Pyridinium-2-carbaldoximes with quinolinium carboxamide moiety are simultaneous reactivators of acetylcholinesterase and butyrylcholinesterase inhibited by nerve agent surrogates

The pyridinium-2-carbaldoximes with quinolinium carboxamide moiety were designed and synthesised as cholinesterase reactivators. The prepared compounds showed intermediate-to-high inhibition of both cholinesterases when compared to standard oximes. Their reactivation ability was evaluated in vitro on human recombinant acetylcholinesterase (hrAChE) and human recombinant butyrylcholinesterase (hrBChE) inhibited by nerve agent surrogates (NIMP, NEMP, and NEDPA) or paraoxon. In the reactivation screening, one compound was able to reactivate hrAChE inhibited by all used organophosphates and two novel compounds were able to reactivate NIMP/NEMP-hrBChE. The reactivation kinetics revealed compound 11 that proved to be excellent reactivator of paraoxon-hrAChE better to obidoxime and showed increased reactivation of NIMP/NEMP-hrBChE, although worse to obidoxime. The molecular interactions of studied reactivators were further identified by in silico calculations. Molecular modelling results revealed the importance of creation of the pre-reactivation complex that could lead to better reactivation of both cholinesterases together with reducing particular interactions for lower intrinsic inhibition by the oxime.     

Interactions of butane, but-2-ene or xylene-like linked bispyridinium para-aldoximes with native and tabun-inhibited human cholinesterases

Kinetic parameters were evaluated for inhibition of native and reactivation of tabun-inhibited human erythrocyte acetylcholinesterase (AChE, EC 3.1.1.7) and human plasma butyrylcholinesterase (BChE, EC 3.1.1.8) by three bispyridinium para-aldoximes with butane (K074), but-2-ene (K075) or xylene-like linker (K114). Tested aldoximes reversibly inhibited both cholinesterases with the preference for binding to the native AChE. Both cholinesterases showed the highest affinity for K114 (K_i was 0.01 mM for AChE and 0.06 mM for BChE). The reactivation of tabun-inhibited AChE was efficient by K074 and K075. Their overall reactivation rate constants were around 2000 min⁻¹ M⁻¹, which is seven times higher than for the classical bispyridinium para-aldoxime TMB-4. The reactivation of tabun-inhibited AChE assisted by K114 was slow and reached 90% after 20 h. Since the aldoxime binding affinity of tabun-inhibited AChE was similar for all tested aldoximes (and corresponded to their K_i), the rate of the nucleophilic displacement of the phosphoryl-moiety from the active site serine was the limiting factor for AChE reactivation. On the other hand, none of the aldoximes displayed a significant reactivation of tabun-inhibited BChE. Even after 20 h, the reactivation maximum was 60% for 1 mM K074 and K075, and only 20% for 1 mM K114. However, lower BChE affinities for K074 and K075 compared to AChE suggest that the fast tabun-inhibited AChE reactivation by these compounds would not be obstructed by their interactions with BChE in vivo.     

Interactions of butane, but-2-ene or xylene-like linked bispyridinium para-aldoximes with native and tabun-inhibited human cholinesterases

Kinetic parameters were evaluated for inhibition of native and reactivation of tabun-inhibited human erythrocyte acetylcholinesterase (AChE, EC 3.1.1.7) and human plasma butyrylcholinesterase (BChE, EC 3.1.1.8) by three bispyridinium para-aldoximes with butane (K074), but-2-ene (K075) or xylene-like linker (K114). Tested aldoximes reversibly inhibited both cholinesterases with the preference for binding to the native AChE. Both cholinesterases showed the highest affinity for K114 (K(i) was 0.01mM for AChE and 0.06mM for BChE). The reactivation of tabun-inhibited AChE was efficient by K074 and K075. Their overall reactivation rate constants were around 2000min(-1)M(-1), which is seven times higher than for the classical bispyridinium para-aldoxime TMB-4. The reactivation of tabun-inhibited AChE assisted by K114 was slow and reached 90% after 20h. Since the aldoxime binding affinity of tabun-inhibited AChE was similar for all tested aldoximes (and corresponded to their K(i)), the rate of the nucleophilic displacement of the phosphoryl-moiety from the active site serine was the limiting factor for AChE reactivation. On the other hand, none of the aldoximes displayed a significant reactivation of tabun-inhibited BChE. Even after 20h, the reactivation maximum was 60% for 1mM K074 and K075, and only 20% for 1mM K114. However, lower BChE affinities for K074 and K075 compared to AChE suggest that the fast tabun-inhibited AChE reactivation by these compounds would not be obstructed by their interactions with BChE in vivo.     

