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

Article abstract of DOI:10.1002/chem.202002314

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.

Full text of DOI:10.1002/chem.202002314

Accepted Article
Accepted Article
Title: Transformation of COUPY fluorophores into a novel class of
visible light-cleavable photolabile protecting groups
Authors: Vicente Marchan, Marta López-Corrales, Anna Rovira, Albert
Gandioso, Manel Bosch, and Santi Nonell
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202002314
Link to VoR: https://doi.org/10.1002/chem.202002314
01/2020

10.1002/chem.202002314
Chemistry - A European Journal
COMMUNICATION
Transformation of COUPY fluorophores into a novel class of
visible light-cleavable photolabile protecting groups
Marta López-Corrales,[a] Anna Rovira,[a] Albert Gandioso,[a] Manel Bosch,[b] Santi Nonell,[c] and Vicente
Marchán*[a]
[a]
M. López-Corrales, A. Rovira, Dr. A. Gandioso, Dr. V. Marchán
Departament de Química Inorgànica i Orgànica
Secció de Química Orgànica, IBUB, Universitat de Barcelona
Martí i Franquès 1-11, E-08028 Barcelona (Spain)
E-mail: vmarchan@ub.edu
[b]
[c]
Dr. M. Bosch
Unitat de Microscòpia Òptica Avançada
Centres Científics i Tecnològics, Universitat de Barcelona
Av. Diagonal, 643, E-08028 Barcelona (Spain)
Prof. S. Nonell
Institut Químic de Sarriꢀ, Universitat Ramon Llull
Vía Augusta 390, E-08017 Barcelona (Spain)
Supporting information for this article is given via a link at the end of the document.
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 physicological-like conditions, thereby offering the possibility
of unmasking functional groups from COUPY photocages under
biological applications,[2] as well as to facilitate the design of
complex wavelength-selective uncaging systems in which two or
more PPGs can be removed sequentially from
a single
compound.[1d] Until recently, most caging groups described in
the literature with photoactivation capability by visible light are
based on classical and non-classical organic chromophores
(e.g., o-nitrobenzyl,[4] coumarin,[5] BODIPY,[6] cyanine[7] and
quinone[8] derivatives) or on metal complexes (e.g., ruthenium
polypyridyl).[9] Besides long-wavelength excitation capability, an
ideal PPG is expected to fulfill certain additional requirements
such as high photolytic efficiency (which requires either large
molar absorption coefficients at the absorption maxima or high
irradiation conditions in which other PPGs remain stable. Additionally, uncaging quantum yields, or both), aqueous solubility and dark
COUPY photocages exhibit excellent cellular uptake and accumulate
selectively in mitochondria, opening the door to delivering caged
analogues of biologically active compounds into this organelle.
stability to spontaneous hydrolysis under physiological
conditions. The structural complexity of the caging chromophore,
molecular weight, synthetic accessibility and conjugatability are
also key parameters to be considered when designing new
caging groups.
Photolabile protecting groups (PPGs; also commonly termed
photoremovable protecting groups or caging groups) have found
widespread applications in several fields of chemistry, biology
and materials manufacturing owing to the extraordinary
properties of light.[1] Indeed, suitable light irradiation can be
delivered with high spatiotemporal precision to control molecular
processes without causing contamination of samples. This is
particularly important in the case of caged analogues of
Coumarin-based caging groups fulfill some of the criteria for an
ideal PPG owing to the privileged architecture of the coumarin
scaffold, which allows the attachment of the compound to be
caged through different types of bonds (e.g., ester, carbamate or
carbonate). In addition, the photophysical and photochemical
properties of coumarin-based PPGs can be fine-tuned through
smart structural modifications such as by replacing electron-
donating N,N-dialkylamino groups at position 7 on the well-
known (coumarin 4-yl)methyl skeleton by azetidine.[10] The
modification of the carbonyl group of the electron-withdrawing
lactone moiety in conventional DEACM or DEACE caging
groups (Scheme 1) has also been used to increase the
electronic delocalization along the π-conjugated system,[5bdef]
dicyanomethylenecoumarin derivatives being particularly
attractive as they exhibit an absorption maxima around 500 nm
which allows uncaging with green light.[5de] So far, we have
synthesized a series of dicyanocoumarinylmethyl (DEAdcCM)-
and dicyanocoumarinylethyl (DEAdcCE)-based photocages of
biologically
active
compounds
(e.g.,
biomolecules,
neurotransmitters, antibiotics, anticancer agents, etc.), since
unmasking of key functionalities can be triggered without using
any chemical reagent.[2] Besides orthogonality, in vivo
applications require the use of PPGs with long-wavelength
absorption to achieve deeper tissue penetration and to avoid the
phototoxicity associated with short wavelengths such as UV and
blue light.[3]
The development of novel PPGs that can be efficiently
photoactivated with visible and near-IR light has raised a
growing interest to expand the photochemical toolbox in
1
This article is protected by copyright. All rights reserved.

