Electron-attracting Substituents Research Articles

Synthesis, DFT Molecular Geometry and Anticancer Activity of Symmetrical 2,2'-(2-Oxo-1H-benzo[d]imidazole-1,3(2H)-diyl) Diacetate and Its Arylideneacetohydrazide Derivatives.

To identify new candidate anticancer compounds, we here report the synthesis of benzimidazole derivatives: diethyl 2,2′-(2-oxo-1H-benzo[d]imidazole-1,3(2H)-diyl) diacetate and its arylideneacetohydrazide derivatives, using ultrasonic irradiation and conventional heating. The compounds were confirmed by Nuclear magnetic resonance (NMR) (JEOL, Tokyo, Japan) and Fourier transform infrared spectroscopy (FTIR) spectroscopy (Thermoscientific, Waltham, MA, USA). The molecular structure and electronic properties of the studied compounds were predicted for the acetohydrazide hydrazones. These compounds exist as a mixture of configurational and conformational isomerism as well as amido-amidic acid tautomerism. The NMR spectral data proved the predominance of syn-E amido isomers. In addition, density functional theory (DFT) predicted stability in the gas phase and showed that syn-E amido isomers are the most stable in the presence of an electron donating group, while the anti-isomer is the most stable in the presence of electron-attracting substituents. The anticancer activity of these synthetic compounds 6a, 6b and 6c towards both colon cancer (HCT-116) and cervical cancer (HeLa) cells was examined by MTT assay and DAPI staining. The MTT assay revealed a strong antiproliferative effect against the cancer cells at low concentrations, and interestingly, no significant inhibitory action against the non-cancerous cell line, HEK-293. The IC50 values for HCT-116 were 29.5 + 4.53 µM, 57.9 + 7.01 µM and 40.6 + 5.42 µM for 6a, 6b, and 6c, respectively. The IC50 values for HeLa cells were 57.1 + 6.7 µM, 65.6 + 6.63 µM and 33.8 + 3.54 µM for 6a, 6b, and 6c, respectively. DAPI staining revealed that these synthesized benzimidazole derivatives caused apoptotic cell death in both the colon and cervical cancer cells. Thus, these synthetic compounds demonstrate encouraging anticancer activity as well as being safe for normal human cells, making them attractive candidates as anticancer agents.

Hammett Correlation in the Accelerated Formation of 2,3-Diphenylquinoxalines in Nebulizer Microdroplets.

The accelerated formation of 2,3-diphenylquinoxalines in microdroplets generated in a nebulizer has been investigated by competition experiments in which equimolar quantities of 1,2-phenylenediamine, C6H4(NH2)2, and a 4-substituted homologue, XC6H3(NH2)2 [X = F, Cl, Br, CH3, CH3O, CO2CH3, CF3, CN or NO2], or a 4,5-disubstituted homologue, X2C6H2(NH2)2 [X = F, Cl, Br, or CH3], compete to condense with benzil, (C6H5CO)2. Electron-donating substituents (X = CH3 and CH3O) accelerate the reaction; in contrast, electron-attracting substituents (X = F, Cl, Br and particularly CO2CH3, CN, CF3 and NO2) retard it. A structure–reactivity relationship in the form of a Hammett correlation has been found by analyzing the ratio of 2,3-diphenylquinoxaline and the corresponding substituted-2,3-diphenylquinoxaline, giving a ρ value of −0.96, thus confirming that the electron density in the aromatic ring of the phenylenediamine component is reduced in the rate-limiting step in this accelerated condensation. This correlation shows that the phenylenediamine acts as a nucleophile in the reaction.

The role of electron-attracting substituents and molecular stacking motifs in the charge transport of tetraazapyrene derivatives

The frontier orbital energies, charge transport properties and photophysical properties of TAPy derivatives were theoretically investigated by means of DFT.

