Design and green synthesis of 2-(diarylalkyl)aminobenzothiazole derivatives and their dual activities as angiotensin converting enzyme inhibitors and calcium channel blockers

Article abstract of DOI:10.1016/j.ejmech.2014.06.035

A series of novel 2-(diarylalkyl)aminobenzothiazoles were designed based on commercial synthetic calcium channel blockers (CCBs) and angiotensin converting enzyme (ACE) inhibitors. Which are further modified based on the natural products which are angiote

Full text of DOI:10.1016/j.ejmech.2014.06.035

European Journal of Medicinal Chemistry 83 (2014) 344e354
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Design and green synthesis of 2-(diarylalkyl)aminobenzothiazole
derivatives and their dual activities as angiotensin converting enzyme
inhibitors and calcium channel blockers
,
b
Praveen Kumar Kalavagunta a, Pankaj K. Bagul b, Anvesh Jallapally a
,
,
,
, *
Srinivas Kantevari a *, Sanjay K. Banerjee b *, Narender Ravirala a
a Crop Protection Chemicals Division, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500 007, India
b Medicinal Chemistry and Pharmacology Division, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel 2-(diarylalkyl)aminobenzothiazoles were designed based on commercial synthetic
calcium channel blockers (CCBs) and angiotensin converting enzyme (ACE) inhibitors. Which are further
modified based on the natural products which are angiotensin converting enzyme (ACE) inhibitors.
Completely green protocol was developed for their synthesis. As they are initially designed based on
CCBs, they were screened for their ACE inhibition property believing that almost all the compounds will
be CCBs. Out of 42 compounds two lead molecules were identified as ACE inhibitors, which were further
screened for CCB. As expected both were identified as CCBs with different selectivity over ACE inhibition.
Their selectivity over ACE and CCB can be used to treat resistant hypertension.
Received 29 October 2013
Received in revised form
11 June 2014
Accepted 17 June 2014
Available online 17 June 2014
Keywords:
ACE inhibitors
Calcium channel blockers
Green synthesis
© 2014 Elsevier Masson SAS. All rights reserved.
2-Aminobenzothiazole
Diarylalkylamine
Resistant hypertension
1. Introduction
market as antihypertensives, are targeting different pathways or
modulators of hypertension. But treating resistant hypertension is
Cardiovascular disease remains number one cause of death
worldwide [1]. Although the causes of cardiovascular disease are
diverse, hypertension remains the most common and crucial one.
Elevated blood pressure is the most common disorder in developed
as well as developing countries. Because of increasing prevalence of
hypertension, efforts were made to find new drug molecules which
may reduce blood pressure by inhibiting several important medi-
ators of hypertension. Multiple etiologies and environmental fac-
tors contribute to the development of hypertension [2,3]. Despite
extensive ongoing research in academia and industry, some forms
of hypertension remain untreatable. Several drugs, available in the
still in infancy. Combination of three or more classes of drugs like
ACE inhibitors (or) angiotensin receptor blocker, CCBs and diuretics
might be the right approach to reduce hypertension-related car-
diovascular deaths [4]. Among all those classes of drugs, angio-
tensin converting enzyme (ACE) inhibitors got a wide acceptance
and become first line of therapy. Several ACE inhibitors like Lisi-
nopril, Enalapril (Fig. 1) etc. are in clinical use for the treatment of
hypertension [5,6]. All these compounds are arylalkylamines in
which aryl and amine groups are separated by a three membered
carbon chain. However, severe associated side effects (i.e. dry
cough, hyperkalemia, rashes, loss of taste and first dose hypoten-
sion) limit their use justifying the development of new safe ACE
inhibitors [7e9]. On the other hand there are several natural
products such as chalcones (Butein, Fig. 1) [10], Styrenes [11], fla-
vanoids (Astragalin, Isoquercitrin etc.) [12], Xanthones [13] with
multiple hydroxyl groups on aromatic rings. It is also evident
that blocking the free hydroxyl groups on Xanthones with acetyl
group decreases the ACE inhibition property of the compounds
indicating that free hydroxyl groups playing a key role in inhibition
of ACE [13].
