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Herein we present the design and the synthesis of novel substituted coumarin– benzimidazole/benzothiazole hybrids bearing a cyclic amidino group on the benzazole core as biologically active agents. All prepared compounds were evaluated for their in vitro antiviral and antioxidative activity as well as for their in vitro antiproliferative activity against a panel of several human cancer cell lines. Coumarin– benzimidazole hybrid 10 (EC50 9.0–43.8 μM) displayed the most promising broad spectrum antiviral activity, while two other coumarin– benzimidazole hybrids 13 and 14 showed the highest antioxidative capacity in the ABTS assay, superior to the reference standard BHT (IC50 0.17 and 0.11 mM, respectively). Computational analysis supported these results and demonstrated that these hybrids benefit from the high C–H hydrogen atom releasing tendency of the cationic amidine unit, and the pronounced ease with which they can liberate an electron, promoted by the electron- donating diethylamine group on the coumarin core. The coumarin ring substitution at position 7 with a N, N-diethylamino group also caused a significant enhancement of the antiproliferative activity, with the most active compounds being derivatives with a 2-imidazolinyl amidine group 13 (IC50 0.3– 1.9 μM) and benzothiazole derivative with a hexacyclic amidine group 18 (IC50 1.3–2.0 μM).

Halohydrin dehalogenases (HHDHs) possess an unnatural activity of introducing functionalities such as N3, CN, NO2 etc., into a molecule through the ring-opening reaction of epoxides. The enantioselectivity of HHDHs is substrate-dependent and not always high enough for synthetic applications. B-group of HHDHs has been neglected in the past, due to observed low enantioselectivity based on performance on a relatively limited number of substrates. Extensive screening of substrates on HheB2 from Mycobacterium sp. GP1 and HheB from Corynebacterium sp. N-1074 was performed. Several highly enantioselective reactions were discovered (E>200), with HheB showing higher enantioselectivity and activity toward larger panel of substrates compared to HheB2. Enzymes HheB and HheB2 are highly homologous ; they differ by only 4 residues. By using site-directed mutagenesis, residues 120 and 125 were found to be responsible for higher enantioselectivity of HheB compared to HheB2. Computational analysis supported experiments and provided evidence that kinetic and thermodynamic parameters of reactions within HheB enzymes are crucial in determining the observed enantioselectivities. Due to remarkable activity and enantioselectivity, B-group HHDHs emerged as a catalyst of choice for the synthesis of bulky tertiary alcohols, as shown in this work.

Seven complexes, [Ni(NCS)2(isn)2(H2O)2]·2H2O (1), [Ni(NCS)2(isn)2(H2O)2] (2), [Ni(NCS)2(isn)3(H2O)]·2.5H2O (3), [Ni(NCS)2(isn)3(H2O)]·3[Ni(NCS)2(isn)4]·9H2O (4), [Ni(NCS)2(isn)4]·3H2O (5), [Ni(NCS)2(isn)4]·2(isn) (6) and [Ni(NCS)2(isn)4]·1.25H2O (7), of Ni(II) thiocyanate with isonicotinamide (isn = pyridine- 4-carboxamide) and water as ligands of biological importance were prepared in aqueous solutions through crystal screening by variation of the isonicotinamide concentration. They were characterized by the single-crystal X-ray diffraction method and DFT calculations, while 1–6 were characterized also by NMR and IR spectroscopy and elemental and thermal analyses. In all complexes, the nickel atom is octahedrally coordinated with two thiocyanate N atoms but with different number of isonicotinamide N and water O atoms. The R46(12) and R46(16) hexamers were found in 1, R24(8) tetramer and R22(8) dimer in 2, while very complex hydrogen bonding ring patterns R24(8), R22(10), R34(14) and R610(24) were observed in 3. In 4, R46(16) and R66(20) hexamers were formed as well as typical head-to-head amide– amide hydrogen bond R22(8) dimers in a combination with two R34(10) tetramers. R24(8) cyclic water tetramers linked in zigzag hydrogen bonded chains, carboxamide catemer C(4) chains with the R68(24) ring and two fused rings R23(12) and R22(16) were found in 5. A 2D corrugated sheet network in the (002) planes with a combination of R44(16), R46(16), R66(24) and R68(24) rings were formed in 6. DFT calculations revealed that altered metal complex stoichiometries originate in different ligand affinities towards nickel, isn > SCN− > H2O. Only neutral complexes were investigated so the nickel : thiocyanate ratio was always 1 : 2 while the concentration of isonicotinamide strongly influenced the number of coordinated isn ligands. The final 3D crystal structures emerged as a compromise between the nucleation process, reactant ratios, ligand affinities and intermolecular interactions in the crystal packing.