Binding interactions of halogenated bisphenol A with mouse PPARα: In vitro investigation and molecular dynamics simulation

The binding of bisphenol A (BPA) and its halogenated derivatives (halogenated BPAs) to mouse peroxisome proliferator-activated receptor α ligand binding domain (mPPARα-LBD) was examined by a combination of in vitro investigation and in silico simulation. Fluorescence polarization (FP) assay showed that halogenated BPAs could bind to mPPARα-LBD* as the affinity ligands. The calculated electrostatic potential (ESP) illustrated the different charge distributions of halogenated BPAs with altered halogenation patterns. As electron-attracting substituents, halogens decrease the positive electrostatic potential and thereby have a significant influence on the electrostatic interactions of halogenated BPAs with mPPARα-LBD*. The docking results elucidated that hydrophobic and hydrogen-bonding interactions may also contribute to stabilize the binding of the halogenated BPAs to their receptor molecule. Comparison of the calculated binding energies with the experimentally determined affinities yielded a good correlation (R2=0.6659) that could provide a rational basis for designing environmentally benign chemicals with reduced toxicities. This work can potentially be used for preliminary screening of halogenated BPAs.

English

Quinones are a family of bioactive compounds with known antibacterial, antiviral and antiparasitic activity. The capacity of quinoid compounds to accept electrons, due to electron-attracting (or donating) substituents at the quinone moiety, modulates their redox activity upon interaction with biological systems. Nine quinone derivate including three 2 - hydroxyl - 1, 4 - naphthoquinone; three 4,5 - and three 4,9 - naphthoquinone scaffolds, were synthesized and evaluated against 3D7 and Dd2 Plasmodium falciparum strains and evaluated the oxidative stress. Cell viability was determined MTT-related colorimetric assay (EZ4u; Biomedical, Austria). Selectivity of these compounds was evaluated by comparing in vitro, of cytotoxicity in human fibroblast and antimalarial activity in Plasmodium falciparum. Peripheral blood mononuclear cells and hemoglobin release from human erythrocytes were evaluated too. Antiplasmodial activity was evaluated by fluorometry methods. In addition, oxidized membrane protein in the malaria parasite was evaluated in vitro by derivatizatión, after treatment at IC50 values on P. falciparum Dd2 strain. Quinones showed IC50 values in the micromole range, selectivity indexes for quinones was variable, compounds 2 and 3 showed excellent selectivity. In vitro antiplasmodial activity was showed; this result is an incentive to continue synthesis and studying the quinoid compounds. Key words: Malaria, Quinones, Plasmodium falciparum.

A subset of N-substituted phenothiazines inhibits NADPH oxidases

NADPH oxidases (NOXs) constitute a family of enzymes generating reactive oxygen species (ROS) and are increasingly recognized as interesting drug targets. Here we investigated the effects of 10 phenothiazine compounds on NOX activity using an extensive panel of assays to measure production of ROS (Amplex red, WST-1, MCLA) and oxygen consumption. Striking differences between highly similar phenothiazines were observed. Two phenothiazines without N-substitution, including ML171, did not inhibit NOX enzymes, but showed assay interference. Introduction of an aliphatic amine chain on the N atom of the phenothiazine B ring (promazine) conferred inhibitory activity toward NOX2, NOX4, and NOX5 but not NOX1 and NOX3. Addition of an electron-attracting substituent in position 2 of the C ring extended the inhibitory activity to NOX1 and NOX3, with thioridazine being the most potent inhibitor. In contrast, the presence of a methylsulfoxide group at the same position (mesoridazine) entirely abolished NOX-inhibitory activity. A cell-free NOX2 assay suggested that inhibition by N-substituted phenothiazines was not due to competition with NADPH. A functional implication of NOX-inhibitory activity of thioridazine was demonstrated by its ability to block redox-dependent myofibroblast differentiation. Our results demonstrate that NOX-inhibitory activity is not a common feature of all antipsychotic phenothiazines and that substitution on the B-ring nitrogen is crucial for the activity, whereas that on the second position of the C ring modulates it. Our findings contribute to a better understanding of NOX pharmacology and might pave the path to discovery of more potent and selective NOX inhibitors.