Abbreviations: ACE, Angiotensin Converting Enzyme; BSC, Benzenesulfonyl
Chloride; tACE, Testicular Angiotensin Converting Enzyme; CCB, Calcium Channel
Blocker; MVD, Molegro Virtual Docker; KHB, KrebseHensleit Buffer; PDB, Protein
Data Bank; RCSB, Research Collaboratory for Structural Bioinformatics; HHL, Hip-
puryl-Histidyl-Leucine; HA, Hippuric Acid; PMA, Phosphomolybdic Acid.
* Corresponding authors.
E-mail addresses: srinivask@iict.res.in (S. Kantevari), skbanerjee@iict.res.in
(S.K. Banerjee), ravindra@iict.res.in, raviralanarender@gmail.com (N. Ravirala).
http://dx.doi.org/10.1016/j.ejmech.2014.06.035
0223-5234/© 2014 Elsevier Masson SAS. All rights reserved.

P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
345
Fig. 2. Structures of R 56865 and Flunarizine.
2. Chemistry
Fig. 1. Structures of ACE Inhibitors and Ca2þ Channel blockers.
In search for the existence of compounds with the above skel-
eton we found few methodologies in which the hydroxyl group is
placed on the napthyl ring [24e26]. However all these methodol-
ogies suffer from serious draw backs such as high temperatures,
long reaction times, use of solvent and catalyst. As a result the re-
action mixture needed to be purified by traditional workup and
column chromatography techniques. The low solubility of the
product in several organic solvents makes the purification difficult
and requires huge amounts of organic solvents for purification.
Moreover, yield of the purified product after column chromatog-
raphy is very low. Hence there is a need to develop a method for the
synthesis of these compounds with better yield, good purity and
least solvent consumption. Several attempts (Tables 1 and 2) were
made to develop a methodology which gives higher yields with
more purity. Finally we found the reaction proceeds smoothly on a
preheated oilbath at a temperature of about 110e120 ꢀC using no
solvent and no catalyst with a relatively short span of time.
Second most common antihypertensive drugs are calcium
channel blockers (CCB) (Figs.1 and 2). Most of these drug molecules
are having the basic skeleton of arylalkylamine, with varying the
length of alkyl chain from one to three and with different sub-
stituents on aryl, amine or on both the groups. There are very few
reports on diarylalkylamines as antihypertensive agents such as
Azelnidipine (Fig. 1) and Flunarizine (Fig. 2) which act as CCB.
Similar to arylalkylamines, several 2-aminobenzothiazoles-
derivatives (Figs. 1 and 2) were also explored for their antihyper-
tensive property. 2-aminobenzothiazoles act as antihypertensive
by inhibiting acid induced Ca2þ uptake [14], altering intracellular
Ca2þ concentration [15] and inhibiting veratridine-induced atrium
contraction [16]. These derivatives are also effective inhibitor of
histamine-induced angiogenesis [17] and veratridine-induced in-
crease in oxygen consumption and uptake of Ca2þ ions [18], and
Initially we attempted a three component reaction using Benz-
aldehyde(1), b-Napthol(2) and 2-Aminobenzothiazole (3) as sub-
showed protection in the veratridine-induced calcium (Ca2þ
)
strates to stabilize the reaction. The methodology so developed is
further applied to the synthesis of several of its derivatives
(4aae4bp). The reaction proceeds smoothly with a variety of sub-
stituents on both aldehyde and 2-aminobenzothiazole moieties
and even with aryl substituted aliphatic aldehydes (compound 4aa,
entry 1, Table 3). Schematically the reaction can be represented as
in Scheme 1.
From the above experiments it was observed that the rate of
reaction is fast under solvent free conditions. But yield is very low
without a catalyst. This is because during the traditional heating
overload model [19]. Commercially available drug Riluzole, a de-
rivative of 2-aminobenzothiazole is known to act as glutamate
uptake stimulator [20], membrane channel activity stimulator [21],
intracellular Ca2þ level reducer [22], high voltage-activated calcium
channel inhibitor [23].
