6-Arylcoumarins: versatile scaffolds for fluorescent sensors

Article abstract of DOI:10.1039/c5nj01609f

Fluorescent sensors are used in many fields of scientific research. Here, we proposed that 6-arylcoumarins could be scaffolds for various types of fluorescent sensor. From our newly synthesized 6-arylcoumarins, 6-(p-cyanophenyl)-7-hydroxycoumarin was foun

Full text of DOI:10.1039/c5nj01609f

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6-Arylcoumarins: Versatile Scaffolds for Fluorescent Sensors
Takuya Shiraishi,a Hiroyuki Kagechikaa and Tomoya Hirano*a
Received 00th January 20xx,
Accepted 00th January 20xx
Fluorescent sensors are used in many fields of scientific research. Here, we proposed that 6-arylcoumarins could be
scaffolds for various types of fluorescent sensor. From our newly synthesized 6-arylcoumarins, 6-(p-cyanophenyl)-7-
hydroxycoumarin was found as a ratiometric viscosity sensor, that is, it exhibits two fluorescent peaks in low-viscosity
solution, but only one in high-viscosity solution. In addition, 6-arylcoumarins bearing a 7-methoxy or 7-hydroxyl group
exhibit large shifts of fluorescence maximum wavelength that are dependent upon the 6-aryl substituents. So we
considered that these compounds would be good candidates as scaffolds for fluorescent sensors that would utilize the
shift of fluorescence maximum wavelength for analyte detection. To validate this idea, we designed, synthesized and
characterized two sodium ion sensors, in which a 15-crown-5 ether moiety is attached to the 6-phenyl group of these
scaffolds as the recognition site; these sensors exhibit a blue shift of the fluorescence maximum wavelength in the
presence of sodium ion. Our results suggest that 6-arylcoumarins are available as versatile scaffolds for various types of
DOI: 10.1039/x0xx00000x
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fluorescent
sensors.
for various ions, proteins, organ or specific types of cells.9 As
this approach, we also constructed a library of coumarin
derivatives, and discovered fluorescent bioactive compound,
i.e., a progesterone receptor (PR) ligand,10 whose fluorescence
intensity was increased upon binding to PR, and fluorescent
sensor that responds to specific range of pH.11 In the present
work, we set out to further expand the library of coumarin
derivatives, focusing on 7-substituted 6-arylcoumarins, with
the aim of discovering suitable scaffolds for novel fluorescent
sensors.
Introduction
Fluorescent sensors, whose fluorescence properties are
altered by a specific analyte, have been widely utilized in
various fields of scientific research.1 For development of novel
sensors, knowledge of the structure-fluorescence relationship
of the scaffold is important. For example, in the case of
fluorescein, derivatives with an electron-donating group (such
as an amino group) attached to the benzoic acid moiety are
weakly fluorescent, whereas those with
a non-electron-
donating group (such as an amido group) are strongly
fluorescent.2 Thus, substituents can be used to regulate the
fluorescence intensity with little change of the fluorescence
maximum wavelength, and this has enabled development of a
range of sensors for various analytes.3 Our group has
synthesized various 6-aryl-7-diethylaminocoumarins (1) (Figure
1) and 6-aryl-3-triazoylarylcoumarins, and based on a study of
their fluorescence properties, we have developed a number of
sensors, including nitric oxide sensors and multi-analyte sensor
candidates, whose modes of fluorescence change vary
depending upon the analyte.4 In addition, a wide diversity of
the structure and fluorescent property of fluorescent
compounds could be utilized to develop a novel sensor,
especially that with unpredictable function. Such a diversity-
oriented fluorescence library approach (DOLFA)5 has been
applied to various dyes, including styryl dyes,6 benzimidazole
dyes7 and xanthene dyes,8 and has yielded fluorescent sensors
Figure 1. Structures of 6-arylcoumarins.
