5-Phenylcoumarin Derivatives: Design, Synthesis, and Vasodilatory Activity

Article abstract of DOI:10.1002/cbdv.201800255

In continuation of our previous efforts towards the development of coumarin derivatives with potential vasodilatory activity, 5-phenylcoumarin derivatives were designed and synthesized. Target compounds and their precursors exhibited moderately vasodilato

Full text of DOI:10.1002/cbdv.201800255

Article Type: Full Paper
5
-Phenyl Coumarin Derivatives: Design, Synthesis and vasodilatory activity
a
b
c
a
a
,a
Cheng Wang, Youjia Li, Ting Zhang, Di Wei, Yajing Hou, and Huaizhen He*
a
School of Medicine, Xi’an Jiaotong University, Xi’an 710061, P. R. China. e-mail:
hehuaizhen@mai.xjtu.edu.cn.
b
The Second Affiliated Hospital of Xi'an Jiaotong University, Xi’an 710004, P. R. China.
c
Northwest Women's and Children's Hospital, Xi’an 710061, P. R. China.
In continuation of our previous efforts towards the development of coumarin derivatives with
potential vasodilatory activity, 5-phenyl coumarin derivatives were designed and synthesized. Target
compounds and their precursors exhibited moderately vasodilatory ability with EC50 at 2.5-49.0 μM.
And docking study also revealed the well binding mode of compound 8c with the target protein.
Moreover, Intermediates and final product also exhibited different fluorescent properties due to the
substituent effect. These results may provide new idea for synthesis and application of 5-substituted
coumarins.
Keywords: 5-Phenyl coumarin • Vasodilatory activity • Fluorescence • Molecular docking
Introduction
Coumarins, structurally composing of fused benzene and a-pyrone rings, formed a great class of
naturally occurring compounds that possess considerable therapeutic prospect due to their diverse
pharmacological activities. Some natural coumarin compounds were confirmed to exhibit inhibitory
effects on LPS-induced NO production, vascular smooth muscle cell proliferation and six human CA
[
1-3]
isozymes (CAs I, II, VII, IX, XII and XIII).
Besides, a series of synthetic coumarin sulfonamides,
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triazole-coumarins, thiazole-coumarins, indolyl-coumarins, imidazole-coumarin and 4-substituted
coumarins derivatives were found to have anti-HIV, antibacterial, antioxidant, inhibiting ACE,
antifungal, scavenging of reactive oxygen species (ROS), anti-inflammatory, and anticancer
[
4-12]
activities.
More importantly, some of them have made their way to clinics including warfarin
(anticoagulant), hymecromone (choleretic and antispasmodic), armillarisin A (antibiotic),
carbochromen (coronary disease), and cloricromene (antithrombotic and antiplatelet), as shown in
Fig 1.
Moreover, coumarin derivatives, both natural and synthetic compounds, also exhibited
cardiovascular activity, such as lipid lowering effects, antihyperglycemic, in vitro vasorelaxant activity
[
13-19]
and in vivo antihypertensive effect.
Najmanová et al summarized the effects of selected
coumarins on experimental major cardiovascular diseases, including cardiac hypertrophy caused by
hypertension, experimental dysrhythmias, myocardial ischaemia/reperfusion, and experimental
myocardial injury and heamorrhagic shock, which all indicating the tremendous potentiality of
[
20]
coumarins on cardiovascular diseases.
Imperatorin (Fig 1), a furanocoumarin compound, was found to induce vasodilatation possibly via
2+
inhibiting voltage dependent calcium channel and receptor-mediated Ca influx and release, and it
[
21][22]
also was identified as a L-type calcium channel blocker in our previous works.
After that, we
have spent great efforts on study of imperatorin, concentrating on the synthesis and screening for
vasorelaxant activity of its derivatives. As a result, a series of furanocoumarin and 5-phenyl
furanocoumarin compounds were obtained, and they all exhibited considerable vasodilatory,
[
23-27]
antihypertensive, vascular remodeling effects and optical property.