10.1002/chem.202002314
Chemistry - A European Journal
COMMUNICATION
carboxylic acids (Scheme 1) and demonstrated
a
faster
C=C bond. Full NMR characterization by using 2D COSY and
NOESY experiments (Figure S1) allowed to conclude that the E
rotamer (as usually drawn in the manuscript) was the major
species in solution. By contrast, only the E rotamer was present
in solution in the case of COUPY-caged compound 3 according
to 1D and 2D NMR spectra (Figure S2), which parallels the
behavior of N-methylated COUPY dyes.[11]
photolysis rate in the DEAdcCE series, which is a consequence
of the higher stability of the secondary carbocation intermediate
generated upon the solvent-assisted photoheterolytic ester bond
cleavage.[5de] A similar behaviour was found in coumarin
analogues in which one of the cyano groups in DEAdcCM and
DEAdcCE was replaced with p-nitrophenyl.[5f]
Scheme 2. Synthesis of COUPY-caged model compound 3.
The photophysical properties of compound 3 were investigated
in a 1:1 (v/v) mixture of PBS buffer and ACN (Table S1) and
compared with those of the parent dye (2). As shown in Figure 1,
compound 3 exhibited an intense, relatively narrow absorption
band in the visible spectrum, with an absorption maximum
centered at 557 nm, slightly extended into the red-light region
and red-shifted with respect to coumarin 2 (ca 11 nm). This
bathochromic effect was more pronounced for the emission
wavelength (em = 619 nm in 3 vs em = 603 nm in 2) and, as a
result, the Stokes’ shift was larger in 3 (62 nm) than in the parent
fluorophore (57 nm). By contrast, the fluorescent quantum yield
was slightly reduced in the caged compound (e.g., ΦF = 0.10 in
3 vs. ΦF = 0.22 in 2). In addition, COUPY photocage exhibited a
relatively large molar absorption coefficient (38,000 M-1 cm-1).
Scheme 1. Previously reported coumarin- and dicyanocoumarin-based PPGs
and transformation of COUPY fluorophore 2 into a novel caging group
synthesized in this work.
With the aim of further red-shifting the absorption and emission
maxima of the conventional coumarin scaffold, we have recently
developed a novel class of coumarin-based fluorophores,
COUPYs, in which the carbonyl function in coumarin 1 was
replaced with cyano(N-alkyl-4-pyridinium)-methylene moieties
(e.g., compound 2 in Scheme 1).[11] Due to a higher push-pull
character compared with dicyanomethylene coumarins, COUPY
dyes exhibit several interesting photophysical properties such as
far-red to NIR emission, large Stokes’ shifts and high
photostability.[11] Conjugatable versions of COUPY fluorophores
can also be obtained through N-alkylation of the pyridine
heterocycle.[12] On the basis of these precedents, we envisaged
the transformation of COUPY fluorophores into novel coumarin-
based PPGs for visible-light uncaging. As shown in Scheme 1,
here we focused on the synthesis of the first COUPY photocage
(compound 3) in which benzoic acid was chosen as a model
cargo and caged through the formation of an ester bond. Taking
into account that the rate of the overall uncaging process in
coumarin-based PPGs depends on the rate constant of the initial
heterolytic C-O bond cleavage,[13] we decided to incorporate a
methyl group in the position adjacent to this bond in the
coumarin skeleton to stabilize the carbocation intermediate and
increase the photodeprotection rate.[5def]
Figure 1. Left: comparison of the absorption (solid lines) and fluorescence
(dotted lines) spectra of COUPY-caged model compound 3 with those of the
parent COUPY dye (2). Right: plot of the temporal evolution of the amount of 3
after irradiation with visible LED light. The lines connecting the experimental
points are meant to aid the reader in visualizing the data. All the experiments
were performed in a 1:1 (v/v) mixture of PBS buffer and ACN.
