Synthesis and optical properties of novel Tr?ger's base derivatives

Article abstract of DOI:10.1016/j.tet.2016.05.042

Diphenylamine, phenothiazine or carbazole were introduced into Tr?ger's base skeleton via Ullmann or Suzuki coupling to afford new TB derivatives. Their optical properties tests, density functional theory (B3LYP; 6-31G*) calculations were investigated. Incidentally anti-cancer activity against human hepatoma HepG2 cells in?vitro (MTT assay) were investigated. All the results indicated that these novel compounds have the potential as fluorescence materials.

Full text of DOI:10.1016/j.tet.2016.05.042

Accepted Manuscript
Synthesis and optical properties of novel Tröger's base derivatives
Rui Yuan, Ming-qi Li, Jiang-biao Xu, Shu-ying Huang, Sheng-liang Zhou, Peng
Zhang, Jin-juan Liu, Hui Wu
PII:
S0040-4020(16)30441-0
10.1016/j.tet.2016.05.042
TET 27769
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 25 February 2016
Revised Date: 6 May 2016
Accepted Date: 16 May 2016
Please cite this article as: Yuan R, Li M-q, Xu J-b, Huang S-y, Zhou S-l, Zhang P, Liu J-j, Wu H,
Synthesis and optical properties of novel Tröger's base derivatives, Tetrahedron (2016), doi: 10.1016/
j.tet.2016.05.042.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Diphenylamine, phenothiazine or carbazole were introduced into
Tröger's base skeleton via Ullmann or Suzuki coupling to afford
new TB derivatives. Their optical properties tests, density
functional theory (B3LYP; 6-31G*) calculations were
investigated. Incidentally anti-cancer activity against human
hepatoma HepG2 cells in vitro (MTT assay) were investigated.
All the results indicated that these novel compounds have the
potential as fluorescence materials.
Synthesis and optical properties of novel
Tröger's base derivatives
Rui Yuanb, Ming-qi Lia, Jiang-biao Xua, Shu-ying Huanga,
Sheng-liang Zhoua, Peng Zhanga, Jin-juan Liua*, Hui Wua*
aSchool of Chemistry and Chemical Engineering, State Key Laboratory Cultivation Construction Base of
Biotechnology on Med-edible Plant of Jiangsu Province, Jiangsu Normal University, Xuzhou, 221116, P. R.
China
bInstitute of Biochemistry and Molecular Biology, School of Life Sciences, Lanzhou University, Lanzhou
730000, China

ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Synthesis and optical properties of novel Tröger's base derivatives
Rui Yuanb, Ming-qi Lia, Jiang-biao Xua, Shu-ying Huanga, Sheng-liang Zhoua, Peng Zhanga, Jin-juan
Liua*, Hui Wua
aSchool of Chemistry and Chemical Engineering, State Key Laboratory Cultivation Construction Base of Biotechnology on Med-edible Plant of Jiangsu
Province, Jiangsu Normal University, Xuzhou, 221116, P. R. China
bInstitute of Biochemistry and Molecular Biology, School of Life Sciences, Lanzhou University, Lanzhou 730000, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
Diphenylamine, phenothiazine or carbazole were introduced into Tröger's base skeleton via
Ullmann or Suzuki coupling to afford new TB derivatives. Their optical properties tests, density
functional theory (B3LYP; 6-31G*) calculations were investigated. Incidentally anti-cancer
activity against human hepatoma HepG2 cells in vitro (MTT assay) were investigated. All the
results indicated that these novel compounds have the potential as fluorescence materials.
Available online
2009 Elsevier Ltd. All rights reserved
.
Keywords:
Tröger's base derivatives
Synthesis
Theoretical calculations
Photoelectric property
Anti-cancer activity
1. Introduction
The unique structure of Tröger's base (TB, Figure 1) and its
derivatives has received more attention since found in 18871.
Structurally, TB is an excellent natural candidate for
luminescence material with high controllability and obvious
advantages: (1) because TB skeleton contains non-coplanar V-
type twisted structure which cannot be rotated, so it can prevent
the intermolecular π-π close stacking and dipole-dipole
interaction. (2) its large dihedral angle (80-104o)2 allows wider
Stokes shift and less self-absorption. (3) the highly rigidity and
steric hindrance can restrict the internal rotation (RIR) and
reduce non-radioactive transition. (4) the two bridge nitrogen
atoms on the skeleton can form N*┄H-C bond which make TB
acting as a hydrogen bond acceptor. Therefore, it is convenient to
adjust the wavelength and intensity of luminescence via binding
with large cavity and combining with various kinds and different
Figure1. Structure of Tröger's Base
Moreover, the unique V-type twisted structure of Tröger's
base (can be classified as a family of molecular tweezers4) enable
it selectively embed specific DNA double helix and cut them off.
Recent studies5-11 indicated that Tröger's base derivatives cut off
the A-T-T base pairs on DNA selectively during the process of
unwinding and rewinding of the DNA helix. To the best of our
knowledge, the hindrance of the rewinding of the DNA helix will
lead to the depression of multiplication of cancer cell. Because
there may be more A-T-T base pairs in tumor cells than that in
normal ones12, Tröger's bases can be used as tumor inhibitor.
numbers
of
objects.
(5)
the intermolecular distance between two terminals is approximate
to 1 nm and the minimum distance between the methylene
adjacent to bridge nitrogen atom and aromatic ring is 2.91Å.2-3
(6) there are eleven sites in the framework that can be modified,
without considering the side chain. So, the TB structure can be
designed, assembled and tailored to meet the needs easily. All of
these advantages can greatly reduce the fluorescence quench and
Therefore, introducing suitable groups to TB skeleton is an
efficient way to take advantage of TB and get novel fluorescence
materials and tumor inhibitor.
Although there are many sites on TB framework can be
modified, the species of new TB derivatives are relatively few in
enhance the fluorescence quantum efficiently.
———
Corresponding author.
E-mail address: wuhui72@aliyun.com (H. Wu).

