Synthesis and biological evaluation of novel substituted 1,3,4-thiadiazole and 2,6-di aryl substituted imidazo [2,1-b] [1,3,4] thiadiazole derivatives

Synthesis and Evaluation of Imidazole Derivatives Bearing Imidazo[2,1-b] [1,3,4]thiadiazole Moiety as Antibacterial Agents

BACKGROUND

Drug-resistant infections kill hundreds of thousands of people globally every year. In previous work, we found that tri-methoxy- and pyridine-substituted imidazoles show strong antibacterial activities.

OBJECTIVE

The aim of this work was to investigate the antibacterial activities and bacterial resistances of imidazoles bearing an aromatic heterocyclic, alkoxy, or polycyclic moiety on the central ring.

METHODS

Three series of 2-cyclopropyl-5-(5-(6-methylpyridin-2-yl)-2-substituted-1H-imidazol-4- yl)-6-phenylimidazo[2,1-b][1,3,4]thiadiazoles (13a-e, 14a-d, and 15a-f) were synthesized and their antibacterial activity was evaluated. The structures were confirmed by their 1H NMR, 13C NMR, and HRMS spectra. All the synthesized compounds were screened against Gram-positive, Gramnegative, and multidrug-resistant bacterial strains.

RESULTS

More than half of the compounds showed moderate or strong antibacterial activity. Among them, compound 13e (MICs = 1-4 μg/mL) showed the strongest activity against Gram-positive and drug-resistant bacteria as well as high selectivity against Gram-negative bacteria. Furthermore, it showed no cytotoxicity against HepG2 cells, even at 100 μM, and no hemolysis at 20 μM.

CONCLUSION

These results indicate that compound 13e is excellent candicate for further study as a potential antibacterial agent.

Thiadiazole and Thiazole Derivatives as Potential Antimicrobial Agents

BACKGROUND

This review summarizes data on heterocyclic systems with thiadiazole and thiazole fragments in molecules as promising antimicrobial agents.

INTRODUCTION

Thiadiazole and thiazole backbones are the most favored and well-known heterocycles, a common and essential feature of various drugs. These scaffolds occupy a central position and are the main structural components of numerous drugs with a wide spectrum of action. These include antimicrobial, antituberculous, anti-inflammatory, analgesic, antiepileptic, antiviral, and anticancer agents.

METHOD

The research is based on bibliosemantic and analytical methods using bibliographic and abstract databases, as well as databases of chemical compounds.

RESULT

This review reports on thiadiazole and thiazole derivatives, which have important pharmacological properties. We are reviewing the structural modifications of various thiadiazole and thiazole derivatives, more specifically, the antimicrobial activity reported over the last years, as we have taken this as our main research area. 80 compounds were illustrated, and various derivatives containing hydrazone bridged thiazole and pyrrole rings, 2-pyridine and 4-pyridine substituted thiazole derivatives, compounds containing di-, tri- and tetrathiazole moieties, spiro-substituted 4- thiazolidinone-imidazoline-pyridines were analyzed. Derivatives of 5-heteroarylidene-2,4- thiazolidinediones, fluoroquinolone-thiadiazole hybrids, and others.

CONCLUSION

1,3,4-thiadiazoles and thiazoles are valuable resource for researchers engaged in rational drug design and development in this area.

Synthesis and antimicrobial activity evaluation of pyrazole derivatives containing the imidazo[2,1-b][1,3,4]thiadiazole moiety

Four series of novel pyrazole derivatives (compounds 17a-m, 18a-m, 19a-g, and 20a-g) were synthesized, and their antibacterial and antifungal activities were evaluated. Most of the target compounds (17a-m, 18k-m, and 19b-g) showed strong antifungal activity and high selectivity relative to both Gram-positive and Gram-negative bacteria. Among them, compounds 17l (minimum inhibitory concentration [MIC] = 0.25 µg/mL) and 17m (MIC = 0.25 µg/mL) showed the strongest antifungal activity, being 2- and 4-fold more active than the positive controls gatifloxacin and fluconazole, respectively. In particular, compound 17l showed little cytotoxicity against human LO2 cells and did not exhibit hemolysis at ultrahigh concentrations, as did the positive control compounds gatifloxacin and fluconazole. These results indicate that these compounds are valuable for further development as antifungal agents.

