John P. Toscano

Johns Hopkins University, Baltimore, Maryland, United States

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Publications (76)290.96 Total impact

  • Gizem Keceli, Cathy D Moore, John P Toscano
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    ABSTRACT: Recent discoveries of important pharmacological properties have drawn attention to the reactivity of HNO (azanone, nitroxyl) with biologically relevant substrates. Apart from its role in thiol oxidation, HNO has been reported to have nitrosative properties, for example, with tryptophan resulting in N-nitrosotryptophan formation. We have investigated the reactivity of HNO with tryptophan and small peptides containing either tryptophan or both a tryptophan and a cysteine residue. Our results point to the more reactive nature of cysteine towards HNO compared with tryptophan.
    Bioorganic & medicinal chemistry letters. 07/2014;
  • Gizem Keceli, John P Toscano
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    ABSTRACT: Nitroxyl (HNO), a potential heart failure therapeutic, is known to target cysteine residues to form sulfinamides and/or disulfides. Because HNO-derived modifications may depend on their local environment, we have investigated the reactivity of HNO with cysteine derivatives and C-terminal cysteine-containing peptides at physiological pH and temperature. Our findings indicate that the nature of HNO-derived modifications of C-terminal cysteines is affected by the C-terminal carboxylate. Apart from the lack of sulfinamide formation, these studies have revealed the presence of new products, a sulfohydroxamic acid derivative (RS(O)2NHOH) and a thiosulfonate (RS(O)2SR), presumably produced under our experimental conditions via the intermediacy of a cyclic structure that is hydrolyzed to give a sulfenic acid (RSOH). Moreover, these modifications are formed independent of oxygen.
    Biochemistry 05/2014; · 3.38 Impact Factor
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    ABSTRACT: It is currently not known whether caffeine has an enhancing effect on long-term memory in humans. We used post-study caffeine administration to test its effect on memory consolidation using a behavioral discrimination task. Caffeine enhanced performance 24 h after administration according to an inverted U-shaped dose-response curve; this effect was specific to consolidation and not retrieval. We conclude that caffeine enhanced consolidation of long-term memories in humans.
    Nature Neuroscience 01/2014; · 15.25 Impact Factor
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    ABSTRACT: α-Diazo arylketones are well-known substrates for Wolff rearrangement to phenylacetic acids through a ketene intermediate by either thermal or photochemical activation. Likewise, α-substituted p-hydroxyphenacyl (pHP) esters are substrates for photo-Favorskii rearrangements to phenylacetic acids by a different pathway that purportedly involves a cyclopropanone intermediate. In this paper, we show that the photolysis of a series of α-diazo-p-hydroxyacetophenones and p-hydroxyphenacyl (pHP) α-esters both generate the identical rearranged phenylacetates as major products. Since α-diazo-p-hydroxyacetophenone (, pHP N2) contains all the necessary functionalities for either Wolff or Favorskii rearrangement, we were prompted to probe this intriguing mechanistic dichotomy under conditions favorable to the photo-Favorskii rearrangement, i.e., photolysis in hydroxylic media. An investigation of the mechanism for conversion of to p-hydroxyphenyl acetic acid () using time-resolved infrared (TRIR) spectroscopy clearly demonstrates the formation of a ketene intermediate that is subsequently trapped by solvent or nucleophiles. The photoreaction of is quenched by oxygen and sensitized by triplet sensitizers and the quantum yields for range from 0.19 to a robust 0.25. The lifetime of the triplet, determined by Stern-Volmer quenching, is 31 ns with a rate for appearance of of k = 7.1 × 10(6) s(-1) in aq. acetonitrile (1 : 1 v : v). These studies establish that the primary rearrangement pathway for involves ketene formation in accordance with the photo-Wolff rearrangement. Furthermore we have also demonstrated the synthetic utility of as an esterification and etherification reagent with a variety of substituted α-diazo-p-hydroxyacetophenones, using them as synthons for efficiently coupling it to acids and phenols to produce pHP protect substrates.
    Photochemical and Photobiological Sciences 12/2013; · 2.92 Impact Factor
