Fluorescent oxazoles from quinones for bioimaging applications

Article abstract of DOI:10.1039/c6ra14701a

This work describes a synthetic strategy for the syntheses of four new fluorescent excited state intramolecular proton transfer (ESIPT) prone oxazole derivatives synthesized from lapachol, a naturally occurring naphthoquinone isolated from the Tabebuia species (ipe tree). DFT calculations were performed to understand the ESIPT stabilizing process of these new derivatives. The new structures were designed to have improved lipophilic and balanced hydrophobic properties toward a selective cellular staining of lipid-based structures, that is, lipid inclusions in the cytosol. Cell-imaging experiments returned interesting results and showed the molecular architecture of the four derivatives had a great influence over the stabilizing processes in the excited state and over the selection of lipid inclusions inside the cells.

Full text of DOI:10.1039/c6ra14701a

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Fluorescent Oxazoles from Quinones for Bioimaging Applications
a
a
a
a
b
Gleiston G. Dias, Pamella V. B. Pinho, Hélio A. Duarte, Jarbas M. Resende, Andressa B. B. Rosa,
b
b
a
José R. Correa, Brenno A. D. Neto * and Eufrânio N. da Silva Júnior *
a
Institute of Exact Sciences, Department of Chemistry, Federal University of Minas Gerais, Belo
Horizonte, 31270ꢀ901, MG, Brazil. Eꢀmail: eufranio@ufmg.br
b
Laboratory of Medicinal & Technological Chemistry, Institute of Chemistry, University of Brasilia,
P.O. Box 4478, Brasilia, 70904970, DF, Brazil. Eꢀmail: brenno.ipi@gmail.com
Table of Contents Graphic
Abstract. This work describes a synthetic strategy for the syntheses of four new fluorescent excited state
intramolecular proton transfer (ESIPT) prone oxazole derivatives synthesized from lapachol, a naturally
occurring naphthoquinone isolated from Tabebuia species (ipe tree). DFT calculations were performed to
understand the ESIPT stabilizing process of these new derivatives. The new structures were designed to
have improved lipophilic and balanced hydrophobic properties toward a selective cellular staining of
lipidꢀbased structures, that is, lipid inclusions in the cytosol. Cellꢀimaging experiments returned
interesting results and showed the molecular architecture of the four derivatives had a great influence over
the stabilizing processes in the excited state and over the selection of lipid inclusions inside the cells.

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INTRODUCTION
The development of new, designed and more efficient bioprobes is a hard and challenge
1
task. Whether one consider the new probes must meet strict requirements of chemicalꢀ
and photostabilities associated with specific responses inside the astonishing cellular
2
ꢀ4
environment, than this task is even more puzzling. Most of the available cellular
probes used for bioimaging applications, especially commercially available structures,
have been built over a few ‘classical’ scaffolds i.e. coumarins, boronꢀdipyrromethenes
(BODIPYs), rhodamines, cyanines, phenoxazines and fluoresceins. The great advances
and drawbacks associated with these fluorescent derivatives have been reviewed
5
elsewhere.
Although derivatives synthesized from these scaffolds are commonly
6
used for the development of bioprobes, many alternatives are emerging aiming to
succeed where those derivatives have already shown their limitations and drawbacks, as
7
some of us recently highlighted. Among the available alternatives, fluorescent
8,9
10,11
12,13
derivatives bearing a unit of benzothiadiazole, benzothiazole,
benzimidazole,
14,15
16,17
imidazopyridine,
technology.
and oxazole
are some promising structures to further bioprobes
Oxazole derivatives are a very attractive class of heterocycles prone to perform
1
8ꢀ
ESIPT (excitedꢀstate intramolecular proton transfer) stabilizing processes (Scheme 1).
2
1
These derivatives may be used in many light technological areas and have been
2
2
23
applied as fluorescent tags for multicomponent adducts, white emitters, probes for
24
25
26
model membranes, metal sensors and others. Although oxazole derivatives are a
promising class of fluorescent heterocycles, the rational design towards cellular
selectivity in bioimaging experiments is a gap not fulfilled hitherto.