Substituent-Modulated Affinities of Halobenzene Derivatives to the HIV-1 Integrase Recognition Site. Analyses of the Interaction Energies by Parallel Quantum Chemical and Polarizable Molecular Mechanics

The C-X bond of halobenzenes (X = Cl, Br) has a dual character, its electron density being depleted in its prolongation and built-up on its sides. We have recently considered three protein or nucleic acid recognition sites of halobenzenes and quantified the energy gains that either electron-attracting substituents or electron-donating ones contribute due to such a character (El Hage et al., paper in revision). Nonadditivity was found to impact the total interaction energies. We focus here on one recognition site, that of the HIV-1 integrase, in which the halobenzene ring of the drug elvitegravir is sandwiched between a guanine and a cytosine base. We perform energy-decomposition analyses of the ab initio quantum-chemistry (QC) binding energies of the parent halobenzene ring and its derivatives with this G-C base pair. In these complexes, the nonadditivity of ΔE could be traced back mostly to the polarization contribution Epol. In view of large-scale applications to the entirety of the complex formed between the integrase, the viral DNA, and the whole drug, the analyses were performed in parallel with a polarizable molecular mechanics method, SIBFA. This method could faithfully reproduce most features of the QC energies. This is due to its use of QC-derived distributed multipoles and polarizabilities, which enable us to account for both nonisotropy and nonadditivity.

Reactions of HNO with metal porphyrins: underscoring the biological relevance of HNO.

Azanone ((1)HNO, nitroxyl) shows interesting yet poorly understood chemical and biological effects. HNO has some overlapping properties with nitric oxide (NO), sharing its biological reactivity toward heme proteins, thiols, and oxygen. Despite this similarity, HNO and NO show significantly different pharmacological effects. The high reactivity of HNO means that studies must rely on the use of donor molecules such as trioxodinitrate (Angeli's salt). It has been suggested that azanone could be an intermediate in several reactions and that it may be an enzymatically produced signaling molecule. The inherent difficulty in detecting its presence unequivocally prevents evidence from yielding definite answers. On the other hand, metalloporphyrins are widely used as chemical models of heme proteins, providing us with invaluable tools for the study of the coordination chemistry of small molecules, like NO, CO, and O2. Studies with transition metal porphyrins have shown diverse mechanistic, kinetic, structural, and reactive aspects related to the formation of nitrosyl complexes. Porphyrins are also widely used in technical applications, especially when coupled to a surface, where they can be used as electrochemical gas sensors. Given their versatility, they have not escaped their role as key players in chemical studies involving HNO. This Account presents the research performed during the last 10 years in our group concerning azanone reactions with iron, manganese, and cobalt porphyrins. We begin by describing their HNO trapping capabilities, which result in formation of the corresponding nitrosyl complexes. Kinetic and mechanistic studies of these reactions show two alternative operating mechanisms: reaction of the metal center with HNO or with the donor. Moreover, we have also shown that azanone can be stabilized by coordination to iron porphyrins using electron-attracting substituents attached to the porphyrin ring, which balance the negatively charged NO¯. Second, we describe an electrochemical HNO sensing device based on the covalent attachment of a cobalt porphyrin to gold. A surface effect affects the redox potentials and allows discrimination between HNO and NO. The reaction with the former is fast, efficient, and selective, lacking spurious signals due to the presence of reactive nitrogen and oxygen species. The sensor is both biologically compatible and highly sensitive (nanomolar). This time-resolved detection allows kinetic analysis of reactions producing HNO. The sensor thus offers excellent opportunities to be used in experiments looking for HNO. As examples, we present studies concerning (a) HNO donation capabilities of new HNO donors as assessed by the sensor, (b) HNO detection as an intermediate in O atom abstraction to nitrite by phosphines, and (c) NO to HNO interconversion mediated by alcohols and thiols. Finally, we briefly discuss the key experiments required to demonstrate endogenous HNO formation to be done in the near future, involving the in vivo use of the HNO sensing device.

Theoretical studies on the reactivity of thiazole derivatives

The global and local quantum chemical reactivity descriptors of a series of thiazole derivatives substituted at 2, 4, and 5 positions with different groups including electron-donating and electron-withdrawing substituents, have been calculated at the B3LYP/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory. The substituents have been selected to cover a wide range of electronic effects. Considering the calculated Fukui functions, thiazole derivatives are found to be suitable nucleophilic sites in the gas-phase. For the most substituents, it was observed that the calculated Fukui function $${\mathbf{\it f}}_{k }^{ - }$$ values at the N-site are small in the case of electron-attracting substituents indicating a preferred N-site for hard reactions. In contrast, large $${\mathbf{\it f}}_{k }^{ - }$$ values in case of electron-releasing groups indicate a preferred N-site for soft reactions. These two local descriptors predicted the reactivity of the electron-rich thiazoles and sequence to be 2-substituted thiazoles >5-substituted thiazoles >4-substituted thiazoles, where reactivity toward electrophilic attack at the pyridine nitrogen atom is enhanced by electron-donor substituents elsewhere in the molecule, due to resonance effect.

