Bispyridinium Compounds Research Articles

LUMO energy of model compounds of bispyridinium compounds as an index for the inhibition of choline kinase

Eleven derivatives of 1,1′-[1,2-ethylenebis(benzene-1,4-diylmethylene)]bis(4-pyridinium) dibromides bearing various groups at C-4 of the pyridinium moiety were synthesized and examined for their inhibition of choline kinase (ChoK) and antiproliferative activities. The C-4 substituents include electron-releasing, neutral or electron-withdrawing groups. A one-parameter regression equation has been derived which satisfactorily describes the ex vivo inhibitory potency of ChoK of the title compounds. The electronic effect plays a critical function in the ex vivo inhibition of ChoK although the role of electrostatic interactions could be altered due to a solvation process of both ChoK and ligands.

Molecular rigidity and potency of bispyridinium type allosteric modulators at muscarinic M 2-receptors

Several bispyridinium compounds have been shown to be potent allosteric modulators of ligand binding to muscarinic M 2-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 μM, 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 μM, 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 M 2-receptors.

Influence of the lateral substituents of bispyridinium compounds on the mode of allosteric action on muscarinic M2-receptors

Influence of the lateral substituents of bispyridinium compounds on the mode of allosteric action on muscarinic M2-receptors

Evidence for a multiple binding mode of bispyridinium-type allosteric modulators of muscarinic receptors

The ligand binding properties of muscarinic receptors can be modulated by allosterically acting compounds. Here, a set of novel bispyridinium-type compounds was investigated which were designed to study structure-activity relationships and to provide more insight into the molecular events underlying the allosteric delay of the dissociation of [ 3H] N-methylscopolamine from muscarinic M 2 receptors in porcine cardiac membranes. The parent compound, a non-substituted bispyridinium oxime, displayed a weak allosteric potency and was unable to prevent radioligand dissociation at maximum concentrations. Introduction of either a phthalimidomethyl-moiety or a dichlorobenzyl-moiety at one end of the parent compound led to a considerable increase of the allosteric activity with regard to both the potency and the maximum effect. In these unilaterally ring-substituted bispyridiniums, homologous contralateral non-aromatic modifications were accompanied by divergent potency shifts depending on whether the unilateral ring was phthalimidomethyl or dichlorobenzyl. The findings point to a multiple binding mode of bispyridinium compounds at M 2 receptors in the [ 3H] N-methylscopolamine-occupied state, i.e., different orientations of the compounds at the allosteric binding area or even an interaction with distinct allosteric recognition sites.

Synthesis and Anticholinesterase Activity of New Bispyridinium Compounds

Synthesis of new bis(1‐methylpyridinium) compounds containing a 1,4‐diacetylbenzene linkage between the pyridinium moieties from commercially available 2‐, 3‐, and 4‐picoline precursors was accomplished via metallation, reaction of the picolyllithium with 1,4‐dicyanobenzene, and subsequent quatemization of the resulting bispyridyl compounds. Acetylcholinesterase inhibitory activity was determined colorimetrically with purified electric eel enzyme. Examination of structure—activity relationships indicated that the 3‐substituted pyridinium compound is the most potent isomer, followed by the 2‐substituted isomer, and that the 4‐substituted analogue is the least active.

Bispyridinium (oxime) compounds antagonize the “ganglion blocking” effect of pyridostigmine in isolated superior cervical ganglia of the rat

The "antidotal effectiveness" of several bispyridinium compounds (HGG 12, HGG 65, HGG 70, HI 6, HLö and HLö 12) against the acetylcholinesterase (AChE) inhibitor pyridostigmine was evaluated in isolated superior cervical ganglia of the rat. Compound action potential amplitudes were inhibited by pyridostigmine in a concentration-dependent manner. HI 6 and atropine proved to be the most effective compounds in antagonizing the "ganglion blocking" action of pyridostigmine. Their relative effectiveness (PE value) was 5.4 and 4.2, respectively. All of the six bispyridinium compounds inhibited carbachol-induced, nicotinic, ganglionic surface depolarizations. The antinicotinic potencies of HI 6 and HLö 7 were about one order of magnitude lower (apparent KI values: 294 and 330 mumol/l) than the antinicotinic potencies of HGG 12, HGG 65, HGG 70 and HLö 12 (apparent KI values ranging from 19 to 41 mumol/l). The antinicotinic potencies of the bispyridinium compounds did not correlate with their in vitro protection of synaptic transmission in sympathetic ganglia. Moreover, the effectiveness of atropine points to the importance of antimuscarinic properties of possible "antidotes" for the maintenance of ganglionic transmission in cases of AChE poisoning.

