Combining Experimental and Computational Methods to Produce Conjugates of Anticholinesterase and Antioxidant Pharmacophores with Linker Chemistries Affecting Biological Activities Related to Treatment of Alzheimer's Disease.

Effective therapeutics for Alzheimer's disease (AD) are in great demand worldwide. In our previous work, we responded to this need by synthesizing novel drug candidates consisting of 4-amino-2,3-polymethylenequinolines conjugated with butylated hydroxytoluene via fixed-length alkylimine or alkylamine linkers (spacers) and studying their bioactivities pertaining to AD treatment. Here, we report significant extensions of these studies, including the use of variable-length spacers and more detailed biological characterizations. Conjugates were potent inhibitors of acetylcholinesterase (AChE, the most active was 17d IC50 15.1 ± 0.2 nM) and butyrylcholinesterase (BChE, the most active was 18d: IC50 5.96 ± 0.58 nM), with weak inhibition of off-target carboxylesterase. Conjugates with alkylamine spacers were more effective cholinesterase inhibitors than alkylimine analogs. Optimal inhibition for AChE was exhibited by cyclohexaquinoline and for BChE by cycloheptaquinoline. Increasing spacer length elevated the potency against both cholinesterases. Structure-activity relationships agreed with docking results. Mixed-type reversible AChE inhibition, dual docking to catalytic and peripheral anionic sites, and propidium iodide displacement suggested the potential of hybrids to block AChE-induced ß-amyloid (Aß) aggregation. Hybrids also exhibited the inhibition of Aß self-aggregation in the thioflavin test; those with a hexaquinoline ring and C8 spacer were the most active. Conjugates demonstrated high antioxidant activity in ABTS and FRAP assays as well as the inhibition of luminol chemiluminescence and lipid peroxidation in mouse brain homogenates. Quantum-chemical calculations explained antioxidant results. Computed ADMET profiles indicated favorable blood-brain barrier permeability, suggesting the CNS activity potential. Thus, the conjugates could be considered promising multifunctional agents for the potential treatment of AD.

Bis-Amiridines as Acetylcholinesterase and Butyrylcholinesterase Inhibitors: N-Functionalization Determines the Multitarget Anti-Alzheimer's Activity Profile.

Using two ways of functionalizing amiridine-acylation with chloroacetic acid chloride and reaction with thiophosgene-we have synthesized new homobivalent bis-amiridines joined by two different spacers-bis-N-acyl-alkylene (3) and bis-N-thiourea-alkylene (5) -as potential multifunctional agents for the treatment of Alzheimer's disease (AD). All compounds exhibited high inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity for BChE. These new agents displayed negligible carboxylesterase inhibition, suggesting a probable lack of untoward drug-drug interactions arising from hydrolytic biotransformation. Compounds 3 with bis-N-acyl-alkylene spacers were more potent inhibitors of both cholinesterases compared to compounds 5 and the parent amiridine. The lead compounds 3a-c exhibited an IC50(AChE) = 2.9-1.4 µM, IC50(BChE) = 0.13-0.067 µM, and 14-18% propidium displacement at 20 µM. Kinetic studies of compounds 3a and 5d indicated mixed-type reversible inhibition. Molecular docking revealed favorable poses in both catalytic and peripheral AChE sites. Propidium displacement from the peripheral site by the hybrids suggests their potential to hinder AChE-assisted Aß42 aggregation. Conjugates 3 had no effect on Aß42 self-aggregation, whereas compounds 5c-e (m = 4, 5, 6) showed mild (13-17%) inhibition. The greatest difference between conjugates 3 and 5 was their antioxidant activity. Bis-amiridines 3 with N-acylalkylene spacers were nearly inactive in ABTS and FRAP tests, whereas compounds 5 with thiourea in the spacers demonstrated high antioxidant activity, especially in the ABTS test (TEAC = 1.2-2.1), in agreement with their significantly lower HOMO-LUMO gap values. Calculated ADMET parameters for all conjugates predicted favorable blood-brain barrier permeability and intestinal absorption, as well as a low propensity for cardiac toxicity. Thus, it was possible to obtain amiridine derivatives whose potencies against AChE and BChE equaled (5) or exceeded (3) that of the parent compound, amiridine. Overall, based on their expanded and balanced pharmacological profiles, conjugates 5c-e appear promising for future optimization and development as multitarget anti-AD agents.

