An off-on fluorescent chemosensor of selectivity to Cr3+ and its application to MCF-7 cells

Article abstract of DOI:10.1016/j.tet.2011.07.008

A 'switching-on' fluorescent chemosensor for the selective and sensitive signaling of intraceullar Cr³⁺ has been designed and synthesized exploiting the guest-induced prohibition of the photoinduced electron transfer process between naphthyridi

Full text of DOI:10.1016/j.tet.2011.07.008

Tetrahedron 67 (2011) 7096e7100
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
An ‘offeon’ fluorescent chemosensor of selectivity to Cr3þ and its application
to MCF-7 cells
Zhanxian Li , Wanying Zhao , Yuna Zhang , Lifeng Zhang , Mingming Yu ,*, Jinxia Liu a,*,
a
a
a
a
a
b,
*
Hongyan Zhang
Department of Chemistry, Zhengzhou University, Zhengzhou 450001, China
a
b
Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, China
a r t i c l e i n f o
a b s t r a c t
A ‘switching-on’ fluorescent chemosensor for the selective and sensitive signaling of intraceullar Cr3þ has
been designed and synthesized exploiting the guest-induced prohibition of the photoinduced electron
transfer process between naphthyridine moiety and 7,10-diphenylfluoranthene moiety, the system
Article history:
Received 5 April 2011
Received in revised form 24 June 2011
Accepted 1 July 2011
Available online 6 July 2011
3þ
shows a Cr -selective chelation-enhanced fluorescence response not only in ethanol but in cell.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Fluorescence
Chemosensor
Metal ion recognition
3þ
Cr -selective sensor
Imaging agents
þ
1
. Introduction
et al. reported di(2-ethylsulfanylethyl)amine as Cr3 -selective
8
3þ
receptor moieties. Liu et al. reported two rhodamine-based Cr
-
9
The development of fluorescent chemical sensors is a promising
field due to their simplicity, high sensitivity, and instantaneous
response.1 Within this field, the design of fluorescent chemo-
sensors for monitoring metal ions, especially heavy and transition-
metal ions such as zinc, mercury, copper, and cadmium is an
important area because of their fundamental role in medical, en-
vironmental, and biological applications. Trivalent chromium, Cr
is one of the most important heavy metal elements and its de-
ficiency causes disturbance in the glucose levels and lipid metab-
olism. On the other hand, Cr adversely affects cellular structures
and plays an important role in the metabolism of carbohydrates,
lipids, proteins and nucleic acids, therefore, there is an urgent need
to develop fluorescent chemical sensors for Cr . But because
paramagnetic chromium ions usually quench fluorescence emis-
sion via the electron transfer and intersystem crossing (isc) pro-
cesses and lack of proper selective fluorescent chemosensors for
Cr , fluorescent sensors for Cr in solution, especially in cell is
rare up to now. Several examples of Cr -selective fluorescent
chemosensors in organic solvents have been reported. Samanta
selective fluorescent chemosensors. Only Li et al. and Duan et al.
3
þ
10
reported sensor monitoring Cr in living cells till now.
This work is aimed at the design and construction of a fluorescent
Cr3 -chemosensor to highly effectively detect Cr both in solution
andcell. In general, a fluorescent probe contains two units: detection
and fluorescence parts. For short metal/metal distance formed in
þ
3þ
2
3
4
5
3
þ
11
,
their building blocks, 1,8-naphthyridine (napy) and its derivatives
have widely been used as bidentate ligands. Therefore, 1,8-
12
13
naphthyridine group could be used as the detection unit. As for
the fluorescence unit, rigid and conjugate organic structure will be
the ideal fluorescent group. Considering the above, (E)-N-(7-((4-
(7,10-diphenylfluoranthen-8-yl)phenylimino)methyl)-5-methyl-1,
8-naphthyridin-2-yl)acetamide (1) was designed, in which, 4-
methy-7-acetamide-1,8-naphthyridyl group as the detection unit
and 4-(7,10-diphenylfluoranthenyl)benzenamine as the fluorescent
unit (Scheme 1). Both parts are linked by a C]N bond to form
a potential fluorescent-sensing molecule (1) for metal cations.
6
3þ
3
þ
3
þ
3þ
3
þ
3þ
Compound 1 possesses an efficient Cr -selective OFFeON behavior
7
3þ
in ethanol. Furthermore, 1 can also detect intracellar Cr
.