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Scheme 1. General structure of an ESIPT prone oxazole derivative and its excitedꢀstate intramolecular
proton transfer mechanism. (i) Absorption, (ii) proton transfer in the excited state, (iii) emission and (iv)
reverse proton transfer.
Because of our interest in the development new fluorescent probes for
2
7ꢀ32
bioimaging applications,
we disclose herein the syntheses of four new fluorescent
oxazole derivatives, their molecular architecture designed for targeting lipophilic
structures (lipids inclusions) inside the cells, their photophysical and theoretical (DFT)
evaluations and their bioimaging applications.
RESULTS AND DISCUSSION
The new fluorescent derivatives were synthesized as shown in Scheme 2. The synthetic
strategy was based on the redox center modification of βꢀlapachone and norꢀβꢀ
lapachone derivatives prepared from the natural occurring lapachol (1), a quinone
3
3ꢀ36
derivative easily obtained from ipe tree.
We have successfully used this sort of
strategy towards the synthesis of boronꢀbased structures applied as superior probes for
29
endocytic pathway tracking in live cancer cells and selective fluorescent sensor for
3
7
cadmium ions. Lapachol (1) could be directed converted to norꢀlapachol (2) by the
38
wellꢀestablished Hooker oxidation method and then transformed in the key

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intermediate 3ꢀazideꢀnorꢀβꢀlapachone (3). Exploring the electrophilicity of the orthoꢀ
quinoidal carbonyls of the respective azide derivative by the reaction with
39
salicylaldehyde in the presence of a nitrogen source the oxazole P1 was prepared. The
4
0ꢀ42
click reaction
of P1 afforded P2 bearing a long side carbon chain. Lapachol (1) was
also used to obtain βꢀlapachone (2) which in turn was used to the synthesis of the
iodinated oxazole (5). Key iodinated intermediate (5) directly afforded P3 and P4
through the Suzuki reaction.
Scheme 2. Synthesis of fluorescent oxazole derivatives named P1ꢀP4.
Derivative P1ꢀP4 had their photophysical evaluated and results are summarized
in Table 1 (also see Figures S41ꢀ43 in the Supporting Information file). P1ꢀP2 showed
small Stokes shifts and reasonable molar extinction coefficients with log
ε values in the

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ꢀ1
ꢀ1
range of 3.41ꢀ3.66 mM cm . These data indicate the ESIPT were not as efficient as
expected to be. P3 and P4 however showed a very distinct behavior. It could be noted
(for P3 and P4) large Stokes shifts (141ꢀ184 nm) and large molar extinction coefficients
ꢀ1
ꢀ1
(log
ε values in the range of 4.08ꢀ4.39 mM cm ). ESIPT prone fluorophores typically
have large Stokes shift and this feature is known to be a spectroscopic signature of the
43
efficient process. Some theoretical calculations have been performed to a better
understand of the photophysical related to the synthesized compounds, as show in
Figure 1.
Table 1. Photophysical data (in different solvents) for P1ꢀP4 (10 ꢀM solutions for all analyses).
λmax. (abs)
nm)
λmax. (em)
(nm)
398
400
400
404
395
396
401
396
397
399
403
393
395
398
528
525
521
534
531
521
528
540
541
540
551
539
540
Stokes
Shift (nm)
28
31
28
30
26
27
27
27
28
28
30
25
27
26
150
148
141
153
153
144
145
177
178
175
184
179
177
Oxazole
Solvent
log ε (ε)
(
ethyl acetate
acetonitrile
dichloromethane
dimethyl sulfoxide
hexane
370
369
372
374
369
369
374
369
369
371
373
368
368
372
378
377
380
381
378
377
383
363
363
365
367
360
363
3.57 (3736)
3.52 (3344)
3.57 (3708)
3.57 (3708)
3.66 (4530)
3.56 (3671)
3.59 (3868)
3.51 (3225)
3.51 (3208)
3.54 (3482)
3.41 (2574)
3.64 (4365)
3.52 (3305)
3.58 (3781)
4.28 (19068)
4.32 (21032)
4.31 (20432)
4.32 (20736)
4.39 (24436)
4.22 (16652)
4.33 (21606)
4.30 (19726)
4.30 (19962)
4.33 (21572)
4.26 (18276)
4.34 (21740)
4.08 (12090)
P1
methanol
toluene
ethyl acetate
acetonitrile
dichloromethane
dimethyl sulfoxide
hexane
P2
methanol
toluene
ethyl acetate
acetonitrile
dichloromethane
dimethyl sulfoxide
hexane
P3
P4
methanol
toluene
ethyl acetate
acetonitrile
dichloromethane
dimethyl sulfoxide
hexane
methanol
toluene
366
4.26 (18284)
541
175
Quantum yields (in dichloromethane) for P1ꢀP4 of 0.70, 0.45, 0.55, and 0.51, respectively.