Nicotinamide adenine dinucleotide (NAD) coenzyme is a vital part of numerous enzymatic reactions that are involved in all major biological processes from energy metabolism to cell survival. Accordingly, it is used in a great number of biocatalytic reactions, as analytical biosensors, and in test kits for diagnostic and analytical purposes. This coenzyme is unstable in aqueous solutions, meaning that the minimization of its degradation during storage, assays, and enzyme- catalysed oxidoreductive reactions is of high importance. Herein, we report on the stabilisation of NAD (NAD+ as oxidised, and NADH as its reduced form) by deep eutectic solvents (DES), an emerging class of solvents that offer numerous remarkable advantages such as high tunability, and capability to stabilise a wide range of commercially important compounds of natural origin. Preliminary DES screening revealed that out of 7 candidates, choline chloride:urea (ChCl:U) shows the best ability to stabilise both NAD forms. Computational analysis (quantum chemical calculations and molecular dynamics simulations) provided a deeper insight into possible mechanisms behind the observed stabilisation, by identifying geometries and the solvation structure of NAD coenzymes in these solvents, and analysing their possible degradation pathways. Finally, prolonged NAD stability (up to 50 days) in ChCl:U is detected and the system is further confirmed as a stable working NAD solution in a model enzymatic assay.

Proučavanje procesa stereoizomerizacije od iznimne je važnosti u farmaceutskoj kemiji i biomedicini. Različiti izomeri mogu pokazivati značajne razlike u interakciji s biološkim makromolekulama, što može dovesti do razlika i u njihovim farmakokinetičkim i farmakodinamičkim svojstvima te, u konačnici, u terapijskim i neželjenim učincima. Iako postoji velik broj primjera koji svjedoče o važnosti stereokemije, u ovome radu dan je pregled nekoliko najznačajnijih i najreprezentativnijih slučajeva u farmaciji., Investigation of the stereoisomerisation process is of the utmost importance in pharmaceutical chemistry and biomedicine. Different isomers can exhibit significant differences when interacting with biological macromolecules, which may result in their modified pharmacokinetic and pharmacodynamic properties, thereby showing different therapeutic and undesirable effects. Although there are numerous examples illustrating the importance of stereochemistry, this article presents an overview of the most significant and representative cases in pharmacy.

The labile β-lactam ring of penicillins and other β-lactam antibiotics is characterized by its pronounced susceptibility to various nucleophiles, acid-base reagents, oxidizing agents or even solvents like water and alcohol. However, the major pathways of β-lactams degradation are similar, leading to various breakdown products. The discovery of cephalosporin and demonstration of its improved stability in aqueous solution, as well as its enhanced in vitro activity against penicillin-resistant organisms, were major breakthroughs in the development of β-lactam antibiotics. Although cephalosporins are more stable with respect to hydrolytic degradation than penicillins, they still experience a variety of chemical and enzymatic transformations. The present study was designed to gain insight into the kinetics of cephalosporin degradation, more specifically, ceftriaxone degradation at its therapeutic concentration. As ceftriaxone is one of the most frequently used parenteral antibiotics in treating specific infections, understanding of its degradation mechanisms at the concentration administered parenterally is essential for development of formulations containing this API. Therefore, our study was focused on obtaining information on the rates and mechanisms of ceftriaxone degradation in aqueous environment at the therapeutic concentration of 20 mg/mL. The study was directed towards obtaining kinetic information on the rates and mechanisms of ceftriaxone degradation in water, a mixture of water and deuterium oxide, and deuterium oxide itself at the neutral pH (range of 6.7 to 7.6). Specific ceftriaxone degradation products were observed in aged samples prepared in the examined solvents using HPLC and MS. By comparing the degradation rates in H2O and D2O, the observation of a kinetic isotope effect (KIE) provided some valuable insight as to the nature of the initial ceftriaxone degradation. This result, in combination with an investigation of the reaction order for the degradation using the method of initial rates, highlighted the important contribution of the formation of a previously unreported dimer-type species. Computational analysis was utilized to get a molecular insight into chemical processes governing the ceftriaxone degradation and to rationalize the stabilizing effect of replacing H2O with D2O. For that purpose, molecular dynamics simulations in both explicit solvents were carried out, together with a range of mechanistic DFT calculations to obtain the underlying kinetic and thermodynamic parameters of the most prevailing reactions in solution. In doing so, focus was on two dominant processes, (i) the opening of the β-lactam ring following the hydrolytic cleavage of its C–N amide bond, and (ii) the breaking of the C–S bond linking the triazine moiety with the rest of the structure.

