Pravin K. Singh

Synthesis and Fungicidal Activity of Novel 3-(Substituted/unsubstituted phenylselenonyl)-1-ribosyl/deoxyribosyl-1H-1,2,4-triazole

Reaction of potassium 1H-1,2,4-triazole-3-selenolate (I) with acetylated ribose/deoxyribose (IIa,b) in the presence of montmorillonite K 10 as a solid adsorbent furnished potassium 1-acetylated ribosyl/deoxyribosyl-1H-1,2,4-triazole-3-selenolate (IIIa,b) with excellent yield under microwave irradiation in solvent-free conditions. This eliminates a series of complex isolation procedures and often minimizes the use of a large amount of expensive, toxic, and hazardous solvents after each step. This procedure reduces reaction time and cost and enhances yield. Reaction of compound (IIIa,b) with substituted/unsubstituted aryl diazonium chloride (IVa-e) at 0-5 °C gave pure 3-(substituted/unsubstituted phenyl selanyl)-1-acetylribosyl/deoxyribosyl-1H-1,2,4-triazole (Va-j). Oxidation of compound (Va-j) with oxone followed by alkaline hydrolysis furnished quantitatively and analytically pure 3-(substituted/unsubstituted phenylselenonyl)-1-ribosyl/deoxyribosyl-1H-1,2,4-triazole (VIIa-j). Compounds VIa-j and VIIa-j were evaluated in vitro for their fungitoxicities against Fusarium oxysporum and Penicillium citrinum. All the compounds were found to be antifungal active. Some of the compounds displayed activities comparable with that of the commercial fungicide Dithane M-45 and griseofulvin. Structure-activity relationships for the screened compounds were discussed. The fact that both of these fungi have developed resistance to several fungicide groups made them optimal candidates as target organisms for ongoing research about the potential application of 1,2,4-triazole and analogue compounds as reduced-risk fungicides.

Mineral Supported Facile Synthesis of Novel 4-Hydroxybenzoxazin-2-Thione N-Nucleosides

One-pot montmorillonite K-10 clay-supported reactions of substituted/unsubstituted salicylaldehyde and ribosyl/deoxyribosyl thioureas expeditiously yielded novel N-nucleosides, 4-hydroxy-3,4-dihydro-3-(β-D-ribofuranosyl or β-D-2 ′-deoxyribofuranosyl)-2 ″-benz[e]-1,3-oxazin-2-thione via cycloisomerization of aldehyde intermediate under solvent-free microwave irradiation conditions.

Three-component solvent-free diastereoselective formation of oxo-thiazolidinylthiazoles under microwave irradiation

The one-pot diastereoselective cyclisation of 4,4′-bis(2″-aminothiazol-4″-yl)bibenzyl to 4,4′-bis[2″-(2″′-aryl-5″′-methyl/carboxymethyl-4″′-thiazolidinon-3″′-yl)thiazol-4″-yl]bibenzyls, in high yields (85-96%) under the influence of microwave radiation, is described.

Nucleophilic heterocyclic carbene promoted one pot multicomponent synthesis of new 6-(1H-indol-3-yl)-2-oxo-4-aryl-1,2,3,4 tetrahydropyrimidine-5-carbonitriles: an eco-compatible approach with PEG as a biodegradable medium

A three-component, one-pot, simple, direct and highly efficient cyclocondensation method has been developed for the synthesis of fourteen 6-(1H-indol-3-yl)-2-oxo-4-aryl-1,2,3,4-tetrahydropyrimidine-5-carbonitriles by combining an arylaldehyde with 3-(cyanoacetyl)-indoles and urea in the presence of the PEG-400 and a catalytic amount of the thiazolium anion. A short reaction time, simple reaction conditions, ease of product isolation, use of a cheap and readily available and reusable catalyst make this method very attractive from an environmental and economic perspective.

Microwave-Mediated InCl3-Catalyzed Three-Component Annelation of Thiadiazinе Ring onto 4-Amino-4H-[1,2,4]Triazole-3-Thiol

A novel efficient three-component annelation of the thiadiazinyl ring onto 4-amino-4H-[1, 2, 4]triazole-3-thiol, catalyzed by nontoxic, recyclable InCl3 under microwave activation, has been developed. The transformation of 4-amino-5-aryl-4H-[1, 2, 4]triazole-3-thiol into triazolothiadiazine involves chemoselective successive double addition reaction consisting of an InCl3-catalyzed dehydrative nucleophilic addition of amino group to an aromatic aldehyde followed by addition of the resulting Schiff base to cyclohexyl isocyanide. The intramolecular cyclization of the adduct results in 3,6-diaryl-5H-[1, 2, 4]triazolo[3,4-b][1, 3, 4]thiadiazine. The reaction proceeds smoothly with good yields.

Photoredox catalysed synthesis of amino alcohol

A mild and efficient one-pot visible light-induced method has been developed for the synthesis of amino alcohols. Amino alcohols are important structural elements that are frequently found in pharmaceutical agents and biologically active natural products. The routine procedure in the drug discovery and development process to prepare and fully characterize amino alcohols makes them a drug candidate for biological evaluation. This protocol utilizes visible light as the greenest reagent and eosin Y as an organophotoredox catalyst to synthesise bioactive amino alcohols. Gram scale reactions demonstrated the potential synthetic applications of this protocol.

Europium activated gadolinium sulfide nanoparticles

In the present work, we report the synthesis and characterization of Eu3+ doped Gd2S3 nanoparticles, a potential candidate for T1-weighted MRI contrast agents and molecular markers. Eu3+ doped Gd2(1−x)S3:Eux (x = 0.0, 0.02, 0.04 and 0.06) were synthesized by a chemical route by varying the Eu concentration. X-ray diffraction and scanning electron microscopy were performed to extract the information about structure and surface morphology of prepared nanoparticles, respectively. The oxidation state of the Eu ions was elucidated from X-ray absorption near edge structure (XANES) spectra, which indicate the presence of only Eu3+ ions without any signature of Eu2+ ions. 120 MeV Ag9+ ions were used for ionoluminescence (IL) measurements to study the optical properties. The IL results show that the luminescence intensity increases with increasing Eu doping and no saturation or degradation of the luminescence were observed for the as-prepared nanoparticles. The nanoparticles doped with 2 and 4% Eu showed an increase in the IL intensity initially before decreasing to saturation at higher fluences. On the other hand, IL intensity from 6% doped samples decreased exponentially and saturated at higher fluences.

Novel, versatile and eco-compatible preparation of new 6-(1 H -indol-3-yl)-2-oxo-4-aryl-1,2,3,4-tetrahydropyrimidine-5-carbonitriles in water

A three-component, one-pot, simple and direct, highly efficient cyclocondensation method has been developed for the synthesis of 11 6-(1H-indol-3-yl)-2-oxo-4-aryl-1,2,3,4-tetrahydropyrimidine-5-carbonitriles by combining an araldehyde with 3-(cyanoacetyl)-indole and urea in the presence of the cationic surfactant, CTAB and a catalytic amount of thiamine hydrochloride in water. A short reaction time, simple reaction conditions, ease of product isolation, and use of a cheap and readily available reusable catalyst make this method very attractive from an environmental and economic perspective.