Introduction

Alzheimer’s disease (AD) is the most common form of dementia, constituting up to 80% of all cases (Duthey 2013; Korolev 2014). It is expected to affect around 66 million people by 2030. Today, the prevalence of AD is reported to be about 3.5% of the world population (>20 million people), with some authors estimating 6% (~35 million people). This disease mostly afflicts the elderly, including 10% of people over 65 and nearly 50% of those over 85. Since life expectancy is on the rise, prevalence is expected to increase (Musiał et al. 2007; Aliabadi et al. 2013; Anand and Singh 2013; Guzior et al. 2014). In 2010, 58% of all AD patients had low or middle incomes and this is projected to reach 63% in 2030 (Prince et al. 2013).

AD is characterized by a progressive degeneration of the brain that leads to loss of memory, disorientation, anxiety, delusion, depression, insomnia, wandering, learning impairment, and deterioration of cognitive functions. Although the etiology of AD is not well understood, various factors contribute to the development of this disease, such as an increase in β-amyloid plaques, an accumulation of neurofibrillary tangles, hyperphosphorylation of tau protein, chronic neuroinflammation, oxidative stress, inflammatory processes, dyshomeostasis of biometals, and decreased levels of acetylcholine caused by a depletion of the cholinergic system (Mandelkow and Mandelkow 1994; Grathwohl et al. 2009; Murphy and LeVine 2010; Iqbal et al. 2010; Heneka et al. 2015; Czarnecka et al. 2017).

All the manifestations of this disorder are linked to a reduction in acetylcholine levels in the brain, resulting from the degeneration of the cholinergic neurons (Ignasik et al. 2012) and the deposition of the β-amyloid peptide as plaque and neurofibrillary tangles in the brain (Lahiri et al. 2002; Wenk 2003; Musiał et al. 2007; Aliabadi et al. 2013; Anand and Singh 2013; Guzior et al. 2014). It is thought that these peptides and protein accumulations are toxic to neurons and contribute to their death, producing cerebral atrophy (Nwidu et al. 2017). Fourteen years ago, the degeneration of cholinergic nuclei was detected in the basal forebrain during the course of AD (Ibach and Haen 2004). Several theories now exist to explain the origin of AD, including the cholinergic theory, the β-amyloid theory (extracellular deposits of β-amyloid in brain parenchyma and neurofibrillary intracellular tangles, which is the most studied hypothesis), the tau hypothesis, and the inflammation theory (Kumar et al. 2015).

Since the 1970s, the stimulation of cholinergic neurotransmission has been the principal strategy of many researchers (Ozadali-Sari et al. 2017), mainly carried out by inhibiting acetylcholinesterase (AChE, EC 3.1.1.7), an enzyme that hydrolyzes the neurotransmitter acetylcholine at cholinergic synapses and thus terminates nerve transmission (Barnard 1974; Kamkwalala and Newhouse 2016; Li et al. 2017). Another non-specific cholinesterase enzyme, butyrylcholinesterase (BuChE), is also a target for treating AD. In the late phases of the disease, antagonizing NMDA forms part of this same strategy (Musiał et al. 2007; Bajda et al. 2013; Anand and Singh 2013; Guzior et al. 2014).

Currently, AChEIs are the only drugs approved by the FDA for the treatment of AD (Musiał et al. 2007). Of these drugs, the most widely used are tacrine, donepezil, rivastigmine, galantamine, and memantine (Musiał et al. 2007; Anand and Singh 2013; Guzior et al. 2014; Kumar et al. 2015). Others such as phenserine are currently in clinical trials (Lahiri et al. 2002; Ozadali-Sari et al. 2017). The most promising agents for AD treatment are dual-binding AChEIs (Ignasik et al. 2012). Diverse studies indicate that the inhibition of AChE in AD patients can improve cognitive function, delay the progression of mental deterioration, and reduce neuropsychiatric symptoms (Lahiri et al. 2002; Ozadali-Sari et al. 2017; Nwidu et al. 2017; Li et al. 2017). Certainly, AChEIs are still the best established treatment for mild to moderate AD, although they do not represent a cure.