Seven bis(2-picolyl)amine (bpa) and five iminodiacetamide (imda) ligands were prepared with different modifications in their side chain structure. The coordination properties of the ligands (L) were influenced by changes in the aliphatic linker length (C1, C2, or C3), amide group isomers and type of chiral terminal group. Complexation with Cu(II) afforded two polymorphs of a ML complex which features tetradentate coordination of a ligand with C2 linkers, while crystal structures of three trans–fac ML2 complexes with Cu (II) and Ni(II) show tridentate coordination of ligands with a C3 linker. The stoichiometry and stereochemistry of Zn(II) and Cu(II) complexes was further studied in solution by NMR and UV-Vis spectroscopy. DFT calculations gave an insight into the relative stability of isomers, as well as potential hydrogen bonding between two ligands in a ML2 complex. Furthermore, ML complexes of Cu(II) exhibited DNA cleavage activity.

A piperidine-catalyzed reaction between 3-formylchromone, 1,3-dimethyl barbituric acid, and ylidenemalononitriles is developed that offers chromonyl diene products in good yields. This cascade reaction proceeds

The synthesis of novel 6- chloro/morpholino/amino/-9-sulfonylpurine derivatives was accomplished in two ways, either (i) involving the condensation reaction of 6- chloropurine with commercially available arylsulfonyl chlorides in acetone and the presence of aqueous KOH at 0 °C, followed by the substitution of C6-chlorine with morpholine, or (ii) employing a reversed synthetic approach where 6-morpholinopurine and commercially available adenine bases were reacted with the corresponding alkyl, 2-arylethene and arylsulfonyl chlorides giving the N9 sulfonylated products, the latter particularly used where prior nonselective sulfonylation was observed. In both approaches, the sulfonylation reaction occurred regioselectively at the purine N9 position lacking any concurrent N7 derivatives, except in the case of a smaller methyl substituent on SO2 and the free amino group at C6 of the purine ring. The tautomeric features of initial N9 unsubstituted purines, as well as stability trends among the prepared N-9-sulfonylpurine derivates, were investigated using DFT calculations with an important conclusion that electron-donating C6 substituents are beneficial for the synthesis as they both promote the predominance of the desired N9 tautomers and help to assure the stability of the final products. The newly synthesized 6- morpholino and 6-amino-9-sulfonylpurine derivatives showed antiproliferative activity on human carcinoma, lymphoma, and leukemia cells. Among the tested compounds, 6-morpholino 17 and 6- amino 22 derivatives, with trans-β-styrenesulfonyl group attached at the N9 position of purine, proved to be the most effective antiproliferative agents, causing accumulation of leukemia cells in subG0 cell cycle phase.

Unlike the closely related and widely investigated amidino-substituted benzimidazoles and benzothiazoles with a range of demonstrated biological activities, the matching benzoxazole analogues still remain a largely understudied and not systematically evaluated class of compounds. To address this challenge, we utilized the Pinner reaction to convert isomeric cyano-substituted 2- aminophenols into their amidine derivatives, which were isolated as hydrochlorides and/or zwitterions, and whose structure was confirmed by single crystal X-ray diffraction. The key step during the Pinner synthesis of the crucial carboximidate intermediates was characterized through mechanistic DFT calculations, with the obtained kinetic and thermodynamic parameters indicating full agreement with the experimental observations. The obtained amidines were subjected to a condensation reaction with aryl carboxylic acids that allowed the synthesis of a new library of 5- and 6-amidino substituted 2- arylbenzoxazoles. Their antiproliferative features against four human tumour cell lines (SW620, HepG2, CFPAC-1, HeLa) revealed sub- micromolar activities on SW620 for several cyclic amidino 2- naphthyl benzoxazoles, thus demonstrating the usefulness of the proposed synthetic strategy and promoting amidino substituted 2-aminophenols as important building blocks towards biologically active systems.

Substituted tetrahedranes offer exceptional carbon bases with the gas‐phase proton affinities (PAs) up to 356 kcal mol−1, due to the strain‐induced ring opening upon protonation. Additional tetrahedrane moieties exert a dramatic basicity amplification to PAs reaching 600 kcal mol−1, being the strongest organic superbases reported, clearly surpassing the proposed limit of achievable basicities (Angew. Chem. Int. Ed. 2015, 54, 9262). However, because protonation/deprotonation of these compounds is not reversible, PAs of the opened‐cage isomers were calculated which were lower than the basiciy limit.