RESULTS AND DISCUSSION
Synthesis of 6-aryl-7-methoxy- and 6-aryl-7-hydroxycoumarins
Our group previously reported the synthesis of various 6-
aryl-7-diethylaminocoumarin derivatives
(
1
)
via Suzuki-
Miyaura coupling between 6-bromocoumarin and various
arylboronic acid derivatives. The fluorescence intensity of
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these compounds is greatly influenced by the substituent Fluorescence properties of 6-aryl-7-methoxy- and 6-aryl-7-
group ( ) on the 6-aryl ring, although the shift of the hydroxycoumarins
R
fluorescence maximum wavelength is relatively small (less
than 20 nm).4a On the other hand, the 7-substituent can
influence both the fluorescence intensity and the fluorescence
maximum wavelength via photophysical processes such as
intermolecular charge transfer (ICT) and twisted
intermolecular charge transfer (TICT).1a,12 Because 6-aryl ring
and 7-positions could interact sterically, we were interested in
further investigating the fluorescence properties of 7-
substituted 6-arylcoumarins. In this work, we synthesized a
The fluorescence properties of 2a - 2f and 3a - 3f were
studied in acetonitrile and methanol (Table 1), and typical
absorption and fluorescence spectra are shown in Figure S1
and Figure S2. In 6-aryl-7-methoxycoumarins (2), the effect of
substituents at the 6-aryl group on the absorption maximum
wavelength was relatively small, whereas the effect on the
fluorescence maximum wavelength was large, up to 76 nm (2b
vs 2d in methanol). 6-Aryl-7-hydroxycoumarins (
similar behavior in acetonitrile, and the range of fluorescent
maximum wavelength was up to 57 nm 3b vs 3e).
3) showed
series of 6-aryl-7-methoxycoumarins
hydroxycoumarins ( ), as shown in Scheme 1. Compounds 2a
2f were derived from 6-bromo-7-methoxycoumarin ( ) and
arylboronic acid derivatives 6a - 6f. Demethylation of 2a 2e
yielded 3a 3e, and 3f was synthesized from 6-bromo-7-
hydroxycoumarin ( ) and 6f
(
2)
and 6-aryl-7-
(
3
-
Interestingly, 3b showed two fluorescence maxima at 390 and
498 nm in methanol. Dimethylamino-substituted compounds
2c and 3c showed little fluorescence in either of these
solvents. Such weak fluorescence of compounds bearing an
electron-donating group was also observed among our
previously reported 6-aryl-7-diethylaminocoumarin derivatives
4
–
-
5
.
(1), as well as in other fluorophores such as xanthene
derivatives,13 and is presumably due to a photo-induced
electron transfer (PeT) process.
Compared with our previously reported 6-aryl-7-
diethylaminocoumarins
fluorescence maximum was less than 20 nm, 6-arylcoumarins
with 7-methoxy or 7-hydroxy group ( ) showed a large
(1), in which the change of
2, 3
dependence of the fluorescence maximum wavelength on the
substituent groups in the 6-aryl ring. Therefore, these
compounds might be useful as scaffolds of fluorescent sensors
that would utilize the shift of fluorescence maximum
wavelength for analyte detection.
Table 1. Photophysical properties of
in acetonitrile
2 and 3.
in methanol
Comp.
(R)
Absmax Emmax Q.Y.c
(nm) (nm)
328
Absmax Emmax
(nm) (nm)
Q.Y.c
2a (H)
2b (CN)
2c (NMe2)
399 0.028 330 403
0.15
0.18
n.d.b
0.13
<0.01
0.16
0.24
328
a
381 0.029 330 385
a
-
n.d.b n.d.b
-
n.d.b
2d (NHAc) 331
2e (OH) 332
2f (OMe) 331
436 0.066 334 461
441 0.047 335 452
435 0.13
334 454
3a (H)
329
330
395 0.031 334 407
3b (CN)
384 0.043 334 390, 498 0.27
3c (NMe2) 342
3d (NHAc) 331
n.d.b n.d.b
436 0.12
441 0.11
345 n.d.b
336 457
339 469
n.d.b
0.14
<0.01
0.34
3e (OH)
332
3f (OMe) 332
433 0.048 337 452
aNot determined. bNo fluorescence peak was detected.
cQuantum yields of fluorescence were determined using that
of quinine sulfate in 0.1 M H2SO4 (0.577) as a standard.1a
Scheme 1. Synthesis of 6-aryl-7-methoxy- and 6-aryl-7-
hydroxycoumarins and
2
3.
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Development of sodium ion sensors utilizing the shift of
fluorescence maximum wavelength
The absorption (Figure S3) and fluorescence spectra (Figure
3) of 2g and 3g were examined. For both compounds, the
absorption spectra showed almost no change upon addition of
sodium ion. On the other hand, the fluorescence maximum
was shifted from 466 nm to 436 nm for 2g and from 467 nm to
433 nm for 3g. These data indicate that 2g and 3g could be
utilized as sodium ion sensors, utilizing the shift of
fluorescence maximum in the presence of sodium ion.
To confirm the suitability of 7-methoxy or 7-hydroxy-6-
arylcoumarins as scaffolds for fluorescent sensors we utilized
them to design candidate sensors for sodium ion, 2g and 3g
(Figure 2), in which a 15-crown-5 ether moiety is attached to
the 6-phenyl group as the recognition site.
