Design, synthesis, and biological evaluation of prenylated chalcones as vasorelaxant agents

Article abstract of DOI:10.1002/ardp.200800229

Five prenylated chalcones and one allylated chalcone were prepared according to the analysis based on support vector machine (SVM) classification model. Most of the synthesized chalcones showed potent vasorelaxant activities through evaluation in aortic r

Full text of DOI:10.1002/ardp.200800229

428
Arch. Pharm. Chem. Life Sci. 2009, 342, 428–432
Full Paper
Design, Synthesis, and Biological Evaluation of Prenylated
Chalcones as Vasorelaxant Agents
Xiaowu Dong, Jing Chen, Chaoyi Jiang, Tao Liu, and Yongzhou Hu
ZJU-ENS Joint Laboratory of Medicinal Chemistry, College of Pharmaceutical Sciences, Zhejiang University,
Hangzhou, China
Five prenylated chalcones and one allylated chalcone were prepared according to the analysis
based on support vector machine (SVM) classification model. Most of the synthesized chalcones
showed potent vasorelaxant activities through evaluation in aortic rings with the endothelium
pre-contracted by phenylephrine (PE), indicating that the experimental activities were in good
agreement with the theoretical ones. Structure-activity relationship of these compounds showed
that the substituent pattern and number of hydroxyl groups were crucial for their vasorelaxant
activities and that the replacement of prenyl group with allyl group retained the potent activity.
Keywords: Flavonoids / Prenylated chalcones / Support vector machine (SVM) / Vasorelaxant activity /
Received: December 19, 2008; accepted: February 6, 2009
DOI 10.1002/ardp.200800229
Introduction
Epidemiological studies suggested that the incidence of
heart diseases can be lowered in humans if they have a
high dietary intake of flavonoids [1, 2]. Cardioprotective
effects of flavonoids are connected and might be
explained by their anti-inflammatory, antioxidant, anti-
platelet, and vascular dysfunction protecting activities
[3, 4]. Recently, many flavonoids have been found to
exhibit vasorelaxant effects in isolated vascular prepara-
tion and animal models [4–6]. Superior to traditional vas-
odilator, flavonoids also exhibited antioxidant activities
[7]. All these facts prompt the strategy to develop novel
and more potent flavonoids as vasorelaxant agents for
the treatment of cardiovascular diseases. Chalcones, a
member of the flavonoid family, have been identified as
interesting compounds that bear antioxidant activity
and could stabilize action on the vascular wall including
vasodilatory and anti-aggregating effects [8, 9]. In our pre-
vious studies, a support vector machine (SVM) was
Figure 1. Results of SVM classification model and structures of
prenylated chalcone derivatives synthesized.
Correspondence: Yongzhou Hu, ZJU-ENS Joint Laboratory of Medicinal
Chemistry, College of Pharmaceutical Sciences, Zhejiang University,
Hangzhou, 310058, China.
E-mail: huyz@zjuem.zju.edu.cn
Fax: +86 571 8820-8460
employed to establish a good classification model using
111 vasodilators and 232 non-vasodilators. As shown in
Fig. 1, the predictibe accuracy of the obtained classifica-
tion model for the training, the test, and overall data sets
were 93.0%, 82.6%, and 89.5%, respectively. In order to
Abbreviations: phenylephrine (PE); support vector machine (SVM)
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Arch. Pharm. Chem. Life Sci. 2009, 342, 428–432
Prenylated Chalcones as Vasorelaxant Agents
429
Table 1. The molecular descriptor values of compounds 4a–f.
Comp.
D/D
Jhetp
TIC1
SEigp
SP20
RDF030m Mor06u
ATS8v
JGI1
4a
4b
4c
4d
4e
4f
210.25
231.39
193.98
193.43
210.71
172.50
2.19
2.12
2.14
2.15
2.14
2.17
157.52
170.90
151.91
151.91
157.52
131.30
–6.00
–6.00
–4.80
–4.80
–6.00
–6.00
8.33
10.24
8.38
10.96
11.15
9.15
6.28
7.19
5.82
8.05
5.85
6.84
–2.11
–0.83
–2.42
–2.34
–1.35
–2.87
3.02
3.06
2.91
2.98
3.03
2.79
0.23
0.22
0.22
0.24
0.25
0.21
Table 2. The experimental and theoretical results of vasorelax-
ant activities of synthesized chalcones.
validate the model, three prenylated chalcones predicted
as vasodilators by the classification model were synthe-
sized and evaluated as moderate vasodilators (Fig. 1) [10].