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HOMO
State
LUMO
State
HOMO
LUMO
1
S State
S
0
S
0
S
1
State
P1
P2
P3
P4
Figure 1. HOMO and LUMO plots and diagram of the frontier molecular orbital energies. Calculations
performed at the PBEPBE/ccꢀpVDZ level of theory.
It is noted in both the ground and excited states the LUMO orbitals of P3ꢀP4 are
centered in the oxazole ring whereas for P1ꢀP2 the same orbitals are more distributed in
the structures. These results allow to a better understanding on the efficiency of the Hꢀ
transfer in the excited state (ESIPT) for P3ꢀP4 and the large Stokes shifts obtained in
the photophysical experiments.

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Finally, compounds P1ꢀP4 had their capacity as bioimaging probes tested
against Cacoꢀ2 (human colorectal adenocarcinoma cells) cells lineage (Figure 2). All
compounds could be visualized at the green channel bearing a strong fluorescence
emission. Their lipophilic nature feature could be beneficially used in the experiments
toward lipid inclusions staining.
Figure 2. (Left) Fixed cacoꢀ2 cell lineages stained with P1ꢀP2 (10 ꢀM). (A) and (B) Fluorescence pattern
of P1 and P2 (respectively) showing a disperse emission in the cytosol but with an accumulation near the
peripheral regions of the cells (yellow arrow heads). These feature was more pronounced using P2 and
the tendency toward lipid droplets (vesicles) could be clearer noted. (C) and (D) show the normal
morphological aspects of the samples by phase. (Right) Fixed cacoꢀ2 cell lineages stained with P3ꢀP4 (10
ꢀ
M). (A) and (B) Fluorescence pattern of P3 and P4 (respectively) showing a disperse emission in the
cytosol for P3 but with clear accumulation in the lipid inclusions for P4 (yellow arrow heads). (C) and
(
D) show the normal morphological aspects of the samples by phase. N = nucleus and scale bar of 25 ꢀM.
Compounds P1ꢀP2 displayed only the soꢀcalled minimum selection and were
found in the cells’ cytosol but not inside the nuclei. P1 was completely dispersed in the
cytosol whereas compound P2 showed a tendency toward lipid droplets but it was also
dispersed in the cytosol (leakage), therefore not suitable as a probe for analyzing these

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lipid inclusions. This tendency could be attributed to the long side carbon chain noted in
P2 structure obtained from the azide in P1. In order to improve this tendency, we
considered the substitution of the carbon chain for lipophilic and hydrophobic groups
(e.g. aromatic groups) and, in this sense, compounds P3 and P4 were synthesized. P3
did not show the expected behavior and it was found mostly dispersed in the cytosol as
P1. Only a tendency for lipids inclusions could be noted using P3. P4 showed however
a better accumulation in the lipid bodies than the three previously tested compounds.
Theoretical logP (c logP) values were calculated using DFT and semiꢀempirical levels
(Table S6). The data corroborated the experimental observations and values of
lipophilicity for P4 larger than those observed for P1ꢀP3 were obtained. Commercial
BODIPY was then used to compare and confirm the preference for lipid droplets of
compound P4 and this feature could be therefore confirmed (Figure 3 and Figure S56).

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Figure 3. Fixed cacoꢀ2 cell lineages stained with P4 (10 ꢀM) and commercial available BODIPY. (A)
Cells stained with P4 showing its accumulation in the lipid droplets (yellow arrowheads) and some part
still dispersed in the cytosol. (B) Lipid droplets stained with BODIPY. (C) and (D) show the normal
morphological aspects of the samples by phase. N = nucleus and scale bar of 25 ꢀM.
Figure 3ꢀA shows the lipid droplets being gradually stained with P4. Even using
the commercially available dye for lipid droplets (Figure 3ꢀB), still some part of the dye
was noted dispersed in the cytosol, especially considering fixed cells are being used.
The selectivity noted for P4 may be attributed to its higher hydrophobic character
indicating the rationale of its synthesis may be applied for further developments of new
oxazoleꢀbased bioprobes. During the experiment time period no notable photobleaching
or degradation could be observed for these dyes thus indicating the chemicalꢀ and
photoꢀ stabilities are sustained inside the cells, in accordance with the photostability
experiment (Figure S57). Commercial BODIPY is known to suffer from photobleaching
and this feature limits long time period experiments. The obtained results for P4 are the
first (to the best of our knowledge) toward a clear cellular selectivity of designed
oxazoles from natural products therefore this work may be the bases for the
development of other fluorescent oxazole derivatives from several classes of natural
products, especially quinones.
CONCLUSIONS
For new fluorescent oxazole derivatives have been obtained from the natural product
lapachol using an efficient synthetic methodology. Two of these derivatives (P3ꢀP4)
prove to perform efficient ESIPT whereas the other two did not show the expected
behavior in the excited state, although they proved to be stable emitters. DFT
calculations allowed for a better understanding on the efficiency of the ESIPT processes

