Acyloxy Nitroso Compounds Research Articles

Visible-Light-Initiated Difunctionalization of Quinoxalin-2(1H)-ones with Acyloxy Nitroso Compounds.

Herein, a photoinitiated radical relay reaction of quinoxalin-2(1H)-ones, with acyloxy nitroso compounds as a source of radicals, is described. Although the C-H functionalization of quinoxalin-2(1H)-ones has been investigated, its difunctionalization, the simultaneous construction of C-C and N-N bonds directly via the radical relay reaction, has rarely been reported. Moreover, the obtained products underwent sequential reactions to access C7-NO2 of quinoxalin-2(1H)-ones under mild conditions.

Photo-Mediated Intermolecular Coupling of Alkenes with Ketones via Acyloxy Nitroso Compounds.

An atom-economic intermolecular radical addition reaction of acyloxy nitroso compounds to electron-deficient alkenes mediated by visible light is reported. The starting nitroso derivatives are readily prepared by oxidation of the corresponding oximes prepared from ketones and the overall transformation represents an oxidative coupling of a ketone with a Michael acceptor. The cascade proceeds smoothly under mild conditions, providing a series of valuable functionalized oximes in moderate to good yields. Mechanistic studies suggest that these cascades proceed via addition/coupling processes that are controlled by the persistent radical effect (PRE) with NO acting as the persistent species.

ChemInform Abstract: Ring Expansions of Acyloxy Nitroso Compounds.

AbstractThe acyloxy nitroso compounds undergo two separate ring expansion reactions.

Ring expansions of acyloxy nitroso compounds

Treatment of cyclopentanone and cyclobutanone-derived oximes with lead(IV) tetraacetate gives the bright blue acyloxy nitroso compounds, which upon basic hydrolysis yields the ring expansion product cyclic hydroxamic acids in 12–81% yield. Reactions of substituted cyclopentanones provide ring expanded products where the –NOH group regioselectively inserts to the more substituted position and gives a better yield compared to the treatment of the same ketone with a basic solution of Piloty’s acid. Reaction of phosphines with acyloxy nitroso compounds generally generates a ring-expanded Beckmann rearrangement product that can be hydrolyzed to the corresponding lactam. Acyloxy nitroso compounds that undergo rapid hydrolysis to HNO do not show this ring expansion reactivity. These results further demonstrate the versatility of acyloxy nitroso compound to yield structurally complex materials.

New acyloxy nitroso compounds with improved water solubility and nitroxyl (HNO) release kinetics and inhibitors of platelet aggregation

New acyloxy nitroso compounds, 4-nitrosotetrahydro-2H-pyran-4-yl 2,2,2-trichloroacetate and 4-nitrosotetrahydro-2H-pyran-4-yl 2,2-dichloropropanoate were prepared. These compounds release HNO under neutral conditions with half-lives between 50 and 120min, identifying these HNO donors as kinetically intermediate to the much slower acetate derivative and the faster trifluoroacetic acid derivative. These compounds or HNO-derived from these compounds react with thiols, including glutathione, thiol-containing enzymes and heme-containing proteins in a similar fashion to other acyloxy nitroso compounds. HNO released from these acyloxy nitroso compounds inhibits activated platelet aggregation. These acyloxy nitroso compounds augment the range of release for this group of HNO donors and should be valuable tools in the further study of HNO biology.

Direct and Nitroxyl (HNO)-Mediated Reactions of Acyloxy Nitroso Compounds with the Thiol-Containing Proteins Glyceraldehyde 3-Phosphate Dehydrogenase and Alkyl Hydroperoxide Reductase Subunit C

Nitroxyl (HNO) reacts with thiols, and this reactivity requires the use of donors with 1-nitrosocyclohexyl acetate, pivalate, and trifluoroacetate, forming a new group. These acyloxy nitroso compounds inhibit glyceraldehyde 3-phosphate dehydrogenase (GAPDH) by forming a reduction reversible active site disulfide and a reduction irreversible sulfinic acid or sulfinamide modification at Cys244. Addition of these acyloxy nitroso compounds to AhpC C165S yields a sulfinic acid and sulfinamide modification. A potential mechanism for these transformations includes nucleophilic addition of the protein thiol to a nitroso compound to yield an N-hydroxysulfenamide, which reacts with thiol to give disulfide or rearranges to sulfinamides. Known HNO donors produce the unsubstituted protein sulfinamide as the major product, while the acetate and pivalate give substituted sulfinamides that hydrolyze to sulfinic acids. These results suggest that nitroso compounds form a general class of thiol-modifying compounds, allowing their further exploration.

