Nitroxyl (HNO) has attracted increasing attention because it has important and unique chemical and biological properties distinct from nitric oxide (NO). Especially, prodrugs of HNO show much promise in treating congestive heart failure. However, HNO is a very reactive molecule that rapidly dimerizes and spontaneously dehydrates to yield nitrous oxide (N2O) and H2O. Thus, precursor molecules named HNO donors are required to generate HNO in situ for chemical and biological studies. Current HNO donors release HNO with half-lives of minutes to hours. Due to the rapid reaction between HNO and biomolecules (k ~ 103-107 M-1s-1), the decomposition of current HNO donors to release HNO is invariably the rate-determining step during the mechanistic studies. Therefore, directly obtaining kinetic and mechanistic data for the reactions of HNO with biomolecules is not feasible because of the slow release of HNO (t1/2 ~ minutes to hours) from current available HNO donors. To address this limitation, we have sought to develop a novel family of photoactivatable HNO donors incorporating various photolabile protecting groups (PPG), which rapidly release HNO on demand. Initial work focused on the development of three N-alkoxysulfonamides incorporating the (3-hydroxy-2-naphthalenyl)methyl (3,2-HNM) phototrigger as HNO donors. Photochemical studies of these 3,2-HNM-based HNO donors revealed the presence of a photo-induced redox O-N cleavage pathway, in addition to the desired HNO generation pathway. Trifluoromethanesulfonyl-based donors maximally released ~ 70% HNO under optimal solvent conditions, and decomposed with a half-life ~ 7 s under a direct xenon light source. The HNO generation was found to occur via a concerted fashion rather than a stepwise mechanism. We also explored the role of 2-nitrobenzyl and 4,5-dimethoxy-2-nitrobenzyl phototriggers in these photoactivatable N-alkoxysulfonamides in an effort to improve the selectivity for the desired HNO generation pathway. However, the photo-induced redox O-N bond cleavage was observed as the major pathway even in the trifluoromethanesulfonyl-based donors. Then the (6-hydroxy-2-naphthalenyl)methyl (6,2-HNM) phototrigger was used to replace the isomeric 3,2-HNM-based moiety in these photoactivatable N-alkoxysulfonamides. The selectivity for the HNO generation pathway from the trifluoromethanesulfonyl-based donor was greatly increased up to ~ 98%. Upon irradiation by a direct xenon lamp, photodecomposition of the trifluoromethanesulfonyl-based donor proceeded rapidly with a half-life ~ 5 s. Finally, we investigated the impact on the selectivity of HNO generation of gem-disubstitution at the benzylic position of the 6,2-HNM-based HNO donor system. Relative to the desphenyl analog, the selectivity for the HNO generation pathway in the methanesulfonyl-based HNO donor was greatly increased up to ~ 42%, and the N-O bond cleavage was greatly suppressed (~ 17%).

Nitroxyl (HNO) is a biologically relevant small molecule with considerable clinical promise for the treatment of heart failure. However, studies of the chemistry and biology of nitroxyl are hampered by its instability in aqueous solution. To aid in biological and chemical studies, nitroxyl donors (molecules that degrade to release HNO) have been synthesized which utilize a 3-hydroxy-2-naphthyl methyl (HNM) OH protecting group. Our group0́9s focus is on the synthesis of nitroxyl donors that rapidly release HNO under physiological conditions through photoactivation. First generation HNO donors released HNO upon photoactivation, but competition was also observed from a redox side reaction. In this study, we are probing the impact of a methyl substituent at the benzylic position on these competing processes. The synthesis and photochemical anaylsis of such a donor are herein described.

Nitroxyl (HNO) is a simple molecule that has been found to have high physiological relevance. HNO is a vasodilator, a positive lusitrope (increases myocardial relaxation), and a positive inotrope (increases the strength of a myocardial muscle contraction) that works independently of cAMP. It has been shown in recent studies to be useful for the treatment of patients with acute heart failure. A complication with HNO is that it rapidly dimerizes and, in order to study the chemistry and mechanisms of the reactions of HNO with biomolecules, there is a need for a rapidly releasing HNO donor. Our group is developing photoactivatable HNO donors that have promise for the rapid release of HNO "on demand". One system under investigation incorporates a hydroxy-2-naphthalenyl (HNM) phototrigger. Our first generation of HNO donors showed a competing photoredox side reaction pathway that did not lead to HNO generation. However, the use the 6,2-HNM phototrigger in compound 1 showed a better selectivity for HNO release. The impact of adding additional substituents at the C* position in 1 is being studied in order to increase HNO generation relative to the unwanted photoredox side reaction. Adding a methyl group to the C* in the first generation of HNO donors showed an increase in the selectivity for HNO generation. In the present work, the effect of the addition of a phenyl group at this position is under study.

HNO (nitroxyl) is a biologically relevant unstable small molecule which rapidly dimerizes in aqueous solution. Thus, there is a need for HNO donors that can quickly release HNO “on demand”. Our group has developed a first generation family of HNO donors which generate HNO rapidly through photolysis. However, some competition from a photoredox side reaction reduces the utility of these molecules. The goal of this thesis was to explore the impact of incorporating a methyl substituent on the rate and selectivity of HNO generation.

The Chemistry and Biology of Nitroxyl (HNO) provides first-of-its-kind coverage of the intriguing biologically active molecule called nitroxyl, or azanone per IUPAC nomenclature, which has been traditionally elusive due to its intrinsically high reactivity. This useful resource provides the scientific basis to understand the chemistry, biology, and technical aspects needed to deal with HNO. Building on two decades of nitric oxide and nitroxyl research, the editors and authors have created an indispensable guide for investigators across a wide variety of areas of chemistry (inorganic, organic, organometallic, biochemistry, physical, and analytical); biology (molecular, cellular, physiological, and enzymology); pharmacy; and medicine. This book begins by exploring the unique molecule’s structure and reactivity, including important reactions with small molecules, thiols, porphyrins, and key proteins, before discussing chemical and biological sources of nitroxyl. Advanced chapters discuss methods for both trapping and detecting nitroxyl by spectroscopy, electrochemistry, and fluorescent inorganic cellular probing. Expanding on the compound’s foundational chemistry, this book then explores its molecular physiology to offer insight into its biological implications, pharmacological effects, and practical issues. Presents the first book on HNO (nitroxyl or azanone), an increasingly important molecule in biochemistry and pharmaceutical research Provides a valuable coverage of HNO’s chemical structure and significant reactions, including practical guidance on working with this highly reactive molecule Contains high quality content from recognized experts in both industry and academia

Chemical Tools for Imaging, Manipulating, and Tracking Biological Systems: Diverse Methods for Optical Imaging and Conjugation, Volume 639, the latest release in the Methods in Enzymology series, continues the legacy of this premier serial with quality chapters authored by leaders in the field. Chapters in this new release include Fluorogenic detection of protein aggregates in live cells using the AggTag method, Synthesis and Application of Ratiometric Probes for Hydrogen Peroxide Detection, Chemical Tools for Multicolor Protein FRET with Tryptophan, Fluorescing Isofunctional Ribonucleosides for Adenosine Deaminase Activity and Inhibition, Temporal profiling establishes a dynamic S-palmitoylation cycle, Solvation-guided design of fluorescent probes for discrimination of amyloids, and much more. Provides the authority and expertise of leading contributors from an international board of authors Presents the latest release in the Methods in Enzymology series Includes the latest information on retinoid signaling pathways

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