Amiridine-piperazine hybrids as cholinesterase inhibitors and potential multitarget agents for Alzheimer's disease treatment.

We synthesized eleven new amiridine-piperazine hybrids 5a-j and 7 as potential multifunctional agents for Alzheimer's disease (AD) treatment by reacting N-chloroacetylamiridine with piperazines. The compounds displayed mixed-type reversible inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Conjugates were moderate inhibitors of equine and human BChE with negligible fluctuation in anti-BChE activity, whereas anti-AChE activity was substantially dependent on N4-substitution of the piperazine ring. Compounds with para-substituted aromatic moieties (5g, 5h, and bis-amiridine 7) had the highest anti-AChE activity in the low micromolar range. Top-ranked compound 5h, N-(2,3,5,6,7,8-hexahydro-1H-cyclopenta[b]quinolin-9-yl)-2-[4-(4-nitro-phenyl)-piperazin-1-yl]-acetamide, had an IC50 for AChE = 1.83 ± 0.03 µM (Ki = 1.50 ± 0.12 and αKi = 2.58 ± 0.23 µM). The conjugates possessed low activity against carboxylesterase, indicating a likely absence of unwanted drug-drug interactions in clinical use. In agreement with analysis of inhibition kinetics and molecular modeling studies, the lead compounds were found to bind effectively to the peripheral anionic site of AChE and displace propidium, indicating their potential to block AChE-induced ß-amyloid aggregation. Similar propidium displacement activity was first shown for amiridine. Two compounds, 5c (R = cyclohexyl) and 5e (R = 2-MeO-Ph), exhibited appreciable antioxidant capability with Trolox equivalent antioxidant capacity values of 0.47 ± 0.03 and 0.39 ± 0.02, respectively. Molecular docking and molecular dynamics simulations provided insights into the structure-activity relationships for AChE and BChE inhibition, including the observation that inhibitory potencies and computed pKa values of hybrids were generally lower than those of the parent molecules. Predicted ADMET and physicochemical properties of conjugates indicated good CNS bioavailability and safety parameters comparable to those of amiridine and therefore acceptable for potential lead compounds at the early stages of anti-AD drug development.

Conjugates of tacrine and 1,2,4-thiadiazole derivatives as new potential multifunctional agents for Alzheimer's disease treatment: Synthesis, quantum-chemical characterization, molecular docking, and biological evaluation.

We synthesized conjugates of tacrine with 1,2,4-thiadiazole derivatives linked by two different spacers, pentylaminopropene (compounds 4) and pentylaminopropane (compounds 5), as potential drugs for the treatment of Alzheimer's disease (AD). The conjugates effectively inhibited cholinesterases with a predominant effect on butyrylcholinesterase (BChE). They were also effective at displacing propidium from the peripheral anionic site (PAS) of acetylcholinesterase (AChE), suggesting that they could block AChE-induced ß-amyloid aggregation. In addition, the compounds exhibited high radical-scavenging capacity. Conjugates 5 had higher anti-BChE activity and greater anti-aggregant potential as well relatively lower potency against carboxylesterase than compounds 4. Quantum-mechanical (QM) characterization agreed with NMR data to identify the most stable forms of conjugates for docking studies, which showed that the compounds bind to both CAS and PAS of AChE consistent with mixed reversible inhibition. Conjugates 4 were more potent radical scavengers, in agreement with HOMO localization in the enamine-thiadiazole system. Computational studies showed that all of the conjugates were expected to have good intestinal absorption, whereas conjugates 4 and 5 were predicted to have medium and high blood-brain barrier permeability, respectively. All conjugates were predicted to have medium cardiac toxicity risks. Overall, the results indicated that the conjugates are promising candidates for further development and optimization as multifunctional therapeutic agents for the treatment of AD.

