Green approach for the synthesis of thiophenyl pyrazoles and isoxazoles by adopting 1,3-dipolar cycloaddition methodology and their antimicrobial activity

Iodine/DMSO-mediated one-pot access towards 1-aryl-2-(pyrazol-5-yl)ethane-1,2-diones via a domino reaction from functionalized pent-2-ene-1,5-diones

A facile one-pot cascade synthesis involving simultaneous in situ pyrazole formation followed by iodine/DMSO-mediated oxidation has been established to afford 1-aryl-2-(3-aryl)-1H-pyrazol-5-yl-ethane-1,2-diones. Primarily, a two-pot approach has been established which includes the reaction of 3-methylthio-1,5-diaryl-2-pentene-1,5-diones with hydrazine in the first step to afford pyrazole, which was eventually oxidized in the next steps in the presence of iodine in DMSO. Furthermore, we performed both steps in the same pot to afford 1,2-dicarbonyl compounds in good yield. The structure of one of the compounds was confirmed by single crystal X-ray analysis. DMSO served as a solvent as well as an oxidant. Moreover, N-substituted hydrazines provided 1-(1-substituted-3-aryl-1H-pyrazol-5-yl)-2-arylethane-1,2-diones regioselectively. Furthermore, for synthetic application, 1-aryl-2-(3-aryl)-1H-pyrazol-5-yl-ethane-1,2-diones were treated with o-phenylenediamine to afford pyrazole-functionalized quinoxaline in good yield. A control reaction was carried out to understand the mechanism of product formation.

DFT Study of Regio- and Stereoselective 13DC Reaction between Diazopropane and Substituted Chalcone Derivatives: Molecular Docking of Novel Pyrazole Derivatives as Anti-Alzheimer's Agents

In the present work, a combination of experimental and density functional theory (DFT) investigation of the (3+2) cycloaddition reactions of diazopropane with chalcone derivatives was reported. All calculations were performed using several DFT approaches (B3LYP, M06, M06-2X) and 6-311+G(d, p) basis set. Based on the NMR, MS analyses and IRC calculations, the pyrazole derivatives are the kinetic adducts over the oxadiazoles. The use of two equivalents of diazopropane leads to thermodynamical products. A molecular docking analysis was performed to investigate the efficiency of the obtained products against selected drug targets in anti-Alzheimer ligand-receptor interactions. We revealed that the ligands selected were bound mainly to the catalytic (CAS) and peripheral (PAS) anionic sites of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors, respectively. The selected ligands 1, 3, 4 and P14 may act as the best inhibitors against Alzheimer's disease (AD).

Thiophene-containing compounds with antimicrobial activity

Thiophene, as a member of the group of five-membered heterocycles containing one heteroatom, is one of the simplest heterocyclic systems. Many synthetic strategies allow the accurate positioning of various functionalities onto the thiophene ring. This review provides a comprehensive, systematic and detailed account of the developments in the field of antimicrobial compounds featuring at least one thiophene ring in their structure, over the last decade.

Design, Synthesis, Herbicidal Activity, and Molecular Docking Study of 2-Thioether-5-(Thienyl/Pyridyl)-1,3,4-Oxadiazoles as Potent Transketolase Inhibitors

Transketolase (TK) has been regarded as a new target for the development of novel herbicides. In this study, a series of 2-thioether-5-(thienyl/pyridyl)-1,3,4-oxadiazoles were designed and synthesized based on TK as the new target. The preliminary bioassay results indicated that compounds 4l and 4m displayed the best herbicidal activities against Amaranthus retroflexus (AR) and Digitaria sanguinalis (DS), with the inhibition exceeding 90% at 100-200 mg/L in vitro. Moreover, they also displayed higher postemergence herbicidal activities (90% control) against AR and DS than all of the positive controls at 45-90 g [active ingredient (ai)]/ha in a greenhouse. Notably, compounds 4l and 4m showed a broad spectrum of weed control at 90 g ai/ha. More significantly, compound 4l exhibited good crop selectivity against maize at 90 g ai/ha. Both fluorescent binding experiments and molecular docking analyses indicated that compounds 4l and 4m exhibited strong TK inhibitory activities with superior binding affinities than the others. Preliminary mechanism studies suggested that they might exert their TK inhibitory effects by occupying the active cavity of At TK and forming more strong interactions with amino acids in the active site. Taken together, these results suggested that compound 4l was a potential herbicide candidate for weed control in maize fields targeting TK.

