Cycloaddition reactions are an integral and weighty part of organic chemistry in pedagogy and research as well. The wealthy literature on cycloaddition reactions from their birth up to now, unequivocally witnesses to their leading chemistry. The so-called ''conventional solvents'' are organic solvents that have indubitably promoted their success. Yet, the toxicity facet of these solvents impedes their use freely and with no fear. Not only is the operating chemist uncomfortable while experimenting, but also the environment is equally threatened. Working out the cycloaddition reactions and other organic ones in aqueous systems would certainly bring some relief to the chemist and to the environment as well. Unusual outcomes in terms of yield, reactivity and selectivity compared to those performed in organic solvents were commonly observed, and have overwhelmed the chemists with surprise indeed. In this review, homo Diels-Alder reactions in aqueous media include those involving the following dienophiles: maleimides, a,b-unsaturated esters, p-benzoquinones, vinyl ketones, phenyl-1-(2-pyridyl)-2-propen-1-one, a,bunsaturated esters. A special case is the organocatalysis of Diels-Alder cycloaddition of a,b-unsaturated ketones (aldehydes). Of no less importance, some hetero Diels-Alder cycloaddition reactions in water systems are delineated. The impact of additives (salts, organic and inorganic chemicals), micellar catalysis and Lewis/Brønste ¨d acid catalysis on outcomes of such cycloaddition reactions is discussed. The 1,3-dipolar cycloaddition methodology applied to aqueous media has brought forth a number of heterocyclic compounds, usually with a regio-and stereoselectivity pecularity. These heterocycles include triazoles, tetrazoles, pyrazoles, isoxazoles, isoxazolidines, pyrroles and pyrrolidines. The superiority of copper(I) catalysis in the azide-alkyne cycloaddition (Huisgen cycloaddition) in water is endorsed by a number of examples.
The aim of this study was to evaluate the antioxidant activities of five amides: benzanilide 1, dodecanilide 2, N-cyclohexyloctamide 3, acetanilide 4, and acetaminophen (paracetamol) 5, and to compare them to those of standard antioxidants, i.e. butylated hydroxyanisole (BHA), butylated hydroxy toluene (BHT), ascorbic acid (vitamin C) and α-tocopherol (vitamin E). Three common experimental tests were used to assess their antioxidant properties: 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, ferric ions reducing antioxidant power (FRAP) and β-carotene/linoleic acid assays. The amides 1-3 proved to be antioxidant as per three methods; the fatty anilide 2 showed the highest radical scavenging activity, whereas the fatty amide 3 showed the lowest one. Increasing the concentration resulted in an increased ferric reducing antioxidant power for all the examined amides; the reducing power of fatty anilide 2 was relatively higher than those of benzanilide 1 and fatty amide 3. Oxidation of the linoleic acid was strongly inhibited by all amides. The obtained results were comparable to antioxidant properties of the standard antioxidants.
A series of mesoionic pyrimidinium betaines were synthesized and tested in vitro for their antioxidant activity using three tests: 2,2-diphenyl-1-picrylhydrazil (DPPH) free radical scavenging, Ferric Reducing Antioxidant Power (FRAP) and bleaching of β-carotene. The results indicated that pyrimidinium betaines possess antioxidant properties with three methods. In the DPPH assay, the monocyclic pyrimidinium betaine showed the highest activity with an IC 50 value of 300 µg/mL. The pyrimidinium betaines also revealed a reducing power lower than that of the control antioxidants, and the monocyclic pyrimidinium betaine was the most active one. In the β-carotene bleaching test, the oxidation of linoleic acid was inhibited by all the betaines. The bicyclic one showed the greatest inhibitory activity of the oxidation of linoleic acid with a relative antioxidant activity (RAA) of 90%, an activity higher than that of the reference antioxidant α-tocopherol (41%). It was found that the antioxidant efficacy increased with increasing concentration of betaine and depended on the nature of the substituent on the pyrimidine ring.
Abstract-Monocyclic, bicyclic and fatty chain mesoionic pyrimidinium betaines were synthesized and separated from other compounds by liquid-liquid extraction method and then recrystallized from acetone or diethyl ether. The thus-purified betaines were characterized by spectroscopic analyses, including UV-visible, IR, 1 H-NMR and MS.
Chemicals and all solvents were of analytical grade and were purchased from Sigma-Aldrich, Merck, Prolabo and Biochem. In this study, pyrimidinium betaines 1-3 dissolved in ethanol were tested at concentrations 0-500µg/mL. Butylated hydroxyanisole (BHA), Butylated hydroxy toluene (BHT) and ascorbic acid (vitamin C) used as control standard antioxidants dissolved in ethanol were tested at concentrations 0-15µg/mL. Methods Synthesis of the compounds: The compounds including bicyclic pyrimidinium betaines: 1, 2 and monocyclic 3 were synthesized from amine derivatives and malonic esters by the reported procedures 17-20
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