Compound 3 was efficiently synthesized in two steps from
thiocoumarin 4, which was previously obtained from
commercially available coumarin 1 in four steps (Scheme 2).[5ef]
First, condensation of 4 with 4-pyridylacetonitrile in the presence
of NaH followed by treatment with silver nitrate afforded COUPY
scaffold 5 with high yield (87%) after purification by silica column
chromatography. After N-methylation of the pyridine heterocycle
with methyl trifluoromethanesulfonate, the target COUPY-caged
model compound 3 was obtained as a pink solid with excellent
yield (98%) and fully characterized by HR ESI-MS and NMR (1H,
13C, and 19F). As previously found with some COUPY
The photoactivation of COUPY-caged model compound 3 was
first evaluated in PBS/ACN 1:1 at 37oC under irradiation with a
LED source covering from the cyan to the red region of the
visible spectrum (470-750 nm; 150 mW cm-2; see Figure S3).
The course of the uncaging process was monitored by reversed-
phase HPLC-MS in terms of the consumption of the starting
caged compound with irradiation time (Figure S4). As shown in
Figure 1, the concentration of 3 decreased gradually with
irradiation time. Photoactivation of 3 proceeded in a clean
fashion and gave a main photolytic product (coumarin alcohol 6)
1
fluorophores,[11] the H NMR spectrum of 5 showed two sets of
proton signals in a ∼85:15 ratio, which accounts for the
existence of two interconverting rotamers around the exocyclic
2
This article is protected by copyright. All rights reserved.

10.1002/chem.202002314
Chemistry - A European Journal
COMMUNICATION
and a minor vinyl coumarin derivative (7), the latter being formed
through a -elimination reaction from the secondary carbocation
intermediate generated upon photoheterolysis of the ester bond
(Scheme 3). Photolysis of 3 was almost complete (ca 90 %)
after 15 min of irradiation with the wide-band LED (ku = 0.172
min-1), whereas it was required more than 90 min to completely
uncage it with the same LED equipped with a 560 nm bandpass
filter (yellow light, 40 mW cm-2, ku = 0.031 min-1; see Figure 1
and Figures S3 and S5), which can be attributed to the reduced
irradiance. Importantly, 3 was found completely stable after
incubation for 2 h at 37 ºC in the dark under the irradiation
conditions. In addition, the uncaging of benzoic acid from
compound 3 and the release of coumarin alcohol 6 was also
and the absorption spectra (Figure S7), 3 took longer to react on
irradiation with red light as compared to yellow light, due to the
lower rate of light absorption (about 50% of 3 was uncaged after
irradiation for 1 h). The actual rate of light absorption under the
three LEDs is shown in Figure S8. It is worth noting that the
same photolytic products (6 and 7) were observed both with
yellow and red light (Scheme 3).
Using the data in Figure S8 and the initial rate of deprotection of
compound 3, the quantum yield (Phot) for deprotection could be
calculated and similar values were found for both the yellow and
red LEDs (6.0 x 10-5 and 5.0 x 10-5, respectively; Figure S9),
confirming that the differences in the rates of deprotection
actually reflect the relative rates of light absorption. The
photolytic efficiency of the uncaging process is then much higher
with yellow light due to the large molar absorptivity of the
compound at 560 nm (Table S2). It is worth noting that the
quantum yields are higher than that previously reported by us for
a coumarin-caged compound containing p-nitrophenyl moiety
instead of N-methylpyridinium,[5f] and of the same order than
other visible-light-sensitive photoprotecting groups, including a
green-light sensitive BODIPY derivative recently described by
Szymanski and collaborators (ca 4 x 10-5).[6b]
1
confirmed by monitoring the photolysis process by H NMR in a
mixture of DMSO-d6 and D2O (Figure 2).
