Fluorescence switching of photochromic vinylpyrene-substituted 2′-deoxyguanosine

Article abstract of DOI:10.1016/j.tetlet.2009.01.029

We synthesized C8-vinylpyrene-substituted 2′-deoxyguanosine ^VPyG and studied the photoregulated reversible E-Z isomerization. When E-isomer was irradiated with visible light (>420 nm), E- to Z-isomerization took place very rapidly, while upon i

Full text of DOI:10.1016/j.tetlet.2009.01.029

Tetrahedron Letters 50 (2009) 1403–1406
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Tetrahedron Letters
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Fluorescence switching of photochromic vinylpyrene-substituted
0
2
-deoxyguanosine
Yoshio Saito a, , Katsuhiko Matsumoto , Yoshiki Takeuchi , Subhendu Sekhar Bag , Satoshi Kodate ,
a
a
a
a
*
b
a,
*
Takashi Morii , Isao Saito
a
Department of Materials Chemistry and Engineering, School of Engineering, Nihon University, Koriyama, Fukushima 963-8642, Japan
Institute of Advanced Energy, Kyoto University, Uji, Kyoto 611-0011, Japan
b
a r t i c l e i n f o
a b s t r a c t
We synthesized C8-vinylpyrene-substituted 2 -deoxyguanosine VPyG and studied the photoregulated
reversible E–Z isomerization. When E-isomer was irradiated with visible light (>420 nm), E- to Z-isomer-
ization took place very rapidly, while upon irradiation with UV-light (ꢀ365 nm), Z-isomer was converted
0
Article history:
Received 14 November 2008
Revised 26 December 2008
Accepted 8 January 2009
Available online 15 January 2009
to E-isomer. When Z-isomer was illuminated with 365–400 nm light, no fluorescence was observed,
while E-isomer showed a very strong fluorescence emission, indicating that
VPy
G could be a useful fluo-
rescence switching molecule.
Ó 2009 Elsevier Ltd. All rights reserved.
The design and synthesis of photoswitching molecules have at-
tracted currently much attention for devising molecular devices
such as molecular switches and sensors. Particularly, fluorescence
of nucleoside 5 with 1-bromopyrene in the presence of sodium
acetate gave compound 6 in a moderate yield, which upon treat-
ment with NH OH afforded the desired photochromic nucleoside
4
1
switch is of special importance due to its high sensitivity and selec-
tivity for the application to optical devices, fluorometric assay of
1. During isolation process under room light, initially formed Z-iso-
mer was gradually photoisomerized to give a mixture of E- and
Z-isomers. Both E- and Z-isomers were separated in a pure form
using HPLC with 100% methanol as an eluting solvent.5
2
biomolecules as well as bioimaging. We now wish to report a un-
0
ique ‘on–off’ fluorescence switching of vinylpyrene-substituted 2 -
deoxyguanosine, which would find widespread application as a
photochromic nucleobase for fluorometric sensing, bioimaging,
optical devices and photoregulation of nucleic acid structures
Next, we examined the photoisomerization in methanol. Upon
illumination of E- G with visible light (k > 420 nm), a photosta-
VPy
tionary state containing Z-form in a major quantity (92%) was ob-
tained as determined by HPLC. E-form was regenerated by
irradiation of Z-form with UV light (ꢀ365 nm), and it was obtained
in 82% yield. The E/Z ratios were calculated at a photostationary
state by measuring HPLC peak area as detected at the wavelength
(Fig. 1).
Our long-term interest in designing base-discriminating fluo-
3
rescent (BDF) nucleosides has led us to develop a novel vinylpy-
VPy
rene-substituted guanosine derivative
G, which reversibly
photoisomerized on illuminating at k > 350 nm where no UV dam-
age occurred on DNA. This molecule showed a fluorescence emis-
sion that can be ‘on–off’ modulated with high sensitivity owing
of isosbestic point (368 nm). These results indicate that highly
VPy
reversible E to Z photoisomerization of
G can be accomplished
6
by illumination at 365 nm and 420 nm (Fig. 2). Thus, the E–Z
VPy
to its rapid photoisomerization between fluorescent (E-form) and
isomerization of photoresponsive
G was conducted by 420 nm
VPy
non-fluorescent states (Z-form).
G can therefore be used as a
light separated from a 100 W Xenon lamp by a filter solution and
fluorescence switching molecule.
We have designed the photoswitchable nucleoside, C8-vinylpy-
0
VPy
rene-substituted 2 -deoxyguanosine 1 ( G). Pyrene was chosen
because its absorption maximum lies around 350 nm where no
natural nucleotides absorb light. The photochromic compound 1
O
N
λ
> 420 nm
O
N
N
N
0
NH
NH2
N
N
was synthesized according to Scheme 1. Thus, 8-bromo-2 -deoxy-
NH
NH2
guanosine 3 was treated with N,N-dimethylformamide diethylac-
etal in methanol at 60 °C to afford N -protected nucleoside 4,
HO
HO
O
2
λ = 365 nm
O
OH
which was then converted to C8-vinyl derivative 5 under Stille
OH
1
2
4
coupling conditions. A second round of Pd(0)-mediated coupling
Fluorescence
Non-fluorescence
*
Corresponding authors.
E-mail address: saitoy@chem.ce.nihon-u.ac.jp (Y. Saito).
Figure 1. Fluorescence ‘on–off’ switching induced by E–Z photoisomerization of
VPy
photochromic base
G.
0
040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.01.029