It was observed that a diarylalkylamine i.e. Flunarizine and a
2-aminobenzothiazole i.e. R 56865 (Fig. 2) suppress veratridine-
induced increase in oxygen consumption and uptake of Ca2þ
ions [18]. Based on all above data, we decided to replace the
amino group in diarylalkylamine with 2-aminobenzothiazole and
thus forming 2-(diarylalkyl)aminobenzothiazole derivatives to
screen CCB properties. It is note worthy that all the CCBs are
having phenyl group as aromatic group and they do not carry any
hydroxyl group, whereas most of the natural products such as
Xanthones, Flavones etc. which are ACE inhibitors, carry multiple
hydroxyl groups on aromatic rings. Based upon earlier report that
decrease in free hydroxyl groups on them decreases ACE inhibi-
tion [13]. We are interested to substitute 2-(diarylalkyl)amino-
benzothiazole derivatives with at least one hydroxyl group on
aryl groups. In over all we designed hybrid molecules in which
two aryl groups and one 2-aminobenzothiazole group are
attached to the same carbon with the properties based on CCB
property and with atleast one hydroxyl group on aryl groups
based on natural products which are ACE inhibitors. With the
above hybrid structure we are expecting that the new analogues
may also act as ACE inhibitors along with CCB, which is their
inherent property.
process
b-Napthol is reacting with aldehyde forming xanthenes
leaving small amount of
b-Napthol available when it reaches
100 ꢀC. This was further confirmed by carrying the reaction at lower
temperature which forms xanthenes exclusively. To overcome the
Table 1
Preliminary studies of three component coupling reaction.
Entry
Solvent (mL)
Temp ꢀC
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
9
PEG-400 (3)
Toluene (3)
Toluene (3)
Toluene (1)
100
100
100
100
100
100
100
50
100
100
150
100
100
100
150
100
150
30
32
30
35
35
20
25
0
m-Xylene (1)
e
e
e
e
75
23

346
P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
Table 2
derivatives 4aae4bp showed concentration dependent depressant
effect on calcium-induced contractions. Our experimental data
indicated that preincubation of both 4as and 4bn, antagonized the
calcium-induced aortic contractions in concentration dependent
manner. Among, both the compounds tested, 4as showed better
inhibition property of Ca2þ induced contraction in isolated aortic
ring. As smooth muscle of blood vessel contracts in response to the
activation of voltage-dependent and receptor-operated Ca2þ
channels, our data suggest that both molecules cause vaso-
relaxation through inhibition of voltage-operated Ca2þ channels in
the isolated rat aortic rings. IC50 values of 4as and 4bn are 3 mM
and 50 mM respectively.
Reactions on a preheated oilbath without solvent.
Entry
Temp (ꢀC)
Time (min)
Yield (%)
1
2
3
4
5
6
7
8
50
80
100
100
100
100
60
40
20
20
0
60
80
95
94
94
47
70
100
110
110
110
110
130
problem we kept the reaction over a preheated oil bath without any
solvent and catalyst, good yields were obtained as shown in Table 2.
As observed above 110 ꢀC was found to be the ideal temperature
to carry out the reaction within a short span of time i.e. 40 min.
Because of the low solubility of the product in many organic sol-
vents the reaction mixture was cooled to room temperature and the
so formed solid is powdered and washed with ethanol or methanol
(3 ꢁ 8 mL) to obtain the pure product 1-((benzo[d]thiazol-2-
ylamino)(phenyl)methyl) naphthalen-2-ol in 94% yield. It's ana-
logues can be washed with 3 ꢁ 8 mL in case of halogenated com-
pounds except fluorinated, 3 ꢁ 4 mL in case of fluoro and methoxy
derivatives. It is noteworthy to handle fluoro and methoxy de-
rivatives carefully which otherwise may easily washed off in
methanol/ethanol. The scope and generality of the reaction is
shown in Table 3.