Next, we investigated if COUPY caging groups could be applied
in the design of selective uncaging systems.[1e] Two main
approaches have been described to control two or more
molecular events with light. On the one hand, we[5e] and others,
including Heckel’s group,[14] have demonstrated that selective
uncaging can be achieved through irradiation with a single
wavelength of light by exploiting the differences in deprotection
kinetics of structurally-related PPGs (e.g., with green light by
using DEAdcCM and DEAdcCE-based caging groups) when
attached to the molecule to be caged through a different atom or
photocleavable bond.[5e] On the other hand, the use of two or
more PPGs with significantly different spectral and/or
photochemical properties (max, , Phot) can also be exploited to
sequentially unmask several functionalities with different
wavelengths of light.
Scheme 3. Mechanistic interpretation of the photolysis process of compound 3
under visible light irradiation.
E
*
D
C
H
On the basis of the photolysis studies with compound 3, we
wondered if sequential uncaging of two coumarin-protected
functionalities in the same reaction mixture could be achieved by
sequentially irradiating with biologically-compatible visible light.
For this purpose, an equimolar mixture of COUPY-caged
compound 3 and DEAdcCE-caged compound 8[5e] (Scheme 4)
was irradiated first with green light (505 nm). Although
dicyanocoumarin 8 was completely uncaged after 15 min, about
75 % of compound 3 was also deprotected (Figure S10), which
is not surprising given its substantial absorbance at 505 nm.
However, by irradiating first with red light (620 nm), 3 was
completely uncaged within 2.5 h while 8 remained stable until
irradiation with green light was carried out (Figure S11). In both
cases, the formation of the expected photolytic coumarins (6 and
9) was confirmed by MS. This experiment demonstrated that the
sequential uncaging with visible light of the same functional
group (a carboxylic acid in our models) from two different caged
compounds can be achieved by combining COUPY caging
groups with other coumarin-based PPGs.
B
A
H
9
6
5
8
7
ppm
Figure 2. Expansion of the 1H NMR spectrum of 3 in DMSO-d6/D2O 7:3 (v/v)
(400 MHz) before irradiation (A) and after 30-min (B) and 2-h (C) photolysis at
37 ºC with visible light (470-750 nm range), and of coumarin 6 (D) and benzoic
acid (E). *DCM traces.
Encouraged by these results and taking into account the
significant absorptivity of the COUPY chromophore around 600
nm, we decided to investigate the photosensitivity of compound
3 under red light irradiation. To our delight, the concentration of
3 decreased gradually with time upon irradiation with a 620 nm-
LED source (130 mW cm-2, Figures 1 and S6) although, as
expected on the basis of the overlap between the LED sources
3
This article is protected by copyright. All rights reserved.

10.1002/chem.202002314
Chemistry - A European Journal
COMMUNICATION
Scheme 4. Sequential uncaging of compounds
3 and 8 by sequential
irradiating with red (2.5 h) and green (15 min) light.
Finally, the cellular uptake and organelle localization of COUPY-
caged model compound 3 in living HeLa cells were investigated
by using confocal microscopy. As shown in Figure 3, the
Figure 4. Co-localization studies with compound 3 and Mitotracker Green FM
(A-C) or Lysotracker Green FM (D-F). Single confocal plane of HeLa cells
incubated with 3 (1 M, red) and Mitotracker Green FM (0.1 M, green) or
Lysotracker Green FM (0.2 M, green). A), D) Overlay of the two staining. C),
F) compound 3, B) Mitotracker Green FM signal. E) Lysotracker Green FM
staining. White arrows point out mitochondria and white arrowheads point out
coumarin 3 vesicles. Scale bar: 10 m. All images are at the same scale than
A.
