Transformation of COUPY Fluorophores into a Novel Class of Visible‐Light‐Cleavable Photolabile Protecting Groups

Abstract

Although photolabile protecting groups (PPGs) have found widespread applications in several fields of chemistry, biology and materials science, there is a growing interest in expanding the photochemical toolbox to overcome some of the limitations of classical caging groups. In this work, the synthesis of a new class of visible‐light‐sensitive PPGs based on low‐molecular weight COUPY fluorophores with several attractive properties, including long‐wavelength absorption, is reported. Besides being stable to spontaneous hydrolysis in the dark, COUPY‐based PPGs can be efficiently photoactivated with yellow (560 nm) and red light (620 nm) under physiological‐like conditions, thereby offering the possibility of unmasking functional groups from COUPY photocages under irradiation conditions in which other PPGs remain stable. Additionally, COUPY photocages exhibit excellent cellular uptake and accumulate selectively in mitochondria, opening the door to the delivery of caged analogues of biologically active compounds into these organelles.

COUPY Coumarins as Novel Mitochondria-Targeted Photodynamic Therapy Anticancer Agents

“… 40 The decrease in the intensity of the absorption band of DPFB at 411 nm as a result of the reaction with singlet oxygen in an air-saturated DCM solution was monitored upon excitation with a high-power LED source of green light (505 nm, 100 mW cm –2 ). 26 As shown in Figures S8 and S9 , a gradual decrease in the absorbance of DPBF at 411 nm was observed upon irradiation in the presence of COUPY derivatives, being much more pronounced in the case of coumarin 15. In good agreement with cellular experiments, the highest efficacy of singlet oxygen production was obtained for coumarin 15 (Φ Δ = 0.11), whereas lower yields were found for 1 and 2 (Φ Δ = 0.049 and 0.046, respectively).…”

“…Furthermore, the singlet oxygen generation by COUPY derivatives 1, 2, and 15 was investigated in a cell-free assay using 1,3-diphenylisobenzofuran (DPBF) as an 1 O 2 scavenger and methylene blue as a reference (Φ Δ s = 0.57 in DCM). − DPBF is a green fluorescent probe that decomposes into a colorless product upon reaction with singlet oxygen . The decrease in the intensity of the absorption band of DPFB at 411 nm as a result of the reaction with singlet oxygen in an air-saturated DCM solution was monitored upon excitation with a high-power LED source of green light (505 nm, 100 mW cm –2 ) . As shown in Figures S8 and S9, a gradual decrease in the absorbance of DPBF at 411 nm was observed upon irradiation in the presence of COUPY derivatives, being much more pronounced in the case of coumarin 15.…”

“…Hence, mitochondria-targeted theranostic agents are highly attractive compounds for both cancer diagnosis and therapy. − Recently, we have developed a new family of low-molecular-weight coumarins (COUPYs) in which the carbonyl group of the lactone function of the classical coumarin scaffold was replaced by the cyano­(4-pyridine/pyrimidine)­methylene moieties (Figure ). − In addition to having attractive photophysical and physicochemical properties for bioimaging and caging applications (e.g., emission in the far-red/NIR region, large Stokes’ shifts, brightness and high photostability, and aqueous solubility), N-alkylated COUPY coumarins exhibit excellent cell membrane permeability in living cells and accumulate preferentially in mitochondria and, to a lesser extent, in nucleoli and in intracellular vesicles. Mitochondria selectivity can be attributed to the lipophilic positively charged N-alkyl pyridinium/pyrimidinium moieties in the coumarin scaffold, which exploit the negative potential across the outer and inner mitochondrial membrane.…”

Inactivation of Competitive Decay Channels Leads to Enhanced Coumarin Photochemistry

“…[8,9] Taking the coumarin photocage as an example, popular methods were the extension of the π-system, or the addition of donor and acceptor substituents (see Figure 1a). [10][11][12][13] Also with other photolabile protecting groups, for example BODIPY, [14,15] fluorenol, [16,17] or nitrobenzyl [18,19] a considerable red-shift was achieved with similar approaches. Nevertheless, the improvement of the second parameter, the uncaging efficiency, has not Structures and photophysical properties of DEACM 1 and ATTO 390.…”

“…Taking the coumarin photocage as an example, popular methods were the extension of the π‐system, or the addition of donor and acceptor substituents (see Figure 1a) [10–13] . Also with other photolabile protecting groups, for example BODIPY, [14,15] fluorenol, [16,17] or nitrobenzyl [18,19] a considerable red‐shift was achieved with similar approaches.…”