Synthesis and biological evaluation of new pyrazolone Schiff bases as monoamine oxidase and cholinesterase inhibitors

In the current work, Schiff base derivatives of antipyrine were synthesized. The chemical characterization of the compounds was confirmed using IR, ¹H NMR, ¹³C NMR and mass spectroscopies. The inhibitory potency of synthesized compounds was investigated towards acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and monoamine oxidases A and B (MAO-A and MAO-B) enzymes. Some of the compounds displayed significant inhibitory activity against AChE and MAO-B enzymes, respectively. According to AChE enzyme inhibition assay, compounds 3e and 3g were found as the most potent derivatives with IC₅₀ values of 0.285 µM and 0.057 µM, respectively. Also, compounds 3a (IC₅₀ = 0.114 µM), 3h (IC₅₀ = 0.049 µM), and 3i (IC₅₀ = 0.054 µM) were the most active derivatives against MAO-B enzyme activity. So as to understand inhibition type, enzyme kinetics studies were carried out. Furthermore, molecular docking studies were performed to define and evaluate the interaction mechanism between compounds 3g and 3h and related enzymes. ADME (Absorption, Distribution, Metabolism, and Excretion) and BBB (Blood, Brain, Barier) permeability predictions were applied to estimate pharmacokinetic profiles of synthesized compounds.     

Compounds with the dioxopyrimidine cycle inhibit cholinesterases from different groups of animals

We firstly synthesized derivatives of 6-methyluracil, alloxazine, and xanthine, containing omega-tetraalkylammonium (TAA) groups at the N(1) and N(3) atoms in a pyrimidine cycle and assayed their anticholinesterase activities. Compounds with triethylpentylammoniumalkyl groups behaved as typical reversible inhibitors of acetylcholinesterase (AChE) (pI(50) 3.20-6.22) and butyrylcholinesterase (BuChE) (pI(50) 3.05-5.71). Compounds, containing two ethyl residues and a substituted benzyl fragment in the tetraalkylammonium group at N(3) atoms or two similar TAA groups at N(1) and N(3) atoms, possessed very high anticholinesterase activity. Although these compounds displayed the activity of typical irreversible AChE inhibitors (a progressive AChE inactivation; k(i) 7.6x10(8) to 3.5x10(9)M(-1)min(-1)), they were reversible inhibitors of BuChE (pI(50) 3.9-6.9). The efficiency of AChE inhibition by some of these compounds was more than 10(4) times higher than the efficiency of BuChE inhibition. Several synthesized TAA derivates of 6-methyluracil reversibly inhibited electric eel and cobra venom AChEs and horse serum BuChE. However, depending on their structure, the tested compounds possessed the time-progressing inhibition of mammalian erythrocyte AChE, typically of irreversible inhibitors. As shown upon dialysis and gel-filtration, the formed mammalian AChE-inhibitor complex was stable. Thus, a new class of highly active, selective, and irreversible inhibitors of mammalian AChE was described. In contrast to classical phosphorylating or carbamoylating AChE inhibitors, these compounds are devoid of acylating functions. Probably, these inhibitors interact with certain amino acid residues at the entrance to the active-site gorge.     

Design, synthesis and evaluation of isaindigotone derivatives as dual inhibitors for acetylcholinesterase and amyloid beta aggregation

A series of isaindigotone derivatives and analogues were designed, synthesized and evaluated as dual inhibitors of cholinesterases (ChEs) and self-induced β-amyloid (Aβ) aggregation. The synthetic compounds had IC(50) values at micro or nano molar range for cholinesterase inhibition, and some compounds exhibited strong inhibitory activity for AChE and high selectivity for AChE over BuChE, which were much better than the isaindigotone derivatives previously reported by our group. Most of these compounds showed higher self-induced Aβ aggregation inhibitory activity than a reference compound curcumin. The structure-activity relationship studies revealed that the derivatives with higher inhibition activity on AChE also showed higher selectivity for AChE over BuChE. Compound 6c exhibiting excellent inhibition for both AChE and self-induced Aβ aggregation was further studied using CD, EM, molecular docking and kinetics.     

