Synthesis, crystal structure, anti-HIV, and antiproliferative activity of new oxadiazole and thiazole analogs

Design and synthesis of newer 5-aryl-N-(naphthalen-2-yl)-1,3,4-oxadiazol-2-amine analogues as anticancer agents

AIM

Cancer is the second leading cause of death and chemotherapy is widely used and well-known for treating cancer, yet it has lots of adverse side effects, making the search for novel compounds imperative. We reported here design, synthesis, DFT analysis, anticancer evaluation and in-silico studies of new 1,3,4-oxadiazoles (4a-e).

MATERIAL AND METHODS

IMC-038525 and IMC-094332 tubulin inhibitors' oxadiazole-linked aryl cores inspired the innovative compounds, and synthesis was accomplished in two steps followed by their characterization by spectral data. The HOMO and LUMO energy gap (ΔE) was determined to investigate compounds' (4a-e) stability followed by their anticancer activity at 10 μM and in-silico studies.

RESULTS AND CONCLUSION

5-(4-Nitrophenyl)-N-(naphthalene-2-yl)-1,3,4-oxadiazol-2-amine (4b) demonstrated substantial anticancer activity against a few cell lines like SR, MDA-MB-435, MOLT-4, K-562, and HL-60(TB). 5-(3,4,5-Trimethoxyphenyl)-N-(naphthalene-2-yl)-1,3,4-oxadiazol-2-amine (4e) demonstrated promising anticancer activity against cell lines, UO-31, NCI-H226, CAKI-1, PC-3, and MCF7. The molecular docking against tubulin's colchicine binding site (PDB ID: 1AS0), displayed a docking score of -7.295 Kcal/mol and a H-bond interaction with Ala317 residue for the ligand 4e. The ligand 4e was found to interacted 24 amino acids of the tubulin protein in MD simulation investigation with moderate local conformational changes with ligand 4e (< 1 Å).

Structure-Based Virtual Screening Identifies 2-Arylthiazole-4-Carboxylic Acids as a Novel Class of Nanomolar Affinity Ligands for the CaMKIIα Hub Domain

The Ca2+/calmodulin-dependent protein kinase II α (CaMKIIα) plays a crucial role in regulating neuronal signaling and higher brain functions, being involved in various brain diseases. Utilization of small molecules targeting the CaMKIIα hub domain has proved to be a promising strategy for specific CaMKIIα modulation and future therapy. Through an in silico structure-based virtual screening campaign, we herein identified 2-arylthiazole-4-carboxylic acids as a new class of high-affinity CaMKIIα hub ligands. Particularly, the 2,6-dichlorophenyl analog, PTCA (compound 1a), displayed mid-nanomolar affinity (pKi = 7.2) and substantial stabilization of the CaMKIIα hub oligomer upon binding. Moreover, the tert-butyl ester prodrug, 14a, was developed to facilitate the brain delivery of PTCA and demonstrated remarkable enhancement in brain penetration compared to PTCA per se after systemic administration. Altogether, our study highlights that PTCA represents a novel and powerful tool compound for future pharmacological interventions targeting CaMKII kinase in the brain.

Multicomponent Synthesis of 2,4,5-Trisubstituted Thiazoles Using a Sustainable Carbonaceous Catalyst and Assessment of Its Herbicidal and Antibacterial Potential

