Development of new caged-NO molecules having aromatic nitro compound as a basic framework and their NO-release abilities

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Photochemical nitric oxide (NO) donors, which make it possible to release NO at the desired time and space, are useful to study various physiological processes in detail. In this work, a variety of 9-nitroanthracene derivatives having a substituent at 10-position was designed and synthesized as NO donor candidates, and the mechanism and ability on the photochemical NO release from the compounds were investigated using matrix-isolation technique and product analyses in solutions. Upon irradiation in matrices at 10 K, it was established that most of the nitroanthracenes with visible light gives NO and the oxyradical-forms via the nitrite-forms, and that the oxyradical + NO and the nitrite can be converted photochemically each other. And also, it was found that 9,10-dinitroanthracene afford NO and anthraquinone without giving the intermediates such as the nitrite and oxyradical. While the irradiation of nitroanthrancenes in solutions at room temperature afforded mainly bianthrone-forms, anthraquinoe, and anthracenedione oxyme accompanied with NO generation. On the basis of the results from the trapping of NO with Griess reagent and the measurements of absolute quantum yield for the photodecomposition of substrates, it was confirmed that the ability of photochemical NO generation increases according to increasing the electron-withdrawing properties of a substituent introduced to 10-position of 9-nitroanthracene. This result can be interpreted as a consequence of accelerating the transformation from nitro-forms to nitrite-forms by increasing the torsion angle between nitro group and anthracene-sp^2 plane.