Colour-responsive fluorescent oxy radical sensors

Abstract

A series of fluorene-fused benzoquinones (Q1-Q5) were prepared by thermolysis of 4-fluorenyl-4-hydroxycyclobutenones. Red fluorescence observed for Q2 is switched by reduction to blue fluorescence by formation of the hydroquinone. Reaction with hydrogen peroxide restores the original fluorescence colour. The potential use of compound Q2 as a reactive oxygen species detector is discussed.

Protecting-Group-Free Total Synthesis and Biological Evaluation of 3-Methylkealiiquinone and Structural Analogues

“…The known chemistry of squaric acid can be inferred to explain the formation of these two regioisomers. In agreement with the previously described mechanism for this chemistry, , the accepted formation of a ketene intermediate such as AI-1 explains the formation of the linear regioisomers ( 20 – 22 ), while the accepted formation of a ketene intermediate such as AI-2 explains the formation of the angular regioisomers ( 17 – 19 ). Both regioisomers were unequivocally assigned by NOESY experimentation (see SI).…”

“…This short study provided several important pieces of information about our synthetic route: (1) the M–H exchange and 1,2-addition over squarate 9 was possible, but an acid-sensitive tertiary alcohol was obtained; (2) we found no 1,2-addition with the benzimidazolone carbonyl; (3) as compared with literature, here, much milder acidic conditions gave rise to the solvolysis of the tertiary alcohol and concomitant carbonyl regeneration; and (4) as soon as prepared, the 1,2-addition products should be immediately subjected to thermolysis in order to obtain the 1,4-quinoid ring. , Considering all the aforementioned learned aspects, it was decided to complete our route to obtain model systems of the fully functionalized kealiiquinone core (Scheme ).…”

“…This four-step and high-yielding sequence was performed on a multigram scale without the use of any chromatography for purification. On the other side of the convergent synthetic process, the isopropyl and methyl squarates 9 and 3 were synthesized according literature procedures, also on gram scales. The starting material 8 was used for the synthesis of the fully functionalized arylbenzimidazolone core 10 via orthogonal Suzuki cross-coupling.…”

“…It is important to mention here that after the thermolysis of 13 , 15 , and 16 , a hydroquinone was formed , that spontaneously oxidized to the corresponding quinoid form. This is a two-step one-pot reaction, and as a consequence, the final yields for 17 – 22 are the result of these two steps and are higher overall.…”

Chalcogen-based ratiometric reversible BODIPY redox sensors for the determination of enantioselective methionine sulfoxide reductase activity

“…[8][9][10][11][12][13][14][15] Most of them utilize irreversible reactions of a redox-sensitive functional group, which is not suitable for distinguishing between transient and chronically elevated ROS levels. 16,17 To overcome this limitation, several probes based on, for example, reversible oxidation/ reduction of nitroxides, 18 quinones, 19 or chalcogens 20 have been developed.…”