Fluorescent Nitric Oxide Photodonors Based on BODIPY and Rhodamine Antennae

Abstract

Twon ovel NO photodonors (NOPDs) based on BODIPYa nd Rhodamine antennae activatable with the highly biocompatible green light are reported. Both NOPDs exhibitc onsiderable fluorescencee mission and release NO with remarkableq uantum efficiencies. Thec ombination of the photoreleasing and emissive performance for both compoundsi ss uperior to those exhibited by otherN OPDs based on similar light-harvesting centres,m aking them very intriguing for image-guided phototherapeutic applications.P reliminaryb iological data prove their easy visualizationi nc ell environment due to the intense green and orange-red fluorescence and their photodynamic action on cancerc ells due to the NO photo-liberated.

A High‐Performing Metal‐Free Photoactivatable Nitric Oxide Donor with a Green Fluorescent Reporter

“…The identical nature of the photoproduct observed under both aerobic and anaerobic conditions, is in good agreement with the formation of the anilinyl radical as logical key intermediate after the loss of NO via homolytic N‐NO cleavage. In fact, this species is expected to be basically insensitive to the presence of oxygen and can evolve to the stable photoproducts NBF via H‐transfer from solvent, in excellent agreement with the mechanism already reported for other N ‐nitrosamine after loss of NO …”

“…NBF‐NO is a nitroso‐derivative of the ABF bearing a short alkyl chain to facilitate its entrapping in hydrophobic carrier systems, and was easily synthesized in two steps in high yield. The rationale behind our design was inspired by the NOPDs based on N ‐nitrosoaniline moieties recently reported by others and our laboratory –. Loss of NO through homolytic cleavage was demonstrated to occur either via direct photoexcitation or mediated by intramolecular photoinduced electron transfer, and is strongly encouraged by the low binding energy of the N‐NO bond (below 30 kcal mol −1 ).…”

DNA‐Targeted NO Release Photoregulated by Green Light

“…Besides, no release of NO was observed upon irradiation with blue light, according with the lack of absorption of the AO at this wavelength. The quantum yield for the NO photorelease, Φ NO , was 0.9×10 −3 in good agreement with the other NOPDs activatable by green light working with a similar mechanism [13, 17] …”

“…In fact, these derivatives are extensively used in biology as standard compounds for nuclear staining due to their strong emission properties as well as for therapeutic applications [14d] . Besides, since AO is an excellent electron acceptor in the excited state [15] it is expected to encourage the NO uncaging from the N ‐nitroso unit according to the mechanism proposed in Scheme 1 and already demonstrated for the BODIPY and rhodamine‐based molecular hybrids [13] . Compound 1 , and the related non‐nitrosated compound 2 , were then synthesized according to the experimental procedures described in the Scheme S1.…”

“…In pursuing the goal object of this work we were inspired by our recent developed NOPDs activatable by green light and based on BODIPY and rhodamine antennae covalently linked to the same N ‐nitroso unit of compound 1 [13] . We demonstrated that NO release in these compounds is triggered by an intramolecular photoinduced electron transfer from the nitroso appendage to the excited antennae.…”