Harmane and harmalan are bioactive components of classical clonidine-displacing substance

Biochemistry. 2004 Dec 28;43(51):16385-92. doi: 10.1021/bi048584v.


Elucidation of the structure of the endogenous ligand(s) for imidazoline binding sites, clonidine-displacing substance (CDS), has been a major goal for many years. Crude CDS from bovine lung was purified by reverse-phase high-pressure liquid chromatography. Electrospray mass spectrometry (ESMS) and nuclear magnetic resonance ((1)H NMR) analysis revealed the presence of L-tryptophan and 1-carboxy-1-methyltetrahydro-beta-carboline in the active CDS extract. Competition radioligand binding studies, however, failed to show displacement of specific [(3)H]clonidine binding to rat brain membranes for either compound. Further purification of the bovine lung extract allowed the isolation of the beta-carbolines harmane and harmalan as confirmed by ESMS, (1)H NMR, and comparison with synthetic standards. Both compounds exhibited a high (nanomolar) affinity for both type 1 and type 2 imidazoline binding sites, and the synthetic standards were shown to coelute with the active classical CDS extracts. We therefore propose that the beta-carbolines harmane and harmalan represent active components of classical CDS. The identification of these compounds will allow us to establish clear physiological roles for CDS.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Carbolines / chemistry
  • Carbolines / metabolism*
  • Cattle
  • Chromatography, High Pressure Liquid
  • Clonidine / analogs & derivatives*
  • Clonidine / chemistry
  • Clonidine / metabolism*
  • Harmine / analogs & derivatives*
  • Harmine / chemistry
  • Harmine / metabolism*
  • Lung / metabolism
  • Spectrometry, Mass, Electrospray Ionization


  • Carbolines
  • Harmine
  • harmalan
  • harman
  • clonidine-displacing substance
  • Clonidine