Herein, a novel, biocatalyzed, and on-water microwave-assisted multicomponent methodology have been developed for the synthesis of trisubstituted thiazoles (4a-4v). The reaction was catalyzed using a sulfonated peanut shell residue-derived carbonaceous catalyst (SPWB). The developed catalyst was characterized using Fourier transform infrared (FTIR), a Brunauer-Emmett-Teller (BET) surface area analyzer, a field emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX), and a particle size analyzer (PSA). The acidic sites have been established using acid-base back-titration methods. The molecular structures of all the synthesized compounds were validated using FT-IR, 1H NMR, 13C NMR, elemental, and HRMS analyses. Herbicidal potential was evaluated by using Raphanus sativus L. as a model. Furthermore, the antibacterial potential of thiazoles was evaluated against Staphylococcus aureus, Bacillus subtilis, Xanthomonas campestris, Escherichia coli, Micrococcus luteus, and Pseudomonas aeruginosa bacterial strains. The compound 4r displayed improved seed growth inhibition in Raphanus sativus L. versus a commercially available herbicide, i.e., pendimethalin. The antibacterial activity was promising against bacterial strains (MIC: 4-64 μg/mL). The compound 4r was the most potent against P. aeruginosa and S. aureus (MIC: 0.0076 μM) versus standard drug streptomycin (MIC: 0.0138 μM). Moreover, in silico studies performed with the most effective compound 4r against P. aeruginosa revealed its potential binding mode within the protein binding pocket. The biological data revealed compound 4r as a potential candidate for the development of potent herbicidal and antibacterial agents. In a nutshell, this study offers peanut shell biowaste to be a sustainable biomass for heterogeneous acid catalyst preparation and its application in the multicomponent synthesis of bioactive thiazoles, accommodating the concept of sustainable development goals and circular bioeconomy.

Synthesis and Anticancer Evaluation of 4-Chloro-2-((5-aryl-1,3,4-oxadiazol-2-yl)amino)phenol Analogues: An Insight into Experimental and Theoretical Studies

We report herein the synthesis, docking studies and biological evaluation of a series of new 4-chloro-2-((5-aryl-1,3,4-oxadiazol-2-yl)amino)phenol analogues (6a-h). The new compounds were designed based on the oxadiazole-linked aryl core of tubulin inhibitors of IMC-038525 and IMC-094332, prepared in five steps and further characterized via spectral analyses. The anticancer activity of the compounds was assessed against several cancer cell lines belonging to nine different panels as per National Cancer Institute (NCI US) protocol. 4-Chloro-2-((5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazol-2-yl)amino)phenol (6h) demonstrated significant anticancer activity against SNB-19 (PGI = 65.12), NCI-H460 (PGI = 55.61), and SNB-75 (PGI = 54.68) at 10 µM. The compounds were subjected to molecular docking studies against the active site of the tubulin-combretastatin A4 complex (PDB ID: 5LYJ); they displayed efficient binding and ligand 4h (with docking score = -8.030 kcal/mol) lay within the hydrophobic cavity surrounded by important residues Leu252, Ala250, Leu248, Leu242, Cys241, Val238, Ile318, Ala317, and Ala316. Furthermore, the antibacterial activity of some of the compounds was found to be promising. 4-Chloro-2-((5-(4-nitrophenyl)-1,3,4-oxadiazol-2-yl)amino)phenol (6c) displayed the most promising antibacterial activity against both Gram-negative as well as Gram-positive bacteria with MICs of 8 µg/mL and a zone of inhibition ranging from 17.0 ± 0.40 to 17.0 ± 0.15 mm at 200 µg/mL; however, the standard drug ciprofloxacin exhibited antibacterial activity with MIC values of 4 µg/mL.

Exploration of Thiourea-Based Scaffolds for the Construction of Bacterial Ureases Inhibitors

A series of 32 thiourea-based urease inhibitors were synthesized and evaluated against native bacterial enzyme and whole cells of Sporosarcina pasteurii and Proteus mirabilis strains. The proposed inhibitors represented structurally diverse thiosemicarbazones and thiocarbohydrazones, benzyl-substituted thiazolyl thioureas, 1H-pyrazole-1-carbothioamides, and dihydropirimidine-2(1H)-thiones. Kinetic characteristics with purified S. pasteurii enzyme determined low micromolar inhibitors within each structural group. (E)-2-(1-Phenylethylidene)hydrazine-1-carbothioamide 19 (Ki = 0.39 ± 0.01 μM), (E)-2-(4-methylbenzylidene)hydrazine-1-carbothioamide 16 (Ki = 0.99 ± 0.04 μM), and N'-((1E,2E)-1,3-diphenylallylidene)hydrazinecarbothiohydrazide 29 (Ki = 2.23 ± 0.19 μM) were used in modeling studies that revealed sulfur ion coordination of the active site nickel ion and hydrogen bonds between the amide group and the side chain of Asp363 and Ala366 carbonyl moiety. Whole-cell studies proved the activity of compounds in Gram-positive and Gram-negative microorganisms. Ureolysis control observed in P. mirabilis PCM 543 (e.g., IC50 = 304 ± 14 μM for 1-benzyl-3-(4-(4-hydroxyphenyl)thiazol-2-yl)thiourea 52) is a valuable achievement, as urease is recognized as a major virulence factor of this urinary tract pathogen.

