John P. Toscano

Johns Hopkins University, Baltimore, Maryland, United States

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Publications (91)532.06 Total impact

  • No preview · Article · Oct 2015
  • Gizem Keceli · John Toscano

    No preview · Article · Apr 2015 · The FASEB Journal

  • No preview · Article · Jan 2015 · Biophysical Journal
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    ABSTRACT: A new and versatile class of HNO donors, the hydroxylaminopyrazolone (HAPY) series of HNO donors utilizing pyrazolone (PY) leaving groups, is described. HNO, the smallest N-based aldehyde equivalent, is used as a reagent along with a variety of PY compounds to synthesize the corresponding HAPY donors in what can be considered an N-selective HNO-aldol reaction in up to quantitative yields. The bimolecular rate constant of HNO with PY to form the desired HAPY product in pH 7.4 phosphate buffer at 37 °C can reach 8 × 105 M-1s-1. The HAPY compounds generate HNO quantitatively (trapped as a phosphine aza-ylide) with half-lives spanning three orders of magnitude (minutes to days) under physiologically relevant conditions. B3LYP/6-31G* calculations confirm the energetically favorable reactions between HNO and the PY enol and enolate, whereas HNO release is expected to occur through the oxyanion of each HAPY compound. HNO has been shown to provide functional support to failing hearts.
    No preview · Article · Jan 2015 · The Journal of Organic Chemistry
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    ABSTRACT: Due to its inherent reactivity, HNO must be generated in situ through the use of donor compounds. One of the primary strategies for the development of new HNO donors has been modifying hydroxylamines with good leaving groups. A recent example of this strategy is the hydroxylaminobarbituric acid (HABA) class of HNO donors. In this case, however, an undesired intramolecular rearrangement pathway to the corresponding hydantoin derivative competes with HNO formation, particularly in the absence of chemical traps for HNO. This competitive non-HNO producing pathway has restricted the development of the HABA class to examples with fast HNO release profiles at physiological pH and temperature (t1/2 < 1 min). Herein, the factors that favor the rearrangement pathway have been examined and two independent strategies that protect against rearrangement to favor HNO generation have been developed. The timecourse and stoichiometry for the in vitro conversion of these compounds to HNO (trapped as a phosphine aza-ylide) and the corresponding barbituric acid (BA) byproduct have been determined by proton NMR spectroscopy under physiologically relevant conditions. These results confirm the successful extension of the HABA class of pure HNO donors with half-lives at pH 7.4, 37 °C ranging from 19 to 107 minutes.
    No preview · Article · Jan 2015 · The Journal of Organic Chemistry
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    ABSTRACT: The irradiation of trans-vinylketones 1a-c yields the corresponding cis isomers 2a-c. Laser flash photolysis of 1a and 1b with 308 and 355 nm lasers results in their triplet ketones (T1K of 1), which rearrange to form triplet 1,2-biradicals 3a and 3b, respectively, whereas irradiation with a 266 nm laser produces their cis-isomers through singlet reactivity. Time-resolved IR spectroscopy of 1a with 266 nm irradiation confirmed that 2a is formed within the laser pulse. In comparison, laser flash photolysis of 1c with a 308 nm laser showed only the formation of 2c through singlet reactivity. At cryogenic temperatures, the irradiation of 1 also resulted in 2. DFT calculations were used to aid in the characterization of the excited states and biradicals involved in the cis-trans isomerization and to support the mechanism for the cis-trans isomerization on the triplet surface.
    No preview · Article · Jul 2014 · The Journal of Physical Chemistry A
  • 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.
    No preview · Article · Jul 2014 · Bioorganic & Medicinal Chemistry Letters
  • 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.
    No preview · Article · May 2014 · Biochemistry
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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.
    Preview · Article · Jan 2014 · Nature Neuroscience
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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.
    Full-text · Article · Dec 2013 · Photochemical and Photobiological Sciences
  • Gizem Keceli · Cathy D Moore · Jason W Labonte · John P Toscano
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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.
    No preview · Article · Sep 2013 · Biochemistry
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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 Ca(2+) uptake and myofilament Ca(2+) 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(2+)-ATPase (SERCA2a) in a redox-dependent manner, improving Ca(2+) handling in isolated myocytes/hearts. Results: Ventriculocytes, sarcoplasmic reticulum (SR) vesicles, and whole hearts were isolated from control (wildtype [WT]) or PLN knockout (pln(-/-)) mice. Compared to WT, pln(-/-) myocytes displayed enhanced resting sarcomere shortening, peak Ca(2+) transient, and blunted β-adrenergic responsiveness. HNO stimulated shortening, relaxation, and Ca(2+) transient in WT cardiomyocytes, and evoked positive inotropy/lusitropy in intact hearts. These changes were markedly blunted in pln(-/-) cells/hearts. HNO enhanced SR Ca(2+) uptake in WT but not pln(-/-) SR-vesicles. Spectroscopic studies in insect cell microsomes expressing SERCA2a±PLN showed that HNO increased Ca(2+)-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 Ca(2+) handling in failing hearts.
    Full-text · Article · Aug 2013 · Antioxidants & Redox Signaling
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    Full-text · Dataset · Jul 2013
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    Full-text · Dataset · Jul 2013
  • Anthony S. Evans · John P. Toscano

    No preview · Article · Nov 2012 · ChemInform
  • Gizem Keceli · Cathy D. Moore · John P. Toscano

    No preview · Article · Nov 2012 · Free Radical Biology and Medicine
  • 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.
    No preview · Article · Oct 2012 · Journal of inorganic biochemistry
  • 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.
    No preview · Article · May 2012 · Biochemistry
  • 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.
    No preview · Article · Apr 2012 · Physical Chemistry Chemical Physics
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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.
    No preview · Article · Feb 2012 · Journal of the American Chemical Society

Publication Stats

2k Citations
532.06 Total Impact Points


  • 1997-2015
    • Johns Hopkins University
      • Department of Chemistry
      Baltimore, Maryland, United States
  • 2010
    • University of California, Los Angeles
      • Department of Chemistry and Biochemistry
      Los Angeles, California, United States
  • 1994-2010
    • The Ohio State University
      • Department of Chemistry and Biochemistry
      Columbus, Ohio, United States
  • 2007
    • Johns Hopkins Medicine
      • Division of Cardiology
      Baltimore, MD, United States
    • Universität Siegen
      Siegen, North Rhine-Westphalia, Germany
  • 2001
    • Rutgers, The State University of New Jersey
      • Department of Chemical Biology
      New Brunswick, New Jersey, United States