Synthesis and evaluation of substituted 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-one derivatives as vasorelaxing agents

Article abstract of DOI:10.1016/j.bmcl.2019.126759

A series of substituted 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-ones (chromeno-coumarin hybrids) was synthesized from scopoletin (11) as vasorelaxing agents. The synthesized compounds 21a-f, 22, 23a-e and scopoletin (11) were evaluated for vasorelaxation in endothelium intact rat main mesenteric artery (MMA). Compounds 11, 21a, 21c-f and 22 showed significant vasorelaxation in precontracted MMA within the range of EC₅₀ value 1.58–5.02 μM. These derivatives presented 29.40–70.89 fold increased sensitivity for experimental tissue compared to scopoletin (11), the parent molecule. Among others, 22 was found to be the most active compound which had EC₅₀ 1.58 μM with 70.89 fold increased sensitivity. The mechanistic evaluation of 22 showed that it exerted vasorelaxation through Ca²⁺-activated K⁺ (BKca) channel and the effect was endothelium-independent.

Full text of DOI:10.1016/j.bmcl.2019.126759

Journal Pre-proofs
Synthesis and evaluation of substituted 8,8-dimethyl-8H-pyrano[2,3-f]chro-
men-2-one derivatives as vasorelaxing agents
Sarita Singh, Karishma Agarwal, Hina Iqbal, Pankaj Yadav, Deepika Yadav,
Debabrata Chanda, Sudeep Tandon, Feroz Khan, Anil Kumar Gupta, Atul Gupta
PII:
S0960-894X(19)30722-X
https://doi.org/10.1016/j.bmcl.2019.126759
BMCL 126759
DOI:
Reference:
To appear in:
Bioorganic & Medicinal Chemistry Letters
Received Date:
Revised Date:
Accepted Date:
9 August 2019
12 October 2019
14 October 2019
Please cite this article as: Singh, S., Agarwal, K., Iqbal, H., Yadav, P., Yadav, D., Chanda, D., Tandon, S., Khan,
F., Kumar Gupta, A., Gupta, A., Synthesis and evaluation of substituted 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-
one derivatives as vasorelaxing agents, Bioorganic & Medicinal Chemistry Letters (2019), doi: https://doi.org/
1
0.1016/j.bmcl.2019.126759
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Synthesis and evaluation of substituted
,8-dimethyl-8H-pyrano[2,3-f]chromen-2-one
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8
derivatives as vasorelaxing agents
Sarita Singh, Karishma Agarwal, Hina Iqbal, Pankaj Yadav, Deepika Yadav, Debabrata Chanda,* Sudeep
Tandon, Feroz Khan, Anil Kumar Gupta, Atul Gupta*
OH
R2
R1
N
X
O
n
OH
H3CO
HO
O
O
O
O
O
O
O
1
1; Scopoletin, a benzopyran-2-one
X = CO or CH2
Glabridin (14), a pyranobenzopyran derivative
with vasorelaxing activity
derivative with vasorelaxing activity 15; Designed prototype

Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com
Synthesis and evaluation of substituted 8,8-dimethyl-8H-pyrano[2,3-f]chromen-
2
-one derivatives as vasorelaxing agents
af
af
c
c
d
c
Sarita Singh, Karishma Agarwal, Hina Iqbal, Pankaj Yadav, Deepika Yadav, Debabrata Chanda, *
b
d
e
af,#
Sudeep Tandon, Feroz Khan, Anil Kumar Gupta, Atul Gupta *
a
e
Medicinal Chemistry Department, bProcess Chemistry and Technology Department, Molecular Bioprospection Department, Plant Biology Division and
c
d
f
Genetic and Plant Breeding Department, CSIR-Central Institute of Medicinal and Aromatic Plants, P.O. CIMAP, Kukrail Road, Lucknow 226015, Academy of
Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh- 201002
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
A series of substituted 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-ones (chromeno-coumarin
hybrids) was synthesized from scopoletin (11) as vasorelaxing agents. The synthesized
compounds 21a-f, 22, 23a-e and scopoletin (11) were evaluated for vasorelaxation in
endothelium intact rat main mesenteric artery (MMA). Compounds 11, 21a, 21c-f and 22
showed significant vasorelaxation in precontracted MMA within the range of EC50 value 1.58-
5
.02 µM. These derivatives presented 29.40-70.89 fold increased sensitivity for experimental
tissue compared to scopoletin (11), the parent molecule. Among others, 22 was found to be the
Keywords:
Scopoletin,
most active compound which had EC50 1.58µM with 70.89 fold increased sensitivity. The
2
+
+
mechanistic evaluation of 22 showed that it exerted vasorelaxation through Ca -activated K
BKca) channel and the effect was endothelium-independent.