Some new carbacylamidophosphates as inhibitors of acetylcholinesterase and butyrylcholinesterase

The differences in the inhibition activity of organophosphorus agents are a manifestation of different molecular properties of the inhibitors involved in the interaction with the active site of enzyme. We were interested in comparing the inhibition potency of four known synthesized carbacylamidophosphates with the general formula RC(O)NHP(O)Cl2, constituting organophosphorus compounds, where R = CCl3 (1), CHCl2 (2), CH2Cl (3) and CF3 (4), and four new ones with the general formula RC(O)NHP(O)(R')2, where R' = morpholine and R = CCl3 (5), CHCl2 (6), CH2Cl (7), CF3 (8), on AChE and BuChE activities. In addition, in vitro activities of all eight compounds on BuChE were determined. Besides, in vivo inhibition potency of compounds 2 and 6, which had the highest inhibition potency among the tested compounds, was studied. The data demonstrated that compound 2 from the compound series 1 to 4 and compound 6 from the compound series 5 to 8 are the most sensitive as AChE and BuChE inhibitors, respectively. Comparing the IC50 values of these compounds, it was clear that the inhibition potency of these compounds for AChE are 2- to 100-fold greater than for BuChE inhibition. Comparison of the kinetics (IC50, Ki, kp, KA and KD) of AChE and BuChE inactivation by these compounds resulted in no significant difference for the measured variables except for compounds 2 and 6, which appeared to be more sensitive to AChE and BuChE by significantly higher kp and Ki values and a lower IC50 value in comparison with the other compounds. The LD50 value of compounds 2 and 6, after oral administration, and the changes of erythrocyte AChE and plasma BuChE activities in albino mice were studied. The in vivo experiments, similar to the in vitro results, showed that compound 2 is a stronger AChE and BuChE inhibitor than the other synthesized carbacylamidophosphates. Furthermore, in this study, the importance of electropositivity of the phosphorus atom, steric hindrance and leaving group specificity were reinforced as important determinants of inhibition activity.     

Design,synthesis and pharmacological evaluation of chalcone derivatives as acetylcholinesterase inhibitors

A novel series of chalcone derivatives (4a–8d) were designed, synthesized, and evaluated for the inhibition activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). The log P values of the compounds were shown to range from 1.49 to 2.19, which suggested that they were possible to pass blood brain barriers in vivo. The most promising compound 4a (IC₅₀: 4.68 μmol/L) was 2-fold more potent than Rivastigmine against AChE (IC₅₀: 10.54 μmol/L) and showed a high selectivity for AChE over BuChE (ratio: 4.35). Enzyme kinetic study suggested that the inhibition mechanism of compound 4a was a mixed-type inhibition. Meanwhile, the result of molecular docking showed its potent inhibition of AChE and high selectivity for AChE over BuChE.     

2-Phenoxy-indan-1-one derivatives as acetylcholinesterase inhibitors: a study on the importance of modifications at the side chain on the activity

As a part of our project aimed at developing new agents of potential application in AD, a new series of 2-phenoxy-indan-1-one derivatives which possess alkylamine side chain were designed, synthesized, and evaluated for their inhibitory activity against AChE and BuChE. Most of the compounds were found to inhibit AChE in the nanomolar range. The optimum inhibitor 3g exhibited 34-fold increase in AChE inhibition than donepezil and displayed neuroprotective effect against H(2)O(2)-induced cell death.     

Design,synthesis and biological activity of novel tacrine-isatin Schiff base hybrid derivatives

