Synthesis, characterization, and pharmacological evaluation of benzothiopyran derivatives as a novel class of calcium channel blockers

Article abstract of DOI:10.1007/s00044-012-0211-y

The current research aimed to investigate the importance of the heterocyclic ring system in the structure of the cardiovascular drug Diltiazem for its calcium channel blocking activity. The manuscript describes the design, synthesis, and biological testing of Benzothiopyran derivatives (7a-7f). The new compounds maintain some Diltiazem pharmacophores. Benzothiopyran has two pharmacophore: the aromatic benzene ring fused with the heterocyclic thiopyrans ring, and the stereo-chemical centers (alkyl ether). In vitro evaluation of Benzothiopyran derivatives (7a-7f) for calcium channel blocking effects revealed moderate activities. Compounds of the current series showed optimum activity when the alkyl ether chain was substituted on the 3-chloro-3,4-dihydro-2H-1- benzothiopyran-4-ol derivatives (7a-7f).

Full text of DOI:10.1007/s00044-012-0211-y

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:2188–2195
DOI 10.1007/s00044-012-0211-y
ORIGINAL RESEARCH
Synthesis, characterization, and pharmacological evaluation
of benzothiopyran derivatives as a novel class of calcium channel
blockers
•
Rajkumari Nalwaya Arvind Sahai
•
•
Subhash Chander Manish Sharma
•
•
Ruchi Malik Gaurav Sarsodia
Received: 27 June 2011 / Accepted: 20 August 2012 / Published online: 19 September 2012
Ó Springer Science+Business Media, LLC 2012
Abstract The current research aimed to investigate the
importance of the heterocyclic ring system in the structure
of the cardiovascular drug Diltiazem for its calcium
channel blocking activity. The manuscript describes the
design, synthesis, and biological testing of Benzothiopyran
derivatives (7a–7f). The new compounds maintain some
Diltiazem pharmacophores. Benzothiopyran has two
pharmacophore: the aromatic benzene ring fused with the
heterocyclic thiopyrans ring, and the stereo-chemical cen-
ters (alkyl ether). In vitro evaluation of Benzothiopyran
derivatives (7a–7f) for calcium channel blocking effects
revealed moderate activities. Compounds of the current
series showed optimum activity when the alkyl ether chain
was substituted on the 3-chloro-3,4-dihydro-2H-1-ben-
zothiopyran-4-ol derivatives (7a–7f).
Kim, 2003). Commercially available calcium channel
blockers belong to either one of three chemical classes:
Dihydropyridines (Amlodipine, Nifedipine, Felodipine,
Isradipine), Phenyl alkyl amines (Verapamil, Gallopamil),
and Benzothiazepine (Diltiazem) (Delgado and Remers,
1998). The intracellular concentration of calcium plays an
important role in maintaining the tone of smooth muscle
and in the contraction of the myocardium. Calcium enters
muscle cells through special voltage-sensitive calcium
channels. Calcium channel antagonists block the inward
movements of calcium by binding it to L-type calcium
channels in the heart and in smooth muscle of the coronary
and peripheral vasculature (Harvey et al., 2000). These
antagonists prevent the calcium ions needed for muscle
contraction from entering the cells of smooth and cardiac
muscle. This decreases intracellular calcium leading to a
reduction in muscle contraction. In heart, a decrease in
calcium available for each beat results in decreased cardiac
contractility. The current research explores the develop-
ment of new and facile synthetic methods for such het-
erocyclic considered for activity (Rios et al., 2006).
Benzothiopyran is a heterocyclic compound that contains
sulfur as a heteroatom, which is responsible for biological
and pharmacological activity (Mehanna and Kim, 2005).
Changing the heterocyclic ring size generated derivatives
that not only retained the calcium channel blocking activity
but also resulted in generation of several other compounds
that were more active than Diltiazem (Rios et al., 2006). A
receptor-binding model identifies the benzene ring as a
lipophilic group that facilitates transport into the channel,
and the absolute stereochemistry for the selective binding
(Dodda et al., 2009). Benzothiopyran has two pharmaco-
phores: aromatic benzene ring fused with heterocyclic
thiopyrans ring and the stereo-chemical centers (alkyl
ether). The benzene ring as a lipophilic group facilitates
Keywords Calcium channel blocker Á Diltiazem Á
Benzothiopyran Á Cardiovascular agents
Introduction
Calcium channel blockers (CCBs) are a group of hetero-
geneous drugs whose main pharmacological effect is to
prevent or reduce the entry of calcium into cell via spe-
cialized calcium channel (Gennaro, 2000; Mehanna and
R. Nalwaya Á S. Chander (&) Á M. Sharma Á
R. Malik Á G. Sarsodia
Department of Medicinal Chemistry, TIFAC-CORE,
Innovator Square, B. R. Nahata College of Pharmacy,
Mandsaur, M.P., India
e-mail: subhu.bishnoi@gmail.com
A. Sahai
Government P.G. College, Mandsaur, M.P., India
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Med Chem Res (2013) 22:2188–2195
2189
transport into channel, and provides absolute stereochem-
istry for the selective binding. Substitution of alkyl ethers
was undertaken as it is highly lipophilic due to the presence
of long chain of carbon atoms (Rios et al., 2006). Sub-
stituents such as methoxy, ethoxy, propoxy, butoxy, pent-
oxy, and phenoxy were found to be highly active for
coronary vasodilating activity, and substitution of chlorine
at the 7 position in benzothiopyran ring led to slight
reduction in activity (Kimball et al., 1993).