Calculated proton affinities (PAs) and gas phase basicities (GPBs) are reported for diamantane (C

Histamine levels in the human brain are controlled by rather peculiar metabolic pathways. In the first step, histamine is enzymatically methylated at its imidazole

A regioselective [3+2] cycloaddition (32CA) reaction to synthesize unsymmetric spiro-barbituric pyrazolines containing a chromone or phenolic pyrazole moiety was achieved, providing good to excellent yields. These rigid spiro-barbiturates exhibited good functional group tolerance, and they remained stable in the presence of an excessive amount of hydrazine. Spectral data and DFT calculations demonstrated the predominance of restricted rotation about a single C–C bond over annular tautomerism. The proposed one-pot sequential synthetic strategy allows for the efficient regio- and chemoselective preparation of new spiro-barbiturate scaffolds containing a locked phenolic pyrazole moiety, offering a much broader scope for obtaining stable drug functionalities under green conditions.

A piperidine-catalyzed reaction between 3- formylchromone, 1, 3-dimethyl barbituric acid, and ylidenemalononitriles is developed that offers chromonyl diene products in good yields. This cascade reaction proceeds via the insertion of ylidenemalononitriles between the Knoevenagel adduct obtained from 3-formylchromone and 1, 3- dimethylbarbituric acid, where the pyrimidine- based enaminone is integrated with the chromone through the central diene linker. Similarly, introducing pyrimidine-based enaminone into the terminal part of the chromonyl diene scaffold gave an equilibrium mixture of rotational isomers in DMSO, which could be separated and isolated by crystallization. The computational analysis confirmed the role of barbiturate in directing the type of final chromonyl diene via kinetic or thermodynamic control. Moreover, computations revealed that one of these species, observed in the NMR spectra, is produced by the bond cleavage in the spirocyclic intermediate.

We describe the synthesis, spectroscopic characterization and computational analysis of the protonation equilibria of several newly designed imidazo[4, 5-b]pyridine derived iminocoumarins to confirm their potential as pH sensing molecules in different solvents. The photophysical characterization and acid/base properties of these chromophores have been carried out in several polar and non-polar organic solvents as well as buffered aqueous solution with different pH values using UV–Vis and fluorescence spectroscopies. Obtained results revealed that both the solvent polarity and the electronic nature of substituents placed at the iminocoumarin and imidazo[4, 5-b]pyridine cores significantly influence spectral responses of studied systems. An excellent agreement in experimentally measured and computationally determined pKa values and electronic excitations suggests that all systems are monoprotonated cations at neutral pH, while their transition to diprotonated forms occurs at pH values between 3.4 and 4.4, whereas they get reverted to neutral unionized molecules between 10.4 and 13.7. These small differences in narrow ranges of borderline pH values are predominantly brought about by variations in a single substituent on the iminocoumarin core, thereby allowing a simple strategy to further modify the observed sensing features and easily tune them for a specific application.

Histamine levels in the human brain are controlled by rather peculiar metabolic pathways. In the first step, histamine is enzymatically methylated at its imidazole Nτ atom, and the produced N-methylhistamine undergoes an oxidative deamination catalyzed by monoamine oxidase B (MAO-B), as is common with other monoaminergic neurotransmitters and neuromodulators of the central nervous system. The fact that histamine requires such a conversion prior to oxidative deamination is intriguing since MAO-B is known to be relatively promiscuous towards monoaminergic substrates; its in-vitro oxidation of N-methylhistamine is about 10 times faster than that for histamine, yet this rather subtle difference appears to be governing the decomposition pathway. This work clarifies the MAO-B selectivity toward histamine and N-methylhistamine by multiscale simulations of the rate-limiting hydride abstraction step for both compounds in the gas phase, in aqueous solution, and in the enzyme, using the established empirical valence bond methodology, assisted by gas-phase density functional theory (DFT) calculations. The computed barriers are in very good agreement with experimental kinetic data, especially for relative trends among systems, thereby reproducing the observed MAO-B selectivity. Simulations clearly demonstrate that solvation effects govern the reactivity, both in aqueous solution as well as in the enzyme although with an opposing effect on the free energy barrier. In the aqueous solution, the transition-state structure involving histamine is better solvated than its methylated analog, leading to a lower barrier for histamine oxidation. In the enzyme, the higher hydrophobicity of N-methylhistamine results in a decreased number of water molecules at the active side, leading to decreased dielectric shielding of the preorganized catalytic electrostatic environment provided by the enzyme. This renders the catalytic environment more efficient for N-methylhistamine, giving rise to a lower barrier relative to histamine. In addition, the transition state involving N-methylhistamine appears to be stabilized by the surrounding nonpolar residues to a larger extent than with unsubstituted histamine, contributing to a lower barrier with the former.