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    ABSTRACT: Nitroxyl (HNO), a potential heart failure therapeutic, is known to post-translationally modify cysteine residues. Among reactive nitrogen oxide species, the modification of cysteine residues to sulfinamides [RS(O)NH2] is unique to HNO. We have applied 15N-edited 1H-NMR techniques to detect the HNO-induced thiol to sulfinamide modification in several small organic molecules, peptides, and the cysteine protease, papain. Relevant reactions of sulfinamides involve reduction to free thiols in the presence of excess thiol and hydrolysis to form sulfinic acids [RS(O)OH]. We have investigated sulfinamide hydrolysis at physiological pH and temperature. Studies with papain and a related model peptide containing the active site thiol suggest that sulfinamide hydrolysis can be enhanced in a protein environment. These findings are also supported by modeling studies. In addition, analysis of peptide sulfinamides at various pH values suggests that hydrolysis becomes more facile under acidic conditions.
    Biochemistry 09/2013; · 3.38 Impact Factor
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    ABSTRACT: Aims: Nitroxyl (HNO) interacts with thiols to act as a redox-sensitive modulator of protein function. It enhances sarcoplasmic reticular Ca2+ uptake and myofilament Ca2+ sensitivity, improving cardiac contractility. This activity has led to clinical testing of HNO donors for heart failure. Here, we tested whether HNO alters the inhibitory interaction between phospholamban (PLN) and the sarcoplasmic reticulum Ca-ATPase (SERCA2a) in a redox-dependent manner, improving Ca2+ handling in isolated myocytes/hearts. Results: Ventriculocytes, SR vesicles and whole hearts were isolated from control (WT) or PLN knockout (PLN-/-) mice. Compared to WT, PLN-/- myocytes displayed enhanced resting sarcomere shortening, peak Ca2+ transient, and blunted β-adrenergic responsiveness. HNO stimulated shortening, relaxation, and Ca2+ transient in WT cardiomyocytes, and evoked positive inotropy/lusitropy in intact hearts. These changes were markedly blunted in PLN-/- cells/hearts. HNO enhanced SR Ca2+ uptake in WT but not PLN-/- SR-vesicles. Spectroscopic studies in insect cell microsomes expressing SERCA2a±PLN showed that HNO increased Ca2+-dependent SERCA2a conformational flexibility but only when PLN was present. In cardiomyocytes, HNO achieved this effect by stabilizing PLN in an oligomeric disulfide bond-dependent configuration, decreasing the amount of free inhibitory monomeric PLN available. Innovation: HNO-dependent redox changes in myocyte PLN oligomerization relieve PLN inhibition of SERCA2a. Conclusions: PLN plays a central role in HNO-induced enhancement of SERCA2a activity, leading to increased inotropy/lusitropy in intact myocytes and hearts. PLN remains physically associated with SERCA2a; however less monomeric PLN is available resulting in decreased inhibition of the enzyme. These findings offer new avenues to improve Ca2+ handling in failing hearts.
    Antioxidants & Redox Signaling 08/2013; · 8.20 Impact Factor
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  • Anthony S. Evans, John P. Toscano
    ChemInform 11/2012; 43(46).
  • Meredith R Cline, Tyler A Chavez, John P Toscano
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    ABSTRACT: Recent research has shown that nitroxyl (HNO) has important and unique biological activity, especially as a potential alternative to current treatments of cardiac failure. HNO is a reactive molecule that undergoes efficient dimerization and subsequent dehydration to form nitrous oxide (N(2)O), making its detection in solution or biologically relevant preparations difficult. Due to this limitation, HNO has not yet been observed in vivo, though several pathways for its endogenous generation have been postulated. Here, we investigate the oxidation of N-hydroxy-l-arginine (NOHA) by hypochlorous acid (HOCl), which is generated in vivo from hydrogen peroxide and chloride by the heme enzyme, myeloperoxidase. NOHA is an intermediate in the enzymatic production of nitric oxide (NO) by NO synthases, and has been shown previously to be chemically oxidized to either HNO or NO, depending on the oxidant employed. Using membrane inlet mass spectrometry and standard N(2)O analysis by gas chromatography, we find that NOHA is oxidized by excess HOCl to form HNO-derived N(2)O. In addition, we also observe the analogous production of HNO from the HOCl oxidation of hydroxylamine, hydroxyurea, and (to a lesser extent) acetohydroxamic acid.
    Journal of inorganic biochemistry 10/2012; · 3.25 Impact Factor