Reactions with ortho-substituted aldehydes were relatively slow
when compared to their meta- and para- counter parts. So such
reactions were kept at a temperature of 120 ꢀC and heated for few
minutes excess. As expected the product 4aa formed using 2-
Phenylpropanal produced four isomers forming a pair of enantio-
mers as major leaving the other pair of enantiomers as minor
products. The reaction mixture was washed repeatedly with
methanol to remove the minor enantiomers. However it was
observed that it is not always possible to purify these isomers by
this method. Only major enantiomeric pair was screened for its ACE
inhibitory activity.
4. Results and discussion
4.1. Chemistry
We developed an efficient atom economic three component
coupling reaction under completely green protocols. The reactions
are fast, easy to handle and the products formed can be easily
purified by simply washing the reaction mixture with methanol or
ethanol which are considered as green solvents with low envi-
ronmental factor.
4.2. Pharmacology
The compounds synthesized above were primarily screened for
their ACE inhibition activity as they were designed based on CCBs
and assuming all of they will be CCBs. Out of 42 compounds
screened for their ACE inhibition activity two lead molecules 4as
and 4bn were identified as strong ACE inhibitors and were further
proved to be CCBs with varying activity against ACE and CCB. The
extent of ACE inhibition is comparably best when compared with
the natural product Butein (IC50 ¼ 730 mM) based on which the
molecules were designed. The structures and IC50 values of the
compounds 4as and 4bn which are dual inhibitors were shown in
Fig. 7.
4.3. Molecular docking
3. Pharmacology
To gain insight into the interaction of the ACE enzyme with two
potent analogues 4as and 4bn, they were docked on to surface of
tACE (PDB code: 1O86) using Molegro Virtual Docker (MVD) soft-
ware. The ligands were generated using Marvin sketch and saved in
mol2 format. The typical poses obtained were presented in Fig. 8.
Results suggest that the docking position of 4aae4bp analogues
showed a similar binding mode to that of A-ring of Lisinopril. The
interactions were mainly seen with the His 353, Ala 354, Tyr 523,
Tyr 520 and Glu 152 which are comparable to the standard drug,
Lisinopril binding mode. We found that docking scores were
matched with in vitro activity data.
3.1. In vitro inhibition of ACE
The ACE inhibition activity for new analogues 4aae4bp and the
standard drug, Lisinopril were presented in Fig. 3. The experiment
was carried out at 1.0
mM concentration of test and standard
compounds. Our data revealed that all compounds tested in the
present study have 7e100% of ACE inhibition activity. Further
analysis ACE inhibition activity indicated that two derivatives 4as
and 4bn exhibited 61.75% and 80.08% ACE inhibition, respectively
and are comparable to standard drug Lisinopril. Further, IC50 value
for test compounds and reference drug was calculated from dos-
eeresponse curves obtained by plotting the percentage inhibition
verses the concentration (Fig. 4). IC50 values of 4as and 4bn are
5. Conclusion
In conclusion, we designed hybrid molecules which are effective
against both ACE inhibition and CCB activity. Demonstrated an
efficient three-component coupling for their synthesis. The syn-
thesis and purification processes were completely green. The re-
action procedure did not utilize any solvent or catalyst and did not
use traditional workup and chromatography techniques for puri-
fication which generally requires huge amounts of solvents. Thus,
we prepared a wide range of 2-(diarylalkyl)aminobenzothiazole
derivatives in a single-step process through a multi-component
reaction and were initially screened for their angiotensin-
converting-enzyme (ACE) inhibition property. Two compounds
0.837 mM and 0.607 mM, respectively.
3.2. Effect of Nifedipine, 4as and 4bn on doseeresponse curve
induced by CaCl2
Preincubation of rat aortic strips with Nifedipine or 4as or 4bn
resulted in non-parallel shift to the right of calcium dose response
curves. In addition, preincubation of aortic ring with Nifedipine
caused a significant reduction of maximal contraction to CaCl2.
(Figs.
