A general synthetic strategy for the design of new BODIPY fluorophores based on pyrroles with polycondensed aromatic and metallocene substituents

Article abstract of DOI:10.1002/chem.201003242

BODIPYrrole: A general strategy for the design of novel BODIPY fluorophores based on pyrroles with polycondensed aromatic and metallocene substituents has been developed. The strategy involves the acylation of the condensed substituent and treatment of the acylated derivative (as oxime) with acetylene in MOH/DMSO (M=alkali metal) to give pyrroles that were then used for assembly of the BODIPY fluorophores (see scheme).

Full text of DOI:10.1002/chem.201003242

COMMUNICATION
DOI: 10.1002/chem.201003242
A General Synthetic Strategy for the Design of New BODIPY Fluorophores
Based on Pyrroles with Polycondensed Aromatic and Metallocene
AHCTUNGTREGUNSNN ubstituents
Elena Yu. Schmidt,[a] Nadezhda V. Zorina,[a] Marina Yu. Dvorko,[a]
Nadezhda I. Protsuk,[a] Kseniya V. Belyaeva,[a] Gilles Clavier,[b]
Rachel Mꢀallet-Renault,[b] Thanh T. Vu,[b] Alꢁbina I. Mikhaleva,[a] and
Boris A. Trofimov*[a]
4,4-Difluoro-4-bora-3a,4a-diaza-s-indacene known as the
trademark BODIPY shows many intriguing optical and
chemical properties like high absorption coefficient and
fluorescence quantum yield, long wavelength emission, and
photochemical stability.[1] BODIPY moieties have been con-
jugated to a variety of biomolecules such as proteins,[2]
DNA,[3] carbohydrates,[4] and cholesterol.[5] Furthermore,
BODIPY derivatives have been used in fluorescent
switches;[6] probes for protons,[7] mercuric ion,[8] and nitric
oxide;[9] biological labeling; and syntheses of molecular de-
vices.[10] Thus, the synthesis of diverse BODIPY derivatives
and their application to biomolecules are of current interest.
Despite this recent progress, synthesis of BODIPY deriva-
tives that have aryl groups remains an important research
objective, because the fluorescence maxima of BODIPY
strongly depend on the structure of aryl substituents. Gener-
ally, fused aromatic and heteroaromatic compounds are in-
tensively studied[11] because the narrow HOMO–LUMO gap
enables high lability of their p-electrons, and consequently
they exhibit a strong optical response to manifold chemical
and physical effects.
To the best of our knowledge, just a few syntheses of pyr-
roles linked with polycondensed aromatics have been re-
ported. Most recently, a series of pyrrole–polycyclic-aromat-
ic ensembles obtained by a two-stage synthetic strategy was
published.[13] Their central 2,5-diaryl-3,4-dinaphthyl-substi-
tuted pyrrole core was constructed by a Paal–Knorr reac-
tion. Furthermore, to introduce the condensed aromatic sub-
stituents, a Suzuki–Miyaura reaction was employed in the
cross-coupling of the corresponding boronic acids with the
triflated sites of the core. Most of the synthesized pyrroles
were blue-light emitters and exhibited high quantum effi-
ciencies.[13] Previously, microwave-assisted synthesis of 2,3-
diphenyl-5-naphthylpyrrole from the corresponding 1,4-
dione and ammonium formate has been reported.[14] Also, 2-
naphthylpyrroles were prepared by the cross-coupling of N-
protected-2-bromopyrrole with naphthylboronic acid.[15] The
functionalized pyrroles with condensed aromatic substitu-
ents, such as 4-methyl-3-(2-methoxy-1-naphthyl)pyrrole-2-
carboxylate and 4-ethyl-3-(10-methoxy-9-phenanthryl)pyr-
role-2-carboxylate, were synthesized from the corresponding
nitroalkenes and ethyl isocyanoacetate.[16] The synthesis of
2-(9-anthrylvinyl)pyrroles was achieved by a Wittig reaction
of 9-anthrylmethyltriphenylphosphonium bromide and the
corresponding aldehyde.[17]
As the above concise overview shows, no approach gener-
al enough to design pyrroles with condensed aromatic sub-
stituents so far exists. A promising general strategy for the
synthesis of these pyrrole systems could be the reaction of
acylated polyaromatic compounds and acylated metallo-
cenes (via their oximes) with acetylene in the presence of
MOH/DMSO (M=Li, Na, K, Cs) superbase systems (the
Trofimov reaction).[18] Indeed, in accordance with this as-
sumption, we reported the first example of such synthesis;
1-vinyl-2-naphthylpyrroles were synthesized from acetyl-
naphthalenes and acetylene in 61–71% yield.[19] Herein, we
further develop the modification of the above reaction to
create a general strategy for the synthesis of polycondensed
aromatic and metallocene–pyrrole ensembles of wide diver-
sity, starting from accessible polycondensed hydrocarbons
and metallocenes.
