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  • Open access
  • 101 Reads
Zn-Catalyzed Direct Synthesis of 3-Iodo-1,3-dienes from α-Allenols

In recent years, the chemistry of allenes has attracted the attention of many chemists giving rise to numerous studies due to the presence of a cumulated diene in the structure of the compound. Therefore, these allenes have allowed to prepare a variety of compounds of chemical and biological interest.

On the other hand, 3-iodo-1,3-dienes are interesting species in organic chemistry because of its wide reactivity. They can undergo Diels-Alder cycloaddition, palladium-catalyzed cross-coupling reactions such as Stille, Negishi, Sonogashira and carbonylation, as well as solvolysis and metallation reactions.

We wish to report herein a new protocol that allows to obtain 3-iodo-1,3-dienes through a sustainable process starting from α-allenols. In this new synthetic route, zinc (II) derivatives are used as metallic promoter which are low cost and are also non-polluting species for the environment.

  • Open access
  • 114 Reads
Heterocyclic aldehydes based on thieno[3,2-b]thiophene core: synthesis and preliminary studies as ion optical chemosensors

Heterocyclic aldehydes show a variety of optical properties and the versatility of their reactivity allows them to yield a wide range of more complex compounds, with application in areas such as medicinal, materials and supramolecular chemistry. The biological and environmental relevance of certain molecules and ions turns them into targets for the design of molecular recognition systems. Recently, heterocyclic aldehydes have been reported in the literature as ion chemosensors.

Following the group’s work on optical chemosensors, for the detection and quantification of ions and molecules with environmental and medicinal relevance, this work reports the synthesis and characterization of two heterocyclic aldehydes based on the thieno[3,2-b]thiophene core, by Suzuki coupling, as well as the synthesis of the corresponding precursors. Preliminary chemosensory studies for the synthesized heterocyclic aldehydes in the presence of selected cations were also performed, in solution, in order to determine their potential application as optical chemosensors.

  • Open access
  • 88 Reads
Design, synthesis and bioactivity of benzimidazole-2-carbamates as soil-borne anti-fungal agents

Worldwide, fungi pathogens considered to be a lead cause of loss for vegetable crop production. Although, several strategies have been used to manage soil borne fungal diseases, however, higher percentage of the loss of crop production is that caused by fungal pathogens especially in Oman. Management of Pythium-induced diseases of cucumber has relied on the use of imported fungicides, biological control and cultural practices. Mefenoxam and hymexazol are two common fungicides for the management of Pythium-induced diseases in Oman. Despite their use in different farms, mefenoxam suffers from rapid biodegradation in soil while resistance has been reported among Pythium species to hymexazol. Thus, in this work we proposed a methodology of preparing a series of 2-carbamate benzimidazole derivatives of potential antifungal activity and use it against the fungal pathogens that cause the most loss of vegetables crop production in Oman.

Benzimidazole scaffolds have been widely used in medicinal chemistry and drug development due to their numerous medical and biological activities. Methyl benzimidazole-2-yl-carbamate (MBC) in particular is a well-known building block found in many fungicidal drugs in agriculture field.

Seventeen benzimidazole derivatives were synthesized in multistep reactions with acceptable yields. Structures of all newly synthesized compounds were identified and characterized using 1H-NMR, IR, HRMS, and melting point. Final compounds were tested on five soil-borne pathogens. Results of bioassays showed some compounds significantly affected the growth of Pythium aphanidermatum, a serious pathogen of vegetable crops worldwide. At least one class of these derivatives was the most efficacious, which resulted in 96% growth inhibition in Pythium at 100 mg L-1.