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of P3ꢀP4 and the LUMO orbitals were most centered in the oxazole ring. P1ꢀP4 had
their abilities as bioprobes tested against cacoꢀ2 cell lineages. P1ꢀP2 returned poor
results whereas P3 showed a tendency to accumulate in lipid inclusions. P4 however
proved to be the most selective fluorescent oxazole tested in this work and its molecular
architecture may be used as the base for the development of new stable and selective
emitters for bioimaging applications. Finally, it is important to add that although a huge
progress is observed with these new designed oxazole derivatives, much is yet
necessary to establish them as a new class of bioprobes and we are on the way to reach
this goal.
EXPERIMENTAL SECTION
General. Melting points were obtained on Thomas Hoover and are uncorrected.
Analytical grade solvents were used. Column chromatography was performed on silica
gel (SiliaFlash G60 UltraPure 60ꢀ200 µm, 60 Å). Infrared spectra were recorded on an
1
13
FTIR Spectrometer IR Prestigeꢀ21 Shimadzu. H and C NMR spectra were recorded at
03 K using a Bruker AVANCE DRX400 spectrometer. All samples for NMR were
prepared in CDCl containing TMS as internal reference. Chemical shifts (δ) are given
3
3
in ppm and coupling constants (J) in Hertz. High resolution mass spectra (electrospray
ionization) were obtained using a MicroTOF Ic – Bruker Daltonics instrument.
Chemistry. Lapachol (1) was initially extracted from the heartwood of Tabebuia
sp. (Tecoma) and purified by a series of recrystallizations. Initially, norꢀlapachol (2) was
3
3
synthesized by Hooker oxidation methodology and data are consistent with those
4
4ꢀ46
reported in the literature.
mmol, 70% yield); m.p. 121ꢀ122 °C. H NMR (400 MHz, CDCl
H, J = 7.5, 1.5 and 0.5 Hz), 8.10 (ddd, 1H, J = 7.5, 1.5 and 0.5 Hz), 7.76 (td, 1H, J =
Compound 2 was obtained as an orange solid (160 mg, 0.7
3
3 1
3
, 303 K) δ: 8.13 (ddd,
1