1
404
Y. Saito et al. / Tetrahedron Letters 50 (2009) 1403–1406
O
N
O
O
N
N
N
N
N
N
NH
NH
N
NH
N
Br
a
Br
b
N
NH2
N
N
N
HO
HO
HO
O
O
O
OH
OH
OH
3
4 (98 %)
5 (62 %)
O
N
O
N
N
N
N
NH
c
NH
N
d
N
N
NH2
HO
HO
O
O
OH
OH
6
(77 %)
1 (quant.)
Scheme 1. Synthesis of photochromic nucleoside VPyG. Reagent and conditions: (a) DMF diethylacetal, methanol, 60 °C, 3 h; (b) Pd(PPh
)
3
4
2 4 3
, Sn(CHCH ) , Et N, DMF, 60 °C,
1
2 h; (c) 1-bromopyrene, Pd(PPh
3 4
) , CH
3
COONa, DMF, 80 °C, 12 h; (d) NH
4
OH/methanol, rt, 8 h.
a
b
E
Z
0
.6
0s
0
0
0
0
0
.5
.4
.3
.2
.1
0
E-isomer
Z-isomer
10s
0
0
0
0
0
.5
.4
.3
.2
.1
0
30s
60s
0s
120s
50s
180s
9
1
2
2
2
3
10s
40s
70s
00s
2
20
270
320
370
420
470
250
300
350
400
450
500
wavelength (nm)
wavelength (nm)
c
e
Z
E
d
1
0
0
0
0
0
.5
.4
.3
.2
.1
0
0
1
3
5
s
s
s
s
00
8
0
0
0
10s
6
4
2
3
4
5
6
0s
0s
0
0s
0s
20
0
250
300
350
400
450
500
0
100
200
300
wavelength (nm)
time (s)
f
365nm 1min >420nm 5min
0.4
100
8
0
0
0
0
0.3
6
4
2
0
.2
.1
0
0
0
0
2
4
6
8
10
0
20
40
60
Cycles
time (s)
Figure 2. (a) Absorption spectra of E- and Z-VPyG. Spectral change for photoirradiation of (b) Z- to E-isomer and (c) E to Z-isomer. Time course for the photoisomerization of
d) Z to E and (e) E to Z. (f) Switching cycles between E- and Z-isomer. It was monitored at 410 nm UV–vis absorbance.
(
by 365 nm light from a UV-transilluminator. Photoirradiation of
E- G at 420 nm resulted in a rapid decrease in the absorption
at 405 nm with a blue shift of ca. 40 nm and in an increase in the
absorption at 280 nm with a blue shift of ca. 2 nm, indicating a
VPy