Since the AChEIs currently on the market have adverse effects (Birks 2006), there are ongoing efforts to seek new drugs with greater potency and less toxicity. As demonstrated by different crystals, AChE is characterized by a deep gorge with the catalytic active site inside. This site is surrounded by numerous other ligand recognition sites, the nearest oxyanionic hole, an aromatic patch, an anionic site, and a peripheral anionic site (Dvir et al. 2010; Shazi 2012; Kiametis et al. 2017). The peripheral anionic site mediates the aggregation rate of β-amyloid. Hence, a moiety or molecule that binds to the latter site could possibly modify the physiopathology of AD (Gupta and Mohan 2014).

The catalytic site for Torpedo californica AChE has been described as having a gorge 20 Å deep and 5 Å wide. The most important part (the stearic site) is surrounded by three essential aminoacids, Ser200, His440, and Gly327, creating the catalytic triad. The anionic site is composed of Trp84, Tyr130, Phe330, and Phe331. The stabilizing transition complex is formed by Gly118, Gly119, and Ala201, while the peripheral anionic site consists of five aminoacids: Tyr70, Asp72, Tyr121, Trp279, and Tyr334 (Bajda et al. 2013).

Isoindolines and isoindolines-1,3-diones, potent pharmacophore groups found in natural and non-natural products, have shown anticonvulsant, anti-inflammatory, analgesic, anti-hypertensive, and antibacterial activity (Kukkola et al. 2001; Kim et al. 2007; Van Goethem et al. 2011; Çizmecioğlu et al. 2011; Davood et al. 2012; Shakir et al. 2012; Raveendra et al. 2014; Barrio et al. 2015; Achary et al. 2017). According to various research teams, isoindoline-1,3-diones are potent and novel inhibitors of AChE with two carbonyl groups of phthalimide that facilitate hydrogen bonds with the catalytic active site and the peripheral anionic site simultaneously. Consequently, this molecule can inhibit both the formation of β-amyloid fibrils and the hydrolytic activity of AChE on acetylcholine. The main interactions with AChE carried out by isoindolines-1,3-diones and their analogs are π–π and π–cation (Mohammadi-Farani et al. 2017). Additionally, isoindolines-1,3-diones are considered to provide neuroprotection (Mary et al. 1998; Zhao et al. 2009; Alipour et al. 2012; Mohammadi-Farani et al. 2013; Guzior et al. 2015; Hebda et al. 2016; Si et al. 2016).

Some researchers have examined the AChE inhibitory capacity of phthalimide derivatives, identifying inhibitory concentrations 50 (IC50) at a micromolar scale (16.42µM) (Mohammadi-Farani et al. 2013). Michalina et al. designed and tested a series of 2-(diethylaminoalkyl)-isoindoline-1,3-dione derivatives, establishing that they bind to the catalytic active site and the peripheral anionic site. The IC50 of the best compound ranged from 0.9 to 19.5µM (Ignasik et al. 2012). Bajda et al. (2013) evaluated different structures of AChEIs by performing fragment-based design, finding 2-(5-(2-fluorobenzylamino)pentyl)isoindoline-1,3-dione to be the most active compound, with an IC50 of 87 nm.

The in silico studies on the latter compounds revealed a CH–π interaction with Trp84, a π–cation interaction with Phe330, an H-bond with Tyr121, hydrophobic interactions in the middle of the active gorge with Phe290, Phe331, and Tyr334, π–π interactions with Trp279, and a CH–π with Tyr70 by the phthalimide moiety residues (Bajda et al. 2013). Others studies with phthalimide have shown that this kind of compound can interact by π–π stacking and CH–π interactions with aromatic amino acids at the anionic subsite (Phe330, Phe331, and Trp84), and/or with residues at the peripheral anionic site (Trp279, Tyr334) of AChE (Ignasik et al. 2012).

Due to the importance of measuring ACh levels, during the last few decades, many techniques have been elaborated to measure AChE activity in experiments. In 1955, Bonting and Featherstone presented their ultramicro assay of cholinesterase, which was an adaptation of the hydroxamic acid method for the determination of choline esters (Bonting and Featherstone 1956). The method is time-consuming and costly in materials. In 1961, Ellman et al. developed the colorimetric analysis of AChE activity, measuring the enzymatic activity based on the intensification of the color yellow produced by thiocholine upon reacting with the dithiobisnitrobenzoate ion (Ellman et al. 1961). Though sensitive, this method can generate errors if the compounds tested are α,β-unsaturated carbonyls or good electrophiles, because these compounds tend to react with the analytical substance.