2. Results and discussion
*
Corresponding authors. Tel./fax: þ86 371 67781205; e-mail addresses:
yumm@zzu.edu.cn (M. Yu), liujx@zzu.edu.cn (J. Liu), zhanghongyan@mail.ipc.ac.cn
H. Zhang).
The optical properties of compound 1, featuring naphthyridine
Schiff base binding sites were studied. The titration experiments
(
0
040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.07.008

Z. Li et al. / Tetrahedron 67 (2011) 7096e7100
7097
Compound 1 hardly exhibits fluorescence emission in ethanol
3
þ
upon excitation at 310 nm (Fig. 2). Upon titration of Cr , a new
fluorescent emission peak at about 447 nm appeared and the in-
3þ
tensity dramatically enhanced, indicating a Cr -selective fluores-
cent signaling behavior. Because of the great enhancement of
emission intensity at 447 nm (I/I
chromium ion, compound 1 indicates an efficient Cr -selective
OFFeON fluorescent behavior, all the other environmentally and
0
¼10) upon addition of trivalent
3þ
3þ
biologically relevant metal ions except Fe did not show such
14
significant response (Fig. 3). Different from that of in literature,
the increased emission intensity and blue shift in emission band
Fig. 3 and inset Figure to Fig. 3) is probably due to the prohibition
(
of the photoinduced electron transfer process between naphthyr-
idine moiety and 7,10-diphenylfluoranthene moiety upon metal
3þ
binding. The possible process of 1 in sensing of Cr is depicted in
3þ
Scheme 2, After Cr was added into the ethanol solution of 1, the
fluorescence decay curve is fitted to one-exponential decay (Fig. 4)
and the lifetime is 12 ns.
Scheme 1. Synthetic route for compound 1.
ꢁ
5
Fig. 2. Changes in fluorescence emission spectra of 1 (1.0ꢀ10 M) in ethanol upon
were carried out in ethanol. The UVevis spectrum of 1 reveals the
typical naphthyridine Schiff base absorption bands at 208, 236, 297
ꢁ5
addition of Cr(NO
3
)
3
(the final concentration is 9.0ꢀ10
M) and the excitation
wavelength is 310 nm. The first trace is compound 1 alone, and each subsequent trace
represents addition of 2.25 equiv of Cr(NO ) . Inset: change in fluorescence of 1
4
ꢁ1
ꢁ1
,
and
and 375 nm (molar extinction coefficient
3
208¼9.59ꢀ10 M cm
3 3
ꢁ
5
ꢁ5
4
4
ꢁ1
ꢁ1
4
ꢁ1
ꢁ1
(1.0ꢀ10 M) upon addition of Cr(NO
3
)
3
(9.0ꢀ10 M) under the irradiation at 365 nm
3
236¼9.21ꢀ10
M
cm
,
3
297¼3.97ꢀ10
M
cm
,
3
þ
(
left: 1 only, right: after addition of Cr ).
ꢁ1
ꢁ1
3
375¼3.55ꢀ10 M cm ) (Fig. 1). These bands may be assigned to
electron transition from
3 3
p to p )
*. The addition of 9 equiv of Cr(NO
3
þ
ꢁ5
5
(
(
3
Cr , 9.0ꢀ10
M), led to change of the original absorbance
ꢁ1
ꢁ1
5
ꢁ1
ꢁ1
,
3
208¼1.67ꢀ10
M
cm
,
3
236¼1.13ꢀ10
M
cm
4
ꢁ1
ꢁ1
4
ꢁ1
ꢁ1
297¼3.84ꢀ10
M
cm , and
3
375¼2.21ꢀ10
M
cm ) (Fig. 1),
3
þ
demonstrating interaction between compound 1 and Cr ion.
ꢁ
5
Fig. 3. Fluorescence spectra changes of 1 (1.0ꢀ10 M) upon addition of different
metal ions (Cr(NO , FeCl , NaCl, MgCl , KCl, CaCl , MnCl , CoCl , NiCl , CuCl , ZnCl
CdCl , HgCl , PbCl
, 9.0ꢀ10 M) in ethanol. Inset: Fluorescence spectra of 4-(7,10-
diphenylfluoranthen-8-yl)benzenamine. The position of fluorescent emission peak is
57 nm.