Homologous and heterologous desensitisation of histamine H 1-receptor mediated contractions of guinea-pig jejunum

Organophosphorus compounds (OPC), i.e. nerve agents or pesticides, are highly toxic due to their strong inhibition potency against acetylcholinesterase (AChE). Inhibited AChE results in accumulation of acetylcholine in the synaptic cleft and thus the desensitisation of the nicotinic acetylcholine receptor (nAChR) in the postsynaptic membrane is provoked. Direct targeting of nAChR to reduce receptor desensitisation might be an alternative therapeutic approach. For drug discovery, functional properties of potent therapeutic candidates need to be investigated in addition to affinity properties. Solid supported membrane (SSM)-based electrophysiology is useful for functional characterisation of ligand-gated ion channels like nAChRs, as charge translocations via capacitive coupling of the supporting membrane can be measured. By varying the agonist (carbamoylcholine) concentration, different functional states of the nAChR were initiated. Using plasma membrane preparations obtained from Torpedo californica electric organ, functional properties of selected nAChR ligands and non-oxime bispyridinium compounds were investigated. Depending on overall-size, the bispyridinium compounds enhanced or inhibited cholinergic signals induced by 100 μM carbamoylcholine. Applying excessive concentrations of the agonist carbamoylcholine provoked desensitisation of the nAChRs, whereas addition of bispyridinium compounds bearing short alkyl linkers exhibited functional recovery of previously desensitised nAChRs. The results suggest that these non-oxime bispyridinium compounds possibly interacted with nAChR subtypes in a manner of a positive allosteric modulator (PAM). The described newly developed functional assay is a valuable tool for the assessment of functional properties of potential compounds such as nAChR modulating ligands, which might be a promising approach in the therapeutically treatment of OPC-poisonings.

1,1′-Alkylene bis-pyridinium compounds as pickling inhibitors

The inhibition efficiencies of 1,1′-alkylene bis-pyridinium compounds have been studied for corrosion of mild steel in 0.5 M H 2SO 4. Substitution in the pyridine ring (R = CH 3, COOH etc.) has a pronounced effect on the inhibition efficiency, though the length of the alkyl chain bound to the quaternary nitrogen atom is markedly reduced. The inhibitors studied showed Langmuirian behaviour.

Binding of soman antidotes to acetylcholine receptors

It has been reported that several bis-quaternary compounds not necessarily having an oxime function can be used to treat soman poisoning in mice. The mechanism for this protection is not clear, but it has been proposed that such compounds may act by blocking muscarinic or nicotinic acetylcholine receptors. We have tested thirty-four compounds for muscarinic binding activity, using displacement of tritiated 3-quinuclidinyl benzilate (QNB) as a criterion, and thirty-two compounds for nicotinic binding based on inhibition of alpha-bungarotoxin (BGT) binding. Only sixteen of these compounds were able to displace QNB from rat brain membranes, and only ten of them affected BGT binding. With one exception, all of the effective compounds belonged to a series of bis-pyridinium compounds that are similar in structure to SAD-128. The binding affinities to muscarinic receptors of all these compounds were low compared to atropine. Some of the compounds bound to nicotinic receptors with affinities approaching that of d-tubocurarine. However, there was not a direct correlation between binding affinity and their reported efficacy against soman.

Effect of the bispyridinium compounds HGG12, HGG42, and obidoxime on synaptic transmission and NAD(P)H-fluorescence in the superior cervical ganglion of the rat in vitro.

Postganglionic compound action potential (AP) and intracellular NAD(P)H-fluorescence were recorded simultaneously in the perifused superior cervical ganglion of the rat (SCG) to study the effects of the bispyridinium oximes HGG12, HGG42 and obidoxime. HGG12 and HGG42 inhibit the compound action potential (AP) (ID50: 70 microM) and the reductive part of NAD(P)H changes (ID50: 75 microM) recorded upon stimulation of the SCG, while obidoxime has no ganglion blocking effects in concentrations up to 1 mM. The effects of inhibitors of cholinergic transmission were also studied in order to understand the mechanisms of action of the oximes. Hexamethonium (C6) and atropine, competitive inhibitors of receptors of nicotinic and muscarinic cholinergic transmission respectively, were found to block synaptic transmission (C6 ID50:150 microM, atropine ID50: 70 microM) and the reductive part of the NAD(P)H response (C6 ID50: 70 microM, atropine ID50: 50 microM) in a quantitatively similar way. Comparison of the ganglionic action of HGG12 and HGG42 with that of the inhibitory agents characterises them as inhibitors of receptors of nicotinic ganglionic transmission. Furthermore at concentrations of about 10 microM, HGG12 behaves like atropine and leads to an increase in AP and reductive fluorescence response. It is therefore probable that HGG12 has in addition an affinity for ganglionic muscarinic receptors which HGG42 does not have.

