1,8-Naphthalimide-based colorimetric and fluorescent sensor for recognition of GMP, TMP, and UMP and its application in in vivo imaging

Article abstract of DOI:10.1016/j.tetlet.2014.09.074

In this study, a series of 1,8-naphthalimide-based analogs were developed for fluorescence imaging of nucleotides in Caenorhabditis elegans. In DMSO, compound 1 proved to be an effective and selective colorimetric and fluorescent sensor for recognition of GMP, TMP, and UMP over other structurally similar nucleotides. Among all the tested nucleotides, only the addition of GMP, TMP, and UMP resulted in a fluorescence color change from blue to brown with a fluorescence enhancement of more than 600-fold, with the colorless solution turning brown. NMR spectroscopic titration, theoretical calculations, and spectral tests performed using various solvent compositions confirmed that compound 1 formed multiple hydrogen bonds with the related base groups in the nucleotide. Compound 1 demonstrated its utility as a fluorescent chemosensor for detecting GMP, TMP, and UMP in in vivo imaging of GMP, TMP, and UMP in C. elegans.

Full text of DOI:10.1016/j.tetlet.2014.09.074

Tetrahedron Letters 55 (2014) 6131–6136
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
1,8-Naphthalimide-based colorimetric and fluorescent sensor for
recognition of GMP, TMP, and UMP and its application in in vivo
imaging
Li Mei Zhang a, Lin E. Guo a, Xue Mei Li c, Yong Gang Shi b, Gao Fen Wu b, Xiao Guang Xie a, Ying Zhou a,
,
⇑
Qi Hua Zhao a, , Jun Feng Zhang b,
⇑
⇑
a College of Chemical Science and Technology, Yunnan University, Kunming 650091, China
b College of Chemisitry and Chemical Engineering, Yunnan Normal University, Kunming 650500, China
c Department of Safety Evaluation, Technology Center of China Tobacco Yunnan Industrial Co., Ltd, Kunming 650231, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2014
Revised 11 September 2014
Accepted 15 September 2014
Available online 18 September 2014
In this study, a series of 1,8-naphthalimide-based analogs were developed for fluorescence imaging of
nucleotides in Caenorhabditis elegans. In DMSO, compound 1 proved to be an effective and selective col-
orimetric and fluorescent sensor for recognition of GMP, TMP, and UMP over other structurally similar
nucleotides. Among all the tested nucleotides, only the addition of GMP, TMP, and UMP resulted in a fluo-
rescence color change from blue to brown with a fluorescence enhancement of more than 600-fold, with
the colorless solution turning brown. NMR spectroscopic titration, theoretical calculations, and spectral
tests performed using various solvent compositions confirmed that compound 1 formed multiple hydro-
gen bonds with the related base groups in the nucleotide. Compound 1 demonstrated its utility as a fluo-
rescent chemosensor for detecting GMP, TMP, and UMP in in vivo imaging of GMP, TMP, and UMP in C.
elegans.
Keywords:
Sensor
Colorimetric and fluorescent
Nucleotide
Naphthalimide
In vivo imaging
Ó 2014 Elsevier Ltd. All rights reserved.
Introduction
However, due to the similarities in the structures of the nucleo-
tides, the design and synthesis of a chemosensor for the recogni-
In recent years, development of sensing systems and methods
to recognize biologically and environmentally important species
has emerged as a significant research area in the field of chemical
sensors.1 Nucleotides are active targets of fluorescence recogni-
tion,2 and they have attracted remarkable attention due to their
biological significance. Compared to the well-investigated adeno-
sine-triphosphate (ATP), sensing systems to recognize other nucle-
otides and nucleotides have rarely been studied. Importantly, other
nucleoside polyphosphates also play pivotal roles in various phys-
iological events. For example, adenosine monophosphate (AMP)
plays significant roles in bioenergetics, metabolism, and transfer
of genetic information; and guanosine monophosphate (GMP) acts
as an intermediate in the synthesis of nucleic acids and plays an
important role in several metabolic processes.3 Thymidine nucleo-
tides, including thymidine-monophosphate (TMP), -diphosphate
(TDP) and -triphosphate (TTP), synthesized in vivo from thymidine,
are essential building blocks in DNA replication and cell division.4
tion of a certain nucleotide among various structurally similar
nucleoside polyphosphates remain a fundamental challenge.5
Recently, we reported a series of 1,8-naphthalimide-based
derivatives displaying selective colorimetric and fluorescence
changes toward the target molecules.6 Therefore, the objective of
this study was to design an efficient nucleotide-selective
colorimetric and fluorescent sensor, based on 1,8-naphthalimide,
to explore its biological application in in vivo imaging of
Caenorhabditis elegans.
In this study, three 1,8-naphthalimide-based analogs were syn-
thesized. Compound 1, a nucleotide-selective fluorescent sensor,
can sense the binding process of GMP, TMP, and UMP by distinct
colorimetric and fluorescent changes. The results of fluorescence
tests revealed that compared to the other examined nucleotides,
only GMP, TMP, and UMP generated a significant fluorescence
response with compound 1, with a fluorescence enhancement of
more than 600-fold. Multiple hydrogen bonds, formed between
the amide NH group of compound 1 and related base groups in
the nucleotides, as well as deprotonation of NH explained the
unique response of compound 1 in nucleotide sensing among the
three synthesized analogs. In in vivo imaging tests of C. elegans,
⇑
Corresponding authors.
E-mail addresses: yingzhou@yun.edu.cn (Y. Zhou), qhzhao@yun.edu.cn (Q.H.
Zhao), junfengzhang@aliyun.com (J.F. Zhang).
http://dx.doi.org/10.1016/j.tetlet.2014.09.074
0040-4039/Ó 2014 Elsevier Ltd. All rights reserved.