  • Gizem Keceli, John P Toscano
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    ABSTRACT: Sulfinamide [RS(O)NH(2)] formation is known to occur upon exposure of cysteine residues to nitroxyl (HNO), which has received recent attention as a potential heart failure therapeutic. Because this modification can alter protein structure and function, we have examined the reactivity of sulfinamides in several systems, including a small organic molecule, peptides, and a protein. Although it has generally been assumed that this thiol to sulfinamide modification is irreversible, we show that sulfinamides can be reduced back to the free thiol in the presence of excess thiol at physiological pH and temperature. We have examined this sulfinamide reduction both in peptides, where a cyclic intermediate analogous to that proposed for asparagine deamidation reactions potentially can contribute, and in a small organic molecule, where the mechanism is restricted to a direct thiolysis. These studies suggest that the contribution from the cyclic intermediate becomes more important in environments with lower dielectric constants. In addition, although sulfinic acid [RS(O)OH] formation is observed upon prolonged incubations in water, reduction of sulfinamides is found to dominate in the presence of thiols. Finally, studies with the cysteine protease, papain, suggest that the reduction of sulfinamide to the free thiol is viable in a protein environment.
    Biochemistry 05/2012; 51(20):4206-16. · 3.38 Impact Factor
  • Yonglin Liu, Anthony S Evans, John P Toscano
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    ABSTRACT: Nanosecond time-resolved infrared (TRIR) spectroscopy has been used to observe singlet thiobenzoylnitrene at 1740 cm(-1) upon photolysis of 5-phenyl-1,2,3,4-thiatriazole in acetonitrile and dichloromethane. Consistent with the experimental observations, thiobenzoylnitrene is predicted by B3LYP/6-31G* calculations to have a singlet ground state with an intense IR band at 1752 cm(-1). Phenyl isothiocyanate is also produced. Kinetic measurements indicate that it is not formed from singlet thiobenzoylnitrene, but rather directly from the thiatriazole. Unlike benzoylnitrene, singlet thiobenzoylnitrene does not react with acetonitrile or dichloromethane on the nanosecond timescale. However, it does react with dimethyl sulfoxide (DMSO) to produce a sulfoximine detected at 1180 cm(-1) (k(DMSO) = 3 × 10(5) M(-1) s(-1)). Benzonitrile (observed at 2230 cm(-1)) is produced from both singlet thiobenzoylnitrene (presumably through a short-lived, unobservable benzonitrile sulfide intermediate) and directly from the thiatriazole. B3LYP/6-31G* calculations also show that the structure of singlet thiobenzoylnitrene is analogous to that of related acylnitrenes, with a significant bonding interaction between the nitrogen and sulfur. Triplet thiobenzoylnitrene, on the other hand, is predicted computationally to have a biradical structure.
    Physical Chemistry Chemical Physics 04/2012; 14(30):10438-44. · 4.20 Impact Factor
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    ABSTRACT: Due to its inherent reactivity, nitroxyl (HNO), must be generated in situ through the use of donor compounds, but very few physiologically useful HNO donors exist. Novel N-substituted hydroxylamines with carbon-based leaving groups have been synthesized, and their structures confirmed by X-ray crystallography. These compounds generate HNO under nonenzymatic, physiological conditions, with the rate and amount of HNO released being dependent mainly on the nature of the leaving group. A barbituric acid and a pyrazolone derivative have been developed as efficient HNO donors with half-lives at pH 7.4, 37 °C of 0.7 and 9.5 min, respectively.
    Journal of the American Chemical Society 02/2012; 134(4):1962-5. · 10.68 Impact Factor
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    ABSTRACT: A wide range of N,O-bis-acylated hydroxylamine derivatives with chloro or arenesulfonyl leaving groups, and a related set of N-hydroxy-N-acylsulfonamides, have been synthesized and evaluated for nitroxyl (HNO) production. Mechanistic studies have revealed that the observed aqueous chemistry is more complicated than originally anticipated, and have been used to develop a new series of efficient HNO precursors (4u-4x, 7c-7d) with tunable half-lives.
    Organic Letters 12/2011; 14(2):472-5. · 6.14 Impact Factor
  • Meredith R. Cline, John P. Toscano