5 and 6). Vasorelaxants effects of newly synthesized

P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
347
Table 3
values are reported in ppm relative to TMS (Tetramethylsilane) or
DMSO as internal reference unless stated. Coupling constant value J
is measured in hertz. s (singlet), d (doublet), t (triplet), brs (broad
singlet), dd (double doublet), m (multiplet). Mass spectra were
recorded on an Agilent LC/MSD trap SL 1100 series spectrometer
with a 70 eV (ESI probe) and high-resolution mass spectra were
obtained by using ESI-QTOF mass spectrometry. Infrared spectra
recorded on a Thermo nicolet Nexus 670 FT-IR spectrometer.
Different derivatives of Aldehydes (R1) and 2-Aminobenzothiazoles (R2) reacting
with
b-Napthol to produce 2-(diarylalkyl)aminobenzothiazoles.
Entry Compound R1
R2
Time Temp Yield
(min) (ꢀC)
(%)
1
2
3
4
5
6
7
8
4aa
4ab
4ac
4ad
4ae
4af
4ag
4ah
4ai
1-Phenylethyl
H
40
110
120
110
110
110
110
110
110
110
120
110
120
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
110
120
110
110
110
110
120
110
110
110
110
110
110
110
115
86
92
89
88
90
88
91
93
92
92
94
92
93
91
94
95
92
90
91
88
94
94
93
90
94
94
94
90
92
88
90
87
91
89
90
91
90
88
89
90
88
90
2,4-Dichlorophenyl
3-Chlorophenyl
4-Fluorophenyl
4-Chloro 55
4-Chloro 45
4-Chloro 45
6-Chloro 45
6-Chloro 45
6-Chloro 50
Phenyl
4-Methylphenyl
4-Bromophenyl
4-(Dimethylamino)phenyl
4-Cyanophenyl
2-Bromo-5-fluorophenyl
Phenyl
2,4-Dichlorophenyl
3-Chlorophenyl
4-Methylphenyl
4-Bromophenyl
4-Fluorophenyl
6.1.1. Typical procedure for the synthesis of 2-(diarylalkyl)
aminobenzothiazole derivatives (4aae4bp)
To a 10 mL RB flask aldehyde (1.0 mmol), 2-aminobenzothiazole
(1.0 mmol) and b-naphthol (1.0 mmol) were added, mixed thor-
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
40
40
50
40
50
40
45
50
40
45
45
45
45
40
40
40
45
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
4aj
4ak
4al
oughly and heated in preheated oil bath at 110e120 ꢀC for appro-
priate time (Table 3). After completion of reaction as indicated by
TLC the reaction mixture was allowed to cool. The so formed solid is
powdered and washed with methanol or ethanol (3 ꢁ 8 mL in case
of halogenated compounds except fluorinated, 3 ꢁ 4 mL in case of
fluoro and methoxy derivatives) to obtain the corresponding pure
2-(diarylalkyl)aminobenzothiazole derivative. It is noteworthy to
handle fluoro and methoxy derivatives carefully which otherwise
may easily washed off in methanol/ethanol.