3
)
3
3
2
2
2
2
2
2
2
,
ꢁ
5
2
2
2
5
It is important for metal ion sensors that they are able to detect
3
þ
ꢁ
5
metal ion selectively over other cations. The selectivity of 1 for Cr
Fig. 1. UVevis spectra of compound
0e9 equiv) in ethanol. The first trace is compound 1 alone, and each subsequent trace
represents addition of 0.9 equiv of Cr(NO
1
(1.0ꢀ10
3 3
M) on addition of Cr(NO )
3
þ
was investigated and the results are depicted in Fig. 5. Cr elicited
a great fluorescence intensity enhancement while the other metal
(
3
)
3
.

7098
Z. Li et al. / Tetrahedron 67 (2011) 7096e7100
Scheme 2. Possible process of 1 in sensing of Cr3þ
.
ꢁ
5
Fig. 6. Fluorescence spectra of of compound 1 (1.0ꢀ10 M) in ethanol upon addition
3þ
of different Cr salts with excitation at 310 nm.
introduced into the same MCF-7 cells, the strong fluorescence was
3
þ
imaged (Fig. 7b), which resulted from the reaction of 1 and Cr
.
The bright field transmission images of these MCF-7 cells in Fig. 7c
is exactly the same as the fluorescence image in Fig. 7b, confirming
an intracellular fluorescence imaged.
3. Conclusion
In conclusion, we have utilized the guest-induced prohibition
Fig. 4. The fluorescence decay curve of 1eCr3þ complex.
effect of the photoinduced electron transfer process between two
moieties in chemical sensor to develop a novel probe for detecting
ions did not show significant response. The experiments of the
3þ
the transition-metal ion Cr . The new fluorescent sensor showed
3
þ
counter ion effect on the selective properties of Cr (Fig. 6) were
also measured. Addition of chromium acetate made the fluores-
cence of compound 1 change very little, and chromium chloride
had similar influence as that of chromium nitrate. Such fluores-
3þ
an excellent selectivity for Cr over other metal ions examined in
similar solutions. Confocal laser scanning microscopy experiments
3þ
have proven that 1 can be used to monitor intraceullar Cr and to
map its subcellular distribution.
4
4
. Experimental section
.1. General instruments
For chromatography, 160e200 mesh silica gel (Qingdao, China)
1
13
was employed. The H and C spectra were recorded at a Varian
Mercury Bruker 400 spectrometer. Chemical shifts are reported in
ppm using tetramethylsilane (TMS) as the internal standard. Mass
spectra were obtained on a VG ZAB-HS mass spectrometer or
a Finnigan LCQ mass spectrometer. High resolution mass spectra
were obtained on high resolution mass spectrometer (IonSpec4.7 T
ꢂ
FTMS-MALDI/DHB). All spectral measurements were taken at 20 C.
UVevis absorption spectra were measured with a Hitachi UV-3100
spectrophotometer and fluorescence spectra were determined on
a Hitachi F-4500 spectrophotometer.
3 3 2 2
Fig. 5. Fluorescence spectra of a solution of the ion (Cr(NO ) , NaCl, MgCl , KCl, CaCl ,
ꢁ
5
MnCl
2
, CoCl
2
, NiCl
2
, CuCl
2
, ZnCl
2
, CdCl
2
, HgCl
2
, PbCl
2
, 9.0ꢀ10 M) of interest and 1
4.2. Synthetic procedure and characterization data
ꢁ
5
(
1.0ꢀ10 M). Bars represent the ratio of I to I
0
. I and I
0
represent the emission intensity
upon addition of different metal ions and that of compound 1 in ethanol at 447 nm,
respectively. The overall emission spectra were measured at excitation of 310 nm.
4
.2.1. 7,9-Diphenyl-8H-cyclopenta[l]acenaphthylen-8-one
(2). Compound 2 was synthesized from acenaphthenequinone and
1
5
1
9
2
,3-diphenylpropane-2-one according literature method. Yield:
1
cence change may be resulted from the different acidity of cobalt
salts (1.85 (CrCl ), 2.92 (Cr(NO) ), and 4.66 (Cr(CHCOO) )).
