Evaluation of the Effects of Heteroaryl Ethylene Molecules in Combination with Antibiotics: A Preliminary Study on Control Strains

The discovery of compounds with antibacterial activity is crucial in the ongoing battle against antibiotic resistance. We developed two QSAR models to design six novel heteroaryl drug candidates and assessed their antibacterial properties against nine ATCC strains, including Enterococcus faecalis, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and also Salmonella enterica and Escherichia coli, many of which belong to the ESKAPE group. We combined PB4, a previously tested compound from published studies, with GC-VI-70, a newly discovered compound, with the best cytotoxicity/MIC profile. By testing sub-MIC concentrations of PB4 with five antibiotics (linezolid, gentamycin, ampicillin, erythromycin, rifampin, and imipenem), we evaluated the combination's efficacy against the ATCC strains. To assess the compounds' cytotoxicity, we conducted a 24 h and 48 h 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on colorectal adenocarcinoma (CaCo-2) cells. We tested the antibiotics alone and in combination with PB4. Encouragingly, PB4 reduced the MIC values for GC-VI-70 and for the various clinically used antibiotics. However, it is essential to note that all the compounds studied in this research exhibited cytotoxic activity against cells. These findings highlight the potential of using these compounds in combination with antibiotics to enhance their effectiveness at lower concentrations while minimizing cytotoxic effects.

Heteroaryl-Ethylenes as New Lead Compounds in the Fight against High Priority Bacterial Strains

The widespread use of antibiotics has led to a gradual increase in drug-resistant bacterial infections, which severely weakens the clinical efficacy of antibacterial therapies. In recent decades, stilbenes aroused great interest because of their high bioavailability, as well as their manifold biological activity. Our research efforts are focused on synthetic heteroaromatic stilbene derivatives as they represent a potentially new type of antibiotic with a wide antibacterial spectrum. Herein, a preliminary molecular modeling study and a versatile synthetic scheme allowed us to define eight heteroaromatic stilbene derivatives with potential antimicrobial activity. In order to evaluate our compound’s activity spectrum and antibacterial ability, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests have been performed on Gram-positive and Gram-negative ATCC strains. Compounds PB4, PB5, PB7, and PB8 showed the best values in terms of MIC and were also evaluated for MBC, which was found to be greater than MIC, confirming a bacteriostatic activity. For all compounds, we evaluated toxicity on colon-rectal adenocarcinoma cells tumor cells (CaCo2), once it was established that the whole selected set was more active than 5-Fluorouracil in reducing CaCo-2 cells viability. To the best of our knowledge, the biological assays have shown for these derivatives an excellent bacteriostatic activity, compared to similar molecular structures previously reported, thus paving the way for a new class of antibiotic compounds.

Alkynoates as Versatile and Powerful Chemical Tools for the Rapid Assembly of Diverse Heterocycles under Transition-Metal Catalysis: Recent Developments and Challenges

Heterocycles, heteroaromatics and spirocyclic entities are ubiquitous components of a wide plethora of synthetic drugs, biologically active natural products, marketed pharmaceuticals and agrochemical targets. Recognizing their high proportion in drugs and rich pharmacological potential, these invaluable structural motifs have garnered significant interest, thus enabling the development of efficient catalytic methodologies providing access to architecturally complex and diverse molecules with high atom-economy and low cost. These chemical processes not only allow the formation of diverse heterocycles but also utilize a range of flexible and easily accessible building units in a single operation to discover diversity-oriented synthetic approaches. Alkynoates are significantly important, diverse and powerful building blocks in organic chemistry due to their unique and inherent properties such as the electronic bias on carbon-carbon triple bonds posed by electron-withdrawing groups or the metallic coordination site provided by carbonyl groups. The present review highlights the comprehensive picture of the utility of alkynoates (2007-2019) for the synthesis of various heterocycles (> 50 types) using transition-metal catalysts (Ru, Rh, Pd, Ir, Ag, Au, Pt, Cu, Mn, Fe) in various forms. The valuable function of versatile alkynoates (bearing multifunctional groups) as simple and useful starting materials is explored, thus cyclizing with an array of coupling partners to deliver a broad range of oxygen-, nitrogen-, sulfur-containing heterocycles alongside fused-, and spiro-heterocyclic compounds. In addition, these examples will also focus the scope and reaction limitations, as well as mechanistic investigations into the synthesis of these heterocycles. The biological significance will also be discussed, citing relevant examples of drug molecules highlighting each class of heterocycles. This review summarizes the recent developments in the synthetic methods for the synthesis of various heterocycles using alkynoates as readily available starting materials under transition-metal catalysis.

The role of π-linkers and electron acceptors in tuning the nonlinear optical properties of BODIPY-based zwitterionic molecules

Intramolecular charge transfer process can play a key role in developing strong nonlinear optical (NLO) response in a molecule for technological application. Herein, two series of boron dipyrromethene (BODIPY)-based push–pull systems have been designed with zwitterionic donor–acceptor groups, and their NLO properties have been evaluated using a density functional theory-based approach. Different π-conjugated linkers and electron acceptor groups were used to understand their roles in tuning the NLO properties. The molecules were analyzed through HOMO–LUMO gaps, frontier molecular orbitals, polarizabilities, hyperpolarizabilities, Δr indices, transition dipole moment densities, ionization potentials, electron affinities and reorganization energies for holes and electrons. These observations correlated well with the computed absorption spectra of the molecules. It is found that with the introduction of different π-linkers in the molecule, planarity is maintained and the HOMO–LUMO gap is systematically decreased, which leads to a large NLO response. It was noted that the electronic absorption wavelength maxima were found in the near-infrared region (934–1650 nm). The results show that compared to the pyridinium acceptor group, the imidazolium acceptor group in the BODIPY systems amplifies the NLO response to a larger extent. It is also observed that the BODIPY-based dye with an imidazolium acceptor and thienothiophene π-linker shows the highest first hyperpolarizability value of 3194 × 10⁻³⁰ esu. Furthermore, the charge transfer occurs in the z-direction, as the z-component of the first hyperpolarizability is the dominant factor in this system. Here, the designed molecules show a characteristic reorganisation energy value, which is a deciding factor in the rate of hole/electron transport for favourable intermolecular coupling. As a whole, this theoretical work highlights that π-conjugated linkers and electron acceptor groups can be used judiciously to design new molecular systems for optoelectronic applications.

