Synthesis and fluorescent study of 5-phenyl furocoumarin derivatives as vasodilatory agents

Article abstract of DOI:10.1016/j.bmcl.2015.11.056

Two series of 5-phenyl furocoumarin derivatives were designed and prepared based on our previous research. All new compounds were characterized by ¹H NMR, ¹³C NMR and mass spectra. Furthermore, they were screened for their vasodilato

Full text of DOI:10.1016/j.bmcl.2015.11.056

Bioorganic & Medicinal Chemistry Letters 26 (2016) 640–644
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and fluorescent study of 5-phenyl furocoumarin
derivatives as vasodilatory agents
⇑
Cheng Wang, Tao Wang, Limin Huang, Wen Lu, Jie Zhang, Huaizhen He
School of Pharmacy, Xi’an Jiaotong University, Xi’an 710061, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2015
Revised 11 November 2015
Accepted 17 November 2015
Available online 17 November 2015
Two series of 5-phenyl furocoumarin derivatives were designed and prepared based on our previous
research. All new compounds were characterized by 1H NMR, 13C NMR and mass spectra. Furthermore,
they were screened for their vasodilatory activity on the mesenteric artery of Sprague-Dawley rats,
and they all presented with moderate vasodilatory activity. Fluorescent properties of the target com-
pounds were tested in methanol. The fluorescence variation of 4a was investigated in different solvents,
various pH and the migration time was determined. All results indicated that this type of fluorescent
compound can be used as vasodilatory agents and probes simultaneously after further structural
modifications.
Keywords:
Furocoumarin
Synthesis
Vasodilatory activity
Fluorescence properties
Theoretical studies
Ó 2015 Elsevier Ltd. All rights reserved.
Hypertension is increasing in prevalence worldwide due to
aging of the population and rising rates of obesity.1 Although novel
agents and channelopathy for the treatment of hypertension have
made substantial progress,2–5 hypertension remains an incurable
disease. Because vasodilatory capacity damnification is a signifi-
cant hallmark of hypertension, vascular studies have become an
interesting field for vasodilatory agents.
which may enhance the conjugation, contributing to the fluores-
cence of the molecule.20,21
Based on these observations, we developed two series of com-
pounds (Scheme 1) to enhance the structural diversity and fluores-
cence potency. The docking results confirm our hypothesis of the
geometric structure of the target compounds. Activity evaluation
indicates all the target compounds possess favorable vasodilatory
activity and optical properties.
The general methods for synthesis of compounds 4a–5c are
summarized in Scheme 2. The option of methoxycarbonyl and
ethoxycarbonyl for R1 was based on theoretical study. The R2 were
selected based on our previous studies in consideration of bioactiv-
ity and fluorescence. Compounds substituted with pyrrolidyl, mor-
pholinyl and piperidyl possessed high bioactivity and fluorescence
compared with other substituents, as previously reported.
Compound 4d was synthesized to investigate the substitution
effect on bioactivity. The reaction were monitored by TLC under
Furocoumarins form a large class of naturally occurring com-
pounds, which possess surprising pharmacological activity, optical
properties and promising therapeutic prospects.6–14 During the
search for novel furocoumarin-based potent antihypertensive
agents, we developed a number of furocoumarin derivatives and
screened them for potent vasodilatory activity, vascular remodel-
ing effects and fluorescent activity.15–19 Theoretical studies reveal
that geometric structures of diphenyl–furocoumarin derivatives
are altered following the change of the ortho-substituent of phenyl.
The dihedral angle between furocoumarin and phenyl gradually
increases with the change of F, Cl, Br, CF3, which is consistent with
their vasodilatory activity. The dihedral angle is almost 90° with
the CF3 substituent. This suggests that the dihedral angle between
furocoumarin (marked in purple) and phenyl (marked in red) may
effect the vasodilatory activity. Further theoretical studies show
that the substituents of methoxycarbonyl and ethoxycarbonyl
could afford a 90° dihedral angle. Moreover, introduction of an
ester group to the phenyl could change the electron distribution,
⇑
Corresponding author. Tel./fax: +86 29 82655451.
E-mail address: hehuaizhen@mail.xjtu.edu.cn (H. He).
Scheme 1. Design strategy of target compounds.
http://dx.doi.org/10.1016/j.bmcl.2015.11.056
0960-894X/Ó 2015 Elsevier Ltd. All rights reserved.

