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  • Open access
  • 81 Reads
Cs-ECH-TMA: A novel and efficient catalyst for green synthesis of polyhydroquinolines and acridinediones

Here, an efficient and biodegradable catalytic system prepared through a simple procedure is presented by using chitosan (Cs), epichlorohydrin (ECH) and trimesic acid (TMA). The obtained bio-based Cs/ECH-TMA was characterized by using energy-dispersive X-ray (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD) and FT-IR analysis. The Cs-ECH-TMA biopolymeric materials were used, as a bifunctional heterogeneous and green catalyst, for efficient synthesis of biologically-active scaffolds including polyhydroquinolines (PHQs) and polyhydroacridinones (PHAs) through Hantzsch reaction in a one-pot reaction. Both PHQs and PHAs were synthesized in the presence of heterogeneous Cs/ECH-TMA catalyst from their corresponding substrates in EtOH under reflux conditions in high to quantitative yields. The Cs/ECH-TMA catalyst is recyclable and can be reused at least four times.

  • Open access
  • 73 Reads
Graphene oxide-THEIC-ECH-Chitosan network nanocomposite: a novel, efficient and recyclable catalyst for green synthesis of polyhydroquinoline derivatives

In this present research, two linkers have been utilized for the covalent attachment of graphene oxide with chitosan. Graphene oxide (GO) and chitosan (Cs) were crosslinked by using 1,3,5-tris(2-hydroxyethyl) isocyanurate (THEIC) and epichlorohydrin (ECH) which resulted in forming the expected biopolymer network nanocomposite. The obtained network was characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and thermal gravimetric analysis (TGA) technique. The catalytic application of the GO-THEIC-ECH-Cs nanocatalyst was then investigated in one-pot four-component Hantzsch condensation reaction for the synthesis of polyhydroquinoline derivatives in EtOH under reflux conditions. The obtained results indicated that the applied catalyst in this study exhibited some the significant advantages such as reusability and highly efficiency, stability, low required loading, avoiding the use of toxic transition metals, short reaction times, higher yields, easy separation and purification of the products.

  • Open access
  • 62 Reads
Synthesis of new meso-porphyrins type A2 B2

New meso-bis(quinolin-3-yl) porphyrins derivatives were synthetized from quinolin-3-carboxaldehydes derivatives and dipyrromethane in 1:1 ratio in CHCl3 at room temperature catalyzed by TFA and DDQ. Synthetized porphyrins were obtained with a low yield.

Characterization has been carried by Mass spectroscopy, 1H NMR spectroscopy.

  • Open access
  • 31 Reads

Usnic acid is a well-known secondary lichen metabolite, the derivatives of which, like itself, show a wide spectrum of biological activity: antibacterial, analgesic, immunomodulatory, antitumor, etc.

The bromine derivative of usnic acid 1 seems to be a convenient platform for the synthesis of various derivatives by the substitution reaction of the bromine atom with various nucleophiles. We have shown that reaction with N- and O-nucleophiles leads to an intramolecular nucleophilic substitution reaction with the formation of furanone 2, whereas reaction with S-nucleophiles leads to a desired substitution bromine atom. For example, earlier, by the reaction of compound 1 with substituted ureas, thiosemicarbazones and thioamides, various substituted thiazoles were obtained, for which significant biological activity were detected.

In this work, we have developed a technique for the synthesis of heterocyclic derivatives of usnic acid by the reaction compound 1 with CS2-based nucleophiles. A series of compounds with dithiolane 3, 1,3,4-thiadiazine 4, and thiophene 5 and 6 fragments has been synthesized.

  • Open access
  • 50 Reads

(+)-Usnic acid (1) is a commercially available lichen metabolite. Its biological activity is diverse: from antibacterial and anticancer to immunomodulating. Its biological properties, as well as broad occurrence in various lichen species and high optical purity of the isolated product make it promising as a base for developing novel pharmaceuticals.

Earlier it was shown that the interaction of (+)-usnic acid 1 with reducing agents occurs along the C ring of the dibenzofuran core. The reaction proceeds either under the action of H2/Pd (C) through the reduction of the C4-C4a double bond with the formation of dihydrousnic acid 2, or under the action of sodium borohydride through the reduction of C1=O and C11=O carbonyl groups to hydroxyl ones with the formation of mixture of diastereomeric compounds 3. We synthesized new dibenzofuran compounds by hydrogenation of (+)-dihydrousnic acid 2 under the action of H2/Pd (C). It was found that the reduction proceeds predominantly at the exocyclic carbonyl group (C11=O) of ring C with the formation of compound 4. Compound 5 (according to NMR data in the enolic tautomeric form) was isolated as a minor product, wherein the endocyclic carbonyl group (C3=O) undergoes reduction to methylene.

The triketone system of the C ring in the new compounds is destroyed, which should contribute to the loss of protonophore properties responsible for the toxicity of the native compound. This feature allow the synthesized compounds to be considered as promising platforms for creating new biologically active compounds with increased safety.