Novel Thioether-Bridged 2,6-Disubstituted and 2,5,6-Trisubstituted Imidazothiadiazole Analogues: Synthesis, Antiproliferative Activity, ADME, and Molecular Docking Studies

In this study, starting from 2-amino-1,3,4-thiadiazole derivatives (3-5), a new series of 2,6-disubstituted (compounds 7-15) and 2,5,6-trisubstituted (compounds 16-33) imidazo[2,1-b][1,3,4]-thiadiazole derivatives were synthesized using cyclization and Mannich reaction mechanisms, respectively. All synthesized compounds were characterized by ¹ H-NMR, ¹³ C-NMR, FT-IR, elemental analysis, and mass spectroscopy techniques. Also, X-ray diffraction analysis were used for compounds 4, 7, 11, 17, and 19. The cytotoxic effects of the new compounds on the viability of colon cancer cells (DLD-1), lung cancer cells (A549), and liver cancer cells (HepG2) were investigated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method in vitro. Compound 15 was found to be the most potent anticancer drug candidate in this series with an IC₅₀ value of 3.63 μM against HepG2 for 48 h. Moreover, the absorption, distribution, metabolism, and excretion (ADME) parameters of the synthesized compounds were calculated and thus, their potential to be safe drugs was evaluated. Finally, to support the biological activity experiments, molecular docking studies of these compounds were carried out on three different target cancer protein structures (PDB IDs: 5ETY, 1M17, and 3GCW), and the amino acids that play key roles in the binding of the compounds to these proteins were determined.

Comparative Study of the Synthetic Approaches and Biological Activities of the Bioisosteres of 1,3,4-Oxadiazoles and 1,3,4-Thiadiazoles over the Past Decade

The bioisosteres of 1,3,4-oxadiazoles and 1,3,4-thiadiazoles are well-known pharmacophores for many medicinally important drugs. Throughout the past 10 years, 1,3,4-oxa-/thiadiazole nuclei have been very attractive to researchers for drug design, synthesis, and the study of their potential activity towards a variety of diseases, including microbial and viral infections, cancer, diabetes, pain, and inflammation. This work is an up-to-date comparative study that identifies the differences between 1,3,4-thiadiazoles and 1,3,4-oxadiazoles concerning their methods of synthesis from different classes of starting compounds under various reaction conditions, as well as their biological activities and structure–activity relationship.

Design, synthesis, characterization, in vitro and in silico evaluation of novel imidazo[2,1-b][1,3,4]thiadiazoles as highly potent acetylcholinesterase and non-classical carbonic anhydrase inhibitors

Imidazole and thiadiazole derivatives display an extensive application in pharmaceutical chemistry, and they have been investigated as bioactive molecules for medicinal chemistry purposes. Classical carbonic anhydrase (CA) inhibitors are based on sulfonamide groups, but inhibiting all CA isoforms nonspecifically, thereby causing undesired side effects, is the main drawback of these types of inhibitors. Here we reported an investigation of novel 2,6-disubstituted imidazo[2,1-b][1,3,4]thiadiazole derivatives (9a-k, 10a, and 11a) and 2,5,6-trisubstituted imidazo[2,1-b][1,3,4]thiadiazole derivatives (12a-20a) that do not possess the zinc-binding sulfonamide group for the inhibition of human carbonic anhydrase (hCA, EC 4.2.1.1) I and II isoforms and also of acetylcholinesterase (AChE, EC 3.1.1.7). Imidazo[2,1-b][1,3,4]thiadiazoles demonstrated low nanomolar inhibitory activity against hCA I, hCA II, and AChE (K_Is are in the range of 23.44-105.50 nM, 10.32-104.70 nM, and 20.52-54.06 nM, respectively). Besides, compound 9b inhibit hCA I up to 18-fold compared to acetazolamide, while compound 10a has a 5-fold selectivity towards hCA II. The synthesized compounds were also evaluated for their cytotoxic effects on the L929 mouse fibroblast cell line. Molecular docking simulations were performed to elucidate these inhibitors' potential binding modes against hCA I and II isoforms and AChE. The novel compounds reported here can represent interesting lead compounds, and the results presented here might provide further structural guidance to discover and design more potent hCA and AChE inhibitors.

