Tomomi Maekawa

Antioxidation mechanism studies of caffeic acid: Identification of antioxidation products of methyl caffeate from lipid oxidation

As a part of a research project on the elucidation of the chain-breaking antioxidation mechanism of natural phenols in food components, caffeic acid, a polyphenolic acid widely distributed in edible plants, was investigated. The identification and time course analysis of the antioxidation reaction products from methyl caffeate were carried out in the ethyl linoleate oxidation system. The antioxidation reaction produced a quinone derivative of methyl caffeate as an antioxidation product during the initial stage, which was identified by (13)C NMR. The quinone, however, was not the final product, and a further reaction occurred to produce several new peroxides. The isolation and structure determination of the peroxides revealed that they had tricyclic structures, which consisted of ethyl linoleate, methyl caffeate, and molecular oxygen. On the basis of the formation pathway of these products, an antioxidation reaction mechanism of methyl caffeate, including the redox reaction of the caffeate and Diels-Alder reaction of the produced peroxides, was proposed.

Solubilization of fullerene into water with fluoroalkyl end-capped amphiphilic oligomers–novel fluorescence properties

Solubilization of fullerene into water was studied by the use of fluoroalkyl end-capped acryloylmorpholine oligomers, N,N-dimethylacrylamide oligomers, and acrylic acid oligomers. In these fluorinated oligomers, fluoroalkyl end-capped acryloylmorpholine oligomers were more effective in solubilizing fullerene into water. Interestingly, the aqueous solutions of fullerene were applicable to fluorescence analyses.

Synthesis of novel fluoroalkylated 4-vinylpyridinium chloride oligomers as functional materials possessing surfactant and biological properties

Abstract Perfluoropropylated and perfluoro-oxaalkylated 4-vinylpyridinium chloride oligomers were prepared by the reactions of fluoroalkanoyl peroxides with 4-vinylpyridinium chloride under very mild conditions. A series of fluoroalkylated 4-vinylpyridinium chloride co-oligomers containing carboxyl or trimethylsilyl segments were also obtained by the reactions of fluoroalkanoyl peroxides with 4-vinylpyridinium chloride and acrylic acid or trimethylvinylsilane under similar conditions. These fluoroalkylated homo- and co-oligomers containing carboxyl or trimethylsilyl segments were soluble in water and methanol. Furthermore, these oligomers were able to reduce the surface tension of water to 10–18 mN m−1 levels with a clear break point resembling a CMC (critical micelle concentration), and are applicable to new fluorinated cationic oligosurfactants. Fluoroalkylated co-oligomers were found to possess antibacterial activity against Staphylococcus aureus. In addition, fluoroalkylated co-oligomers containing carboxyl groups were potent and selective inhibitors of HIV-1 (human immunodeficiency virus type 1) in MT-4 cells. Interestingly, one of these fluoroalkylated co-oligomers containing carboxyl groups was clarified to show both antibacterial and anti-HIV-1 activities. Therefore, these oligomers are suggested to have high potential for new functional materials through their surfactant and biological properties.

A novel ring-expanded product with enhanced tyrosinase inhibitory activity from classical Fe-catalyzed oxidation of rosmarinic acid, a potent antioxidative Lamiaceae polyphenol

The iron-ion catalyzed oxidation of the ethanol solution of rosmarinic acid, a potent antioxidant polyphenol of Lamiaceae (Labiatae) plants, afforded a highly tyrosinase-inhibitory active product. The structure of the active product in the oxidation product mixture was determined using extensive NMR spectroscopy to have a novel oxygen-containing seven-membered ring system. The formation mechanism of the unique ring structure from the catechol part of the rosmarinic acid was proposed.

A novel radical terminated compound produced in the antioxidation process of curcumin against oxidation of a fatty acid ester

Abstract Isolation and structure elucidation of a radical coupling product between curcumin and a lipid under atmospheric conditions was successful for the first time. The compound has a novel tricyclic structure including a peroxyl linkage.

Synthesis and properties of novel perfluorocyclohexylated compounds with bis(perfluorocyclohexane carbonyl) peroxide

Bis(perfluorocyclohexane carbonyl) peroxide was prepared by the reaction of the corresponding acyl fluoride and hydrogen peroxide. This peroxide was applied to the preparation of perfluorocyclohexylated end-capped oligomers via a radical process under very mild conditions. In cyclic perfluorocyclohexylated end-capped oligomers containing hydroxy segments, these oligomers could cause a gelation in water and in polar organic solvents such as MeOH, EtOH, dimethylformamide (DMF), and dimethylsulfoxide (DMSO), and the gelling ability of these oligomers was superior to that of the corresponding linear perfluorooxaalkylated oligomers. Furthermore, perfluroocyclo-hexylation of polystyrene or benzene was proceeded via a single electron transfer reaction by using this peroxide.

Identification of cytotoxic dimers in oxidation product from sesamol, a potent antioxidant of sesame oil.

Phytophenols of edible plants have recently attracted much attention as potent antioxidants and related bioactive substances. These antioxidative phytophenols are very oxidizable due to their chemical properties, and their oxidation products must accumulate in the oxidizing foods when they are contained as active ingredients. In this investigation, several phytophenols, which are well known as potent antioxidants in food science, were oxidized by oxygen in the presence of a catalytic amount of Ferric ion. Caffeic acid, catechin, chlorogenic acid, rosmarinic acid, and sesamol were quickly oxidized, whereas eugenol, resveratrol, rutin, and quercetin were not under the stated conditions. The oxidation product mixtures of the quickly oxidized phytophenols were next subjected to a cytotoxic assay using normal cells. Among the products, the oxidation product from sesamol showed a remarkably high cytotoxic activity. To clarify the cytotoxic principle of the oxidation products, an assay-guided fractionation and subsequent isolation of the oxidation compound of sesamol was carried out. Structure analysis of the isolated compounds revealed that they are new dimeric compounds (2-5) of sesamol. The cytotoxic activity of the dimers was evaluated from the population of dead cells by a flow cytometric analysis of rat thymocytes in the presence of 100 μM of each compound. Compound 2 showed the most potent cytotoxic activity among them. Compound 2 has a typical conjugated carbonyl moiety and the moiety possibly contributes to its high toxicity from a structure-activity point of view.

Synthesis and surface properties of novel fluoroalkyl end-capped amphiphilic fullerene cooligomers

Abstract New fluoroalkyl end-capped fullerene cooligomers were prepared by the reactions of fluoroalkanoyl peroxides with fullerene and comonomers such as acryloylmorpholine, N , N -dimethylacrylamide and acrylic acid. These fluorinated fullerene cooligomers were easily soluble in water and common organic solvents, and were able to reduce the surface tensions of both water and benzene, quite effectively. Additionally, these fullerene cooligomers were found to form a stable monomolecular film at the air–water interface, and the modified polystyrene surface treated with these cooligomers was shown to have a strong hydrophilicity with good oil repellency.

Identification of the Antioxidation Reaction Products from a Sinapic Ester in a Lipid Oxidation System

As a part of our research project on the elucidation of the chain-breaking antioxidation mechanism for natural phenols in food components, the antioxidation products from a sinapic acid methyl ester in lipid oxidation were identified. Sinapic acid is a potent antioxidative phenolic acid widely distributed in edible plants. The structural determination of the four isolated products revealed them each to have a tricyclic structure consisting of ethyl linoleate, methyl sinapate and molecular oxygen, and these were isomeric compounds for the substituents on the tricyclic moiety.