The integration of condensed aromatic moieties with the
BODIPY scaffold in one molecule has been shown to lead
to synergism of their properties and to high-performance
optical materials.[12] Therefore, the design of molecules com-
bining the pyrrole moiety and condensed aromatic frame-
works represents a long-standing challenge in BODIPY
chemistry.
[a] Dr. E. Yu. Schmidt, Dr. N. V. Zorina, Dr. M. Yu. Dvorko,
Dr. N. I. Protsuk, Dr. K. V. Belyaeva, Prof. Dr. A. I. Mikhaleva,
Prof. Dr. B. A. Trofimov
A. E. Favorsky Irkutsk Institute of Chemistry
Siberian Branch, Russian Academy of Sciences
1 Favorsky Str., 664033 Irkutsk (Russia)
Fax : (+7)3952-419346
E-mail: boris_trofimov@irioch.irk.ru
[b] Dr. G. Clavier, Prof. Dr. R. Mꢀallet-Renault, T. T. Vu
PPSM, ENS Cachan, CNRS, UniverSud
61 avenue du Prꢀsident Wilson, 94230 Cachan (France)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201003242.
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We have devised a synthesis to enable the preparation of
polycondensed aromatic and metallocene–pyrrole ensem-
bles, such as 2-(anthr-2-yl)-, 2-(phenanthr-2-yl)-, 2-(pyren-1-
yl)-, and 2-(ferrocen-1-yl)pyrroles, in just two steps. The cor-
responding hydrocarbons are acylated and the resulting ke-
tones further react (as ketoximes) with acetylene in the
The Cs-oximates 1b and 1c were then treated with excess
acetylene in DMSO at 1008C for 1 h under pressure (initial
pressure was 14 atm at RT, which reached 25–30 atm at the
reaction temperature) to give the anticipated pyrroles 2b
and 2c (in 32 and 37% yields, respectively) and 1-vinyl pyr-
roles 3b and 3c (in 30 and 29% yields, respectively,
Table 1). Notably, pyrroles and their 1-vinyl derivatives are
easily separated by column chromatography (Al2O3, diethyl
ether/n-hexane).
presence of
a
superbase suspension MOH/DMSO
(Scheme 1, only one example is given).
However, these conditions (1008C, 1 h, 12–14 atm) ap-
peared to be invalid for the transformation of anthracene to
anthrylpyrrole through the corresponding oxime 1a
(Table 1). The reaction of oxime 1a with acetylene proceed-
ed with intense tar formation and deoximation to acetylan-
thracene. Under milder conditions (808C, 5 min, other reac-
tion parameters remained as above), the only product
formed was the O-vinyloxime 4, isolated in 45% yield
(Scheme 2).
Scheme 1. From condensed aromatics or metallocenes to pyrroles in two
steps.