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7
3
1
.5, 7.5 and 1.5 Hz), 7.69 (td, 1H, J = 7.5, 7.5 and 1.5 Hz), 6.03ꢀ5.99 (m, 1H), 2.0 (d,
13
H, J = 1.5 Hz), 1.68 (d, 3H, J = 1.2 Hz). C NMR (100 MHz, CDCl , 303 K) δ: 184.7,
3
81.5, 151.1, 143.6, 134.9, 133.0, 132.9, 129.5, 126.9, 126.0, 120.9, 113.6, 26.5, 21.7.
Synthesis of 3ꢀazidoꢀ2,2ꢀdimethylꢀ2,3ꢀdihydronaphtho[1,2ꢀb]furanꢀ4,5ꢀdione
(3): To a solution of norꢀlapachol (2) (228 mg, 1.0 mmol) in 25 mL of chloroform, 2
mL of bromine was added. The bromo intermediate precipitated immediately as an
orange solid. After removal of bromine, by adding dichloromethane and then removing
the organic solvent with dissolved bromine by rotary evaporator, an excess of sodium
2 2
azide (2 mmol) was added in CH Cl and the mixture was stirred overnight. The crude
reaction mixture was poured into 50 mL of water. The organic phase was extracted with
organic solvent, dried over sodium sulfate, filtered, and evaporated under reduced
pressure. The product 3 was obtained after recrystallization as an orange solid (263 mg,
1
0
.98 mmol, 98% yield); m.p. 200ꢀ202 °C. H NMR (400 MHz, CDCl
3
, 303 K) δ: 8.14
(ddd, 1H, J = 6.9, 2.1 and 0.9 Hz), 7.72ꢀ7.65 (3H, m), 4.77 (1H, s), 1.67 (3H, s), 1.55
13
(
3H, s). C NMR (100 MHz, CDCl
3
, 303 K) δ: 180.3, 175.2, 170.2, 134.5, 132.7,
131.1, 113.5, 129.5, 125.1, 126.7, 95.5, 67.3, 27.1, 21.9. Data are consistent with those
4
7
reported in the literature.
General procedure for the synthesis of βꢀlapachone (4): Sulfuric acid was
slowly added to lapachol (1) (1 mmol, 242 mg) until complete dissolution of the
quinone. Then, the solution was poured into ice and the precipitate formed was filtered
and washed with water. βꢀLapachone (4) was recrystallized in an appropriate solvent, as
for instance, ethanol. Compound 4 was obtained as an orange solid (240 mg, 99%
1
yield); m.p. 153ꢀ155 ºC. H NMR (400 MHz, CDCl
3
, 303 K) δ: 8.06 (dd, 1H, J = 7.6
and 1.4 Hz), 7.81 (dd, 1H, J = 7.8 and 1.1 Hz), 7.65 (ddd, 1H, J = 7.8, 7.6 and 1.4 Hz),
.51 (td, 1H, J = 7.6, 7.6 and 1.1 Hz), 2.57 (t, 2H, J = 6.7 Hz), 1.86 (t, 2H, J = 6.7 Hz),
7

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13
1
.47 (s, 6H). C NMR (100 MHz, CDCl , 303 K) δ: 179.8, 178.5, 162.0, 134.7, 132.6,
3
130.6, 130.1, 128.5, 124.0, 112.7, 79.3, 31.6, 26.8, 16.2. Data are consistent with those
4
8,49
reported in the literature.
General Procedure for the Syntheses of P1 and the iodinated derivative 5
3
9,50
(Oxazole Formation):
To a solution of 3ꢀazideꢀnorꢀβꢀlapachone (3) (1.0 mmol) or
βꢀlapachone (4) (242 mg, 1 mmol) in acetic acid (10 mL), salicylaldehyde (244 mg, 0.2
mL, 2.0 mmol) or 2ꢀhydroxyꢀ3,5ꢀdiiodobenzaldehyde (561 mg, 1.5 mmol) was added,
and the mixture was heated to 70 ºC; at this point, ammonium acetate (1.54 g, 20 mmol)
was slowly added, and the temperature was maintained at 110 ºC. All the reactions were
monitored by thin layer chromatography and it was observed that after four hours all the
starting material was consumed. At this point, the reaction was cooled to room
temperature and extracted with dichloromethane and dried with Na SO . The solvent
2
4
was removed under reduced pressure to afford the crude product, which was purified on
a silica column using a gradient mixture of hexane/ethyl acetate as eluent (1% of ethyl
acetate in hexane).
Compound P1 was obtained as a white solid (196 mg, 0.7 mmol, 72% yield);
1
m.p. 169ꢀ170 °C
.
H NMR (400 MHz, CDCl , 303 K) δ: 1.58 (s, 3H), 1.73 (s, 3H), 5.13
3
(s, 1H), 7.03 (ddd, 1H, J = 7.9, 7.3 and 1.1 Hz), 7.15 (ddd, 1H, J = 8.3, 1.1 and 0.4 Hz),
7.42 (ddd, 1H, J = 8.3, 7.3 and 1.7 Hz), 8.06 (ddd, 1H, J = 7.9, 1.7 and 0.4 Hz), 7.55
(ddd, 1H, J = 8.3, 7.0 and 1.2 Hz), 7.71 (ddd, 1H, J = 8.3, 7.0 and 1.2 Hz), 8.11 (ddd,
13
1
H, J = 8.3, 1.2 and 0.8 Hz), 8.44 (ddd, 1H, J = 8.3, 1.2 and 0.8 Hz), 11.38 (s, 1H). C
NMR (100 MHz, CDCl , 303 K) δ: 22.3, 27.4, 69.4, 91.4, 102.7, 111.1, 117.3, 119.1,
3
119.7, 122.5, 123.4, 125.4, 126.5, 126.6, 128.6, 130.1, 132.7, 143.2, 155.5, 157.7,
+
+
1
17 4 3
60.6. EI/HRMS (m/z) [M+H] : 373.1285. Cald. for [C21H N O ] : 373.1300.