BODIPY-based zwitterionic molecules with pyridinium and imidazolium electron acceptors and thienothiophene π-linkers reveal significant first hyperpolarizability.

Chemo- and regioselective synthesis of polysubstituted 2-aminothiophenes by the cyclization of gem-dibromo or gem-dichloroalkenes with β-keto tertiary thioamides

A facile and practical method for the synthesis of 2,3,4-trisubstituted 2-aminothiophenes by the cyclization of gem-dibromoalkenes or gem-dichloroalkenes with β-keto tertiary thioamides has been developed. The cyclization reaction proceeded chemoselectively and regioselectively under metal-catalyst-free conditions, providing various structurally diverse 2,3,4-trisubstituted N,N'-dialkyl 2-aminothiophenes in good to excellent yields.

Push-pull D-π-Ru-π-A chromophores: synthesis and electrochemical, photophysical and second-order nonlinear optical properties

The present work describes the one-pot synthesis and electrochemical, photophysical and second-order nonlinear optical (NLO) properties of a series of dipolar π-delocalized Ru(ii) dialkynyl complexes. The eight new asymmetrical D-π-Ru-π-A push-pull chromophores incorporate pyranylidene ligands as pro-aromatic donor groups (D) and formaldehyde, indane-1,3-dione, pyrimidine or pyrimidinium as electron-attracting groups (A) separated by ruthenium bis-acetylide fragments and π-conjugated linkers. The second-order nonlinear optical (NLO) properties of all eight complexes were determined by the Electric-Field-Induced Second Harmonic generation (EFISH) technique (operating at 1907 nm), and were compared to those of their purely organic analogs. All investigated compounds (organic and organometallic) exhibited positive μβ values, which dramatically increased for the complexes due to the presence of ruthenium in the π-conjugated core. The second-order NLO response could also be easily modulated by changing the nature of alkynyl substituents. The most promising ruthenium complexes 7 and 8 of the series with the pyrimidinium fragment displayed μβ values of 14 000 × 10^-48 esu. The effect of structural modifications on the redox and spectroscopic properties of the complexes was also studied. The intramolecular charge transfer (ICT) occurring through the ruthenium center of the push-pull σ-dialkynyl complexes was investigated by combining experimental and theoretical data.

Understanding the interplay between the solvent and nuclear rearrangements in the negative solvatochromism of a push–pull flexible quinolinium cation

The main effects (solvation, vibronic progression) affecting the band position and shape of a push–pull flexible quinolinium cation OPA are highlighted.

Synthesis of N,N-disubstituted 2-aminothiophenes by the cyclization of gem-difluoroalkenes with β-keto thioamides

A novel and effective method for the construction of highly functionalized aminothiophenes via the cyclization of gem-difluoroalkenes with β-keto tertiary thioamides is described.

Twisting in the excited state of an N-methylpyridinium fluorescent dye modulated by nano-heterogeneous micellar systems

The fluorescence of an N-methylpyridinium dye was modulated by nano-heterogeneous micellar systems, where its excited state twisting is gradually impaired by the increasing viscosity of the surrounding environment.

Direct synthesis of polysubstituted 2-aminothiophenes by Cu(II)-catalyzed addition/oxidative cyclization of alkynoates with thioamides

A facile and direct synthetic method was developed for the construction of structurally important 2-aminothiophenes in moderate to excellent yields (up to 91%), via Cu(II)-catalyzed addition/oxidative cyclization of readily available thioamides with alkynoates under an air atmosphere.

Inclusion of push–pull N-methylpyridinium salts within surfactant hydrogels: is their excited state intramolecular charge transfer mediated by twisting?

By confining two push–pull N-methylpyridinium derivatives within the rigid domains of surfactant hydrogels, the twisted nature of their intramolecular charge transfer state (formed in water upon excitation) was unravelled.

An ultrafast spectroscopic and quantum mechanical investigation of multiple emissions in push–pull pyridinium derivatives bearing different electron donors

An interconversion between rotamers in S₁ was evidenced for a cationic push–pull pyrenyl derivative through a joint femtosecond fluorescence up-conversion and density functional theoretical study.

Photobehaviour of methyl-pyridinium and quinolinium iodide derivatives, free and complexed with DNA. A case of bisintercalation

Interaction between azinium iodides and DNA. A bicationic dye acts as a bisintercalative agent which could increase the cytotoxicity with low dose and less collateral effects.

Design, synthesis and in vitro antitumour activity of new heteroaryl ethylenes

Almond and VolSurf + modelling procedures allowed the structural design of new di- and mono-heteroaryl-ethylenes. The structural modifications suggested by the molecular modelling were verified by the synthesis of the designed molecules and by the evaluation of their in vitro activities against two lung tumour cell lines, A549 and H226. 2-{(E)-2-[5'-(Dibutylamino)-2,2'-bithien-5-yl]vinyl}-1-methylquinolinium iodide exhibited in vitro antiproliferative activity two orders of magnitude higher than that of the most active compound previously synthesized in our laboratory.