Water soluble acyloxy nitroso compounds: HNO release and reactions with heme and thiol containing proteins

Nitroxyl (HNO) has gained interest as a potential treatment of congestive heart failure through the ability of the HNO donor, Angeli's salt (AS), to evoke positive inotropic effects in canine cardiac muscle. The release of nitrite during decomposition limits the use of AS requiring other HNO sources. Acyloxy nitroso compounds liberate HNO and small amounts of nitrite upon hydrolysis and the synthesis of the water-soluble 4-nitrosotetrahydro-2H-pyran-4-yl acetate and pivalate allows for pig liver esterase (PLE)-catalysis increasing the rate of decomposition and HNO release. The pivalate derivative does not release HNO, but the addition of PLE catalyzes hydrolysis (t1/2=39min) and HNO formation (65% after 30min). In the presence of PLE, this compound converts metmyoglobin (MetMb) to iron nitrosyl Mb and oxyMb to metMb indicating that these compounds only react with heme proteins as HNO donors. The pivalate in the presence and the absence of PLE inhibits aldehyde dehydrogenase (ALDH) with IC50 values of 3.5 and 3.3μM, respectively, in a time-dependent manner. Reversibility assays reveal reversible inhibition of ALDH in the absence of PLE and partially irreversible inhibition with PLE. Liquid chromatography–mass spectrometry (LC–MS) reveals formation of a disulfide upon incubation of an ALDH peptide without PLE and a mixture of disulfide and sulfinamide in the presence of PLE. A dehydroalanine residue forms upon incubation of this peptide with excess AS. These results identify acyloxy nitroso compounds as unique HNO donors capable of thiol modification through direct electrophilic reaction or HNO release.

Abstract 219: Acyloxy Nitroso Compounds Inhibit LIF Signaling in Endothelial Cells and Cardiac Myocytes: Evidence That STAT3 Signaling is Redox-Sensitive

Nitroxyl donors have positive inotropic and lusitropic effects that may have therapeutic potential for treating heart failure, but their effects on other signaling pathways are not well studied. Previously we showed that leukemia inhibitory factor (LIF)-induced signaling is inhibited by oxidative stress, which targets JAK1 activation. In addition, we recently reported evidence for a cysteine-based redox switch in the JH1 catalytic domain of JAK 1 and 2. Since nitroxyl is thiophylic, we postulated that nitroxyl donors would inhibit LIF-induced JAK-STAT3 activation. Pretreatment of human microvascular endothelial cells (HMEC-1) or neonatal rat ventricular myocytes with the nitroxyl donors Angeli’s salt and the recently-described nitrosocyclohexyl acetate (NCA) inhibited LIF-induced STAT3 activation as indexed by Y705 phosphorylation. Pretreatment of HMEC-1 with NCA also blocked LIF-induced expression of the inflammation-related genes, ICAM-1 and CEBPD. The related acyloxy nitroso compound 1-nitrosocyclohexyl pivalate (NCP), which is not a nitroxyl donor, was equally effective in inhibiting STAT3 activation, suggesting that these compounds were acting as electrophiles on a thiolate residue. NCA had no effect on the catalytic activity of JAK1 and modestly affected JAK1-induced tyrosine phosphorylation of the LIF receptor. Thus, the JH1 redox switch is not a direct target of the acyloxy nitroso compound. However, pretreatment of recombinant human STAT3 with NCA or NCP reduced the labeling of free sulfhydryl residues with fluorescein-5-maleimide. In addition, we document by dimedone labeling that oxidation of STAT3 is associated with formation of sulfenic acid residues, a hallmark of redox-sensitive proteins. Altogether our evidence indicates that STAT3 has redox-sensitive cysteines that regulate its activation and are targeted by nitroxyl donors and related acyloxy nitroso compounds. These findings raise the possibility of new therapeutic strategies to target STAT3 signaling.

Acyloxy Nitroso Compounds Inhibit LIF Signaling in Endothelial Cells and Cardiac Myocytes: Evidence That STAT3 Signaling Is Redox-Sensitive

We previously showed that oxidative stress inhibits leukemia inhibitory factor (LIF) signaling by targeting JAK1, and the catalytic domains of JAK 1 and 2 have a cysteine-based redox switch. Thus, we postulated that the NO sibling and thiophylic compound, nitroxyl (HNO), would inhibit LIF-induced JAK-STAT3 activation. Pretreatment of human microvascular endothelial cells (HMEC-1) or neonatal rat cardiomyocytes with the HNO donors Angeli’s salt or nitrosocyclohexyl acetate (NCA) inhibited LIF-induced STAT3 activation. NCA pretreatment also blocked the induction of downstream inflammatory genes (e.g. intercellular adhesion molecule 1, CCAAT/enhancer binding protein delta). The related 1-nitrosocyclohexyl pivalate (NCP; not a nitroxyl donor) was equally effective in inhibiting STAT3 activation, suggesting that these compounds act as thiolate targeting electrophiles. The JAK1 redox switch is likely not a target of acyloxy nitroso compounds, as NCA had no effect on JAK1 catalytic activity and only modestly affected JAK1-induced phosphorylation of the LIF receptor. However, pretreatment of recombinant human STAT3 with NCA or NCP reduced labeling of free sulfhydryl residues. We show that NCP in the presence of diamide enhanced STAT3 glutathionylation and dimerization in adult mouse cardiac myocytes and altered STAT3 under non-reducing conditions. Finally, we show that monomeric STAT3 levels are decreased in the Gαq model of heart failure in a redox-sensitive manner. Altogether, our evidence indicates that STAT3 has redox-sensitive cysteines that regulate its activation and are targeted by HNO donors and acyloxy nitroso compounds. These findings raise the possibility of new therapeutic strategies to target STAT3 signaling via a redox-dependent manner, particularly in the context of cardiac and non-cardiac diseases with prominent pro-inflammatory signaling.

