Human AChE Research Articles

Three N-Glycosylation Sites of Human Acetylcholinesterase Shares Similar Glycan Composition.

Acetylcholinesterase (AChE; EC 3.1.1.7) is a glycoprotein possessing three conserved N-linked glycosylation sites in mammalian species, locating at 296, 381, and 495 residues of the human sequence. Several lines of evidence demonstrated that N-glycosylation of AChE affected the enzymatic activity, as well as its biosynthesis. In order to determine the role of three N-glycosylation sites in AChE activity and glycan composition, the site-directed mutagenesis of N-glycosylation sites in wild-type human AChE(T) sequence was employed to generate the single-site mutants (i.e., AChE(T) (N296Q), AChET (N381Q), and AChE(T) (N495Q)) and all site mutant (i.e., AChE(T) (3N→3Q)). The mutation did not affect AChE protein expression in the transfected cells. The mutants, AChE(T) (3N→3Q) and AChE(T) (N381Q), showed very minimal enzymatic activity, while the other mutants showed reduced activity. By binding to lectins, Con A, and SNA, the glycosylation profile was revealed in those mutated AChE. The binding affinity with lectins showed no significant difference between various N-glycosylation mutants, which suggested that similar glycan composition should be resulted from different N-glycosylation sites. Although the three glycosylation sites within AChE sequence have different extent in affecting the enzymatic activity, their glycan compositions are very similar.

Synthesis, biological evaluation and molecular modeling of new tetrahydroacridine derivatives as potential multifunctional agents for the treatment of Alzheimer’s disease

A novel series of 9-amino-1,2,3,4-tetrahydroacridine derivatives with 4-dimethylaminobenzoic acid moiety was synthesized and tested towards inhibition of cholinesterases and amyloid β aggregation. Target compounds were designed as dual binding site cholinesterase inhibitors able to bind to both the catalytic and the peripheral site of the enzyme and therefore potentially endowed with other properties. The obtained derivatives were very potent inhibitors of both cholinesterases (EeAChE, EqBChE) with IC50 values ranging from sub-nanomolar to nanomolar range, and the inhibitory potency of the most promising agents was higher than that of the reference drugs (rivastigmine and tacrine). The kinetic studies of the most active compound 3a revealed competitive type of AChE inhibition. Moreover, all target compounds were more potent inhibitors of human AChE than tacrine with the most active compound 3b (IC50=19nM). Compound 3a was also tested and displayed inhibitory potency against AChE-induced Aβ 1–42 aggregation (80.6% and 91.3% at 50μM and 100μM screening concentration, respectively). Moreover, cytotoxicity assay performed on A549 cells did not indicate toxicity of this agent. Compound 3a is a promising candidate for further development of novel multi-functional agents in the therapy of AD.

Preparation of 7‐Methoxy Tacrine Dimer Analogs and Their In vitro/In silico Evaluation as Potential Cholinesterase Inhibitors

Novel types of symmetric bis‐7‐methoxytacrines connected by oligoethyleneoxy chains 3–5 and nonsymmetric monomeric 7‐methoxytacrines containing hydroxyl‐terminated oligoethyleneoxy chains 6–8 were prepared, and their in vitro/in silico effects on human recombinant AChE (hAChE) and human plasmatic butyrylcholinesterase (hBChE) were compared, with 7‐MEOTA (2) as the standard compound. The symmetric bis‐7‐MEOTA derivatives 3–5 showed hAChE inhibition similar to that of 2. On the other hand, their effects on hBChE revealed an increasing inhibition trend when the oligoethyleneoxy units between the two 7‐MEOTA moieties became longer. Accordingly, compounds 4 and 5 showed better selectivity towards hBChE. The most effective in the inhibition hAChE and hBChE was compound 8 with the longest oligoethyleneglycol chain, whereas compounds 6 and 7 resulted in similar IC50 values. A molecular modeling study using substrates 5 and 8 showed a possible binding conformation and protein–ligand interaction between the substrates and AChE/BChE.

Catalytic Soman Scavenging by the Y337A/F338A Acetylcholinesterase Mutant Assisted with Novel Site-Directed Aldoximes.