Figure 1. Structures of clinically used coumarin derivatives and imperatorin.
In view of our interest in developing coumarin derivatives with vasodilatory activity to expand its
structural diversity, coumarin substructure in skeleton of imperatorin was kept. Following this idea, a
new series of 5-phenyl coumarin compounds were designed, synthesized, explored for their
bioactivity and fluorescence in present study. The docking study was also performed to investigate
the structural influence on the bioactivity and binding mode.
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Results and Discussion
Chemistry
Target compounds were prepared via seven facile reactions, esterification, Fries rearrangement,
methylation, Baeyer-Villiger oxidation, bromination, etherification and Suzuki-coupling reaction, as
depicted in scheme 1. Initially, with triethylamine as alkaline reagent, 7-OH coumarin (1) was
esterified by Ac O in anhydrous THF within 0.5 h to give 7-acetyloxy coumarin (2) with >90% yield.
2
Fries reaction of 2 could afford two rearrangement products at 6-substitute and 8-substituted,
respectively. Since 8-substitute was thermodynamic product rather than the dynamic compound (6-
substitute), enhanced temperature could result in improved yield of 8-acetyl-7-hydroxycoumarin (3),
and 3 can obtained with 67.5% yield at 160℃. Dimethyl sulphate can exhibit the strongest reaction
activity only at 50℃, hence, 8-acetyl-7-methoxycoumarin (4) was obtained with remarkable yield
under this moderate condition. Baeyer-Villiger oxidation was the limited step of targets due to its
low yield. Concentrated sulphuric acid served as solvent and reagent, inducing carbonization during
the process, which may contribute to the low yield. Moreover, as oxidant, hydrogen peroxide must
be dropwise added, in case of overheating even explosion. Finally, 8-hydroxy-7-methoxy coumarin
(5) was achieved. 5-Bromo-8-Hydroxy-7-methoxycoumarin (6) was then obtained by electrophilic
substitution reaction at C-5 of compound 5 within acetic acid in presence of Br , which attributed to
2
the stronger orientation effect of 8-hydroxy than 7-methoxyl. As the reaction progressed, product
precipitated from the solution, which made it convenient to purify. Compounds 7 were given by a
similar procedure with 4, and etherification of 8-hydroxy ensured the success of last step. Finally,
target compounds 8 were constructed by the classical Suzuki–Miyaura cross-coupling reaction, while
it could not be accomplished on 6 with hydroxy group. Overall, we realized our goals via the
operable designed path.
Scheme 1. Design route of target compounds. Reagents and conditions: (a) Et N, (CH
3
3 2 3 2 3 2 4 2 2
CO) O; (b) AlCl , 160℃; (c) acetone, K CO , reflux; (d) H SO , H O , 0℃;
(
e) CH COOH, Br , 0℃, -r.t.; (f) acetone, K CO , reflux; (g) 1, 4-dioxane, H O, Na CO , 2-(trifluoromethyl)-phenylboronicacid, 90℃.
3
2
2
3
2
2
3
Vasodilatory activity
+
To evaluate the potential vasodilatory activity of compounds 8, a K -induced contractions model of
rat mesenteric artery rings was introduced. Compounds 7 were performed to investigate the
substituent effect between them. As leading compound, imperatorin was also tested. And the
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results were shown in table 1. 8b with N, N-diethyl ethylamine substituent was more effective than
a with N, N-dimethyl ethylamine substituent, and change from N, N-diethyl to pyrrole group
afforded 8c, the rigid structure may be favor to vasodilatory effect, comparing the EC50 and Emax
8
%
between 8c and 8b. However, when the larger group, piperidyl, replaced pyrrole group, a lower
vasodilatory 8d was obtained, indicating the smaller rigid substituent may be beneficial for
bioactivity. Morpholinyl, a more hydrophilic group, induced slightly decrease of activity, compared
8
d with 8e. On account of above rules, 8c exhibited most potent vasodilator activity. And the same
phenomenon in compounds 7 further supported our speculation. Similarly, table 1 revealed 7
generally possessed higher bioactivity than corresponding 8, may suggested that CF -substituted
3
phenyl in 5-coumarin was not suitable for their vasodilator activity. Furthermore, compounds 8 even
showed poorer vasodilator activity compared with imperatorin, the lead compound. Which suggests
that further study still need to improve.