In the present study, with the aim to discover more
potent prenylated chalcones and to study the structure-
activity relationship (SAR) of these compounds, five pre-
nylated chalcones and one allylated chalcone were pre-
pared according to the analysis based on the SVM classifi-
cation model. Among these compounds, desmethylxan-
thohumol 4a and isobavachalcone 4c were natural prod-
ucts, and their antioxidant, anticancer, and other bio-
activities had been reported [11–13]. However, few stud-
ies about their vasorelaxant activities were available.
Herein, the vasorelaxant activities of all these synthe-
sized compounds were evaluated against rat-aorta rings
pretreated with 1 lM phenylephrine (PE). The structure-
activity relationship was also discussed.
Compound
EC50 (10 lM)
Emax (%)a)
Classificationb)
Quercetin
24.4
0.85
805
10.2
12.3
1.07
2.40
4.21
N.D.e)
679
91 l 13
80 l 13
55 l 5
101 l 5
92 l 9
Active
Active
Activec)
Active
Active
Active
Active
Active
Active
Activec)
4a
4b
4c
4d
4e
4f
81 l 5
108 l 3
90 l 13
79 l 20
64 l 11
1d)
2d)
3d)
a)
These compounds were reported in our previous studies [10].
each value is the mean l SD from four experiments.
The classification of compounds was provided by SVM model.
N.D.: not determined.
The compounds misclassified by the SVM classification
model could not significantly relax the PE-induced vascular
contraction (Emax a 70% and EC50 A 1 mM) were classified as
inactive vasodilators misclassified compounds.
b)
c)
d)
e)
Results and discussion
Data preparation and SVM prediction
[14, 15]. Condensation of 5a–d with corresponding ben-
All the chalcone derivatives were sketched, optimized, zaldehydes in aqueous alcoholic alkali solution afforded
and finally energy-minimized using CHARMm, and to chalcones 6a–f. Demethoxymethylation of 6a–f was car-
obtain stable structures for further studies Discovery Stu- ried out in catalytic amounts of 3 N HCl in MeOH / THF
dio 2.0 software (Accelrys, Inc. San Diego, CA) was used. (1 : 1, v/v) at reflux temperature, leading to the products
The resulted geometry was transferred into Dragon soft- 4a–f. The structures of the synthesized compounds were
ware (TELETE, srl, Milano, Italy), which could calculate elucidated by 1H-NMR and ESI-MS.
constitutional descriptors, topological descriptors, walk-
and-path counts, information indices, 2-D autocorrela- Vasorelaxant activities
tions, edge adjacency indices, Burden eigenvalue descrip- Vasorelaxant activities of compounds 4a–f were investi-
tors, etc. In addition, nine most relevant descriptors in gated in aortic rings with the endothelium pre-con-
the SVM classification model were calculated for the tar- tracted with 1 lM phenylephrine. Quercetin, a well
get compounds as shown in Table 1. The predicted classes known vasodilator, was used as the positive control. The
(active or inactive) of these compounds were calculated vasorelaxant abilities of the tested compounds were
as shown in Table 2 using the obtained SVM classification based on their potency (EC50) and efficacy (Emax). The
model.
results are shown in Table 2. All tested compounds 4a–f
promoted relaxation in a dose-dependent manner with
the maximum effect observed at 300 lM (Fig. 2). All but
Chemistry
The synthetic route for prenylated and allylated chal- compound 4b showed potent vasorelaxant activities,
cones 4a–f is outlined in Scheme 1. Acetophenones 5a–d which demonstrated that the predicted vasorelaxant
were prepared according to the reported methods activities were in good agreement with the experimental
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X. Dong et al.
Arch. Pharm. Chem. Life Sci. 2009, 342, 428–432
Scheme 1. Synthesis of chalcone derivatives 4a–f.
4e without 6-OH at the A-ring of chalcones exhibited
effects similar to 4a rather than 4c or 4d (EC50 and Emax of
4e: 10.7 lM, 81%, respectively), suggesting that the num-
ber of hydroxyl groups at the chalcone skeleton is also
crucial for their vasorelaxant activity, as shown in the
examples of 4a and 4e, which bear the same number of
hydroxyl groups. In addition, compound 4f, a chalcone
with an allyl group replacing the prenyl group of 4a,
showed more efficacy (Emax: 4f A 4a) but less potency (EC50:
4f A 4a), indicating that the replacement of the prenyl
with an allyl group retained the potent activity.
Chalcones were added cumulatively to achieve the appropriate concentrations.