8
,8-Dimethyl-8H-pyrano[2,3-f]chromen-2-one,
(
chromeno-coumarin,
coumarin, vasorelaxation,
vascular dysfunction
2019 Elsevier Ltd. All rights reserved.
In drug discovery, oxygen heterocyclic compounds are preferred
choice of medicinal chemists over sulfur and nitrogen heterocyclic
compounds owing to their relatively less susceptibility for inherent
C-3 position of osthole (10), a benzopyran-2-one derivative,
improved its anticancer activity 100 times against estrogen receptor
1
5
positive breast cancer. Similarly, introduction of an aryl group at
C-3 position or substitution of phenacyl or alkylamine group at C-7
of scopoletin (11), another benzopyran-2-one derivative, improved
1
toxicity. Plants have good repository of oxygen heterocycles
including furans such as menthofuran (1), benzofurans such as
machicendiol (2), conocarpan (3) and Cicerfuran (4), benzopyrans
such as daidzein (5), genistein (6), precocene-I and II (7 and 8),
glabridin (9), osthole (10), scopoletin (11), and benzoxepins such as
ovafolinin A-C (12-14) which often have pharmacological activities
and serve as templates for novel drugs (Fig. 1).2-8 Among these,
majority of compounds incorporate benzopyran core as an integral
part of their structure. These molecules possess benzopyran core
mainly in three forms (1) benzopyran (e.g. glabridin), (2)
1
6,17
its anticancer activity significantly.
Besides, functional group
manipulations, hybridization of stilbenes such as resveratrol and
pterostilbene with benzopyran-2-one derivatives either at C-4 or C-6
position presented superior anticancer activity compared to parent
18,19
molecules.
Taken together, positions C-3, C-4, C-6 and C-7 of
O
OCH3
O
HO
OH
O
O
O
O
O
O
H3CO
benzopyran-4-one (e.g. flavonoids) and (3) benzopyran-2-one (e.g.
OH OH
coumarins including neoflavones).3,5,9
1; Menthofuran
2; Machicendiol
3; Conocarpan
4; Cicerfuran
OH
It has been observed that in general, compounds having benzopyran-
OR2
R3
R
O
4
-one and benzopyran core presents superior biological activities
R
OH
compared to benzopyran-2-one derivatives possibly due to their
structural arrangement which dictates physicochemical properties.
Despite this fact, the diverse biological activities such as antioxidant,
anticoagulant, antibacterial, antiviral, anticancer, osteoprotective,
hepatoprotective, antihypertensive and aromatase inhibitory
activities, etc. of benzopyran-2-one derivatives (e.g. 10 and 11)
H3CO
O
O
O
R1
; Daidzein, R, R1, R2
6; Genistein, R = OH, R1, R2
O
O
R3 = H,
R3 = H,
7; Precocene-I, R = H
8; Precocene-II, R = OCH3
5
,
9; Glabridin
,
OH
X
H3CO
O
H
H3CO
R1
HO
HO
H3CO
O
reveal that benzopyran-2-one core is a valuable pharmacophore for
HO
H3CO
O
the development of potential bioactive molecules.8-12 Literature
O
O
H3CO
R
H3CO
OCH3
reports suggest that adequate structural changes in benzopyran-2-one
HO
10; Osthole R =
OCH3
HO
12; Ovafolinin A
core through introduction or transformation of a functional group or
11; Scopoletin, R = H, R1 = OCH3
13; Ovafolinin B, X = CH2
14; Ovafolinin C, X = C=O
core modification leads to its better pharmacological activities.13,14 In
their efforts, You et. al. showed that introduction of an aryl group at
Fig.
1 Structures of naturally occurring oxygen heterocycles (1-14)
*
To whom correspondence should be addressed: Tel: +915222718556, E-
mail: atisky2001@yahoo.co.in, #CIMAP communication
No.CIMAP/PUB/2019/AUG/64
incorporating furan, benzofuran, pyran, benzopyran, benzoxepins core.

benzopyran-2-one core are prime positions for structural
modifications in order to improve its pharmacological activities. 25
22 was synthesized through O-alkylation followed by cyclization
reaction on 11 using 1,1-diethoxy-3-methyl-2-butene in dry xylene at
1
60°C in 75% yield.
Considering above observations and medicinal importance of
benzopyran-2-one core, in this study, we undertook structural
hybridization of scopoletin (11), a benzopyran-2-one derivative, with
benzopyran (chromene) nucleus as present in precocene-I and II (6a
and b), to yield substituted chromeno-coumarin hybrids (15) in
anticipation to have effective vasorelaxant agents (Fig. 2). It is
known that benzopyran-2-one core is responsible for vasorelaxing
activity of many active molecules.21-24 Moreover, pyranobenzopyran
core present in glabridin (14), a known vasorelaxing agent, is an
important core for biological activity of 14.25 It was assumed that
these 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-ones (chromeno-
coumarin hybrids, 15) may have improved physicochemical
properties required for better interaction with biological targets as
compared to scopoletin (11) which is known for its moderate
vasorelaxant activity rather at high concentration.21 The results are
reported in this communication.