A series of novel tacrine-isatin Schiff base hybrid derivatives (7a-p) were designed, synthesized and evaluated as multi-target candidates against Alzheimer’s disease (AD). The biological assays indicated that most of these compounds displayed potent inhibitory activity toward acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) and specific selectivity for AChE over BuChE. It was also found that they act as excellent metal chelators. The compounds 7k and 7m were found to be good inhibitors of AChE-induced amyloid-beta (Aβ) aggregation. Most of the compounds inhibited AChE with the IC₅₀ values, ranging from 0.42 nM to 79.66 nM. Amongst them, 7k, 7m and 7p, all with a 6 carbon linker between tacrine and isatin Schiff base exhibited the strongest inhibitory activity against AChE with IC₅₀ values of 0.42 nM, 0.62 nM and 0.95 nM, respectively. They were 92-, 62- and 41-fold more active than tacrine (IC₅₀ = 38.72 nM) toward AChE. Most of the compounds also showed a potent BuChE inhibition among which 7d with an IC₅₀ value of 0.11 nM for BuChE is the most potent one (56-fold more potent than that of tacrine (IC₅₀ = 6.21 nM)). In addition, most compounds exhibited the highest metal chelating property. Kinetic and molecular modeling studies revealed that 7k is a mixed-type inhibitor, capable of binding to catalytic and peripheral site of AChE. Our findings make this hybrid scaffold an excellent candidate to modify current drugs in treating Alzheimer’s disease (AD).     

α-Tetralone derivatives as inhibitors of monoamine oxidase

In the present study, a series of fifteen α-tetralone (3,4-dihydro-2H-naphthalen-1-one) derivatives were synthesised and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The α-tetralone derivatives examined are structurally related to a series of chromone (1-benzopyran-4-one) derivatives which has previously been shown to act as MAO-B inhibitors. The results document that the α-tetralones are highly potent MAO-B inhibitors with all compounds exhibiting IC₅₀ values in the nanomolar range (<78 nM). Although most compounds are selective inhibitors of MAO-B, the α-tetralones are also potent MAO-A inhibitors with ten compounds exhibiting IC₅₀ values in the nanomolar range (<792 nM). The most potent MAO-B inhibitor, 6-(3-iodobenzyloxy)-3,4-dihydro-2H-naphthalen-1-one, exhibits an IC₅₀ value of 4.5 nM with a 287-fold selectivity for MAO-B over the MAO-A isoform, while the most potent MAO-A inhibitor, 6-(3-cyanobenzyloxy)-3,4-dihydro-2H-naphthalen-1-one, exhibits an IC₅₀ value of 24 nM with a 3.25-fold selectivity for MAO-A. Analyses of the structure–activity relationships for MAO inhibition show that substitution on the C6 position of the α-tetralone moiety is a requirement for MAO-A and MAO-B inhibition, and that a benzyloxy substituent on this position is more favourable for MAO-A inhibition than phenylethoxy and phenylpropoxy substitution. For MAO-B inhibition, alkyl and halogen substituents on the meta and para positions of the benzyloxy ring enhance inhibitory potency. It may be concluded that α-tetralone derivatives are promising leads for design of therapies for Parkinson’s disease and depression.     

Comparison of the inhibitory potential towards carbonic anhydrase,acetylcholinesterase and butyrylcholinesterase of chalcone and chalcone epoxide

Chalcones and chalcone epoxides are important synthetic intermediates in organic and medicinal chemistry. Chalcones possess a broad spectrum of biological activities; however, 1,3‐diphenyl‐2‐propenone or chalcone has not been given the attention it deserve as its substituted derivatives. In this study, the inhibition effects of chalcone and its epoxidated derivative chalcone epoxide against human carbonic anhydrase isozymes I and II (hCA I and hCA II), acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) were evaluated. The results obtained showed that both compounds exhibited potent inhibitory activity, with IC₅₀ values less than 10 µM. IC ₅₀ values in the submicromolar (hCA I and hCA II) to low micromolar range (AChE and BuChE) were observed for both compounds. The mechanism of inhibition and the inhibitory constants ( K _i values) for each compound were also determined. Furthermore, chalcone epoxide was docked within the active sites of hCA I, hCA II, AChE, and BuChE to explore its binding mode with the enzymes.     