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Compound 5 was obtained as a grey solid (378 mg, 0.76 mmol, 76% yield); m.p.
1
279ꢀ280 °C
.
H NMR (400 MHz, CDCl , 303 K) δ: 1.43 (s, 6H), 1.95 (t, 2H, J = 6.6
3
Hz), 3.06 (t, 2H, J = 6.6 Hz), 7.43ꢀ7.49 (m, 1H), 7.53ꢀ7.60 (m, 1H), 8.05 (d, 1H, J = 2.1
1
3
Hz), 8.20 (d, 1H, J = 2.1 Hz), 8.21ꢀ8.26 (m, 2H). C NMR (100 MHz, CDCl
3
, 303 K)
δ: 17.4, 26.7, 31.6, 75.7, 81.0, 86.5, 101.6, 113.2, 121.6, 122.9, 124.3, 125.2, 127.2,
127.4, 134.4, 139.1, 146.9, 148.4, 149.0, 156.2, 157.7.
Click chemistry reaction for preparing P2 was accomplished as previously
4
0
classical procedure described by Sharpless with minor modifications. Compound P1
.
(136 mg, 0.5 mmol) was reacted with CuSO
4
5H
2
O (0.04 mmol), sodium ascorbate
(0.15 mmol) and 1ꢀpentadecyne (217 mg, 0.28 mL, 1.0 mmol) in a mixture of
CH Cl :H O (15 mL, 2:1, v/v). The mixture was stirred at room temperature, and, the
2
2
2
reaction was monitored by thin layer chromatography. The aqueous phase was extracted
with CH Cl , dried over anhydrous Na SO and concentrated under reduced pressure.
2
2
2
4
The residue was purified by column chromatography on silica gel eluting with a
gradient mixture of hexane:ethyl acetate. With 1% of ethyl acetate in hexane the product
was eluted and isolated as a white solid. Compound P2 was obtained as a white solid
1
(
162 mg, 0.38 mmol, 75% yield); m.p. 143ꢀ144 °C. H NMR (400 MHz, CDCl , 303 K)
3
δ: 0.87 (t, 3H J = 7.0 Hz), 1.10ꢀ1.33 (m, 23H), 1.55 (q, 2H, J = 7.4 Hz), 1.76 (s, 3H),
2
.53ꢀ2.68 (m, 2H), 6.47 (s, 1H), 6.81 (s, 1H), 6.96 (ddd, 1H, J = 7.9, 1.7 and 0.4 Hz),
.11 (ddd, 1H, J = 8.3, 1.1 and 0.4 Hz), 7.39 (ddd, 1H, J = 8.3, 7.2 and 1.7 Hz), 7.62
7
(ddd, 1H, J = 8.3, 7.0 and 1.2 Hz), 7.78 (ddd, 1H, J = 8.3, 7.0 and 1.2 Hz), 7.87 (ddd,
1
8
2
9
H, J = 7.9, 1.7 and 0.4 Hz), 8.19 (ddd, 1H, J = 8.3, 1.2 and 0.8 Hz), 8.48 (ddd, 1H, J =
13
3
.3, 1.2 and 0.8 Hz), 11.31 (s, 1H). C NMR (100 MHz, CDCl , 303 K) δ: 14.1, 21.7,
2.7, 25.7, 27.3, 29.1, 29.2, 29.3, 29.4(6), 29.5(5), 29.5(8), 29.6(1), 29.6(4), 31.9, 68.1,
1.9, 117.2, 101.3, 110.7, 119.1, 119.7, 119.9, 122.6, 123.5, 125.8, 126.6, 126.9, 129.1,