Exposure to the nerve agent soman is difficult to treat due to the rapid dealkylation of the soman-acetylcholinesterase (AChE) conjugate known as aging. Oxime antidotes commonly used to reactivate organophosphate inhibited AChE are ineffective against soman, while the efficacy of the recommended nerve agent bioscavenger butyrylcholinesterase is limited by strictly stoichiometric scavenging. To overcome this limitation, we tested ex vivo, in human blood, and in vivo, in soman exposed mice, the capacity of aging-resistant human AChE mutant Y337A/F338A in combination with oxime HI-6 to act as a catalytic bioscavenger of soman. HI-6 was previously shown in vitro to efficiently reactivate this mutant upon soman, as well as VX, cyclosarin, sarin, and paraoxon, inhibition. We here demonstrate that ex vivo, in whole human blood, 1 μM soman was detoxified within 30 min when supplemented with 0.5 μM Y337A/F338A AChE and 100 μM HI-6. This combination was further tested in vivo. Catalytic scavenging of soman in mice improved the therapeutic outcome and resulted in the delayed onset of toxicity symptoms. Furthermore, in a preliminary in vitro screen we identified an even more efficacious oxime than HI-6, in a series of 42 pyridinium aldoximes, and 5 imidazole 2-aldoxime N-propylpyridinium derivatives. One of the later imidazole aldoximes, RS-170B, was a 2-3-fold more effective reactivator of Y337A/F338A AChE than HI-6 due to the smaller imidazole ring, as indicated by computational molecular models, that affords a more productive angle of nucleophilic attack.

Carbamate and pyrethroid resistance in the akron strain of Anopheles gambiae

Insecticide resistance in the malaria vector, Anopheles gambiae, is a serious problem, epitomized by the multi-resistant Akron strain, originally isolated in the country of Benin. Here we report resistance in this strain to pyrethroids and DDT (13-fold to 35-fold compared to the susceptible G3 strain), but surprisingly little resistance to etofenprox, a compound sometimes described as a “pseudo-pyrethroid.” There was also strong resistance to topically-applied commercial carbamates (45-fold to 81-fold), except for the oximes aldicarb and methomyl. Biochemical assays showed enhanced cytochrome P450 monooxygenase and carboxylesterase activity, but not that of glutathione-S-transferase. A series of substituted α,α,α,-trifluoroacetophenone oxime methylcarbamates were evaluated for enzyme inhibition potency and toxicity against G3 and Akron mosquitoes. The compound bearing an unsubstituted phenyl ring showed the greatest toxicity to mosquitoes of both strains. Low cross resistance in Akron was retained by all analogs in the series. Kinetic analysis of acetylcholinesterase activity and its inhibition by insecticides in the G3 strain showed inactivation rate constants greater than that of propoxur, and against Akron enzyme inactivation rate constants similar to that of aldicarb. However, inactivation rate constants against recombinant human AChE were essentially identical to that of the G3 strain. Thus, the acetophenone oxime carbamates described here, though potent insecticides that control resistant Akron mosquitoes, require further structural modification to attain acceptable selectivity and human safety.

AVCRI104P3, a novel multitarget compound with cognition-enhancing and anxiolytic activities: Studies in cognitively poor middle-aged mice

The present work describes, for the first time, the in vivo effects of the multitarget compound AVCRI104P3, a new anticholinesterasic drug with potent inhibitory effects on human AChE, human BuChE and BACE-1 activities as well as on the AChE-induced and self-induced Aβ aggregation. We characterized the behavioral effects of chronic treatment with AVCRI104P3 (0.6μmolkg−1, i.p., 21 days) in a sample of middle aged (12-month-old) male 129/Sv×C57BL/6 mice with poor cognitive performance, as shown by the slow acquisition curves of saline-treated animals. Besides, a comparative assessment of cognitive and non-cognitive actions was done using its in vitro equipotent doses of huprine X (0.12μmolkg−1), a huperzine A-tacrine hybrid. The screening assessed locomotor activity, anxiety-like behaviors, cognitive function and side effects. The results on the ‘acquisition’ of spatial learning and memory show that AVCRI104P3 exerted pro-cognitive effects improving both short- and long-term processes, resulting in a fast and efficient acquisition of the place task in the Morris water maze. On the other hand, a removal test and a perceptual visual learning task indicated that both AChEIs improved short-term ‘memory’ as compared to saline treated mice. Both drugs elicited the same response in the corner test, but only AVCRI104P3 exhibited anxiolytic-like actions in the dark/light box test. These cognitive-enhancement and anxiolytic-like effects demostrated herein using a sample of middle-aged animals and the lack of adverse effects, strongly encourage further studies on AVCRI104P3 as a promising multitarget therapeutic agent for the treatment of cholinergic dysfunction underlying natural aging and/or dementias.

