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Results for “Hydroxylamines”

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At least 973 records · Page 54Linked to original sources
PubMed1998

Both hydroxylamine and nitroxide protect cardiomyocytes from oxidative stress.

The unique anti-oxidative activity of nitroxide radicals protecting against reactive oxygen-derived species (ROS) has been recently demonstrated in several model systems. The present study focuses on the activity of nitroxide and of its reduced form in cultured rat ventricular cardiomyocytes exposed to O2.- and H2O2 generated by hypoxanthine (HX) and xanthine oxidase (XO). To evaluate cell injury, spontaneous beating, leakage of lactate dehydrogenase (LDH), and depletion of cellular ATP were determined. The protective effect of 4-OH-2,2,6,6-tetramethyl-piperidine-N-oxyl (TPL) was compared with that of 4-OH-2,2,6,6-tetramethyl-1-hydroxypiperidine (TPL-H) and of several common anti-oxidants. A rapid exchange between TPL and TPL-H, is mediated by cellular metabolism and through reactions with ROS. In particular, TPL under O2.- flux is oxidized to oxo-ammonium cation (TPL+) which comproportionates with TPL-H yielding two nitroxide radicals. Because this exchange limits the distinction between the biological activities of TPL and TPL-H, NADH which can reduce TPL+ was included in order to maintain the nitroxide in its reduced form. The results demonstrate that both TPL and TPL-H protect cardiomyocytes against beating loss and LDH leakage. Conversely, cellular ATP depletion induced by HX/XO is inhibited by TPL-H, though not by TPL, suggesting that different mechanisms underlie their protective activities. Through a flip-flop between the two forms, which coexist in the system, the levels of TPL-H and TPL are continuously replenished. The conversion, upon reaction, of each antioxidant into the other one enables them, contrary to common antioxidants which operate in a stoichiometric mode, to act catalytically.

Animals↗
PubMed2005

Kinetic and mechanistic study of the Pt(II) versus Pt(IV) effect in the platinum-mediated nitrile-hydroxylamine coupling.

The metal-mediated coupling between coordinated EtCN in the platinum(II) and platinum(IV) complexes cis- and trans-[PtCl(2)(EtCN)(2)], trans-[PtCl(4)(EtCN)(2)], a mixture of cis/trans-[PtCl(4)(EtCN)(2)] or [Ph(3)PCH(2)Ph][PtCl(n)(EtCN)] (n = 3, 5), and dialkyl- and dibenzylhydroxylamines R(2)NOH (R = Me, Et, CH(2)Ph, CH(2)C(6)H(4)Cl-p) proceeds smoothly in CH(2)Cl(2) at 20-25 degrees C and the subsequent workup allowed the isolation of new imino species [PtCl(n){NH=C(Et)ONR(2)}(2)] (n = 2, R = Me, cis-1 and trans-1; Et, cis-2 and trans-2; CH(2)Ph, cis-3 and trans-3; CH(2)C(6)H(4)Cl-p, cis-4 and trans-4; n = 4, R = Me, trans-9; Et, trans-10; CH(2)Ph, trans-11; CH(2)C(6)H(4)Cl-p, trans-12) or [Ph(3)PCH(2)Ph][PtCl(n){NH=C(Et)ONR(2)}] (n = 3, R = Me, 5; Et, 6; CH(2)Ph, 7; CH(2)C(6)H(4)Cl-p, 8; n = 5, R = Me, 13; Et, 14; CH(2)Ph, 15; CH(2)C(6)H(4)Cl-p, 16) in excellent to good (95-80%) isolated yields. The reduction of the Pt(IV) complexes 9-16 with the ylide Ph(3)P=CHCO(2)Me allows the synthesis of Pt(II) species 1-8. The compounds 1-16 were characterized by elemental analyses (C, H, N), FAB-MS, IR, (1)H, (13)C{(1)H}, and (31)P{(1)H} NMR (the latter for the anionic type complexes 5-8 and 13-16) and by X-ray crystallography for the Pt(II) (cis-1, cis-2, and trans-4) and Pt(IV) (15) species. Kinetic studies of addition of R(2)NOH (R = CH(2)C(6)H(4)Cl-p) to complexes [Ph(3)PCH(2)Ph][Pt(II)Cl(3)(EtCN)] and [Ph(3)PCH(2)Ph][Pt(IV)Cl(5)(EtCN)] by the (1)H NMR technique revealed that both reactions are first order in (p-ClC(6)H(4)CH(2))(2)NOH and Pt(II) or Pt(IV) complex, the second-order rate constant k(2) being three orders of magnitude larger for the Pt(IV) complex. The reactions are intermolecular in nature as proved by the independence of k(2) on the concentrations of added EtC triple bond N and Cl(-). These data and the calculated values of Delta H++ and Delta S++ are consistent with the mechanism involving the rate-limiting nucleophilic attack of the oxygen of (p-ClC(6)H(4)CH(2))(2)NOH at the sp-carbon of the C triple bond N bond followed by a fast proton migration.