and potassium hydrogen sulfide provided the common
intermediate 3-(2-sulfanylphenyl)prop-2-enal(4). Reaction
of 3-(2-sulfanylphenyl)prop-2-enal(4) with different alco-
hols gave the corresponding intermediate (6a–6f). Reaction
of 6a–6f with hypochlorous acid and water provided the
final compounds 3-chloro-2-methoxy-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7a), 3-chloro-2-ethoxy-3,4-dihydro-
2H-1-benzothiopyran-4-ol(7b), 3-chloro-2-(propan-2-
yloxy)-3,4-dihydro-2H-1-benzothiopyran-4-ol(7c), 2-but-
oxy-3-chloro-3,4-dihydro-2H-1-benzothiopyran-4-ol(7d),
3-chloro-2-(2-methylbutoxy)-3,4-dihydro-2H-1-benzothio-
pyran-4-ol(7e), and 3-chloro-2-phenoxy-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7f).
Results and discussion
Chemistry and synthesis
In vitro biological evaluation
Scheme 1 depicts the route to synthesize the target ben-
zothiopyran derivatives (compounds 7a–7f, Scheme 1).
Substituents such as methoxy, ethoxy, propoxy, butoxy,
pentoxy, and phenoxy were found to be highly active for
coronary vasodilating activity, and substitution of chlorine
at the 7 position in benzothiopyran ring led to slight
reduction in activity (Kimball et al., 1993). Compounds
7a–7f are benzothiopyran derivatives that mimic diltiazem
pharmacophoric group. Compound(s) 7a–7f have an alkyl
ether chain part of a benzothiopyran ring system substi-
tuted with different alcohols as shown in Scheme 1 which
depicts the synthetic route to prepare the target compounds.
Reaction of 3-(2-nitrophenyl)prop-2-enal(1) with SnCl2 in
ethanol provided the common intermediate 3-(2-amino-
phenyl)prop-2-enal(2). Reaction of 3-(2-aminophenyl)
prop-2-enal(2) with sodium nitrate, hydrochloric acid,
All six compounds (7a–7f) were tested for In vitro calcium
channel blocking activity, on contractions of potassium
depolarized isolate of guinea-pig ileum according to a
previously reported protocol. A series of substituted
3-chloro-3,4-dihydro-2H-1-benzothiopyran-4-ol(7b–7e) has
been investigated for their calcium channel blocking
activity on guinea-pig ileum. The guinea-pig ileum showed
spontaneous contraction when KCl solution was added to
tissue bath at concentration of 80 mM, after that different
derivatives were tested for their antagonistic activity with
reference to nifedipine. It was observed that with increase
in concentration of test compounds, significant antagonistic
activity was exhibited. In all derivatives, the 100 mM
concentration of test compound showed the highest
antagonistic activity that was the highest muscle relaxation
Scheme 1 Synthesis of
NO2
N2Cl
NH2
benzothiopyran derivatives.
Reagents and conditions: (1)
SnCl2, Ethanol, HCl; (2)
i
ii
CH CH CHO
CH CH CHO
CH CH CHO
NaNO2, HCl; (3) KSH, HCl; (4)
Different Alcohol, HCl; (5)
Cyclization; (6) HOCl, H2O
1
3
2
iii
SH
S
R
SH
v
iv
R
CH CH C OH
H
CH CH CHO
5
6a-f
4
vi
R
Compounds
-OCH3
-OCH2CH3
-OCH2(CH3)CH3
-OCH2CH2CH2CH3
-OCH2CH(CH3)CH2CH2CH3
-OC6H5
7a
7b
7c
7d
7e
7f
S
R
Cl
OH
7a-f
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Med Chem Res (2013) 22:2188–2195
as compared to KCl-induced muscle contraction. Table 1
and Figs. 1, 2, 3, 4 list the calcium channel blocking
activities for the new compounds, expressed, with Nifedi-
pine as the reference drug. Table 1 and Figs. 1, 2, 3, 4 data
indicate that in spite of lacking heterocyclic ring system,
the new compounds were moderately active as calcium
channel blockers.
Veego apparatus and are uncorrected. FT-IR spectra were
obtained with KBr on FT-IR 8400 S (Shimadzu, Japan)
spectrophotometer model using Nujol and potassium bro-
mide and on Perkin Elmer RX1 using potassium bromide
cell for liquid sample and potassium pellets for solid
sample(tmax in cm-1). 1HNMR spectra were recorded on a
Brucker Avance II 400 NMR spectrometer with tetra-
methylsilane (TMS) as an internal standard. The values of
chemical shift (d) are given in parts per million (ppm) and
coupling constants (J) in Hertz (Hz). The reaction progress
was monitored using TLC on silica gel plate (Merck Pvt.