Active site mutant acetylcholinesterase interactions with 2-PAM, HI-6, and DDVP

We used mouse recombinant wild-type acetylcholinesterase (AChE; EC 3.1.1.7), butyrylcholinesterase (BChE; EC 3.1.1.8), and AChE mutants with mutations (Y337A, F295L, F297I, Y72N, Y124Q, and W286A) that resemble residues found at structurally equivalent positions in BChE, to find the basis for divergence between AChE and BChE in following reactions: reversible inhibition by two oximes, progressive inhibition by the organophosphorus compound DDVP, and oxime-assisted reactivation of the phosphorylated enzymes. The inhibition enzyme-oxime dissociation constants of AChE w.t. were 150 and 46 microM, of BChE 340 and 27 microM for 2-PAM and HI-6, respectively. Introduced mutations lowered oxime binding affinities for both oximes. DDVP progressively inhibited cholinesterases yielding symmetrical dimethylphosphorylated enzyme conjugates at rates between 104 and 105/min/M. A high extent of oxime-assisted reactivation of all conjugates was achieved, but rates by both oximes were up to 10 times slower for phosphorylated mutants than for AChE w.t.     

Potency of several oximes to reactivate human acetylcholinesterase and butyrylcholinesterase inhibited by paraoxon in vitro

Organophosphorus pesticides (e.g. chlorpyrifos, malathion, and parathion) and nerve agents (sarin, tabun, and VX) are highly toxic organophosphorus compounds with strong inhibition potency against two key enzymes in the human body—acetylcholinesterase (AChE; EC 3.1.1.7) and butyrylcholinesterase (BuChE; EC 3.1.1.8). Subsequent accumulation of acetylcholine at synaptic clefts can result in cholinergic crisis and possible death of intoxicated organism. For the recovery of inhibited AChE, derivatives from the group of pyridinium or bispyridinium aldoximes (called oximes) are used. Their efficacy depends on their chemical structure and also type of organophosphorus inhibitor. In this study, we have tested potency of selected cholinesterase reactivators (pralidoxime, obidoxime, trimedoxime, methoxime and H-oxime HI-6) to reactivate human erythrocyte AChE and human plasma BuChE inhibited by pesticide paraoxon. For this purpose, modified Ellman's method was used and two different concentrations of oximes (10 and 100 μM), attainable in the plasma within antidotal treatment of pesticide intoxication were tested. Results demonstrated that obidoxime (96.8%) and trimedoxime (86%) only reached sufficient reactivation efficacy in case of paraoxon-inhibited AChE. Other oximes evaluated did not surpassed more than 25% of reactivation. In the case of BuChE reactivation, none of tested oximes surpassed 12.5% of reactivation. The highest reactivation efficacy was achieved for trimedoxime (12.4%) at the concentration 100 μM. From the data obtained, it is clear that only two from currently available oximes (obidoxime and trimedoxime) are good reactivators of paraoxon-inhibited AChE. In the case of BuChE, none of these reactivators could be used for its reactivation.     

New group of xylene linker-containing acetylcholinesterase reactivators as antidotes against the nerve agent cyclosarin

Nerve agents such as sarin, cyclosarin and tabun are organophosphorus substances able to inhibit the enzyme acetylcholinesterase (AChE; EC 3.1.1.7). AChE reactivators and anticholinergics are generally used as antidotes in the case of intoxication with these agents. None of the known AChE reactivators is able to reactivate AChE inhibited by all nerve agents used. In this work, reactivation potency of nine newly developed AChE reactivators with an incorporated xylene ring in their structure was measured in vitro. Cyclosarin was chosen as an appropriate member of the nerve agent family. Reactivation potency of the tested AChE reactivators was compared with the gold standard of AChE reactivators--pralidoxime. Two oximes (K107 and K108) surpassed the reactivation potency of pralidoxime. Moreover, from the obtained results it could be deduced that AChE reactivators with a functional oxime group in position-2 are the most potent AChE reactivators in the case of cyclosarin intoxications.     

