Development of enantioselective synthetic routes to the hasubanan and acutumine alkaloids

J Org Chem. 2013 Oct 18;78(20):10031-57. doi: 10.1021/jo401889b. Epub 2013 Sep 27.

Abstract

We describe a general strategy to prepare the hasubanan and acutumine alkaloids, a large family of botanical natural products that display antitumor, antiviral, and memory-enhancing effects. The absolute stereochemistry of the targets is established by an enantioselective Diels-Alder reaction between 5-(trimethylsilyl)cyclopentadiene (36) and 5-(2-azidoethyl)-2,3-dimethoxybenzoquinone (24). The Diels-Alder adduct 38 is transformed to the tetracyclic imine 39 by a Staudinger reduction-aza-Wittig sequence. The latter serves as a universal precursor to the targets. Key carbon-carbon bond constructions include highly diastereoselective acetylide additions to the N-methyliminium ion derived from 39 and Friedel-Crafts and Hosomi-Sakurai cyclizations to construct the carbocyclic skeleton of the targets. Initially, this strategy was applied to the syntheses of (-)-acutumine (4), (-)-dechloroacutumine (5), and four hasubanan alkaloids (1, 2, 3, and 8). Herein, the synthetic route is adapted to the syntheses of six additional hasubanan alkaloids (12, 13, 14, 15, 18, and 19). The strategic advantage of 5-(trimethylsilyl)cyclopentadiene Diels-Alder adducts is demonstrated by site-selective functionalization of distal carbon-carbon π-bonds in the presence of an otherwise reactive norbornene substructure. Evaluation of the antiproliferative properties of the synthetic metabolites revealed that four hasubanan alkaloids are submicromolar inhibitors of the N87 cell line.

Publication types

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

MeSH terms

  • Alkaloids / chemical synthesis*
  • Alkaloids / chemistry
  • Cycloaddition Reaction
  • Heterocyclic Compounds, 4 or More Rings / chemical synthesis*
  • Heterocyclic Compounds, 4 or More Rings / chemistry
  • Molecular Structure
  • Spiro Compounds / chemical synthesis*
  • Spiro Compounds / chemistry
  • Stereoisomerism

Substances

  • Alkaloids
  • Heterocyclic Compounds, 4 or More Rings
  • Spiro Compounds
  • acutumine
  • hasubanan