Synthesis and Antimicrobial Activity Evaluation of Imidazole-Fused Imidazo[2,1-b][1,3,4]thiadiazole Analogues

Three series of new imidazole-fused imidazo[2,1-b][1,3,4]thiadiazole analogues (compounds 20 a-g, 21 a-g, and 22 a-g) have been synthesized, and their antibacterial and antifungal activities have been evaluated. All the target compounds showed strong antifungal activity and high selectivity for the test fungus Candida albicans over Gram-positive and -negative bacteria. N-((4-(2-Cyclopropyl-6-(4-fluorophenyl)imidazo[2,1-b][1,3,4]thiadiazol-5-yl)-5-(6-methyl-pyridin-2-yl)-1H-imidazol-2-yl)methyl)aniline (21 a) showed the highest activity against C. albicans (MIC₅₀ =0.16 μg/mL), 13 and three times that of the positive control compounds gatifloxacin and fluconazole, respectively. Compounds 21 a and 20 e did not show cytotoxicity against human foreskin fibroblast-1 cells, and compound 21 a was as safe as the positive control compounds in hemolysis tests. These results strongly suggest that some of the compounds produced in this work have value for development as antifungal agents.

Metal-free Catalyzed One-Pot Multicomponent Synthesis of (E)-3-(2-((5-(Benzylideneamino)-1,3,4-thiadiazol-2-yl)thio) Acetyl)-2H-chromen-2-one Derivatives and Their Biological Evaluation

A series of (E)-3-(2-((5-(benzylideneamino)-1,3,4-thiadiazol-2-yl)thio) acetyl)-2H-chromen-2-one and its derivatives (4a-h) have been obtained using a one-pot multicomponent reaction with good yields. The compounds have been synthesized from 3-(2-bromoacetyl)chromen-2-ones (1), 5-amino-1,3,4-thiadiazole-2-thiol (2), and substituted benzaldehydes (3) in anhydrous ethanol and conc. H2SO4. Subsequently, all the synthesized compounds have been screened for their antimicrobial activity and characterized by analytical and spectral data.

Hypolipidemic effect of novel 2,5-bis(4-hydroxybenzylidenamino)-1,3,4-thiadiazole as potential peroxisome proliferation-activated receptor-α agonist in acute hyperlipidemic rat model

The development of new antihyperlipidemic agents with higher potency and lower side effects is of high priority. In this study, 1,3,4 thiadiazole Schiff base derivatives were synthesized as potential peroxisome proliferation-activated receptor-α (PPARα) agonists and characterized using elemental analysis, FTIR, ¹H-NMR, ¹³C-NMR and mass spectroscopy and then tested for their hypolipidemic activity in Triton WR-1339-induced acute hyperlipidemic rat model in comparison with bezafibrate. The compounds showed significant hypolipidemic activity. Induced fit docking showed that the compounds are potential activators of PPARα with binding scores - 8.00 Kcal/mol for 2,5-bis(4-hydroxybenzylidenamino)-1,3,4-thiadiazole. PCR array analysis showed an increase in the expression of several genes involved in lipid metabolism through mitochondrial fatty acid β oxidation and are part of PPARα signaling pathway including Acsm3, Fabp4 and Hmgcs1. Gene expression of Lrp12 and Lrp1b involved in LDL uptake by liver cells and Cyp7a1 involved in cholesterol catabolism were also found to be upregulated.