Oxadiazole: A highly versatile scaffold in drug discovery

As a pharmacologically important heterocycle, oxadiazole paved the way to combat the problem associated with the confluence of many commercially available drugs with different pharmacological profiles. The present review focuses on the potential applications of five-membered heterocyclic oxadiazole derivatives, especially 1,2,4-oxadiazole, 1,2,5-oxadiazole, and 1,3,4-oxadiazole, as therapeutic agents. Designing new hybrid molecules containing the oxadiazole moiety is a better solution for the development of new drug molecules. The designed molecules may accumulate a biological profile better than those of the drugs currently available on the market. The present review will guide the way for researchers in the field of medicinal chemistry to design new biologically active molecules based on the oxadiazole nucleus. Antitubercular, antimalarial, anti-inflammatory, anti-HIV, antibacterial, and anticancer activities of various oxadiazoles have been reviewed extensively here.

Urease inhibitory kinetics, molecular docking, SAR and ADME studies of imine analogues

A series of synthesized imine derivatives (3a–m), including thio-semicarbazone, semicarbazone, thiazole and oxazole functional moieties, were examined for in vitro urease inhibition activity.

Urea-thiazole/benzothiazole hybrids with a triazole linker: synthesis, antimicrobial potential, pharmacokinetic profile and in silico mechanistic studies

Some urea-thiazole/benzothiazole hybrids with a triazole linker were synthesized via Cu(I)-catalysed click reaction. After successfully analysed by various spectral techniques including FTIR, NMR and HRMS, antimicrobial screening of the synthesized hybrids along with their precursors was carried out against two Gram (+) bacteria (Staphylococcus aureus and Bacillus endophyticus), two Gram (-) bacteria (Escherichia coli and Pseudomonas fluorescens) and two fungi (Candida albicans and Rhizopus oryzae). All the synthesized compounds (4a-4l) displayed better biological response than the standard fluconazole against both of the tested fungi. Compounds 4h and 4j were found to be the most active compounds against R. oryzae and C. albicans, respectively. Molecular docking of hybrid 4j and its alkyne precursor 1b in the active site of C. albicans target sterol 14-α demethylase was also performed and was also supported by molecular dynamics studies. In silico ADME prediction of synthesized urea-thiazole/benzothiazole hybrids with a triazole linker and their alkyne precursors was also predicted.

High throughput screening identifies inhibitors for parvovirus B19 infection of human erythroid progenitor cells

Parvovirus B19 (B19V) infection can cause hematological disorders and fetal hydrops during pregnancy. Currently, no antivirals or vaccines are available for the treatment or the prevention of B19V infection. To identify novel small-molecule antivirals against B19V replication, we developed a high throughput screening assay, which is based on an in vitro nicking assay using recombinant N-terminal 1-176 amino acids of the viral large nonstructural protein (NS1N) and a fluorescently labeled DNA probe (OriQ) that spans the nicking site of the viral DNA replication origin. We collectively screened 17,040 compounds and identified 2,178 (12.78%) hits that possess >10% inhibition of the NS1 nicking activity, among which 84 hits were confirmed to inhibit nicking in a dose-dependent manner. Using ex vivo expanded primary human erythroid progenitor cells (EPCs) infected by B19V, we validated 24 compounds demonstrated >50% in vivo inhibition of B19V infection at 10 μM, which can be categorized into 7 structure scaffolds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, the top 4 compounds were chosen to examine their inhibitions of B19V infection in EPCs at two times of the 90% maximal effective concentration (EC₉₀). A purine derivative (P7), demonstrated an antiviral effect (EC₅₀=1.46 μM) without prominent cytotoxicity (CC₅₀=71.8 μM) in EPCs, exhibited 92% inhibition of B19V infection in EPCs at 3.32 μM, which can be used as the lead compound in future studies for the treatment of B19V infection caused hematological disorders. Importance B19V encodes a large non-structural protein NS1. Its N-terminal domain (NS1N) consisting of 1-176 amino acids binds to viral DNA and serves as an endonuclease to nick the viral DNA replication origins, which is a pivotal step in rolling hairpin-dependent B19V DNA replication. For high throughput screening (HTS) of anti-B19V antivirals, we miniaturized a fluorescence-based in vitro nicking assay, which employs a fluorophore-labeled probe spanning the trs and the NS1N protein, into a 384-well plate format. The HTS assay showed a high reliability and capability in screening 17,040 compounds. Based on the therapeutic index [half maximal cytotoxic concentration (CC₅₀)/half maximal effective concentration (EC₅₀)] in EPCs, a purine derivative demonstrated an antiviral effect of 92% inhibition of B19V infection in EPCs at 3.32 μM (two times EC₉₀). Our study demonstrated a robust HTS assay for screening antivirals against B19V infection.