  • Open access
  • 70 Reads
Preparation and Hydro-lipophilic Properties of Novel Fluorinated Benzyl Carbamates of 4-Aminosalicylanilides

A series of seven fluorinated benzyl carbamates of 4-aminosalicylanilides and unsubstituted benzyl [3-hydroxy-4-(phenylcarbamoyl)phenyl]carbamate designed as agents with the expected anticholinesterase and anti-inflammatory activity were prepared and characterized. As lipophilicity significantly influences the biological activity of compounds, the hydro-lipophilic properties of these mono-, di- and tri-substituted carbamates were investigated in the study. All the discussed derivatives 4-{[(benzyloxy)carbonyl]amino}-2-hydroxybenzoic acid were analysed using the reversed-phase high performance liquid chromatography method to measure lipophilicity. The procedure was performed under isocratic conditions with methanol as an organic modifier in the mobile phase using an end-capped non-polar C18 stationary reversed-phase column. In the present study, the correlations between the logarithm of the capacity factor k, logarithm of the distributive parameter D at pH 7.4 and log P/Clog P values calculated in various ways as well as the relationships between the lipophilicity and the chemical structure of the studied compounds are discussed.

  • Open access
  • 58 Reads
On the use of CeCl3.7H2O as catalyst for the synthesis of hydrazones derived from aromatic aldehydes and ketones

The hydrazone functional group has been extensively studied and used in fields as diverse as organic chemistry, materials and biomedical sciences. In this work, the hydrazonation of acetophenones and benzaldehydes under CeCl3-assistance was evaluated. The transformations entailed the use of the respective hydrazines (H2N-NH2.HCl, Me2N-NH2 or Ph2N-NH2.HCl) and CeCl3.7H2O (2-5 mol%). The use of different solvents in a model reaction between 3,4-dimethoxybenzaldehyde and N,N-dimethylhydrazine was studied.

  • Open access
  • 60 Reads
Influence of copper(I) halides on the reactivity of aliphatic carbodiimides

Carbodiimides are widely exploited in organic synthesis, and the reactivity of these compounds can be enhanced by the addition of copper(I) halides to the reaction medium. The mild reaction conditions provide an alternative and selective synthetic approach with respect to the utilization of Brønsted acids.

The influence of copper(I) halides CuX (X = Cl, Br, I) on the electronic structure of diisopropylcarbodiimide and dicyclohexylcarbodiimide was investigated by means of DFT methods. The coordination of the considered carbodiimides occurs by one of the nitrogen atoms, with the formation of linear complexes having formula [CuX(carbodiimide)]. Besides varying the carbon-nitrogen bond lengths and orders, the interaction with Cu(I) reduces the electron density on the carbodiimides and alters the energies of the [NCN]-centred unoccupied orbitals, enhancing the reactivity towards nucleophiles. The computed Fukui functions suggest negligible interaction of Cu(I) with incoming nucleophiles, and the reactivity of carbodiimides is altered by coordination mainly because of the increased electrophilicity of the [NCN] fragments. CuX essentially behave as Lewis acids, and the nature of X influences the Cu-N bond strength, the carbodiimide→CuX donation and the energies of frontier unoccupied orbitals. CuCl is actually the most employed catalyst in combination with carbodiimides, but some of the results here provided suggest that the reactivity could be yet more enhanced by its replacement with CuI.

  • Open access
  • 84 Reads
A comparative theoretical and spectroscopic study of aminomethylbenzoic acid derivatives as potential NLO candidates

Three aminomethylbenzoic acid derivatives were theoretically studied at M062X/6-311++G(d,p) level in vacuum, namely 2-ammonio-5-methylcarboxybenzene perchlorate (1), 4-(ammoniomethyl) carboxybenzene nitrate (2) and 4-(ammoniomethyl) carboxybenze perchlorate (3). The compounds’ structures were fully-optimized and compared with the single-crystal x-ray diffraction results, showing a very close agreement with the experimental structural parameters. Their IR, 1H- and 13C-NMR spectra were calculated and examined in detail. Furthermore, the molecular electrostatic potential (MEP) maps of the studied compounds were investigated and the strength of the non-covalent interactions evaluated. In addition to these results, the NLO properties of the three compounds were predicted.