Calculated proton affinities (PAs) and gas phase basicities (GPBs) are reported for diamantane (C14H20), triamantane (C18H24), ‘globular and planar’ isomers of tetramantane (C22H28) and pentamantane (C26H32), and for one ‘globular’ isomer of each of the larger diamondoid molecules: C51H58, C78H72, C102H90, and C131H116. Assuming CxHy as the parent diamondoid molecule, we calculated PA and GPB values for a variety of CxHy+1+ isomers, as well as for the reaction CxHy + H+ yielding CxHy−1+ + H2(g) ; the latter is slightly favored based on GPB values for diamantane through pentamantane, but less favored compared to certain CxHy+1+ isomers of C51H58, C102H90, and C131H116. Indeed, the GPB values of C51H58, C102H90, and C131H116 classifiy them as ‘superbases’. Calculations that had the initial location of the proton in an interstitial site inside the diamondoid molecule always showed the H having moved to the outside of the diamondoid molecule ; for this reason, we focused on testing a variety of initial configurations with the proton placed in an initial position on the surface. Additional protons were added to determine the limiting number that could be, per these calculations, taken up by the diamondoid molecules and the maximum number of protons are shown in parentheses: C14H20(2), C18H24(3), C22H28(3), C26H32(3), C51H58(4). Bader charge distributions obtained for CxHy+1+ isomers (for diamantane through pentamantane) suggest that the positive charge is essentially completely delocalized over all the H atoms. NMR spectra were calculated for different isomers of C14H19+, and compared to the published NMR spectrum for when diamantane was mixed with magic acid and H2(g) was produced.

Although COVID-19 has been primarily associated with pneumonia, recent data show that its causative agent, the SARS-CoV-2 coronavirus, can infect many vital organs beyond the lungs, including the heart, kidneys and the brain. The literature agrees that COVID-19 is likely to have long-term mental health effects on infected individuals, which signifies a need to understand the role of the virus in the pathophysiology of brain disorders that is currently unknown and widely debated. Our docking and molecular dynamic simulations show that the affinity of the spike protein from the wild type (WT) and the South African B.1.351 (SA) variant towards the MAO enzymes is comparable to that for its ACE2 receptor. This allows for the WT/SA…MAO complex formation, which changes MAO affinities for their neurotransmitter substrates, thus consequently impacting the rates of their metabolic conversion and misbalancing their levels. Knowing that this fine regulation is strongly linked with the etiology of various brain pathologies, these results are the first to highlight the possibility that the interference with the brain MAO catalytic activity is responsible for the increased neurodegenerative illnesses following a COVID-19 infection, thus placing a neurobiological link between these two conditions in the spotlight. Since the obtained insight suggests that a more contagious SA variant causes even larger disturbances, and with new and more problematic strains likely emerging in the near future, we firmly advise that the presented prospect of the SARS-CoV-2 induced neurological complications should not be ignored, but rather requires further clinical investigations to achieve an early diagnosis and timely therapeutic interventions.TABLE OF CONTENTS ENTRYDocking and molecular dynamic simulations highlight the possibility that the interference with the brain monoamine oxidase (MAO) catalytic activity is responsible for the increased neurodegenerative illnesses following a COVID-19 infection.