3 3 3
5%. H NMR (400 MHz, CDCl
3
, Me
4
Si):
d
(ppm) 8.08 (d, J¼6.8 Hz,
3
3
H), 7.86 (m, 6H), 7.61 (dd, J(H,H), J¼7.6 Hz, J(H,H), J¼8.0 Hz, 2H),
3
þ
3
3
3
The sensitivity of 1 to Cr was examined in living cells by using
confocal microscopy. Fluorescence images were recorded with ex-
citation at 408 nm by a diode laser, Spinhole aperture, 100% gain of
detector, and an oil objective with 60ꢀ magnification and 1.40 NA.
The qualitatively in vitro results are exhibited in Fig. 7. After MCF-7
7
.54 (dd, J(H,H), J¼7.6 Hz, J(H,H), J¼8.0 Hz, 4H), 7.42 (t, J(H,H),
13
J¼7.2 Hz, 2H). C NMR (100 MHz, CDCl
3
): d (ppm) 154.2, 132.1,
131.5, 131.4, 129.0, 128.6, 128.3, 127.8, 121.7, 120.9.
4
.2.2. 4-(Trimethylsilylethynyl)aniline (4). 4-(Trimethylsilylethynyl)
ꢁ3
16
cells were incubated with 10
mmol 1 and 1 mL PBS for 30 min at
aniline was performed according to the literature.
ꢂ
3
7 C, no obvious fluorescence can be imaged (Fig. 7a). At the same
To a three-neck round bottomed flask was added 4-iodoaniline
ꢁ2
3þ
mmol of Cr was
experimental conditions, 10 min after 2ꢀ10
(1.10 g, 5.0 mmol), bistriphenylphosphine palladium(II) chloride

Z. Li et al. / Tetrahedron 67 (2011) 7096e7100
7099
Fig. 7. The intracellular Cr3 was imaged in living cells at 37 C with use of confocal microscopy. (a) MCF-7 cells incubated with 10
þ
ꢂ
m
M of compound 1 solution (the volume ratio of
ꢁ
2
ethanol and water is 4e6) for 30 min. (b) MCF-7 cells in part a 10 min after being treated with 2ꢀ10
3 3
mmol of Cr(NO ) aqueous solution. (c) Bright field image of living MCF-7 cells
in parts a and b.
(
702 mg, 0.200 mmol), and CuI (5 mg, 0.027 mmol). The mixture
[Mþ1]þ 657 (100). HRMS calcd for C46
32 4
H N O (m/z): 656.2576;
was purged with Ar gas and dry THF (10 mL) and TEA (3 mL)
was added via syringe. The trimethylsilyl acetylene
found: 657.2649.
(
0.85 mL, 6.0 mmol) was subsequently added via syringe and the
Acknowledgements
reaction mixture was stirred for 2 h at room temperature. The
solvent and TEA were removed under vacuum. Dried by anhy-
drous MgSO , the crude product was separated by column chro-
4
matography with a solvent system of 1:1 dichloromethane/
petroleum ether (40e60 C) to afford a light yellow solid (0.756 g,
We thank the NSFC (50903075, 60978034, and 50873093) for
financial support.
ꢂ
References and notes
7
4% yield).
To a stirred solution of potassium hydroxide (1.34 g, 23.8 mmol)
mL methanol, 4-(Trimethylsilylethynyl)aniline (1.10 g,
.86 mmol) in tetrahydrofuran (5 mL) was added, and the solution
1. (a) Bozdemir, O. A.; Sozmen, F.; Buyukcakir, O.; Guliyev, R.; Cakmak, Y.; Akkaya,
in
0
6
E. U. Org. Lett. 2010, 12, 1400e1403; (b) Rurack, K. Spectrochim. Acta, Part A 2001,
57, 2161e2195; (c) Carpenter, R. D.; Verkman, A. S. Org. Lett. 2010, 12,
1160e1163; (d) He, Q.; Miller, E. W.; Wong, A. P.; Chang, C. J. J. Am. Chem. Soc.
was refluxed overnight. Upon cooling to room temperature, the
product was filtered to remove insoluble substance, and the solvent
2
2
006, 128, 9316e9317; (e) Dodani, S. C.; He, Q.; Chang, C. J. J. Am. Chem. Soc.
009, 131, 18020e18021; (f) Ellis-Davies, G. C. R. Chem. Rev. 2008, 108,
was removed under vacuum. The residue was dissolved in CH
50 mL), filtered, dried over anhydrous MgSO , and concentrated
under reduced pressure providing the product as a yellow solid.