2
Tetrahedron
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number. In most cases aromatic nucleus are modified to afford
unilateral or bilateral TB derivatives. Halo-substituted TB was
chosen as starting material, via Buchwald-Hartwig amination and
various coupling reactions such as Corrius-Kumada, Sonogashira
and Suzuki coupling to obtain novel TB derivatives13-16
.
Unfortunately, most of them focused on improving yields by
optimizing the reaction conditions.
Recently, the luminescence properties, molecular recognition
abilities and host-guest chemical properties applications of TB
and its derivatives have been reported17-19, but taken altogether,
there are few researches on the luminescence properties of new
TB derivatives, also, no researches about the bioactivity have
been mentioned.
Diphenylamine (DPA), phenothiazine and carbazole are
widely used in the field of dyes20-21 and pharmaceuticals
aspects22-23. In this work, they were introduced into TB skeleton
to obtain series of new TB derivatives and the optical properties
and anticancer activity of products were studied subsequently.
2. Results and discussion
2.1. Synthesis of new compounds 3a-b, 4a-k and 5a-d
Seventeen novel TB derivatives were prepared according to
the synthetic routes showed in Scheme 1 and 2. Thirteen of them
(3a-b, 4a-k) were obtained via Suzuki C-C coupling, and four of
them (5a-d) were obtained via Ullmann C-N coupling. (Scheme
1 and Figure 2).
Figure 2. Compound 4a-k and 5a-d
In order to enhance the total yield, reaction conditions were
optimized. Table 1 showed that tetrahydrofuran was the best
solvent for 3a and 3b because of the good solubility. Toluene
was the ideal solvent for 4a-b, 4e, 4h-i and 5a-d and benzene
was the best solvent for 4c, 4g, 4j and 4k. The optimum reaction
time for 5a-b was 48 h, while 5c was 36 h and 5d was 24 h.
(Table 2)
Table 1 The effect of different solvents on total yield.a
Compound
Tolueneb / %
Tetrahydrofuranc / %
Benzened / %
Scheme 1. Synthetic route of 3a and 3b: (i)
paraformaldehyde, TFA, -15oC to 0oC, 6 d; (ii) n-BuLi,
trimethylborate,-78oC to r.t.; (iii) Pd(PPh3)4, K2CO3, toluene,
110 oC ( or THF, 70oC).
3a
3b
4a
4b
4c
4d
4e
4f
35
30
68
52
25
15
30
18
26
46
25
38
30
37
22
42
27
54
62
58
43
32
27
25
16
30
35
19
42
32
29
17
31
23
28
31
40
38
17
32
27
20
28
37
18
36
25
21
17
29
24
4g
4h
4i
4j
4k
5a
5b
5c
5d
Scheme 2. Synthetic route of 4a-k and 5a-d: (i) TFA, -15oC,
6 d; (ii) Pd (PPh3)4, K2CO3, toluene, 110oC; (iii) CuI, 1,10-
Phenanthroline, Cs2CO3, toluene, 110oC.
aThe loading of 2 and 1b was 0.5 mmol. bAt 110oC. cAt 65oC.
dAt 80oC.