For the present study, it was decided to improve the 1956 technique by Bonting and Featherstone because of its accuracy and easiness AChE catalytic activity detection. Hence, it was modified to make it inexpensive and straightforward. In a previous investigation based on this method, we crystallized and tested an isoindoline-1,3-dione as an AChEI (paper in peer review), finding good inhibitory activity (inhibitory constant Ki = 330–930 µM; p < 0.05). Therefore, new isoindolines and dioxoisoindolines with were herein evaluated in terms of their inhibition of AChE. Both sets of compounds were compared in order to elucidate how carbonyl groups influence the inhibition of the enzyme.

Materials and methods

Synthesis and characterization of 2,3-dihydro-1H-isoindoles and N-substituted phthalimide

Our previously reported synthetic methodology was followed without any modifications (Andrade-Jorge et al. 2017). In brief, reagents and solvents from Sigma-Aldrich were used as received. The reactions were carried out in a flask at the melting point of the starting material and agitated with a stirring bar for a few minutes in solventless conditions (green chemistry), and then the products were purified as described (Andrade-Jorge et al. 2017). The reactions were monitored by TLC (0.25 mm thick silica gel, 60 F254 plates) and the products were characterized by nuclear magnetic resonance (NMR) spectra, recorded on a Varian Mercury 300 spectrometer at 300MHz for 1H and 75MHz for 13C, with tetramethylsilane as internal reference.

Solutions

For the phosphate buffer (0.1 M, pH 8), 7.48 g of K2HPO4 were weighed and added to 430 mL of distilled water, while 0.916 g of KH2PO4 were mixed with 70 mL of distilled water. Then both solutions were combined to provide the buffer solution, which had a final volume of 500 mL and a pH of 8 (monitoring pH with a potentiometer). For the sodium hydroxide solution (4.2 M NaOH), 16.96 g NaOH were dissolved in distilled water to attain a final volume of 100 mL. For the hydroxylamine solution (2.4 M NH2OH), 16.84 g NH2OH·HCl were dissolved in distilled water to obtain a final volume of 100 mL. For the alkaline hydroxylamine solution, equal volumes of sodium hydroxide and hydroxylamine solution were mixed immediately before use. For the ferric chloride (FeCl3) solution, 20.31 g FeCl3·6H2O were slowly mixed (to avoid any damage) with an HCl solution (61.95%) to reach a final volume of 100 mL. For the stock acetylcholine solution, 50 mg ACh iodide were dissolved in 0.695 mL phosphate buffer to afford a solution of 256 mM. Subsequently, different dilutions were prepared for the kinetic experiment (Scheme 1a). For the stock AChE solution, 10 U/mL lyophilized powder of AChE from Electric electricus (EE-AChE, Sigma Chemical Co. C1682) were prepared from the original source, and the solutions were kept at −20 °C. The three synthesized compounds and neostigmine were prepared at concentrations of 2, 4, and 8 mM, with DMSO (<1%) or distilled water as the dissolution medium. The dilutions were stored at −20 °C.

Scheme 1
scheme 1

a Dilutions performed for ACh curve. b Representation of the procedure of the improved method in a 96-well microplate

Full size image

Docking

The ligands were modeled on GaussView 5.0.9 software and the protonation state was considered at physiological conditions (pH 7.4). Conformational analysis was performed on Gaussian 09 (Frisch et al. 2009) with a semi-empirical method (PM3). The rotating bonds, torsional degree of freedom, atomic partial charges, and non-polar H-bonds were assigned with AutoDock tools 1.5.4. (Morris et al. 2009). One of the crystal structures of AChE of Electrophorus electricus was downloaded from the Protein Data Bank (PDB code: 1C2O) (Bourne et al. 1999).

Docking conditions were programmed with AutoDock tools 1.5.4 and Raccoon (Forli et al. 2016), by utilizing a hybrid Lamarckian Genetic Algorithm (Morris et al. 1998), an initial population of 100 randomly placed individuals, Kollmann partial charges for all protein atoms, and Gasteiger charges for ligands. Subsequently, the grid parameter file was established, using a 60 × 60 × 60 Å gridbox with the coordinates X = 42.095, Y = 66.809, and Z = −81.47 and a mesh spacing of 0.375 Å. The calculations were run on AutoDock4 software in a Linux operative system (Fedora 22).