H3CO
HO
HO
HO
HO
O
a
b
O
O
O
O
O
O
O
+
1
1
16
O
HO
O
8
1
7
1
b
c
H3CO
O
O
O
O
O
H3CH2CO
OO
O
n
n
d
HO
n
O
O
O
O
O
O
22
1
9a; n = 1
b; n = 3
c; n = 4
20a; n = 1
b; n = 3
c; n = 4
e
R1
R2
n
2
1
O
a. CH3
b. CH3
c. CH3
d. CH3
e. CH3
n-butyl
n-butyl
n-butyl
n-pentyl
n-pentyl
n-pentyl
1
3
4
1
3
4
R1
O
N
R2
n
O
O
O
f.
CH3
2
1
Scheme 1. Reagents and reaction conditions: (a) pyridinium hydrochloride at
150°C (b) 1,1-diethoxy-3-methyl-2-butene, 3-picoline in dry p-xylene at
160°C (c) alkyl bromoester, anhy K CO , dry acetone, reflux (d) 5%
2 3
aq.NaOH, MeOH at room temperature (e) EDC, HOBt, DMAP, DCM at
room temperature.
OH
R2
R1
N
X
O
n
OH
H3CO
HO
O
O
O
O
O
O
O
Furthermore, 6-hydroxy-8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-
one (17) was modified to its alkylamine substituted derivatives (23)
through the reaction of 17 with substituted alkylamine
1
0b; Scopoletin, a benzopyran-2-one
X = CO or CH2
Glabridin (14), a pyranobenzopyran derivative
with vasorelaxing activity
derivative with vasorelaxing activity 15; Designed prototype
2 3
hydrochlorides in presence of anhydrous K CO in dry acetone
(Scheme-2). Thus, alkylation reaction on 17 yielded corresponding
alkylamine substituted derivatives 23 in 51-76% yields
Fig. 2 Structures of benzopyran-2-one (scopoletin, 11) and pyranobenzopyran
glabridin, 8) based vasorelaxing agents and designed prototype.
(
The designed chromeno-coumarin hybrids (15) were synthesized
using efficient chemistry (Scheme-1). For synthesis of target
compounds, scopoletin (11) was required as starting material which
was isolated from stem part of the plant Artemisia annua L. cv CIM
sanjeevnai collected from CIMAP research form. The stem of this
plant is a major bio-waste of the Artemisia research and was taken
for its value addition in this study. The dried and powdered plant
material was extracted with hot methanol. The obtained crude
material was subjected to column chromatography in order to purify
scopoletin (11). Subsequently, scopoletin (11) was demethylated
using pyridinium hydrochloride at 150°C which yielded 6,7-
dihydroxybenzopyran-2-one (16) in 70% yield. O-alkylation
followed by cyclization reaction was performed on 16 using 1,1-
diethoxy-3-methyl-2-butene in dry xylene at 160°C to yield 6-
hydroxy-8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-one (17) along
with 7-hydroxy-8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-one (18)
in 77 and 11 % yields respectively. Compound 17 was reacted with
alkyl bromoesters of variable lengths in presence of anhydrous
HO
O
RO
O
a
O
O
O
O
1
7
23 (a-e)
c. R=
d. R=
e. R=
N
N
a. R=
b. R=
N
N
N
Scheme 2; Reaction conditions and reagents: (a) alkylaminoethyl
chloride.hydrochloride, anhy K CO , dry acetone, 80°C.
2
3
The synthesized compounds were analyzed with the help of H, 13C
NMR and mass spectrometry and compounds with minimum 97 %
purity were evaluated for their vasorelaxant activity in isolated rat
main mesenteric artery (MMA), one of the main circulatory bed,
using ex-vivo model [see supplementary information].
The vasorelaxant potential of target molecules was studied in
endothelium intact MMA precontracted with U46619 (100nM). The
endothelium integrity of isolated arterial rings was confirmed using
acetylcholine-induced relaxation. Initially, 11, 21a-f, 22 and 23a-e
were evaluated for vasorelaxation in MMA at 30µM except 11 which
was evaluated at 1000 µM concentration, to have a general idea
about vasorelaxant activity of compounds. Results showed that 11,
1
2 3
K CO in dry acetone to yield 19 in 81-92% yields. The ester
derivatives (19) were hydrolyzed to the corresponding acid
derivatives (20) in 70-82 yields using 10% aqueous NaOH in MeOH
at room temperature. Finally, 20 was transformed into target amide
derivatives (21) using different alkylamines in presence of EDC,
HOBt in DCM at room temperature in 50-71 % yields. In 2002,
Rokotoarison et. al. reported vasorelaxing activity of crude
hydroalcoholic extract of trunk bark of Cedrelopsis grevie Baill.
