Synthesis, antibacterial evaluation and QSAR studies of 7-[4-(5-aryl-1,3,4-oxadiazole-2-yl)piperazinyl] quinolone derivatives

Development of reliable quantitative structure-toxicity relationship models for toxicity prediction of benzene derivatives using semiempirical descriptors

The Health and environmental hazards of benzene and nitrobenzene (NB) derivatives have remained a topic of interest of researchers. In silico methods for prediction of toxicity of chemicals have proved their worth in accurate forecast of environmental as well as health toxicity and are strongly recommended by regulatory authorities. Two quantitative structure-toxicity relationship (QSTR) models explaining Scenedesmus obliquus toxicity trends among 39 benzene derivatives and Tetrahymena pyriformis toxicity of 103 NB and 392 benzene derivatives are developed using semiempirical quantum chemical parameters. The best constructed QSTR models have good fitting ability (R² = 0.8053, 0.7591, and 0.8283) and robustness (Q²_LOO = 0.7507, 0.7227, and 0.8194; Q²_LMO = 0.7338, 0.7153, and 0.8172). The external predictivity of all the models are quite good (R²_EXT = 0.8256, 0.9349, and 0.8698). Electronegativity, Cosmo volume, total energy, and molecular weight are responsible for the increase and decrease of toxicity of benzene derivatives against S. obliquus while electronegativity, electrophilicity index, the heat of formation, total energy, hydrophobicity, and cosmo volume are responsible for modulation of toxicity of NB and benzene derivatives toward T. pyriformis. These models fulfill the requirements of all the five OECD principles.

1,3,4-oxadiazole derivatives as potential antimicrobial agents

Due to the emergence of drug-resistant microbial strains, different research groups are continuously developing novel drug molecules against already exploited and unexploited targets. 1,3,4-Oxadiazole derivatives exhibited noteworthy antimicrobial activities. The presence of 1,3,4-oxadiazole moiety in antimicrobial agents can modify their polarity and flexibility, which significantly improves biological activities due to various bonded and non-bonded interactions viz. hydrogen bond, steric, electrostatic, and hydrophobic with target sites. The present review elaborates the therapeutic targets and mode of interaction of 1,3,4-oxadiazoles as antimicrobial agents. 1,3,4-oxadiazole derivatives target enoyl reductase (InhA), 14α-demethylase in the mycobacterial cell; GlcN-6-P synthase, thymidylate synthase, peptide deformylase, RNA polymerase, dehydrosqualene synthase in bacterial strains; ergosterol biosynthesis pathway, P450-14α demethylase, protein-N-myristoyltransferase in fungal strains; FtsZ protein, interfere with purine and functional protein synthesis in plant bacteria. The present review also summarizes the effect of different moieties and functional groups on the antimicrobial activity of 1,3,4-oxadiazole derivatives.

Novel radial distribution function approach in the study of point mutations: the HIV-1 protease case study

Background: Mutations are one of the engines of evolution. Under constant stress pressure, mutations can lead to the emergence of unwanted, drug-resistant entities. Methodology: The radial distribution function weighted by the number of valence shell electrons is used to design quantitative structure-activity relationship (QSAR) model relating descriptors with the inhibition constant for a series of wild-type HIV-1 protease inhibitor complexes. The residuals of complexes with mutant HIV-1 protease were correlated with the energy of the highest occupied molecular orbitals of the residues introduced to enzyme via point mutations. Conclusion: Successful identification of residues Ile3, Asp25, Val32 and Ile50 as the one whose substitution influences the inhibition constant the most, demonstrates the potential of the proposed methodology for the study of the effects of point mutations.

Ciprofloxacin derivatives and their antibacterial activities

Bacterial infections represent a significant health threat globally, and are responsible for the majority of hospital-acquired infections, leading to extensive mortality and burden on global healthcare systems. The second generation fluoroquinolone ciprofloxacin which exhibits excellent antimicrobial activity and pharmacokinetic properties as well as few side effects is introduced into clinical practice for the treatment of various bacterial infections for around 3 decades. The emergency and widely spread of drug-resistant pathogens making ciprofloxacin more and more ineffective, so it's imperative to develop novel antibacterials. Numerous of ciprofloxacin derivatives have been synthesized for seeking for new antibacterials, and some of them exhibited promising potency. This review aims to summarize the recent advances made towards the discovery of ciprofloxacin derivatives as antibacterial agents and the structure-activity relationship of these derivatives was also discussed.