Our initial experiments have shown that for the pyrrole
synthesis, the reaction of
oximes 1a–1e with acetylene
needs to be modified. For ex-
Table 1. Synthesis of pyrroles and 1-vinyl pyrroles from oximes and acetylen.
ample, in the NaOH/DMSO
system, under common widely
varied conditions[19,20] (100–
1408C, 1–5 h, acetylenic pres-
sure from atmospheric to 12–
14 atm), none of the anticipated
pyrroles were formed. Also, in
Oxime
Reaction conditions
Pyrrole
(Yield [%])[a]
1-Vinyl pyrrole
ACHTUNGTRENNUNG
(Yield [%])[a]
G
the
KOH/DMSO
system,
oximes 1a–1c gave only trace
amounts of the expected pyr-
roles, despite the wide variation
of the reaction conditions. In-
stead, the deoximation of ke-
toximes 1a–1c occurred to give
the starting ketones as the
major products.
CsF/LiOH; 12–14 atm;
90–1008C, 5 min–1 h
CsF/LiOH; 14 atm;
1008C, 1 h
Pyrroles 2d, 2e, and their 1-
vinyl derivatives 3d and 3e
were obtained from oximes 1d
and 1e in 29–46% and 16–30%
yields, respectively, under at-
mospheric pressure at 1208C
for 5 h in the KOH/DMSO
system (Table 1).
CsF/LiOH; 14 atm;
1008C, 1 h
To synthesize pyrroles 2b, 2c,
3b, and 3c another modifica-
tion was elaborated. For this,
the system LiOH/CsF/DMSO
was chosen as a catalyst precur-
sor and the cesium salts of the
ketoximes (instead of free ke-
toximes 1b and 1c) were used.
The Cs-oximates were generat-
ed in situ, by removal of water
from the reaction mixture
under vacuum.
KOH; 1 atm;
1208C, 5 h
KOH; 1 atm;
1208C, 5 h
[a] Yields of products isolated.
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Design of New BODIPY Fluorophores
COMMUNICATION
Scheme 2. Synthesis of O-vinyloxime 4 and its rearrangement to pyrrole
2a.
O-Vinyloximes were proven to be key intermediates in
the pyrrole synthesis from ketoximes and acetylene.[21] Ac-
cording to the established mechanism, a [3,3] sigmatropic re-
arrangement of a tautomeric form of O-vinyloxime 5 leads
to pyrrole 2a (Scheme 2). Indeed, rearrangement of 4 upon
heating in DMSO (1208C, 30 min) occurred to give pyrrole
2a in 24% yield.
Scheme 3. One-pot synthesis of BODIPY derivatives; DDQ=2,3-di-
chloro-5,6-dicyano-1,4-benzoquinone.
All the pyrroles synthesized are meltable, faintly to
brightly colored powders or crystals that are soluble in
common organic solvents (benzene, diethyl ether, chloro-
form, ethyl acetate), but are scarcely soluble in hexane. The
corresponding N-vinyl pyrroles 3a–3e can be considered as
protected NH-pyrroles because they can be easily deprotect-
ed by treatment with the HgACHTNUGTRNEUNG(OAc)2/NaBH4 system in aque-
ous MeCN according to known procedures.[20b]
The pyrroles 2b–2d, together with 2-(naphth-1-yl)- and 2-
(naphth-2-yl)pyrroles (synthesized previously by devinyla-
tion of the corresponding N-vinyl derivatives[19]), were fur-
ther used to assemble the novel 4,4-difluoro-3,5-diaryl-8-me-
sityl-4-bora-3a,4a-diaza-s-indacenes (BODIPY derivatives)
6–9 as prospective fluorophores.
The assembly was achieved by using a one-pot procedure
involving condensation of the pyrroles with mesityl aldehyde
in the presence of trifluoroacetic acid to give dipyrrome-
thanes, followed by oxidation with 2,3-dichloro-5,6-dicyano-
1,4-benzoquinone (DDQ) to the corresponding dipyrrome-
thenes, which then underwent complexation with boron tri-
fluoride etherate (Scheme 3). Scheme 4 presents the chemi-
cal structure and yields of the novel boron dipyrromethene
dyes with polycondensed aromatic frameworks at the C3
and C5-positions.