(Meliaceace) containing scopoletin derivatives, [6, 7-dimethoxy
benzopyran-2-one and 8-(3-methylprop-2-enyl)- benzopyran-2-one]
and chromeno-coumarin hybrids [ 6-hydroxy 8,8-dimethyl-8H-
2
1a, 21c-f and 22 showed 63.57-96.70 % relaxation (Emax) in intact
pyrano[2,3-f]chromen-2-one (norbraylin, 17),
dimethyl-8H-pyrano[2,3-f]chromen-2-one (cedrecoumarin A, 18)
and 7-methoxy- 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-one
braylin, 22)].2 Despite of their interest, these authors could not
7-hydroxy-8,8-
MMA precontracted with U46619 (100nM) whereas compounds 21b
and 23a-e showed less than 10% relaxation and were considered
inactive (Table 1). Compounds 21a, 21c-f and 22 were further
evaluated for their efficacy in a concentration-dependent manner.
The vasorelaxation by each compound was normalized to calculate
percentage of the maximal vasorelaxation obtained in the normal
control group. The concentration of the test compound causing half-
maximal relaxation (EC50) and maximal relaxation (Emax) were
calculated by fitting the original concentration-response curves with
nonlinear regression equation. The activity of compounds is
6
(
study vasorelaxaing effect of individual constituents except one of
the scopoletin derivative i.e. 6, 7-dimethoxy benzopyran-2-one, due
to their insufficient quantities. Encouraged with the observed activity
of extract and 6, 7-dimethoxy benzopyran-2-one, we were interested
to study 22 in detail. Accordingly, we synthesized 7-methoxy-8,8-
dimethyl-8H-pyrano[2,3-f]chromen-2-one (braylin, 22). Compound

represented by pD2 value which is the negative decadic logarithm of
EC50 (Table 1). It was observed that 21a, 21c-f and 22 presented
significant vasorelaxation in MMA precontracted with U46619
compound, which had EC50 112 µM (Table 1 and Fig. 1S). In this
experiment, sodium nitroprusside was used as positive control and
presented Emax 91.39 at 1µM (Table 1). Among others, 22 was found
to be the most active compound [EC50 1.58µM with 70.89 fold
increased sensitivity (Emax 94.01 for 22 and 89.23% for 11
respectively) Table 1] and was selected for further characterization.
(100nM) within the range of EC50 value 1.58-5.02 µM and pD2
value 5.299±0.09-5.802±0.08 (Table 1). Accordingly, the increased
sensitivity of experimental tissue for 21a, 21c-f and 22 was observed
from 22.31-70.89 fold compared to scopoletin (11), the parent
Table 1. Vasorelaxation potential of 11, 21a-f, 22 and 23a-e in rat main mesenteric artery.
Fold increase
in sensitivity
S. No.
1
Compound
E
max (at 30 µM)#
pD2 (-LogM EC50
)
EC50 in µM
Scopoletin (11)*
89.23
65.67
<10
3.95±0.09
5.575±0.09
ND
112
2.66
ND
1.00
42.11
ND
2
.
21a
3
21b
4
5
6
7
8
9
21c
63.57
94.05
95.06
83.12
96.70
<10
5.674±0.08
5.419±0.07
5.491±0.10
5.299±0.09
5.802±0.08
ND
2.12
3.81
3.23
5.02
1.58
ND
52.83
29.40
34.67
22.31
70.89
ND
21d
21e
21f
22
23a
1
0
1
2
3
4
23b
<10
ND
ND
ND
1
1
1
1
23c
<10
ND
ND
ND
23d
23e
<10
ND
ND
ND
<10
ND
ND
ND
Sodium Nitroprusside≠
91.39
8.524±0.11
0.003
Standard
*
3
E
max of scopoletin (11) is measured at 1000 µM. ≠
0 µM in comparison to scopoletin, 11). ND = not determined.
E
max of Sodium Nitroprusside is measured at 1000 µM. #Emax is the maximal relaxation in terms of percent at
BKca channel) for 20min. It was found that pre-incubation of the
arterial rings with TEA (1mM) for 20 min significantly blocked the
relaxation response to 22 with Emax 54.13±5.58 % compared to
control (Emax 94.01±1.49 %) (Fig. 4).
In order to elucidate the role of endothelium integrity on
vasorelaxation, 22 was evaluated on MMA both in presence and
absence of endothelium. Result showed that 22 relaxed MMA both
in presence and absence of endothelium. The concentration-
dependent relaxation response of 22 in endothelium intact and
denuded showed no statistical difference with Emax 94.87% for
endothelium intact and 93.69% for endothelium-denuded aortic rings
respectively (Fig. 3). This observation showed that relaxation
response of 22 was endothelium-independent.