P65. Acyloxy nitroso compounds as hno donors, without the release of nitrite, and their reactions with thiol and heme proteins

P65. Acyloxy nitroso compounds as hno donors, without the release of nitrite, and their reactions with thiol and heme proteins

The chemistry of nitroxyl-releasing compounds.

Nitroxyl (HNO) demonstrates a diverse and unique biological profile compared to nitric oxide, a redox-related compound. Although numerous studies support the use of HNO as a therapeutic agent, the inherent chemical reactivity of HNO requires the use of donor molecules. Two general chemical strategies currently exist for HNO generation from nitrogen-containing molecules: (i) the disproportionation of hydroxylamine derivatives containing good leaving groups attached to the nitrogen atom and (ii) the decomposition of nitroso compounds (X-N=O, where X represents a good leaving group). This review summarizes the synthesis and structure, the HNO-releasing mechanisms, kinetics and by-product formation, and alternative reactions of six major groups of HNO donors: Angeli's salt, Piloty's acid and its derivatives, cyanamide, diazenium diolate-derived compounds, acyl nitroso compounds, and acyloxy nitroso compounds. A large body of work exists defining these six groups of HNO donors and the overall chemistry of each donor requires consideration in light of its ability to produce HNO. The increasing interest in HNO biology and the potential of HNO-based therapeutics presents exciting opportunities to further develop HNO donors as both research tools and potential treatments.

Acyloxy Nitroso Compounds as Nitroxyl (HNO) Donors: Kinetics, Reactions with Thiols, and Vasodilation Properties

Acyloxy nitroso compounds hydrolyze to nitroxyl (HNO), a nitrogen monoxide with distinct chemistry and biology. Ultraviolet-visible spectroscopy and mass spectrometry show hydrolysis rate depends on pH and ester group structure with the observed rate being trifluoroacetate (3) > acetate (1) > pivalate (2). Under all conditions, 3 rapidly hydrolyzes to HNO. A combination of spectroscopic, kinetic, and product studies show that addition of thiols increases the decomposition rate of 1 and 2, leading to hydrolysis and HNO. Under conditions that favor thiolates, the thiolate directly reacts with the nitroso group, yielding oximes without HNO formation. Biologically, 3 behaves like Angeli's salt, demonstrating thiol-sensitive nitric oxide-mediated soluble guanylate cyclase-dependent vasorelaxation, suggesting HNO-mediated vasorelaxation. The slow HNO-donor 1 demonstrates weak thiol-insensitive vasorelaxation, indicating HNO release kinetics determine HNO bioavailability and activity. These results show that acyloxy nitroso compounds represent new HNO donors capable of vasorelaxation depending on HNO release kinetics.

Hydrolysis of Acyloxy Nitroso Compounds Yields Nitroxyl (HNO)

Nitroxyl (HNO/NO(-)), the reduced form of nitric oxide, has gained attention based on its separate chemistry and biology from nitric oxide. The inherent reactivity of HNO requires new and mechanistically unique donors for the detailed study of HNO chemistry and biology. Oxidation of cyclohexanone oxime with lead tetraacetate yields 1-nitrosocyclohexyl acetate, whereas oxidation of oximes in the presence of excess carboxylic acid gives various acyloxy nitroso compounds. These bright blue compounds exist as monomers as indicated by their infrared, proton, and carbon NMR spectra, and X-ray crystallographic analysis reveals the nitroso groups possess a "nitroxyl-like" bent configuration. Hydrolysis of these compounds produces nitrous oxide, the dimerization and dehydration product of HNO, and provides evidence for the intermediacy of HNO. Both thiols and oxidative metal complexes inhibit nitrous oxide formation. Hydrolysis of these compounds in the presence of ferric heme complexes forms ferrous nitrosyl complexes providing further evidence for the intermediacy of HNO. Kinetic analysis shows that the rate of hydrolysis depends on pH and the structure of the acyl group of the acyloxy nitroso compound. These compounds relax pre-constricted rat aortic rings similar to known HNO donors. Together, these results identify acyloxy nitroso compounds as a new class of HNO donors.

3,2]‐Sigmatropic Rearrangement of Acyloxy Nitronic Acids into Geminal Acyloxy Nitroso Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

3,2]-Sigmatropic Rearrangement of Acyloxy Nitronic Acids into Geminal Acyloxy Nitroso Compounds

Acylation of secondary nitroalkanes is accompanied by [3,2]-sigmatropic rearrangement of acyloxy nitronic acids into geminal acyloxy nitroso compounds which are formed in preparative yields.