Finally, the lowest energy state, expressed as Gibbs free energy (∆G), was obtained for each compound. The dissociation constant (Kd), the –log(10) dissociation constant (pKd), the number of interactions, and the distance and type of binding were determined with the Visual Molecular Dynamics program (VMD v.1.8.6) (Humphrey et al. 1996).

Anticholinesterase activity assay

Dilutions of ACh were made to prepare different concentrations, which were mixed in an Analog Vortex Mixer (Thomas Scientific). Twenty μL of each solution (at 128, 96, 64, 48, 32, 16, 8, and 2mM) were placed in each well of a 96-well microplate, following the pattern described in Scheme 1b. The microplate was allowed to incubate for 20min at 37°C in a water bath (Felisa). Completing this period, the reaction was stopped with 40μL alkaline hydroxylamine solution and then 100μL of FeCl3 solution was added to each well and the optical density was read at 540nm in a microplate reader (Benchmark BIO-RAD), with a pre-mixed of 40 s. The standard curve of ACh was constructed with these values.

The same dilutions as well as incubation and reading procedures were employed to construct the standard curve for AChE, with 20μL of AChE in the starting mixture (utilized to make subsequent dilutions, see Scheme 1b). The standard and test compounds were used at 2, 4, and 8mM. The process for evaluating AChE activity was repeated, this time including 20μL of the test compounds before adding AChE. All experiments were performed in triplicate and data are expressed as the average of three values. The AChE activity/inhibition analysis was made with a Michaelis–Menten plot and non-linear regression to find the characteristic parameters. To compare the modified method with the original one, additional experiments adhered to the latter (Bonting and Featherstone 1956) and a curve was constructed for AChE activity as well as AChE inhibition elicited by neostigmine.

Statistical analysis

The data from the anticholinesterase activity assay are expressed as the mean ± 95% confidence intervals. Each treatment was compared to the control group (AChE+ACh). Non-linear regression analysis was carried out with 95% confidence intervals on GraphPad Prism statistical software with the enzyme kinetic module.

Results and discussion

Synthesis

IsoA, IsoB, and DioxoA were synthesized (Table 1 and Scheme 2). These are derived from isoindoline and dioxoisoindoline following our previously described above green chemistry technique (Andrade-Jorge et al. 2017) without modifications. Thus, the chemical characterization is in agreement with those reported in our previous report.

Table 1 Structure of the isoindolines and isoindoline-1,3-diones used presently as AChE inhibitors
Full size table
Scheme 2
scheme 2

Structure and route for the synthesis of isoindoline/isoindoline-1,3-dione (Andrade-Jorge et al. 2017)

Full size image

2-(2-Phenyletyl)-1,3-dihydroisoindoline hydrobromide (IsoA): It was obtained as a white solid, 90% yield; mp 165–166 °C; 1H NMR (DMSO-D6, 300 MHz) δ (PPM) 2.85 (t, H-11), 3.65 (t, H-10), 4.72 (dd, H-1,3), 7.36 (m, H-4,5,6,7,13,14,15,16,17); 13C NMR (CDCl3, 75 MHz) δ 58.4 (C-1,3), 123.5 (C-4,7), 127.4 (C-5,6), 137.9 (C-8,9), 55.4 (C-10), 33.5 (C-11), 134.9 (C-12), 129.2 (C-13,14,16,17), 127.5 (C-15). IR (ATR, cm−1) ύ: 3031 (C–H, Aromatic), 2908 (C–H, Aliphatic), 2546 (NH+), 1705 (C=O), 1600 (C=C), 1427 (CH2), 1391 (C–N). MS (m/z): 224.1447 (M+1).

2-(2-(3,4-Dimethoxyphenyl)etyl)-1,3-dihydroisoindoline hydrobromide (IsoB): It was obtained as a white solid, 80% yield; mp 197–198 °C; 1H NMR (DMSO-D6, 300 MHz) δ (PPM) 3.00 (t, H-11), 3.64 (t, H-10), 3.71 (s, H-18), 3.74 (s, H-19), 4.71 (s, H-1,3), 6.95 (m, H-13,16,17), 7.40 (m, H-4,5,6,7); 13C NMR (CDCl3, 75 MHz) δ 58.5 (C-1,3), 129.1 (C-4,7), 123.5 (C-5,6), 134.9 (C-8,9), 55.7 (C-10), 31.8 (C-11), 129.8 (C-12), 112.6 (C-13), 148.4 (C-14), 149.4 (C-15), 113.2 (C-16), 121.3 (C-17), 56.2 (C-18,19). IR (ATR, cm−1) ύ: 3063 (C–H, Aromatic), 2990 (C–H, Aliphatic), 2842 (O–CH3, Aliphatic), 2547 (NH+), 1600 (C=C), 1462 (CH2), 1453 (CH3), 1390 (C–N), 1228 (O–CH3). MS (m/z): 284.1624 (M+1).