Table 2 The effect of different reaction time on total yield.a
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Compound
24 h / %
36 h / %
48 h / %
5a
5b
5c
5d
22
32
37
14
38
25
10
10
42
45
27
25
aThe loading of 2 and 1b was 0.5 mmol, in toluene at 110oC.
Figure 5. The fluorescence emission spectra of 3a and 3b (1×10-6 mol·L-1
in CH2Cl2)
2.2. Optical Properties
UV-vis absorption spectra of the new compounds (4a-k and
5a-d) in DCM were shown in Figure 3 and Figure 4. The
maximum UV-vis absorption wavelength of 4a-k was in the
range of 250-340 nm and 5a-d was in the range of 285-310 nm.
Due to the more delocalized and extended π-conjugated system,
there was a strong maximum absorption peak at 275 nm for
compound 4c. Compound 4d red-shifted because more
conjugated groups were introduced.
The fluorescence emission spectra of 4a-k were in the range
of blue or green light 382-447 nm excitated at 300 nm (Figure 6).
When more conjugate groups were introduced, the new
compounds red-shifted except 4c. The fluorescence emission
spectra of 4c exhibited strong fluorescence emission at 445 nm,
and it may be caused by the unilateral introduction of
phenanthrene.
Figure 6. The fluorescence emission spectra of 4a-k (1×10-6 mol·L-1 in
CH2Cl2)
Figure 3. The absorption spectra of 4a-k (1×10-6 mol·L-1 in
CH2Cl2)
The fluorescence emission spectra of 5a-d were in the range
of 350-430 nm. Figure 7 showed that compound 5d red shifted,
partly because the introduction of larger conjugated system made
the flow of electrons smoother.
Figure 7. The fluorescence emission spectra of 5a-d (1×10-6
Figure 4. The absorption spectra of 5a-d (1×10-6 mol·L-1 in CH2Cl2)
mol·L-1 in CH2Cl2)
The fluorescence emission spectra of the new compounds (3a-
b, 4a-k and 5a-d) in dichloromethane were shown in Figure 5, 6
and 7. Compound 3a had a strong emission peak at 435 nm
which caused by the π-π* transitions. Compound 3b red-shifted
and the emission intensity decreased which may due to the longer
conjugated chain. (Figure 5)
2.3. DFT calculations
The electronic configurations were performed on compounds
3a-b, 4a-k and 5a-d using Gaussian 09 program24 and the
B3LYP/6-31G(d) basis sets were used for the calculations. The
HOMO and LUMO distributions of all the compounds were
shown in Table 3. Because of the introduction of electron
donating or electron-withdrawing groups and the extended