Y. Saito et al. / Tetrahedron Letters 50 (2009) 1403–1406
1405
a
b
E-isomer Z-isomer
E-isomer Z-isomer
c
140
d
6
3463
E-emission
Z-emission
E-excitation
Z-excitation
6
4
2
0000
1
1
20
00
0000
0000
0
8
0
0
0
0
6
4
2
599
0
3
00
400
500
600
E-isomer
Z-isomer
wavelength (nm)
Figure 3. (a) Visible color of Z- and E-isomers in methanol. (b) Fluorescence image of E- and Z-isomers illuminated at 365 nm. (c) Fluorescence spectra and fluorescence
excitation spectra of E- and Z-isomers. (d) Fluorescence intensity of E- and Z-isomers as determined by fluorescence plate reader.
Table 1
quantitative E to Z photoisomerization (Fig. 2b). On the other hand,
when Z- G was illuminated at 365 nm, the absorbance of the
Photophysical data for E- and Z- VPyG in methanol
VPy
a
peak at 280 nm decreased with a red shift of 2 nm, while the inten-
sity of the peak at 365 nm increased with a red shift of ca. 40 nm
Isomer
e
360
e
410
k
max (nm)
u
F
F
s (ns)
E
Z
22,200
30,800
38,600
3800
489
—
0.43 (kex = 410 nm)
ꢀ0 (kex = 410 nm)
2.3
—
(Fig. 2c). In the case of Z to E photoisomerization, the photostation-
ary state was attained within 60 s (Fig. 2e). To reach the photosta-
tionary state from E-isomer, longer irradiation time (>170 s) was
required (Fig. 2d). Such reversible photoisomerization was re-
peated more than 10 times without any side reaction (Fig. 2f).
Interestingly, we observed a visible yellow color and bright bluish
green fluorescent for E-isomer, while no visible color and no fluo-
a
A single component.
In conclusion, we have successfully developed photochromic
0
VPy
C8-vinylpyrene-substituted 2 -deoxyguanosine ( G) as a photos-
witching molecule. The nucleoside showed a very rapid and
reversible photoisomerization without any side reaction. We have
also demonstrated that E-isomer emits a strong fluorescence, while
8
rescence were observed for Z-isomer (Fig. 3a and b). We examined
VPy
the fluorescence behavior of photochromic
G as a photoswitch-
ing fluorescent molecule in more detail. Interestingly, when ex-
cited in the 365–400 nm region, Z-isomer 2 showed almost no
fluorescence, whereas E-isomer 1 showed a strong fluorescence
with an emission maximum at 490 nm (Fig. 3c). Very weak fluores-
cence at 490 nm observed for Z-isomer (Fig. 3c) was ascribable to
the fluorescence of a small amount of E-isomer formed during fluo-
rescence measurement. This was further confirmed by the fluores-
cence excitation spectra of the low intensity fluorescence peak at
Z-isomer does not. Therefore, due to the drastic fluorescence
VPy
change, the photochromic guanine base
fluorescence switching molecule.
G might be a very useful
Acknowledgments
This work was supported by a Grant-in-Aid for Scientific re-
search of MEXT, Japanese Government.
4
90 nm, which was identical with that of the fluorescence excita-
tion spectra of E-isomer, not for the Z-isomer. We also measured
the fluorescence intensity of E- and Z-isomers by using fluores-
cence plate reader within a time scale of 0.1 s in methanol (excited
at 355 nm, detected at 535 nm) (Fig. 3d). The data clearly indicated
that Z-isomer is non-fluorescent. The fluorescence lifetime of E-iso-
mer was also measured in methanol at room temperature. These
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2009.01.029.
References and notes
VPy
photophysical properties of E- and Z- G are summarized in Table
1
.
1
.
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K.; Shin, Y. S.; Tseng, H.-R.; Stoddart, J. F.; Heath, J. R. Nature 2007, 445, 414;
Thus, we concluded that E-isomer is in the fluorescence ‘on’
state, while Z-isomer is in the ‘‘off” state. The lack of fluorescence
emission for Z-isomer is probably due to the strong interaction of
photoexcited pyrene moiety with neighboring electron-donating
guanine base. We observed a good reversibility of E–Z photoiso-
merization without any side reaction (Fig. S1).
(
c)Molecular Devices and Machines: A Journey into the Nano World; Balzani, V.,
Credi, A., Venturi, M., Eds.; Wiley-VCH: Weinheim, 2003; (d) Irie, M.; Mrozek, T.;
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2.

