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  • Open access
  • 35 Reads
The aminometylation of 4-(alkylthio)-6-amino-2-oxo(thioxo)-1,2-dihydropyridine-3,5-dicarbonitriles

Easily available 2-(bis(alkylthio)methylene)malononitriles react with cyanoacetamide or cyanothioacetamide to give 4-(alkylthio)-6-amino-2-oxo(thioxo)-1,2-dihydropyridine-3,5-dicarbonitriles. Upon treatment with primary amines and/or HCHO, the compounds undergo heterocyclization to afford new pyrido[1,2-а][1,3,5]triazines or ring-condensed 1,3,5,7-tetrazocine derivatives.

  • Open access
  • 85 Reads
SYNTHESIS OF BENZO[b]CARBAZOLS BY TANDEM Au(I)-CATALYZED CYCLIZATION/MIGRATION/CYCLIZATION

The initial results on a novel procedure for the synthesis of benzo[b]carbazols via gold(I)-catalyzed tandem cyclization/Migration/cyclization is described. The procedure allowed the access to a highly functionalized benzo[b]carbazols in a one-pot process starting from tertiary anilines. The mechanism of this reaction by using gold(I) catalysis, interestingly proceeded via 5-endo-dig cyclization with successively migration of benzyl substituent on 2 and 3 position of indole, leading to the formation of benzyl substituted indole derivatives. We are proposing a cyclodimerization and aromatization via 6-exo-dig with the help of gold(I)-carbene.

Preparation of Starting material tertiary aniline required four step- Step 1. Methylation -( 2-iodo aniline, Methyl-iodide, NaH, 0 0C, 30 min. then 23 0C. 12 hr). Step 2. Bis-alkylation-(Methylated compound 1, Benzyl bromide, K2CO3, Reflux, 24 hr). Step 3. Sonogashira Cross-coupling reaction (Bis-alkylated compound 2, Tri-methyl-silyl-acetylene, Pd(PPh3)2Cl2, CuI, Et3N, 23 0C, 2 hr). Step 4. Deprotection of TMS (Compound 3, K2CO3, MeOH, 23 0C, 4 hr and finally, we get Tertiary-aniline 4, as a starting material. Initial optimization with Tertiary Aniline 4, 5mol% of (Acetonitrile)[(2-biphenyl)di-tert-butylphosphine]gold(I) hexafluoroantimonate as Gold(I)-catalyst, Dry-DCM or Dry-DCE at 23 0C. But unfortunately, we do not get result. Then we rise the temp of reaction in Dry-DCE upto 60 0C with 10mol% of gold(I) catalyst and then we get substituted indole as a cyclized product with 95% yield which is confirmed by H1, C13 and NOE spectrum.

Overall, we get first intermolecular cyclized product of benzyl substituted indole with excellent yield.

  • Open access
  • 39 Reads
Novel semicarbazone-based α-amidoalkylating reagents: general synthesis and reactions with H-, O-, S-, N-, and P-nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), and P-nucleophiles (trialkyl phosphites) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones.

  • Open access
  • 58 Reads
TOWARDS GREENER MECHANOSYNTHESIS OF FUNCTIONAL CALIXARENES

The awareness for sustainability led to an increasing global demand for processes that use lower energy, produce reduced waste, use fewer organic solvents and offer improved selectivity. In this context, mechanochemistry reemerged as a powerful green methodology. Besides matching all these requirements, a major advantage and an extraordinary feature of mechanosynthesis is the elimination of solubility issues, thus ensuing chemical transformations by simple, mostly solventless, grinding. Moreover, mechanochemistry is a truly new synthetic tool, by allowing the access to products otherwise found possible only in classical solution reactions. Nevertheless, and despite great achievements made in the last few years, the field of mechanosynthesis is still rather unexplored.