Ltd). Reported yields are for the purified products and are
Chemistry
General information: Melting points were determined
using digital melting point apparatus model VMP-DS,
3
2
1
0
3
2
1
0
Concentration(mM)
Concentration(mM)
Fig. 3 Bar diagram showing the effect of compound (7d) on various
concentration (60, 80, 100 mM) and reference drug (Nifedipine
10 mM)
Fig. 1 Bar diagram showing the effect of compound (7b) on various
concentration (60, 80, 100 mM) and reference drug (Nifedipine
10 mM)
3
2
1
0
3
2
1
0
Concentration(mM)
Concentration(mM)
Fig. 2 Bar diagram showing the effect of compound (7c) on various
concentration (60, 80, 100 mM) and reference drug (Nifedipine
10 mM)
Fig. 4 Bar diagram showing the effect of compound (7e) on various
concentration (60, 80, 100 mM) and reference drug (Nifedipine
10 mM)
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2191
Table 1 Calcium channel blocking activity of the new compounds expressed as concentration–response curve
Dose
Conc. (mM)
Mean S.E.M. (7b)
Mean S.E.M. (7c)
Mean S.E.M. (7d)
Mean S.E.M. (7e)
KCl
80
60
2.567 0.066
2.533 0.033
2.700 0.057
2.533 0.033
I
2.067 0.033***
1.467 0.033***
0.83 0.033***
0.13 0.033***
1.933 0.033***
1.433 0.088***
0.733 0.033***
0.100 0.0***
2.000 0.057***
1.500 0.057***
0.733 0.033***
0.133 0.033***
1.933 0.033***
1.400 0.047***
0.633 0.033***
0.133 0.033***
II
80
III
100
10
Nifedipine
***
Significance coefficient P \ 0.001
not optimized. Elemental analysis were performed by Va-
rio EL III model. All the animal experiments were carried
out at Department of Pharmacology, B.R. Nahata College
of Pharmacy, Mandsaur, (M.P.) and permission for con-
ducting this experiment was obtained from Institutional
Animal Ethical Committee, Mandsaur (M.P.).
intermediate (4) as yellow powder. M.p. = 275–280 °C; IR
(KBr, t cm-1): 3,045.11, 2,925.81, 2,735.13, 1,681.81,
1,618.17, 1,519.80, 1,456.16, 671.18, 1,035.70, 964.34,
1
746.40; HNMR (400 MHz, d ppm, DMSO): 3.11 (s, 1H,
mercapto-H), 6.79 (td, 1H, J = 7.36, Ar–H), 7.11 (d, 1H,
J = 13.36, –C=CH–), 7.25 (dd, 1H, J = 6.72 Hz, Ar–H),
7.41 (td, 1H, J = 6.80 Hz, Ar–H), 7.57 (dd, 1H,
J = 6.96 Hz, Ar–H), 8.11 (d, 1H, J = 10.72 Hz, –CH=C–),
9.69 (s, 1H, aldehyde-H).
3-(2-Aminophenyl)prop-2-enal(2)
2 gm (0.01 mol) of 3-(2-nitrophenyl)prop-2-enal(1) was
weighed and dissolved in 80 ml ethanol and 7.5 gm
(0.03 mol) of tin(II) chloride dihydrate was added with
10 ml of concentrated hydrochloric acid. Reaction mixture
was refluxed on oil bath for 3 h at 80 °C, the reaction
mixture was cooled, and water was added to obtain the
yield (Furniss et al., 1989a, b, c; Desilets and Hamer,
1993). The precipitate was recrystallized using acetone to
produce 0.95 gm (55.00 %) of intermediate(2) as white
crystals. M.p. = 240–245 °C; IR (KBr, t cm-1): 3,482.91,
3,370.76, 3,049.25, 2,975.96, 2,736.80, 1,680.56, 1,627.81,
1,610.43, 1,442.66, 1,569.95, 1,172.64, 1,037.63, 738.69;
1HNMR (400 MHz, d ppm, CDCl3): d 4.13 (s, 2H, amino-
H), 6.59 (d, 1H, J = 12.72 Hz, –CH=C–), 6.62 (dd, 1H,
J = 8.0 Hz, Ar–H), 6.84 (td, 1H, J = 6.56, Ar–H), 6.97
(dd, 1H, J = 2.42, Ar–H), 7.36 (td, 1H, J = 6.16, Ar–H),
7.61 (d, 1H, J = 12.44 Hz, C=CH–), 9.59 (s,1H, alde-
hyde-H).
2-Methoxy-2H-thiochromene(23a)
2 gm (0.012 mol) powder of 3-(2-sulfanylphenyl)prop-2-
enal(4) was weighed and placed in 250 ml round bottom
flask and 4 ml (0.13 mol) methanol was added with few
microliters of concentrated hydrochloric acid. The solution
was stirred over night at room temperature. The solution
was concentrated by solvent evaporation of methanol with
a rotary evaporator at 50 °C. The concentrated solution
was heated at 60 °C in alkaline condition for 4 h (Salam
and Marguerite, 1990). Recrystallization was done using
mixture of chloroform and ethyl acetate to produce
1.65 gm (76.38 %) of intermediate (6a) as off white
powder. M.p. = 255–260 °C; IR (KBr, t cm-1) :3,032.68,
2,867.96, 1,595.46, 1,486.10, 1,446.51, 1,370.08,
1,255.00,1,035.70, 1,080.06, 746.61, 669.25; 1HNMR
(400 MHz, d ppm, CDCl3): 3.43 (s, 3H, methoxy-H), 5.45
(d, 1H, J = 6.00, –S–CH–), 5.97 (dd, 1H, J = 10.88, –S–
C–CH–), 6.60 (d, 1H, J = 10.52 Hz, –S–C–C=CH–), 7.01
(td, 1H, J = 5.94, Ar–H), 7.15 (dd, 1H, J = 7.44,
Ar–H), 7.36 (td, 1H, J = 6.98, Ar–H), 7.43 (dd, 1H,
J = 7.54, Ar–H).