An efficient synthesis of imidazo[2,1-b][1,3,4]thiadiazol-7-ium hydroxides by a one-pot, three-component reaction in water

An improved synthesis of 2-ethyl-5-(2-hydroxy-4-oxoquinolin-3(4H)-ylidene)-6-aryl-5,6-dihydroimidazo[2,1-b][1,3,4]thiadiazol-7-ium hydroxide derivatives 4a–k via the reaction of aryl glyoxal monohydrates 1a–k, quinoline-2,4-diol 2 and 2-amino-[1,3,4]thiadiazole (3) in the presence of Et3N/sulfamic acid in H2O is described. This green protocol is characterized by the use of the readily available catalyst and reactants, short reaction times, operational simplicity and high yields of products. The structures of all compounds were characterized by 1H NMR, 13C NMR and Fourier-transform infrared (FT-IR) spectral data and microanalyses.

An integrated approach towards the development of novel antifungal agents containing thiadiazole: synthesis and a combined similarity search, homology modelling, molecular dynamics and molecular docking study

Background

This study aims to synthesise and characterise novel compounds containing 2-amino-1,3,4-thiadiazole and their acyl derivatives and to investigate antifungal activities. Similarity search, molecular dynamics and molecular docking were also studied to find out a potential target and enlighten the inhibition mechanism.

Results

As a first step, 2-amino-1,3,4-thiadiazole derivatives (compounds 3 and 4) were synthesised with high yields (81 and 84%). The target compounds (6a–n and 7a–n) were then synthesised with moderate to high yields (56–87%) by reacting 3 and 4 with various acyl chloride derivatives (5a–n). The synthesized compounds were characterized using the IR, ¹H-NMR, ¹³C-NMR, Mass, X-ray (compound 7n) and elemental analysis techniques. Later, the in vitro antifungal activities of the synthesised compounds were determined. The inhibition zones exhibited by the compounds against the tested fungi, their minimum fungicidal activities, minimum inhibitory concentration and the lethal dose values (LD₅₀) were determined. The compounds exhibited moderate to high levels of activity against all tested pathogens. Finally, in silico modelling was used to enlighten inhibition mechanism using ligand and structure-based methods. As an initial step, similarity search was carried out and the resulting proteins that belong to Homo sapiens were used as reference in sequence similarity search to find the corresponding amino acid sequences in target organisms. Homology modelling was used to construct the protein structure. The stabilised protein structure obtained from molecular dynamics simulation was used in molecular docking.

Conclusion

The overall results presented here might be a good starting point for the identification of novel and more active compounds as antifungal agents.

Electronic supplementary material

The online version of this article (10.1186/s13065-018-0485-3) contains supplementary material, which is available to authorized users.

Construction of 1,3,4-Oxadiazole and 1,3,4-Thiadiazole Library with a High Level of Skeletal Diversity Based on Branching Diversity-Oriented Synthesis on Solid-Phase Supports

An efficient solid-phase synthetic route for the construction of 1,3,4-oxadiazole and 1,3,4-thiadiazole libraries based on branching diversity-oriented synthesis (DOS) has been developed in this study. The core skeleton resins, 1,3,4-oxadiazole and 1,3,4-thiadiazole, were obtained through desulfurative and dehydrative cyclizations of thiosemicarbazide resin, respectively. Various functional groups have been introduced to the core skeleton resins, such as aryl, amine, amide, urea, thiourea, and an amino acid. Most of the libraries were purified by simple trituration without extraction or column chromatography after cleavage of the products from the solid-supported resin. As a result, we obtained high yields of pure 1,3,4-oxadiazole and 1,3,4-thiadiazole derivatives (total numbers = 128). Finally, we confirmed the drug-like properties of our library by calculation of physicochemical properties, displays of the skeletal diversities of the library in 3D-space, and occupation of a broad range of areas by their functional groups.