New group of xylene linker-containing acetylcholinesterase reactivators as antidotes against the nerve agent cyclosarin

Nerve agents such as sarin, cyclosarin and tabun are organophosphorus substances able to inhibit the enzyme acetylcholinesterase (AChE; EC 3.1.1.7). AChE reactivators and anticholinergics are generally used as antidotes in the case of intoxication with these agents. None of the known AChE reactivators is able to reactivate AChE inhibited by all nerve agents used. In this work, reactivation potency of nine newly developed AChE reactivators with an incorporated xylene ring in their structure was measured in vitro. Cyclosarin was chosen as an appropriate member of the nerve agent family. Reactivation potency of the tested AChE reactivators was compared with the gold standard of AChE reactivators – pralidoxime. Two oximes (K107 and K108) surpassed the reactivation potency of pralidoxime. Moreover, from the obtained results it could be deduced that AChE reactivators with a functional oxime group in position-2 are the most potent AChE reactivators in the case of cyclosarin intoxications.     

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.     

Mechanistic studies of new oximes reactivators of human butyryl cholinesterase inhibited by cyclosarin and sarin

Butyryl cholinesterase (BChE) has been seen as a key enzyme in the search for new strategies in the treatment of poisoning by organophosphates (OPs), since human BChE (HssBChE), complexed with the appropriate oxime, can be a suitable scavenger and deactivator for OPs in the blood stream. However, the efficacy of HssBChE is limited by its strict stoichiometric scavenging, slow reactivation, and propensity for aging. The improvement of the reactivation rate by new and more efficient oximes could contribute to mitigate this problem and increase the HssBChE efficiency as scavenger. Several oximes have been synthesized and tested with this goal, some with promising results, but the mechanistic aspects of the reactivation reaction are not fully understood yet. In order to better investigate this mechanism, docking and mixed quantum and molecular mechanics combined with principal components analysis were performed here to evaluate the capacity of reactivation and determine the preferred route for the reactivation reaction of two new oximes on HssBChE inhibited by the neurotoxic agents cyclosarin and sarin. Plots of potential energies were calculated and all the transition states of the reactional mechanism were determined. Our results showed a good correlation with experimental data and pointed to the most efficient oxime with both OPs. The protocol used could be a suitable tool for a preliminary evaluation of the HssBChE reactivation rates by new oximes.     

New Cholinesterase Inhibitory Constituents from Lonicera quinquelocularis

A phytochemical investigation on the ethyl acetate soluble fraction of Lonicera quinquelocularis (whole plant) led to the first time isolation of one new phthalate; bis(7-acetoxy-2-ethyl-5-methylheptyl) phthalate (3) and two new benzoates; neopentyl-4-ethoxy-3, 5-bis (3-methyl-2-butenyl benzoate (4) and neopentyl-4-hydroxy-3, 5-bis (3-methyl-2-butenyl benzoate (5) along with two known compounds bis (2-ethylhexyl phthalate (1) and dioctyl phthalate (2). Their structures were established on the basis of spectroscopic analysis and by comparison with available data in the literature. All the compounds (1–5) were tested for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities in dose dependent manner. The IC₅₀ (50% inhibitory effect) values of compounds 3 and 5 against AChE were 1.65 and 3.43 µM while the values obtained against BChE were 5.98 and 9.84 µM respectively. Compounds 2 and 4 showed weak inhibition profile.     

