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The characterization of a novel, relatively long-lived 5, 6-indolequinone along with its semiquinone using an integrated chemical, pulse radiolytic, and computational approach is described. Pulse radiolytic investigations have revealed the generation of one or more transient radical or radical-anion forms of the semiquinone which rapidly disproportionates to give the o-indolequinone.

The isolation and structural characterization of the main products formed by acid-promoted reaction of ((E)-3,4',5-trihydroxystilbene) with N[[O.sub.2].sup-] under mild conditions is described. The oxygen-independent N[[O.sub.2].sup-] -mediated oxidative fission of the double bond under mild, physiologically relevant conditions is unprecendented in stilbene chemistry and is proposed to involve breakdown of hydroxynitro(so) intermediates.

The results of detailed investigation into the nature of the oligomer products formed by phenolic oxidation of 17beta-estradiol are presented. The results provide the first systematic inventory of oxidative coupling products of 17beta-estradiol and lay the foundation for future studies aimed to develop novel estrogen derivatives based on oligomeric scaffolds.

Research has been conducted on the antipyretic drug paracetamol. The oxidation chemistry of this drug with UV/H (sub)2 O (sub)2 system has been examined via various techniques including (super)15 N NMR analysis and the details are reported.

Research has been conducted on the polysaturated fatty acids and their methyl esters. The isolation, spectral characterization and biological screening of the nitration products of the reaction of these acids and their esters with NO (sub)2 (super)- in acidic media are reported.

Research has been conducted on the reaction of L-3,4-dihydroxyphenylalanine and dopamine with D-glucose. The nature of the competing pathways, the role of the transition metal cations and the chemical viability of the nonenzymatic glycation processes have been investigated.

The reaction between a polyunsaturated fatty acid derivative ethyl linoleate with nitrite in acidic media provides a direct route for preparing nitrated lipid products on a small scale. The methodology yields nitration products of unsaturated fatty acids, such as nitroalkanes, nitro alcohols, and dienes.

Research describes the urinary melanogen 5-S-cysteinyldopa exhibiting an octahydropyridobenzothazepine skeleton and examines the origin of the heterocyclic ring system from double condensation reaction between 5-S-cysteinyldopa and formaldehyde. Data discuss the reaction of 5-alkylthiocatecholamines with formaldehyde under biomimetic Pictet-Spengler conditions.

An efficient nitroselenenylation/oxidation pathway to 9-nitrolinoleic acid and 10-nitrolinoleic acid which facilitated comparative product studies under physiologically relevant conditions is reported. The studies on the position-dependent influence of the nitro group on the oxidation behavior of the 1,4-pentadienyl moiety is also reported.

The article explains the nitration, as well as the nitrosation chemistry of menthofuran, a toxic furan obtained from various mint oils. It also demonstrates the synthetic and biomedical significance of menthofuran-derived scaffolds.

Chemical or enzymatic oxidation of 5,6-dihydrocyindole has led to the rapid deposition of a black solid by using a complex oligomerization/polymerization process that has proceeded in the early stages via dimers and trimers characterized by 2,4'- and 2,7'-couplings. Three additional tetramers are obtained by the oxidation of 5,5',6,6'-tetrahydroxy-2,7biindolyl with the peroxidase/[H.sub.2][O.sub.2] system.

Provides insights into acid-promoted reaction of caffeic acid and esters with nitrite. Decarboxylation on chain nitrozation pathway to oxime derivatives; Isomerization of nitrous group to stable aldoxime functionality; Exhibition of mutual reactivity to hydrogen-concentration ion.

Studies the oxidation of 5,6 dihydroxyindole in acidic aqueous media. Characterization of the products formed by acid promoted oxidation of 1a; Experimental procedures utilized; Formation of diindolocarbazoles; Description of the oxidation of indolic compounds in acidic media.

The mechanism of the acid-dependent interring dehydrogenation in the conversion of the single-bonded 3-phenyl-2 H -1,4-benzothiazine dimer 2 to the Δ 2,2 ' -bi(2 H -1,4-benzothiazine) scaffold of red hair pigments is disclosed herein. Integrated chemical oxidation and oxygen consumption experiments, coupled with electron paramagnetic resonance (EPR) analyses and DFT calculations, allowed the identification of a key diprotonated free-radical intermediate, which was implicated in a remarkable oxygen-dependent chain process via peroxyl radical formation and evolution to give the Δ 2,2 ' -bi(2 H -1,4-benzothiazine) dimer 3 by interring dehydrogenation. The critical requirement for strongly acidic conditions was rationalized for the first time by the differential evolution channels of isomeric peroxyl radical intermediates at the 2- versus 3-positions. These results offer for the first time a rationale to expand the synthetic scope of the double interring dehydrogenation pathway for the preparation of novel symmetric double-bond bridged captodative heterocycles.

The chemical and spectroscopic characterization of 5,6-indolequinones and their semiquinones, key transient intermediates in the oxidative conversion of 5,6-dihydroxyindoles to eumelanin biopolymers, is a most challenging task. In the present paper, we report the characterization of a novel, relatively long-lived 5,6-indolequinone along with its semiquinone using an integrated chemical, pulse radiolytic, and computational approach. The quinone was obtained by oxidation of 5,6-dihydroxy-3-iodoindole (1a) with o-chloranil in cold ethyl acetate or aqueous buffer: it displayed electronic absorption bands around 400 and 600 nm, was reduced to 1a with Na2S2O4, and reacted with o-phenylenediamine to give small amounts of 3-iodo-1H-pyrrolo[2,3-b]phenazine (2). The semiquinone exhibited absorption maxima at 380 nm (sh) and 520 nm and was detected as the initial species produced by pulse radiolytic oxidation of 1a at pH 7.0. DFT investigations indicated the 6-phenoxyl radical and the N-protonated radical anion as the most stable tautomers for the neutral and anion forms of the semiquinone, respectively. Calculated absorption spectra in water gave bands at 350 (sh) and 500 nm for the neutral form and at 310 and 360 (sh) nm for the anion. Disproportionation of the semiquinone with fast second-order kinetics (2k = 1.1 x 1010 M-1 s-1) gave a chromophore with absorption bands resembling those of chemically generated 1a quinone. Computational analysis predicted 1a quinone to exist in vacuo as the quinone-methide tautomer, displaying low energy transitions at 380 and 710 nm, and in water as the o-quinone, with calculated absorption bands around 400 and 820 nm. A strong participation of a p orbital on the iodine atom in the 360-380 nm electronic transitions of the o-quinone and quinone-methide was highlighted. The satisfactory agreement between computational and experimental electronic absorption data would suggest partitioning of 1a quinone between the o-quinone and quinone-methide tautomers depending on the medium.