Figure 2. Structure of sodium ion sensors.
These compounds were synthesized as shown in Scheme 2.
An arylboronic acid derivative bearing 15-crown-5 ether (6g
was prepared from 4-bromobenzo-15-crown 5-ether, and
coupled with 6-bromo-7-methoxycoumarin to afford
compound 2g. On the other hand, coupling between 6-bromo-
7-hydroxylcoumarin ( ) and 6g did not proceed. Thus, 6-
bromo-7-methoxymethoxycoumarin ( ) was prepared from
then coupled with 6g to obtain , which was deprotected to
afford compound 3g
)
(4)
5
7
5,
8
.
Figure 3. Fluorescence spectra of sodium ion sensors.
Fluorescent spectra excited at 330 nm of (a) 2g and (b) 3g with
sodium perchlorate (0
µM ~ 1000 µM) were measured in
acetonitrile (0.3% DMSO as a cosolvent).
Scheme 2. Synthesis of sodium ion sensor candidates 2g and
3g
.
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Development of viscosity sensor utilizing viscosity-sensitive
fluorescence change
and aging.16 Therefore, monitoring viscosity with high spatial
and temporal resolution is expected to be useful in cellular
biology studies and for clinical diagnosis, and several
fluorescent viscosity sensors such as 9-(dicyanovinyl)julolidine
(DCVJ) have been developed.17 To see whether our
Variations in the viscosity in biological systems are related
to physiological functions at both microscopic and macroscopic
levels.14 At the cellular level, membrane and cytoplasmic
viscosity can influence signaling pathways via modulation of
the activity or intermolecular interaction of biomolecules.15 In
the level of the organism, changes of viscosity of blood, plasma
or lymphatic fluid occur in cardiovascular diseases, diabetes
compounds
2 and 3 would also be applicable for this purpose,
we examined their fluorescence properties in various mixtures
of glycerol and ethylene glycol (0 : 100, 30 : 70, 60 : 40), which
would exhibit marked changes of viscosity (Figure 4).
Figure 4. Fluorescence spectra of compounds 2 and 3 in mixtures of glycerol and ethylene glycol.
Among these compounds, 3b showed two fluorescent
peaks at 395 nm and 492 nm in low-viscosity solution
(ethylene glycol : glycerol = 0 : 100), but only one peak at 395
nm in high-viscosity solution (ethylene glycol : glycerol = 60 :
40). The related compound 2b, which has a 7-methoxy group
instead of the 7-hydroxyl group of 3b, did not show this
feature. Compounds with a dimethylamino- or hydroxyl
group in the 6-aryl ring (2c 2e 3c 3e) showed weak
fluorescence, whereas 2a 2d 2f 3a 3d and 3f showed only
,
,
,
,
,
,
,
small fluorescence changes in response to viscosity change.
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depending on the measurement conditions, such as
concentration and temperature, x is the sensitivity of the dye
response to viscosity change, and η is the viscosity. Compared
with previously reported viscosity sensors such as DCVJ (x =
0.542),20 the value of x (0.406) is sufficiently large, suggesting
that compound 3b could be practically useful as a fluorescent
sensor for ratiometric measurement of solvent viscosity. The
7-methoxy compound (2b), did not show viscosity-dependent
fluorescence change (Figure 4), so the viscosity sensitivity
appears to depend upon the nature of the 7-substituent. If
this is so, it should be possible to develop a range of related
viscosity sensors, whose function could be activated only in
specific cells or subcellular compartments like recently
reported lysosomal viscosity sensor.21 In the case of 3b, a
little enhancement of fluorescence at basic conditions was
observed in aqueous solution, however, the intensity was
relatively weak compared with that in mixtures of ethylene
glycol and glycerol (data not shown). The elucidation of the
mechanism of fluorescent change and the work for the
development of novel functional sensor are in progress.