In the reaction of purines with ferrocenoyl chloride in dimethylformamide (DMF), a regioselective acylation occurred. The two products have been isolated and, according to detailed NMR analysis, identified as N7- and N9-ferrocenoylated isomers. In a more polar solvent, for example, in dimethylsulfoxide (DMSO), the two isomers interconvert to each other. The N7/N9 isomerization was followed by 1H NMR spectroscopy, until dynamic equilibrium was reached. Both kinetics and thermodynamics of the transacylation process are governed by a C6-substituent on the purine ring (R = NH2, Me, NHBz, OBz). The observed rate constant for the N7/N9-isomerization in the adenine system (R = NH2) is kobs = 0.3668 h-1, whereas the corresponding process in the C6-benzyloxypurine is 56 times slower. By use of density functional theory calculations and molecular dynamics simulations, several reaction pathways were considered and explored. Only the reaction mechanism involving DMSO as a nucleophilic reactant is in harmony with the experimental kinetic data. The calculated barrier (ΔG⧧ = 107.9 kJ/mol; at the M06L/6-311+G(d,p)/SDD level of theory) for this SN2-like reaction in the adenine system agrees well with the experimental value of 102.7 kJ/mol. No isomerization was detected in other organic solvents, for example, acetonitrile, N,N-dimethylformamide, or acetone, which indicated the exceptional nucleophilicity of DMSO. Our results raise a warning when treating or dissolving acylated purines in DMSO as they are prone to isomerization. We observed that the N7/N9-group transfer was specific not only for the organometallic moiety only, but for other acyl groups in purines as well. The relevance of this isomerization may be expected for a series of nucleobases and heterocyclic systems in general.

© 2022 Elsevier Masson SAS. All rights reserved., Malaria remains one of the major health problems worldwide. The lack of an effective vaccine and the increasing resistance of Plasmodium to the approved antimalarial drugs demands the development of novel antiplasmodial agents that can effectively prevent and/or treat this disease. Harmiquins represent hybrids that combine two moieties with different mechanisms of antiplasmodial activity in one molecule, i.e., a chloroquine (CQ) scaffold, known to inhibit heme polymerization and a β-carboline ring capable of binding to P. falciparum heat shock protein 90 (PfHsp90). Here we present their synthesis, evaluation of biological activity and potential mechanism of action. The synthesized hybrids differed in the type of linker employed (triazole ring or amide bond) and in the position of the substitution on the β-carboline core of harmine. The antiplasmodial activity of harmiquins was evaluated against the erythrocytic stage of the Plasmodium life cycle, and their cytotoxic effect was tested on HepG2 cells. The results showed that harmiquins exerted remarkable activity against both CQ-sensitive (Pf3D7) and CQ-resistant (PfDd2, PfK1, and Pf7G8). P. falciparum strains. The most active compound, harmiquine 32, displayed single-digit nanomolar IC50 value against Pf3D7 (IC50 = 2.0 ± 0.3 nM). Importantly, it also showed significantly higher activity than CQ against the resistant Plasmodium strains and had a very high selectivity index (4450). Harmiquins may act through the inhibition of heme polymerization and binding to the ATP binding site of the PfHsp90, which would explain their increased activity against the CQ-resistant Plasmodium strains. These results establish harmiquins as valuable antiplasmodial hits for future optimization., The authors acknowledge the financial support by the Croatian Science Foundation (research project UIP-2017-05-5160), University of Zagreb (support for 2020), and Fundação para a Ciência e Tecnologia (grant 02/SAICT/2017/29550). This work has been supported in part by project Strengthening the scientific research and innovation capacities of the Faculty of Pharmacy and Biochemistry, University of Zagreb (FarmInova; project number KK.01.1.1.02.0021), financed from the European Regional Development Fund, Operational Program Competitiveness and Cohesion for the period 2014–2020. T.T. and R.V. would like to thank the Zagreb University Computing Centre (SRCE) for granting computational resources on the ISABELLA cluster. T.T. and R.V. would like to thank the Zagreb University Computing Centre (SRCE) for granting computational resources on the ISABELLA cluster.

We present the design, synthesis and biological activity of novel N-substituted benzimidazole based acrylonitriles as potential tubulin polymerization inhibitors. Their synthesis was achieved using classical linear organic and microwave assisted techniques, starting from aromatic aldehydes and N-substituted-2-cyanomethylbenzimidazoles. All newly prepared compounds were tested for their antiproliferative activity in vitro on eight human cancer cell lines and one reference non-cancerous assay. N,N-dimethylamino substituted acrylonitriles 30 and 41, bearing N-isobutyl and cyano substituents placed on the benzimidazole nuclei, showed strong and selective antiproliferative activity in the submicromolar range of inhibitory concentrations (IC50 0.2-0.6 μM), while being significantly less toxic than reference systems docetaxel and staurosporine, thus promoting them as lead compounds. Mechanism of action studies demonstrated that two most active compounds inhibited tubulin polymerization. Computational analysis confirmed the suitability of the employed benzimidazole-acrylonitrile skeleton for the binding within the colchicine binding site in tubulin, thus rationalizing the observed antitumor activities, and demonstrated that E-isomers are active substances. It also provided structural determinants affecting both the binding position and the matching affinities, identifying the attached NMe2 group as the most dominant in promoting the binding, which allows ligands to optimize favourable cation∙∙∙π and hydrogen bonding interactions with Lys352. ispartof: EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY vol:211 ispartof: location:France status: published