fluorescence signal after excitation with a yellow light laser (ex
=
561 nm) was clearly observed inside the cells after only 30 min
of incubation (1 M) owing to the great brightness of the COUPY
chromophore, and the overall pattern of staining suggested
accumulation in mitochondria, and, to a lesser extent, in
intracellular vesicles. In addition, no cell toxicity was observed
during these studies. These observations confirmed that the
incorporation of a small cargo at the 4-position of the coumarin
skeleton (benzoic acid) does not negatively influences neither
the good cellular uptake nor organelle selectivity of the parent
COUPY fluorophores.[11] Indeed, co-localization experiments
using two commercially available specific markers for labeling
mitochondria (MitoTracker Green FM, MTG) and lysosomes
(Lysotracker Green FM, LTG) confirmed the observed
subcellular localization. In the case of mitochondria (Figure 4, A-
C), a Pearson’s sample correlation coefficient of 0.85±0.05 was
obtained indicating a good correlation between 3 and MTG.
Manders’ colocalization coefficients were also measured and
showed that 68%±0.12 of compound 3 staining colocalized with
MTG and that 90%±0.08 of MTG colocalized with compound 3
signal. On the other hand, co-localization experiments with LTG
(Figure 4, D-F) confirmed that most of fluorescence observed in
intracellular vesicles along the cytoplasm was associated with
lysosome accumulation. Pearson’s coefficient was 0.59±0.07
In summary, we have developed a new class of visible-light-
sensitive PPGs based on COUPY fluorophores for the protection
of carboxylic acids, which exhibit several attractive properties for
application in biological systems, such as long wavelength
absorption owing to a large -conjugated system, large molar
extinction coefficient and high deprotection rate in aqueous
media. This novel caging group is completely stable to
spontaneous hydrolysis in the dark but can be efficiently
photoactivated by green- (505 nm), yellow- (560 nm) and red-
LED light (620 nm) under physicological-like conditions (PBS
buffer, 37 ºC), proceeding in a clean fashion as confirmed both
by HPLC-MS and NMR analysis. COUPY caging groups
presented here will complement the photochemical toolbox of
known coumarin-based PPGs, since they offer the possibility of
unmasking functional groups from COUPY photocages under
visible light irradiation conditions (e.g., with yellow/red light) in
which other conventional (e.g., DEACM/DEACE) and non-
conventional (e.g., DEAdcCE/DEAdcCE) coumarin-based
caging groups remain stable. Importantly, the COUPY-caged
model compound described here exhibited an excellent cellular
uptake and accumulated selectively in mitochondria owing to the
N-alkylpyridinium-based structure of COUPY chromophore,
which opens the door to delivering biologically-active
compounds selectively into this key organelle.[5i,6d] Work is in
progress to further red-shift the absorption maxima of COUPY-
based caging groups to the phototherapeutic window region
(650−900 nm), as well as to improve the deprotection efficiency
through additional chemical modifications in the COUPY
chromophore.
and Mander’s coefficients were 4%±0.04 (compound
colocalizing with LTG) and 80%±0.24 (LTG colocalizing with 3).
3
Figure 3. Confocal section of HeLa cells stained with compound 3. Arrows
point out mitochondria, white arrowheads point out vesicles and yellow
arrowheads point out the nucleoli. LUT = Fire. Scale bar = 20 m.
Acknowledgements
This work was supported by funds from the Spanish
Government (MCIU/AEI/FEDER, UE; grants CTQ2017-84779-R
and CTQ2016-78454-C2-1-R) and the Generalitat de Catalunya
(2017 DI 072). The authors acknowledge helpful assistance of
4
This article is protected by copyright. All rights reserved.

10.1002/chem.202002314
Chemistry - A European Journal
COMMUNICATION
[11] a) A. Gandioso, R. Bresolí-Obach, A. Nin-Hill, M. Bosch, M. Palau, A.
Galindo, S. Contreras, A. Rovira, C. Rovira, S. Nonell, V. Marchꢂn, J.
Org. Chem., 2018, 83, 1185−1195; b) A. Gandioso, M. Palau, R.