3-(2-Sulfanylphenyl)prop-2-enal(4)
2 gm (0.01 mol) of 3-(2-Aminophenyl)prop-2-enal(2) was
weighed and dissolved in 6.5 ml concentrated hydrochloric
acid and 6.5 ml water. The mixture was cooled at 0 °C in
an ice-salt bath. A solution of 1.6 gm (0.02 mol) sodium
nitrite was added in 8 ml water at 0–5 °C for 10–15 min
with addition of a little crushed ice from time to time. The
cold diazonium chloride solution was poured slowly into
the cold potassium hydrogen sulfide. The mixture was
allowed to warm up to room temperature, on a water bath
to about 60 °C (Furniss et al., 1989a, b, c; Desilets and
Hamer, 1993). Recrystallization was done using mixture of
chloroform and ethanol to produce 1.20 gm (53.33 %) of
3-Chloro-2-methoxy-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7a)
In a 100 ml round bottom flask with a stirrer, 7.31 ml water
and 1.70 ml (0.032 mol) hypochlorous acid were taken.
1.00 gm (0.005 mol) of 2-Methoxy-2H-thiochromene(6a)
was added to the reaction mixture and the temperature of
the reaction was maintained between 40 and 45 °C for 4 h.
The mixture was then allowed to stand overnight at room
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Med Chem Res (2013) 22:2188–2195
temperature. The solvent was removed and put in water
bath, and then ice-cold solution of 1 gm of sodium
hydroxide in 1.8 ml of water was added. The temperature
was not allowed to rise above 45 °C. This alkaline mixture
solution was warmed up to 45 °C and an equal volume of
ethyl acetate was added. The ethyl acetate extract was
concentrated under reduced pressure (Furniss et al., 1989a,
b, c). Recrystallization was done using mixture of ethyl
acetate and acetone to produce 1.2 gm (58.00 %) of com-
pound (7a). M.p. = 190–195 °C; IR (KBr, t cm-1):
3,347.66, 3,048.28, 2,881.45, 1,587.30, 1,504.37, 1,434.94,
1,369.37, 1,137.70, 1,247.07, 1,039.31, 1,099.81, 747.63,
reaction was maintained between 40 and 45 °C for 4 h. The
solvent was removed and put in water bath, and then ice-
cold solution of 1 gm of sodium hydroxide in 1.8 ml of
water was added. This solution was warmed to 45 °C and
equal volume of ethyl acetate was added. The ethyl acetate
extract was concentrated under reduced pressure. Recrys-
tallization was done using mixture of ethyl acetate and
methanol to produce 0.750 gm (55.11 %) of compound
(7b); M.p. = 310–315 °C; IR (KBr, t cm-1): 3,344.46,
3,044.58, 2,885.42, 1,584.34, 1,501.37, 1,445.44, 1,370.30,
1,249.01, 1,042.13, 1,139.11, 1,097.32, 1,072.37, 761.61,
1
693.61; HNMR (400 MHz, d ppm, DMSO): 1.18 (t, 3H,
1
639.61; HNMR (400 MHz, d ppm, CDCl3): 2.12 (s, 1H,
J = 5.88 Hz, methoxy-H), 2.23 (s, 1H, hydroxy-H), 3.87
(q, 2H, J = 7.00 Hz, ethoxy-H), 4.19 (d, 1H, J = 12.36
Hz, –S–C–C=CH–), 4.99 (dd, 1H, J = 15.04 Hz, –S–C–
CH–), 5.32 (d, 1H, J = 6.32 Hz, –S–CH–), 6.82 (td, 1H,
J = 6.64 Hz, Ar–H), 7.06 (dd, 1H, J = 7.40 Hz, Ar–H),
7.20 (td, 1H, J = 7.68 Hz, Ar–H), 7.39 (dd, 1H,
J = 7.36 Hz, Ar–H); Mass: MS (ESI) m/z 244.32 (M?),
m/z 244.10 (M ? 1); Calcd for C11H13ClO2S: C, 53.98; H,
5.35; O, 13.07. Observed: C, 53.58; H, 5.01; O, 12.98 %.
hydroxy-H), 3.31 (s, 3H, methoxy-H), 4.63 (d, 1H,
14.00 Hz, –S–C–C=CH–), 4.75 (d, 1H, J = 5.40 Hz, –S–
CH–), 5.03 (dd, 1H, J = 10.88 Hz, –S–C–CH–), 6.95 (td,
1H, J = 7.10 Hz, Ar–H), 7.07 (dd, 1H, J = 6.90 Hz, Ar–
H), 7.19 (td, 1H, J = 7.44 Hz, Ar–H), 7.39 (dd, 1H,
J = 6.76 Hz, Ar–H); Mass: MS (ESI) m/z 230.13 (M?),
m/z 231.12 (M ? 1), m/z 232.01 (M ? 2). Calcd for
C10H11ClO2S: C, 52.06; H, 4.81; O, 13.87. Observed: C,
51.92; H, 4.77; O, 13.85 %.