Results are expressed as means € SD in terms of percentage relaxation of the con-
traction to PE (n = 4).
Conclusion
Figure 2. Effects of chalcones derivatives on relaxation in aortic
rings with the endothelium pre-contracted by 1 lM phenylephr-
ine.
A series of prenylated chalcones bearing different sub-
stituents were prepared and evaluated for their vasore-
laxant activities according to the results of our previous
studies. Most of the tested compounds showed potent vas-
orelaxant activities, which indicated that experimental
activities were in good agreement with theoretical
results. The preliminary structure-activity relationships
showed that the hydroxyl group at the B-ring of chal-
cones usually resulted in better vasorelaxant activity; the
substituent pattern and the number of hydroxyl groups
are also crucial for their vasorelaxant activity, and the
replacement of the prenyl with an allyl group retains the
potent activity.
results. Study on the effects of different substituents at
the B-ring of prenylated chalcones revealed that the
hydroxyl group commonly resulted in higher activity
(4a, 4c–f A 4b, 2, 3), regardless of the presence of prenyl
groups at the 3- or 5-position of the A-ring. Compounds
4c and 4d without 6-OH at the A-ring of chalcones (EC50 of
4c and 4d: 102 and 123 lM, respectively) exhibited a
much weaker potency than compound 4a (EC50 of 4a:
8.5 lM), but showed more efficacy (Emax of 4c, 4d and 4a:
101%, 92%, and 80%, respectively). However, compound
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Arch. Pharm. Chem. Life Sci. 2009, 342, 428–432
Prenylated Chalcones as Vasorelaxant Agents
431
The authors are grateful to the support of National Undergrad- 2-Hydroxy-4,49-di(methoxymethoxy)-3-(3,3-
uate Innovative Training program (NO. G2008029) and the dimethylallyl)chalcone 6c
Reagent: compound 5b (501 mg, 1.90 mmol), 4-methoxyme-
thoxy-benzaldehyde (330 mg, 1.99 mmol); purification: silica gel
column chromatography (petroleum ether / ethyl acetate =
15 : 1, v/v). A yellow oil (615 mg, 75%); 1H-NMR (CDCl3, 400 MHz)
d: 1.72 (s, 3H), 1.82 (s, 3H), 3.44 (d, J = 6.8 Hz, 2H), 3.51 (s, 6H), 5.25
(s, 2H), 5.27 (m, 1H), 5.31 (s, 2H), 6.70 (d, J = 8.4 Hz, 1H), 7.08 (d, J =
8.8 Hz, 2H), 7.51 (d, J = 15.6 Hz, 1H), 7.64 (d, J = 8.8 Hz, 2H), 7.80
(d, J = 8.4 Hz, 1H), 7.88 (d, J = 15.6 Hz, 1H), 12.80 (s, 1H, OH). ESI-
MS m/z: 413 [M + H]+.
support of College of Pharmaceutical Sciences of Zhejiang Uni-
versity for Dragon software.
The authors have declared no conflict of interest.
Experimental
2-Hydroxy-39,4-di(methoxymethoxy)-5-(3,3-
dimethylallyl)chalcone 6d
Chemistry
Reagent: compound 5c (500 mg, 1.89 mmol), 3-methoxybenzal-
dehyde (329 mg, 1.99 mmol); purification: silica gel column
chromatography (petroleum ether / ethyl acetate = 15 : 1, v/v). A
yellow oil (557 mg, 70%);1H-NMR (CDCl3, 400 MHz) d: 1.80 (s, 3H),
1.82 (s, 3H), 3.34 (d, J = 6.8 Hz, 2H), 3.53 (s, 3H), 3.56 (s, 3H), 5.28 (s,
2H), 5.31 (s, 2H), 5.33 (m, 1H), 6.70 (s, 1H), 7.17 (dd, J = 2.0, 8.0 Hz,
1H), 7.36 (t, J = 8.0 Hz, 1H), 7.41 (t, J = 8.0 Hz, 2H), 7.60 (d, J =
16.0 Hz, 1H), 7.67 (s, 1H), 7.87 (d, J = 16.0 Hz, 1H), 13.27 (s, 1H,
OH). ESI-MS m/z: 413 [M + H]+.
Melting points were determined on a Bꢀchi B-540 apparatus
(Bꢀchi Labortechnik, Flawil, Switzerland) and are uncorrected.