Table 1. In vitro vasodilator activity of compounds 7-8.
EC50(μM)
n=6)
EC50(μM)
Compds
E
max
%
Compds
max
E %
(
(n=6)
7
a
b
5.3±0.7
3.0±0.5
2.5±0.2
3.4±0.3
3.6±0.3
12.6±0.6
93.9±5.0
101.7±6.2
102.4±0.9
103.8±3.1
102.7±4.2
83.1±0.65%
8a
8b
8c
8d
8e
---
49.0±1.5
8.3±1.4
4.2±0.1
13.2±1.2
20.0±1.2
---
102.9±2.5
95.8±3.4
113.4±6.4
104.0±5.9
100.2±2.0
---
7
7
c
7
d
e
7
imperatorin
Chains E and F of transmembrane segments (Fig. 4B) of L-type calcium channels (PDB code: 3G43)
was demonstrate participate in binding with L-type calcium channel blocker, as well as
[
28]
imperatorin. Molecule docking study was further performed to investigate the binding mode of
these compounds to the target protein, 3G43. The best vasodilatory compound, 8c was chosen for
docking study, and the result was presented in Fig. 4a. Generally, four critical hydrogen bonds
formed between compound 8c and protein, contributing to its potent bioactivity. Two oxygen atoms
of pyrone formed two hydrogen bonds with HIS107 and THR110 with bond lengths of 2.50 Å and
2
.14 Å, respectively. Two hydrogen bonds were found between two fluorine atoms in
trifluoromethyl bond with GLU82 with distance of 2.24 Å and 2.45 Å, respectively. Docking mode in
this study was quite different from that of 5-phenyl furanocoumarins, which revealed our target
compounds may work in a diverse way to function vasodilatory effect. Fig. 4b clearly depicted that
coumarin kept a certain angle with 5-phenyl in 8c while bonding with protein.
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Figure 4. Binding mode of compounds 8c to L-calcium channel (PDB code: 3G43); (a) binding mode; (b) stereochemistry of compound 8c.
Fluorescent study
Dual functional biomaterials or compounds, especially the bioactive fluorescence probes have drawn
much attention because they opened up the possibility of visualized imaging in diagnosis and
[
29-31]
treatment of tumor and other disease.
And we wished that our target compounds could also
served as fluorescence probes. Thus, the fluorescence of the compounds was also discussed. The
substituent effect on coumarin was explored by comparing the fluorescence of compounds 1-8. As
an electrophilic group, appearance of acetyl reduced electron density in 2 and 3, consequently,
generating obviously decreased fluorescence intensity. After 7-hydroxy was methylated,
fluorescence intensity of 4 was clearly stronger than that of 3, as shown in Fig. 2a. When acetyl was
lost to afford 5, apparent red shift can be detected. And bromination of 5 obtained 6, fluorescence
intensity and λem both increased, which may attribute to the lone pairs in bromine, forming
conjugated system with coumarin. Substituted amine contributed to the electron density, resulting
the increasing fluorescence intensity in 7. 5-(2-CF )-phenyl in 8 offered less electron than Br in 7,
3
resulting reduced fluorescence intensity.
Figure 2. Fluorescent property of compounds 1-8; (a) fluorescent property of 1-4; (b) fluorescent property for 5, 6, 7c and 8c.
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Fig. 3 depicted the effect of solvents and pH on 8c. The increasing polarity of the solvents resulted in parabola trend in fluorescence
intensity and red-shift. 8c exhibited highest and lowest fluorescence intensity in DMF and MeCN, respectively (Fig. 3a). As shown in Fig.
