Molecular rigidity and potency of bispyridinium type allosteric modulators at muscarinic M2-receptors

Life Sci. 1997;60(22):1995-2003. doi: 10.1016/s0024-3205(97)00164-1.


Several bispyridinium compounds have been shown to be potent allosteric modulators of ligand binding to muscarinic M2-receptors. ,,Uno compounds" are benzyl derivatives of the bispyridinium "TMB4" (trimethylene-bis-[4-hydroxy-iminomethyl-pyridinium]). To gain more insight into structure activity relationships, eleven derivatives with varying structure of the oxime-linked aromatic substituent were tested for their ability to inhibit the equilibrium-binding of [3H]N-methylscopolamine ([3H]NMS) in guinea pig cardiac membranes and to retard [3H]NMS-dissociation allosterically. At a concentration of 3 microM, all compounds reduced [3H]NMS-binding to about 40 % of the control level, indicating a similar potency to inhibit the association of [3H]NMS. Allosteric retardation of [3H]NMS-dissociation required higher concentrations. Comparing the effects of the compounds at 30 and 300 microM, respectively, revealed considerable differences in potency. Therefore, the concentration-dependency of the delay of [3H]NMS-dissociation was determined for selected compounds. The results indicate that introduction of a benzyl-moiety into TMB4 leads to a 20-fold increase in allosteric potency. A further increment by a factor of 10 is obtained with the 2,6-dichlorobenzyl-substitution and with the naphthyl-derivative. The other compounds were less potent. An inverse correlation was found between the rotational freedom of the aromatic substituent and the allosteric potency. In conclusion, the aromatic moiety of non-symmetric bispyridinium-type modulators does not seem to be part of the pharmacophore involved in the inhibitory effect on the association of [3H]NMS. In contrast, a rigid aromatic lateral moiety appears to be essential for the interaction with the recognition site mediating the allosteric delay of [3H]NMS dissociation from muscarinic M2-receptors.

MeSH terms

  • Allosteric Regulation
  • Animals
  • Guinea Pigs
  • Half-Life
  • In Vitro Techniques
  • Kinetics
  • N-Methylscopolamine
  • Pyridinium Compounds / chemistry
  • Pyridinium Compounds / pharmacology*
  • Radioligand Assay
  • Receptors, Muscarinic / drug effects*
  • Receptors, Muscarinic / metabolism
  • Scopolamine Derivatives / metabolism
  • Scopolamine Derivatives / pharmacokinetics


  • Pyridinium Compounds
  • Receptors, Muscarinic
  • Scopolamine Derivatives
  • trimethylene-bis(4-hydroxyiminomethylpyridinium)
  • N-Methylscopolamine