Kinetics of reversible inhibition of cholinesterases by quaternary diaminoalkyl esters of aromatic dicarboxylic acids]

Reversible inhibition of acetylcholinesterase (AChE) from bovine erythrocytes and butyrylcholinesterase (BuChE) from horse blood serum by quaternary diaminoalkyl esters of suberic (D-6), p-phenylenediacetic (PK-139), p-phenylenedipropionic (PK-154 and PK-155), p-phenylenediacrylic (PK-150 and PK-151) and phthalic (PK-105) acids, was studied under the following incubation conditions: pH 7.5, 25 degrees C, 0.1 M KCl. The inhibition kinetics were of a mixed competitive-incompetitive type, the incompetitive component alpha'-having higher values for AChE (0.26-0.60) than for BuChE (0.10-0.20). Diester PK-150 selectively inhibited BuChE (Ki=3.0-10(-6) M); its Ki value for AChE was 4.0-10(-4) M. The other diesters had a stronger inhibitory effect on AChE than on BuChE. High values of alpha' observed during AChE inhibition cannot be interpreted in terms of interaction of those bisquaternary compounds with the anionic site of the acetylated active centre and are probably due to their sorbtion at the peripheral anionic sites. Incompetitive inhibition constants (K'i=Ki/alpha') of BuChE by the diesters PK-139, PK-154 and PK-150 were found to be values of the same order as substrate inhibition constants determined in the course of BuChE hydrolysis of these diesters. Incompetitive inhibition found for the esters studied and substrate inhibition during hydrolysis of these compounds are presumably due to the same mechanism.     

Design, synthesis and evaluation of isaindigotone derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors

A series of isaindigotone derivatives 5a-d and 6a-d were designed, synthesized and evaluated as acetylcholinesterase and butyrylcholinesterase inhibitors. Results showed that the novel class of isaindigotone derivatives could inhibit both cholinesterases and the selectivity of AChE over BuChE inhibition was related to the aromatic, the species and length of the alkyl amino side chain of compounds. The structure-activity relationships were discussed and their multiple binding modes were further clarified in the molecular docking studies.     

Design,synthesis, and pharmacological evaluation of 2-amino-5-nitrothiazole derived semicarbazones as dual inhibitors of monoamine oxidase and cholinesterase: effect of the size of aryl binding site

A series of 2-amino-5-nitrothiazole derived semicarbazones were designed, synthesised and investigated for MAO and ChE inhibition properties. Most of the compounds showed preferential inhibition towards MAO-B. Compound 4, (1-(1-(4-Bromophenyl)ethylidene)-4-(5-nitrothiazol-2-yl)semicarbazide) emerged as lead candidate (IC₅₀?=?0.212?µM, SI?=?331.04) against MAO-B; whereas compounds 21 1-(5-Bromo-2-oxoindolin-3-ylidene)-4-(5-nitrothiazol-2-yl)semicarbazide (IC₅₀?=?0.264?µM) and 17 1-((4-Chlorophenyl) (phenyl)methylene)-4-(5-nitrothiazol-2-yl)semicarbazide (IC₅₀?=?0.024?µM) emerged as lead AChE and BuChE inhibitors respectively; with activity of compound 21 almost equivalent to tacrine. Kinetic studies indicated that compound 4 exhibited competitive and reversible MAO-B inhibition while compounds 21 and 17 showed mixed-type of AChE and BuChE inhibition respectively. Docking studies revealed that these compounds were well-accommodated within MAO-B and ChE active sites through stable hydrogen bonding and/or hydrophobic interactions. This study revealed the requirement of small heteroaryl ring at amino terminal of semicarbazone template for preferential inhibition and selectivity towards MAO-B. Our results suggest that 5-nitrothiazole derived semicarbazones could be further exploited for its multi-targeted role in development of anti-neurodegenerative agents.

A library of 2-amino-5-nitrothiazole derived semicarbazones (4–21) was designed, synthesised and evaluated for in vitro MAO and ChE inhibitory activity. Compounds 4, 21 and 17 (shown) have emerged as lead MAO-B (IC₅₀:0.212?µM, competitive and reversible), AChE (IC₅₀:0.264?µM, mixed and reversible) and BuChE (IC₅₀:0.024?µM, mixed and reversible) inhibitor respectively. SAR studies disclosed several structural aspects significant for potency and selectivity and indicated the role of size of aryl binding site in potency and selectivity towards MAO-B. Antioxidant activity and neurotoxicity screening results further suggested their multifunctional potential for the therapy of neurodegenerative diseases.     