4am
4an
4ao
4ap
4aq
4ar
4as
4at
4au
4av
4aw
4ax
4ay
4az
4ba
4bb
4bc
4bd
4be
4bf
4bg
4bh
4bi
3-Phenoxyphenyl
2-Napthyl
4-Methoxyphenyl
3,4,5-Trimethoxyphenyl
3-Bromophenyl
3,4-Dichlorophenyl
3-Fluorophenyl
4-Isopropylphenyl
3,4-Dichlorophenyl
3,4-Dichlorophenyl
3,4-Dichlorophenyl
2,4-Dimethoxyphenyl
2-Chlorophenyl
4-Trifluoromethyphenyl
3,4-Dimethoxyphenyl
3,4-Difluorophenyl
4-Chlorophenyl
2,3-Dichlorophenyl
Phenyl
6.1.1.1. 1-(1-(benzo[d]thiazol-2-ylamino)-2-phenylpropyl)naph-
thalen-2-ol (4aa). The reaction forms two enantiomeric pairs as
expected. One of them being major, only that was obtained after
several successful washings with methanol while the minor
enantiomeric pair washed off with methanol. White solid;
4-Chloro 45
6-Chloro 43
4-Methyl 40
H
H
H
H
H
H
H
4-Chloro 40
4-Chloro 45
4-Chloro 45
4-Chloro 45
4-Chloro 45
4-Chloro 50
4-Chloro 50
50
50
40
45
40
40
50
mp ¼ 197e199 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d 10.12e9.95
(brs, 1H), 8.41e8.08 (brs, 1H), 7.59 (d, 2H, J ¼ 7.4 Hz), 7.51 (d, 1H,
J ¼ 8.7 Hz), 7.40e7.28 (m, 2H), 7.21e6.82 (m, 11H), 6.07e5.98 (brs,
1H), 4.00e3.88 (brs, 1H), 1.51 (d, 1H, J ¼ 6.8 Hz); 13C NMR (75 MHz,
DMSO-d6):
d 166.6, 153.2, 152.2, 143.9, 130.2, 128.6, 128.1, 127.9,
127.5, 127.2, 125.8, 125.6, 125.4, 121.9, 120.7, 120.6, 118.2, 117.7, 57.6,
42.7, 19.8; IR (KBr): nmax 3450, 3371, 3062, 2964, 1602, 1551, 1448,
1331, 1266, 741, 701 cmꢂ1; ESI-MS: m/z: 411(M þ H); HRMS calcd.
for C26H23ON2S: 411.15256, found: 411.15381.
4bj
4bk
4bl
4bm
4bn
4bo
4bp
4-Methylphenyl
4-Bromophenyl
3-Phenoxyphenyl
2-Napthyl
4-Methoxyphenyl
3,4,5-TrimethoxyPhenyl
4-(Dimethylamino)phenyl 4-Chloro 45
6.1.1.2. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(2,4-dichlorophenyl)
methyl)naphthalen-2-ol (4ab). Pink solid; mp ¼ 212e214 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d
10.04 (s, 1H), 9.22 (d, 1H, J ¼ 7.2 Hz),
4as and 4bn which were found active against ACE inhibition, were
further screened for their calcium channel blocker (CCB) property
by using rat aortic contraction method. Both the compounds were
found effective against calcium channel blocking property. From
the present study, we developed two new lead molecules 4as and
4bn with dual inhibitory property, which may be useful in treating
resistant hypertension. Treating resistant hypertension uses com-
bination of drugs which usually contains an ACE inhibitor (or)
angiotensin receptor blocker, CCBs and diuretics The compounds
4as and 4bn being CCB along with ACE inhibition could be utilized
as novel molecules to treat resistant hypertension.
8.17 (d, 1H, J ¼ 8.7 Hz), 7.79 (t, 2H, J ¼ 7.2 Hz), 7.67e7.58 (m, 2 h),
7.53 (d,1H, 2.1 Hz), 7.48e7.38 (m, 2H), 7.32e7.11 (m, 4H), 6.98 (t,1H,
7.9 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.0, 153.9, 148.8, 138.2,
133.3, 132.6, 132.1, 132.0, 131.2, 130.1, 128.7, 128.6, 128.3, 126.6,
125.6, 122.9, 122.5, 121.7, 121.7, 119.9, 118.4, 115.8, 52.5; IR (KBr):
nmax 3336, 2932, 1585, 1537, 1434, 1326, 1252, 882, 812, 735 cmꢂ1
;
ESI-MS: m/z: 485 (M þ H); HRMS calcd. for C24H16ON2Cl3S:
485.00434, found: 485.00457.