2-(Propan-2-yloxy)-2H-thiochromene(6c)
2-Ethoxy-2H-thiochromene(6b)
2 gm (0.012 mol) of crystal powder of 3-(2-Sulfanylphe-
ny)prop-2-enal(4) was weighed and placed in 250 ml round
bottom flask with addition of 4 ml (0.06 mol) propan-2-ol
with few milliliters of concentrated hydrochloric acid. The
solution was stirred over night at room temperature. The
solution was concentrated by solvent evaporation of pro-
pan-2-ol with rotary evaporator at 50 °C.The concentrated
solution was heated at 60 °C in alkaline condition for 4 h.
Recrystallization was done using mixture of methanol and
ethyl acetate to produce 1.50 gm (60.00 %) of intermediate
(6c): M.p. = 290–294 °C; IR (KBr, t cm-1) : 3,048.53,
2,918.73, 1,577.66, 1,402.15, 1,457.02, 1,370.23, 1,253.64,
2 gm (0.012 mol) of crystal powder of 3-(2-Sulfanylphe-
nyl)prop-2-enal(4) was weighed and placed in 250 ml
round bottom flask with addition of 4 ml (0.09 mol) etha-
nol with few milliliters of concentrated hydrochloric acid.
The solution was stirred over night at room temperature.
The solution was concentrated by solvent evaporation of
propan-2-ol with rotary evaporator at 50 °C. The concen-
trated solution was heated at 60 °C in alkaline condition for
4 h. Recrystallization was done using mixture of chloro-
form and ethyl acetate to produce 1.50 gm (64.65 %) of
intermediate (6b); M.p. = 270–274 °C; IR (KBr, t cm-1):
3,074.32, 2,877.37, 1,589.23, 1,499.36, 1,456.16, 1,374.46,
1,250.91, 1,039.7, 1,191.93, 753.62, 667.32; 1HNMR
(400 MHz, d ppm, CDCl3): 1.18 (t, 3H, J = 5.80 Hz,
ethoxy-H), 3.88 (q, 2H, J = 5.92 Hz, methoxy-H), 4.72 (d,
1H, J = 7.44 Hz, –S–CH–), 6.13 (dd, 1H, J = 13.8 Hz, –
S–C–CH–), 6.39 (d, 1H, J = 11.84 Hz, –S–C–C=CH–),
6.93 (td, 1H, J = 7.36 Hz, Ar–H), 7.16 (dd, 1H,
J = 7.64 Hz, Ar–H), 7.35 (td, 1H, J = 7.34 Hz, Ar–H),
7.43 (dd, 1H, J = 7.08 Hz, Ar–H).
1
1,053.23, 1,122.45, 771.47, 636.47; HNMR (400 MHz, d
ppm, DMSO): 1.13 (d, 6H, J = 5.88 Hz, propoxy-H), 3.88
(m, 1H, J = 6.68 Hz, methoxy-H), 5.53 (d, 1H,
J = 8.6 Hz, –S–CH–), 5.98 (dd, 1H, J = 11.80 Hz, –S–C–
CH–), 6.61 (d, 1H, J = 12.60 Hz, –S–C–C=CH–), 6.99 (td,
1H, J = 6.68 Hz, Ar–H), 7.12 (dd, 1H, J = 7.00 Hz, Ar–
H), 7.37 (td, 1H, J = 7.60 Hz, Ar–H), 7.59 (dd, 1H,
J = 7.20 Hz, Ar–H).
3-Chloro-2-(propan-2-yloxy)-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7c)
3-Chloro-2-ethoxy-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7b)
In a 100 ml round bottom flask with a stirrer, 7.31 ml water
and 1.70 ml (0.032 mol) hypochlorous acid were taken.
1.00 gm (0.004 mol) of 2-(Propan-2-yloxy)-2H-thio-
chromene(23c) was added to the reaction mixture and tem-
perature of the reaction was maintained between 40 and
In a 100 ml round bottom flask with a stirrer, 7.31 ml water
and 1.70 ml (0.032 mol) Hypochlorous acid were taken.
1.00 gm (0.005 mol) of 2-Ethoxy-2H-thiochromene(6b)
was added to the reaction mixture and temperature of the
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2193
45 °C for 4 h. The solvent was removed and put in water
bath, and then ice-cold solution of 1 gm of sodium hydroxide
in 1.8 ml of water was added. This alkaline mixture solution
was warmed up to 45 °C and equal volume of ethyl acetate
was added. The ethyl acetate extract was concentrated under
reduced pressure. Recrystallization was done using mixture
of ethyl acetate and ethanol to produce 0.64 gm (66.40 %) of
compound (7c); M.p. = 295–301 °C; IR (KBr, t cm-1):
3,324.19, 3,032.18, 2,898.30, 1,602.74, 1,400.22, 1,485.09,
1,374.47, 1,228.10, 1,041.49, 1,204.83, 1,139.85, 1,085.85,
1.00 gm (0.0045 mol) of 2-Butoxy-2H-thiochromene(6d)
was added to the reaction mixture and temperature of the
reaction was maintained between 40 and 45 °C for 5 h. The
solvent was removed and put in water bath, and then ice-
cold solution of 1 gm of sodium hydroxide in 1.8 ml of
water was added. The temperature was not allowed to rise
above 45 °C. This alkaline mixture solution was warmed
up to 45 °C and equal volume of ethyl acetate was added.