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    ABSTRACT: Recent research has shown that nitroxyl (HNO) has important and unique biological activity, especially as a potential alternative to current treatments of cardiac failure. HNO is a reactive molecule that spontaneously dimerizes and subsequently dehydrates to form nitrous oxide (N2O), making its detection in solution or biologically relevant preparations difficult. The prefluorescent probe 4-((9-acridinecarbonyl)amino)-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-9-AC) has been used to detect HNO in aqueous solution and to differentiate it from nitric oxide (NO). TEMPO-9-AC reacts with HNO via a net hydrogen abstraction to produce the highly fluorescent TEMPO-9-AC-H and NO. The utility of TEMPO-9-AC as a probe for HNO has been shown using the common HNO donors Angeli's salt and Piloty's acid (PA) along with a recently reported HNO donor, 2-bromo-PA. The use of TEMPO-9-AC is complicated by intermolecular fluorescence quenching and competitive HNO trapping by the NO produced, but nonetheless, it can be used to study HNO reactivity in aqueous solution. Copyright © 2011 John Wiley & Sons, Ltd.
    Journal of Physical Organic Chemistry 10/2011; 24(10). · 1.58 Impact Factor
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    ABSTRACT: Membrane inlet (or introduction) mass spectrometry (MIMS) was used to detect nitroxyl (HNO) in aqueous solution for the first time. The common HNO donors Angeli's salt (AS) and Piloty's acid (PA), along with a newly developed donor, 2-bromo-N-hydroxybenzenesulfonamide (2-bromo-Piloty's acid, 2BrPA), were examined by this technique. MIMS experiments revealed that under physiological conditions 2BrPA is an essentially pure HNO donor, but AS produces a small amount of nitric oxide (NO). In addition, MIMS experiments also confirmed that PA is susceptible to oxidation and NO production, but that 2BrPA is not as prone to oxidation.
    Free Radical Biology & Medicine 02/2011; 50(10):1274-9. · 5.27 Impact Factor
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    ABSTRACT: Acyl nitroso compounds have been generated by photolysis of several different classes of precursors including 9,10-dimethylanthracene adducts, nitrodiazo compounds, and 1,2,4-oxadiazole-4-oxides. Consideration of the nitronate-like resonance structure of nitrodiazo compounds led to an examination of the photochemistry of nitronates with α-leaving groups. Photolysis of such nitronates has been shown to generate an acyl nitroso species along with a carbene intermediate. Nanosecond time-resolved infrared (TRIR) spectroscopy has been used to detect photogenerated acyl nitroso compounds directly and to examine their reaction kinetics with amines and thiols. The mechanism of acyl nitroso aminolysis by primary amines involves general base catalysis, while the mechanism of aminolysis by secondary amines is strictly bimolecular. Thiols do not seem to be reactive with acyl nitroso compounds on the microsecond time scale, but thiolates are quite reactive. The reaction between benzoyl nitroside and an organic-soluble thiolate, tetrabutylammonium dodecanethiolate, proceeds via a proposed tetrahedral intermediate, which is observable by TRIR spectroscopy.
    Canadian Journal of Chemistry 01/2011; 89(2):130-138. · 0.96 Impact Factor
  • Anthony S. Evans, John P. Toscano
    11/2010; , ISBN: 9780470682531
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    ABSTRACT: A chloromethylhydroxamiccarbene was generated photochemically in an attempt to form an intramolecularly stabilized carbene. A rapidly formed intermediate at 1645 cm(-1) decayed with an observed rate of 1.99 × 10(6) s(-1). Other intermediates were also observed. These also decayed, albeit much more slowly (k(obs) = 3.47 × 10(3) and 1.98 × 10(4) s(-1)). Multiple intermediates are apparently a function of both the proximal N,O-dimethylhydroxamic ester and multiple conformers of both the carbene and precursor.
    Organic Letters 10/2010; 12(20):4616-9. · 6.14 Impact Factor
  • Biophysical Journal 01/2010; 98(3). · 3.67 Impact Factor

Publication Stats

342 Citations
290.96 Total Impact Points

Institutions

  • 1997–2014
    • Johns Hopkins University
      • Department of Chemistry
      Baltimore, Maryland, United States
  • 2007–2013
    • Johns Hopkins Medicine
      • Division of Cardiology
      Baltimore, Maryland, United States
  • 2001
    • Rutgers, The State University of New Jersey
      • Department of Chemical Biology
      New Brunswick, New Jersey, United States
  • 1994–1997
    • The Ohio State University
      • Department of Chemistry and Biochemistry
      Columbus, Ohio, United States