All 1H-NMR spectra were recorded on Bruker 400 MHz-spectrom-
eter (Bruker Bioscience, Billerica, MA, USA) with CDCl3 or ace-
tone-d6 as solvent. Chemical shifts were reported in d values
(ppm), relative to internal TMS, and J values were reported in
Hertz (Hz). Mass spectra (ESI, positive ion) were recorded on an
Esquire-LC-00075 spectrometer (Bruker Bioscience). Reagents
and solvents were purchased from known commercial suppliers
and were used without further purification. Compounds 5a–d
and 4f were prepared according to the approaches in previous
references [14, 15].
2-Hydroxy-29,4,49-tri(methoxymethoxy)-5-(3,3-
dimethylallyl)-chalcone 6e
Reagent: compound 5c (502 mg, 1.90 mmol), 2,4-di(methoxyme-
thoxy)-benzaldehyde (451 mg, 2.00 mmol); purification: silica
gel column chromatography (petroleum ether / ethyl acetate =
10 : 1, v/v). A yellow oil (582 mg, 62%); 1H-NMR (CDCl3, 400 MHz)
d: 1.74 (s, 3H), 1.76 (s, 3H), 3.29 (d, J = 6.8 Hz, 2H), 3.48 (s, 3H), 3.50
(s, 3H), 3.52 (s, 3H), 5.21 (s, 2H), 5.25 (s, 2H), 5.28 (s, 2H), 5.29 (m,
1H), 6.64 (s, 1H), 6.76 (dd, J = 2.0, 8.0 Hz, 1H), 6.87 (d, J = 2.0 Hz,
1H), 7.58 (d, J = 16.0 Hz, 1H), 7.61 (d, J = 8.0 Hz, 1H), 7.62 (s, 1H),
8.17 (d, J = 16.0 Hz, 1H), 13.41 (s, 1H, OH). ESI-MS m/z: 473 [M + H]+.
General method for synthesis of compounds 6a–e
To a cold solution of the acetophenone 5a–c and the appropri-
ate benzaldehyde in 3 mL of H2O / EtOH (1 : 4, v/v), 600 mg KOH
in 3 mL H2O / EtOH (1 : 4, v/v) was added with stirring. The result-
ing mixture was stirred under N2 atmosphere at room tempera-
ture for 36 h. Then, the reaction mixture was poured into ice-
water, acidified to pH l 5 with 2 N HCl, and extracted with ethyl
acetate. The organic phase was washed with brine, dried over
anhydrous Na2SO4, and was concentrated in vacuo. The residue
was purified to give chalcone 6a–e.
General method for synthesis of compounds 4a–e
To a solution of 6a–e in 5 mL methanol / THF (1 : 1, v/v), 0.5 mL
3 N HCl was added, and the mixture was stirred at 408C for 6 h.
After cooling to room temperature, the reaction mixture was
poured into cold water and extracted with ethyl acetate. The
organic phase was washed with brine, dried over anhydrous
Na2SO4. After removal of the solvent, the residue was purified to
give 4a–e.
2-Hydroxy-4,49,6-tri(methoxymethoxy)-3-(3,3-
dimethylallyl)chalcone 6a
Reagent: compound 5a (500 mg, 1.54 mmol), 4-methoxyme-
thoxy-benzaldehyde (269 mg, 1.62 mmol); purification: silica gel
column chromatography (petroleum ether / ethyl acetate =
12 : 1, v/v). A yellow oil (548 mg, 70%); 1H-NMR (CDCl3, 400 MHz)
d: 1.67 (s, 3H,), 1.79 (s, 3H), 3.34 (d, J = 6.8 Hz, 2H), 3.49 (s, 3H),
3.50 (s, 3H), 3.52 (s, 3H), 5.21 (m, 1H), 5.22 (s, 2H), 5.25 (s, 2H), 5.27
(s, 2H), 6.40 (s, 1H,), 7.06 (d, J = 8.8 Hz, 2H), 7.55 (d, J = 8.8 Hz, 2H),
7.76 (d, J = 15.6 Hz, 1H), 7.83 (d, J = 15.6 Hz, 1H), 13.83 (s, 1H, OH).
ESI-MS m/z: 473 [M + H]+.
2,4,49,6-Tetrahydroxy-3-(3,3-dimethylallyl)chalcone 4a
Reagent: compound 6a (300 mg, 0.64 mmol); purification: silica
gel column chromatography using petroleum ether / ethyl ace-
tate (1 : 1, v/v). Yellow amorphous powder (119 mg, 55%), m.p.:
154–1558C. 1H-NMR (Acetone-d6, 400 MHz) d: 1.61 (s, 3H), 1.69 (s,
3H), 3.13 (d, J = 7.2 Hz, 2H), 5.14 (m, 1H), 6.03 (s, 1H), 6.85 (d, J =
8.0 Hz, 2H), 7.52 (d, J = 8.0 Hz, 2H), 7.72 (d, J = 16.0 Hz, 1H), 8.07
(d, J = 16.0 Hz, 1H), 8.81 (s, 1H, OH), 9.01 (s, 1H, OH), 9.62 (s, 1H,
OH), 14.41 (s, 1H, OH). ESI-MS m/z: 341 [M + H]+.