C. Wang et al. / Bioorg. Med. Chem. Lett. 26 (2016) 640–644
641
Table 1
Structures and in vitro vasodilator activity of title compounds
Compd
4a
R1
R2
pEC50 (lM) (n = 6) Emax (%)
CH3OCO
CH3OCO
4.71 0.03
5.59 0.06
102.2 2.22
N
N
O
4b
100.1 2.44
115.9 3.04
4c
CH3OCO
5.35 0.07
N
N
4d
5a
CH3OCO
5.27 0.01
5.15 0.01
101.5 0.05
100.1 0.10
C2H5OCO
N
N
N
Scheme 2. Synthetic route of target compounds. Reagents and conditions: (i) Br2,
AcOH, 0 °C–rt; (ii) BBr3, CH2Cl2, À5 °C to rt; (iii) K2CO3, acetone, reflux; (iv) Na2CO3,
Pd(PPh3)4, dioxane/H2O (v/v = 3:1).
O
5b
C2H5OCO
5.81 0.13
113.3 1.17
5c
C2H5OCO
5.38 0.03
113.4 6.45
365 nm because compounds 4a–5c showed favorable primary
fluorescence.
Imperatorin
Verapamil
—
—
—
—
4.95 0.14
7.51 0.09
85.6 0.40
95.8 1.92
The vasodilator activities of the synthesized derivatives were
evaluated on the in vitro rat mesenteric artery rings against a
K+-induced contractions model, and the results were summarized
in Figure 1 and Table 1. Generally, all novel designed compounds
were more effective than the parent scaffold. Compounds with
an ethoxycarbonyl substituent had higher vasodilator activity than
that of methoxycarbonyl, as shown in compound 4a compared
with 5a, 4b compared with 5b, 4c compared with 5c, separately.
This may be because the ethoxycarbonyl group contributes more
electrons to the molecule, and the larger substituent favors the
forming of a vertical dihedral angle. The result also supports our
hypothesis. The pentacyclic pyrryl in 4a was replace with a larger
moiety piperidyl to yield 4c, and the vasodilator activities were
simultaneously improved. The same trend is observed in 5a and
5c. However, 4d exhibited higher activity than 4a and 5a, which
suggests that a flexible substituent is beneficial for activity.
Altering the piperidyl of 4c to an oxygen-contained isostere
morpholinyl yielded the more effective compound 4b, which was
consistent with 5b. This result may be because an oxygen atom
in the morpholinyl is beneficial for forming a hydrogen bond with
the target protein. In conclusion, the lipophilic substituent ethoxy-
carbonyl in the R1 position enhances the bioactivity as well as the
morpholinyl moiety in R2 position. Compound 5b with
pEC50 = 5.81 0.13 was the most efficient agent.
a
Figure 1. In vitro vasodilator activity induced by title compounds.