2-(2-Phenyletyl) isoindolin-1,3-dione (DioxoA): It was obtained as a white solid, 85% yield; mp 130–131 °C; 1H NMR (CDCl3, 300 MHz) δ (PPM) 2.98 (t, H-11), 3.92 (t, H-10), 7.26 (m, H-13,14,15,16,17), 7.70 (m, H-5,6), 7.82 (m, H-4,7); 13C NMR (CDCl3, 75 MHz) δ 168.1 (C-1,3), 123.2 (C-4,7), 133.9 (C-5,6), 132.0 (C-8,9), 39.2 (C-10), 34.6 (C-11), 137.9 (C-12), 128.5 (C-13,17), 128.8 (C-14,16), 126.6 (C-15). IR (ATR, cm−1) ύ: 3031 (C–H, Aromatic), 2935 (C–H, Aliphatic), 1705 (C=O), 1600 (C=C), 1427 (CH2), 1391 (C–N). MS (m/z): 274.0752 (M+Na).

2-(2-(3,4-Dimethoxyphenyl)etyl) isoindolin-1,3-dione (DioxoB): It was obtained as a light yellow solid, 90% yield; mp 171–172 °C; 1H NMR (CDCl3, 300 MHz) δ (PPM) 2.93 (t, H-11), 3.90 (t, H-10), 3.80 (s, H-19), 3.83 (s, H-18), 6.78 (m, H-13,16,17), 7.70 (m, H-5,6), 7.82 (m, H-4,7); 13C NMR (CDCl3, 75 MHz) δ 168.2 (C-1,3), 123.19 (C-4,7), 132.0 (C-5,6), 130.4 (C-8,9), 39.3 (C-10), 34.0 (C-11), 133.9 (C-12), 111.1 (C-13), 148.7 (C-14), 147.6 (C-15), 111.8 (C-16), 120.8 (C-17), 55.7 (C-18,19). IR (ATR, cm−1) ύ: 3063 (C–H, Aromatic), 2943 (C–H, Aliphatic), 2842 (O–CH3, Aliphatic), 1705 (C=O), 1600 (C=C), 1466 (CH2), 1427 (CH3), 1394 (C–N), 1228 (O–CH3). MS (m/z): 334.0956 (M+Na).

Kinetic test validation

The inhibitory effects on AChE were assessed by modifying the ultramicro assay developed by Bonting and Featherstone in 1955. We achieved a more efficient and faster technique, obtaining up to 12 kinetic curves at the same time. After running assays with the original and modified methods, a standard curve was constructed for AChE activity as well as for the AChE inhibition elicited by the reference compound. The values of the Michaelis–Menten constant (Km) for the AChE curves showed no significant difference between the two methods (Table 2), nor did the Ki values of the two antagonist curves. Since the modified method did not affect the results, it could be used to estimate the kinetic parameters of the new compounds.

Table 2 Activity of AChE of Electrophorus electricus, alone and with neostigmine, was obtained with both methods (B&F and IM)
Full size table

Anticholinesterase activity assay

By employing the improved method, an assessment was made of acetylcholinesterase inhibition for three compounds: IsoA, IsoB, and DioxoA. Another compound (DioxoB) was considered, which had been evaluated in a previous work (paper in peer review). Consequently, the inhibition induced by two isoindolines and two dioxoisoindolines was compared (Table 2). The latter compounds are derivatives of two arylamines, the only difference being the addition of two carbonyls groups (Table 1). Dioxoisoindolines with different substituents in their structure are known to be fairly good inhibitors of AChE, due in part to their carbonyl groups in the pyrrolidine ring. This kind of moiety is important for recognition between the enzyme and inhibitors, forming H-bonds in the catalytic triad site.