Further, to elucidate the role of potassium channels, relaxation
efficacy of 22 was assessed in MMA pre-contracted with high
potassium depolarizing solution [80mM KCl containing Modified
Krebs-Henseleit Solution (MKHS)] which prevents opening of
potassium channels through increase in external potassium ion
concentrations. The relaxation response by 22 was found to be
significantly blocked with Emax 94.01 % for control and 53.34 % for
The observed vasorelaxation in MMA by 22 was validated through
in-silico docking study on BKca channel target (PDB ID: 3NAF)
using Auto Dock Vina v1.1.2 software. In this experiment,
tetraethylammonium (TEA) was used as control molecule. The
results showed that 22 accommodated itself well within the binding
-1
pocket of target protein with binding energy -7.5 kcal.mol and
formed two hydrogen bonds with ARG-514 residue through C=O
and one of the O-atom (form pyranone ring) whereas TEA interacted
-1
within target with binding energy -3.7 kcal.mol . It was seen that
binding pocket of TEA and 22 within the target was not same. The
results are presented in Fig. 5. The in-silico results indicated that 22
had ability to target BKca channel for its vasorelaxation activity.
8
0mM KCl containing MKHS respectively. Furthermore, the
contribution of subtypes of potassium channels in the relaxation
response of 22 was studied by incubating MMA with
2
+
+
Tetraethylammonium (TEA, Ca -activated K channel blocker;

Fig 3. Traces showing acetylcholine (10 µM) induced relaxation in endothelium intact (A), endothelium-denuded (B), isolated rat mesenteric arterial rings
preconstricted with U46619 (100 nM). Raw traces shows 22 induced concentration-dependent relaxation in endothelium intact (C), endothelium-denuded (D),
isolated rat mesenteric arterial rings preconstricted with U46619 (100 nM). (E) graph shows the sigmoidal concentration-response curve obtained in C and D.
Relaxation is expressed as the Mean ± S.E.M. percentage reversal of U46619-induced contraction.

+
Fig 4. Traces showing 22 induced concentration-dependent relaxation in rat mesenteric arterial rings preconstricted with 80 mM High K containing MKHS (A)
and pre-incubated with potassium channel blocker; Tetraethyl ammonium (TEA, 1 mM), for 20 min and preconstricted with U46619 (100 nM) Tracing (B).
Graph shows the sigmoidal concentration-response curve (C). Relaxation is expressed as the Mean ± S.E.M. percentage reversal of contraction.
(A)
(B)
(C)
Fig 5. (A).Structural crystallographic model of human BKca channel (PDB ID: 3NAF) showing binding site in orange color sphere. (B).Docking pose
conformation of tetraethylammonium with BKca channel (C) Represent the docking pose of 22 with BKca channel.
These findings indicated that vasorelaxation effect of 22 was
antagonistic action of coumarins at thromboxane-A
good platelet aggregation activity of 22, the antagonistic action of 22
at thromboxane-A receptor may be another possible mode for its
vasorelaxation effect.
The above results showed that structural modification of scopoletin
(11) to yield substituted 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-
ones (chromeno-coumarin hybrids, 15) improved its vasorelaxation
efficacy. Compounds having amide group at position C-6 of 8,8-
dimethyl-8H-pyrano[2,3-f]chromen-2-one presented better activity
with enhanced sensitivity towards MMA compared to scopoletin
2
receptor and
2
+
+
mediated through Ca -activated K (BKca) channel. It has been
reported that Voltage-Dependent Calcium Channel (VDCC) and
store-operated calcium channels are putative targets of coumarins.27
Further, in myocardial infarction, enhanced platelet aggregation
followed by thrombus formation is a causative factor which is
2
modulated by calcium mobilization, cox-1 and thromboxane A
2
receptors etc. It is reported that 4-methylcoumarin derivatives are
reported to inhibit platelet aggregation induced by U-46619 through
2
8
antagonistic action at thromboxane-A
2
receptor. Considering,

(
11). Compound 22 which had methoxy group instead of amide
8.
Kashima K, Sano K, Yun YS, Ina H, Kunugi A, Inoue H.
Ovafolinins A-E, Five New Lignans from Lyonia ovalifolia,
Chem. Pharm. Bull., 2010, 58, 191-194.
Kontogiorgis C, Detsi A, Hadjipavlou-Litina D. Coumarin-based
drugs: a patent review (2008-present). Expert Opin. Ther. Pat.,
group at C-6 presented even more pronounced activity. It was
assumed that long-chain modification at this position is not favorable
perhaps due to its bulky nature. In a similar study, it was observed
that 4-hydroxymethylcoumarins bearing 2-oxopropyl group at its C-7
and C-8 positions were devoid of vasorelaxant effect, however,
transformation of 2-oxopropyl group present at C-7, to a methyl
group (a small lipophilic group analogous to methoxy group of 22)
9
.