Conclusions
We synthesized 6-arylcoumarins bearing a 7-methoxy or
7-hydroxyl group, and found that they exhibit large shifts of
fluorescence maximum wavelength that are dependent upon
the nature of the 6-aryl substituent. We considered that
these compounds would be good candidates as scaffolds for
fluorescent sensors. To validate this idea, we designed,
synthesized and characterized two sodium ion sensors
bearing a 15-crown-5-ether recognition site in the aryl group
and confirmed that they exhibit
fluorescence maximum in the presence of sodium ion. In
addition, we found that 6-(p-cyanophenyl)-7-
a blue shift of the
Figure 5. Fluorescence properties of compound 3b. (a)
Fluorescence spectra excited at 330 nm of 3b (5 μM) in
mixtures of ethylene glycol and glycerol (0.3% DMSO as a
cosolvent). (b) Regression line between log(I395/I492) and
log(viscosity) (R2 = 0.994, x = 0.406).
hydroxycoumarin 3b exhibits two fluorescent peaks in low-
viscosity solution, but only one in high-viscosity solution, and
we show that this compound can be used as a ratiometric
solvent viscosity sensor. Our results indicate that 7-methoxy
and 7-hydroxy- 6-arylcoumarin, as well as our previously
reported 7-diethylamino derivatives, are promising scaffolds
for design of various types of fluorescent sensors.
Ratiometric measurement of fluorescence intensities at
two wavelengths is a useful technique to minimize assay
variability due to factors such as differences of sensor
concentration and photobleaching. However, only a few
ratiometric fluorescent sensors for viscosity change have
been reported.18 Since our compound 3b showed
enhancement of fluorescence intensity at 492 nm with little
change at 395 nm in response to a decrease of viscosity, it
may be a good candidate as a ratiometric sensor. Therefore,
we examined the spectra of 3b in mixtures of glycerol /
ethylene glycol with 10% increments of ethylene glycol (0% ~
70%). The absorption spectra (Figure S4) showed almost no
change, while the fluorescence spectra (Figure 5) gradually
changed as expected from the preliminary study. The
logarithmic value of the ratio of fluorescence intensities at
395 nm and 492 nm (log(I395/I492)) showed a good linear
relationship with log(viscosity) (R2 = 0.994), in accordance
with the Förster–Hoffmann equation,19 logIf = C + xlogη. In
this equation, If is the fluorescence intensity, C is a constant
EXPERIMENTAL SECTION
General: All reagents were purchased from Sigma-Aldrich
Chemical, Tokyo Kasei Kogyo, Wako Pure Chemical Industries,
and Kanto Kagaku. Silica gel for column chromatography was
purchased from Kanto Kagaku. Preparative GPC (gel
permeation chromatography) was carried out using an LC-
9201 instrument (Japan Analytical Industry). NMR spectra
were recorded on Bruker AVANCE 400 or Bruker Advance 500
spectrometer. Mass spectral data was obtained on Brucker
Daltonics microTOF-2focus in the positive and negative ion
detection modes. Melting points were taken on a Yanagimoto
micro melting point apparatus and are uncorrected. UV
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spectra were recorded with JASCO V-550, and fluorescence
spectra were recorded with JASCO FP-6600.
2e: Mp 271.0-274.8°C; 1H NMR (400 MHz, CDCl3) δ 7.45 (s,
1H), 7.38 (dd, J = 6.5, 2.1 Hz, 2H), 6.91 (dd, J = 6.6, 2.2 Hz, 2H),
6.90 (s, 1H), 6.17 (d, J = 1.2 Hz, 1H), 4.82 (s, 1H), 3.88 (s, 3H),
2.41 (d, J = 1.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 161.3,
159.6, 155.1, 154.5, 152.6, 130.9, 129.6, 127.5, 126.0, 115.2,
113.4, 112.2, 99.4, 56.1, 18.7; Anal. Calcd for C17H14O4·1/3
H2O: C, 70.82; H, 5.13. Found: C, 70.90; H, 5.08; HRMS (ESI)
calcd for C17H14O4 (M+H)+ 283.0965. Found 283.0959.
2f: Mp 220.8-222.9°C; 1H NMR (500 MHz, CDCl3) δ 7.45 (s,
1H), 7.43 (dd, J = 6.8, 2.1 Hz, 2H), 6.98 (dd, J = 6.7, 2.1 Hz, 2H),
6.90 (s, 1H), 6.17 (d, J = 1.2 Hz, 1H), 3.88 (s, 3H), 3.86 (s, 3H),
2.41 (d, J = 1.2 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 161.3,
159.6, 159.1, 154.4, 152.6, 130.6, 129.4, 127.6, 126.0, 113.7,
113.3, 112.2, 99.3, 56.1, 55.3, 18.7; Anal. Calcd for
C18H16O4·1/4 H2O: C, 71.87; H, 5.53. Found: C, 72.09; H, 5.25;
HRMS (ESI) calcd for C18H16O4 (M+H)+ 297.1121. Found
297.1126.