New Hybrids of 4-Amino-2,3-polymethylene-quinoline and p-Tolylsulfonamide as Dual Inhibitors of Acetyl- and Butyrylcholinesterase and Potential Multifunctional Agents for Alzheimer's Disease Treatment.

New hybrid compounds of 4-amino-2,3-polymethylene-quinoline containing different sizes of the aliphatic ring and linked to p-tolylsulfonamide with alkylene spacers of increasing length were synthesized as potential drugs for treatment of Alzheimer's disease (AD). All compounds were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity toward BChE. The lead compound 4-methyl-N-(5-(1,2,3,4-tetrahydro-acridin-9-ylamino)-pentyl)-benzenesulfonamide (7h) exhibited an IC50 (AChE) = 0.131 ± 0.01 µM (five times more potent than tacrine), IC50(BChE) = 0.0680 ± 0.0014 µM, and 17.5 ± 1.5% propidium displacement at 20 µM. The compounds possessed low activity against carboxylesterase, indicating a likely absence of unwanted drug-drug interactions in clinical use. Kinetics studies were consistent with mixed-type reversible inhibition of both cholinesterases. Molecular docking demonstrated dual binding sites of the conjugates in AChE and clarified the differences in the structure-activity relationships for AChE and BChE inhibition. The conjugates could bind to the AChE peripheral anionic site and displace propidium, indicating their potential to block AChE-induced ß-amyloid aggregation, thereby exerting a disease-modifying effect. All compounds demonstrated low antioxidant activity. Computational ADMET profiles predicted that all compounds would have good intestinal absorption, medium blood-brain barrier permeability, and medium cardiac toxicity risk. Overall, the results indicate that the novel conjugates show promise for further development and optimization as multitarget anti-AD agents.

New Multifunctional Agents Based on Conjugates of 4-Amino-2,3-polymethylenequinoline and Butylated Hydroxytoluene for Alzheimer's Disease Treatment.

New hybrids of 4-amino-2,3-polymethylenequinoline with different sizes of the aliphatic ring linked to butylated hydroxytoluene (BHT) by enaminoalkyl (7) or aminoalkyl (8) spacers were synthesized as potential multifunctional agents for Alzheimer's disease (AD) treatment. All compounds were potent inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity toward BChE. Lead compound 8c, 2,6-di-tert-butyl-4-{[2-(7,8,9,10- tetrahydro-6H-cyclohepta[b]quinolin-11-ylamino)-ethylimino]-methyl}-phenol exhibited an IC50(AChE) = 1.90 ± 0.16 µM, IC50(BChE) = 0.084 ± 0.008 µM, and 13.6 ± 1.2% propidium displacement at 20 µM. Compounds possessed low activity against carboxylesterase, indicating likely absence of clinically unwanted drug-drug interactions. Kinetics were consistent with mixed-type reversible inhibition of both cholinesterases. Docking indicated binding to catalytic and peripheral AChE sites; peripheral site binding along with propidium displacement suggest the potential of the hybrids to block AChE-induced ß-amyloid aggregation, a disease-modifying effect. Compounds demonstrated high antioxidant activity in ABTS and FRAP assays as well as inhibition of luminol chemiluminescence and lipid peroxidation in mouse brain homogenates. Conjugates 8 with amine-containing spacers were better antioxidants than those with enamine spacers 7. Computational ADMET profiles for all compounds predicted good blood-brain barrier distribution (permeability), good intestinal absorption, and medium cardiac toxicity risk. Overall, based on their favorable pharmacological and ADMET profiles, conjugates 8 appear promising as candidates for AD therapeutics.

Cocrystals of a 1,2,4-thiadiazole-based potent neuroprotector with gallic acid: solubility, thermodynamic stability relationships and formation pathways.