3b, fluorescence intensity obviously decreased along with reducing pH, probably because of tertiary amine substructure in 8c. In acidic
condition, 8c bond proton, as a result, electron density decreased, resulting in reducing fluorescence intensity.
Figure 3. Solvents (a) and pH (b) effects on Fluorescence of 8c.
F
Moreover, the ability of 8c to emit the absorbed light energy was characterized quantitatively by the fluorescence quantum yield (Φ ).
F
7-Hydroxy-4-methylcoumarin (Φ =0.63, λex=450 nm) was served as reference to calculate the fluorescence quantum yield. And the
fluorescence quantum yield of 8c was found to be 0.15, which implied that out compound may serve as fluorescence probe as well as
vasodilatory entity.
Conclusions
In summary, we designed, synthesized novel 5-phenyl coumarin derivatives and determined their
vasodilator activity. Fluorescent investigation revealed the substituent influence on optical property
of coumarin, leading us the direction for further modification. Study on structure-activity
relationship among compounds 7 (a-e) and 8 (a-e), and molecular docking suggested that the
prepared compounds in this paper may act via different mechanism from that of previously reported
5
-phenyl furocoumarin. These results may point out a different idea for further structural
optimization aiming at more potential coumarin-based entities, and further research is well
underway.
Experimental Section
All reagents and solvents were purified and dried by standard techniques. Melting points were
determined on an X-4 apparatus without correction. Thin layer chromatography (TLC) on silica gel
plates was routinely employed to follow the course of reactions and to check the purity of the
products. Mass spectra were performed on a Shimadzu GC-MS QP 2010 instrument (Shimadzu,
1
13
Japan). H NMR and C NMR spectra were recorded on a Bruker AVANCF 400 MHz instrument in
CDCl solution with TMS as internal standard. Chemical shift multiplicities were reported as follows:
3
s, singlet; d, doublet; t, triplet; m, multiplet.
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7
-Hydroxycoumarin (1, 6.48 g, 40.0 mmol) was dissolved in tetrahydrofuran, followed adding
triethylamine (7.50 mL). Acetic anhydride was dropwise added in. The mixture was stirred at room
temperature for 0.5 h. Product was obtained after evaporated solvent in vacuum and washed with
1
alcohol. Yield: 93.4%. M.p.142-144 ℃. H NMR (400 MHz, DMSO) δ 8.08 (d, J = 9.6 Hz, 1H), 7.77 (d, J
=
3
8.4 Hz, 1H), 7.28 (d, J = 2.1 Hz, 1H), 7.17 (dd, J = 8.4, 2.2 Hz, 1H), 6.48 (d, J = 9.6 Hz, 1H), 2.31 (s,
H).
Mixture of 7-Acetoxycoumarin (2, 7.10 g, 34.8 mmol) and aluminium trichloride (19.9 g, 149.2
mmol) powder was heated at 160°C for 2.5 h. After cooled, water was added and stirred for 0.5 h.
The aqueous phase was extracted with ethyl acetate (100×3 mL), the combined organic phase was
washed with saturated brines, dried with Na
2
SO
4
and evaporated in vacuo. The residue was purified
on a silica gel column eluting with CHCl
Yield: 67.5%. M.p.166-168 ℃. H NMR (400 MHz, DMSO) δ 11.81 (s, 1H), 7.99 (d, J = 9.6 Hz, 1H), 7.67
3
/EtOAc (20:3) to give yellow-green needle crystal (4.79 g).
1
(d, J = 8.6 Hz, 1H), 6.91 (d, J = 8.6 Hz, 1H), 6.29 (d, J = 9.5 Hz, 1H), 2.62 (s, 3H).