Synthesis
General procedure for preparation of 6-aryl-7-
methoxycoumarins (2) (2a as an example)
A solution of 6-bromo-7-methoxy-4-methylcoumarin (4) (99.5
mg, 0.370 mmol), 6a (218 mg, 1.07 mmol), cesium fluoride
(284 mg, 1.87 mmol) and PdCl2(dppf)·CH2Cl2 (60.3 mg, 0.0738
mmol) in dry N,N-dimethylformamide (7.0 ml) was stirred for
3 h at 60°C under an atmosphere of argon. Then, the reaction
mixture was cooled to room temperature and saturated
aqueous ammonium chloride was added. The mixture was
extracted with dichloromethane. The organic solution was
washed with brine and concentrated. Purification of the
residue by column chromatography (silica gel) gave 2a (86.5
mg, 88%) as yellow crystals. A small amount of the compound
was recrystallized to give an analytical sample. Mp 213.1-
General procedure for preparation of 6-aryl-7-
hydroxycoumarins (3) (3a as an example)
1
215.9°C; H NMR (500 MHz, CDCl3) δ 7.51-7.36 (m, 6H), 6.91
(s, 1H), 6.18 (d, J = 1.1 Hz, 1H), 3.88 (s, 3H), 2.42 (d, J = 1.1 Hz,
3H); 13C NMR (125 MHz, CDCl3) δ 161.2, 159.6, 154.7, 152.6,
137.1, 129.5, 128.2, 128.0, 127.5, 126.3, 113.4, 112.2, 99.4,
56.1, 18.7; Anal. Calcd for C17H14O3·1/5 H2O: C, 75.65; H, 5.38.
Found: C, 75.77; H, 5.39; HRMS (ESI) calcd for C17H14O3
(M+H)+ 267.1016. Found 267.1021.
Boron tribromide (1 M solution in dichloromethane, 3.4 ml,
3.4 mmol) was added to a solution of 2a (46.5 mg, 0.175
mmol) in dry dichloromethane (2.5 ml) at -78°C under an
atmosphere of argon. The reaction mixture was stirred for 21
h at room temperature, and added to iced water. The
mixture was extracted with dichloromethane. The organic
solution was washed with brine and concentrated to give 3a
(40.3 mg, 91%) as white cubes. A small amount of the
compound was recrystallized to give an analytical sample. Mp
235.3-239.7°C; 1H NMR (500 MHz, CDCl3) δ 7.56-7.45 (m, 6H),
6.96 (s, 1H), 6.18 (d, J = 1.1 Hz, 1H), 5.66 (s, 1H), 2.40 (d, J =
1.1 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 161.3, 156.0, 154.6,
152.5, 135.5, 129.6, 129.2, 128.6, 126.1, 125.8, 114.0, 112.4,
103.7, 18.7; Anal. Calcd for C16H12O3·1/3 H2O: C, 74.41; H,
4.94. Found: C, 74.16; H, 4.98; HRMS (ESI) calcd for C16H12O3
(M+H)+ 253.0859. Found 253.0864.
Other compounds (2b – 2f) were prepared from
4
and the
corresponding arylboronic acids (6b
– 6f). Analytical data are
given below.
2b: Mp 287.1-289.5°C; 1H NMR (500 MHz, CDCl3) δ 7.72 (d, J =
8.0 Hz, 2H), 7.61 (d, J = 8.2 Hz, 2H), 7.46 (s, 1H), 6.93 (s, 1H),
6.20 (s, 1H), 3.90 (s, 3H), 2.43 (s, 3H); 13C NMR (125 MHz,
CDCl3) δ 161.0, 159.6, 155.6, 152.4, 142.1, 132.2, 130.5,
126.5, 126.2, 119.1, 113.9, 112.9, 111.4, 100.0, 56.4, 18.9;
Anal. Calcd for C18H13NO3·1/4 H2O: C, 73.09; H, 4.60; N, 4.74.
Found: C, 73.22; H, 4.65; N, 4.76; HRMS (ESI) calcd for
C18H13NO3 (M+H)+ 292.0968. Found 292.0964.
2c: Mp 278.5-283.7°C; 1H NMR (500 MHz, CDCl3) δ 7.46 (s,
1H), 7.40 (dd, J = 6.8 Hz, 2.1 Hz, 2H), 6.88 (s, 1H), 6.80 (dd, J =
6.8 Hz, 2.1 Hz, 2H), 6.16 (d, J = 1.0 Hz, 1H), 3.88 (s, 3H), 3.00
(s, 6H), 2.41 (d, J = 1.0 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ
161.7, 160.0, 154.3, 153.0, 150.2, 130.4, 128.4, 125.9, 125.0,
113.6, 112.4, 112.2, 99.5, 56.3, 40.8, 19.0; Anal. Calcd for
C19H19NO3: C, 73.77; H, 6.19; N, 4.53. Found: C, 73.67; H, 6.20;
N, 4.81; HRMS (ESI) calcd for C19H19NO3 (M+H)+ 310.1438.