Thiadiazole inhibitors: a patent review

INTRODUCTION

Four isomeric structures of thiadiazole motifs have outstanding pharmacological inhibitory applications are reported in this review. Thiadiazole nucleus is present in several biologically active natural products and commercial drugs. Most of thiadiazoles reported herein are emphasized to have broad spectrum of medicinal activities. Areas covered: This review represents the recent inhibitory activities of thiadiazole isomeric scaffolds and their broad-spectrum biological applications published as full texts during 2010-2016 as well as the patents published during 2005-2016. The inhibition areas covered included anti-inflammatory, antimicrobial, antitumor, antioxidant, antitubercular, antiviral, antileishmanial, anticonvulsant, herbicidal and algicidal activities in addition to enzymes, human platelet aggregation and neuroprotective inhibitors. Expert opinion: This survey revealed very interesting data about the applications of thiadiazoles, where some synthetic or natural thiadiazole derivatives were components of drugs available in the market. Many thiadiazole derivatives can be considered as lead compounds for drug synthesis. The most inhibitory active 1,3,4-thiadiazole compounds are those incorporating secondary alkyl(aryl)amido- and/or benzylthio(mercapto) groups at positions 2 and 5. Several thiadiazole derivatives demonstrated higher antibacterial, antitumor and antiviral activities than the standard drugs. Some thiadiazole derivatives exhibited high selective enzymes inhibitory activities based on the electronic properties of the substituents at positions 2 or 5.

QSAR models of antiproliferative activity of imidazo[2,1-b][1,3,4]thiadiazoles in various cancer cell lines

Imidazo[2,1-b][1,3,4]thiadiazoles have been recognized to possess antiproliferative potency towards a wide spectrum of cancer cell lines. QSAR investigations on a set of 42 di(tri)substituted imidazo[2,1-b][1,3,4]thiadiazoles were carried out to find the descriptors determining their biological potency. Three-variable equations were obtained by combinatorial protocols in multiple linear regression (CP MLR) for all three studied cancer cell lines. They showed that lipophilicity, electronic, and steric factors are decisive for the antiproliferative potency of compounds and indicate the important role of nitrogen atoms of imidazothiadiazole ring in the interactions with the molecular target. The best models gave high r squared values in the range from 0.887 to 0.924. They also have good predictive accuracy confirmed by the high value LOO cross-validation coefficient [Formula: see text] (from 0.842 to 0.904) and by the external validation quantities.

Solid-Phase Synthesis of 1,3,4-Thiadiazole Derivatives via Desulfurative Cyclization of Thiosemicarbazide Intermediate Resin

A 1,3,4-thiadiazole library was constructed by solid-phase organic synthesis. The key step of this solid-phase synthesis involves the preparation of polymer-bound 2-amido-5-amino-1,3,4-thiadiazole resin by the cyclization of thiosemicarbazide resin using p-TsCl as the desulfurative agent, followed by the functionalization of the resin by alkylation, acylation, alkylation/acylation, and Suzuki coupling reactions. Both the alkylation and acylation reactions chemoselectively occurred at the 2-amide position of 2-amido-5-amino-1,3,4-thiadiazole resin and the 5-amine position of 2-amido-5-amino-1,3,4-thiadiazole resin, respectively. Finally, these functionalized 1,3,4-thiadiazole resins were treated with trifluoroacetic acid in dichloromethane, affording diverse 1,3,4-thiadiazole analogs in high yields and purities. The 1,3,4-thiadiazole analogs show a different distribution of physicochemical and biological properties compared with our previously constructed 1,3,4-oxadiazole and 1,3,4-thiadiazole libraries in a range of orally available drug properties.