6.1.1.3. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(3-chlorophenyl)
methyl)naphthalen-2-ol (4ac). White solid; mp ¼ 221e223 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d 10.33e10.13 (brs, 1H), 8.17 (d, 1H,
6. Experimental protocols
6.1. Chemistry
Commercially available reagent grade chemicals and solvents
were used in all the reaction and purification processes. All the
reactions were monitored by TLC on E. Merck Kieselgel 60 F254, with
detection by UV light, charring with PMA charring solution or
exposure to I2 vapours. The 1H (300 and 500 MHz) and 13C NMR (75,
100 and 125 MHz) were recorded on Avance-300, Inova-400,
Avance-500 and Inova-500 in DMDO-d6 and CDCl3. Chemical shift
Scheme 1. Schematic representation of condensation of an Aldehyde,
2-Aminobenzothiazole derivative producing 2-(diarylalkyl)aminobenzothiazole.
b-Napthol and a

348
P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
Fig. 3. In vitro Angiotensin Converting Enzyme (ACE) inhibition of new Diarylalkylamine analogues 4aae4bp and standard drug, Lisinopril.
153.3, 148.6, 137.8, 132.0, 129.7, 128.5, 128.0, 127.9, 126.3, 125.5,
123.4,122.4,121.6, 119.7, 118.3, 118.1, 114.9, 114.6, 52.9; IR (KBr): nmax
3337, 2938, 1591, 1542, 1507,1436, 1271, 1157, 812, 764 cmꢂ1; ESI-
MS: m/z: 435 (M
435.07287, found: 435.07248.
þ
H); HRMS calcd. for C24H17ON2ClFS:
6.1.1.5. 1-((6-chlorobenzo[d]thiazol-2-ylamino)(phenyl)methyl)
naphthalen-2-ol (4ae). White solid; mp ¼ 202e204 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d
10.16 (s, 1H), 8.92 (d, 1H, J ¼ 7.6 Hz),
7.90e7.75 (m, 4H), 7.39e7.12 (m, 11H); 13C NMR (75 MHz, DMSO-
d6): 166.8, 153.1, 151.0, 142.2, 132.4, 132.0, 129.5, 128.5, 128.5,
d
128.0, 126.2, 125.9, 125.5, 124.6, 123.6, 122.3, 120.4, 118.9, 118.4,
118.3, 53.1; IR (KBr): nmax 3375, 3059, 3021, 1598, 1546, 1515, 1447,
1260, 806, 738 cmꢂ1; ESI-MS: m/z: 417 (M þ H); HRMS calcd. for
C
24H18ON2ClS: 417.08229, found: 417.08234.
Fig. 4. Dose Response Curves of new Diarylalkylamine derivatives 4as and 4bn for ACE
inhibition.
6.1.1.6. 1-((6-chlorobenzo[d]thiazol-2-ylamino)(p-tolyl)methyl)
naphthalen-2-ol (4af). White solid; mp ¼ 191e193 ꢀC; 1H NMR
(300 MHz, DMSO-d6): 10.18e10.10 (brs, 1H), 8.91 (d, 1H, J ¼ 7.6 Hz),
7.96e7.71 (m, 4H), 7.39e7.02 (m, 10H), 2.22 (s, 1H); 13C NMR
J ¼ 6.4 Hz), 8.02 (d, 1H, J ¼ 6.8 Hz), 7.86e7.78 (m, 2H), 7.64 (d, 1H,
J ¼ 9.1 Hz), 7.46e7.16 (m, 9H), 6.99 (t, 1H, J ¼ 7.9 Hz); 13C NMR
(75 MHz, DMSO-d6):
d 166.8, 153.4, 148.6, 144.7, 132.9, 132.1, 130.1,
(75 MHz, DMSO-d6):
d 166.8, 153.1, 151.0, 139.1, 137.1, 135.2, 132.4,
129.9, 128.6, 128.5, 126.6, 126.4, 125.7, 125.6, 124.8, 123.3, 122.6,
121.7, 119.9, 118.4, 118.0, 52.9; IR (KBr): nmax 3376, 3064, 1590, 1546,
1413, 1307, 1264, 817, 770 cmꢂ1; ESI-MS: m/z: 451 (M þ H); HRMS
calcd. for C24H17ON2Cl2S: 451.04332, found: 451.04224.
