Quantitative structure-activity relationships for the pre-steady state acetylcholinesterase inhibition by carbamates

Design and synthesis of garlic-related unsymmetrical thiosulfonates as potential Alzheimer's disease therapeutics: In vitro and in silico study

Garlic contains a wide range of organosulfur compounds, which exhibit a broad spectrum of biological activities. Amongst the sulfur-containing compounds in garlic, the thiosulfonates are considerably popular in various fields. In light of this, we decided to investigate the enzyme inhibition ability of thiosulfonates. In this paper, the synthesis and biological activity of a small library of unsymmetrical thiosulfonates as inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are described. The activity evaluation revealed nanomolar IC₅₀ and K_i values against both enzymes tested. Furthermore, molecular docking studies allowed for the determination of possible binding interactions between the thiosulfonates and AChE.

A molecular approach in drug development for Alzheimer's disease

An increase in dementia numbers and global trends in population aging across the world prompts the need for new medications to treat the complex biological dysfunctions, such as neurodegeneration associated with dementia. Alzheimer's disease (AD) is the most common form of dementia. Cholinergic signaling, which is important in cognition, is slowly lost in AD, so the first line therapy is to treat symptoms with acetylcholinesterase inhibitors to increase levels of acetylcholine. Out of five available FDA-approved AD medications, donepezil, galantamine and rivastigmine are cholinesterase inhibitors while memantine, a N-methyl d-aspartate (NMDA) receptor antagonist, blocks the effects of high glutamate levels. The fifth medication consists of a combination of donepezil and memantine. Although these medications can reduce and temporarily slow down the symptoms of AD, they cannot stop the damage to the brain from progressing. For a superior therapeutic effect, multi-target drugs are required. Thus, a Multi-Target-Directed Ligand (MTDL) strategy has received more attention by scientists who are attempting to develop hybrid molecules that simultaneously modulate multiple biological targets. This review highlights recent examples of the MTDL approach and fragment based strategy in the rational design of new potential AD medications.

Molecular modeling and docking calculations of 4-acyloxy-biphenyl-4′-N-butylcarbamates as potential inhibitors of human butyrylcholinesterase

The kinetic studies and drug designs of butyrylcholinesterase play an important role in the development of Alzheimer’s disease therapeutics. In this research, automated docking studies were performed to provide useful insights into butyrylcholinesterase inhibition binding modes with designed 4-acyloxy-biphenyl-4′-N-butylcarbamates (compounds 1–8). Moreover, several significant linear correlations between experimental and calculated docking results are observed. Among compounds 1–7, compound 3, which exhibits the strongest hydrophobicity and has four carbonyl hydrogen bindings, shows the highest binding affinity (Ki = 1.4 μmol/L) with a binding energy of −7.99 kcal/mol. The observed linear correlation of experimental and calculated inhibition constants (Ki) indicates that the molecular docking results are reliable. Moreover, a good linear correlation is observed between calculated binding energies and experimental pKi. The experimental Hansch hydrophobicity constants (π values) are also correlated with the docked binding energy. This study reveals important correlations between butyrylcholinesterase experimental and docking results that contribute to the kinetic based identification of antagonists for the treatment of Alzheimer’s disease. Furthermore, these docked models provide important insights into a potential series of 4,4′-biphenol-based inhibitors of butyrylcholinesterase.

Synthesis and in vitro evaluation of new derivatives of 2-substituted-6-fluorobenzo[d]thiazoles as cholinesterase inhibitors

A series of novel cholinesterase inhibitors based on 2-substituted 6-fluorobenzo[d]thiazole were synthesised and characterised by IR, (1)H, (13)C and (19)F NMR spectroscopy and HRMS. Purity was checked by elemental analyses. The novel carbamates were tested for their ability to inhibit acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The toxicity of the most active compounds was investigated using a standard in vitro test with HepG2 cells, and the ratio between biological activity and toxicity was determined. In addition, the toxicity of the most active compounds was evaluated against MCF7 cells using the xCELLigence system. Structure-activity relationships reflecting the dependence of cholinesterase inhibitors on the lipophilicity of the compounds as well as on the Taft polar and steric substituent constants are discussed. The specific orientation of the inhibitors in the binding site of acetylcholinesterase was determined using molecular docking of the most active compound.