7-MEOTA–donepezil like compounds as cholinesterase inhibitors: Synthesis, pharmacological evaluation, molecular modeling and QSAR studies

A novel series of 7-methoxytacrine (7-MEOTA)–donepezil like compounds was synthesized and tested for their ability to inhibit electric eel acetylcholinesterase (EeAChE), human recombinant AChE (hAChE), equine serum butyrylcholinesterase (eqBChE) and human plasmatic BChE (hBChE). New hybrids consist of a 7-MEOTA unit, representing less toxic tacrine (THA) derivative, connected with analogues of N-benzylpiperazine moieties mimicking N-benzylpiperidine fragment from donepezil. 7-MEOTA–donepezil like compounds exerted mostly non-selective profile in inhibiting cholinesterases of different origin with IC50 ranging from micromolar to sub-micromolar concentration scale. Kinetic analysis confirmed mixed-type inhibition presuming that these inhibitors are capable to simultaneously bind peripheral anionic site (PAS) as well as catalytic anionic site (CAS) of AChE. Molecular modeling studies and QSAR studies were performed to rationalize studies from in vitro. Overall, 7-MEOTA–donepezil like derivatives can be considered as interesting candidates for Alzheimer's disease treatment.

Inhibitor profile of bis(n)-tacrines and N-methylcarbamates on acetylcholinesterase from Rhipicephalus (Boophilus) microplus and Phlebotomus papatasi

The cattle tick, Rhipicephalus (Boophilus) microplus (Bm), and the sand fly, Phlebotomus papatasi (Pp), are disease vectors to cattle and humans, respectively. The purpose of this study was to characterize the inhibitor profile of acetylcholinesterases from Bm (BmAChE1) and Pp (PpAChE) compared to human and bovine AChE, in order to identify divergent pharmacology that might lead to selective inhibitors. Results indicate that BmAChE has low sensitivity (IC50=200μM) toward tacrine, a monovalent catalytic site inhibitor with sub micromolar blocking potency in all previous species tested. Similarly, a series of bis(n)-tacrine dimer series, bivalent inhibitors and peripheral site AChE inhibitors possess poor potency toward BmAChE. Molecular homology models suggest the rBmAChE enzyme possesses a W384F orthologous substitution near the catalytic site, where the larger tryptophan side chain obstructs the access of larger ligands to the active site, but functional analysis of this mutation suggests it only partially explains the low sensitivity to tacrine. In addition, BmAChE1 and PpAChE have low nanomolar sensitivity to some experimental carbamate anticholinesterases originally designed for control of the malaria mosquito, Anopheles gambiae. One experimental compound, 2-((2-ethylbutyl)thio)phenyl methylcarbamate, possesses >300-fold selectivity for BmAChE1 and PpAChE over human AChE, and a mouse oral LD50 of >1500mg/kg, thus providing an excellent new lead for vector control.

AhR-Mediated Effects of Dioxin on Neuronal Acetylcholinesterase Expression in Vitro

Background: Deficits in cognitive functioning have been reported in humans exposed to dioxins and dioxin-like compounds. Evidence suggests that dioxins induce cholinergic dysfunction mediated by hypothyroidism. However, little is known about direct effects of dioxins on the cholinergic system.Objectives: We investigated the action of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on acetylcholinesterase (AChE), a key enzyme in cholinergic neurotransmission.Methods: We used SK-N-SH human-derived neuronal cells to evaluate the effect of dioxin exposure on AChE.Results: We consistently found a significant decrease in enzymatic activity of AChE in cultured neurons treated with TCDD. We also found that, unlike organophosphate pesticides that directly act on the catalytic center of AChE, the suppressive effect of dioxin was through transcriptional regulation. The addition of CH223191, an inhibitor of the aryl hydrocarbon receptor (AhR)-dependent pathway, counteracted the TCDD-induced suppression of AChE, suggesting involvement of the AhR-dependent pathway. The existence of putative dioxin-responsive element (DRE) consensus sequences in the human ACHE promoter region further supported this hypothesis. Consistent with the absence of DRE elements in mouse or rat ACHE promoter regions, suppression of AChE by TCDD did not occur in rat neuronal cells, indicating a potential species-specific effect.Conclusions: In SK-N-SH cells, dioxin suppressed the activity of neuronal AChE via AhR-mediated transcriptional down-regulation. This is the first study to report direct interference by dioxin with the cholinergic neurotransmission system.