Theoretical investigation on electronic, optical, and charge transport properties of 7,8,15,16-tetraazaterrylene and its derivatives with electron-attracting substituents

Electronic, optical, and charge transport properties of 7,8,15,16-tetraazaterrylene (TAT) and its three tetrasubstituted derivatives with the electron-attracting substituent have been studied theoretically using density functional theory (DFT) calculations coupled with the incoherent charge-hopping model. The calculated results reveal that the introduction of electron-attracting substituents, which does not break down the planar skeleton of TAT core, can stabilize the extended π-system and then improve the electron injection efficiency as well as the ambient stability. Based on TAT single-crystal structure, the predicted 3D-average electron mobility reaches as high as 3.404 × 10−2 cm2 V−1 s−1 at 300 K, but the hole mobility is only 6.516 × 10−4 cm2 V−1 s−1, which indicates that TAT single crystal may be a promising candidate as n-channel materials. The simulation of the angle-resolved electron mobility shows that TAT single-crystal possesses a remarkably anisotropic electron-conducting behaviour, and the maximum electron mobility is found to be along the crystallographic a-axis direction. In addition, the calculated reorganization energies and electronic coupling values show that the three TAT derivates (4F-TAT, 4Cl-TAT, and 4CN-TAT) designed in this work may well be potential n-channel materials with the high electron mobility. TD-DFT B3LYP/6-311G(d,p) calculations reveal the most relevant electronic transitions for the studied compounds present the π → π* character and the strongest absorption and emission peaks are dominated by the transitions of HOMO → LUMO. The introduction of electron-withdrawing substituents red-shifts the maximal absorption and emission wavelengths.

Synthesis and Spectral Studies on Heteroleptic Chelated Copper (II) Complexes of Diamine and Acetylacetonate

The infrared and electronic absorption spectra of a series of new heteroleptic chelated copper (II) complexes (Cu(diamine)(acac))X that encompass N,N'-1,6-bis(2-bromophenyl)-2,5-diazahexane (diamine), acetylacetonate (acac) and ClO , BPh , PF and BF (X) were studied. The IR, electronic absorption spectra and 4 4 6 4 - - - - the molar conductivity of the newly prepared complexes were presented and discussed. The molar conductivity in dichloromethane reveals a predominance of electrostatic interactions between (Cu(diamine)(acac)) entity + and anions, X that counterbalance the positive charge. The resulting complexes with local symmetry of CuO N - 2 2 attain a square-coplanar structure and exhibit the tendency for axial ligation, which is enhanced when an electron-attracting substituent is attached to the phenyl ring of diamine moiety. The tendency for axial ligation is particularly fulfilled when suitable nucleophiles (solvents) with different donor abilities exist, leading to solvatochromism. The solute-solvent interactions are revealed by shifts in the ligand field absorption spectra that are enhanced as the donor power of the solvent increases. Linear dependence of the ligand field absorption maximum on solvent donor number is generally observed.

Synthesis, cytotoxicity and calcium antagonist activity of novel imidazolyl derivatives of 1,8-acridinediones

A series of novel imidazolyl derivatives of fully and partially hydrogenated 1,8-acridinediones were synthesized and assessed for their cytotoxic activity on four different human cancer cell lines (HeLa, MCF-7, LS-180, and Raji cells). Although being inactive on LS-180 and Raji cell lines, the compounds showed weak to moderate anti-tumor activities on other cell lines and their IC50 ranged from 31.7 to more than 100 μM. Among the synthesized compounds 12b, 13b, 12c and 13c, bearing an electronattracting substituent on the imidazole ring, and 12f and 13f, with a benzyl substituent, showed higher activities. Furthermore, the calcium channel antagonist activity of the derivatives, an undesired effect when these compounds are used as anti-tumor agents, was much lower than that of Nifedipine, a reference antagonist. Imidazolyl derivatives of 1,8-acridinedione represent an interesting template, showing promising biological properties. Further investigation on this chemical scaffold could potentially lead to the discovery of cytotoxic agents with low calcium channel blocking activity.