1
3
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Y. Saito et al. / Tetrahedron Letters 50 (2009) 1403–1406
(complex 10H), 10.74 (br, 1H); 13C NMR (DMSO-d
C.; Hell, S. W.; Jakobs, S. Nature Biotechnol. 2008, 26, 1035; (b) Folling, J.; Belov,
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6
, 100 MHz) d 40.5, 61.2, 70.3,
82.5, 87.3, 116.7, 118.2, 122.4, 123.8, 123.9, 124.2, 125.3, 125.3, 125.6, 126.4,
127.3, 127.5, 128.0, 128.0, 128.4, 130.0, 130.3, 130.7, 130.9, 144.5, 151.8, 153.3,
156.4. 2 (Z-isomer): 1H NMR (DMSO, 400 MHz) d; 1.82 (ddd, 1H, J = 2.8, 6.4,
13.1 Hz), 2.74–2.81 (m, 1H), 3.56–3.65 (m, 1H), 3.67–3.72 (m, 1H), 4.38–4.42 (m,
1H), 5.04 (dd, 1H, J = 5.76, 5.76 Hz), 5.20 (d, 1H, J = 4.4 Hz), 6.28 (dd, 1H, J = 6.4,
.
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1
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8.2 Hz), 7.09 (d, 1H, J = 12.3 Hz), 7.76 (d, 1H, J = 12.3 Hz), 7.99 –8.73 (complex,
+
9H), 10.58 (br, 1H); HR-ESIMS m/z calcd for [C28
H
23
5
N O
4
+ Na] 516.1648 found
516.1643.
4
.
.
(a) Milstein, D.; Stille, J. K. J. Am. Chem. Soc. 1978, 100, 3636; (b) Stille, J. K. Angew.
Chem., Int. Ed. Engl. 1986, 25, 508; (c) Mitchell, T. N. Synthesis 1992, 803; (d)
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S. S.; Giovanni, B. R.; Ronaldo, A. P.; Marcos, N. E. J. Org. Chem. 2007, 72, 5809.
6. Quantum yields of E- to Z- and Z- to E-conversions were approximately 0.09 and
0.46, respectively, as determined by using azobenzene as an actinometer.7
7. (a) Yamashita, S.; Ono, H.; Toyama, O. Bull. Chem. Soc. 1962, 35, 1849; (b) Conti,
I.; Marchioni, F.; Credi, A.; Orlandi, G.; Rosini, G.; Garavelli, M. J. Am. Chem. Soc.
2007, 129, 3198.
0
1
5
C8-vinylpyrene-substituted 2 -deoxyguanosine (1). (E-isomer): H NMR (DMSO,
400 MHz) d; 2.18 (ddd, 1H, J = 2.3, 6.2, 13.1), 2.51 (m, 1H), 3.69–3.80 (complex,
2H), 3.90 (ddd, 1H, 3.6, 3.6, 3.6), 4.52 (m, 1H), 5.27 (dd, 1H, J = 5.3, 5.3), 5.34 (d,
1H, J = 4.1), 6.50 (dd, 1H, 6.2, 8.7), 6.59 (s, 2H), 7.84 (d, 1H, J = 15.5 Hz), 8.10–8.70
8. For recent reports on photochromic nucleobases, see; (a) Ogasawara, S.; Saito, I.;
Maeda, M. Tetrahedron Lett. 2008, 49, 2479; (b) Ogasawara, S.; Maeda, M. Angew.
Chem., Int. Ed. 2008, 47, 8839.