Bresolí-Obach, A. Galindo, A. Rovira, M. Bosch, S. Nonell, V. Marchꢂn,
J. Org. Chem., 2018, 83, 11519−11531; c) A. Rovira, M. Pujals, A.
Gandioso, M. López-Corrales, M. Bosch, V. Marchán, J. Org. Chem.,
2020, 85, 6086−6097.
Dr. Francisco Cárdenas (NMR) and Dr. Irene Fernández and
Laura Ortiz (MS) from CCiTUB, and of Arturo Prudencio
(Microbeam, Spain) in the development of the irradiation device.
A.R. and A.G. were recipient fellows of the University of
Barcelona.
[12] a) A. Rovira, A. Gandioso, M. Goñalons, A. Galindo, A. Massaguer, M.
Bosch, V. Marchán, J. Org. Chem., 2019, 84, 1808−1817; b) V.
Novohradsky, A. Rovira, C. Hally, A. Galindo, G. Vigueras, A. Gandioso,
M. Svitelova, R. Bresolí-Obach, H. Kostrhunova, L. Markova, J.
Kasparkova, S. Nonell, J. Ruiz, V. Brabec, V. Marchán, Angew. Chem.,
Int. Ed., 2019, 58, 6311−6315.
Keywords: coumarin • protecting groups • caged compounds •
photolysis • mitochondria
[1]
a) G. Mayer, A. Heckel, Angew. Chem. Int. Ed. 2006, 45, 4900–4921;
b) C. Brieke, F. Rohrbach, A. Gottschalk, G. Mayer, A. Heckel, Angew.
Chem. Int. Ed., 2012, 51, 8446−8476; c) P. Klán, T. Solomek, C. G.
Bochet, A. Blanc, R. Givens, M. Rubina, V. Popik, A. Kostikov, J. Wirz,
Chem. Rev., 2013, 113, 119−191; d) W. A. Velema, W. Szymanski, B. L.
Feringa, J. Am. Chem. Soc., 2014, 136, 2178−2191; e) M. J. Hansen,
W. A. Velema, M. M. Lerch, W. Szymanski, B. L. Feringa, Chem. Soc.
Rev., 2015, 44, 3358−3377; f) A. Bardhan, A. Deiters, Curr. Opin. Str.
Biol., 2019, 57, 164−175.
[13] T. Eckardt, V. Hagen, B. Schade, R. Schmidt, C. Schweitzer, J. Bendig,
J. Org. Chem., 2002, 67, 703–710.
[14] A. Rodrigues-Correia, D. Knapp-Behle, J. W. Engels, A. Heckel, Org.
Lett., 2014, 16, 5128−5131.
[2]
[3]
[4]
[5]
J. M. Silva, E. Silva, R. L. Reis, J. Control. Release, 2019, 298,
154−176.
a) K. Kalka, H. Merk, H. Mukhtar, J. Am. Acad. Dermatol., 2000, 42,
389−413; b) S. L. Jacques, S. L, Phys. Med. Biol., 2013, 58, R37−R61.
H. K. Agarwal, R. Janicek, S.-H. Chi, J. W. Perry, E. Niggli, G. C. R.
Ellis-Davies, J. Am. Chem. Soc., 2016, 138, 3687–3693.
a) C. Menge, A. Heckel, Org. Lett., 2011, 13, 4620−4623; b) L. Fournier,
I. Aujard, T. Le Saux, S. Maurin, S. Beaupierre, J.-B. Baudin, L. Jullien,
Chem. Eur. J., 2013, 19, 17494−17507; c) J. P. Olson, H.-B. Kwon, K.
T. Takasaki, C. Q. Chiu, M. J. Higley, B. L. Sabatini, G. C. R. Ellis-
Davies, J. Am. Chem. Soc., 2013, 135, 5954−5957; d) A. Gandioso, M.
Cano, A. Massaguer, V. Marchán, J. Org. Chem., 2016, 81,
11556−11564; e) A. Gandioso, M. Palau, A. Nin-Hill, I. Melnyk, C.
Rovira, S. Nonell, D. Velasco, J. García-Amorꢁs, V. Marchꢂn,
ChemistryOpen, 2017, 6, 375−384; f) A. Gandioso, S. Contreras, I.