Found 310.1442.
Other compounds (3b
– 3e) were prepared from the
corresponding 7-methoxycoumarins (2b
– 2e). Analytical data
are given below.
1
3b: Mp 290.8-294.9°C; H NMR (500 MHz, DMSO-d6) δ 7.89
(dd, J = 6.6 Hz, 1.8 Hz 2H), 7.82 (dd, J = 6.7 Hz, 1.8 Hz, 2H),
7.67 (s, 1H), 6.88 (s, 1H), 6.18 (d, J = 1.0 Hz, 1H), 2.42 (d, J =
0.9 Hz, 3H) ; 13C NMR (125 MHz, DMSO-d6) δ 160.2, 158.6,
154.7, 153.9, 142.3, 132.1, 130.4, 127.5, 123.9, 119.2, 112.6,
110.9, 109.7, 103.0, 18.3; Anal. Calcd for C17H11NO3: C, 73.64;
H, 4.00; N, 5.05. Found: C, 73.36; H, 4.25; N, 5.13; HRMS (ESI)
calcd for C17H11NO3 (M+H)+ 278.0812. Found 278.0815.
1
2d: Mp 279.9-284.0°C; H NMR (400 MHz, DMSO-d6) δ 9.99
(s, 1H), 7.61 (d, J = 8.7 Hz, 2H), 7.57 (s, 1H), 7.44 (d, J = 8.6 Hz,
2H), 7.13 (s, 1H), 6.22 (d, J = 1.1 Hz, 1H), 3.85 (s, 3H), 2.43 (d, J
= 1.1 Hz, 3H) , 2.05 (s, 3H) ; 13C NMR (100 MHz, DMSO-d6) δ
168.8, 160.6, 159.8, 154.5, 154.1, 139.0, 131.8, 130.2, 127.1,
126.8, 119.1, 113.4, 111.8, 100.1, 56.8, 24.5, 18.6; Anal. Calcd
for C19H17NO4: C, 70.58; H, 5.30; N, 4.38. Found: C, 70.35; H,
5.38; N, 4.35; HRMS (ESI) calcd for C19H17NO4 (M+H)+
324.1230. Found 324.1227.
3c: Mp 238.8-242.1°C; 1H NMR (500 MHz, CDCl3) δ 7.40 (s,
1H), 7.31 (dd, J = 6.6 Hz, 2.1 Hz, 2H), 6.94 (s, 1H), 6.85 (dd, J =
6.8 Hz, 1.9 Hz, 2H), 6.15 (d, J = 1.2 Hz, 1H), 5.73 (s, 1H), 3.03
(s, 6H), 2.39 (d, J = 1.2 Hz, 3H) ; 13C NMR (125 MHz, CDCl3) δ
161.4, 156.2, 154.2, 152.6, 150.6, 129.9, 126.0, 125.7, 122.2,
113.8, 113.1, 112.1, 103.2, 40.4, 18.7; Anal. Calcd for
C18H17NO3·2/3 H2O: C, 70.34; H, 6.01; N, 4.56. Found: C,
6 | J. Name., 2012, 00, 1-3
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70.23; H, 5.83; N, 4.57; HRMS (ESI) calcd for C18H17NO3
(M+H)+ 296.1281. Found 296.1284.
hydroxide, and washed with dichloromethane. The aqueous
layer was extracted with ethyl acetate. The organic solution
was washed with brine and concentrated to give 6g as a
white solid (237 mg, 21%). 6g was used without further
purification for the next reaction. 1H NMR (400 MHz, CDCl3) δ
7.39 (dd, J = 8.0, 1.2 Hz, 1H), 7.29 (d, J = 1.2 Hz, 1H), 6.85 (d, J
= 8.0 Hz, 1H), 4.17 (m, 4H), 3.90 (m, 4H), 3.76 (m, 8H), 1.33 (s,
12H).
1
3d: Mp 243.2-247.1°C; H NMR (400 MHz, DMSO-d6) δ 9.98
(s, 1H), 7.61 (d, J = 8.7 Hz, 2H), 7.55 (s, 1H), 7.51 (d, J = 8.7 Hz,
2H), 6.85 (s, 1H), 6.14 (d, J = 1.1 Hz, 1H), 2.41 (d, J = 1.0 Hz,
3H), 2.05 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 168.5,
160.4, 158.3, 153.9, 153.7, 138.5, 131.9, 129.7, 126.8, 125.5,
118.8, 112.4, 110.7, 102.7, 24.2, 18.3; HRMS (ESI) calcd for
C18H15NO4Na (M+Na)+ 332.0893. Found 322.0894.