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3
1
30.6, 132.9, 142.6, 148.8, 156.1, 157.7, 160.9. Two C resonances were observed at
13
2
9.2, as confirmed by HSQC analysis. Some of the C chemical shifts were indicated
with two decimals in order to differentiate nuclei with very similar resonance
+
+
45 4 3
frequencies. EI/HRMS (m/z) [M+H] : 581.3501. Cald. for [C36H N O ] : 581.3491.
General Procedure for the Syntheses of P3 and P4 (Suzuki reaction): In a
Schlenk tube was added iodinated oxazole 5 (239 mg, 0.4 mmol), phenylboronic acid
(1,0 mmol), palladium(II) acetate (3 mg, 0.01 mmol), triphenylphosphine (11 mg, 0.04
mmol) sodium carbonate (350 mg, 3.2 mmol), 2 mL of water, 1 mL of methanol and 12
mL of toluene. The Schlenk tube was sealed and heated to 70 °C for 36 hours. The
reaction was cooled to room temperature and the solvent was evaporated under reduced
pressure. The product was extracted with dichloromethane and dried with Na SO . The
2
4
solvent was removed under reduced pressure to afford the crude product, which was
purified on a silica column using a gradient mixture of hexane/ethyl acetate as eluent
(1% of ethyl acetate in hexane).
Compound P3 was obtained as a yellow solid (160 mg, 0.30 mmol, 80% yield);
1
m.p. 247ꢀ248 °C. H NMR (400 MHz, CDCl , 303 K) δ: 1.49 (s, 6H), 2.01 (t, 2H, J =
3
6.6 Hz), 3.14 (t, 2H, J = 6.6 Hz), 7.44ꢀ7.53 (m, 5H), 7.60 (ddd, 1H, J = 8.3, 6.9 and 1.2
Hz), 7.66ꢀ7.69 (m, 2H), 7.72ꢀ7.76 (m, 2H), 8.23 (d, 1H, J = 2.4 Hz), 8.30 (dd, 2H, J =
1
3
8
7
1
3
.3 and 1.1 Hz), 12.20 (s, 1H). C NMR (100 MHz, CDCl , 303 K) δ: 17.5, 26.8, 31.7,
5.5, 101.7, 112.1, 121.6, 122.8, 123.8, 124.2, 124.4, 124.9, 126.9, 127.1, 127.4, 127.5,
28.2, 128.9, 129.5, 130.6, 132.1, 132.7, 137.9, 140.4, 146.5, 148.4, 154.4, 160.4. Two
C resonances were observed at 127.1, as confirmed by HSQC analysis. EI/HRMS
1
3
+
+
(
3
m/z) [M+H] : 498.2063. Cald. for [C34H28NO ] : 498.2069.
Compound P4 was obtained as a yellow solid (100 mg, 0.18 mmol, 61% yield);
1
m.p. 227ꢀ228 °C. H NMR (400 MHz, CDCl
3
, 303 K) δ: 1.48 (s, 6H), 2.00 (t, 2H, J =

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.4 Hz), 3.13 (t, 2H, J = 6.4 Hz), 3.85 (s, 3H), 3.87 (s, 3H), 6.99 (d, 1H, J = 8.7 Hz),
.03 (d, 1H, J = 8.4 Hz), 7.44ꢀ7.52 (m, 1H), 7.55ꢀ7.63 (m, 4H), 7.67 (d, 2H, J = 8.4 Hz),
13
.12 (d, 1H, J = 1.8 Hz), 8.28 (d, 1H, J = 8.6 Hz), 12.11 (s, 1H). C NMR (100 MHz,
, 303 K) δ: 17.5, 26.8, 31.7, 55.4, 75.5, 101.7, 111.9, 113.7, 114.3, 121.6, 122.8,
22.9, 124.1, 124.4, 124.8, 127.0, 127.5, 127.9, 130.1, 130.3, 130.6, 131.6, 132.4,
CDCl
3
1
1
+
33.1, 146.4, 148.3, 159.0, 159.1, 153.9, 160.6. EI/HRMS (m/z) [M+H] : 558.2285
+
Cald. for [C H NO ] : 558.2280.
36
32
5
ASSOCIATED CONTENT
D and 2D NMR spectra, HRMS [ESI(+)ꢀMS], photophysical analyses, cellular
1
experimental procedures and Cartesian coordinates for the calculated structures, and
energy and thermal corrections. The Supporting Information is available free of charge
at DOI: xxxxx.
ACKNOWLEDGMENTS
This research was funded by grants from CNPq (PVE 401193/2014ꢀ4), FAPEMIG
(Edital 01/2014 (APQꢀ02478ꢀ14) and Programa Pesquisador Mineiro – PPM X),
CAPES, FAPDF, FINATEC, DPPꢀUnB, INCTꢀTranscend group and
CAPES/PROCAD.
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