  • Open access
  • 184 Reads
Influence of nonpolar medium on antioxidant capacity of bergaptol and xanthotoxol - kinetic DFT study

Within this study, the antioxidant capacity of bergaptol (BER) and xanthotoxol (XAN) in a nonpolar environment (benzene) was investigated against the reference standard trolox (Tx). The ability to inactivate HO radicals from the kinetic aspect was examined through hydrogen atom transfer (HAT), single-electron transfer–proton transfer (SET-PT), sequential proton loss electron transfer (SPLET) and radical adduct formation (RAF) mechanisms. The rate constants of the chemical reaction were calculated using the conventional transition state theory (TST) and Eckart method (ZCT_0). The research is based on a QM-ORSA (Quantum Mechanics–based test for Overall free-Radical Scavenging Activity) protocol. For this purpose, the Gaussian 09 software package with the M06-2X/6-311++G(d,p) theoretical model was used. It has been shown that both compounds in benzene can inactivate the HO radical via HAT and RAF mechanisms. The calculated kinetic parameters indicate that the TST method, in some positions, is not suitable for calculating reaction rate constants at room temperature. Based on relative antioxidant capacity (rT), both compounds showed better antioxidant capacity than Tx, and it should be emphasized that BER showed better activity than XAN. Based on the relative amount of products (Гi) of both compounds, it was concluded that the formation of a radical adduct in positions C-3, C-5, C-8, and C-2' is the most represented.

  • Open access
  • 373 Reads
synthesis of heterocycle via Vilsmeier-haack reaction

Since its discovery, the Vilsmeier-Haack reaction has always been a subject of great interest to organic chemists and continues to attract considerable attention. It is a powerful tool for synthesis in organic chemistry. It is well known that inorganic acid halides react with disubstituted amides to form active complexes, halomethyl-eniminium salts, called Vilsmeier-Haack reagents. Due to its mild conditions, the commercial availability of the reagents and the better understanding of the mechanism, the Vilsmeier-Haack reagent was initially used to introduce formyl groups into activated aromatic and heteroatomic compounds and then it knows several uses in chlorination, chloroformylation , aromatization, cyclization,...etc . In recent years, the Vilsmeier Haack reagent has also found increasing application in the domino reactions of heteroatomic compounds. It is also important in various recent synthesis methodologies, using microwave chemistry. For years of research our laboratory interested in the development and functionalization of heterocyclic compounds such as aminopyridines, aminopyridopyrimidines, chromenopyrimidines,…etc with promising biological and pharmacological activities including some new concept of green chemistry ; as a part of our research, new heterocyclic systems were achieved in good yields via the Vilsmeier-Haack reaction starting from derivatives of 2-aminothiophene. All newly synthesized compounds were confirmed by 1H NMR, 13C NMR analysis and some showed a positive biological activity.

  • Open access
  • 189 Reads
Design, synthesis and photophysical properties of bodipy-labeled lupane triterpenoids

The BODIPY family fluorophores have been covalently linked to numerous classes of biomolecules, including proteins, carbohydrates, fatty acids, and steroids. Still, only two research papers on the synthesis and fluorescent biological analysis of BODIPY-labeling of triterpenoid compounds have been reported so far. In these works, fluorescent pentacyclic triterpene conjugates have been prepared by covalent binding to the known BODIPY-FL fluorophore through the 3-OH and 17-COOH functional groups. Here we aimed to work out a new approach for the synthesis of BODIPY-triterpenoid acids conjugates avoiding covalent binding of the triterpene core to the BODIPY-platform at the C-3 and C-17 positions. Novel BODIPY-lupane triterpenoid conjugates bearing a fluorescent marker at the C-2 position of ring A of the triterpene core were obtained via the Sonogashira reaction as a key step. The starting compounds in the cross-coupling reaction were C-2 propynyl derivatives of betulinic or betulonic acids and fluorescent dyes with an iodo-group at C-2 or meso position of BODIPY-platform. The elaborated coupling procedure might have applicability in the synthesis of fluorescent-labeled triterpenoid conjugates suitable for biological assays