Nitroxyl

Nitroxyl (HNO/NO^-) or hyponitrous acid, in chemistry is the reduced form of nitric oxide (NO). HNO and NO^- form an acid/base pair (pKa = 11.4) with NO^- isoelectronic with dioxygen. Nitroxyl is very reactive towards nucleophiles (especially thiols) and quickly dimerizes to H₂N₂O₂ which then is dehydrated to nitrous oxide N₂O.. Therefore, HNO is generally prepared in situ for example with the compounds such as Angeli’s salt (Na₂N₂O₃) and Piloty’s acid (PhSO₂NHOH) when it is needed.

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Nitroxyl shows potential in the treatment of heart failure and ongoing research is focused on finding new nitroxyl donors. In one study ^[1] such donor is prepared by organic oxidation of cyclohexanone oxime with lead tetraacetate to 1-nitrosocyclohexyl acetate:

This compound can be hydrolyzed under basic conditions in a phosphate buffer to nitroxyl HNO, acetic acid and cyclohexanone.

Other studies that have been conducted on HNO precursors include those from Nagasawa et al. in which Piloty's acid is derivatized and produces HNO upon thermal decomposition. Other notable studies on the production of HNO come from Toscano et al. in which cycloadducts of acyl nitroso species (which are known to decompose via hydrolysis to HNO and acyl acid) are synthesized. Upon photolysis these compounds release the acyl nitroso species which then further decomposes.

References

1. ^ Hydrolysis of Acyloxy Nitroso Compounds Yields Nitroxyl (HNO) Xin Sha, T. Scott Isbell, Rakesh P. Patel, Cynthia S. Day, and S. Bruce King J. Am. Chem. Soc.; 2006; 128(30) pp 9687 - 9692; (Article) doi:10.1021/ja062365a 10.1021/ja062365a

2. Nagasawa, H. T.; Kawle, S. P.; Elberling, J. A.; DeMaster, E. G.; Fukuto, J. M. J. Med. Chem., 38, 1865-1871.

3. Cohen, A. D.; Zeng, B.-B.; King, S. B.; Toscano, J. P. J. Am. Chem. Soc. 2003, 125, 1444-1445.