ChemInform Abstract: Substituent Effects in the Solvolysis of p-(2-Substituted Cyclopropyl)- α-Methylbenzyl Chlorides.

The solvolysis rates of p-(cis- or trans-2-substituted cyclopropyl)-α-methylbenzyl chlorides including electron-donating and electron-attracting substituents relative to a hydrogen substituent were measured in 80% aqueous acetone. The trans isomers were more reactive than the corresponding cis derivatives where cyclopropyl and phenyl groups could not get a most favorable “bisected” conformation for the cyclopropyl group to release electrons to the benzene ring. The relative rates of the trans isomers at 45°C were best correlated by means of σm values with a ρ value of −3.14 and a correlation coefficient of 0.97, indicating that the cyclopropane ring was a poor transmitter of a resonance effect. The substituent effects were analyzed by means of the LSFE equation.

Substituent effect in the γ-position of acetylacetonate on the solvatochromic property of mixed-chelate copper(II) complexes consisting of diamine and acetylacetonate ligands

The infrared and electronic absorption spectra of a series of new mixed-chelate copper(II) complexes that encompass N, N-dibenzylethylenediamine (diamine) and 3-substituted derivatives of acetylacetone (x-acacH) were studied. The IR and electronic absorption spectra and the molar conductivity of the newly prepared complexes are presented and discussed. The molar conductivity in dichloromethane reveals a predominance of electrostatic interactions between [Cu(diamine)(x-acac)] + entity and perchlorate anions that counterbalance the positive charge. The resulting complexes with local symmetry of CuO 2N 2 attains a square-coplanar structure and exhibits the tendency for axial ligation, which is enhanced when an electron-attracting substituent is attached to the γ-position of acetylacetonate moiety. The tendency for axial ligation is particularly fulfilled when suitable nucleophiles (solvents) with deferent donor abilities exist, leading to solvatochromism. The solute–solvent interactions are revealed by shifts in the ligand field absorption spectra that are enhanced as the donor power of the solvent increases. Linear dependence of the ligand field absorption maximum on solvent donor number is generally observed.

Crystal Chemistry and Prototropic Tautomerism in 2-(1-Iminoalkyl)- phenols (or naphthols) and 2-Diazenyl-phenols (or naphthols)

This review reports a systematic investigation, carried out on the Cambridge Crystallographic Database (CSD), on the structural features of iminoalkyl-phenols (or naphthols) as well as azo-phenols (or naphthols). All these compounds form N-H … O/O-H … N intramolecular hydrogen bonds assisted by resonance (RAHB) in tautomeric equilibrium which can be finely tuned by the substituents. Accordingly, they can present reversible proton transfer leading to interesting properties such as thermochromism and photochromism. The phenol derivatives 2-(1-aryliminoalkyl)phenols and 2- arylazophenols display the predominance of the O-H … N form. Furthermore, they display the following features: i) strongly electron-donating substituents in p-position on the N-phenyl group shorten the N … O contact distance but not enough to produce the O-H … N to O-H … N/N-H … O transition; ii) such a transition can be however induced by strongly electron-withdrawing substituents at the phenol ring which increase the phenol acidity; iii) very similar effects are determined by intermolecular hydrogen-bonded O-H … O contacts with the phenolic oxygen which, stabilizing the N-H … O bond produce the O-H … N to O-H … N/N-H … O transition and, sometimes, the complete proton transfer to the pure NH … O form. The naphthol derivatives (1-(1-aryliminoalkyl-2-naphthols and 1-arylazo-2-naphthols) display the most interesting situation of two roughly isoenergetic O-H … N/N-H … O tautomers which can be tuned by modifying the Nsubstituent, the effects of substitution at the N-phenyl moiety being by far the most extensively studied. The structures of variously aryl-substituted 1-(1-aryliminoalkyl)-2-naphthols, though collected only at room temperature, indicate that almost all of them are tautomeric equilibria, even if full information on proton populations and dynamic or static nature of the proton disorder are not available. Conversely, the structures of a series of aryl-substituted 1-arylazo-2-naphthols have been recently determined at variable temperature showing that strongly electron-attracting substituents stabilize the pure N-H … O form, while substituents with increasing electron-donating properties transform the system into a dynamic, or static, N-H … O → O-H … N tautomeric equilibrium in the solid with an ever increasing population of the O-H … N azoenol tautomer.