It is thought that carbonyl groups are necessary in the molecule to achieve a good inhibitory effect. Despite not having carbonyl groups, nonetheless, the isoindolines inhibited AChE better than the isoindoline-1,3-diones (Table 2; Fig. 1). The comparison of the analog compounds IsoA and DioxoA revealed that the isoindoline afforded a 1.5-fold greater inhibition of the enzyme than the dioxoisoindoline. Regarding IsoB vs. DioxoB, the isoindoline derivative displayed a 5-fold greater inhibition than the corresponding dioxoisoindoline, likely due to the kind of interactions between the ligands and AChE. Although much research has examined the inhibitory effect of isoindolines-1,3-diones (as aforementioned), such is not the case with isoindolines. Therefore, one aim of the current contribution was to explore the latter molecules as a new kind of inhibitor.

Fig. 1
figure 1

Inhibitory effect of the test compounds on AChE of Electrophorus electricus: a IsoA; b IsoB; c DioxoA; and d neostigmine (the reference compound). Non-linear regression analysis was carried out with 95% confidence intervals

Full size image

Molecular docking

In silico experiments were performed to provide insights into the in vitro results. The competitive inhibitory activity of dioxoisoindolines allows for analysis by molecular docking, while the uncompetitive activity of isoindolines does not. Molecular docking was carried out on a 3D model of AChE to study the binding of well-known inhibitors (donepezil, galantamine, rivastigmine, or tacrine) and the dioxoisoindolines (Fig. 2). The ∆G is clearly exergonic for the two dioxoisoindolines and four reference compounds (Table 3), with very similar values for all these molecules. For the two dioxoisoindolines, the principal interactions and the main amino acid residues in AChE involved in such interactions are described (see Tables 4 and 5; Fig. 3).

Fig. 2
figure 2

Binding mode of the ligands with AChE of Electrophorus electricus, in the catalytic active site, peripheral anionic site, and aromatic patch (obtained by molecular docking): (A) Binding site of DioxoA, DioxoB, and donepezil in AChE; (A′) the dioxoisoindolines show a binding mode similar to donepezil; (B) the binding site of DioxoA, DioxoB, and rivastigmine in AChE; (B′) the dioxoisoindolines have a binding mode similar to rivastigmine

Full size image
Table 3 Gibbs free energy (ΔG), the dissociation constant (Kd), and –log (10) dissociation constant (pKd) for the interactions between the ligands and AChE of Electrophorus electricus
Full size table
Table 4 Amino acid residues involved in the interaction between AChE of Electrophorus electricus and the ligands: the isoindoline-1,3-diones and reference molecules
Full size table
Table 5 Binding distances between amino acid residues involved in the interaction and the ligands
Full size table
Fig. 3
figure 3

Binding mode and main amino acid residues in the catalytic active site, peripheral anionic site, and aromatic patch of AChE of Electrophorus electricus when interacting with the ligands (observed by docking simulation): (A) DioxoA interactions; (A′) DioxoA binding site; (B) DioxoB interactions; (B′) DioxoB binding site; (C) the orientations of DioxoA and DioxoB in AChE

Full size image

After considering all the interactions, some conclusions were drawn. First, the binding sites for both dioxoisoindolines are the catalytic active site (consisting of a triad of amino acids; Fig. 3A′, B′), the peripheral anionic site, and the aromatic patch. The kind of inhibition can be explained by the fact that these molecules bind to the catalytic active site, thus competing with acetylcholine and accounting for the competitive inhibition found in vitro. Second, the principal interactions between the dioxoisoindolines and AChE are very similar to those described in literature: H-bonds with the oxygen atoms of the carbonyl groups as well as π–π interactions with the aromatic rings. Even the methoxy group supports the exergonic nature of the ∆G. Finally, the isoindoline-1,3-diones herein tested had a binding mode very similar to each other (Fig. 3C).

Conclusions

We developed and tested a method for evaluating the inhibitory activity of ligands on AChE. The slight modifications to Bonting and Featherston afforded a faster and more efficient method, while yielding similar results. The in vitro assays demonstrated that the isoindolines have higher affinity and a greater ability to inhibit AChE than the dioxoisoindolines. These pharmacodynamic properties are probably due to the distinct kind of key interactions carried out on AChE by isoindolines vs. dioxoisoindolines mediated for the presence of carbonyl group. IsoB showed affinity for AChE similar to neostigmine. Further research is needed to analyze the pharmacodynamic and pharmacokinetic profiles of this compound.