The interaction of bis-pyridinium oximes with mouse brain muscarinic receptor

The bispyridinium oximes toxogonin [ N, N′-oxydimethylene bis (pyridinium 4-aldoxim) dichloride] and its structural analogs HS-3, HS-6, HI-6 and MMB-4, and the bispyridinium salt SAD-128, which serve as antidotes to certain types of organophosphorus poisoning, bind competitively to mouse brain muscarinic receptors. This was determined in vitro employing the potent and specific muscarinic antagonist 3H-4NMPB ( 3H-4- N-methyl piperidyl benzilate). All the bispyridinium compounds also exerted a mild anti-acetylcholine activity ( K d = 10 −4−10 −5M) measured physiologically in the guinea pig ileum, which correlated well with the dissociation constants obtained from binding studies with mouse brain homogenate. The most potent muscarinic blocker was SAD-128 ( K′ d = (7.1 ± 1.2) × 10 −6M for whole mouse brain), whose remarkable therapeutic action against soman intoxication may be partly attributed to this antimuscarinic activity. The binding data are best fitted by a competitive model, and the deviation from the law of mass action observed here may be related either to the heterogeneity of muscarinic receptors in the mouse brain or to nonequivalency of the number of binding sites for bisquaternary pyridines and 4-NMPB.

Ganglion blocking properties of some bispyridinium soman antagonists

Various doses of several bispyridinium compounds (HS-6, HI-6, HGG-12, HGG-42 and SAD-128) known to protect animals against the irreversible cholinesterase inhibitor soman were examined to determine their effects on the cardiovascular and respiratory system of cats. Although the potency varied considerably all of the compounds tested lowered the blood pressure, which appeared to be the result of ganglion blocking properties as determined by their reduction of the pressor response to dimethylphenylpiperazinium and the blockade of the contraction of the preganglionically stimulated cat nictitating membrane. Some of the compounds caused cessation of respiration at much lower doses than others but did so at doses greater than those causing ganglion blockade.

Influence of acetyl-β-methylcholine, carbamoylcholine, and bis-pyridinium compounds on the activity of acetylcholinesterase

The decomposition rate of the substrate acetyl-β-methylcholine by AChE in presence of the antagonists TMB 4, ∗ ∗ [1,1′-trimethylene bis-(4-formylpyridinium bromide)] dioxime. toxogonin, † † Obidoxime = [1,1′-oxydimethylene bis-(4-formylpyridinium chloride)] dioxime. and HS 6 ‡ ‡ [l ,I′-oxydimethylene (2-formyl-3-carbamyl-pyridinium chloride)]. was measured in vitro. The results are compared with those of previous studies using acetylcholine as substrate. Furthermore the reactivating potency of toxogonin on the carbamoylcholine-inhibited enzyme was investigated. The antagonists showed different effects on the substrate decomposition rates of the enzyme, depending on the nature of the substrate. It is concluded that the antagonists as well as the substrates react not only with the active centre of AChE but also with a secondary binding site. In the reactivating reaction of carbamoyl-inhibited AChE, a reaction at a secondary binding site is also involved.

Activating and inhibitory effects of bispyridinium compounds on bovine red cell acetylcholinesterase

The action of 6 bispyridinium compounds on the enzymatic activity of acetylcholinesterase has been investigated in vitro. The influence was either an activation or an inhibition of the enzyme, depending not only on the concentration of the antagonist, but also on that of the substrate. These compounds owe their activity mainly to their bisquaternary structure. The influence of substituents on the pyridine moiety is less important. It is assumed that binding of the bispyridinium compounds occurs not only on the active center, but also on another site of the enzyme. An interaction between these two binding sites is also postulated. The mechanism of inhibition is suggested to be a mixed competitive and noncompetitive one.