Synthesis of the three monopyridinium oximes and evaluation of their potency to reactivate acetylcholinesterase inhibited by nerve agents

Understanding OxymaPure as a Peptide Coupling Additive: A Guide to New Oxyma Derivatives

An in silico study, using the GALAS algorithm available in ACD/PhysChem Suite, was performed to calculate the pK _a(s) of various oximes with potential application as peptide coupling additives. Among the known oximes and predicted structures, OxymaPure is superior based on the pK _a values calculated, confirming the results described in the literature and validating this algorithm for further use in that field. Among the nondescribed oximes, based on pK _a calculation, ethyl 2-(hydroxyimino)-2-nitroacetate seems to be a potential candidate to be used as an additive during peptide coupling.

Evaluation of Potency of Known Oximes (Pralidoxime, Trimedoxime, HI-6, Methoxime, Obidoxime) to in vitro Reactivate Acetylcholinesterase Inhibited by Pesticides (Chlorpyrifos and Methylchlorpyrifos and Nerve Agent (Russian VX)

Nerve agents and pesticides belong to the group of organophosphates. They are able to inhibit irreversibly the enzyme acetylcholinesterase (AChE). Acetylcholinesterase reactivators were designed for the treatment of nerve agent intoxications. Their potency to reactivate pesticide-inhibited AChE was many times evaluated. In this study, five commonly used AChE reactivators (pralidoxime, methoxime, HI-6, obidoxime, trimedoxime) for the reactivation of AChE inhibited by two pesticides (chlorpyrifos and methylchlorpyrifos) were used. Russian VX (nerve agent) as a member of nerve agents’ family was taken for comparison. Obtained results show that oximes developed against nerve agent intoxication are less effective for intoxication with organophosphorus pesticides. Especially, methylchlorpyrifos-inhibited AChE was found to be poorly reactivated by the compounds used.

Oximes-induced reactivation of rat brain acetylcholinesterase inhibited by VX agent

A comparison of one mono- and seven bisquaternary acetylcholinesterase (AChE) reactivators of acetylcholinesterase inhibited by VX agent was performed. As a source of the acetylcholinesterase, a rat brain homogenate was taken. There were significant differences in reactivation potency of all tested oximes. The oxime TO205 seems to be the most efficacious followed by TO046, HI-6, HS-6, K027, obidoxime, MMC and 2-PAM. In addition, the results of this study showed that the reactivation potency of the tested reactivators depends on many factors-such as the number of pyridinium rings, the number of oxime groups and their position, as well as the length and the shape of linkage bridge between two pyridinium rings.

The Ability of Oxime Mixtures to Increase the Reactivating and Therapeutic Efficacy of Antidotal Treatment of Cyclosarin Poisoning in Rats and Mice

The reactivating and therapeutic efficacy of two combinations of oximes (HI‑6 + trimedoxime and HI‑6 + K203) was compared with the effectiveness of antidotal treatment involving single oxime (HI‑6, trimedoxime, K203) using in vivo methods. In vivo determined percentage of reactivation of cyclosarin‑inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of both combinations of oximes is slightly higher than the reactivating efficacy of the most effective individual oxime in blood, diaphragm as well as in brain. Moreover, both combinations of oximes were found to be slightly more efficacious in the reduction of acute lethal toxic effects in cyclosarin‑poisoned mice than the antidotal treatment involving single oxime. Based on the obtained data, we can conclude that the antidotal treatment involving chosen combinations of oximes brings a beneficial effect for its ability to counteract the acute poisoning with cyclosarin.

A comparison of the reactivating and therapeutic efficacy of chosen combinations of oximes with individual oximes against VX in rats and mice

The ability of 2 combinations of oximes (HI-6 + trimedoxime and HI-6 + K203) to reactivate VX-inhibited acetylcholinesterase and reduce acute toxicity of VX was compared with the reactivating and therapeutic efficacy of antidotal treatment involving a single oxime (HI-6, trimedoxime, K203) in rats and mice. Our results showed that the reactivating efficacy of both combinations of oximes studied in rats is significantly higher than the reactivating efficacy of all individual oximes in diaphragm and roughly corresponds to the most effective individual oxime in blood and brain. Both combinations of oximes were found to be more effective in the reduction of acute lethal toxicity of VX in mice than the antidotal treatment involving the most efficacious individual oxime although the difference is not significant. Based on the obtained data, we can conclude that the antidotal treatment involving the chosen combinations of oximes brings benefit for the reactivation of VX-inhibited acetylcholinesterase in rats and for the antidotal treatment of VX-induced acute poisoning in mice.

The benefit of combinations of oximes for the reactivating and therapeutic efficacy of antidotal treatment of sarin poisoning in rats and mice

The influence of the combinations of oximes on the reactivating and therapeutic efficacy of antidotal treament of acute sarin poisoning was evaluated in this study. The ability of two combinations of oximes (HI-6 + trimedoxime and HI-6 + K203) to reactivate sarin-inhibited acetylcholinesterase and reduce acute toxicity of sarin was compared with the reactivating and therapeutic efficacy of antidotal treatment involving single oxime (HI-6, trimedoxime, K203) using in vivo methods. Studies determining percentage of reactivation of sarin-inhibited blood and tissue acetylcholinesterase in poisoned rats showed that the reactivating efficacy of the combination of oximes involving HI-6 and K203 is slightly higher than the reactivating efficacy of the most effective individual oxime in diaphragm and brain but the difference between them is not significant. The ability of combination of oximes involving HI-6 and trimedoxime to reactivate sarin-inhibited acetylcholinesterase roughly corresponds to the reactivating effects of the most effective individual oxime in blood as well as tissues. Moreover, both combinations of oximes were found to be as efficacious in the reduction of acute lethal toxic effects in sarin-poisoned mice as the most effective individual oxime. A comparison of reactivating and therapeutic efficacy of individual oximes showed that the oxime HI-6 is markedly more effective than the oxime K203 and trimedoxime. Based on the obtained data, we conclude that the antidotal treatment involving chosen combinations of oximes does not significantly influence the ability of the most effective individual oxime (HI-6) to reactivate sarin-inhibited rat acetylcholinesterase and to reduce acute toxicity of sarin in mice.