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C. Wang et al. / Bioorg. Med. Chem. Lett. 26 (2016) 640–644
Figure 2. (a) The emission spectra of 4a–5c in CHCl3; (b) solvent effect on fluorescence emission spectra of 5a.
The optical properties of the target compounds were also
evaluated in methanol, N,N-dimethyl formamide, acetonitrile,
acetic acid and chloroform in Figure 2b. It distinctly revealed that
5a is sensitive to different solvents. The decreasing polarity of
the solvents resulted in a blue-shift of the maximum emission
peaks (kem) from 482 nm (in methanol) to 463 nm (in chloroform),
except for acetic acid. It may be because acetic acid could react
with 5a and greatly changes its conjugation.
Figure 3 shows the influence of pH on 5a. As depicted in Fig-
ure 3a, 5a maintained its fluorescence property at both pH 7.4
and 9.2, whereas the relative fluorescence intensity was slightly
decreased in acidic solution. Figure 3b–d and Table 2 describe
explored. As shown in Figure 2a, 4a–5c all showed blue emission
with kem at 480 1 nm, except 4d showed emission with kem at
493 nm. Series 4 had a stronger relative fluorescence intensity than
series 5, possibly due to the ethoxycarbonyl devoting more to the
conjugation. Furthermore, with the same R1, the relative fluores-
cence intensity generally decreased with a larger substitution at
R2 in 4a compared with 4b, 4c compared with 4d, and 5a compared
with 5c. Larger substitution may influence the conjugation, and
relative fluorescence intensity consequently decreased. The effect
of solvents on the most highly fluorescent agent, 5a, was also
Figure 3. (a) Fluorescence spectra of 5a at various pH; (b) fluorescence spectra of 5a at different time at pH 5.8; (c) fluorescence spectra of 5a at different time at pH 7.4; (d)
fluorescence spectra of 5a at different time at pH 9.2.

C. Wang et al. / Bioorg. Med. Chem. Lett. 26 (2016) 640–644
643
Table 2
Change of kem and relative fluorescence intensity of 5a in various pH and migration time
pH 5.8
pH 7.4
pH 9.2
kem (nm)
RFI*
kem (nm)
RFI*
kem (nm)
RFI*
0 min
5 min
10 min
15 min
30 min
507
510
511
507
506
555
565
594
616
618
500
498
501
498
501
632
615
614
615
631
496
497
509
505
504
654
682
665
665
709
*
Relative fluorescence intensity.
Figure 4. Binding mode of compounds 5b to L-calcium channel (PDB code: 3G43).
the change of kem and relative fluorescence intensity with time in
the above three buffer solutions. The kem ranged successively from
506–511 nm, 498–501 nm and 496–509 nm. The relative fluores-
cence intensity ranged from 555–618 nm, 614–632 nm and
654–709 nm. Although the relative fluorescence intensity in the
alkaline solution (pH 9.2) was better than in the neutral solution
(pH 7.4), there was a larger change of kem and relative fluorescence
intensity in both the acidic solution (pH 5.8) and alkaline solution
(pH 9.2) than in the neutral solution (pH 7.4) indicating that these
compounds may be stable for labels in vivo.
Our previous studies confirmed that imperatorin, the scaffold
core of 5-phenyl furocoumarin derivatives, possessed calcium
antagonism and affinity to L-type calcium channel (PDB code:
3G43).22 A molecule docking study was performed to investigate
the binding mode of these compounds to the L-calcium channel.
The result is presented in Figure 4a. Generally, the target com-
pound 5b formed five critical hydrogen bonds with the protein,
thus contributing to its potent bioactivity. The oxygen atom of
furan and the oxygen atom connected to the benzene ring formed
two hydrogen bonds with LYS94. The bond lengths were 2.03 Å
and 2.02 Å, respectively. The oxygen atom in lactone and the oxy-
gen atom connected to the benzene ring formed two hydrogen
bonds with HIS107. The bond lengths were 2.03 Å and 2.47 Å,
respectively. The oxygen atom in the carbonyl formed a hydrogen
bond with THR110 with distance of 2.48 Å.
moderate vasodilator activity and photoluminescent properties.
The optical study on 5a indicates that this series of compounds
possesses favorable stability in different solvents and in various
pH solutions. This study offers new ideas for the structural opti-
mization for potent agents, and provides bioactive labeled entity
for further efforts.
Acknowledgment
Financial support from the National Natural Science Foundation
of China (Nos. 81202494, 81302737) is greatly appreciated.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2015.11.
056.
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