196,428 research outputs found
M. d'Ischia, C. Costantini, G. Prota. Reaction of dopamine with malondialdehyde: a possible underlying event in Parkinson's disease.
No full textUnder physiologically relevant conditions, malondialdehyde reacts with the neurotransmitter dopamine to give three major adducts that were identified as the enaminal 1, the dihydropyridine 2 and the novel oxaazabicyclo[3.3.1]nonadiene 3
Nitrosation and nitration of bioactive molecules: toward the basis of disease and its prevention
No full textTraditionally raised by the toxicological implications of excess exposure to nitrogen oxides and nitrite ions, interest in the chemistry of biological nitrosations and nitrations has gained new impetus in the past decade following the discovery of nitric oxide (NO) as an endogenous physiological regulator and an amplifier of oxidative stress-dependent toxic processes. This account is concerned with an overview of the reactions of nitrosating and nitrating agents of pathophysiological relevance with two potential biochemical targets, namely polyunsaturated fatty acids and catecholamines. The results of model studies on the mechanism of the antinitrosating activity of caffeic acid and chlorogenic acid are also presented
Oxygen-dependent nitration of ethyl linoleate with nitric oxide
No full textExposure of linoleic acid or its ethyl ester to NO in air-equilibrated cyclohexane led to an exceedingly complex pattern of products, a fraction of which (30-40% w/w) consisted of an unseparable mixture of isomeric nitroolefin and nitronitrate derivatives, including 1-3
Nitrosation-oxidative ring contraction of alfa-tocopherol by reaction with nitric oxide under aerobic conditions.
No full textExposure of α-tocopherol [I; R = Me(CHMeCH2CH2CH2)3] to nitric oxide (NO) in air-satd. cyclohexane leads to a complex mixt. of products, one of which, relatively more polar, has been isolated and identified as the novel 2,3-dimethyl-4-acetyl-4-hydroxy-5-nitroso-2-cyclopentenone deriv. II [R = Me(CHMeCH2CH2CH2)3]
The moving frontiers of melanin research: chasing transient (semi)quinones in 5,6-dihydroxyindole polymerization
No full textNew Insights into the Acid-Promoted Reaction of Caffeic Acid and Its Esters with Nitrite: Decarboxylation Drives Chain Nitrosation Pathways toward Novel Oxime Derivatives and Oxidation/Fragmentation Products Thereof.
No full textIn 0.05 M acetate buffer, pH 4, containing 1% methanol, caffeic acid (1a) (2 x 10(-3) M) reacted smoothly with nitrite (NO2-) (4 x 10(-3) M) to afford as main products the novel 2-hydroxy- and 2-methoxyaldoximes 7a,b, the 2-oxoaldoxime 9a, 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzaldehyde, and the known furoxan 3c and benzoxazinone 4b in smaller amounts. At lower 1a concentration (e.g., 1 x 10(-4) M), 7a was the main product, whereas with 0.1 M 1a and 0.5 M NO2- 3c and 9a were prevailing. At pH 2, 7a was still the most abundant product, together with 3,4dihydroxybenzaldehyde and some 9a, whereas at pH 1 9a and 3,4-dihydroxybenzaldehyde were formed in higher yields. No evidence for ring nitration products, including the previously reported 4,5-dihydroxy-2-nitrobenzaldehyde, was obtained. At 2 x 10(-3) M concentration and at pH 4, caffeic acid methyl ester (1b) reacted with NO2- chiefly via ring nitration and/or dimerization to give 5a, the novel nitrated neolignan derivative 10, and the parent 6. Chlorogenic acid (1c) afforded only the ring nitrated derivative 5b. A unifying mechanism for the reaction of 1a and its esters with NO2- is proposed involving reversible formation of nitroso intermediates via chain nitrosation at the 2-position of the (E)-3-(3,4-dihydroxyphenyl)propenoic system. In the case of 1a, decarboxylation would drive the nitroso intermediates toward the formation of oximes 7a,b and 3c, reflecting nucleophilic addition of water, methanol, and NO2-, and their oxidation or breakdown products, viz. 9a, 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzoic acid, and the benzoxazinone 4b. In the case of esters 1b,c, to which decarboxylation is precluded, ring nitration or dimerization become the favored routes, triggered by preliminary oxidation at the catechol moiety
Medium-dependent competitive pathways in the reactions of polyunsaturated fatty acids with nitric oxide in the presence of oxygen. Structural characterisation of nitration products and a theoretical mechanistic insight
No full textReactions of Me arachidonate and Et linoleate with NO in the presence of O2 gave complex mixts. of products via interaction with NO2 and related nitrogen oxides. In cyclohexane, the reaction afforded chiefly nitroalkene and nitronitrate adducts, characterized by spectroscopic techniques. In 0.1 M phosphate buffer, pH 7.4, a different pattern of products was formed, comprising mainly conjugated hydroperoxide derivs. Quantum mech. calcns. on a model 1,4-diene system suggested that medium-dependent changes in product distribution can be ascribed in part to solvation effects on the NO2-induced addn./H-atom abstraction competition, but reflect also a complex interplay of solvent-sensitive mechanisms
A virtual revolution for chemical evolution: Pushing the limits of prediction en route from complexity to the molecular code of life: Comment on “A never-ending story in the sky: The secrets of chemical evolution” by Vincenzo Barone et al.
No full textThiouracil Antithyroid Drugs as a New Class of Neuronal Nitric Oxide Synthase Inhibitors.
No full textTwo established antithyroid drugs, 6-propyl-2-thiouracil and 6-methyl-2-thiouracil, as well as S-methylthiouracil, are shown to be competitive inhibitors of nitric oxide synthase (NOS) (K-1 values ranging from 14 to 60 muM), with moderate selectivity for the neuronal isoform, Other thioureylene and thioamide-containing heterocyclic systems proved virtually ineffective as NOS inhibitors, Besides offering novel useful leads for inhibitor design as well as to probe the active site of neuronal NOS, the results of this study may have interesting implications in relation to the antithyroid activity of thiouracils and their possible neurological effect
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