Scheme 4. Chemical structures and yields of the novel BODIPY deriva-
tives with polycondensed aromatic frameworks.
The introduction of the mesityl group at the meso 8-posi-
tion of the BODIPY derivatives was carried out to impart
additional constraints on the molecules to ensure a higher
fluorescence quantum yield. Commonly, the BODIPY fluo-
rescence emission is known to be deactivated by free rota-
tion of the aryl group at the meso position.[22] Therefore, the
additional methyl groups were introduced into the benzene
ring (mesityl substituent) to hinder this rotation.
Our attempt to synthesize the corresponding BODIPY
from 3-ethyl-2-ferrocenylpyrrole 2e and mesityl aldehyde
failed. From the reaction mixture obtained by using the
above conditions, only dipyrrolylhydroxymethane 10
(Scheme 5), an unexpected adduct of the intermediate dipyr-
Scheme 5. Attempted synthesis of BODIPY from pyrrole 2e, resulting in
the formation of the unexpected adduct 10.
romethene with water molecules, was detected (by analysis
of NMR data and MS).
All the new BODIPY dyes are violet crystals with no
melting point (decomposed upon heating above 2508C) and
are soluble in chloroform, light petroleum, and dichlorome-
thane.
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B. A. Trofimov et al.
The photophysical properties of the BODIPY derivatives
have been investigated in dichloromethane (Figure 1). All
the derivatives displayed an intense, sharp absorption band
in the visible spectra between 538 and 580 nm. Other bands
are observed in the UV range, which result from the overlap
Figure 2. Space orientation of the BODIPY derivatives based on B3LYP/
6-31+G(d) calculations.
(Figure 2). Hence, planarity is better achieved in 7 and 8
than in 6 and 9 (see calculated angle in Table 2). This result
correlates well with the position of the absorption maxima.
All the BODIPY derivatives are highly fluorescent (Ffluo
up to 0.95) with a lifetime around 5 ns and have modest
Stokes shifts, which are typical for this type of fluorophore.
The largest Stokes shifts are observed for compounds 6 and
9, which implies that in the excited state of 6 and 9, the sub-
stituents are more coplanar with the BODIPY core than in
the ground state. The emission spectra of 8 and 9 have also
been recorded after excitation in the absorption band of the
aromatic substituent (310 and 340 nm respectively). Interest-
ingly, no fluorescence signal arising from the phenanthrene
or the pyrene could be detected (See Figures S1 and S2 in
the Supporting Information). It can then be inferred that a
very efficient excited-state energy transfer (EET) takes
place from the attached aromatic to the BODIPY.
In conclusion, a general and convenient strategy for the
design of novel BODIPY fluorophores based on pyrroles
with polycondensed aromatic and metallocene substituents
has been developed. The pyrroles synthesized, due to the
long-range conjugation in their molecules and size variation
of the attached aromatics, proved to be promising building
blocks for assembling BODIPY fluorophores with enhanced
quantum yield and red emission in solution. Current work is
focused on the study of the spectroscopic and electrochemi-
cal properties of the novel BODIPY dyes and their struc-
ture–performance relationship as potential solid state fluo-
rophores. These results will be disclosed in due course.
Figure 1. Normalized absorption (full lines) and emission (broken lines)
spectra of BODIPY derivatives 6, 7, 8, and 9 recorded in dichlorome-
thane.
of the second absorption of the BODIPY and those of the
appended aromatics. For example, an intense band can be
noted for 9 at 340 nm, arising from the pyrene moiety.
Interestingly, increasing the size of the aromatic substitu-
ent does not yield an automatic red shift of the absorption
band (Table 2). Indeed, the maximum absorption for 9 (1-
pyrenyl) is centered at 562 nm, whereas for 7 (2-naphthyl)
and 8 (2-phenanthryl) it is found at 573 and 579 nm, respec-
Table 2. Photophysical data (recorded in dichloromethane) and the cal-
culated angle between the BODIPY and appended aromatic planes.