Novel benzenesulfonamide-bearing pyrazoles and 1,2,4-thiadiazoles as selective carbonic anhydrase inhibitors

Two series comprising 20 novel benzenesulfonamides bearing thioureido-linked pyrazole 8 and amino-1,2,4-thiadiazole 10 were synthesized and assayed as human carbonic anhydrase (hCA) inhibitors against isoforms I and II as well as the tumor-associated isoforms IX and XII. Molecular modeling studies of some potent derivatives (8a, 8c, 10a, and 10c) were also performed against isoforms hCA I, II, and XII. Both the promising series of compounds were synthesized by using commercially available mtethyl ketones and sulfanilamide as the starting materials. Interestingly, this paper also reports a novel methodology for the synthesis of amino-1,2,4-thiadiazoles 10 using 3-amino isoxazoles and 4-isothiocyanatobenzenesulfonamide as reactants. The activity profile of all the newly synthesized compounds reveals that amino-linked 1,2,4-thiadiazoles 10 were better inhibitors of the cytosolic isoform, hCA I, as compared to thioureido-linked pyrazoles 8. Further, hCA II was strongly inhibited by nearly all the newly synthesized sulfonamides, while all the compounds were less effective as hCA IX and XII inhibitors compared to the standard drug acetazolamide. However, in terms of selectivity, compound 8e was found to be the most selective inhibitor of hCA II, which is the isoform associated with glaucoma, edema, altitude sickness, and epilepsy.

An overview of metal-free synthetic routes to isoxazoles: the privileged scaffold

In the field of drug discovery, isoxazole is a five-membered heterocyclic moiety commonly found in many commercially available drugs. In view of their enormous significance, it is always imperative to unleash new eco-friendly synthetic strategies. Among various novel synthetic techniques in use for isoxazole synthesis, most synthetic methods employ Cu(i) or Ru(ii) as catalysts for (3 + 2) cycloaddition reaction. The particular disadvantages associated with metal-catalyzed reactions are high costs, low abundance, toxicity, a significant generation of waste, and difficulty to separate from the reaction mixtures. In view of these drawbacks, it is always imperative to develop alternate metal-free synthetic routes. This review article highlights a comprehensive overview on the potential application of metal-free synthetic routes for the synthesis of isoxazoles with significant biological interests.

Transition Metal-Free De Novo Synthesis of Sulfonated Pyrazoles from Sulfonyl Hydrazides, 1,3-Diketones, and Sodium Sulfinates at Room Temperature

A transition metal-free method for de novo construction of diverse sulfonated pyrazoles from readily available sulfonyl hydrazides, 1,3-diketones, and sodium sulfinates was established under mild conditions. Pyrazoles bearing two different sulfonyl groups were obtained in one step. The method features a diversity of substituents of the pyrazole products and a remarkably simple work-up.

Molecular properties prediction, synthesis, and antimicrobial activity of bis(azolyl)sulfonamidoacetamides

A library of bis(azolyl)sulfonamidoacetamides was prepared by the reaction of azolylsulfonylamines with azolylchloroacetamides in the presence of pyridine/4-(dimethylamino)pyridine (DMAP) under ultrasonication. The reaction proceeded well with DMAP, resulting in a higher yield of the products. The antimicrobial activity of the compounds indicated that N-{5-[N-(2-{[4-(4-chloro-1H-pyrrol-2-yl)-1H-imidazol-2-yl)amino}-2-oxoethyl)sulfamoyl]-4-phenylthiazol-2-yl}benzamide (22a), N-{5-[N-(2-{[4-(4-chloro-1H-pyrrol-2-yl)-1H-imidazol-2-yl]amino}-2-oxoethyl)sulfamoyl]-4-(4-chlorophenyl)thiazol-2-yl}benzamide (22c), and N-{5-[N-(2-{[4-(4-chloro-1H-pyrrol-2-yl)-1H-imidazol-2-yl]amino}-2-oxoethyl)sulfamoyl]-4-(4-chloro-phenyl)-1H-imidazol-2-yl}benzamide (24c) exhibited a low minimal inhibitory concentration (MIC) against Bacillus subtilis, equal to the standard drug, chloramphenicol. Compounds 22c and 24c also showed low MICs against Aspergillus niger, equal to the standard drug, ketoconazole. The molecular properties of the synthesized molecules were studied to identify druglikeness properties of the target compounds. On the basis of molecular properties prediction, 19a, 19b, 20b, 20c, 21a-c, 22b, 22c, and 23a-c can be treated as drug candidates.