1
3e: Mp 284.8-289.2°C; H NMR (400 MHz, DMSO-d6) δ 10.6
Preparation of 2g
(brs, 1H), 9.44 (s, 1H), 7.50 (s, 1H), 7.39 (dd, J = 6.6, 2.0 Hz,
2H), 6.83 (s, 1H), 6.80 (dd, J = 6.7, 2.0 Hz, 2H), 6.14 (d, J = 1.2
Hz, 1H), 2.40 (d, J = 1.0 Hz, 3H) ; 13C NMR (100 MHz, DMSO-
d6) δ 160.4, 158.2, 156.7, 153.9, 153.4, 130.5, 127.9, 126.5,
125.9, 115.0, 112.4, 110.6, 102.6, 18.3; Anal. Calcd for
C16H12O4·1/6 H2O: C, 70.84; H, 4.58. Found: C, 71.10; H, 4.76;
HRMS (ESI) calcd for C16H12O4 (M+H)+ 269.0808. Found
269.0811.
Compound 2g was prepared from
4 and 6g according to the
procedure described for 2a (yield 20%, yellow solid). Mp
1
208.3-211.5°C; H NMR (400 MHz, CDCl3) δ 7.45 (s, 1H), 7.04
(d, J = 2.0 Hz, 1H), 7.02 (dd, J = 8.1, 2.0 Hz, 1H), 6.94 (d, J = 8.1
Hz, 1H), 6.89 (s, 1H), 6.17 (d, J = 1.2 Hz, 1H), 4.19 (m, 4H),
3.94 (m, 4H), 3.87 (s, 3H), 3.77 (m, 8H), 2.42 (d, J = 1.2 Hz,
3H); 13C NMR (100 MHz, CDCl3) δ 161.2, 159.6, 154.4, 152.6,
148.9, 148.7, 130.3, 127.6, 126.0, 122.5, 116.1, 113.8, 113.3,
112.2, 99.4, 71.1 (2C), 70.6 (2C), 69.7, 69.6, 69.5, 69.2, 56.1,
18.7; Anal. Calcd for C25H28O8: C, 65.78; H, 6.18. Found: C,
65.78; H, 5.98; HRMS (ESI) calcd for C25H28O8 (M+Na)+
479.1676. Found 479.1681.
Preparation of 3f
A solution of 6-bromo-7-hydroxy-4-methylcoumarin (5) (49.0
mg, 0.192 mmol), 6f (81.7 mg, 0.538 mmol) and Pd(PPh3)4
(42.1 mg, 0.0364 mmol) in dimethoxyethane (3.5 ml) was
mixed with 2 M sodium carbonate in water (2.8 ml), then
stirred for 3.5 h at 60°C under an atmosphere of argon. The
reaction mixture was cooled to room temperature, and
saturated aqueous ammonium chloride was added. The
mixture was extracted with dichloromethane. The organic
solution was washed with brine and concentrated.
Purification of the residue by column chromatography (silica
gel) gave 3f (16.7 mg, 31%) as a white powder. A small
amount of the compound was recrystallized to give an
analytical sample. Mp 243.5-246.2°C; 1H NMR (400 MHz,
CDCl3) δ 7.41 (s, 1H), 7.38 (dd, J = 6.6, 2.0 Hz, 2H), 7.06 (dd, J
= 6.7, 2.1 Hz, 2H), 6.96 (s, 1H), 6.17 (d, J = 1.1 Hz, 1H), 5.70 (s,
1H), 3.88 (s, 3H), 2.40 (d, J = 1.2 Hz, 3H); 13C NMR (100 MHz,
CDCl3) δ 161.2, 159.9, 156.0, 154.5, 152.4, 130.4, 127.4,
125.9, 125.4, 115.0, 113.9, 112.4, 103.5, 55.4, 18.7; Anal.
Calcd for C17H14O4·1/3 H2O: C, 70.82; H, 5.13. Found: C, 70.63;
H, 4.88; HRMS (ESI) calcd for C17H14O4 (M+H)+ 283.0965.
Found 283.0957.