Spontaneous S-alkylation of methimazole (1) with 1,2-dichloroethane (DCE) into 1,2-bis[(1-methyl-1H-imidazole-2-yl)thio]ethane (2), that we have described recently, opened the question about its formation pathway(s). Results of the synthetic, NMR spectroscopic, crystallographic and computational studies suggest that, under given conditions, 2 is obtained by direct attack of 1 on the chloroethyl derivative 2-[(chloroethyl)thio]-1-methyl-1H-imidazole (3), rather than through the isolated stable thiiranium ion isomer, i.e., 7-methyl-2H, 3H, 7H-imidazo[2,1-b]thiazol-4-ium chloride (4a, orthorhombic, space group Pnma), or in analogy with similar reactions, through postulated, but unproven intermediate thiiranium ion 5. Furthermore, in the reaction with 1, 4a prefers isomerization to the N-chloroethyl derivative, 1-chloroethyl-2,3-dihydro-3-methyl-1H-imidazole-2-thione (7), rather than alkylation to 2, while 7 further reacts with 1 to form 3-methyl-1-[(1-methyl-imidazole-2-yl)thioethyl]-1H-imidazole-2-thione (8, monoclinic, space group P 21/c). Additionally, during the isomerization of 3, the postulated intermediate thiiranium ion 5 was not detected by chromatographic and spectroscopic methods, nor by trapping with AgBF4. However, trapping resulted in the formation of the silver complex of compound 3, i.e., bis-{2-[(chloroethyl)thio]-1-methyl-1H-imidazole}-silver(I)tetrafluoroborate (6, monoclinic, space group P 21/c), which cyclized upon heating at 80 °C to 7-methyl-2H, 3H, 7H-imidazo[2,1-b]thiazol-4-ium tetrafluoroborate (4b, monoclinic, space group P 21/c). Finally, we observed thermal isomerization of both 2 and 2,3-dihydro-3-methyl-1-[(1-methyl-1H-imidazole-2-yl)thioethyl]-1H-imidazole-2-thione (8), into 1,2-bis(2,3-dihydro-3-methyl-1H-imidazole-2-thione-1-yl)ethane (9), which confirmed their structures.

Density functional theory calculations elucidated the precise reaction mechanism for the conversion of diphenylacetylenes into benzonitriles involving the cleavage of the triple C≡C bond, with N-iodosuccinimide (NIS) as an oxidant and trimethylsilyl azide (TMSN3) as a nitrogen donor. The reaction requires six steps with the activation barrier ΔG‡ = 33.5 kcal mol−1 and a highly exergonic reaction free-energy ΔGR = −191.9 kcal mol−1 in MeCN. Reaction profiles agree with several experimental observations, offering evidence for the formation of molecular I2, interpreting the necessity to increase the temperature to finalize the reaction, and revealing thermodynamic aspects allowing higher yields for alkynes with para-electron-donating groups. In addition, the proposed mechanism indicates usefulness of this concept for both internal and terminal alkynes, eliminates the option to replace NIS by its Cl- or Br-analogues, and strongly promotes NaN3 as an alternative to TMSN3. Lastly, our results advise increasing the solvent polarity as another route to advance this metal-free strategy towards more efficient processes.

Two structurally different 1D cobalt(II) coordination polymers with 4, 4’‐bipyridine (4, 4’‐bpy) and 2‐chloronicotinate (2‐Cl‐nic) or 5‐ bromonicotinate (5‐Br‐nic), namely {; ; ; ; [Co(2‐ Cl‐ nic)2(4, 4’‐bpy)(H2O)2] ⋅ 4H2O}; ; ; ; n (1) and {; ; ; ; [Co(4, 4’‐bpy)(H2O)4] [Co(5‐Br‐ nic)4(H2O)2] ⋅ 4, 4’‐bpy ⋅ 2H2O}; ; ; ; n (2), were prepared under the same experimental conditions. The cobalt(II) ions in 1 are bridged by 4, 4’‐bipyridine ligands into a 1D polymeric chain, each cobalt(II) ion being coordinated with two O‐ monodentate 2‐ chloronicotinate ligands and two water molecules as well, while 2 consists of a complex cation {; ; ; ; [Co(4, 4’‐bpy)(H2O)4]2+}; ; ; ; n, in which cobalt(II) ions are bridged by 4, 4’‐ bipyridine ligands into a 1D polymeric chain, and a complex anion [Co(5‐Br‐ nic)4(H2O)2]2−, in which cobalt(II) ion is coordinated with four 5‐bromonicotinate ligands (two of them being O‐ monodentate and the other two are N‐ monodentate) and two water molecules. DFT calculations revealed a correlation between the halosubstituent (chlorine or bromine) positions in the employed nicotinate ligands and the cobalt(II) coordination environments in the obtained coordination polymers, being responsible for their different structural types.