Oximes: Reactivators of phosphorylated acetylcholinesterase and antidotes in therapy against tabun poisoning

One of the therapeutic approaches to organophosphate poisoning is to reactivate AChE with site-directed nucleophiles such as oximes. However, pyridinium oximes 2-PAM, HI-6, TMB-4 and obidoxime, found as the most effective reactivators, have limiting reactivating potency in tabun poisoning. We tested oximes varying in the type of ring (pyridinium and/or imidazolium), the length and type of the linker between rings, and in the position of the oxime group on the ring to find more effective oximes to reactivate tabun-inhibited human erythrocyte AChE. Three of our tested pyridinium oximes K027, K048, K074, along with TMB-4, were the most promising for AChE reactivation. Promising oximes were further tested in vivo on tabun poisoned mice not only as antidotes in combination with atropine but also as pretreatment drug. Herein, we showed that a promising treatment in tabun poisoning by selected oximes and atropine could be improved if oximes are also used in pretreatment. Since the reactivating efficacy of the oximes in vitro corresponded to their therapeutic efficacy in vivo, it seems that pharmacological effect of these oximes is indeed primarily related to the reactivation of tabun-phosphorylated AChE.     

Synthesis,in vitro screening and molecular docking of isoquinolinium-5-carbaldoximes as acetylcholinesterase and butyrylcholinesterase reactivators

Abstract

The series of symmetrical and unsymmetrical isoquinolinium-5-carbaldoximes was designed and prepared for cholinesterase reactivation purposes. The novel compounds were evaluated for intrinsic acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) inhibition, when the majority of novel compounds resulted with high inhibition of both enzymes and only weak inhibitors were selected for reactivation experiments on human AChE or BChE inhibited by sarin, VX, or paraoxon. The AChE reactivation for all used organophosphates was found negligible if compared to the reactivation ability of obidoxime. Importantly, two compounds were found to reactivate BChE inhibited by sarin or VX better to obidoxime at human attainable concentration. One compound resulted as better reactivator of NEMP (VX surrogate)-inhibited BChE than obidoxime. The in vitro results were further rationalized by molecular docking studies showing future directions on designing potent BChE reactivators.     

Design,synthesis and cholinesterase inhibitory properties of new oxazole benzylamine derivatives

Abstract

The enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are primary targets in attenuating the symptoms of neurodegenerative diseases. Their inhibition results in elevated concentrations of the neurotransmitter acetylcholine which supports communication among nerve cells. It was previously shown for trans-4/5-arylethenyloxazole compounds to have moderate AChE and BChE inhibitory properties. A preliminary docking study showed that elongating oxazole molecules and adding a new NH group could make them more prone to bind to the active site of both enzymes. Therefore, new trans-amino-4-/5-arylethenyl-oxazoles were designed and synthesised by the Buchwald-Hartwig amination of a previously synthesised trans-chloro-arylethenyloxazole derivative. Additionally, naphthoxazole benzylamine photoproducts were obtained by efficient photochemical electrocyclization reaction. Novel compounds were tested as inhibitors of both AChE and BChE. All of the compounds exhibited binding preference for BChE over AChE, especially for trans-amino-4-/5-arylethenyl-oxazole derivatives which inhibited BChE potently (IC₅₀ in µM range) and AChE poorly (IC₅₀?100?µM). Therefore, due to the selectivity of all of the tested compounds for binding to BChE, these compounds could be applied for further development of cholinesterase selective inhibitors.

• HIGHLIGHTS

• Series of oxazole benzylamines were designed and synthesised

• The tested compounds showed binding selectivity for BChE

• Naphthoxazoles were more potent AChE inhibitors

     

Novel tacrine-pyridinium hybrid reactivators of organophosphorus-inhibited acetylcholinesterase: Synthesis,molecular docking,and in vitro reactivation study