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L. M. Zhang et al. / Tetrahedron Letters 55 (2014) 6131–6136
an obvious blue to brown fluorescence change was clearly
observed; demonstrating that compound 1 exhibited excellent cell
permeability and it could combine with GMP, TMP, and UMP in dif-
ferent organs to trace their enrichment and distribution.
Results and discussion
In the design of the three 1,8-naphthalimide-based analogs
(Scheme 1), we introduced O and N, as hydrogen bond acceptors,
in the 4 position of 1,8-naphthalimide, in an attempt to promote
hydrogen bond interactions with nucleotides. An acryloyl group
and a (e)-2-butenoyl group were introduced in compounds 1–3
to compare the steric hindrances. Compounds 5–8 were synthe-
sized with improved yields using a previously reported procedure.7
Compounds 1–3 were synthesized in high yields, and the target
compounds were purified prior to characterization. Detailed exper-
imental procedures and 1H and 13C NMR spectra are explained in
the Supporting information. The spectroscopic data of compounds
1–3 are listed in Table S1. In DMSO, compounds 1–3 displayed
emission bands mainly in the regions of 415–463 nm, with weak
fluorescent intensities. The results showed that the characteristic
of the substituent did not significantly influence the luminescence
of compounds 1–3.
To clearly investigate the interaction of compounds 1–3 with
nucleotide, the ultraviolet–visible (UV–Vis) absorption and fluores-
cence spectra of 1–3 were first studied in DMSO. ATP, ADP, AMP,
GTP, GDP, GMP, UTP, UDP, UMP, and TMP were used to measure
the selectivity of probes 1–3. Spectra for all the nucleotides were
recorded after 3 min of the addition of 10 equiv of each of the
above mentioned molecules. Figure 1a shows that in the absence
of nucleotide, compound 1 exhibits a major absorption band cen-
tered at 375 nm in DMSO. Only the addition of GMP, UMP, and
TMP led to obvious red shifts from 375 to 500 nm in the absorption
maximum. These red shifts resulted in dramatic color changes in
Figure 1. (a) Absorbance spectra of 1 (2.0 Â 10À5 M) in DMSO with 10 equiv of ATP,
ADP, AMP, GTP, GDP, GMP, UTP, UDP, UMP and TMP, down: the picture of 1 and 1
upon the addition of 10 equiv of selected ions (a: 1, b: GMP, c: UMP, d: TMP, e: ATP,
f: UTP, g: UDP); (b) fluorescence spectra of 1 (2.0 Â 10À5 M) in DMSO with 10 equiv
of ATP, ADP, AMP, GTP, GDP, GMP, UTP, UDP, UMP and TMP, down: the fluorescence
picture of 1 and 1 upon the addition of 10 equiv of selected ions (a: 1, b: GMP, c:
UMP, d: TMP, e: ATP, f: UTP, g: UDP). Inset: the fluorescence spectrum of 1.
the solution (colorless to brown). No significant spectrum change
was observed in the presence of other nucleotides. Addition of dif-
ferent nucleotides to the solution of compounds 2–3 results in a
similar obvious increase in the absorption maximum at 480 nm
for ADP, GTP, GMP, UMP, and TMP, with the color of the solution
changing from colorless to yellow as shown in Figures S1 and S2.
Moreover, a slight decrease in the intensity of the peaks around
330 nm was observed for compounds 2–3 revealing that the
selectivity of compounds 2–3 in absorption toward the tested
nucleotides was not as good as that of 1.
Compared to other examined nucleotides, only UMP, TMP, and
GMP, when added to compound 1, generated
a significant
Scheme 1. The synthetic route of compounds 1–3.

