A. N. Proshin

Neuroprotective and cognition-enhancing properties of MK-801 flexible analogs. Structure-activity relationships.

Abstract: Neuroprotective and biobehavioral properties of a series of novel open chain MK‐801 analogs, as well as their structure‐activity relationships have been investigated. Three groups of compounds were synthesized: monobenzylamino, benzhydrylamino, and dibenzylamino (DBA) analogs of MK‐801. It was revealed that DBA analogs exhibit pronounced glutamate‐induced calcium uptake blocking properties and anti‐NMDA activity. The hit compound of DBA series, NT‐1505, was investigated for its ability to improve cognition functions in animal model of Alzheimers disease type dementia, simulated by treating animals with cholinotoxin AF64A. The results from an active avoidance test and a Morris water maze test showed that experimental animals, treated additionally with NT‐1505, exhibited much better learning ability and memory than the control group (AF64A treated) and close to that of the vehicle group of animals (treated with physiological solution). Study of NT‐1505 influence on locomotor activity revealed that it is characterized by a spectrum of behavioral activity radically different from that of MK‐801, and in contrast to the latter one does not produce any psychotomimetic side effects in the therapeutically significant dose interval. The computed docking of MK‐801 and its flexible analogs on the NMDA receptor elucidated the crucial role of the hydrogen bond formed between these compounds and the asparagine residue for magnesium binding in the NMDA receptor. It was suggested that strong hydrophobic interaction between MK‐801 and the hydrophobic pocket in the NMDA receptor‐channel complex determines much higher irreversibility of this adduct compared to the intermediates formed between this site and Mg ions or flexible DBA derivatives, which might explain the absence of PCP‐like side effects of the latter compounds.

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.

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.

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.

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.

Concomitant manipulation of murine NMDA- and AMPA-receptors to produce pro-cognitive drug effects in mice

Bifunctional drug therapy targeting distinct receptor signalling systems can generate increased efficacy at lower concentrations compared to monofunctional therapy. Non-competitive blockade of the NMDA receptors or the potentiation of AMPA receptors is well documented to result in memory enhancement. Here, we compared the efficacy of the low-affinity NMDA receptor blocker memantine or the positive modulator of AMPA receptor QXX (in C57BL/6J at 1 or 5mg/kg, ip) with new derivatives of isothiourea (0.5-1 mg/kg, ip) that have bifunctional efficacy. Low-affinity NMDA blockade by these derivatives was achieved by introducing greater flexibility into the molecule, and AMPA receptor stimulation was produced by a sulfamide-containing derivative of isothiourea. Contextual learning was examined in a step-down avoidance task and extinction of contextual memory was studied in a fear-conditioning paradigm. Memantine enhanced contextual learning while QXX facilitated memory extinction; both drugs were effective at 5 mg/kg. The new derivative IPAC-5 elevated memory scores in both tasks at the dose 0.5 mg/kg and exhibited the lowest IC₅₀ values of NMDA receptor blockade and highest potency of AMPA receptor stimulation. Thus, among the new drugs tested, IPAC-5 replicated the properties of memantine and QXX in one administration with increased potency. Our data suggest that a concomitant manipulation of NMDA- and AMPA-receptors results in pro-cognitive effects and supports the concept bifunctional drug therapy as a promising strategy to replace monofunctional therapies with greater efficacy and improved compliance.

5-Amino-3-(2-aminopropyl)-1,2,4-thiadiazoles as the basis of hybrid multifunctional compounds

An approach to the synthesis of hybrid multifunctional compounds starting from 1,2,4-thiadiazoles containing an amino group in the side chain was developed.

Novel 1,2,4-thiadiazoles with an NO-producing fragment

311 At present, the design of hybrid multitarget phar maceuticals by introduction of nitric oxide producing fragment in a molecule of known medicinal agent is one of promising directions of medicinal chemistry [1]. Nitric oxide (NO) is an endogenous signaling molecule with a wide spectrum of biological activity and plays an important role in nervous system func tioning. Therefore, NO donors are used for the treat ment of different neurodegenerative disorders, Alzhe imer disease including [2]. The introduction of an NO producing fragment into known pharmaceuti cals, for example, NO donor drugs based on Tacrine, is also applied for this purpose [3]. One of promising approaches to search for phar maceuticals for the treatment of Alzheimer disease and related neurodegenerative disorders is the search for blocking agents for glutamate mediated influx of Ca2+ [4]. In recent time, molecules containing a thiadiazole pharmacophore fragment and showing interesting pharmacological properties, including neuroprotec tive ones, attract much attention as promising phar maceuticals [5].