2
012,
22,
437-454.
https://doi.org/10.1517/13543776.2012.678835.
10. Gnonlonfin GJB, Sanni A, Brimer L. Review Scopoletin-A
Coumarin Phytoalexin with Medicinal Properties. Crit. Rev. Plant
bearing furan ring fused coumarin (through C-6 and C-7 positions)
Sci.,
2012,
31,
47-56.
induced vasorelaxant effect.29 This observation indicated the
https://doi.org/10.1080/07352689.2011.616039.
1
1. Singh H, Singh JV, Bhagat K, Gulati HK, Sanduja M, N. K. N.
Kinarivala NKN, Sharma S. Rational Approaches, Design
Strategies, Structure Activity Relationship and Mechanistic
Insights for Therapeutic Coumarin Hybrids. Bioorg. Med. Chem.
importance of a small lipophilic group at C-6 and medium sized at
C-8 in coumarins for their vasorelaxant effect. Similarly,
vasorelaxant activity of umbelliferone-chalcone hybrids which had
lipophilic cinnamoyl group at C-8 also validated this fact.30 The
observed activity of compounds along with the these literature
reports indicated that structurally, active compound required a small
lipophilic group (of two atoms) at C-6 and medium sized at C-8,
which may or may not be connected to C-7 through an O-atom. As
anticipated, the modification of scopoletin (11) to chromeno-
coumarin hybrids significantly improved its vasorelaxation efficacy;
however, a proper structure-activity relationship could not be
established in this series.
In conclusion, a series of 8,8-dimethyl-8H-pyrano[2,3-f]chromen-2-
ones (chromeno-coumarin hybrids) has been synthesized efficiently
through structural modification of scopoletin (11) and characterized
as vasorelaxing agent with enhanced vasorelaxation and sensitivity
in rat main mesenteric artery (MMA) compared to scopoletin (11),
the parent molecule. Amongst other, 22 showed significant
Lett.,
https://doi.org/10.1016/j.bmc.2019.06.033.
12. (a)Jameel E, Umar T, Kumar J, Hoda N. Coumarin: A Privileged
Scaffold for the Design and Development of
Antineurodegenerative Agents. Chem. Biol. Drug Des. 2016, 87,
1-38. https://doi.org/10.1111/cbdd.12629. (b) Grover J, Jachak
SM. Coumarins as privileged scaffold for anti-inflammatory drug
development. RSC Adv., 2015, 5, 38892-38905.
2019,
27,
3477-3510.
2
https://doi.org/10.1039/C5RA05643H. (c) Peng XM., Damu GLV,
Zhou CH. Current developments of coumarin compounds in
medicinal chemistry. Curr. Pharm. Design, 2013, 19, 3884-3930.
DOI:10.2174/1381612811319210013.
13. Emamia S, Dadashpour S. Current developments of coumarin-
based anti-cancer agents in medicinal chemistry. Eur. J. Med.
Chem.,
2015,
102,
611-630.
https://doi.org/10.1016/j.ejmech.2015.08.033.
1
4. Thakur A, Singla R, Jaitak V. Coumarins as anticancer agents: A
review on synthetic strategies, mechanism of action and SAR
studies, Eur. J. Med. Chem., 2015, 101, 476-495.
https://doi.org/10.1016/j.ejmech.2015.07.010.
2
+
+
vasorelaxation through Ca activated K (BKca) channel.
Together with the observed activity, it is assumed that 8H-
pyrano[2,3-f]chromen-2-one based molecules such as 22, could be
developed as novel vasorelaxing agents after further structural
refinements and detailed biological characterizations.
15. You L, An R, Wang X, Li Y. Discovery of novel osthole
derivatives as potential anti-breast cancer treatment. Bioorg. Med.
Chem.
Lett.,
2010,
20,
7426-7428.
https://doi.org/10.1016/j.bmcl.2010.10.027.
6. Cai X, Yang J, Zhou J, Lu W, Hu C, Gu Z, Huo J, Wang X, Cao
P. Synthesis and biological evaluation of scopoletin derivatives.
Acknowledgments
1
1
The authors thank the Director, CSIR-CIMAP for kind support and
CSIR, India for financial assistance.
Bioorg.
Med.
Chem.,
2013,
21,
84-92.
https://doi.org/10.1016/j.bmc.2012.10.059.
7. Yang J, Guo-Yun L, Dai F, Cao XY, Kang YF, Hu LM., Tang JJ,
Li XZ, Li Y, Jin XL, Zhou B, Synthesis and biological evaluation
of hydroxylated 3-phenylcoumarins as antioxidants and
antiproliferative agents. Bioorg. Med. Chem. Lett., 2011, 21, 6420-
References and notes
1
.