2-Arylbenzofuran-based molecules as multipotent Alzheimer's disease modifying agents

The complex etiology of Alzheimer's disease prompts scientists to develop multi-target strategies to combat causes and symptoms. In line with this modern paradigm and as a follow-up to our previous studies, we designed and synthesized a focused collection of new 2-arylbenzofurans and evaluated their biological properties towards specific targets involved in AD, namely human AChE and human BuChE, and Aβ fibril formation. Selected compounds were also tested for their ability to inhibit Aβ neurotoxicity in terms of neuronal viability loss, and to prevent Aβ peptide-binding to cell membrane and intracellular reactive oxygen species (ROS) formation. The different modifications introduced in the structure of our lead compound led to an increase in activity towards one or more of the selected targets: the anticholinesterase activity of some compounds was found to be significantly higher than previously obtained related molecules, and the compounds also proved to possess Aβ anti-aggregating properties and neuroprotective effects. The most interesting multi-target compounds were 18, and 1. Interestingly, 1 also showed good selectivity and moderate affinity for CB1 receptor, opening new perspectives in the field of research on AD, since cannabinoid ligands have been widely reported to have neuroprotective properties.

Design, synthesis, and bioevaluation of benzamides: Novel acetylcholinesterase inhibitors with multi-functions on butylcholinesterase, Aβ aggregation, and β-secretase

Alzheimer’s disease (AD) is a multifactorial syndrome with several target proteins contributing to its etiology. In this study, we conducted a structure-based design and successfully produced a series of new multi-site AChE inhibitors with a novel framework. Compound 2e, characterized by a central benzamide moiety linked to an isoquinoline at one side and acetophenone at the other, was the most potent candidate with Ki of 6.47nM against human AChE. Particularly, it showed simultaneous inhibitory effects against BChE, Aβ aggregation, and β-secretase. We therefore conclude that compound 2e is a very promising multi-function lead for the treatment of AD.

Screening of new huprines—Inhibitors of acetylcholinesterases by electrospray ionization ion trap mass spectrometry

Acetylcholinesterase inhibitors (AChEI) are one of the drugs families validated for clinical use in the treatment of Alzheimer's disease (AD). For this reason, finding new more potent and more selective AChEIs is always of interest. Since 1961, the inhibitory activity of AChEI is evaluated through the Ellman's method. Herein, we reported a MS-based evaluation of potential new AChEI with the determination of their inhibitory activity (IC(50) and K(I)). Compared to the Ellman's method, that uses the substrate analog acetylthiocholine, the electrospray ionization ion trap mass spectrometry (ESI-IT-MS) consists in monitoring the conversion ratio of a low concentration of the natural substrate - acetylcholine to choline. We present here the inhibition activity of huprine X and six of its derivates (bearing different functional groups at position 9) towards the recombinant human (rhAChE) and Electrophorus electricus acetylcholinesterase (EelAChE). Mechanisms of action of selected inhibitors were evaluated by means of Lineweaver-Burk plot analysis. The Michaelis-Menten constants (K(M)), inhibitory constants (K(I)) were examined as well as the IC(50) to allow classifying a series of huprine derivatives by inhibition potency by a comparison with a reference (huprine X). Our results demonstrate that these drugs are very potent AChE inhibitors, especially (±)-huprine 6 with an inhibitory activity on recombinant human AChE (rhAChE) in the picomolar range. This study reveals the interest of huprine compounds in the treatment of AD.

Selective Cholinesterase Inhibitors from Buxus sempervirens L. and their Molecular Docking Studies

In this work, two alkaloids namely (+)-buxabenzamidienine (1) and (+)-buxamidine (2) were isolated from Buxus sempervirens, using bioassay-guided fractionation and isolation method. Their acetyl- (AChE) and butyrylcholinesterase (BChE) inhibitory activities were studied and the compounds were found to be quite selective inhibitors of AChE. IC50 values of compound 1 for electric eel AChE and horse BChE were 0.787 and 7.68 mM, respectively; while the corresponding IC50 of compound 2 were 1.70 and 549.98 mM, respectively. Theoretical (quantum mechanical, homology modelling and docking) calculations were performed in order to explain their interactions with different AChE (electric eel and human) and BChE (horse and human). The x-ray crystal structures of electric eel AChE, human AChE, human BChE and a model of horse BChE constructed by homology with human BChE were used for docking of compounds 1 and 2. Density functional theory (DFT) calculations of the compounds were performed at the B3LYP/6- 31G** level using the program Spartan™, and their HOMO and LUMO energy levels were calculated. Docking studies exhibited that compound 1 interacts with the acyl-binding pocket of the active site gorge of huAChE, and including several other hydrophobic interactions.