The ethyl acetate extract was concentrated under reduced
pressure. Recrystallization was done using mixture of
methanol and acetone to produce 0.75 gm (60.97 %) of
compound (7d); M.p. = 298–305 °C; IR (KBr, t cm-1):
3,323.12, 3,033.64, 2,934.39, 1,575.73, 1,502.44, 1,461.94,
1,378.10, 1,251.36, 1,042.02, 1,180.35, 1,114.78,1,080.06,
746.40, 688.54; 1HNMR (400 MHz, d ppm, DMSO): d
0.93 (t, 3H, J = 6.24 Hz, buthoxy-H), 1.40 (m, 2H,
J = 6.00 Hz, propoxy-H), 1.56 (q, 2H, J = 7.64 Hz, eth-
oxy-H), 2.09 (s, 1H, hydroxy-H), 3.36 (t, 2H, J = 7.60 Hz,
methoxy-H), 4.98 (d, 1H, J = 11.68 Hz, –S–C–C=CH–),
5.04 (dd, 1H, J = 11.92, 8.12 Hz, –S–C–CH–), 5.17 (d,
1H, J = 11.68 Hz, –S–CH–), 7.06 (td, 1H, J = 6.72 Hz,
Ar–H), 7.20 (dd, 1H, J = 7.68 Hz, Ar–H), 7.31 (td, 1H,
J = 7.60 Hz, Ar–H), 7.42 (dd, 1H, J = 6.24 Hz, Ar–H);
Mass: MS (ESI) m/z 272.21 (M?), m/z 273.03
(M ? 1). Calcd for C13H17ClO2S: C, 57.24; H, 6.28; O,
11.73. Observed: C, 56.96; H, 6.12; O, 11.70 %.
1
740.61, 669.25; HNMR (400 MHz, d ppm, DMSO): 1.12
(d, 6H, J = 6.60 Hz, propoxy-H), 2.40 (s,1H, hydroxy-H),
3.66 (m, 1H, J = 7.00 Hz, methoxy-H), 4.97 (dd, 1H,
J = 13.00 Hz, –S–C–CH–), 5.17 (d, 1H, J = 8.52 Hz, –S–
C–C=CH–), 5.65 (d, 1H, J = 11.80 Hz, –S–CH–), 7.08 (td,
1H, J = 6.80 Hz, Ar–H), 7.12 (dd, 1H, J = 6.76 Hz, Ar–H),
7.28 (td, 1H, J = 6.36 Hz, Ar–H), 7.55 (dd, 1H,
J = 5.80 Hz, Ar–H); Mass: MS (ESI) m/z 258.17 (M?), m/z
259.21 (M ? 1), m/z 260.16 (M ? 2); Calcd for
C12H15ClO2S: C, 55.70; H,5.84; O, 12.37. Observed: C,
55.35; H, 5.28; O, 11.96 %.
2-Butoxy-2H-thiochromene(6d)
2 gm (0.012 mol) of crystal powder of 3-(2-Sulfanylphe-
ny)prop-2-enal(4) was weighed and placed in 250 ml round
bottom flask with addition of 4 ml (0.053 mol) butan-1-ol
with few milliliters of concentrated hydrochloric acid. The
solution was stirred over night at room temperature. The
solution was concentrated by solvent evaporation of butan-
1-ol with rotary evaporator at 50 °C.The concentrated
solution was heated at 60 °C in alkaline condition for 6 h.
Recrystallization was done using mixture of dimethyl
sulfoxide to produce 1.65 gm (61.56 %) of intermediate
(6d); M.p. = 248–255 °C; IR (KBr, t cm-1): 3,064.32,
2,892.46, 1,589.23, 1,483.36, 1,463.16, 1,374.44,
1,255.93,1,044.17, 1,191.13, 732.31, 667.32; 1HNMR
(400 MHz, d ppm, CDCl3): 0.93 (t, 3H, J = 6.00 Hz,
buthoxy-H), 1.22 (m, 2H, J = 6.72 Hz, propoxy-H), 1.82
(q, 2H, J = 7.44 Hz, ethoxy-H), 3.35 (t, 2H, J = 7.00 Hz,
methoxy-H), 5.23 (d, 1H, J = 7.92 Hz, –S–CH–), 5.95 (dd,
1H, J = 12.00 Hz, –S–C–CH–), 6.59 (d, 1H,
J = 11.76 Hz, –S–C–C=CH–), 6.96 (td, 1H, J = 7.80 Hz,
Ar–H), 7.15 (dd, 1H, J = 5.84 Hz, Ar–H), 7.34 (td, 1H,
J = 6.40 Hz, Ar–H), 7.41 (dd, 1H, J = 7.80 Hz, Ar–H).