Derivatives of oxoisoaporphine alkaloids: a novel class of selective acetylcholinesterase inhibitors

A series of 9-aminoalkanamido-1-azabenzanthrones derviatives (3a-i Ar-NHCO(CH(2))(n)NR(1)R(2)) and their quaternary methiodide salts (4a-g Ar-NHCO(CH(2))(n)N(+)(CH(3))R(1)R(2)I(-)) were designed and synthesized as acetylcholinesterase (AChE) or butyrylcholinesterase (BuChE) inhibitors. The synthetic compounds exhibited high AChE inhibitory activity with IC(50) values in the nanomolar range and high selectivity for AChE over BuChE (45- to 1980-fold). The structure-activity relationships (SARs) were discussed.     

Structure-activity relationships for inhibition of human cholinesterases by alkyl amide phenothiazine derivatives

Several lines of evidence indicate that inhibition of butyrylcholinesterase (BuChE) is important in the treatment of certain dementias. Further testing of this concept requires inhibitors that are both BuChE-selective and robust. N-alkyl derivatives (2, 3, 4) of phenothiazine (1) have previously been found to inhibit only BuChE in a mechanism involving pi-pi interaction between the phenothiazine tricyclic ring system and aromatic residues in the active site gorge. To explore features of phenothiazines that affect the selectivity and potency of BuChE inhibition, a series of N-carbonyl derivatives (5-25) was synthesized and examined for the ability to inhibit cholinesterases. Some of the synthesized derivatives also inhibited AChE through a different mechanism involving carbonyl interaction within the active site gorge. Binding of these derivatives takes place within the gorge, since this inhibition disappears when the molecular volume of the derivative exceeds the estimated active site gorge volume of this enzyme. In contrast, BuChE, with a much larger active site gorge, exhibited inhibition that increased directly with the molecular volumes of the derivatives. This study describes two distinct mechanisms for binding phenothiazine amide derivatives to BuChE and AChE. Molecular volume was found to be an important parameter for BuChE-specific inhibition.     

Synthesis,biological evaluation and molecular modeling of substituted 2-aminobenzimidazoles as novel inhibitors of acetylcholinesterase and butyrylcholinesterase

A series of novel 2-aminobenzimidazole derivatives were synthesized under microwave irradiation. Their biological activities were evaluated on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A number of the 2-aminobenzimidazole derivatives showed good inhibitory activities to AChE and BuChE. Among them, compounds 9, 12 and 13 were found to be >25-fold more selective for BuChE than AChE. No evidence of cytotoxicity was observed by MTT assay in PC12 cells or HepG2 cells exposed to 100 μM of the compounds. Molecular modeling studies indicate that the benzimidazole moiety of compounds 9, 12 and 13 forms a face-to-face π–π stacking interaction in a ‘sandwich’ form with the indole ring of Trp82 (4.09 Å) in the active gorge, and compounds 12 and 13 form a hydrogen bond with His438 at the catalytic site of BuChE. In addition, compounds 12 and 13 fit well into the hydrophobic pocket formed by Ala328, Trp430 and Tyr332 of BuChE. Our data suggest the 2-aminobenzimidazole drugs as promising new selective inhibitors for AChE and BuChE, potentially useful to treat neurodegenerative diseases.     

Design,synthesis and preliminary structure–activity relationship investigation of nitrogen-containing chalcone derivatives as acetylcholinesterase and butyrylcholinesterase inhibitors: a further study based on Flavokawain B Mannich base derivatives

In order to study the structure–activity relationship of Flavokawain B Mannich-based derivatives as acetylcholinesterase (AChE) inhibitors in our recent investigation, 20 new nitrogen-containing chalcone derivatives (4?a–8d) were designed, synthesized, and evaluated for AChE inhibitory activity in vitro. The results suggested that amino alkyl side chain of chalcone dramatically influenced the inhibitory activity against AChE. Among them, compound 6c revealed the strongest AChE inhibitory activity (IC₅₀ value: 0.85?μmol/L) and the highest selectivity against AChE over BuChE (ratio: 35.79). Enzyme kinetic study showed that the inhibition mechanism of compound 6c against AChE was a mixed-type inhibition. The molecular docking assay showed that this compound can both bind with the catalytic site and the peripheral site of AChE.     