Three distinct solid forms, namely anhydrous cocrystals with 2 : 1 and 1 : 1 drug/acid ratios ([TDZ : GA] (2 : 1), [TDZ : GA] (1 : 1)), and a hydrated one having 1 : 1 : 1 drug/acid/water stoichiometry ([TDZ : GA : H2O] (1 : 1 : 1)), have been formed by cocrystallization of the biologically active 1,2,4-thiadiazole derivative (TDZ) with gallic acid (GA). The thermodynamic stability relationships between the cocrystals were rationalized in terms of Gibbs energies of the formation reactions and further verified by performing a set of competitive and exchange mechanochemical reactions. Interestingly, competitive grinding in the presence of the structurally related vanillic acid led to the formation of a new polymorphic form of the [TDZ : Vanillic acid] (1 : 1) cocrystal, which was promoted by gallic acid. The mechanochemical method was also applied to elucidate the alternative pathways of the [TDZ : GA : H2O] (1 : 1 : 1) cocrystal formation. Direct cocrystallization of TDZ with GA monohydrate was found to proceed much faster than the reaction of TDZ and anhydrous GA in the presence of an acetonitrile/water mixture, which may indicate the presence of a transitional stage. According to dissolution studies, the [TDZ : GA : H2O] (1 : 1 : 1) cocrystal was ca. 6.6 times more soluble than the parent 1,2,4-thiadiazole at pH 2.0 and 25.0 °C. The apparent two-step dehydration behavior of the [TDZ : GA : H2O] (1 : 1 : 1) cocrystal monohydrate was clarified by analyzing the intermolecular interactions of water molecules with the crystalline environment derived from solid state DFT calculations.

Synthesis, molecular docking and biological evaluation of N,N-disubstituted 2-aminothiazolines as a new class of butyrylcholinesterase and carboxylesterase inhibitors.

A series of 31 N,N-disubstituted 2-amino-5-halomethyl-2-thiazolines was designed, synthesized, and evaluated for inhibitory potential against acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and carboxylesterase (CaE). The compounds did not inhibit AChE; the most active compounds inhibited BChE and CaE with IC50 values of 0.22-2.3µM. Pyridine-containing compounds were more selective toward BChE; compounds with the para-OMe substituent in one of the two dibenzyl fragments were more selective toward CaE. Iodinated derivatives were more effective BChE inhibitors than brominated ones, while there was no influence of halogen type on CaE inhibition. Inhibition kinetics for the 9 most active compounds indicated non-competitive inhibition of CaE and varied mechanisms (competitive, non-competitive, or mixed-type) for inhibition of BChE. Docking simulations predicted key binding interactions of compounds with BChE and CaE and revealed that the best docked positions in BChE were at the bottom of the gorge in close proximity to the catalytic residues in the active site. In contrast, the best binding positions for CaE were clustered rather far from the active site at the top of the gorge. Thus, the docking results provided insight into differences in kinetic mechanisms and inhibitor activities of the tested compounds. A cytotoxicity test using the MTT assay showed that within solubility limits (<30µM), none of the tested compounds significantly affected viability of human fetal mesenchymal stem cells. The results indicate that a new series of N,N-disubstituted 2-aminothiazolines could serve as BChE and CaE inhibitors for potential medicinal applications.

Novel 1,2,4-thiadiazole derivatives as potent neuroprotectors: approach to creation of bioavailable drugs.

Novel 1,2,4-thiadiazole derivatives as potent neuroprotectors were synthesized and identified. Their ability to inhibit the glutamate stimulated Ca uptake was measured. Permeation experiments on the phospholipid membranes were conducted, and the apparent permeability coefficients were obtained. The partition coefficients in n-octanol/buffer (pH 7.4) and n-hexane/buffer (pH 7.4) immiscible phases (as model systems for characterizing gastrointestinal tract membranes and BBB) were determined. A classification of the studied compounds from the standpoint of "permeability-activity" properties was proposed.

Thermodynamic and structural aspects of novel 1,2,4-thiadiazoles in solid and biological mediums.