Acetylcholinesterase-inhibiting activity of salicylanilide N-alkylcarbamates and their molecular docking

A series of twenty-five novel salicylanilide N-alkylcarbamates were investigated as potential acetylcholinesterase inhibitors. The compounds were tested for their ability to inhibit acetylcholinesterase (AChE) from electric eel (Electrophorus electricus L.). Experimental lipophilicity was determined, and the structure-activity relationships are discussed. The mode of binding in the active site of AChE was investigated by molecular docking. All the discussed compounds expressed significantly higher AChE inhibitory activity than rivastigmine and slightly lower than galanthamine. Disubstitution by chlorine in C'_(3,4) of the aniline ring and the optimal length of hexyl-undecyl alkyl chains in the carbamate moiety provided the most active AChE inhibitors. Monochlorination in C'₍₄₎ exhibited slightly more effective AChE inhibitors than in C'₍₃₎. Generally it can be stated that compounds with higher lipophilicity showed higher inhibition, and the activity of the compounds is strongly dependent on the length of the N-alkyl chain.

Mechanistic studies of the inactivation of TEM-1 and P99 by NXL104, a novel non-beta-lactam beta-lactamase inhibitor

NXL104 is a potent inhibitor of class A and C serine β-lactamases, including KPC carbapenemases. Native and NXL104-inhibited TEM-1 and P99 β-lactamases analyzed by liquid chromatography-electrospray ionization-time of flight mass spectrometry revealed that the inactivated enzymes formed a covalent adduct with NXL104. The principal inhibitory characteristics of NXL104 against TEM-1 and P99 β-lactamases were determined, including partition ratios, dissociation constants (K), rate constants for deactivation (k(2)), and reactivation rates. NXL104 is a potent inhibitor of TEM-1 and P99, characterized by high carbamylation efficiencies (k(2)/K of 3.7 × 10(5) M(-1) s(-1) for TEM-1 and 1 × 10(4) M(-1) s(-1) for P99) and slow decarbamylation. Complete loss of β-lactamase activity was obtained at a 1/1 enzyme/NXL104 ratio, with a k(3) value (rate constant for formation of product and free enzyme) close to zero for TEM-1 and P99. Fifty percent inhibitory concentrations (IC(50)s) were evaluated on selected β-lactamases, and NXL104 was shown to be a very potent inhibitor of class A and C β-lactamases. IC(50)s obtained with NXL104 (from 3 nM to 170 nM) were globally comparable on the β-lactamases CTX-M-15 and SHV-4 with those obtained with the comparators (clavulanate, tazobactam, and sulbactam) but were far lower on TEM-1, KPC-2, P99, and AmpC than those of the comparators. In-depth studies on TEM-1 and P99 demonstrated that NXL104 had a comparable or better affinity and inactivation rate than clavulanate and tazobactam and in all cases an improved stability of the covalent enzyme/inhibitor complex.

High-throughput pKa screening and prediction amenable for ADME profiling

Recent technological advances have made it possible for several new pK(a) assays to be used in drug screening. In this review, a critical overview is provided of current new methodologies for high-throughput screening and prediction of pK(a). Typical applications of using pK(a )constants and charge state for absorption, distribution, metabolism and excretion (ADME) profiling and quantitative structure-activity relationship modelling complements the methodological comparisons and discussions. The experimental methods discussed include high-throughput screening of pK(a) by multiplexed capillary with ultraviolet absorbance detection on a 96-capillary format instrument, capillary electrophoresis and mass spectrometry (CEMS) based on sample pooling, determination of pK(a) by pH gradient high-performance liquid chromatography, and measurement of pK(a) by a mixed-buffer liner pH gradient system. Comparisons of the different experimental assays are made with emphasis on the newly developed CEMS method. The current status and recent progress in computational approaches to pK(a) prediction are also discussed. In particular, the accuracy limits of simple fragment-based approaches as well as quantum mechanical methods are addressed. Examples of pK(a) prediction from in-house drug candidates as well as commercially available drug molecules are shown and an outline is provided for how drug discovery companies can integrate experiments with computational approaches for increased applications for ADME profiling.

