De Novo Construction of Fluorophores via CO Insertion-Initiated Lactamization: A Chemical Strategy toward Highly Sensitive and Highly Selective Turn-On Fluorescent Probes for Carbon Monoxide

Abstract

Extensive studies in the last few decades have led to the establishment of CO as an endogenous signaling molecule and subsequently to the exploration of CO’s therapeutic roles. In the current state, there is a critical conundrum in CO-related research: the extensive knowledge of CO’s biological effects and yet an insufficient understanding of the quantitative correlations between the CO concentration and biological responses of various natures. This conundrum is partially due to the difficulty in examining precise concentration–response relationships of a gaseous molecule. Another reason is the need for appropriate tools for the sensitive detection and concentration determination of CO in the biological system. We herein report a new chemical approach to the design of fluorescent CO probes through de novo construction of fluorophores by a CO insertion-initiated lactamization reaction, which allows for ultra-low background and exclusivity in CO detection. Two series of CO detection probes have been designed and synthesized using this strategy. Using these probes, we have extensively demonstrated their utility in quantifying CO in blood, tissue, and cell culture and in cellular imaging of CO from exogenous and endogenous sources. The probes described will enable many biology and chemistry labs to study CO’s functions in a concentration-dependent fashion with very high sensitivity and selectivity. The chemical and design principles described will also be applicable in designing fluorescent probes for other small molecules.

Sensing a CO-Releasing Molecule (CORM) Does Not Equate to Sensing CO: The Case of DPHP and CORM-3

“…We hope that all future CO probe work will use more than a chemically reactive CORM as the sole CO source. This is actually a minimal requirement for developing a viable CO probe, especially considering the known chemical reactivity of the commonly used CORMs. − ,,− , …”

“…This is actually a minimal requirement for developing a viable CO probe, especially considering the known chemical reactivity of the commonly used CORMs. [13][14][15][16][17][18][19][20]23,[25][26][27][28][29]34 ■ ASSOCIATED CONTENT…”

“…In parallel, He and colleagues developed the first protein-based CO sensing method by taking advantage of the conformational change of a hemoprotein upon binding to CO . Subsequently, there are other innovative approaches reported, including the application of Pd-mediated de-allylation reaction for fluorophore activation and thus CO detection. − Recently, we reported a strategy of designing CO probes through de novo construction of a fluorophore via Pd-mediated carbonylation chemistry, leading to exclusivity and very high sensitivity for CO detection and quantification …”

“…9−12 Recently, we reported a strategy of designing CO probes through de novo construction of a fluorophore via Pd-mediated carbonylation chemistry, leading to exclusivity and very high sensitivity for CO detection and quantification. 13 In developing fluorescent CO probes, typically used CO sources include CO gas, commercially available "CO-releasing molecules" (CORMs) such as CORM-2 and CORM-3, 14,15 or metal-free CO prodrugs. 16 Ideally, the source of CO should not make any difference in probe sensitivity and a valid probe should be able to detect CO regardless of its source.…”

“…Fluorescence spectra were recorded on a Shimadzu RF5301PC fluorometer (Kyoto, Japan). 1 H NMR (400 MHz) and 13 C NMR (101 MHz) were acquired with a Bruker AV-400 MHz Ultra Shield NMR. Crystal data were acquired by the Emory Crystallography Center.…”