Zhao L, Yuan X, Wang J, Feng Y, Ji F, Li Z, Bian J. A review on
flavones targeting serine/threonine protein kinases for potential
anticancer drugs. Bioorg. Med. Chem., 2019, 27, 677-685.
https://doi.org/10.1016/j.bmc.2019.01.027; (b) Kumar D, Sharma
P, Singh H, Nepali K, Gupta G. K, Jain S. K, Ntie-Kang F. The
value of pyrans as anticancer scaffolds in medicinal chemistry.
6
425. https://doi.org/10.1016/j.bmcl.2011.08.090.
1
1
8. W. Shen, J. Mao, J. Sun, M. Sun, C. Zhang, Synthesis and
biological evaluation of resveratrol–coumarin hybrid compounds
as potential antitumor agents. Med. Chem. Res., 2013, 22, 1630-
1
640. https://doi.org/10.1007/s00044-012-0159-y.
9. Belluti F, Fontana G, Bo LD, Carenini N, Giommarelli C, Zunino
F, Design, synthesis and anticancer activities of stilbene-coumarin
hybrid compounds: Identification of novel proapoptotic agents,
RSC
Adv.,
2017,
7,
36977-36999.
https://doi.org/10.1039/C7RA05441F.
2
3
.
.
Dawood KM. Benzofuran derivatives: a patent review. Expert
Opin. Ther. Patents, 2013, 23, 1133-1156.
Bioorg.
Med.
Chem.,
2010,
18,
3543-3550.
https://doi.org/10.1016/j.bmc.2010.03.069.
(a) Ren W, Qiao Z, Wang H, Zhu L, Zhang L. Flavonoids:
Promising anticancer agents. Med. Res. Rev., 2003, 23, 519-534.
https://doi.org/10.1002/med.10033; (b) Raffa D, Maggio B,
Raimondi MV, Plescia F, Daidone G. Recent discoveries of
anticancer flavonoids. Eur. J. Med. Chem., 2017, 142, 213.
https://doi.org/10.1016/j.ejmech.2017.07.034.
2
2
2
0. Dandriyal J, Singla R, Kumar M, Jaitak V, Recent developments
of C-4 substituted coumarin derivatives as anticancer agents, Eur.
J.
Med.
Chem.,
2016,
119,
141-168.
https://doi.org/10.1016/j.ejmech.2016.03.087.
1. Kwon EK, Jin SS, Choi MH, Hwang KT, Shim JC, Hwang IT,
Han JH, Mechanism of relaxation of rat aorta by scopoletin; an
active constitutent of Artemisia capillaris. Kor. J. Ori. Med.
Physiol. Pathol., 2002, 16, 389-396.
2. Vilar S, Quezada E, Santana L, Uriarte E, Yanez M, Fraiz N,
Alcaide C, Cano E, Orallo F, Design, synthesis, and vasorelaxant
and platelet antiaggregatory activities of coumarin–resveratrol
hybrids. Bioorg. Med. Chem. Lett., 2006, 16, 257-261.
https://doi.org/10.1016/j.bmcl.2005.10.013.
3. Wang C, Wang T, Huang L, Lu W, Zhang J, He H, Synthesis and
fluorescent study of 5-phenyl furocoumarin derivatives as
vasodilatory agents. Bioorg. Med. Chem. Lett., 2016, 26, 640-644.
https://doi.org/10.1016/j.bmcl.2015.11.056.
4. Wang T, Wang C, Zhou N, Pan X, He H, Synthesis and
vasorelaxation evaluation of novel biphenyl-furocoumarin
derivatives. Med. Chem. Res., 2015, 24, 2417-2431.
https://doi.org/10.1007/s00044-014-1303-7.
4
5
6
.
.
.
Kamboj A, Saluja AK. Ageratum conyzoides L.: A review on its
phytochemical and pharmacological profile. Int. J. Greeen.
Pharma, 2008, 2, 59-68.
Simmler C, Pauli GF, Chen AN. Phytochemistry and biological
properties of glabridin. Fitoterapia, 2013, 90, 160-184.
https://doi.org/10.1016/j.fitote.2013.07.003.
Yao L, Lu P, Li Y, Yang L, Feng H, Huang Y, Zhang D, Chen J,
Zhu D. Osthole relaxes pulmonary arteries through endothelial
phosphatidylinositol 3-kinase/Akt-eNOS-NO signaling pathway in
2
2
rats.
Eur.
J.
Pharmacol.,
2013,
699,
23-32.
https://doi.org/10.1016/j.ejphar.2012.11.056.
7
.
Lee SH, Ding Y, Yan XT, Kim YH, Jang HD. Scopoletin and
Scopolin Isolated from Artemisia iwayomogi Suppress
Differentiation of Osteoclastic Macrophage RAW 264.7 Cells by
Scavenging Reactive Oxygen Species. J. Nat. Prod., 2012, 76,
6
15-620. https://doi.org/10.1021/np300824h.