電子吸引性置換基を持つ1-Phenylethyl Tosylates のソルボリシス

電子吸引性置換基を持つ1-Phenylethyl Tosylates のソルボリシス

How the Shape of the NH2 Group Depends on the Substituent Effect and H-Bond Formation in Derivatives of Aniline

The geometry and electronic structure of the amino group in aniline and its derivatives are very sensitive to both intramolecular interactions such as substituent effects and intermolecular ones such as H-bonding. An analysis of experimental geometries retrieved from the CSD base and computational modeling of aniline and its derivatives and their H-bonded complexes by use of B3LYP/6-311+G** and MP2/aug-cc-pVDZ showed that the degree of pyramidalization of the amino group depends on H-bonding, which exists in two forms, (i) NH...B (base) and (ii) N...HB (Brønsted acid), both of which affect the shape of the NH2 group. The effect may be significantly enhanced by a substituent through resonance interaction from electron-attracting substituents. The NH...B interactions lead to a substantial planarization of the group, whereas N...HB interactions do not. The natural bond orbital analysis allowed the authors to show that the changes in occupancy of the "lone pair" orbital and in geometry parameters describing pyramidalization of the group depend on the substituent constants.

Cytotoxic and Topographical Properties of 6-Arylidene-2-dimethylaminomethylcyclohexanone Hydrochlorides and Related Compounds

A number of 2-arylidenecyclohexanones (1a–h) were converted into the corresponding Mannich bases (2a–h) and (3a,f). Evaluation against murine L1210 cells as well as human Molt 4/C8 and CEM T-lymphocytes revealed the marked cytotoxicity of the Mannich bases and also the fact that almost invariably these compounds were more potent than the precursor enones (1a–h). Further evaluation of most of the Mannich bases towards a panel of nearly 60 human tumour cell lines confirmed their utility as potent cytotoxins. In this assay, the compounds showed growth-inhibiting properties greater than the anticancer alkylator melphalan. QSAR studies revealed that in some cell lines compounds possessing small electron-attracting aryl substituents showed the greatest potencies. Molecular modeling and X-ray crystallography demonstrated that various interatomic distances and torsion angles correlated with cytotoxicity. A representative compound (2a) demonstrated weak inhibiting properties towards human N-myristoyltransferase and stimulated a tyrosine protein kinase. A single dose of 100 mg/kg of most of the compounds did not prove to be lethal in mice.

Geometry at the aliphatic tertiary carbon atom: computational and experimental test of the Walsh rule.

The geometrical parameters of molecules of 2-substituted 2-methylpropanes and 1-substituted bicyclo[2.2.2]octanes were calculated at the B3LYP/6-311+G(d,p) level. They agreed reasonably well with the mean crystallographic values retrieved from the Cambridge Structural Database for a set of diverse non-cyclic structures with a tertiary C atom. The angle deformations at this C atom produced by the immediately bonded substituent are also closely related to those observed previously in benzene mono derivatives (either as calculated or as derived from crystallographic data). The calculated geometrical parameters were used to test the classical Walsh rule: It is evidently true that an electron-attracting substituent increases the proportion of C-atom p-electrons in the bond to the substituent and leaves more s-electrons to the remaining bonds; as a consequence the C-C-C angles at a tertiary carbon are widened and the C-C bonds shortened. However, this rule describes only part of the reality since the bond angles and lengths are controlled by other factors as well, for instance by steric crowding. Another imperfection of the Walsh rule is that the sequence of substituents does not correspond to their electronegativities, as measured by any known scale; more probably it is connected with the inductive effect, but then only very roughly.

Microwave‐Assisted Synthesis of Diaryl Ethers Without Catalyst.

AbstractFor Abstract see ChemInform Abstract in Full Text.