First-line medical treatment against nerve agents consists of co-administration of anticholinergic agents and oxime reactivators, which reactivate inhibited AChE. Pralidoxime, a commonly used oxime reactivator, is effective against some nerve agents but not against others; thus, new oxime reactivators are needed. Novel tacrine-pyridinium hybrid reactivators in which 4-pyridinealdoxime derivatives are connected to tacrine moieties by linear carbon chains of different lengths (C2–C7) were prepared (Scheme 1, 5a–f). Their binding affinities to electric eel AChE were tested because oximes can inhibit free AChE, and the highest AChE activity (95%, 92%, and 90%) was observed at 1?μM concentrations of the oximes (5a, 5b, and 5c, respectively). Based on their inhibitory affinities towards free AChE, 1?μM concentrations of the oxime derivatives (5) were used to examine reactivation of paraoxon-inhibited AChE. Reactivation ability increased as the carbon linker chains lengthened (n?=?2–5), and 5c and 5d showed remarkable reactivation ability (41%) compared to that of 2-PAM (16%) and HI-6 (4%) against paraoxon-inhibited electric eel AChE at 1?μM concentrations. Molecular docking simulation showed that the most stable binding free energy was observed in 5c at 73.79?kcal?mol^?1, and the binding mode of 5c is acceptable for the oxygen atom of oximate to attack the phosphorus atom of paraoxon and reactivate paraoxon-inhibited eel AChE model structure.     

A comparison of the reactivating and therapeutic efficacy of newly developed bispyridinium oximes (K250, K251) with commonly used oximes against tabun in rats and mice

The potency of newly developed bispyridinium compounds (K250, K251) in reactivating tabun-inhibited acetylcholinesterase and reducing tabun-induced lethal toxic effects was compared with currently available oximes (obidoxime, trimedoxime, the oxime HI-6) using in vivo methods. Studies determined percentage of reactivation of tabun-inhibited blood and tissue AChE in poisoned rats and showed that the reactivating efficacy of both newly developed oximes is comparable with the oxime HI-6 but it is significantly lower than the reactivating effects of obidoxime and trimedoxime, especially in diaphragm and brain. Both newly developed oximes were also found to be able to slightly reduce lethal toxic effects in tabun-poisoned mice. Their therapeutic efficacy is higher than the potency of the oxime HI-6 but it is lower than the therapeutic effects of trimedoxime and obidoxime. Thus, the reactivating and therapeutic potency of both newly developed oximes (K250, K251) does not prevail over the effectiveness of currently available oximes and, therefore, they are not suitable for their replacement for the treatment of acute tabun poisoning.     

Potency of new structurally different oximes to reactivate cyclosarin-inhibited human brain acetylcholinesterases

Antidotes currently used for organophosphorus pesticide and nerve agent intoxications consist of anticholinergics (atropine mainly) and acetylcholinesterase (AChE, EC 3.1.1.7) reactivators called oximes. Owing to the wide-spread of these toxic compounds worldwide, development of antidotes in the case of first aid is needed. To select the most promising AChE reactivators is a very time consuming process, which is necessary before approval of these compounds to be used as human antidotes. Because of ethical reasons, many developing experiments have been conducted on laboratory animals. However, these results often could not be transferred directly to human. Here, we have tested five newly developed AChE reactivators--K027, K033, K048, K074 and K075, which showed promising reactivation activity on rodents, as reactivators of inhibited human brain cholinesterases. For this purpose, cyclosarin was used as member of the nerve agent family. Oxime HI-6 and pralidoxime were used as AChE reactivator standards. Two AChE reactivators, K027 and K033, achieved comparable reactivation potency as HI-6. Moreover, oxime K033 reached its maximal reactivation potency at the lowest concentration which could be attained in humans.     

Morpholine-based chalcones as dual-acting monoamine oxidase-B and acetylcholinesterase inhibitors: synthesis and biochemical investigations

Nine compounds (MO1–MO9) containing the morpholine moiety were assessed for their inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE). Most of the compounds potently inhibited MAO-B; MO1 most potently inhibited with an IC₅₀ value of 0.030 µM, followed by MO7 (0.25 µM). MO5 most potently inhibited AChE (IC₅₀ = 6.1 µM), followed by MO9 (IC₅₀ = 12.01 µM) and MO7 most potently inhibited MAO-A (IC₅₀ = 7.1 µM). MO1 was a reversible mixed-type inhibitor of MAO-B (K_i = 0.018 µM); MO5 reversibly competitively inhibited AChE (K_i = 2.52 µM); and MO9 reversibly noncompetitively inhibited AChE (K_i = 7.04 µM). MO1, MO5 and MO9 crossed the blood–brain barrier, and were non-toxic to normal VERO cells. These results show that MO1 is a selective inhibitor of MAO-B and that MO5 is a dual-acting inhibitor of AChE and MAO-B, and that both should be considered candidates for the treatment of Alzheimer’s disease.     