Antimicrobial, Antioxidant, and Anticancer Activities of Some Novel Isoxazole Ring Containing Chalcone and Dihydropyrazole Derivatives

Our previous work identified isoxazole-based chalcones and their dihydropyrazole derivatives as two important five-membered heterocycles having antitubercular activity. Hence, in the present study, we biologically evaluated 30 compounds, including 15 isoxazole ring-containing chalcones (17-31) and 15 dihydropyrazoles (32-46) derived from these chalcones for their antimicrobial, antioxidant, and anticancer activities. Chalcones exhibited superior antibacterial and antioxidant activities compared to dihydropyrazoles. Among the chalcones, compound 28 showed potent antibacterial (MIC = 1 µg/mL) and antioxidant activities (IC₅₀ = 5 ± 1 µg/mL). Dihydropyrazoles, on the contrary, demonstrated remarkable antifungal and anticancer activities. Compound 46 (IC₅₀ = 2 ± 1 µg/mL) showed excellent antifungal activity whereas two other dihydropyrazoles 45 (IC₅₀ = 2 ± 1 µg/mL) and 39 (IC₅₀ = 4 ± 1 µg/mL) exhibited potential anticancer activity. The compounds were also tested for their toxicity on normal human cell lines (LO2) and were found to be nontoxic. The active compounds that have emerged out of this study are potential lead molecules for the development of novel drugs against infectious diseases, oxidative stress, and cancer.

Synthesis of Amido Sulfonamido Heteroaromatics Under Ultrasonication and Their Antimicrobial Activity

A convenient and facile methodology for N-sulfonylation of heteroaryl amines with ethyl chlorosulfonylacetate in the presence of dispersed sodium in THF under ultrasonication is reported. The corresponding heteroaryl sulfonamido esters are directly condensed with heteroaryl amines to get amido sulfonamido heteroaromatics in the presence of a mild base in THF under ultrasonication. Utilization of easy reaction conditions, shorter reaction times, and isolation of products in high yields under ultrasonication make this process as economically viable. The compounds 12c, 12d, 12f and 13f are potential antibacterial agents against B. subtilis and the compounds 12f, 13c and 13f are potential antifungal agents against A. niger.

Synthesis and antifungal activities of novel thiophene-based stilbene derivatives bearing an 1,3,4-oxadiazole unit

BACKGROUND

Natural stilbenes (especially resveratrol and its derivatives) are well-known phytoalexins that are active against many plant diseases. However, oxidative degradation and low bioavailability limit their exogenous application as fungicides on crops. In this study, a new class of resveratrol-inspired thiophene-based stilbene derivatives bearing an 1,3,4-oxadiazole unit was synthesized and the derivatives' antifungal activities against phytopathogenic fungi were investigated.

RESULTS

The results revealed that compounds 5h and 5j exhibited improved antifungal activity against Botrytis cinerea with median effective concentrations (EC₅₀ ) of 168.5 and 155.4 µg mL^-1 , respectively, which were superior to the EC₅₀ of resveratrol (263.1 µg mL^-1 ). Compound 5j was shown to effectively control disease development in B. cinerea-infected tomatoes in vivo. Notably, considerably abnormal mycelial morphology and increased cell membrane conductivity were observed in the presence of compound 5j.

CONCLUSION

A new class of thiophene-containing stilbene derivatives was designed and synthesized. Bioassay results showed that compound 5j exhibited promising antifungal activity, suggesting practical potential for fungal disease control. © 2018 Society of Chemical Industry.

Domino C-H Sulfonylation and Pyrazole Annulation for Fully Substituted Pyrazole Synthesis in Water Using Hydrophilic Enaminones

The cascade reactions between NH₂-functionalized enaminones and sulfonyl hydrazines have been developed for the synthesis of fully substituted pyrazoles. By making use of the hydrophilic primary amino group in the enaminones, the reactions proceed well in the medium of pure water in the presence of molecular iodine, TBHP, and NaHCO₃ via cascade C-H sulfonylation and pyrazole annulation. The cleavage of the C-N bond in enaminones is confirmed by the experiment using ¹⁵ N-labeled enaminone.

Design of a simple and efficient synthesis for bioactive novel pyrazolyl–isoxazoline hybrids

A simple and new methodology has been developed for the synthesis of novel bioactive pyrazolyl–isoxazoline hybrids using pyrazoline-substituted oxime. Among the hybrid materials, 6m and 6p were found to show the best anti-bacterial and anti-fungal activities.