ChemInform Abstract: First Efficient Uncharged Reactivators for the Dephosphylation of Poisoned Human Acetylcholinesterase.

AbstractThe title compounds (I) are extremely promising uncharged reactivators for poisoned human AChE with a superior or similar in vitro ability to reactivate the enzyme as that of HI‐6, obidoxime, TMB‐4 and HL‐7.

A facile and single pot strategy for the synthesis of novel naphthyridine derivatives under microwave irradiation conditions using ZnCl2 as catalyst, evaluation of AChE inhibitory activity, and molecular modeling studies

A series of novel naphthyridine derivatives 3 and 4 was prepared from substituted pyridine 2 and ketones using ZnCl2 as catalyst under microwave irradiation conditions. All the compounds were evaluated for AChE inhibitory activity and promising compounds 3d, 3e, 4b, and 4g was identified. Representative compounds 3d and 3e were found to show insignificant THLE-2 liver cell viability/toxicity. The binding mode between X-ray crystal structure of human AChE and compounds was studied using molecular docking method and fitness scores were found to be in good correlation with the activity data.

The characterization of Lucilia cuprina acetylcholinesterase as a drug target, and the identification of novel inhibitors by high throughput screening

Acetylcholinesterase (AChE, EC3.1.1.7.) is the molecular target for the carbamate and organophosphate pesticides that are used to combat parasitic arthropods. In this paper we report the functional heterologous expression of AChE from Lucilia cuprina (the sheep blowfly) in HEK293 cells. We show that the expressed enzyme is cell-surface-exposed and possesses a glycosyl-phosphatidylinositol membrane anchor. The substrates acetyl-, propionyl- and butyrylthiocholine (AcTC, PropTC, ButTC), and also 11 further thiocholine and homo-thiocholine derivatives were chemically synthesized to evaluate and compare their substrate properties in L. cuprina AChE and recombinant human AChE. The Michaelis–Menten constants KM for AcTC, PropTC and ButTC were found to be 3–7-fold lower for the L. cuprina AChE than for the human AChE. Additionally, 2-methoxyacetyl-thiocholine and isobutyryl-thiocholine were better substrates for the insect enzyme than for the human AChE. The AcTC, PropTC and ButTC specificities and the Michaelis–Menten constants for recombinant L. cuprina AChE were similar to those determined for AChE extracted from L. cuprina heads, which are a particularly rich source of this enzyme. The median inhibition concentrations (IC50 values) were determined for 21 organophosphates, 23 carbamates and also 9 known non-covalent AChE inhibitors. Interestingly, 11 compounds were 100- to >4000-fold more active on the insect enzyme than on the human enzyme. The substrate and inhibitor selectivity data collectively indicate that there are structural differences between L. cuprina and human AChE in or near the active sites, suggesting that it may be possible to identify novel, specific L. cuprina AChE inhibitors. To this end, a high throughput screen with 107,893 compounds was performed on the L. cuprina head AChE. This led to the identification of 195 non-carbamate, non-organophosphate inhibitors with IC50 values below 10μM. Analysis of the most potent hit compounds identified 19 previously unknown inhibitors with IC50 values below 200nM, which were up to 335-fold more potent on the L. cuprina enzyme than on the human AChE. Some of these compounds may serve as leads for lead optimization programs to generate fly-specific pesticides.

In vitro kinetic interactions of pyridostigmine, physostigmine and soman with erythrocyte and muscle acetylcholinesterase from different species

The low effectiveness of atropine and oxime treatment in soman poisoning may be enhanced by carbamates pre-treatment. For ethical reasons medical countermeasures can only be tested in animal models despite the fact of substantial species differences. With this kinetic in vitro study the interactions between pyridostigmine, physostigmine and soman with human, Rhesus monkey, swine and guinea pig erythrocyte AChE were investigated. In addition, the effect of the carbamates on the residual activity and enzyme recovery after soman inhibition was examined with erythrocyte and intercostal muscle AChE from these species with a dynamic in vitro model with real-time determination of AChE activity. Only small to moderate species differences of the inhibition and decarbamylation kinetics were recorded. It was possible to show that with erythrocyte and muscle AChE a similar level of protection by carbamates and reactivation after discontinuation of the carbamates and soman could be observed. Thus, these data indicate that carbamate pre-treatment is expected to protect a critical level of muscle AChE and confirm the presumption that erythrocyte AChE may serve as a surrogate for synaptic AChE. Hence, these and previous data fortify the notion that erythrocyte AChE is a proper tool for in vitro kinetic studies as well as for therapeutic monitoring in experimental and clinical studies.