Synthesis,biological activity and molecular modeling studies on 1H-benzimidazole derivatives as acetylcholinesterase inhibitors

A series of N-{2-[4-(1H-benzimidazole-2-yl)phenoxy]ethyl}substituted amine derivatives were designed to assess cholinesterase inhibitor activities. Acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitor activities were evaluated in vitro by using Ellman’s method. It was discovered that most of the compounds displayed AChE and/or BuChE inhibitor activity and few compounds were selective against AChE/BuChE. Compound 3c and 3e were the most active compounds in the series against eeAChE and hAChE, respectively. Molecular docking studies and molecular dynamics simulations were also carried out.     

Pyridoxine-resveratrol hybrids Mannich base derivatives as novel dual inhibitors of AChE and MAO-B with antioxidant and metal-chelating properties for the treatment of Alzheimer’s disease

A series of pyridoxine-resveratrol hybrids Mannich base derivatives as multifunctional agents have been designed, synthesized and evaluated for cholinesterase (ChE) and monoamine oxidase (MAO) inhibitory activity. To further explore the multifunctional properties of the new derivatives, their antioxidant activities and metal-chelating properties were also tested. The results showed that most of these compounds could selectively inhibit acetylcholinesterase (AChE) and MAO-B. Among them, compounds 7d and 8b exhibited the highest potency for AChE inhibition with IC₅₀ values of 2.11 μM and 1.56 μM, respectively, and compound 7e exhibited the highest MAO-B inhibition with an IC₅₀ value of 2.68 μM. The inhibition kinetic analysis revealed that compound 7d showed a mixed-type inhibition, binding simultaneously to the CAS and PAS of AChE. Molecular modeling study was also performed to investigate the binding mode of these hybrids with MAO-B. In addition, all target compounds displayed good antioxidant and metal-chelating properties. Taken together, these preliminary findings can be a new starting point for further development of multifunctional agents for Alzheimer’s disease.     

Cholinesterase inhibitors: SAR and enzyme inhibitory activity of 3-[omega-(benzylmethylamino)alkoxy]xanthen-9-ones

In this work, we further investigated a previously introduced class of cholinesterase inhibitors. The removal of the carbamic function from the lead compound xanthostigmine led to a reversible cholinesterase inhibitors 3. Some new 3-[omega-(benzylmethylamino)alkoxy]xanthen-9-one analogs were designed, synthesized, and evaluated for their inhibitory activity against both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). The length of the alkoxy chain of compound 3 was increased and different substituents were introduced. From the IC(50) values, it clearly appears that the carbamic residue is crucial to obtain highly potent AChE inhibitors. On the other hand, peculiarity of these compounds is the high selectivity toward BuChE with respect to AChE, being compound 12 the most selective one (6000-fold). The development of selective BuChE inhibitors may be of great interest to clarify the physiological role of this enzyme and to provide novel therapeutics for various diseases.     

Discovery of isoalloxazine derivatives as a new class of potential anti-Alzheimer agents and their synthesis

This article describes discovery of a novel and new class of cholinesterase inhibitors as potential therapeutics for Alzheimer’s disease. A series of novel isoalloxazine derivatives were synthesized and biologically evaluated for their potential inhibitory outcome for both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). These compounds exhibited high activity against both the enzymes AChE as well as BuChE. Of the synthesized compounds, the most potent isoalloxazine derivatives (7m and 7q) showed IC₅₀ values of 4.72 μM and 5.22 μM respectively against AChE; and, 6.98 μM and 5.29 μM respectively against BuChE. These two compounds were further evaluated for their anti-aggregatory activity for β-amyloid (Aβ) in presence and absence of AChE by performing Thioflavin-T (ThT) assay and Congo red (CR) binding assay. In order to evaluate cytotoxic profile of these two potential compounds, cell viability assay of SH-SY5Y human neuroblastoma cells was performed. Further, to understand the binding behavior of these two compounds with AChE and BuChE enzymes, docking studies have been reported.