4-Quinolone derivatives and their activities against Gram positive pathogens

Gram-positive bacteria are responsible for a broad range of infectious diseases, and the emergency and wide spread of drug-resistant Gram-positive pathogens including MRSA and MRSE has caused great concern throughout the world. 4-Quinolones which are exemplified by fluoroquinolones are mainstays of chemotherapy against various bacterial infections including Gram-positive pathogen infections, and their value and role in the treatment of bacterial infections continues to expand. However, the resistance of Gram-positive organisms to 4-quinolones develops rapidly and spreads widely, making them more and more ineffective. To overcome the resistance and reduce the toxicity, numerous of 4-quinolone derivatives were synthesized and screened for their in vitro and in vivo activities against Gram-positive pathogens, and some of them exhibited excellent potency. This review aims to outlines the recent advances made towards the discovery of 4-quinolone-based derivatives as anti-Gram-positive pathogens agents and the critical aspects of design as well as the structure-activity relationship of these derivatives. The enriched SAR paves the way to the further rational development of 4-quinolones with a unique mechanism of action different from that of the currently used drugs to overcome the resistance, well-tolerated and low toxic profiles.

A revisit to the Gattermann reaction: interesting synthesis of nitrogen heterocyclic aromatic halides and their fluorescence properties

The Gattermann reaction and an electrophilic substitution reaction, which were conducted in a one-pot reaction, are reported, and four aromatic dihalides of similar structure were obtained. 2-Chloro-5-(3-chloro-4-methoxy-phenyl)-1,3,4-thiadiazole was applied as a highly efficient fluorescence sensor for the detection of TNP.

Bioactivity-guided mixed synthesis and evaluation of α-alkenyl-γ and δ-lactone derivatives as potential fungicidal agents

In view of the great antifungal activities of sesquiterpene lactones and natural product Tulipalin A, 52 derivatives derived from α-methylene-γ-butyrolactone substructures were synthesized to study antifungal activities.

Novel ligands of Choline Acetyltransferase designed by in silico molecular docking, hologram QSAR and lead optimization

Recent reports have brought back the acetylcholine synthesizing enzyme, choline acetyltransferase in the mainstream research in dementia and the cholinergic anti-inflammatory pathway. Here we report, a specific strategy for the design of novel ChAT ligands based on molecular docking, Hologram Quantitative Structure Activity Relationship (HQSAR) and lead optimization. Molecular docking was performed on a series of ChAT inhibitors to decipher the molecular fingerprint of their interaction with the active site of ChAT. Then robust statistical fragment HQSAR models were developed. A library of novel ligands was generated based on the pharmacophoric and shape similarity scoring function, and evaluated in silico for their molecular interactions with ChAT. Ten of the top scoring invented compounds are reported here. We confirmed the activity of α-NETA, the only commercially available ChAT inhibitor, and one of the seed compounds in our model, using a new simple colorimetric ChAT assay (IC50 ~ 88 nM). In contrast, α-NETA exhibited an IC50 of ~30 μM for the ACh-degrading cholinesterases. In conclusion, the overall results may provide useful insight for discovering novel ChAT ligands and potential positron emission tomography tracers as in vivo functional biomarkers of the health of central cholinergic system in neurodegenerative disorders, such as Alzheimer's disease.

