title: Molecular rigidity and potency of bispyridinium type allosteric modulators at muscarinic M2-receptors.
abstract: 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.
authors.affiliation: Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Bonn, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Tränkle
authors.forename: K
authors.initials: K
authors.lastname: Elis
authors.forename: M
authors.initials: M
authors.lastname: Wiese
authors.forename: K
authors.initials: K
authors.lastname: Mohr
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D006168:Guinea Pigs; D006207:Half-Life; D066298:In Vitro Techniques; D007700:Kinetics; D019832:N-Methylscopolamine; D011726:Pyridinium Compounds / Q000737:chemistry / Q000494:pharmacology*; D011869:Radioligand Assay; D011976:Receptors, Muscarinic / Q000187:drug effects* / Q000378:metabolism; D012602:Scopolamine Derivatives / Q000378:metabolism / Q000493:pharmacokinetics
chemical_list: D011726:Pyridinium Compounds; D011976:Receptors, Muscarinic; D012602:Scopolamine Derivatives; C106320:trimethylene-bis(4-hydroxyiminomethylpyridinium); D019832:N-Methylscopolamine