Yield: 98%. 1H NMR (400 MHz; CDCl
; Me Si): (ppm) 7.32 (d,
J¼2.4 Hz, 2H), 6.61 (d, J¼2.4 Hz, 2H), 3.83 (s, 2H), 2.98 (s, 1H).
NMR (100 MHz, CDCl ): (ppm) 147.0, 133.5, 114.6, 111.3, 84.4, 77.4,
2
Cl
2
1603e1613; (g) Nolan, E. M.; Lippard, S. J. Chem. Rev. 2008, 108, 3443e3480; (h)
Jameson, D. M.; Ross, J. A. Chem. Rev. 2010, 110, 2685e2708; (i) Han, J.; Burgess,
K. Chem. Rev. 2010, 110, 2709e2728.
. (a) Xu, Z.; Baek, K.; Kim, H. N.; Cui, J.; Qian, X.; Spring, D. R.; Shin, I.; Yoon, J. J.
Am. Chem. Soc. 2010, 132, 601e610; (b) Royzen, M.; Durandin, A.; Young, V. G.;
Geacintov, N. E.; Canary, J. W. J. Am. Chem. Soc. 2006, 128, 3854e3855; (c) Qian,
F.; Zhang, C.; Zhang, Y.; He, W.; Gao, X.; Hu, P.; Guo, Z. J. Am. Chem. Soc. 2009,
(
4
2
3
4
d
1
3
C
3
d
131, 1460e1468; (d) Wong, B. A.; Friedle, S.; Lippard, S. J. J. Am. Chem. Soc. 2009,
7
7.1, 76.7, 74.9.
131, 7142e7152; (e) Komatsu, K.; Kikuchi, K.; Kojima, H.; Urano, Y.; Nagano, T. J.
Am. Chem. Soc. 2005, 127, 10197e10204; (f) Tamanini, E.; Flavin, K.; Motevalli,
M.; Piperno, S.; Gheber, L. A.; Todd, M. H.; Watkinson, M. Inorg. Chem. 2010, 49,
4.2.3. 4-(7,10-Diphenylfluoranthen-8-yl)benzenamine (6). A stirred
3789e3800; (g) Woodroofe, C. C.; Lippard, S. J. J. Am. Chem. Soc. 2003, 125,
mixture of 4-ethynylaniline (0.70 g, 6 mmol) and 7,9-diphenyl-8H-
cyclopenta[l]acenaphthylen-8-one (1.78 g, 5 mmol) in degassed o-
xylene (20 mL) was refluxed for 15 h. The solvent was removed
under vacuum. A pale yellow powder was purified by column
1
1458e11459; (h) Carol, P.; Sreejith, S.; Ajayaghosh, A. Chem. Asian. J. 2007, 2,
338e348; (i) Chang, C. J.; Nolan, E. M.; Jaworski, J.; Okamoto, K.; Hayashi, Y.;
Sheng, M.; Lippard, S. J. Inorg. Chem. 2004, 43, 6774e6779; (j) Partha, R.;
Koushik, D.; Mario, M.; Jagnyeswar, R.; Pradyot, B. Inorg. Chem. 2007, 46,
6405e6412; (k) Maruyama, S.; Kikuchi, K.; Hirano, T.; Urano, Y.; Nagano, T. J.
chromatography (200e300 mesh), using a CH
2
Cl
2
/hexane mixture
; Me Si): (ppm)
Am. Chem. Soc. 2002, 124, 10650e10651; (l) Pearce, D. A.; Jotterand, N.; Carrico,
I. S.; Imperiali, B. J. Am. Chem. Soc. 2001, 123, 5160e5161; (m) Mameli, M.;
Aragoni, M. C.; Arca, M.; Atzori, M.; Bencini, A.; Bazzicalupi, C.; Blake, A. J.;
Caltagirone, C.; Devillanova, F. A.; Garau, A.; Hursthouse, M. B.; Isaia, F.; Lippolis,
V.; Valtancoli, B. Inorg. Chem. 2009, 48, 9236e9249.