Novel 1,2,4-thiadiazoles were synthesized. Crystal structures of these compounds were solved by X-ray diffraction experiments, and comparative analysis of packing architecture and hydrogen bond networks was carried out. Thermodynamic aspects of sublimation processes of the compounds under study were analyzed using temperature dependencies of vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation and structural parameters. The melting points correlate with sublimation Gibbs energies. Moreover, an increase of donor-acceptor interactions in crystal structures leads to growth of Gibbs energy values. Relationships between the melting points and the fragmental contributions to the packing energies were established: R(1)-R(4) fragmental interactions are responsible for the fusion processes of this class of compounds. Solubility and solvation processes of 1,2,4-thiadiazoles in buffer, n-hexane and n-octanol were studied within a wide range of temperature intervals, and their thermodynamic functions were calculated. Specific and nonspecific interactions of molecules resolved in crystals and solvents were estimated and compared. It was found that the melting points correlate with sublimation Gibbs energies. Distribution processes of compounds in buffer/n-octanol and buffer/n-hexane systems (describing different types of membranes) were investigated. Transfer processes of the studied molecules from the buffer to n-octanol/n-hexane phases were analyzed by the diagram method with evaluation of the enthalpic and entropic terms. This approach allowed us to design drug molecules with optimal passive transport properties. Calcium-blocking properties of the substances were evaluated. The trend between the ability to inhibit Glu-Ca uptake and the distribution coefficients in buffer/hexane system was observed.

Cocrystal formation, crystal structure, solubility and permeability studies for novel 1,2,4-thiadiazole derivative as a potent neuroprotector.

The cocrystallization approach has been applied to modify the poor solubility profile of the biologically active 1,2,4-thiadiazole derivative (TDZ). Extensive cocrystal screening with a library of coformers resulted in formation of a new solid form of TDZ with vanillic acid in a 1:1 molar ratio. The cocrystalline phase was identified and characterized by thermal and diffraction analyses including single-crystal X-ray diffraction. The energies of intermolecular interactions in the crystal were calculated by solid-state DFT and PIXEL methods. Both calculation schemes show good consistency in terms of total energy of the intermolecular interactions and suggest that the cocrystal is mainly stabilized via hydrogen bonds, which provide ca. 44% of the lattice energy. Since the cocrystal contained the hydroxybenzoic acid derivative as a coformer, the solubility profile of the cocrystal was investigated at different pHs using eutectic concentrations of the components. Furthermore, the influence of the cocrystallization on the permeability performance of the 1,2,4-thiadiazole through an artificial regenerated cellulose membrane was also evaluated. In addition, the thermodynamic functions of the cocrystal formation were estimated from the solubility of the cocrystal and the corresponding solubility of the pure compounds at various temperatures. The cocrystal formation process was found to have a relatively small value of the driving force (-5.3kJ·mol-1). The most significant contribution to the Gibbs energy was provided by the exothermic enthalpy of formation.

Crystal structure analysis and sublimation thermodynamics of bicyclo derivatives of a neuroprotector family.

The crystal structures of three new structurally related drug-like bicyclo derivatives are correlated with measured thermodynamic quantities for their sublimation and melting processes. The sublimation thermodynamics are determined using the temperature dependencies of the vapour pressure, and the melting processes are examined using differential scanning calorimetry. The three compounds contain a common N-(3-thia-1-azabicyclo[3.3.1]non-2-ylidene)aniline core, with either a CH3, F or CF3 substituent at the 4-position of the aniline ring. Lattice energy calculations are made using both the PIXEL and Coulomb-London-Pauli (CLP) models, and the conformational flexibility of the molecules is examined using gas-phase density functional theory (DFT) calculations. The experimentally measured crystal lattice energies (ΔH(0)sub) decrease in the order: CH3 > F > CF3. The calculated lattice energies using the PIXEL approach are in good agreement with the experimental values, and the partitioned intermolecular interaction energies suggest that dispersion contributions dominate the crystal structures of all three compounds. The sublimation energies and melting points are inversely correlated for the three molecules, with the melting points increasing in the order CF3 < F < CH3.

Synthesis, biological activity, distribution and membrane permeability of novel spiro-thiazines as potent neuroprotectors.