2
2
2
2
5. Chanda D, Prieto-Lloret J, Singh A, Iqbal H, Yadav P, Snetkov V,
Aaronson PI, Glabridin-induced vasorelaxation: Evidence for a
role of BKCa channels and cyclic GMP. Life Science, 2016, 165,
2
6-34. https://doi.org/10.1016/j.lfs.2016.09.018.
6. Rakotoarison O, Rabenau I, Lobstein A,. Um BH, Schott C, Anton
R, Randriantosa A, Andriantsitohaina R, Vasorelaxing Properties
and Bio-Guided Fractionation of Cedrelopsis grevei.Planta Med.,
2
003, 69, 179-181. https://doi.org/10.1055/s-2003-37717.
7. Najmanová I, Doseděl M, Hrdina R, Anzenbacher P, Filipsky T,
Říha M, Mladěnka P, Cardiovascular effects of coumarins besides
their antioxidant activity. Curr. Top. Med. Chem., 2015, 15, 830-
8
49. https://doi.org/10.2174/1568026615666150220112437.
8. Macáková K , Reháková Z,Mladenka P,Karlícková J, Filipský T,
Ríha M, Prasad AK, Parmar VS, Jahodár L, Pávek P, Hrdina R,
Saso L. In vitro platelet antiaggregatory properties of 4-
methylcoumarins.
Biochimie,
2012,
94,
268-2686.
http://dx.doi.org/10.1016/j.biochi.2012.09.006.
2
3
9. Campos-Toimil M, Orallo F, Santana L. Uriarte E. Synthesis and
Vasorelaxant Activity of New Coumarin and Furocoumarin
Derivatives. Bioorg. Med. Chem. Lett., 2002, 12, 783-786.
0. Amin KM, Awadalla FM, Eissa AAM, Abou-Seri SM, Hassan
GS. Design, synthesis and vasorelaxant evaluation of novel
coumarins-pyrimidine hybrids. Bioorg. Med. Chem., 2011, 19,
6
087-6097. https://doi.org/10.1016/j.bmc.2011.08.037.

Graphical Abstract
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Synthesis and evaluation of substituted
Leave this area blank for abstract info.
8
,8-dimethyl-8H-pyrano[2,3-f]chromen-2-one
derivatives as vasorelaxing agents
Sarita Singh, Karishma Agarwal, Hina Iqbal, Pankaj Yadav, Deepika Yadav, Debabrata Chanda,* Sudeep
Tandon, Feroz Khan, Anil Kumar Gupta, Atul Gupta*
OH
R2
R1
N
X
O
n
OH
H3CO
HO
O
O
O
O
O
O
O
1
1; Scopoletin, a benzopyran-2-one
X = CO or CH2
Glabridin (14), a pyranobenzopyran derivative
with vasorelaxing activity
derivative with vasorelaxing activity 15; Designed prototype
Fonts or abstract dimensions should not be changed or altered.

with 70.89 fold increased sensitivity. The mechanistic
evaluation of 22 showed that it exerted vasorelaxation
2
+
+
through Ca -activated K (BKca) channel and the effect
was endothelium independent.
Thanking you in anticipation.
Best regards,
Dr. Atul Gupta,
Scientist
Medicinal Chemistry Department,
Central Institute of Medicinal and Aromatic Plants,
P.O. CIMAP, Kukrail Road, Lucknow-226015, India
Date: October 12, 2019
To,
The Editor,
Email: atisky2001@yahoo.co.in
Bioorganic and Medicinal Chemistry Letters
Subject: Submission of revised manuscript (BMCL-
D-00909) to Bioorganic and Medicinal Chemistry
Letters for publication
Dear Sir/Madam,
Please find enclosed our revised manuscript
entitled “Synthesis and evaluation of substituted 8,8-
dimethyl-8H-pyrano[2,3-f]chromen-2-one derivatives
as vasorelaxing agents” for publication in “Bioorganic
and Medicinal Chemistry Letters.”
This study reports design and synthesis substituted 8,8-
dimethyl-8H-pyrano[2,3-f]chromen-2-ones (chromeno-
coumarin hybrids) from scopoletin (11) which were
evaluated for their vasorelaxation in endothelium intact
rat Main Mesenteric Artery (MMA).
Compounds 11, 21a, 21c-f and 22 showed significant
vasorelaxation in precontracted MMA within the range
of EC50 value 1.58-5.02 µM with 29.40-70.89 fold
increased sensitivity for experimental tissue compared to
scopoletin (11), the parent molecule.
Among others, 22 was found to be the most active
compound which had EC 1.58µM and pD2 5.802±0.08
5
0