  • Open access
  • 80 Reads
Intramolecular cyclization of alkenyl alcohols: towards the synthesis of oxacycles

The presence of tetrahydropyrans, and other sized oxacycles, in natural products with interesting pharmacological properties has prompted researchers to try to develop new strategies for their selective synthesis. Moreover, these methodologies enable the introduction of structural modifications in the molecule for the synthesis of analogues with potential biological activity. An attractive atom economy process for the synthesis of these scafolds is the intramolecular hydroalkoxylation of alkenes. However, this method has several drawbacks (such as the lack of generality and the presence of multiple side reactions) which have diminished its development.

For many years our research group has been devoted to develop different strategies for the regio-and stereoselective synthesis of oxigen and nitrogen heterocycles. Herein we present our results on the effective acid catalyzed cyclization alkenyl lacohols which bear a silyl group in their structure. As we will show, the presence of the silicon group is necessary for the cyclization to take place. Moreover, the cyclization towards tetrahydropyrans occurs with high stereoselectivity.

  • Open access
  • 68 Reads
Chiral-Chiral communication mechanisms and modulation of the helical sense and the secondary structure

Helical sense is found in important biological macromolecules from living organisms, DNA and proteins are the most representative of the importance in the helicity. New and important functions emerge from the control in the helicity. Different Poly(phenylacetylene)s copolymers made of chiral monomers are being used for the comprehension of the communication effects like Sergeants and Soldiers Effect (SSE), which modulate the helical sense and the secondary structure. Copolymers made of two chiral monomers, (R)-α-methoxy-α-(trifluoromethyl)phenylacetic acid (MTPA) and (S/R)-α-methoxy-α-phenylacetic acid (MPA) derivatives, can exhibit complex systems for different solvents following classic or novel effects. At certain conditions we can find systems that follow lack of communication, Chiral Conflict and Chiral Accord will emerge depending of the helical sense of the two chiral monomers. Achieving this command in P and M helix preference, different applications have been discovered and future upgrades in this field can be done for stationary phase in HPLC, sensors, novel materials, etc.

  • Open access
  • 153 Reads
In vitro antioxidant activity, phytochemical screening and total phenolic and flavonoid content from the leaves extracts of Stachys germanica subs cordigera briq

This study is planned to perform phytochemical screening, evaluate antioxidant activity and assess total phenolics and flavonoids content of methanolic and ethyl acetate extracts from the leaves of Stachys germanica subs cordigera briq. The dried powdered leaves of Stachys germanica subs cordigera briq (80 g) were extracted exhaustively by Soxhlet apparatus with increasing polarity of solvents (hexane, ethyl acetate and methanol). The total phenol and flavonoid contents in the methanolic and ethyl acetate extracts were determined by using the Folin-Ciocalteu reagent and aluminum chloride method, respectively. The antioxidant activities were examined by three different methods, namely 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging activity, reducing power scavenging activity (FRAP) and total antioxidant capacity. Phytochemical analysis of all extracts showed the presence of major classes of phytochemicals such as, flavonoids, tannins and polyphenols. Total phenolic and flavonoid contents results are showed in a large dominance in ethyl acetate extract. In vitro antioxidant activities of both extracts (ethyl acetate and methanol) were significant and ethyl acetate extract showed a higher potency than reference antioxidant Butylated Hydroxy Toluene (BHT) in total antioxidant capacity essay. It can be concluded that the crude extracts from the leaves of Stachys germanica subs cordigera briq. are a potential source of natural antioxidants which can be used in preventing the progression of many diseases.

  • Open access
  • 83 Reads
An improved stereoselective synthesis of (1R,2S,3S,4R,5R)-4-amino-5-(hydroxymethyl)- cyclopentane-1,2,3-triol

Iminosugars are sugar mimetics present in plants and microorganisms that were first reported in the1960s.[1] They can formally resulted from the replacement of the endocyclic oxygen atoms monosaccharides by a basic nitrogen and the lack of the anomeric hydroxy group (Figure 1). Taking into account their ability to inhibit carbohydrate-processing enzymes such as glucosidases, they have been proposed as a source for therapeutic agents.[2] Thus, two derivatives of the natural iminosugar deoxynojirimycin (DNJ) are now marketed drugs: miglitol for the treatment of type 2 diabetes and miglustat for the treatment of the lysosomal storage disorders Gaucher’s and Nieman–Pick type 2 diseases.

Aminocyclopentitols are also inhibitors of glucosidases that can be considered as carbohydrate mimics resulting from the lack of the endocyclic oxygen atom of furanoses and that carry an exocyclic amino group[3] Similarly to the deoxynojirimycins, they are mimicking either the protonated glycoside[4] or the intermediate glycosyl (oxycarbenium) cation.[5]

As part of our continued interest on glycosidase inhibitors, we will report an improved stereoselective synthesis of aminocyclopentitol V.

The oxidation of this compound V to the corresponding 2,3,4-trihydroxy-5-aminocyclopentanecarboxylic acid will also be discussed.

  • Open access
  • 128 Reads

Various 2-aryl benzimidazole derivatives were synthesized using Microwave assisted reaction. The solvent and catalyst were selected to get product with good yield. From o-phenylenediamine and different substituted aromatic carboxylic acid using ethyl acetate as a catalyst derivative of 2-substituted benzimidazole were synthesized. All the synthesized compounds were screened by FTIR and 1H-NMR spectra.