8
-Acetyl-7-hydroxycoumarin (3, 4.79 g, 23.5 mmol) was dissolved in anhydrous acetone, followed
adding anhydrous potassium carbonate (12.98 g, 94.0 mmol) and stirring at room for 0.5 h. Dimethyl
sulphate (3.31 mL) was added and heated at 50°C for 2 h. After that, the reaction mixture was
filtered and the filtrate was concentrated in vacuum. The crude product was washed with petroleum
1
ether for white product (4.99 g). Yield: 97.3%. M.p.117-118 ℃. H NMR (400 MHz, DMSO) δ 8.03 (d, J
=
9.6 Hz, 1H), 7.78 (d, J = 8.7 Hz, 1H), 7.18 (d, J = 8.6 Hz, 1H), 6.34 (d, J = 9.5 Hz, 1H), 3.91 (s, 3H), 2.51
(s, 3H).
8
-Acetyl-7-methoxycoumarin (4, 4.99 g, 22.9 mmol) was dissolved in sulphuric acid under ice bath,
and hydrogen peroxide was slowly dropwise added in. After reacting for 10 min, the result mixture
was poured slowly into a stirred solution of ice water and adjusted to neutral with sodium
bicarbonate. The aqueous phase was extracted with ethyl acetate (100×3 mL), the combined organic
phase was washed with saturated brines, dried with Na
2
SO and evaporated in vacuo. The residue
4
was purified by flash chromatography on a silica gel column eluting with CHCl
yellow-green needle crystal (0.77 g). Yield: 17.5%. M.p.175-177 ℃. H NMR (400 MHz, DMSO) δ 9.48
3
/EtOAc (20:3) to give
1
(s, 1H), 7.95 (d, J = 9.5 Hz, 1H), 7.16 (d, J = 8.6 Hz, 1H), 7.04 (d, J = 8.6 Hz, 1H), 6.27 (d, J = 9.5 Hz, 1H),
3
.89 (s, 3H).
8
-Hydroxy-7-methoxycoumarin (5, 0.77 g, 4.0 mmol) was dissolved in cooled acetic acid, followed
dropwise adding bromine (22.0 mmol). After reacting completed, the reaction mixture was filtered
and filter cake was washed with ice water. The filtrate was diluted by water and extracted with ethyl
acetate (30×3 mL), the combined organic phase was washed with saturated brines, dried with
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Na
2
SO and evaporated in vacuo. Total product was 0.98 g. Yield: 89.8%. M.p.172~173 ℃. MS: EI-MS
4
+
1
(m/z) 272.0 [M ]. H NMR (400 MHz, DMSO) δ 8.28 (s, 1H), 7.93 (d, J = 9.6 Hz, 1H), 7.37 (s, 1H), 6.22
d, J = 9.5 Hz, 1H), 3.92 (s, 3H).
(
5
-Bromo-8-hydroxy-7-methoxycoumarin (6, 0.50 g, 1.8 mmol) was dissolved in anhydrous
acetone, followed adding anhydrous potassium carbonate (1.02 g, 7.4 mmol) and stirring at room for
.5 h. Substituted amine hydrochlorides (2.16 mmol) was added and reflux. After reaction
0
completed, the mixture was filtered and evaporated in vacuo. The residue was purified by flash
chromatography on a silica gel column eluting with EtOAc/ MeOH (1:1), EtOAc/ MeOH (5:1) or
EtOAc/MeOH (10:1).
+
1
7
a M.p. 162-166 ℃. MS: EI-MS (m/z): 342.80 [M ]. H NMR (400 MHz, CDCl
3
) δ 7.95 (d, J = 9.8 Hz,
1
H), 7.12 (s, 1 H), 6.34 (d, J = 9.8 Hz, 1H), 4.59 (s, 2H), 3.97 (s, 3H), 3.41 (s, 2H), 1.62 (s, 6H).
+
1
7
1
2
b M.p. 193-195 ℃. MS: EI-MS (m/z): 370.85 [M ]. H NMR (400 MHz, CDCl ) δ 7.94 (d, J = 9.8 Hz,
3
H), 7.12 (s, 1H), 6.34 (d, J = 9.8 Hz, 1H), 4.26 (t, J = 6.1 Hz, 2H), 3.95 (s, 3H), 3.06 (t, J = 6.0 Hz, 2H),
.82 (s, 4H), 1.14 (t, J = 7.1 Hz, 6H).
