-akuammiline, and (-)-Ψ-akuammigine. Our strategy relies on the development of the reductive interrupted Fischer indolization reaction to construct a common pentacyclic intermediate bearing five contiguous stereocenters, in addition to late-stage formation of the methanoquinolizidine framework using a deprotection-cyclization cascade. The total syntheses of (-)-Ψ-akuammigine and (+)-akuammiline mark the first preparations of akuammiline alkaloids containing both a methanoquinolizidine core and vicinal quaternary centers. Lastly, we describe the bioinspired reductive rearrangements of (+)-strictamine and (+)-akuammiline to ultimately provide (-)-10-demethoxyvincorine and a new analogue thereof.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Alkaloids / chemical synthesis*
  • Alkaloids / chemistry
  • Biological Products / chemical synthesis*
  • Biological Products / chemistry
  • Chemistry Techniques, Synthetic
  • Cyclization
  • Models, Molecular
  • Plants / chemistry
  • Quinolizidines / chemical synthesis*
  • Quinolizidines / chemistry
  • Secologanin Tryptamine Alkaloids / chemical synthesis*
  • Secologanin Tryptamine Alkaloids / chemistry
  • Stereoisomerism
  • Terpenes / chemical synthesis*
  • Terpenes / chemistry

Substances

  • Alkaloids
  • Biological Products
  • Quinolizidines
  • Secologanin Tryptamine Alkaloids
  • Terpenes
  • cathafoline
  • akuammine
  • raubasine
  • strictamine