4
Tetrahedron
conjugated system, the band gaps of HOMOs and LUMOs were
inhibition rate is 73.5% and 76.8% respectively. The result
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reduced which conducive to efficient electronic transmission.
The result indicated that these new TB derivatives possess
significant charge-transfer property.
indicated these compounds have the profound value for further
study.
Because some of the new compounds may have the potential
anti-tumor activity, so incidentally compounds 3a-b, 4a-k and
5a-d were subjected to biological assessment against human
hepatoma HepG2 cell lines in vitro. Cell proliferation was
determined by MTT assay and HepG2 cells were firstly treated
with 5 µg/mL of the compounds. The results indicated the
inhibition rate of compounds 3a, 3b and 4b on the HepG2 cells
was over 10% which showed their effectiveness on this cancer
cell. (Table 4)
Table 3 Electrochemical property of 3a-5d
Compound
HOMO (eV)
-5.33
-6.13
-5.78
-4.69
-3.78
-4.75
-4.87
-3.98
-5.37
-4.86
-4.33
-4.58
4.91
LUMO (eV)
-0.13
-2.32
-1.67
-0.92
-1.13
-0.87
-1.13
-0.67
-1.32
-0.97
-1.04
-1.23
-1.57
-0.89
-0.54
-2.81
-1.86
-2.04
Band (eV)
5.2
TB
3a
3b
4a
4b
4c
4d
4e
4f
3.81
3.51
3.77
2.65
3.88
3.74
3.31
4.05
3.89
3.29
3.35
3.34
4.24
4.21
2.58
2.49
3.17
Table 5 Inhibition rate (%) and IC50 of TB derivatives on
HepG2 cell in different concentrationa
Inhibition rate in difference
concentration ( µg/mL)
Entry
IC50 (µM)
5
25
50
3a
3b
4d
18.1±1.1
30.0±1.4
11.6±1.8
73.5±2.6
76.8±1.8
28.2±1.0
81.0±1.5
78.8±1.6
80.9±1.5
24.68±1.39
12.61±1.10
50.34±1.70
4g
4h
4i
aThe TB derivatives were dissolved in DMSO, and the
absorbance value was measured at 490 nm in
Enzyme Linked Immunosorbent Assay (ELISA). Experiments
4j
a
4k
5a
5b
5c
5d
-5.13
-4.75
-5.39
-4.35
-5.21
were performed in triplicate, and the results were expressed as
mean of percentage inhibition.
3. Conclusions
In this work, diphenylamine (DPA), phenothiazine or
carbazole were introduced into TB skeleton via Ullmann or
Suzuki coupling and series of new TB derivatives were
synthesized. The results of their optical properties indicated that
some product exhibited strong fluorescence emission. The
electronic configurations calculated by DFT indicated the
extended conjugated system conducive to efficient electronic
transmission and the new TB derivatives possess significant
charge-transfer property. The results showed they have the
potential as fluorescence materials. Finally, the results of their
anticancer activity on the HepG2 cells indicated that three
compounds could inhibit the growth of cancer cells effectively.
So, they are worth further study and can be developed as high-
performance anticancer drugs in the future.
2.4. Anti-cancer activity against human hepatoma HepG2 cells
Table 4 Inhibition rate (%) of TB derivatives (5 µg/mL) on
HepG2 cella
Entry
1a
1b
2
Inhibition rate (%)
Entry
4f
Inhibition rate (%)
3.8±2.4
0.0±3.1
5.3±1.8
4g
4h
4i
1.4±2.8
-5.0±1.4
18.1±1.1
30.0±1.4
-5.6±3.1
1.3±2.7
0.5±3.1
3a
3b
4a
4b
4c
2.3±1.7
4j
2.1±1.4
4k
5a
5b
5c
-1.3±0.7
6.4±3.8
1.7±2.5
-3.±1.8
Acknowledgments
4d
4e
11.6±1.8
-0.6±2.1
-2.5±2.7
-0.9±1.9
We are grateful to the foundation of the “National Natural Sci
ences Foundation of China” (No. 31300067), “Priority Academic
Program Development of Jiangsu Higher Education Institutions”
, "Major Project of Natural Science Research of University in Jia
ngsu" (No. 14KJA430003, 15KJA180002), “Aid project for PhD
faculties in Jiangsu Normal University” (13XLR007), “Science a
nd Technology Planning Project of Xuzhou” (KC15SH080), “Nat
ural Sciences Foundation of Jiangsu Normal University" (No. 13
XLA01)” for financial support.
5d
aTB derivatives were dissolved in DMSO, and the absorbance
value was measured at 490 nm in
a Enzyme Linked Immunosorbent Assay (ELISA). Experiments
were performed in triplicate, and the results were expressed as
mean of percentage inhibition.
Then compounds 3a, 3b and 4b were determined further in
different concentrations. (Table 5) The result showed that the
inhibition rate was increased with the increase of their
concentration. Compound 4b showed a significantly increased of
inhibition rate when the concentration is 50 µg/mL compare to 25
µg/mL. 25 µg/mL of 3a and 3b showed very good inhibitory
effects against human hepatoma HepG2 cells in vitro and the

Supplementary Material
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Supplementary data (experimental details including synthetic
procedures, NMR spectra, mass spectrometry, IR) associated
with this article can be found, in the online version, at
http://dx.doi.org/
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