[a]
[b]
[c]
Compound labs eꢂ103
lem Stokes Ffluo tfluo Calculated
[nm] [LmolÀ1 cmÀ1] [nm] shift
[ns] angle[d] [8]
[cmÀ1
]
6
7
8
9
538
573 105.1
579
562
66.3
601 1948
618 1271
624 1246
626 1819
0.95 5.5
60
42
42
58
0.95 5.5
0.77 4.8
0.64 4.5
69
51
Experimental Section
[a] Excitation was set equal to the maximum of absorption. [b] Sulfo-
rhodamine 101 in ethanol Ffluo =0.9[23] was used as the reference. [c] Ex-
citation at 495 nm. [d] Calculations were performed at the B3LYP/6-31+
G(d) level of theory.[24]
For experimental details, see the Supporting Information.
Acknowledgements
tively. In addition, compared with 6, compound 7 produces a
35 nm shift of the absorption band just by a simple change
of the attachment position by one carbon. At first glance
this result can seem strange but can be rationalized by per-
forming a geometry optimization of the BODIPY deriva-
tives (Figure 2). The relative orientation of the planes of the
BODIPY and the attached aromatics is driven by the size of
the substituent, which cannot be coplanar when it is too
large because of constraints imposed by the BF2 moiety
This work was supported by the Russian Foundation for Basic Research
(Grants: 07-03-92162-PICS and 08-03-00002).
Keywords: BODIPY · condensed aromatics · fluorescence ·
pyrroles · synthetic methods
[1] A. Loudet, K. Burgess, Chem. Rev. 2007, 107, 4891–4932.
3072
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Design of New BODIPY Fluorophores
COMMUNICATION
[2] a) K. Tan, L. Jaquinod, R. Paolesse, S. Nardis, C. Di Natale, A. Di
Carlo, L. Prodi, M. Montalti, N. Zaccheroni, K. M. Smith, Tetrahe-
dron 2004, 60, 1099–1106; b) M.-c. Yee, S. C. Fas, M. M. Stohlmeyer,
T. J. Wandless, K. A. Cimprich, J. Biol. Chem. 2005, 280, 29053–
29059.
pp. 55–89; b) Z. Wang, Comprehensive Organic Name Reactions
and Reagents, Part 3, Wiley, New York, 2009, p. 2793.
[19] M. V. Markova, L. V. Morozova, I. V. Tatarinova, A. I. Mikhaleva,
S. H. Hyun, E. Yu. Schmidt, N. V. Zorina, G. F. Myachina, B. A. Tro-
fimov, Dokl. Chem. 2010, 434, 219–222.
[3] M. L. Metzker (Baylor College of Medecine), WO/2003/066812,
2003.
[20] a) S. E. Korostova, R. N. Nesterenko, A. I. Mikhaleva, R. I. Polovni-
kova, N. I. Golovanova, Khim. Geterotsikl. Soedin. 1989, 63, 901–
906; b) B. A. Trofimov, E. Yu. Schmidt, A. I. Mikhaleva, C. Pozo-
Gonzalo, J. A. Pomposo, M. Salsamendi, N. I. Protzuk, N. V. Zorina,
A. V. Afonin, A. V. Vashchenko, E. P. Levanova, G. G. Levkovskaya,
Chem. Eur. J. 2009, 15, 6435–6445.
[21] B. A. Trofimov, Curr. Org. Chem. 2002, 6, 1121–1162.
[22] a) S. Mula, A. K. Ray, M. Banerjee, T. Chaudhuri, K. Dasgupta, S.
Chattopadhyay, J. Org. Chem. 2008, 73, 2146–2154; b) T. T. Vu, S.
Badre, C. Dumas-Verdes, J.-J. Vachon, C. Julien, P. Audebert, E. Yu.