We used classical linear and microwave-assisted synthesis methods to prepare novel N-substituted, benzimidazole-derived acrylonitriles with antiproliferative activity against several cancer cells in vitro. The most potent systems showed pronounced activity against all tested hematological cancer cell lines, with favorable selectivity towards normal cells. The selection of lead compounds was also tested in vitro for tubulin polymerization inhibition as a possible mechanism of biological action. A combination of docking and molecular dynamics simulations confirmed the suitability of the employed organic skeleton for the design of antitumor drugs and demonstrated that their biological activity relies on binding to the colchicine binding site in tubulin. In addition, it also underlined that higher tubulin affinities are linked with (i) bulkier alkyl and aryl moieties on the benzimidazole nitrogen and (ii) electron-donating substituents on the phenyl group that allow deeper entrance into the hydrophobic pocket within the tubulin's β-subunit, consisting of Leu255, Leu248, Met259, Ala354, and Ile378 residues. ispartof: PHARMACEUTICALS vol:14 issue:10 ispartof: location:Switzerland status: published

The enzyme-catalyzed degradation of the biogenic amine serotonin is an essential regulatory mechanism of its level in the human organism. In particular, monoamine oxidase A (MAO A) is an important flavoenzyme involved in the metabolism of monoamine neurotransmitters. Despite extensive research efforts, neither the catalytic nor the inhibition mechanisms of MAO enzymes are currently fully understood. In this article, we present the quantum mechanics/molecular mechanics simulation of the rate-limiting step for the serotonin decomposition, which consists of hydride transfer from the serotonin methylene group to the N5 atom of the flavin moiety. Free-energy profiles of the reaction were computed by the empirical valence bond method. Apart from the enzymatic environment, the reference reaction in the gas phase was also simulated, facilitating the estimation of the catalytic effect of the enzyme. The calculated barrier for the enzyme-catalyzed reaction of 14.82 +/- 0.81 kcal mol(-1) is in good agreement with the experimental value of 16.0 kcal mol(-1), which provides strong evidence for the validity of the proposed hydride-transfer mechanism. Together with additional experimental and computational work, the results presented herein contribute to a deeper understanding of the catalytic mechanism of MAO A and flavoenzymes in general, and in the long run, they should pave the way toward applications in neuropsychiatry.

Quinolino[7,8

The pyridinium oximes are known esterolytic agents, usually classified in the literature as catalysts, which mimic the catalytic mode of hydrolases. Herein, we combined kinetic and computational studies of the pyridinium-4-oxime-mediated acetylthiocholine (AcSCh+) hydrolysis to provide novel insights into their potential catalytic activity. The N-methyl- and N-benzylpyridinium-4-oximes have been tested as oximolytic agents toward the AcSCh+, while the newly synthesized O-acetyl-N-methylpyridinium-4-oxime iodide was employed for studying the consecutive hydrolytic reaction. The relevance of the AcSCh+ hydrolysis as a competitive reaction to AcSCh+ oximolysis was also investigated. The reactions were independently studied spectrophotometrically and rate constants, koxime, kw and kOH, were evaluated over a convenient pH-range at I = 0.1 M and 25 &deg, C. The catalytic action of pyridinium-4-oximes comprises two successive stages, acetylation (oximolysis) and deacetylation stage (pyridinium-4-oxime-ester hydrolysis), the latter being crucial for understanding the whole catalytic cycle. The complete mechanism is presented by the free energy reaction profiles obtained with (CPCM)/M06&ndash, 2X/6&ndash, 311++G(2df,2pd)//(CPCM)/M06&ndash, 31+G(d) computational model. The comparison of the observed rates of AcSCh+ oximolytic cleavage and both competitive AcSCh+ and consecutive pyridinium-4-oxime-ester hydrolytic cleavage revealed that the pyridinium-4-oximes cannot be classified as non-enzyme catalyst of the AcSCh+ hydrolysis but as the very effective esterolytic agents.