Antimicrobial ambiguine isonitriles from the cyanobacterium Fischerella ambigua

J Nat Prod. 2009 May 22;72(5):894-9. doi: 10.1021/np800751j.


Five new antibacterial ambiguine K-O isonitriles (1-5) and eight previously described indole alkaloids were isolated from the cultured cyanobacterium Fischerella ambigua (UTEX 1903) by bioassay-guided fractionation. The planar structures of the new compounds were determined by spectroscopic analysis including MS and 1D and 2D NMR. X-ray crystallography was used to determine the absolute stereoconfiguration of ambiguine K isonitrile. The isolates were evaluated for their antibacterial activities against a set of bacterial targets, including Mycobacterium tuberculosis and Bacillus anthracis. Ambiguine K and M isonitriles showed the most potent activity against M. tuberculosis, with MIC values of 6.6 and 7.5 microM, respectively. Ambiguine A isonitrile showed the most potent activity against B. anthracis, with a MIC of 1.0 microM.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Anti-Bacterial Agents / chemistry
  • Anti-Bacterial Agents / isolation & purification*
  • Anti-Bacterial Agents / pharmacology*
  • Bacillus anthracis / drug effects
  • Cyanobacteria / chemistry*
  • Indole Alkaloids / chemistry
  • Indole Alkaloids / isolation & purification*
  • Indole Alkaloids / pharmacology*
  • Microbial Sensitivity Tests
  • Molecular Structure
  • Mycobacterium tuberculosis / drug effects
  • Nuclear Magnetic Resonance, Biomolecular


  • Anti-Bacterial Agents
  • Indole Alkaloids
  • ambiguine I isonitrile
  • ambiguine K isonitrile
  • ambiguine M isonitrile