L. M. Zhang et al. / Tetrahedron Letters 55 (2014) 6131–6136
6133
‘turn-on’ fluorescence response of the peak at 572 nm with 109 nm
red-shift corresponding to a fluorescent change in color from blue
to orange (Fig. 1b). A significant fluorescence enhancement of up to
690-fold for GMP, 635-fold for UMP and 690-fold for TMP was
observed indicating high selectivity of 1 for UMP, GMP, and TMP
compared to the other tested nucleotides. Addition of nucleotides
to solutions of compounds 2–3 in DMSO did not result in a regular
change in the fluorescence spectra (Figs. S1 and S2) revealing that 1
exhibits the best fluorescent selectivity toward the tested nucleo-
tides, such as GMP, UMP, and TMP, among the three synthesized
analogs. Therefore, further investigations and tests were per-
formed on 1.
To obtain insight into the binding of nucleotides with 1, the UV–
Vis and fluorescence spectra of 1 upon titration with different
equivalents of GMP (Fig. 2), UMP (Fig. S3) and TMP (Fig. 3) are
recorded. Figure 2a shows that upon titration with GMP, the absor-
bance band at 500 nm increased sharply; however, the peak at
375 nm decreased slowly. Addition of GMP to a solution of 1 led
to an increase in the fluorescence emission intensity at 575 nm
by 690-fold which reached a maximum value after 10 equiv of
GMP was added. The solutions of 1 treated with GMP undergo
drastic changes in their fluorescence spectroscopic properties cor-
responding to a change in color from blue to orange as shown in
Figure 2b. A similar change in UV–Vis spectra with a sharp
decrease in the intensity at 375 nm and an increase at 500 nm
was observed for TMP. Moreover, the fluorescence intensity of
the peak at 575 nm, attributed to the interaction of 1 with TMP,
is enhanced significantly by 690-fold and levels up on the addition
of 5 equiv of TMP as shown in Figure 3b. Figure S3 demonstrates
that the addition of UMP to a solution of 1 leads to a decrease in
the intensity of absorbance at 375 nm and an increase in the band
at 498 nm. 635-fold increase in fluorescence was observed at
575 nm with the addition of 5 equiv of UMP.
Figure 3. (a) Absorbance titration spectra of 1 (2.0 Â 10À5 M) in the presence of
varying concentrations of TMP in DMSO. (b) Fluorescence emission titration spectra
of 1 (2.0 Â 10À5 M) in the presence of varying concentrations of TMP in DMSO.
Figure 4. (a) Absorbance spectra of 1 (2.0 Â 10À5 M) in DMSO with 10 equiv of GMP
containing water (4%, 6%, 8%, 10%, 15%, 20%, 25%, v/v). (b) Fluorescence spectra of 1
in DMSO with 10 equiv of GMP containing water (0%, 2%, 6%, 8%, 10%, 15%, 20%, 25%,
v/v).
The binding constant for a 1:1 receptor–nucleotide complex
formation was determined for 1 and UMP, TMP, and GMP by using
the Job-plot equations (Figs. S5–S7). The corresponding binding
constants of 1 with nucleotides were estimated to be 2.09 Â 103,
2.77 Â 104, and 2.31 Â 104 MÀ1 for GMP, UMP, and TMP, respec-
tively (Figs. S11–S13). Stabilities of the complexes of nucleotides
concentration constant, the absorption of 1-GMP at 490 nm
dropped in intensity with a concomitant growth of a new band
at 372 nm with well-defined isosbestic points at 340 and
415 nm. Moreover, the intense emission at 575 nm decreased with
the increasing water compositions. Drastic reverse color changes
from brown to colorless displayed by solutions of 1-GMP were
due to the interference from the water molecules. Similar spectral
changes are observed for 1-TMP (Fig. 5) and 1-UMP (Fig. S3) with a
successive increase in the water content indicating that 1-nucleo-
tides complexes (1-GMP, 1-TMP and 1-UMP) are affected signifi-
cantly by change in the polarity of the solvent and sensitive to
the microenvironment.
with
1-UMP > 1-GMP. The fluorescence intensity of 1 was linearly pro-
portional to the concentrations (0–10 M) of GMP, UMP, and
1 were found to be in the following order: 1-TMP >
l
TMP and detection limits as low as 1.48 Â 10À7 M concentration
of GMP, 1.45 Â 10À6 M of UMP and 1.20 Â 10À6 M of TMP were
established using 1, with a signal-to-noise ratio of 3 (Figs. S8–S10).
Figure 4 shows the UV–Vis absorption changes and fluorescence
changes of 1-GMP (1:10 equiv) using various solvent compositions.
Upon increasing the water content while maintaining the
Figure 5. (a) Absorbance spectra of 1 (2.0 Â 10À5 M) in DMSO with 10 equiv of TMP
containing water (0%, 2%, 4%, 6%, 8%, 10%, 12%, 15%, 20%, 25%, v/v). (b) Fluorescence
spectra of 1 in DMSO with 10 equiv of TMP containing water (0%, 2%, 4%, 8%, 10%,
12%, 15%, 20%, 25%, v/v).
Figure 2. (a) Absorbance titration spectra of 1 (2.0 Â 10À5 M) in the presence of
varying concentrations of GMP in DMSO. (b) Fluorescence emission titration spectra
of 1 (2.0 Â 10À5 M) in the presence of varying concentrations of GMP in DMSO.