Semicarbazones, thiosemicarbazone, thiazole and oxazole analogues as monoamine oxidase inhibitors: Synthesis, characterization, biological evaluation, molecular docking, and kinetic studies

A series of semicarbazone, thiosemicarbazone, thiazole, and oxazole derivatives were designed, synthesized, and examined for monoamine oxidase inhibition using two isoforms, i.e., MAO-A and MAO-B. Among all the analogues, 3c and 3j possessed substantial activity against MAO-A with IC₅₀ values of 5.619 ± 1.04 µM and 0.5781 ± 0.1674 µM, respectively. Whereas 3d and 3j were active against monoamine oxidase B with the IC₅₀ values of 9.952 ± 1.831 µM and 3.5 ± 0.7 µM, respectively. Other derivatives active against MAO-B were 3c and 3g with the IC₅₀ values of 17.67 ± 5.6 µM and 37.18 ± 2.485 µM. Moreover, molecular docking studies were achieved for the most potent compound (3j) contrary to human MAO-A and MAO-B. Kinetic studies were also performed for the most potent analogue to evaluate its mode of interaction with MAO-A and MAO-B.

Synthesis, antioxidant, antimicrobial and antiviral docking studies of ethyl 2-(2-(arylidene)hydrazinyl)thiazole-4-carboxylates

A series of ethyl 2-(2-(arylidene)hydrazinyl)thiazole-4-carboxylates (2a-r) was synthesized in two steps from thiosemicarbazones (1a-r), which were cyclized with ethyl bromopyruvate to ethyl 2-(2-(arylidene)hydrazinyl)thiazole-4-carboxylates (2a-r). The structures of compounds (2a-r) were established by FT-IR, ¹H- and ¹³C-NMR. The structure of compound 2a was confirmed by HRMS. The compounds (2a-r) were then evaluated for their antimicrobial and antioxidant assays. The antioxidant studies revealed, ethyl 2-(2-(4-hydroxy-3-methoxybenzylidene)hydrazinyl)thiazole-4-carboxylate (2g) and ethyl 2-(2-(1-phenylethylidene)hydrazinyl)thiazole-4-carboxylate (2h) as promising antioxidant agents with %FRSA: 84.46 ± 0.13 and 74.50 ± 0.37, TAC: 269.08 ± 0.92 and 269.11 ± 0.61 and TRP: 272.34 ± 0.87 and 231.11 ± 0.67 μg AAE/mg dry weight of compound. Beside bioactivities, density functional theory (DFT) methods were used to study the electronic structure and properties of synthesized compounds (2a-m). The potential of synthesized compounds for possible antiviral targets is also predicted through molecular docking methods. The compounds 2e and 2h showed good binding affinities and inhibition constants to be considered as therapeutic target for M^pro protein of SARS-CoV-2 (COVID-19). The present in-depth analysis of synthesized compounds will put them under the spot light for practical applications as antioxidants and the modification in structural motif may open the way for COVID-19 drug.

1,3,4-Oxadiazole Containing Compounds As Therapeutic Targets For Cancer Therapy

BACKGROUND

Cancer is the first or second leading cause of premature death in 134 of 183 countries in the world. 1,3,4-Oxadiazoles are five memebered heterocyclic rings containing two nitrogen (two atoms) and oxygen (one atom). They show better thermal stability, metabolic stability, aqueous solubility and lower lipophilicity than the other isomeric oxadiazoles. They are important class of heterocycles present in many drug structures like Raltegravir, Furamizole Tidazosin, Nesapidil, Setileuton (MK-0633) and Zibotentan. Presence of this nucleus in the therapeutics has made them an indispensable anchor for drug design and development. Several 1,3,4-oxadiazoles are prepared and reported as anticancer agents by numerous scientists worldwide.