New spiro-derivatives of 1,3-thiazine - potential neuroprotectors have been synthesized. It has been determined that the obtained compounds are biologically active and capable of blocking the glutamate-induced calcium ion uptake into synaptosomes of rat brain cortex. The inhibitory activity of the test substances was shown to depend on the chemical nature and structure of the substituents bound with an exocyclic nitrogen atom. Non-polar alkyl and polar radicals with halogen, oxygen and nitrogen atoms were used as substituents. It is typical of the active spiro-thiazines to have alkyl substituents in ortho- and para-position of the benzene ring. Among the investigated spiro-thiazines it is the derivatives with ethyl- and isopropyl-groups in the aril part of the molecules that are the lead-compounds with a high inhibitory ability. We measured the distribution coefficients of the substances in octanol/buffer and hexane/buffer systems and made conclusions about the ability of the investigated drug-like compounds to penetrate the biological membranes. By using the parabolic model we derived a quadratic equation that allowed us to evaluate quantitatively the inhibitory activity of spiro-thiazines with hydrophobic substituents based on lipophilicity data. We also studied the permeability through the phospholipidic membrane and introduced a correlation equation describing the dependence of the investigated spiro-thiazines activity on the descriptors characterizing the donor-acceptor properties.

Novel 1,2,4-thiadiazole derivatives: crystal structure, conformational analysis, hydrogen bond networks, calculations, and thermodynamic characteristics of crystal lattices.

The results of X-ray crystallographic and computational studies of twelve 1,2,4-thiadiazole derivatives are reported. The effect of orientation of different parts of the molecules on crystal organization and hydrogen bond network were studied. DFT calculations were carried out in order to explore conformational preferences of the molecules inside and outside of crystal environment. The role of hydrogen bonds was found to be essential for the stabilization of conformationally strained molecules as well as for the packing density of such molecules in a crystal. Thermodynamic aspects of sublimation processes of the studied compounds were analyzed using temperature dependencies of their vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation enthalpy and the structural parameters. The influence of crystal structure features on the sublimation enthalpy and on the melting temperature was analyzed.

Synthesis, pharmacology, crystal properties, and quantitative solvation studies from a drug transport perspective for three new 1,2,4-thiadiazoles.

A novel 1,2,4-thiadiazoles were synthesized. Crystal structures of these compounds were solved by X-ray diffraction experiments and comparative analysis of molecular conformational states, packing architecture, and hydrogen bonds networks were carried out. Thermodynamic aspects of sublimation processes of studied compounds were determined using temperature dependencies of vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation and structural parameters. Solubility and solvation processes of 1,2,4-thiadiazoles in buffer, n-hexane and n-octanol were studied within the wide range of temperature intervals and thermodynamic functions were calculated. Specific and nonspecific interactions of molecules resolved in crystals and solvents were estimated and compared. Distribution processes of compounds in buffer/n-octanol and buffer/n-hexane systems (describing different types of membranes) were investigated. Analysis of transfer processes of studied molecules from the buffer to n-octanol/n-hexane phases was carried out by the diagram method with evaluation of the enthalpic and entropic terms. This approach allows us to design drug molecules with optimal passive transport properties. Calcium-blocking properties of the substances were evaluated.

Novel isothiourea derivatives as potent neuroprotectors and cognition enhancers: synthesis, biological and physicochemical properties.

Various salts of 3-allyl-1,1-dibenzyl-2-ethyl-isothiourea, 1 (hydrochloride), 2 (hydrobromide), and 3 (hydroiodide), were synthesized. Ca-blocking properties of these salts were studied. Comparative analysis of the potentiating effects of 3 and cyclothiazide (CT) on transmembrane currents caused by kainic acid (KA) and glutamate in Purkinje neurons was performed. Analysis of the effects of 1 on N-methyl-D-aspartate (NMDA) receptors was performed on primary culture of heterogeneous neurons of rat cerebral cortex. Single crystals were grown and X-ray diffraction experiments solving the crystal structures of 1-3 were carried out. Analysis of conformations of the molecules in the crystal lattices was performed. The temperature dependencies of the solubility of 1-3 in water and n-octanol were obtained, and the thermodynamic parameters of solubility process were calculated. The effect of halogen atoms on the solubility was analyzed. The partitioning processes in the water-octanol system were studied at 25 degrees C. Chemical stability of tested salts in pH 7.4 phosphate buffer was determined at 25 degrees C.