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L. M. Zhang et al. / Tetrahedron Letters 55 (2014) 6131–6136
Further, theoretical calculations were performed to confirm the
recognition. Figure 6b exhibits that each molecule of 1 is connected
to one molecule of UMP, TMP, and GMP via two OÁ Á ÁHAN bonds.
Distances of OÁ Á ÁH bonds are 1.831 and 1.808 Å in 1-UMP, 1.839
and 1.805 Å in 1-TMP, and 1.837 and 1.732 Å in 1-GMP. All the
distances of OÁ Á ÁHAN in these three cases are in good agreement
with the description of intermolecular hydrogen bonds, strongly
supporting the H-bond interactions in the recognition process.
Compared to the above mentioned three nucleotides, adenine
group in AMP (Fig. 6a) could not form multi-hydrogen bonds with
1; therefore, no obvious signal response was observed for AMP.
Meanwhile, the intramolecular H-bond formation of UDP was
calculated. It showed that two intramolecular hydrogen bonds
are formed inside one UDP molecule, which explained why no
response toward UDP was found (Fig. S30).
binding patterns of 1 with GMP, UMP, and TMP. In this study, the
density functional theory (B3LYP/6-31G⁄ level)8 was used to
describe the binding pattern and H-bond interactions. The results
showed that multi-hydrogen bonds were first formed between
the amide NH group of 1 and related base groups in the nucleo-
tides. As reported in the literatures,9 the large red-shift of the
UV–Vis absorption and fluorescence spectra of 1 could be attrib-
uted to the deprotonation of N–H, thus, explaining the unique
response of 1 among the three synthesized analogs. Amide NH
group is a principal H-bond donor, and the similar structural
features of uracil group (in UMP), thymine group (in TMP), and
guanine group (in GMP) are the major reasons for the multi-
hydrogen bond formation (Fig. 6a), in this study on nucleotide
Figure 6. (a) The proposed binding mechanism of compound 1 with UMP, TMP and GMP. (b) Calculated structure of 1 binding with UMP, TMP and GMP.