1
as eluent (1.23 g, 55%). H NMR (400 MHz; CDCl
3
4
d
3
7
4
2
.73 (d, J(H,H), J¼6.8 Hz, 4H), 7.54 (m, 2H), 7.43 (m, 6H), 7.30 (m,
H), 7.03 (d, J¼8.4 Hz, 2H), 6.67 (d, J¼7.2 Hz, 1H), 6.52 (d, J¼8.0 Hz,
H), 3.60 (s, 2H). 13C NMR (100 MHz, CDCl
3. (a) Rurack, K.; Kollmannsberger, M.; Resch-Genger, U.; Daub, J. J. Am. Chem. Soc.
000, 122, 968e969; (b) Kim, S.; Kim, J.; Park, S.; Chang, S. Org. Lett. 2006, 8,
71e374; (c) Huang, J.; Xu, Y.; Qian, X. J. Org. Chem. 2009, 74, 2167e2170; (d)
Zhou, Y.; Zhu, C.-Y.; Gao, X.-S.; You, X.-Y.; Yao, C. Org. Lett. 2010, 12, 2566e2569;
e) Du, J.; Fan, J.; Peng, X.; Sun, P.; Wang, J.; Li, H.; Sun, S. Org. Lett. 2010, 12,
76e479; (f) Lee, M. H.; Lee, S. W.; Kim, S. H.; Kang, C.; Kim, J. S. Org. Lett. 2009,
1, 2101e2104.
3
): (ppm) 144.5, 140.9,
d
2
3
1
38.2, 135.1, 133.1, 130.4, 129.1, 127.2, 126.5, 123.3, 122.7, 114.5, 77.3.
þ
ESI-MS [Mþ1] 446 (100). HRMS (EI) calcd for C34
H23N [M],
(
4
1
4
45.1830; found 445.1824.
4
.2.4. (E)-N-(7-((4-(7,10-Diphenylfluoranthen-8-yl)phenylimino)
4. (a) Jung, H. S.; Kwon, P. S.; Lee, J. W.; Kim, J.; Hong, C. S.; Kim, J. W.; Yan, S.; Lee,
J. Y.; Lee, J. H.; Joo, T.; Kim, J. S. J. Am. Chem. Soc. 2009, 131, 2008e2012; (b)
Domaille, D. W.; Zeng, L.; Chang, C. J. J. Am. Chem. Soc. 2010, 132, 1194e1195; (c)
Kramer, R. Angew. Chem., Int. Ed. 1998, 37, 772e773; (d) Weng, Y.-Q.; Yue, F.;
Zhong, Y.-R.; Ye, B.-H. Inorg. Chem. 2007, 46, 7749e7755; (e) Qi, X.; Jun, E. J.; Xu,
L.; Kim, S.-L.; Hong, J. S. J.; Yoon, Y. J.; Yoon, J. J. Org. Chem. 2006, 71, 2881e2884;
methyl)-5-methyl-1,8-naphthyridin-2-yl)acetamide (1). A mixture
of aniline (97 mg) and 1,8-naphthyridine aldehydes (50 mg) in
methanol (15 mL) was refluxed for 5 h under an argon atmo-
sphere. After cooling to room temperature, the crude product
was dried in vacuum. Subsequently, the solid was purified by
column chromatography (200e300 mesh) on silica gel with
(f) Xu, Z.; Xiao, Y.; Qian, X.; Cui, D. Org. Lett. 2005, 7, 889e892; (g) Wen, Z.-C.;
Yang, R.; He, H.; Jiang, Y.-B. Chem. Commun. 2006, 106e108; (h) Goswami, S.;
Sen, D.; Das, N. K. Org. Lett. 2010, 12, 856e859.
5. (a) Cheng, T.; Xu, Y.; Zhang, S.; Zhu, W.; Qian, X.; Duan, L. J. Am. Chem. Soc. 2008,
1
dichloromethane to afford yellow 1 (107 mg, yield: 71%). H NMR
130, 16160e16161; (b) Lu, C.; Xu, Z.; Cui, J.; Zhang, R.; Qian, X. J. Org. Chem. 2007,
(
3 4
400 MHz; CDCl ; Me Si): d (ppm) 8.71 (s, 1H, NH), 8.57 (d,
72, 3554e3557; (c) Xue, L.; Liu, C.; Jiang, H. Org. Lett. 2009, 11, 1655e1658; (d)
J¼9.2 Hz, 1H), 8.57 (d, J¼9.2 Hz, 1H), 8.18 (s, 1H), 7.79 (m, 5H),
Xue, L.; Liu, Q.; Jiang, H. Org. Lett. 2009, 11, 3454e3457; (e) Peng, X.; Du, J.; Fan,
J.; Wang, J.; Wu, Y.; Zhao, J.; Sun, S.; Xu, T. J. Am. Chem. Soc. 2007, 129,
1500e1501.