Preparation of 7
Chloromethyl methyl ether (0.15 ml, 2.0 mmol) was added to
a solution of
5 (346 mg, 1.36 mmol) and NaH (72.1 mg, 3.00
mmol) in dry N,N-dimethylformamide (3.7 ml) at 0°C under
an atmosphere of argon. The mixture was stirred for 5 h at
room temperature, and saturated aqueous ammonium
chloride was added. The mixture was extracted with AcOEt.
The organic solution was washed with brine, dried over
Na2SO4, and concentrated. Purification of the residue by open
column chromatography (silica gel) gave
7 (384 mg, 99%) as a
1
white powder. H NMR (400 MHz, CDCl3) δ 7.76 (s, 1H), 7.14
(s, 1H), 6.18 (d, J = 1.2 Hz, 1H), 5.31 (s, 2H), 3.52 (s, 3H), 2.39
(d, J = 1.2 Hz, 3H).
Preparation of 8
Compound
8 was prepared from 7 and 6g according to the
1
procedure described for 2a. Yield 39% (yellow solid). H NMR
(400 MHz, CDCl3) δ 7.47 (s, 1H), 7.16 (s, 1H), 7.04 (d, J = 2.0
Hz, 1H), 7.02 (dd, J = 8.1, 2.0 Hz, 1H), 6.94 (d, J = 8.1 Hz, 1H),
6.19 (d, J = 0.9 Hz, 1H), 5.20 (s, 2H), 4.19 (m, 4H), 3.94 (m,
4H), 3.78 (m, 8H), 3.42 (s, 3H), 2.41 (d, J = 0.8 Hz, 3H).
Preparation of 6g
n-Butyllithium (1.6 M solution in hexane, 2.3 ml, 3.7 mmol)
was added to a solution of 4’-bromobenzo-15-crown 5-ether
(1.00 g, 2.88 mmol) in dry tetrahydrofuran (30 ml) at -78°C
under an atmosphere of argon. The reaction mixture was
stirred for 10 min, and trimethyl borate (0.40 ml, 3.7 mmol)
was added. Stirring was continued for another 30 min at -
78°C, and then the mixture was allowed to warm to room
temperature. Stirring was continued for 1.5 h, then a solution
of pinacol (429 mg, 3.63 mmol) in dry tetrahydrofuran (5 ml)
was added, and the mixture was further stirred for 5 h at
room temperature. Acetic acid (0.20 ml, 3.7 mmol) was
added, and after further stirring for 13 h, the solvent was
removed. The residue was diluted with 2 M aqueous sodium
Preparation of 3g
Trifluoroacetic acid (0.10 ml, 1.3 mmol) was added to a
solution of 8 (20.5 mg, 0.0421 mmol) in dichloromethane (0.6
ml) at 0°C. The reaction mixture was stirred for 1 h at room
temperature, and water was added. The mixture was
extracted with dichloromethane. The organic solution was
washed with brine and concentrated. Purification of the
residue by r-GPC gave 3g (18.1 mg, 97%) as a brown solid. Mp
180.1-181.9°C; 1H NMR (400 MHz, CDCl3) δ 7.41 (s, 1H), 7.01-
6.95 (m, 4H), 6.16 (s, 1H), 5.95 (brs, 1H), 4.20 (m, 4H), 3.95
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(m, 4H), 3.78 (m, 8H), 2.40 (s, 3H); 13C NMR (100 MHz, CDCl3)
δ 161.5, 156.6, 154.3, 152.8, 149.4, 149.1, 128.8, 125.7,
122.1, 115.0, 114.3, 113.6, 112.0, 103.6, 70.9 (2C), 70.3 (2C),
69.4, 69.0, 68.9, 18.7; HRMS (ESI) calcd for C24H26O8 (M+Na)+
465.1520. Found 465.1526.
Ando, Y. Kawazoe, K. Aiba, K. Nagata, E. Kawase, Y.-T.
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Acknowledgements
The work described in this paper was partially supported
by Grants-in-Aid for Scientific Research from The Ministry of
Education, Science, Sports and Culture, Japan (Grants No
24950005 and 15K08019 to TH, 26670052 and 22136013 to
HK). TH also gratefully acknowledges funding from Takeda
Science Foundation and an Azuma Medical & Dental Research
Grant. This work was partially supported by Project for
Development of Innovative Research on Cancer Therapeutics,
the Platform for Drug Discovery, Informatics, and Structural
Life Science (MEXT, Japan), and JSPS Core-to-Core Program A,
Advanced Research Networks.
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8 | J. Name., 2012, 00, 1-3
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6-arylcoumarins are available as versatile scaffolds for various types of fluorescent sensors like those for
cation and viscosity.
41x24mm (300 x 300 DPI)