A Highly Efficient Diversification of 2-Amino/Amido-1,3,4-oxadiazole and 1,3,4-Thiadiazole Derivatives via Reagent-Based Cyclization of Thiosemicarbazide Intermediate on Solid-Phase

A 2-amino/amido-1,3,4-oxadiazole and 1,3,4-thiadiazole library has been constructed on solid-phase organic synthesis. The key step on this solid-phase synthesis involves the preparation of polymer-bound 2-amino-1,3,4-oxadiazole and 1,3,4-thiadiazole core skeleton resin by cyclization of thiosemicarbazide with EDC·HCl and p-TsCl, respectively. The resulting core skeleton undergoes functionalization reaction with various electrophiles such as alkyl halides, and acid chlorides to generate N-alkylamino and N-acylamino-1,3,4-oxadiazole, and 1,3,4-thiadiazole resin, respectively. Finally, the 2-amino and 2-amido-1,3,4-oxadiazole and 1,3,4-thiadiazole library was then generated in good yields and high purities by cleavage of the respective resin under trifluoroacetic acid(TFA) in dichloromethane(DCM). The constructed library shows reasonable, oral bioavailability drug properties as determine by using the Lipinski's Rule and similar parameters.

Selective Cytotoxicity of 1,3,4-Thiadiazolium Mesoionic Derivatives on Hepatocarcinoma Cells (HepG2)

In this work, we evaluated the cytotoxicity of mesoionic 4-phenyl-5-(2-Y, 4-X or 4-X-cinnamoyl)-1,3,4-thiadiazolium-2-phenylamine chloride derivatives (MI-J: X=OH, Y=H; MI-D: X=NO2, Y=H; MI-4F: X=F, Y=H; MI-2,4diF: X=Y=F) on human hepatocellular carcinoma (HepG2), and non-tumor cells (rat hepatocytes) for comparison. MI-J, M-4F and MI-2,4diF reduced HepG2 viability by ~ 50% at 25 μM after 24-h treatment, whereas MI-D required a 50 μM concentration, as shown by 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyltetrazolium bromide assays. The cytotoxicity was confirmed with lactate dehydrogenase assay, of which activity was increased by 55, 24 and 16% for MI-J, MI-4F and MI-2,4diF respectively (at 25 μM after 24 h). To identify the death pathway related to cytotoxicity, the HepG2 cells treated by mesoionic compounds were labeled with both annexin V and PI, and analyzed by flow cytometry. All compounds increased the number of doubly-stained cells at 25 μM after 24 h: by 76% for MI-J, 25% for MI-4F and MI-2,4diF, and 11% for MI-D. It was also verified that increased DNA fragmentation occurred upon MI-J, MI-4F and MI-2,4diF treatments (by 12%, 9% and 8%, respectively, at 25 μM after 24 h). These compounds were only weakly, or not at all, transported by the main multidrug transporters, P-glycoprotein, ABCG2 and MRP1, and were able to slightly inhibit their drug-transport activity. It may be concluded that 1,3,4-thiadiazolium compounds, especially the hydroxy derivative MI-J, constitute promising candidates for future investigations on in-vivo treatment of hepatocellular carcinoma.

Synthesis and biological evaluation of new pleuromutilin derivatives as antibacterial agents

Several pleuromutilin derivatives possessing thiadiazole moieties were synthesized via acylation reactions under mild conditions. The in vitro antibacterial activities of the derivatives against methicillin-resistant S. aureus, methicillin-resistant S. epidermidis, S. aureus, S. epidermidis, E. coli, and B. cereus were tested by the agar dilution method and Oxford cup assay. All the screened compounds displayed potent activity. Compound 6d was the most active antibacterial agent because of its lowest MIC value and largest inhibition zone. Docking experiments were performed to understand the possible mode of the interactions between the derivatives and 50S ribosomal subunit. Moreover, the absorption, distribution, metabolism, excretion and toxicity properties of the synthesized compounds were analyzed after prediction using the Advanced Chemistry Development/Percepta Platform available online.