Journal Article↗
PubMed2005

Investigating the reaction of N-carbobenzoxy-O-carbobenzoxy- hydroxylamine with dimethyl sulfoxide: formation of S,S-dimethyl-N-[(phenylmethoxy)- carbonyl]sulfoximine.

[Reaction: see text]. N-carbobenzoxy-O-carbobenzoxyhydroxylamine (1a) underwent a thermally induced reaction in DMSO in which there is net N-alpha-eliminative oxidation with tandem oxidative incorporation of DMSO to yield S,S-dimethyl-N-[(phenylmethoxy)carbonyl]sulfoximine. Mechanisms for the formation of the sulfoximine are presented as well as the product characterizations, including the X-ray crystal structure.

Journal Article↗
PubMed1997

An Efficient Route to beta-D-Isoxazolidinyl Nucleosides via Diastereoselective Michael Addition of Hydroxylamine to Unsaturated Esters.

Enantioselective syntheses of beta-D-isoxazolidinyl pyrimidine and purine nucleosides are described. Michael addition of N-methylhydroxylamine to alpha,beta-unsaturated esters was investigated. Both E- and Z-esters 10E and 10Z produced the same intermediates which were cyclized to isoxazolidin-5-ones 8 with high diastereoselectivity. The major isoxazolidin-5-one 8a was reduced and acetylated to acetate 11 for the preparation of nucleosides. The coupling reaction of acetate 11 with silylated thymine, uracil, and N(4)-benzoylcytosine using TMSOTf as a Lewis acid yielded the corresponding nucleoside derivatives. The related purine analogue was produced by the BF(3).Et(2)O-catalyzed condensation of acetate 11 with silylated 6-chloropurine. The predominant formation of the cis isomers for both pyrimidine and purine analogues was unexpected and the reaction mechanism was investigated. The nucleoside intermediates were converted to the corresponding 1,2-diols, which were latter oxidized and reduced to the desired monoalcohol products such as 14, 16, 19, and 24.

Journal Article↗
PubMed2005

Bis(hydroxyamino)triazines: versatile and high-affinity tridentate hydroxylamine ligands for selective iron(III) chelation.

A new versatile family of chelating agents based on bis(hydroxyamino)-1,3,5-triazines, BHTs, is described. The properties of different BHT ligands are determined by electrochemistry, spectroscopy and titrimetry revealing high redox stability, transparency in the visible range, and diprotic acid-like behaviour in the 5-9 pH range. The iron(III) and iron(II)-BHT complexes were studied revealing high affinity of BHTs to iron(III). Electrochemical studies show exceptional preference of the BHT ligands to iron(III) over iron(II), this, in addition to their small size and their fast and reversible electrochemistry makes them potentially useful electrochemical redox couples for the low end of the aqueous potential window (<0.6 V, vs. NHE). The synthetic versatility of the new ligands allows easy tuning of the hydrophobicity, redox potential, and to some extent the stability constant of the complexes by alteration of the peripheral groups appended to the BHTs.

Journal Article↗