Design,Synthesis, and Biological Evaluation of Novel Indanone Derivatives as Cholinesterase Inhibitors for Potential Use in Alzheimer's Disease

Indanone derivatives containing meta/para-substituted aminopropoxy benzyl/benzylidene moieties were designed based on the structures of donepezil and ebselen analogs as the cholinesterase inhibitors. The designed compounds were synthesized and their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities were measured. Inhibitory potencies (IC₅₀ values) for the synthesized compounds ranged from 0.12 to 11.92 μM and 0.04 to 24.36 μM against AChE and BChE, respectively. Compound 5 c showed the highest AChE inhibitory potency with IC₅₀ value of 0.12 μM, whereas the highest BChE inhibition was achieved by structure 7 b (IC₅₀=0.04 μM). Structure-activity relationship (SAR) analysis revealed that there is no significant difference between meta and para-substituted derivatives in AChE and BChE inhibition. However, the most potent AChE inhibitor 5 c belongs to meta-substituted compounds, while the most active BChE inhibitor is para-substituted derivative 7 b . The order of enzyme inhibition potency based on the substituted amine group is dimethyl amine>piperidine>morpholine. Compounds containing C=C linkage are more potent AChE inhibitors than the corresponding saturated structures. Molecular docking studies indicated that 5 c interacts with AChE in a very similar way to that observed experimentally for donepezil. The introduced indanone-aminopropoxy benzylidenes could be used in drug-discovery against Alzheimer's disease.     

A comparison of the therapeutic and reactivating efficacy of newly developed bispyridinium compounds (K206, K269) with currently available oximes against tabun in rats and mice

The potency of newly developed bispyridinium compounds (K206, K269) in reactivating tabun-inhibited acetylcholinesterase and eliminating tabun-induced lethal toxic effects was compared with commonly used oximes (obidoxime, trimedoxime, the oxime HI-6) using in vivo methods. Studies which determined percentage of reactivation of tabun-inhibited blood and tissue AChE in poisoned rats showed that the reactivating efficacy of both newly developed oximes is comparable with obidoxime and trimedoxime in blood but lower than the reactivating potency of trimedoxime and obidoxime in the diaphragm and brain. Nevertheless, the differences in reactivating efficacy of obidoxime, trimedoxime and K206 was not significant while the potency of K269 to reactivate tabun-inhibited acetylcholinesterase was significantly lower. Both newly developed oximes were also found to be relatively efficacious in elimination of the lethal toxic effects in tabun-poisoned mice. Their therapeutic efficacy corresponds to the therapeutic potency of obidoxime. The oxime HI-6, relatively efficacious against soman, did not seem to be an adequately effective oxime in reactivation of tabun-inhibited AChE and to counteract lethal effects of tabun. Both newly developed oximes (K206, K269) are significantly more efficacious in reactivating tabun-inhibited AChE in rats and to eliminate lethal toxic effects of tabun in mice than the oxime HI-6 but their reactivating and therapeutic potency does not prevail over the effectiveness of currently available obidoxime and trimedoxime and, therefore, they are not suitable for their replacement of commonly used oximes for the treatment of acute tabun poisoning.     

Alkynyl and β-ketophosphonates: Selective and potent butyrylcholinesterase inhibitors

A series of thirty-three alkynyl and β-ketophosphonates were evaluated for their in vitro acetyl- and butyryl-cholinesterase (AChE and BChE) inhibitory activities using Ellman’s spectrophotometric method. None of the examined compounds inhibited AChE activity at tested concentrations while twenty-nine of them showed significant and selective inhibition of BChE with IC₅₀ values between 38.60 µM and 0.04 µM. In addition, structure-activity relationships were discussed. The most effective inhibitors were the dibutyl o-methoxyphenyl alkynylphosphonate 3dc and dibutyl o-methoxyphenyl β-ketophosphonate 4dc. Activities of most potent compounds were also compared with a commercial organophosphorus compound. These results could inspire the design of new inhibitors with stronger activity against BChE.