Design, Synthesis and Antibacterial Evaluation of Some New 2-Phenyl-quinoline-4-carboxylic Acid Derivatives

A series of new 2-phenyl-quinoline-4-carboxylic acid derivatives was synthesized starting from aniline, 2-nitrobenzaldehyde, pyruvic acid followed by Doebner reaction, amidation, reduction, acylation and amination. All of the newly-synthesized compounds were characterized by ¹H-NMR, ¹³C-NMR and HRMS. The antibacterial activities of these compounds against Gram-negative (Escherichia coli, Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus, Bacillus subtilis), as well as one strain of methicillin-resistant Staphylococcus aureus (MRSA) bacteria were evaluated by the agar diffusion method (zone of inhibition) and a broth dilution method (minimum inhibitory concentration (MIC)), and their structure-activity relationships were obtained and discussed. The results revealed that some compounds displayed good antibacterial activity against Staphylococcus aureus, and Compounds 5a₄ and 5a₇ showed the best inhibition with an MIC value of 64 μg/mL against Staphylococcus aureus and with an MIC value of 128 μg/mL against Escherichia coli, respectively. The results of the MTT assay illustrated the low cytotoxicity of Compound 5a₄.

Synthesis and quantitative structure–activity relationship (QSAR) studies of novel rosin-based diamide insecticides

The quantitative structure–activity relationship (QSAR) of two series of rosin-based diamides with insecticidal activity against P. xylostella was studied.

Substituted oxadiazoles: a patent review (2010 - 2012)

INTRODUCTION

The oxadiazoles represent a class of five-membered heterocyclic compounds which are of considerable interest in different areas of medicinal chemistry and drug discovery. Oxadiazoles can exist in different regioisomeric forms and employ in various agents with a broad range of biological activities. This review covers the work reported on various biological activities of oxadiazole derivatives from 2010 to 2012.

AREAS COVERED

Oxadiazole derivatives attract great attention due to their different kinds of pharmaceutical activities including antiviral, antimicrobial, anticancer, anticonvulsant, antidiabetic and anti-inflammatory activity. This paper provides a general review of oxadiazole derivatives published in international journals and patented between 2010 and 2012.

EXPERT OPINION

Oxadiazoles have been used frequently in drug-like molecules as bioisosteres for ester and amide functionalities and displayed numerous prominent pharmacological effects. The broad pharmacological profile of oxadiazole derivatives has attracted the attention of many researchers to explore this scaffold to its multiple potential against several activities. Therefore, oxadiazole motif is likely to be present in other therapeutic molecules in the future.

Synthesis and antifungal activity of 3-(1,3,4-oxadiazol-5-yl)-indoles and 3-(1,3,4-oxadiazol-5-yl)methyl-indoles

On the basis of the principle of combination of active structural moieties, a modified and efficient synthetic method for three series of novel indole-based 1,3,4-oxadiazoles is described. Bioassays conducted at Syngenta showed that several of the synthesized compounds exhibit higher antifungal activity than pimprinine, the natural product which inspired this synthesis. Two main structural alterations were found to broaden the spectrum of biological activity in most cases. Compounds 3g, 6c, 6e, 6h, 9d, 9e, 9h and 9m (Fig. 1) were identified as the most active on the biological assays, and will be studied further.

Synthetic approaches and pharmacological activity of 1,3,4-oxadiazoles: a review of the literature from 2000-2012

This review provides readers with an overview of the main synthetic methodologies for 1,3,4-oxadiazole derivatives, and of their broad spectrum of pharmacological activities as reported over the past twelve years.

A general, enantioselective synthesis of protected morpholines and piperazines

A short, high yielding protocol has been developed for the enantioselective and general synthesis of C2-functionalized, benzyl protected morpholines and orthogonally N,N'-protected piperazines from a common intermediate.

Design and one-pot and microwave-assisted synthesis of 2-amino/5-aryl-1,3,4-oxadiazoles bearing a benzimidazole moiety as antioxidants

In this study, two new series of 2-amino-1,3,4-oxadiazoles and 5-aryl-1,3,4-oxadiazoles carrying a benzimidazole moiety were synthesized. The antioxidant properties of these compounds were investigated in vitro by the determination of the microsomal NADPH-dependent inhibition of lipid peroxidation levels (LP), the microsomal ethoxyresorufin O-deethylase activity (EROD), and DPPH radical scavenger effects. Among the tested compounds, 2-[(2-(4-chlorophenyl)-1H-benzo[d]imidazole-1-yl)methyl]-5-(4-fluorophenyl)-1,3,4-oxadiazole (9) was found to be the most active compound in all three in vitro systems.