Photogeneration and reactivity of acyl nitroso compounds

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.

Recent advances in the chemical biology of nitroxyl (HNO) detection and generation

“…93 Besides these 9,10-DMA hetero cycloadducts, nitrodiazo compounds, nitronates with α-leaving groups and 1,2,4-oxadiazole-4-oxides demonstrate acyl nitroso compound formation upon irradiation making these compounds potential HNO donors (Figure 11). 96 Both HPLC and GC–MS analysis reveal photo degradation of nitrodiazo compounds yields quantitative HNO in acetonitrile/water mixtures while nitronates with α-leaving groups in methanol also release HNO upon photolysis.…”

Nitrogen Dioxide Reaction with Nitroxide Radical Derived from Hydroxamic Acids: The Intermediacy of Acyl Nitroso and Nitroxyl (HNO)

“…Hydroxamic acids (RC­(O)­NHOH, HXs) form a class of compounds that display interesting chemical and biological properties. , Recent studies have highlighted HXs’ biological activities, some of which are associated with their ability under oxidative stress to generate nitroxyl (HNO) and nitric oxide (NO). − The chemistry of HXs is associated with one- and two-electron oxidations forming the respective nitroxide radical (RC­(O)­NHO • ) and acyl nitroso (RC­(O)­NO), respectively, which are relatively unstable species. Hydrolysis of acyl nitroso (denoted also nitrosocarbonyl) and its reaction with nucleophiles generates HNO, ,− which readily undergoes dimerization followed by dehydration to give N 2 O . The presumed generation of acyl nitroso has been generally evidenced by trapping it with conjugated 1,3-dienes yielding stable cycloadducts , or by detection of N 2 O. ,,,− So far, the only direct evidence for acyl nitroso was provided by time-resolved infrared spectroscopy in nonaqueous solution. , …”

“…Hydrolysis of acyl nitroso (denoted also nitrosocarbonyl) and its reaction with nucleophiles generates HNO, ,− which readily undergoes dimerization followed by dehydration to give N 2 O . The presumed generation of acyl nitroso has been generally evidenced by trapping it with conjugated 1,3-dienes yielding stable cycloadducts , or by detection of N 2 O. ,,,− So far, the only direct evidence for acyl nitroso was provided by time-resolved infrared spectroscopy in nonaqueous solution. , …”

Direct Observation of Acyl Nitroso Compounds in Aqueous Solution and the Kinetics of Their Reactions with Amines, Thiols, and Hydroxamic Acids

“…In most cases where the intermediacy of RC(O)NO has been invoked, its generation has been indirectly confirmed by trapping it with conjugated 1,3-dienes that produces stable cycloadducts 4 or by detection of N 2 O. [4][5][6]8,11,14,15 Spectroscopic evidence has been reported for HC(O)NO in the gas phase 16 and various RC(O)NO by time-resolved infrared spectroscopy where the lifetime has been estimated to be about 1 ms in nonaqueous solutions. 8,17 We have previously demonstrated that in aqueous solutions one-electron oxidation of acetohydroxamic acid and suber-oylanilide hydroxamic acid (SAHA) by radiolytically borne radicals such as • OH, • N 3 , and Br 2…”