Preparation and in vitro screening of symmetrical bis-isoquinolinium cholinesterase inhibitors bearing various connecting linkage – Implications for early Myasthenia gravis treatment

Inhibitors of acetylcholinesterase are compounds widely used in the treatment of various diseases, such as Alzheimer’s disease, glaucoma and Myasthenia gravis (MG). Compounds used in the therapy of MG posses a positive charge in the molecule to ensure peripheral effect of action and minimal blood–brain barrier penetration. The most prescribed carbamate inhibitors are however known for many severe side effects related to the carbamylation of AChE. This paper describes preparation and in vitro evaluation of 20 newly prepared bis-isoquinolinium inhibitors of potential concern for MG. The newly prepared compounds were evaluated in vitro on human recombinant AChE and human plasmatic butyrylcholinesterase (BChE). Their inhibitory ability was expressed as IC 50 and compared to chosen standards ambenonium dichloride, edrophonium chloride, BW284c51 and ethopropazine hydrochloride. Three novel compounds presented promising inhibition (in nM range) of both enzymes in vitro better or similar to edrophonium and BW284c51, but worse to ambenonium. The novel inhibitors did not present higher selectivity toward AChE or BChE. The kinetic assay confirmed non-competitive inhibition of hAChE by two selected promising novel compounds. Two newly prepared compounds were also chosen for docking studies that confirmed apparent π–π or π–cationic interactions aside the cholinesterases catalytic sites. The SAR findings were discussed.

In vitro evaluation of bis-pyridinium oximes bearing methoxy alkane linker as reactivators of sarin inhibited human acetylcholinesterase

A series of bis-pyridinium oximes connected by methoxy alkane linkers were synthesized and their in vitro reactivation efficacy was evaluated against sarin-inhibited human AChE, and data were compared with 2-PAM and obidoxime. Among the synthesized compounds, 1,2-dimethoxy ethylene bis-[4,4′-(hydroxyiminomethyl) pyridinium] dichloride ( 4P-2) and 1,2-dimethoxy ethylene bis-[3,3′-(hydroxyiminomethyl) pyridinium] dichloride ( 3P-2) were found to be the most potent reactivators of human AChE inhibited by nerve agent sarin. The oximes 4P-2 and 3P-2 exhibited 41% and 36% regeneration of sarin-inhibited AChE, respectively, whereas 2-PAM showed 32% regeneration. The higher reactivation efficacy of the oximes was attributed to their acid dissociation constants (p K a). The p K a values of all the oximes were determined by UV–vis spectrophotometric method and correlated with their observed reactivation potential. Overall, the study reveals that the oxime 4P-2 may have therapeutic potential in the reactivation of human AChE inhibited by sarin.

Chromatographic preparation and kinetic analysis of interactions between tabun enantiomers and acetylcholinesterase

The easy accessibility to highly toxic OP (organophosphorus)-type chemical warfare agents (nerve agents) underlines the necessity for an effective medical treatment. Acute OP toxicity is primarily caused by inhibition of acetylcholinesterase (AChE, EC 3.1.1.7). Reactivators (oximes) of inhibited AChE are a mainstay of treatment. However, the commercially available compounds, obidoxime and pralidoxime, are considered rather ineffective against various nerve agents, including tabun. OP-type chemical warfare agents include an asymmetrical P-atom and consist of at least two stereoisomers. Previous studies with the nerve agents sarin and soman showed marked differences between (−)- and (+)-P isomers regarding AChE inhibition and stability in biological matrices. Hence, stereoselectivity is a key parameter for the development of optimized treatment. In the present study, the tabun enantiomers were isolated by semi-preparative liquid-chromatography (LC) with offline analysis by GC–PCI-MS and final characterization of optical purity (99.98% (−)-tabun and 99.83% (+)-tabun) and specific optical rotation. The inhibition and reactivation kinetics of the tabun enantiomers were determined with human and swine AChE and the aging kinetics with human AChE. The results show a large difference in the inhibitory potency between (−)- and (+)-tabun. The determination of reactivation and aging kinetics indicates that both reactions are at least in part determined by the residual (−)-tabun contamination (0.17%) of the (+)-tabun preparation. These data provide further insight into the kinetic interactions between tabun enantiomers and AChE and may contribute to the development of more effective treatment options.