+
1
7
c M.p. 166-169 ℃. MS: EI-MS (m/z): 368.85 [M ]. H NMR (400 MHz, CDCl
3
) δ 7.93 (d, J = 9.8 Hz,
1
H), 7.11 (s, 1H), 6.32 (d, J = 9.8 Hz, 1H), 4.57-4.40 (m, 2H), 3.99 (s, 3H), 3.43-3.38 (m, 6H), 2.16-2.10
(m, 4H).
+
1
7
1
4
d M.p. 173-178 ℃. MS: EI-MS (m/z): 380.85 [M ]. H NMR (400 MHz, CDCl ) δ 7.94 (d, J = 9.8 Hz,
3
H), 7.11 (s, 1H), 6.32 (d, J = 9.8 Hz, 1H), 4.38 (s, 2H), 3.91 (s, 3H), 3.00 (s, 2H), 2.74 (s, 4H), 1.69 (s,
H), 1.50 (s, 2H).
+
1
7
1
4
e M.p. 130-135 ℃. MS: EI-MS (m/z): 382.80 [M ]. H NMR (400 MHz, CDCl ) δ 7.93 (d, J = 9.8 Hz,
3
H), 7.10 (s, 1H), 6.33 (d, J = 9.8 Hz, 1H), 4.27 (s, 2H), 3.94 (s, 3H), 3.79 (s, 4H), 2.90 (s, 2H), 2.70 (s,
H).
A mixture of compound 7, Na
triphenylphosphine) palladium, dioxane and H
2
CO
3
, 2-(trifluoromethyl) phenylboronic acid, tetrakis
°
(
2
O was stirred at 90 C for 2.5 h. After cooling, H
2
O
was added in. The aqueous phase was extracted with ethyl acetate (50×4 mL), the combined organic
phase was dried with Na SO and evaporated in vacuo. The residue was purified by flash
chromatography on a silica gel column eluting with EtOAc/Ether (2:1) and EtOAc/MeOH (10:1).
2
4
+
1
8
a Yeild: 43.3%. White solid. M.p.145-147 ℃. MS: EI-MS (m/z): 407.1 [M ]. H NMR (400 MHz, CDCl
3
)
δ 7.88 (d, J = 7.4 Hz, 1H), 7.66-7.58 (m, 2H), 7.45 (d, J = 7.3 Hz, 1H), 7.13 (d, J = 9.7 Hz, 1H), 6.68 (s,
1
H), 6.15 (d, J = 9.7 Hz, 1H), 4.57 (s, 2H), 3.92 (s, 3H), 3.45 (s, 2H), 2.62 (s, 6H).
+
1
8
b Yeild: 45.6%. White solid. M.p.136-138 ℃. MS: EI-MS (m/z): 435.1[M ]. H NMR (400 MHz, CDCl )
3
δ 7.83 (d, J = 7.4 Hz, 1H), 7.71-7.59 (m, 2H), 7.42 (d, J = 7.2 Hz, 1H), 7.15 (d, J = 9.7 Hz, 1H), 6.79 (s,
1
H), 6.16 (d, J = 9.7 Hz, 1H), 4.65 (s, 2H), 4.00 (s, 3H), 3.94 (s, 4H), 3.55 (s, 2H), 1.53-1.50 (m, 6H).
+
8
c Yeild: 33.30%. White solid. M.p. 90-92 ℃. MS: EI-MS (m/z): 433.1 [M ].