Synthesis of a novel series of bispyridinium compounds bearing a xylene linker and evaluation of their reactivation activity against chlorpyrifos-inhibited acetylcholinesterase

Nine potential AChE reactivators were synthesized using a modification of currently known synthetic pathways. Their potency to reactivate AChE inhibited by insecticide chlorpyrifos was tested in vitro. 2,2'-Bis(hydroxyiminomethyl)-1,1'-(1,4-phenylenedimethyl)-bispyridinium dibromide seems to be the most potent AChE reactivator. The reactivation potency of these compounds depends on structural factors such as length of the linking chain between both pyridinium rings and position of the oxime moiety on the pyridinium ring.

In vitro potency of H oximes (HI-6, HLö-7), the oxime BI-6, and currently used oximes (pralidoxime, obidoxime, trimedoxime) to reactivate nerve agent-inhibited rat brain acetylcholinesterase

The efficacy of H oximes (HI-6, HLö-7), the oxime BI-6, and currently used oximes (pralidoxime, obidoxime, trimedoxime) to reactivate acetylcholinesterase inhibited by two nerve agents (tabun, VX agent) was tested in vitro. Both H oximes (HI-6, HLö-7) and the oxime BI-6 were found to be more efficacious reactivators of VX-inhibited acetylcholinesterase than pralidoxime and obidoxime. On the other hand, their potency to reactivate tabun-inhibited acetylcholinesterase was low and did not reach the reactivating efficacy of trimedoxime and obidoxime. Thus, none of these compounds can be considered to be a broad-spectrum reactivator of nerve agent-inhibited acetylcholinesterase in spite of high potency to reactivate acetylcholinesterase inhibited by some nerve agents. More than one oxime may be necessary for the antidotal treatment of nerve agent-exposed individuals.

Strategy for the development of new acetylcholinesterase reactivators - antidotes used for treatment of nerve agent poisonings

The mechanism of intoxication with organophosphorus compounds, including highly toxic nerve agents, is based on the formation of irreversibly inhibited acetylcholinesterase (AChE; EC 3.1.1.7) that could be followed by a generalized cholinergic crisis. Nerve agent poisoning is conventionally treated using a combination of a cholinolytic drug (atropine mostly) to counteract the accumulation of acetylcholine at muscarinic receptors and AChE reactivators (pralidoxime or obidoxime) to reactivate inhibited AChE. At the Department of Toxicology, the strategy of the development of new more potent AChE reactivators consists of several steps: description of the nerve agent intoxication mechanism on the molecular basis (molecular design), prediction of the biological active structure of AChE reactivators (artificial neural networks), their synthesis, in vitro evaluation of their potencies (potentiometric titration and Ellman's method), in vivo studies (therapeutic index, LD(50) of newly synthesized reactivators, reactivation in different tissues, neuroprotective efficacy).

New quaternary pyridine aldoximes as casual antidotes against nerve agents intoxications

In this work, the ability of four newly synthesized oximes--K005 (1,3-bis(2-hydroxyiminomethylpyridinium) propane dibromide), K027 (1-(4-hydroxyiminomethylpyridinium)-3-(4-carbamoylpyridinium) propane dibromide), K033 (1,4-bis(2-hydroxyiminomethylpyridinium) butane dibromide) and K048 (1-(4-hydroxyiminomethylpyridinium)-4-(4-carbamoylpyridinium) butane dibromide) to reactivate acetylcholinesterase (AChE, EC 3.1.1.7) inhibited by nerve agents is summarized. Reactivation potency of these compounds was tested using standard in vitro reactivation test. Tabun, sarin, cyclosarin and VX agent were used as appropriate testing nerve agents. Rat brain AChE was used as a source of the enzyme. Efficacies of new reactivators to reactivate tabun-, sarin-, cyclosarin- and VX-inhibited AChE were compared with the currently used AChE reactivators (pralidoxime, obidoxime and HI-6). Oxime K048 seems to be promising reactivator of tabun-inhibited AChE. Its reactivation potency is significantly higher than that of HI-6 and pralidoxime and comparable with the potency of obidoxime. The best reactivator of sarin-inhibited AChE seems to be oxime HI-6. None of the new AChE reactivators reached comparable reactivation potency. The same results were obtained for cyclosarin-inhibited AChE. However, oxime K033 is also potent reactivator of AChE inhibited by this nerve agent. In the case of VX inhibition, obidoxime and new oximes K027 and K048 seem to be the best AChE reactivators. None from the currently tested AChE reactivators is able to reactivate AChE inhibited by all nerve agents used and, therefore, the search for new potential broad spectrum AChE reactivators is needed.