Calixarenes are synthetic macrocycles that are among one the most interesting 3D structures, like cucurbiturils and dendrimers. Presenting considerable functional and tunable diversity, its synthesis and functionalization is highly defying. The conventional synthesis and functionalization of calix[4]arenes, both on the upper and lower rim, has been the subject of numerous studies, however only a few were reported using mechanochemical approach.

Herein, we present for the first time a new mechanically assisted key synthetic steps towards a more sustainable route to several calix[4]arenes derivatives functionalized in the lower rim (e.g. p-iodobenzyl derivatives) to be used as functional precursors toward the synthesis of conjugated polymers by Sonogashira-Hagihara cross-coupling.

The syntheses were performed in a planetary ball mill using a zirconium oxide reactor, under solventless conditions, with good yields and much lower reaction times, in comparison with conventional methods.

  • Open access
  • 33 Reads
ANIONIC LOW BAND GAP CONJUGATED POLYELECTROLYTES AS HOLE TRANSPORTING LAYER IN OPTOELECTRONIC DEVICES

Conjugated polyelectrolytes (CPEs) are conjugated polymers bearing side-chain ionic functionalities likes anionic, cationic or zwitterionic groups1.

CPEs have emerged as new class of interfacial materials in thin film based electronic devices such as solar cells and OLEDs thanks to their ability to reduce the barrier between electrode and active layer resulting from the formation of an aligned interfacial dipole at the metal/organic semiconductor interface

CPEs have several advantages compared to conventional organic and inorganic interlayers like good solubility in polar solvent, included water, which allow deposition from orthogonal solvents and the possibility of tuning the optoelectronic and photophysical properties by tailoring the chemical structure of conjugated backbone and side-chains.

Recently, Bazan and coworkers2 have demonstrated anionic low bandgap CPEs polymer can be easily doped after dialysis in water and such doped conjugated polyelectrolytes, thanks to their pH-neutral nature are a promising alternative to acidic poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)3.

Although this kind of CPEs with pH neutral nature can be applied in perovskite based devices notoriously sensitive to the environment or as anode interfacial layer of OLEDs and OPVs with inverted geometry, currently there are only few materials with this characteristics and the material developed by Bazan remains the one with the best results.

In this logic, in order to obtain ever more effective CPE, it is particularly important to understand the role of the conjugated backbone and of the polar groups4,5.

Here we present the synthesis and preliminary optoelectrical characterization of two new donor-acceptor (D-A) anionic CPEs, one containing cyclopentadithiophene (CPDT) functionalized with one sulfonate terminated side-chain alternate to benzothiadiazole (BTD) units and the other containing a stronger donor unis, dithienopyrrole (DTP), functionalized with one carboxylate terminated side chain, alternate to BTD units.

The preliminary data confirmed the self doped nature of our CPEs but also a strong tendency to aggregation responsible for the poor quality of the films. Moreover sulfonate group seems to play a crucial role in the interfacial engineering.

  • Open access
  • 50 Reads
Synthesis and antioxidant activity of 2-amino-5-R-1,3,4-oxadiazoles with hindered phenol fragments

Compounds with hindered phenolic moiety are known to be effective inhibitors of oxidative processes in different materials, moreover a number of phenols found to show wide spectrum of biological activity. At the same time, five-membered heterocycles exhibit unique properties, including antioxidant activity. One of the ways to create new effective antioxidants with a set of useful properties is to combine hindered phenol and a heterocyclic fragment in one molecule.

In this work new 1-acyl-4-R-thiosemicarbazides were obtained during the reaction between 3-(4-hydroxy-3,5-di-tert-butylphenyl) propanoic acid hydrazide and a number of isothiocyanates. 2-Amino-5-R-1,3,4-oxadiazoles were prepared in good yelds by heterocyclization of 1-acyl-4-R-thiosemicarbazides in presence of iodoxybenzoic acid ant triethylamine. The antioxidant activity of 1,3,4-oxadiazoles was studied in vitro and was found to be higher than that of 4-methyl-2,6-di-tert-butylphenol.