. Singh, A. K.; Gupta, V. K.; Gupta, B. Anal. Chim. Acta 2007, 585, 171e178.
. (a) Wu, H.; Zhou, P.; Wang, J.; Zhao, L.; Duan, C. New J. Chem. 2009, 33,
7
.56 (m, 3H), 7.40 (m, 7H), 7.30 (m, 4H), 7.19 (d, J¼8.4 Hz, 2H),
13
6
.73 (d, J¼7.2 Hz, 1H), 2.78 (s, 3H), 2.32 (s, 3H). C NMR
): 169.45, 160.44, 157.39, 146.38, 140.69, 138.01,
31.04, 128.50, 127.43, 123.41, 120.67, 22.99, 18.39. ESI-MS
6
7
(
100 MHz, CDCl
3
1
653e658; (b) Weerasinghe, A. J.; Schmiesing, C.; Sinn, E. Tetrahedron Lett. 2009,

7100
Z. Li et al. / Tetrahedron 67 (2011) 7096e7100
5
2
0, 6407e6410; (c) Wang, D.; Shiraishi, Y.; Hirai, T. Tetrahedron Lett. 2010, 51,
545e2549.
. Mao, J.; Wang, L.; Dou, W.; Tang, X.; Yan, Y.; Liu, W. Org. Lett. 2007, 9,
567e4570.
. Sarkar, M.; Banthia, S.; Samanta, A. Tetrahedron Lett. 2006, 47, 7575e7578.
0. (a) Huang, K.; Yang, H.; Zhou, Z.; Yu, M.; Li, F.; Gao, X.; Yi, T.; Huang, C. Org. Lett.
008, 10, 2557e2560; (b) Zhou, Z.; Yu, M.; Yang, H.; Huang, K.; Li, F.; Yi, T.;
12. (a) Cristian, S. C.; Lisa, M. T.; Jos eꢀ , R. G.; Xiang, O.; Kim, R. D. Inorg. Chem. 2002,
41, 1523e1533; (b) Kobori, A.; Horie, S.; Suda, H.; Saito, I.; Nakatani, K. J. Am.
Chem. Soc. 2004, 126, 557e562; (c) He, C.; Lippard, S. J. Inorg. Chem. 2000, 39,
5225e5231; (d) Katz, J. L.; Geller, B. J.; Foster, P. D. Chem. Commun. 2007,
1026e1028.
8
4
9
1
13. (a) Xiang, Y.; Tong, A.; Lu, Y. J. Am. Chem. Soc. 2009, 131, 15352e15357; (b) Yu,
M.; Li, Z.; Wei, L.; Wei, D.; Tang, M. Org. Lett. 2008, 10, 5115e5118; (c) Satake, H.;
Nishizawa, S.; Teramae, N. Anal. Sci. 2006, 22, 195e197.
2
Huang, C. Chem. Commun. 2008, 3387e3389; (c) Hu, X.; Zhang, X.; He, G.; He,
C.; Duan, C. Tetrahedron 2011, 67, 1091e1095.
1. (a) Djurdjevic, S.; Leigh, D. A.; McNab, H.; Parsons, S.; Teobaldi, G.; Zerbetto, F. J.
Am. Chem. Soc. 2007, 129, 476e477; (b) Quinn, J. R.; Zimmerman, S. C.; Del Bene,
J. E.; Shavitt, I. J. Am. Chem. Soc. 2007, 129, 934e941.
14. Wu, J.; Liu, W.; Zhuang, X.; Wang, F.; Wang, P.; Tao, S.; Zhang, X.; Wu, S.; Lee, S.
Org. Lett. 2007, 9, 33e36.
1
15. Wehmeier, M.; Wagner, M.; M u€ llen, K. Chem.dEur. J. 2001, 7, 2197e2205.
16. Flavin, K.; Chaur, M. N.; Echegoyen, L.; Giordani, S. Org. Lett. 2010, 12, 840e843.