Seizo Tamagaki

Fe(III)-catalyzed hydroxylation of benzene with H2O2 in the presence of quinones

Abstract In the presence of quinones as cocatalysts, Fe 3+ -catalyzed hydroxylation of benzene with H 2 O 2 provided phenol in moderate yields. 1,2-Naphthoquinone-4-sulfonate facilitated the hydroxylation with much greater efficiency.

Synthesis of a Novel Water-Soluble Polyazobenzene Dendrimer and Photoregulation of Affinity Toward DNA

Abstract A novel water-soluble polyazobenzene dendrimer modified with L-lysines at the periphery was synthesized. The results from light scattering and gel filtration chromatography showed that the particle size is controllable upon UV or visible light irradiation. Furthermore, a gel shift assay with plasmid DNA and an electrophoretic light scattering analysis demonstrated that the affinity of this cationic dendrimer toward DNA is photo-controllable on the basis of zeta potential alteration on dendrimers surface.

The mechanism of the reactions of 2- and 4-alkylpyridine N-oxides with acetic anhydride

Abstract The reaction of 2-benzylpyridine, 2- and 4-picoline N-oxides with acetic anhydride has been investigated by means of kinetic and 18O-tracer experiments. The large kinetic isotope effects found for all these reactions suggest the proton-removal step to be rate-determining. The uneven distribution of 18O between the alcohol and carbonyl O- atoms of the esters formed appears to result from the confonnational preference of the “anhydrobase” intermediates. The slight effect of salts and substituents on the rate are also discussed.

Rearrangements of tertiary amine oxides—XXIII : Reaction of α, N-diphenylnitrone with acetic anhydride

Abstract The reaction of the α, N-diphenylnitrone with acetic anhydride has been investigated using homogeneously 18O-labelled acetic anhydride. The amount of 18O incorporated into the carbonyl group of the resulting benzamide suggests an intramolecular reaction. The rates of the reaction were measured by changing the solvent and the substituents. The large reactivity of the nitrones having electron-releasing substituents and others suggests that the NO bond cleavage is the rate-determining step of the reaction.

Rearrangement of tertiary amine N-oxides—XXVII : Mechanism of the reaction of isoquinoline N-oxide with substituted benzenesulfonyl chlorides☆

Abstract Kinetic experiments have been carried out on the reactions of isoquinoline N-oxide with p-toluenesulfonyl and other substituted benzenesulfonyl chlorides, varying solvent and salt compositions. The rate was correlated by the second-order equation, i.e., v = [N → O] × [ArSO2Cl], and was found to be accelerated in polar media. The addition of chloride ion was found to increase the rate considerably, while the rates of the over-all reaction became greater with arenesulfonyl chlorides bearing stronger electron-withdrawing substituents (ϱ = +2·0). By the use of 1-deuterated isoquinoline N-oxide a small kinetic isotope effect (kH/kD = 1·2) was observed for this reaction. Based on these kinetic observations the rate-determining step of this reaction is considered to be the cleavage of NO bond. Meanwhile, from the 18O-tracer experiments in several solvents using uniformly 18O-labelled p-toluenesulfonyl or p-bromobenzenesulfonyl chloride the migration of arenesulfonate was found to proceed mainly via oxygen-bridged ion pair pathway.

Photoxidation of di-t-butyl thioketone

Abstract The photo-oxygenation of the title compound leads to the corresponding ketone and sulfine. A mechanism for the reaction is elucidated.

Reaction of lepidine, quinaldine and 1-methylisoquinoline N-oxides with acetic anhydride

Abstract The mechanism of the reactions of lepidine, quinaldine and 1-methylisoquinoline N-oxides with acetic anhydride has been studied by means of both kinetic and 18 O tracer experiments. In all cases, the over-all rate of the reaction is markedly affected both by the change of solvent and by the addition of salts. In the case of lepidine N-oxide, a large kinetic isotope effect, k H /k D = 7·7 in acetonitrile, suggests that the proton-removal is the rate-determining step. This is also the case for 6-methylquinaldine N-oxide which gives the kinetic isotope effect, k H / k D = 7·4 (at 30·). In the case of quinaldine N-oxide, however, the kinetic isotope effect is small, k H / k D (at 30°), while quinaldine N-oxide originally trideuterated loses deuterium during the reaction, depicting that the proton-removal is a reversible step and the succeeding NO bond cleavage is the rate-determining step. In the case of 1-methylisoquinoline N-oxide, in which k H / k D is 3·5 in dioxan at 30· both proton-removal and NO bond cleavage are equally important in the energy profile of the reaction.

Synthesis of a novel azobenzene-based trihydroxamate siderophore and photoregulation of its ferric complex structure

Abstract In order to develop an artificial photoresponsive siderophore by utilizing the photo-isomerization of an azobenzene group, a novel trihydroxamate siderophore based on an azobenzene skeleton was synthesized. The 1:1 and 2:2 stoichiometry of the ferric complex can be almost perfectly regulated reversibly by irradiation with UV and visible light, respectively.

Sugar-induced Stereoselectivity in the Fe3+-complexation of Boronic Acid-appended Trihydroxamate-type Artificial Siderophores

Abstract Two linear- and two tripodal-trihydroxamate siderophore mimics, suspending phenylboronic acid as the sugar-binding site, have been newly prepared. These siderophore mimics strongly bind Fe3+ ions to give rise to the ligand-Fe3+ 1:1 complexes over a wide range of pH 2 to 11. Circular dichroism (CD) spectra of these complexes in the presence of a sugar, D-fructose, exhibit moderately strong bisignate Cotton effects of first negative and second positive signs in aqueous alkaline media. The sign and extent of the observed CD signals depend largely on the solution pH and the concentration and absolute configuration of the bound sugars, implying that the phenylboronate-sugar covalent interactions are capable of inducing a chirality around the metal center.

C 3-symmetric ferrichrome-mimicking Fe3+-complexes containing the 1-hydroxypyrimidinone Fe3+-binding moieties based on α-cyclodextrin: helicities in solvent environments

Two homologous C3-symmetric ferrichrome mimics, La and Lb, equipped with three 1-hydroxypyrimidinone terminals for receiving an Fe3+ ion have been designed and synthesized; the side chains of La and Lb, which include dimethylene and pentamethylene spacers, respectively, are anchored to the narrower rim of the α-cyclodextrin framework through an amide linkage. The 1∶1 Fe3+-complexes of La and Lb provide strong circular dichroic exciton coupling of negative and positive signs at 480 nm, showing Δ- and Λ-helices, respectively, in polar aprotic solvents such as dimethylformamide and dimethyl sulfoxide. The magnitude of the signals increases with the increasing hydrogen-bond accepting ability of the solvent. It is inferred, therefore, that hydrogen-bonding interactions of the linker amide N–H groups with the solvent play a primary role in inducing a helicity within aprotic solvents. The mechanisms of the helicity inductions are discussed. Meanwhile, the signals for La are still negative, but weak in alcohols and water. However, the signal sign for Lb having the relatively flexible spacers depends on the nature of alcohols, and no CD signal was observed in water. p