Substrate activation of butyrylcholinesterase and substrate inhibition of acetylcholinesterase by 3,3-dimethylbutyl-N-n-butylcarbamate and 2-trimethylsilyl-ethyl-N-n-butylcarbamate

Carbamates are used to treat Alzheimer's disease. These compounds inhibit acetylcholinesterase and butyrylcholinesterase. The goal of this work is to use the substrate analogs of butyrylcholinesterase, 3,3-dimethylbutyl-N-n-butylcarbamate (1) and 2-trimethylsilyl-ethyl-N-n-butylcarbamate (2) to probe the substrate activation mechanism of butyrylcholinesterase. Compounds 1 and 2 are characterized as the pseudo substrate inhibitors of acetylcholinesterase; however, compounds 1 and 2 are characterized as the essential activators of butyrylcholinesterase. Therefore, compounds 1 and 2 mimic the substrate in the acetylcholinesterase-catalyzed reactions, but the behavior of compounds 1 and 2 mimics the substrate activation in the butyrylcholinesterase-catalyzed reactions.

Probing the peripheral anionic site of acetylcholinesterase with quantitative structure activity relationships for inhibition by biphenyl-4-acyoxylate-4'-N-Butylcarbamates

Biphenyl-4-acyoxylate-4'-N-butylcarbamates 1-8 are synthesized from 4,4'-biphenol and are characterized as the pseudosubstrate inhibitors of acetylcholinesterase. In other words, the inhibitors bind to the enzyme and react with the enzyme to form the tetrahedral intermediates for the K(i) steps, and then the tetrahedral intermediates exclude the leaving groups to form a common N-butycarbamyl enzyme intermediate for the k(c) steps. Due to a linear character of the 4,4'-biphenyl moiety, the 4'-N-butylcarbamate moieties of the inhibitors react with the Ser200 residue of the enzyme while the 4-acyoxylate moieties of the inhibitors, on the other hand, should fit in the peripheral anionic site of the enzyme, which is located at the mouth of the deep active site gorge. Thus, carbamates with varied acyl substituents at the 4-position of the biphenyl ring are good candidates for probing the quantitative structure activity relationships for the peripheral anionic site of the enzyme. The fact that the pK(i), log k(c), and log K(i) values are correlated with neither the Taft substituent constant (sigma*) nor the Taft steric constant (E(s)) indicates that the 4-acyoxylate moieties of the inhibitors are too far away from the reaction center. However, the pK(i), log k(c), and log K(i) values are linearly correlated with the Hansch hydrophobicity constant, pi. The intensity constants (psi) for these correlations are 0.16, -0.035, and 0.13, respectively. These results indicate that interactions between the 4-acyoxylate groups of the inhibitors and the peripheral anionic site of the enzyme are mainly hydrophobic ones. The correlation results are slightly improved by using the two-parameter correlations with the Taft substituent steric constant, E(s), and pi. For pK(i), log k(c), and log K(i)-E(s)-pi correlations, the psi values are 0.21, -0.021, and 0.19, respectively; the intensity constants for steric effect (delta) are 0.08, 0.022, and 0.10, respectively. Besides hydrophobic interactions, the two-parameter correlations also suggest that little steric hindrance occurs for the bulkier inhibitors to pass by the peripheral anionic site of the enzyme.

Quantitative Structure-Activity Relationships for the Pre-Steady State of Pseudomonas Species Lipase Inhibitions by p-Nirophenyl-N-Substituted Carbamates

The pre-steady states of Pseudomonas species lipase inhibitions by p-nitrophenyl-N-substituted carbamates (1-6) are composed of two steps: (1) formation of the non-covalent enzyme-inhibitor complex (E:I) from the inhibitor and the enzyme and (2) formation of the tetrahedral enzyme-inhibitor adduct (E-I) from the E:I complex. From a stopped-flow apparatus, the dissociation constant for the E:I complex, KS, and the rate constant for formation of the tetrahedral E-I adduct from the E:I complex, k2 are obtained from the non-linear least-squares of curve fittings of first-order rate constant (k(obs)) versus inhibition concentration ([I]) plot against k(obs)=k2+k2[I]/(KS+[I]). Values of pKS, and log k2 are linearly correlated with the sigma* values with the rho* values of -2.0 and 0.36, respectively. Therefore, the E:I complexes are more positive charges than the inhibitors due to the rho* value of -2.0. The tetrahedral E-I adducts on the other hand are more negative charges than the E:I complexes due to the rho* value of 0.36. Formation of the E:I complex from the inhibitor and the enzyme are further divided into two steps: (1) the pre-equilibrium protonation of the inhibitor and (2) formation of the E:I complex from the protonated inhibitor and the enzyme.