Melnyk, J. Oliva, S. Nonell, D. Velasco, J. García-Amorꢁs, V. Marchꢂn,
J. Org. Chem., 2017, 82, 5398−5408; g) Y. Chitose, M. Abe, K.
Furukawa, J.-Y. Lin, T.-C. Lin, C. Katan, Org. Lett., 2017, 19,
2622−2625; h) Q. Lin, L. Yang, Z. Wang, Y. Hua, D. Zhang, B. Bao, C.
Bao, X. Gong, L. Zhu, Angew. Chem. Int. Ed., 2018, 57, 3722−3726; i)
N. Wagner, M. Stephan, D. Höglinger, A. Nadler, Angew. Chem. Int.
Ed., 2018, 57, 13339−13343; j) M. Klausen, V. Dubois, G. Clermont, C.
Tonnelé, F. Castet, M. Blanchard-Desce, Chem. Sci., 2019, 10,
4209−4219; k) M. Bojtꢂr, A. Kormos, K. Kis-Petik, M. Kellermayer, P.
Kele, Org. Lett. 2019, 21, 9410−9414.
[6]
a) T. Slanina, P. Shrestha, E. Palao, D. Kand, J. A. Peterson, A. S.
Dutton, N. Rubinstein, R. Weinstain, A. H. Winter, P. Klꢂn, J. Am.
Chem. Soc. 2017, 139, 15168-15175; b) K. Sitkowska, B. L. Feringa, W.
Szymanski, J. Org. Chem., 2018, 83, 1819−1827; c) J. A. Peterson, C.
Wijesooriya, E. J. Gehrmann, K. M. Mahoney, P. P. Goswami, T. R.
Albright, A. Syed, A. S. Dutton, E. A. Smith, A. H. Winter, J. Am. Chem.
Soc., 2018, 140, 7343−7346; d) D. Kand, L. Pizarro, I. Angel, A. Avni, D.
Friedmann-Morvinski, R. Weinstain, Angew. Chem. Int. Ed., 2019, 58,
4659−4663.
[7]
a) R. R. Nani, A. P. Gorka, T. Nagaya, H. Kobayashi, M. J.
Schnermann, Angew. Chem. Int. Ed., 2015, 54, 13635−13638; R. R.
Nani, A. P. Gorka, T. Nagaya, T. Yamamoto, J. Ivanic, H. Kobayashi, M.
J. Schnermann, ACS Cent. Sci., 2017, 3, 329−337.
[8]
[9]
D. P. Walton, D. A. Dougherty, J. Am. Chem. Soc., 2017, 139, 4655–
4658.
(a) M. Salierno, E. Marceca, D. S. Peterka, R. Yuste, J. Inorg. Biochem.,
2010, 104, 418−422; b) J. Mosquera, M. I. Sánchez, J. L. Mascareñas,
M. E. Vázquez, Chem. Comm., 2015, 51, 5501−5504; c) T. Voelker, E.
Meggers, Curr. Opin. Chem. Biol., 2015, 25, 48−54; d) A. Li, C. Turro, J.
Kodanko, Acc. Chem. Res., 2018, 51, 1415−1421; e) A. Li, C. Turro, J.
J. Kodanko, Chem. Commun. 2018, 54, 1280−1290.
[10] G. Bassolino, C. Nanꢃoz, Z. Thiel, E. Bois, E. Vauthey, P. Rivera-
Fuentes. Chem. Sci. 2018, 9, 387-391.
5
This article is protected by copyright. All rights reserved.

10.1002/chem.202002314
Chemistry - A European Journal
COMMUNICATION
Entry for the Table of Contents
Insert graphic for Table of Contents here.
Insert text for Table of Contents here.
We report here the transformation of coumarin-based COUPY fluorophores into a new class of visible light-sensitive photolabile
protecting groups which expand the current photochemical toolbox. Besides exhibiting an excellent cellular uptake, COUPY
photocages accumulate selectively in mitochondria, thereby offering the possibility of delivering biologically active compounds within
this organelle in a selective manner.
Institute and/or researcher Twitter usernames: University of Barcelona
6
This article is protected by copyright. All rights reserved.