Senotrusova, E. Yu. Schmidt, B. A. Trofimov, R. B. Pansu, G. Cla-
vier, R. Mꢀallet-Renault, J. Phys. Chem. C. 2009, 113, 11844–11855.
[23] M. Sauer, K.-T. Han, R. Muller, S. Nord, A. Schulz, S. Seeger, J.
Wolfrum, J. Arden-Jacob, G. Deltau, N. J. Marx, C. Zander, K. H.
Drexhage, J. Fluoresc. 1995, 5, 247–263.
[24] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann,
O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y.
Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O.
Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Fores-
man, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski,
B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L.
Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A. Na-
nayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wallingford
CT, 2004.
[4] Y. Luo, G. D. Prestwich, Bioconjugate Chem. 1999, 10, 755–763.
[5] Z. Li, E. Mintzer, R. Bittman, J. Org. Chem. 2006, 71, 1718–1721.
[6] a) T. A. Golovkova, D. V. Kozlov, D. C. Neckers, J. Org. Chem.
2005, 70, 5545–5549; b) C. Trieflinger, K. Rurack, J. Daub, Angew.
Chem. 2005, 117, 2328–2331; Angew. Chem. Int. Ed. 2005, 44, 2288–
2291.
[7] M. Baruah, W. Qin, N. Basariæ, W. M. De Borggraeve, N. Boens, J.
Org. Chem. 2005, 70, 4152–4157.
[8] X. Qi, S. K. Kim, E. J. Jun, L. Xu, S.-J. Kim, J. Yoon, Bull. Korean
Chem. Soc. 2007, 28, 2231–2234.
[9] Y. Gabe, Y. Urano, K. Kikuchi, H. Kojima, T. Nagano, J. Am.
Chem. Soc. 2004, 126, 3357–3367.
[10] R. W. Wagner, J. S. Lindsey, Pure Appl. Chem. 1996, 68, 1373–1380.
[11] a) Sh.-H. Lu, S. Selvi, J.-M. Fang, J. Org. Chem. 2007, 72, 117–122;
b) C. Pietsch, A. Vollrat, R. Hoogenboom, U. S. Schubert, Sensors
2010, 10, 7979–7990; c) Y. Zhou, J. W. Kim, M. J. Kim, W.-J. Son,
S. J. Han, H. N. Kim, S. Han, Y. Kim, C. Lee, S.-J. Kim, D. H. Kim,
J.-J. Kim, J. Yoon, Org. Lett. 2010, 12, 1272–1275.
[12] a) C.-I Lin, S. Selvi, J.-M. Fang, P.-T. Chou, C.-H. Lai, Y.-M. Cheng,
J. Org. Chem. 2007, 72, 3537–3542; b) R. Ziessel, T. Bura, J.-H.
Olivier, Synlett 2010, 2304–2310.
[13] Ch.-Sh. Li, Y.-H. Tsai, W.-Ch. Lee, W.-J. Kuo, J. Org. Chem. 2010,
75, 4004–4013.
[14] H. S. P. Rao, B. K. Gorityala, K. Vasantham, Indian J. Chem. 2007,
45, 1470–1474.
[15] a) A. Burghart, H. Kim, M. B. Welch, L. H. Thoresen, J. Reibens-
pies, K. Burgess, J. Org. Chem. 1999, 64, 7813–7819; b) P. H. Lee,
Bull. Korean Chem. Soc. 2008, 29, 261–264.
[16] Y. Furusho, A. Tsunoda, T. Aida, J. Chem. Soc. Perkin Trans. 1
1996, 183–190.
[17] E. J. Shin, Bull. Korean Chem. Soc. 2004, 25, 907–909.
[18] a) R. J. Tedeschi in Encyclopedia of Physical Science and Technolo-
gy, Vol. 1 (Ed.: R. A. Meyers), Academic Press, San Diego, 2001,
Received: November 11, 2010
Published online: February 14, 2011
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