2-(2-Methylbutoxy)-2H-thiochromene(6e)
2 gm (0.012 mol) of crystal powder of 3-(2-Sulfanylphe-
ny)prop-2-enal(4) was weighed and placed in 250 ml round
bottom flask with addition of 5 ml (0.056 mol) 2-meth-
ylbutan-1-ol with few milliliters of concentrated hydro-
chloric acid. The solution was stirred over night at room
temperature. The solution was concentrated by solvent
evaporation of 2-methylbutan-1-ol with rotary evaporator
at 50 °C.The concentrated solution was heated at 60 °C in
alkaline condition for 5 h. Recrystallization was done using
mixture of methanol to produce 1.68 gm (58.94 %) of
intermediate (6e); M.p. = 260–265 °C; IR (KBr, t cm-1):
3,046.22, 2,882.66, 1,589.18, 1,415.77, 1,470.01, 1,358.09,
1,255.76, 1,041.49, 1,139.85, 744.47, 696.61; 1HNMR
(400 MHz, d ppm, DMSO): 0.88 (t, 3H, J = 7.44 Hz,
buthoxy-H), 1.37 (q, 2H, J = 6.72 Hz, propoxy-H), 1.49
(d, 3H, J = 7.84 Hz, isopropoxy-H), 2.17 (m, 1H,
J = 7.60 Hz, ethoxy-H), 3.37 (d, 2H, J = 6.16 Hz, meth-
oxy-H), 5.63 (d, 1H, J = 8.16 Hz, –S–CH–), 5.95 (dd, 1H,
J = 12.00 Hz, –S–C–CH–), 6.59 (d, 1H, J = 11.76 Hz, –
S–C–C=CH–), 7.01 (td, 1H, J = 5.60 Hz, Ar–H), 7.15 (dd,
1H, J = 7.80 Hz, Ar–H), 7.36 (td, 1H, J = 6.36 Hz, Ar–
H), 7.42 (dd, 1H, J = 5.80 Hz, Ar–H).
2-Butoxy-3-chloro-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7d)
In a 100 ml round bottom flask with a stirrer, 7.31 ml water
and 4.70 ml (0.089 mol) hypochlorous acid were taken.
123

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Med Chem Res (2013) 22:2188–2195
3-Chloro-2-(2-methylbutoxy)-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7e)
Ar–H), 7.34 (td, 1H, J = 6.32 Hz, Ar–H), 7.42 (dd, 1H,
J = 5.88 Hz, Ar–H).
In a 100 ml round bottom flask with a stirrer, 7.31 ml water
and 4.70 ml (0.089 mol) hypochlorous acid were taken.
1.00 gm (0.0042 mol) of 2-(2-methylbutoxy)-2H-thio-
chromene(6e) was added to the reaction mixture and tem-
perature of the reaction was maintained between 40 and
45 °C for 8 h. The solvent was removed and put in water
bath, and then ice-cold solution of 1 gm of sodium
hydroxide in 1.8 ml of water was added. This alkaline
mixture solution was warmed up to 45 °C and equal vol-
ume of ethyl acetate was added. The ethyl acetate extract
was concentrated under reduced pressure. Recrystalli-
zation was done using mixture of methanol and Ethanol
to produce 0.85 gm (69.67 %) of compound (7e);
3-Chloro-2-phenoxy-3,4-dihydro-2H-1-
benzothiopyran-4-ol(7f)
In a 100 ml round bottom flask with a stirrer, 7.31 ml water
and 4.70 ml (0.089 mol) hypochlorous acid were taken.
1.00 gm (0.0041 mol) of 2-Phenoxy-2H-thiochromene(6f)
was added to the reaction mixture and temperature of the
reaction was maintained between 40 and 45 °C for 4 h. The
solvent was removed and put in water bath, and then ice-
cold solution of 1 gm of sodium hydroxide in 1.8 ml of
water was added. The temperature was not allowed to rise
above 45 °C. This alkaline mixture solution was warmed
up to 45 °C and equal volume of ethyl acetate was added.
The ethyl acetate extract was concentrated under reduced
pressure. Recrystallization was done using mixture of
acetone and ethanol (0.75 gm, 61 %) of compound (7f);
M.p. = 250–256 °C; IR (KBr, t cm-1) : 3,332.21, 3,044.18,
1,599.59, 1,451.61, 1,244.43, 1,042.13, 1,199.35, 1,126.71,
1,070.76, 746.40, 654.88; 1HNMR (400 MHz, d ppm,
DMSO): 2.55 (s, 1H, hydroxy-H), 4.98 (d, 1H, J =
11.72 Hz, –S–C–C=CH–), 5.29 (dd, 1H, J = 11.92 Hz, –S–
C–CH–), 5.72 (d, 1H, J = 8.32 Hz, –S–CH–), 6.92 (tt, 1H,
J = 6.46 Hz, Ar–H), 7.01 (td, 2H, J = 5.60 Hz, Ar–H),
7.06 (td, 1H, J = 6.32 Hz, Ar–H), 7.18 (dd, 1H,
J = 6.72 Hz, Ar–H), 7.25 (dt, 2H, J = 7.04 Hz, Ar–H),
7.29 (td, 1H, J = 6.08 Hz, Ar–H), 7.38 (dd, 1H,
J = 5.80 Hz, Ar–H); Mass: MS (ESI) m/z 292.32 (M?), m/z
293.23 (M ? 1), m/z 294.08 (M ? 2). Calcd for
C15H13ClO2S: C, 61.53; H, 4.48; O, 10.95. Observed: C,
61.50; H, 4.43; O, 10.90 %.