  • Open access
  • 51 Reads
Lactamomethylation of phenols: synthesis, in silico study of reactivity, and possible applications

Lactamomethylation of phenols with various substituents was provided by pyrrolidone, valerolactam, caprolactam and 4-phenylpyrrolidone derivatives. The structures of the target compounds were confirmed by IR and NMR study. The behavior of alkylphenols (2,4-di-tert-butyl- and thymol), diphenols (catechol and hydroquinone), formylphenol (vanillin) and hydroxybenzoic acids (salicylic and resorcylic) in this reaction was compared by quantum-chemical calculations.

For several compounds, the energy of dissociation of ArO-H bond was calculated by quantum-chemical method to reveal their possible antioxidant activity. In addition, the ability of the synthesized compounds to destruct cumene hydroperoxide was studied. It was estimated that 1-(4-hydroxy-5-isopropil-2-methylbenzyl)azepan-2-one and 1-(4-hydroxy-5-isopropil-2-methylbenzyl)pyrrolidin-2-one possess the best antioxidant effect, comparable to the one of industrial additive BHT.

  • Open access
  • 52 Reads
Development of new selenopyrylium salts for its application in PDT

Among the great challenges facing the Society is the search for solutions to cancer. This disease presents high cellular oxidative stress, as a result of the imbalance between the oxidizing species generated in the cells and antioxidant compounds. One of the strategies used in the treatment of cancer is based on the use of Photodynamic therapy (PDT). PDT is a safe and non-invasive technique for the treatment of different types of cancer in diverse locations, as well as non-cancer diseases.

PDT consists of the local or systemic application of a photosensitive compound (the photosensitizer), which accumulates mainly in the pathological tissues. Photosensitive molecules absorb light of the appropriate wavelength, initiating the activation processes that lead to the selective destruction of tumor cells. An adequate photosensitizer must obey a number of features such as maximum absorption length between 600 and 800 nm, minimum absorption length between 400 and 600 nm, high purity and stability at room temperature, and high selectivity with tumor tissues, among others. In this context, selenopyrylium salts emerge as potential candidates to photosensitizers due to fit with most of these features.

Therefore, the aims in the present work are the synthesis and characterization of monocationic selenopyrillium salts, using a methodology that does not involve organometallic reagents, and the evaluation of their photophysical properties for their possible application as photosensitizers in PDT.

  • Open access
  • 64 Reads
Xanthine Oxidase Inhibition by Aqueous Extract of Limonium brasiliense (Plumbaginaceae)

Limonium brasiliense (Boiss.) Kuntze is a medicinal plant belonging to the Plumbaginaceae family that is popularly used in the folk medicine and it is believed to have cardioprotective properties.

Xanthine oxidase (XO) is a key enzyme that catalyze the oxidation of hypoxanthine and xanthine to uric acid causing hyperuricemia in humans.

In this study, we examined XO inhibitory activities of the aqueous fraction of Limonium brasiliense extract, and its polar bioactive constituents, using the enzymatic HX–XO system in vitro.

Seven active compounds isolated from the aqueous extract were identified by comparison of their 1H and 13C NMR data with those reported in the literature. Myricetin, apigenin, taxifolin, 3-O-acetyltaxifolin, myricetin-3-O-α-rhamnopyranoside and gallic acid have proved to be strong XO inhibitors.

Prodelphinidin B1‐3,3’‐digallate was effective for scavenging superoxide radicals (O2_), generated enzymatically by a hypoxanthine (HX)/xanthine oxidase (XO) system and/or for inhibiting XO activity. This compound showed the most potent inhibitory activity with an IC50 value of 6,61 µM, comparable to allopurinol, the drug of choice for inhibition of XO in gout patients.

For the first time, this study provides a rational basis for the use of aqueous fraction of L. brasiliense against hyperuricemia, displaying potent XO inhibitory activity with an IC50 value of 48.3 µg/ml. This inhibitory effect is compatible with the presence of Prodelphinidin B1‐3,3’‐digallate in this extract.

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