L. M. Zhang et al. / Tetrahedron Letters 55 (2014) 6131–6136
6135
analysis significantly supported the sensing mode of 1 and the
related nucleotide.
To demonstrate the feasibility of 1 for its application in in vivo
imaging, fluorescence imaging tests were performed in C. elegans.10
Previously, the author successfully used C. elegans to test and eval-
uate the toxicity levels of heavy metal mercury.11 In the present
study, the application of 1 in in vivo imaging was evaluated by
visualizing the distribution of GMP, TMP, and UMP in nematodes
incubated with nucleotide (100 lM) for 15 h. C. elegans larvae at
developmental stage 4 (L4) were used. For demonstrating the
fluorescence-imaging of accumulations of UMP, TMP, and GMP in
the nematode, the previously exposed worms were incubated in
centrifuge tube filled with 1 mL of M9 buffer, containing 10 lM
of 1, at 20 °C for 1 h. Figure 8 shows that the addition of GMP,
TMP, and UMP leads to a significant change in the color of the
fluorescence from blue to yellowish-brown, demonstrating that 1
was readily internalized into C. elegans and it could trace the
enrichment and distribution of the related nucleotide. The above
mentioned results revealed that 1 exhibited excellent cell perme-
ability and that it could be effectively utilized to monitor GMP,
TMP, and UMP in living cells and C. elegans.
Conclusion
Of the three 1,8-naphthalimide-based analogs that were
developed, compound 1 has demonstrated effective and selective
colorimetric and fluorescent sensing for recognition of GMP, TMP
and UMP over other structurally similar nucleotides. Among all
the tested nucleotides, addition of only GMP, TMP, and UMP
resulted in significant fluorescence enhancements, and the color-
less solution turned brown. Compound 1’s nucleotide binding
mechanism involves multiple hydrogen bonds with the related
base groups in the nucleotide and the deprotonation of the nitro-
gen acceptor at position 4 being the primary reasons for successful
recognition. This binding mechanism was supported by NMR
spectroscopic titration, theoretical calculations and spectral tests
performed using various solvent compositions. Compound 1 was
successfully applied to fluorescence imaging for GMP, TMP and
UMP in C. elegans, demonstrating its utility as a fluorescent chemo-
sensor for detecting GMP, TMP, and UMP in in vivo imaging.
Figure 7. The 1H NMR spectra of compound 1 (0.012 mM) with GMP in DMSO-d6;
equivalents of GMP are related to the concentration of compound 1.
Further evidence for the binding interactions of 1-GMP (Fig. 7),
1-TMP (Fig. S14) and 1-UMP (Fig. S15) was obtained by NMR
titration studies. Figure 7 demonstrates that, with the addition of
varying concentrations of GMP to 1 (0.012 mM) in DMSO-d6, the
upfield shifts of protons (Ha, Hb, Hc, and Hd) are observed indicat-
ing the occurrence of hydrogen bond interactions between 1 and
GMP in the 1-GMP complex. The disappearance of He is the evi-
dence for the deprotonation of N–H. Results of NMR spectroscopic
Figure 8. Phase contrast (top) and fluorescence images (bottom) of C. elegans. C. elegans were exposed to 100
1 for 1 h. (e) Fluorescence images of C. elegans treated with 10 M of 1 only. (f) Fluorescence images of C. elegans treated with 100
M UMP for 15 h and 10 M of 1 for 1 h. (h) Fluorescence images of C. elegans treated with 100
l
M GMP, UMP, and TMP for 15 h and then treated with 10
M GMP for 15 h and 10 M of 1 for 1 h. (g)
M TMP for 15 h and 10 lM
lM of
l
l
l
Fluorescence images of C. elegans treated with 100
of 1 for 1 h.
l
l
l

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Kawai, K.; Kawabata, K.; Tojo, S.; Majima, T. Bioorg. Med. Chem. Lett. 2002, 12,
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This work was supported by the Natural Science Foundation of
China (NSFC Grant Nos. 21102127, 21262045, 21262050,
21302165, 21371151 and 21462050); the Foundation of the
Department of Science and Technology of the Yunnan Province of
China (Nos. 2011FB013, 2011FB047 and 2013HB062); and Student
Research Training of the Yunnan Normal University (KY-2013-
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