M.p. = 280–285 °C; IR (KBr, t cm-1
)
:3,309.62,
3,042.18, 2,893.02, 1,585.73, 1,437.13, 1,467.83, 1,375.79,
1,253.13, 1,043.42, 1,206.23, 1,147.43, 1,078.32, 756.04,
1
628.75; HNMR (400 MHz, d ppm, DMSO): 0.86 (t, 3H,
J = 6.72 Hz, buthoxy-H), 1.29 (d, 3H, J = 6.00 Hz, iso-
propoxy-H), 1.36 (p, 2H, J = 6.60 Hz, propoxy-H), 1.85
(m, 1H, J = 7.48 Hz, ethoxy-H), 2.53 (s, 1H, Hydroxy-H),
3.44 (d, 2H, J = 7.00 Hz, methoxy-H), 4.76 (d, 1H,
J = 11.92 Hz, –S–C–C=CH–), 4.93 (d, 1H, J = 8.24
Hz, –S–CH–), 5.27 (dd, 1H, J = 11.80 Hz, –S–C–CH–),
7.06 (td, 1H, J = 6.00 Hz, Ar–H), 7.23 (dd, 1H, J =
5.60 Hz, Ar–H), 7.30 (td, 1H, J = 6.16 Hz, Ar–H), 7.45
(dd, 1H, J = 6.72 Hz, Ar–H); Mass: MS (ESI) m/z 286.10
(M?), m/z 287.18 (M ? 1); Calcd for C14H19ClO2S: C, 58.63;
H, 6.68; O, 11.16. Observed: C, 58.62; H, 6.60; O, 10.98 %.
2-Phenoxy-2H-thiochromene(6f)
Pharmacological evaluation
2 gm (0.012 mol) of crystal powder of 3-(2-Sulfanylphe-
ny)prop-2-enal(4) was weighed and placed in 250 ml round
bottom flask with addition of 5 ml (0.053 mol) phenol with
few milliliters of concentrated hydrochloric acid. The
solution was stirred over night at room temperature. The
solution was concentrated by solvent evaporation with
rotary evaporator at 50 °C. The concentrated solution was
heated at 60 °C in alkaline condition for 5 h. Recrystalli-
zation was done using dimethyl sulfoxide to produce
1.85 gm (63.35 %) of intermediate (6f); M.p. =
260–267 °C; IR (KBr, t cm-1) : 3,045.21, 1,587.16,
1,481.23, 1,248.88, 1,053.06, 1,128.78, 767.97, 669.25;
1HNMR (400 MHz, d ppm, DMSO): 5.95 (dd, 1H,
J = 11.92 Hz, –S–C–CH–), 6.27 (d, 1H, J = 11.64 Hz, –
S–C–C=CH–), 6.53 (d, 1H, J = 8.24 Hz, –S–CH–), 6.80
(tt, 1H, J = 6.52 Hz, Ar–H), 6.94 (dt, 2H, J = 6.30 Hz,
Ar–H), 7.02 (td, 1H, J = 5.60, 1.80 Hz, Ar–H), 7.14 (td,
2H, J = 6.48 Hz, Ar–H), 7.18 (dd, 1H, J = 6.60 Hz,
All the synthesized compounds were evaluated for their
calcium channel blocking activity using concentration–
response curve. All the experimental work was carried out
at Department of Pharmacology, B. R. Nahata College of
Pharmacy, Mandsaur (M.P.).
Drugs and chemicals
Nifedipine tablet (Unique Pvt. Ltd. India) and all synthe-
sized compounds were diluted in water and ethanol. Vol-
ume of injection was 60–100 Mm.
Animals
Guinea pig of 3–4 months old and both sex weighing
around 400–500 gm were used in this study. Animals were
procured from disease-free animal house, Calcutta Fish
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Med Chem Res (2013) 22:2188–2195
2195
Aquarium, Indore. The animals had free access to food and
water and were maintained under 12:12 h light and dark
cycles. All experiments were carried out during day time
from 0800 to 1300 hours, the IAEC approved the experi-
mental protocol, and care of animals was taken as per
guidelines of Committee for the Purpose of Control and
Supervision on Experiments on Animals (CPCSEA),
Department of Animal Welfare, Govt. of India.
Conclusion
The current research reports the synthesis, characterization,
and pharmacological evaluation of 6 benzothiopyran
derivatives (7a–7f) as a novel series of calcium channel
blockers. In the research, substituted 3-chloro-3,4-dihydro-
2H-1-benzothiopyran-4-olderivatives (7a–7f) were synthe-
sized, with elaborate characterization by spectral data.
Synthesized compounds were obtained in satisfactory yield
and were characterized by TLC, FT-IR, 1HNMR, Mass and
Elemental analysis. In pharmacological evaluation, syn-
thesized compounds 7b, 7c, 7d, and 7e exhibited in vitro
calcium channel antagonist activity. On the basis of the
above study, it is suggested that substituted 3-chloro-3,4-
dihydro-2H-1-benzothiopyran-4-ol derivatives(7b,7c,7d,
and 7e) include significant calcium channel antagonistic
action agents, KCl induce contraction. Further study is
needed to confirm exact mechanism for calcium channel
antagonistic activity.
Isolated tissue preparations
Guinea pigs had been sacrificed by cervical dislocation, the
ileum was immediately removed. Segments of 1.5–2.0 cm
length were mounted vertically in a 10 ml organ bath
containing Tyrode’s solution, aerated with a mixture of
95 % oxygen and 5 % carbon dioxide, and maintained at
37 °C. The composition of the Tyrode’s solution was: KCl
27 (0.2 gm), NaCl 137 (8.0 gm), MgCl2 1.8 (0.60 gm),
NaHCO3 11.9 (1.0 gm), NaH2PO4 0.4 (0.05 gm), and
glucose 5.55 (1.0 gm) mM. Each tissue was allowed to
equilibrate for at least 30 min before the addition of any
drug. The contractile effect of the test material was
assessed as the percent of the maximum effect produced by
the control drug, nifedipine (10 mM).
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