2-Hydroxy-4,6-di(methoxymethoxy)-49-methoxy-3-(3,3-
dimethylallyl)chalcone 6b
Reagent: compound 5a (500 mg, 1.54 mmol), 4-methoxybenz-
aldehyde (220 mg, 1.62 mmol); purification: silica gel column
chromatography (petroleum ether / ethyl acetate = 15 : 1, v/v). A
1
yellow oil (557 mg, 65%); H-NMR (CDCl3, 400 MHz) d: 1.68 (s,
2,4,6-Trihydroxy- 49-methoxy-3-(3,3-
dimethylallyl)chalcone 4b
Reagent: compound 6b (300 mg, 0.68 mmol); purification: silica
gel column chromatography using petroleum ether / ethyl ace-
3H,), 1.81 (s, 3H), 3.34 (d, J = 6.8 Hz, 2H), 3.50 (s, 3H), 3.53 (s, 3H),
3.87 (s, 3H), 5.21 (m, 1H), 5.26 (2H, s), 5.28 (2H, s), 6.41 (s, 1H), 6.94
(d, J = 8.4 Hz, 2H), 7.57 (d, J = 8.4 Hz, 2H), 7.78 (d, J = 16.0 Hz, 1H),
7.82 (d, J = 16.0 Hz, 1H), 13.90 (s, 1H, OH). ESI-MS m/z: 443 [M + H]+.
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X. Dong et al.
Arch. Pharm. Chem. Life Sci. 2009, 342, 428–432
tate (4 : 1, v/v). Yellow amorphous powder (162 mg, 67%), m.p.:
151–1528C. 1H-NMR (Acetone-d6, 400MHz) d: 1.58 (s, 3H), 1.70 (s,
3H), 3.21 (d, J = 7.2 Hz, 2H), 3.81 (s, 3H), 5.19 (m, 1H), 6.05 (s, 1H),
6.95 (d, J = 8.4 Hz, 2H), 7.59 (d, J = 8.4 Hz, 2H), 7.71 (d, J = 16.0 Hz,
1H), 8.10 (d, J = 16.0 Hz, 1H), 9.12 (s, 1H, OH), 9.56 (s, 1H, OH),
14.30 (s, 1H, OH). ESI-MS m/z: 355 [M + H]+.
compounds were added to the bath at 15–20 min intervals (the
time needed to obtain steady-state relaxation). Control tissues
were simultaneously subjected to the same procedures, but
omitting the compounds and adding the vehicle. All data were
expressed as mean l SD (n = 3l4). The flavonoids-induced maxi-
mal relaxation (Emax) in aortic rings was calculated as a percent-
age of the contraction in response to PE (1 lM). The half-maxi-
mum effective concentration (EC50) was defined as the concen-
tration of the flavonoids that induced 50% of maximum relaxa-
tion from the contraction elicited by PE (1 lM) and was calcu-
lated from the concentration-response curve by nonlinear
regression (curve fit) using GraphPad Prism.
2,4,49-Trihydroxy-3-(3,3-dimethylallyl)chalcone 4c
Reagent: compound 6c (300 mg, 0.73 mmol); purification: silica
gel column chromatography using petroleum ether / ethyl ace-
tate (2 : 1, v/v). Yellow amorphous powder (165 mg, 70%), m.p.:
157–1598C; 1H-NMR (Acetone-d6, 400MHz) d: 1.64 (s, 3H), 1.77 (s,
3H), 3.36 (d, J = 7.2 Hz, 2H), 5.27 (m ,1H), 6.52 (d, J = 8.4 Hz, 1H),
6.92 (d, J = 8.4 Hz, 2H), 7.72 (d, J = 8.4 Hz, 2H), 7.74 (d, J = 16.0 Hz,
1H), 7.82 (d, J = 16.0 Hz, 1H), 7.96 (d, J = 8.4 Hz, 1H), 8.97(s, 1H,
OH), 9.31 (s, 1H, OH), 13.97 (s, 1H, OH). ESI-MS m/z: 325 [M + H]+.
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