Photosensitization of Fluorofuroxans and Its Application to the Development of Visible Light-Triggered Nitric Oxide Donor

Nitric oxide (NO) is an endogenous signaling molecule used in multiple biochemical processes. The development of switchable NO donors that deliver an NO payload under spatiotemporal control harbors many medicinal benefits. Previously, 4-fluorofuroxans were found to function as a UV light-induced NO donor under physiological conditions based on the photoinduced isomerization mechanism; however, the isomerization of fluorofuroxans with longer wavelength light is desired for further application into living systems. Herein, we report the use of photosensitizers in the photochemical isomerization of fluorofuroxan, enabling the use of visible light to induce isomerization. Among the tried photosensitizers, anthraquinone derivatives showed a good sensitizing ability to isomerize 4-fluorofuroxan to 3-fluorofuroxan using visible light. This new phenomenon was applied to the synthesis of a water-soluble anthraquinone-fluorofuroxan all-in-one molecule, which demonstrated promising NO-releasing ability using 400-500 nm irradiation. A high level of control is displayed with "on" and "off" NO-release functionality suggesting that photosensitizer-furoxan hybrids would make valuable donors. Furthermore, unlike most furoxans, NO is released in the absence of thiol cofactor.