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+
1
8
d Yeild: 53.4%. White solid. M.p. 133-135 ℃. MS: EI-MS (m/z): 447.1 (M ). H NMR (400 MHz, CDCl
3
)
δ 7.82 (d, J = 7.4 Hz, 1H), 7.64-7.60 (m, 2H), 7.29 (s, 1H), 7.13 (d, J = 9.7 Hz, 1H), 6.76 (s, 1H), 6.14 (d, J
=
9.7 Hz, 1H), 4.38 (s, 2H), 3.91 (s, 3H), 3.00 (s, 2H), 2.74 (s, 4H), 1.69 (s, 4H), 1.50 (s, 2H).
+
1
8
e Yeild: 49.2%. White solid. M.p. 114-117 ℃. MS: EI-MS (m/z): 449.1 [M ]. H NMR (400 MHz, CDCl )
3
δ 7.82 (d, J = 7.5 Hz, 1H), 7.65-7.57 (m, 2H), 7.29 (d, J = 7.4 Hz, 1H), 7.14 (d, J = 9.7 Hz, 1H), 6.77 (s,
H), 6.14 (d, J = 9.7 Hz, 1H), 4.33 (t, J = 5.3 Hz, 2H), 3.90 (s, 3H), 3.76 (s, 4H), 2.90 (s, 2H), 2.66 (s, 4H).
1
34
Activity evaluation was performed following our previous reports. Briefly, Sprague-Dawley rats
were anesthetized and sacrificed by decapitation. 2 mm segments of second order branch of
mesenteric artery were obtained. The segments were mounted in Multi-wire myograph system at 37
°C and maintained in physiological Krebs buffer and carbogen (95% O
2
, 5% CO ). After equilibration
2
for 30 min, vessel tension increased to 3 mN, followed by equilibrating for another 1.5 h. The
+
sustained tension of segments was obtained by exposure to a K -rich Krebs solution (with 60 mM
KCl), target compounds were then added cumulatively, and the concentration response curves were
constructed. Control vessels were subjected to the same processes simultaneously with adding
vehicle only. This study was carried out in strict accordance with the recommendations in the Guide
for the Care and Use of Laboratory Animals from the National Institutes of Health. The experimental
protocols for using the mice were approved by the Animal Ethics Committee at Xi’an Jiaotong
University, Xi’an, China (Permit Number: XJTU 2011-0045).
35
Molecular docking was carried out following our previous study. Briefly, the small molecules and
the X-ray crystal structure of protein (PDB code: 3G43) were imported. Water molecules were
removed and hydrogen was added. Tripos force field and Pullman charge were applied to minimize.
8
c was depicted by Sybyl/Sketch module (Tripos Inc.), optimized by Powell’s method with Tripos
force field with convergence criterion at 0.005 kcal / (Å mol), and assigned with Gasteiger–Hückel
method.
The spectral characteristics of the compounds were also measured. Compounds 1-6, 7c and 8c were
-
2
performed by dissolved them in methanol separately obtaining 4×10 mol/L stock solutions. 8c was
dissolved separately in methanol, ethyl acetate, N, N-dimethylformamide, acetonitrile and chlorform
-
5
to obtain 4×10 mol/L solution. In another experiment, the solution of 8c in methonal was freshly
prepared by the buffer solution to the corresponding pH (5.7, 7.4 and 8.0). The emission spectra
were obtained by using RF-5301 spectrofluorometer. Test conditions: room temperature, adjust the
excitation wavelength λex, the sample pool is 1 cm×1 cm×4 cm quartz cuvette, slit width of 5 nm.
[
32]
Moreover, 7-Hydroxy-4-Methylcoumarin (ΦF=0.63 in ethanol, λex=450 nm)
was chosen as
standard dye to measure and calculate the fluorescence quantum yields of the synthesized dye (8c)
[
33]
follow our previous procedure.
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Acknowledgements
This work was supported by the Natural Science Basic Research Plan in Shaanxi Province of China
(No. 2016JM8076).
Author Contribution Statement
H. Z. He designed and managed the project. C. Wang and Y. J. Li contributed to synthetic work
activity evaluation. T. Zhang and D. Wei
conducted the optical experiments. Y. J. Hou worked on the docking study.
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