OBJECTIVES

The present review discusses the anticancer potentials together with the molecular targets of 1,3,4-oxadiazoles reported since 2010. The structure activity relationship (SAR) and molecular docking simulation on different targets have also been discussed herein. Some of the important cancer targets have also been explored.

METHODS

The most potent 1,3,4-oxadiazoles reported in literature was highlighted in the manuscript. The anticancer activity was reported in terms of growth percent (GP), percent growth inhibition (%GI), GI50, IC50, and LC50 and TGI.

RESULTS

1,3,4-Oxadiazoles are an important heterocyclic scaffolds with broad spectrum biological activities. They may be either mono substituted or disubstituted and act as an indispensable anchor for drug design and discovery due to their thermal stability together with low lipophilicity. They exhibited anticancer potentials and showed the inhibitions of various cancer targets.

CONCLUSION

The discussion outlined herein will proved to be a helpful and vital tool for medicinal chemists investigating and working with 1,3,4-oxadiazoles and anticancer research programs.

Synthesis, Antiproliferative, and Antioxidant Activities of Substituted N-[(1,3,4-Oxadiazol-2-yl) Methyl] Benzamines

Background:

Oxadiazole emerged as an important class of heterocyclic compound with diverse biological activities like anticancer, antitubercular, anticonvulsant, anti-tubulin, antimicrobial, anti-inflammatory, antioxidant etc.

Objective:

The objective of this study is to synthesis series of twelve substituted N-[(1,3,4-oxadiazol-2- yl)methyl]benzamines (6a-l) and their evaluation as antiproliferative and antioxidant agents.

Methods:

The substituted N-[(1,3,4-oxadiazol-2-yl)methyl]benzamines (6a-l) analogues were synthesized as per the reported procedure. The antiproliferative activity was tested against nine different panels cancer cell lines (leukemia, colon, renal, non-small cell lung, breast, CNS, melanoma, prostate, and ovarian cancer) at 10 µM drug concentrations as per the NCI US Protocol.

Results:

2-(5-((3-Chloro-4-fluorophenylamino)methyl)-1,3,4-oxadiazol-2-yl)phenol (6e) revealed the significant antiproliferative activity among the series of title compounds (6a-l). The compound, 6e showed maximum sensitivity towards CCRF-CEM, MCF-7, MOLT-4, T-47D, and SR cell lines with percent growth inhibitions (%GIs) of 79.92, 56.67, 39.62, 34.71 and 33.35, respectively. Furthermore, the compounds, 6e and 6c showed promising antioxidant activity with an IC50 value of 15.09 and 19.02 µM, respectively in DPPH free radicals (FR) scavenging activity.R

Conclusion:

The present study may support a significant value in cancer drug discovery programme.

Crystal structures and Hirshfeld surface analysis of 2-(adamantan-1-yl)-5-(4-fluoro-phen-yl)-1,3,4-oxa-diazole and 2-(adamantan-1-yl)-5-(4-chloro-phen-yl)-1,3,4-oxa-diazole

The crystal structures of the title adamantane-oxa-diazole hybrid compounds, C18H19FN2O (I) and C18H19ClN2O (II), are built up from an adamantane unit and a halogenophenyl ring, [X = F (I), Cl (II)], in position 5 on the central 1,3,4-oxa-diazole unit. The mol-ecular structures are very similar, only the relative orientation of the halogenophenyl ring in comparison with the central five-membered ring differs slightly. In the crystals of both compounds, mol-ecules are linked by pairs of C-H⋯N hydrogen bonds, forming inversion dimers with R 2 2(12) ring motifs. In (I) the dimers are connected by C-H⋯F inter-actions, forming slabs lying parallel to the bc plane. In (II), the dimers are linked by C-H⋯π and offset π-π inter-actions [inter-planar distance = 3.4039 (9) Å], forming layers parallel to (10).