132.1, 129.4, 128.6, 128.5, 126.1, 125.9, 125.5, 124.6, 123.7, 122.3,
120.4, 118.9, 118.5, 118.3, 53.1, 20.5; IR (KBr): nmax 3364, 3054, 2915,
1599, 1547, 1513, 1447, 1260, 806, 765 cmꢂ1; ESI-MS: m/z: 431
(M þ H); HRMS calcd. for C25H20ON2ClS: 431.09794, found:
431.09840.
6.1.1.4. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(4-fluorophenyl)
methyl)naphthalen-2-ol (4ad). White solid; mp ¼ 205e207 ꢀC; 1H
6.1.1.7. 1-((6-chlorobenzo[d]thiazol-2-ylamino)(4-bromophenyl)
methyl)naphthalen-2-ol (4ag). White solid; mp ¼ 217e219 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d 10.25e10.11 (brs, 1H), 9.16 (d, 1H,
NMR (300 MHz, DMSO-d6):
d 10.25e10.16 (brs, 1H), 8.92 (d, 1H,
J ¼ 7.6 Hz), 7.97 (d, 1H, 7.6 Hz), 7.84e7.76 (m, 2H), 7.63 (d, 1H,
J ¼ 7.3 Hz), 7.87e7.76 (m, 4H), 7.46 (d, 2H, J ¼ 8.5 Hz), 7.41e7.33 (m,
J ¼ 7.7 Hz), 7.43e7.21 (m, 7H), 7.11 (t, 2H, J ¼ 8.7 Hz), 6.99 (t, 1H,
2H), 7.30e7.14 (m, 6H); 13C NMR (75 MHz, DMSO-d6):
d
166.8,
J ¼ 7.9 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.8, 162.4, 159.2,
153.2, 150.9, 141.9, 132.5, 132.0, 130.9, 129.8, 128.6, 128.3, 126.4,
125.5, 124.9, 123.4, 122.5, 120.5, 119.2, 119.0, 118.3, 118.0, 52.8; IR
(KBr): nmax 3560, 3366, 3054, 1598, 1545, 1447, 1258, 1070, 804, 767,
Fig. 6. Inhibitory effect of 4as and 4bn on aortic ring contraction induced by extra-
cellular Ca2þ influxes at different cumulative concentration (10ꢂ1 M, 10ꢂ2 M, 10ꢂ3 M,
10ꢂ5 M and 10ꢂ6 M).
Fig. 5. Dose-response curve of calcium-induced aortic ring contraction in presence and
absence of standard (Nifedipine) and test compounds (4as and 4bn).

P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
349
566 cmꢂ1
;
ESI-MS: m/z: 495 (M
þ
H); HRMS calcd. for
C24H17N2OSClBr: 494.9933, found: 494.9928.
6.1.1.8. 1-((benzo[d]thiazol-2-ylamino)(4-(dimethylamino)phenyl)
naphthalen-2-ol (4ah). White solid; mp ¼ 156e158 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d 10.22e10.04 (brs, 1H), 8.71 (d, 1H,
J ¼ 7.4 Hz), 7.93 (d, 1H, J ¼ 7.5 Hz), 7.77 (t, 2H, J ¼ 9.1 Hz), 7.64 (d, 1H,
J ¼ 7.4 Hz), 7.39e7.29 (m, 2H), 7.28e7.11 (m, 4H), 7.07 (d, 2H,
J ¼ 8.5 Hz), 6.99 (t, 1H, J ¼ 7.9 Hz), 6.63 (d, 2H, J ¼ 8.9 Hz), 2.80 (s,
6H); 13C NMR (75 MHz, DMSO-d6):
d 166.2, 153.0, 152.1, 149.0, 132.1,
130.5, 129.5, 129.1, 128.6, 128.4, 126.8, 125.9, 125.3, 122.2, 120.7,
118.9, 118.4, 117.9, 112.2, 53.1, 40.1; IR (KBr): nmax 3315, 2849, 1602,
1538, 1446, 1318, 1264, 1165, 810, 745 cmꢂ1; ESI-MS: m/z: 426
(M þ H); HRMS Calcd. for C26H24N3OS: 426.1640, found: 426.1639.
Fig. 7. Structures and IC50 values of compounds 4as and 4bn which are showing dual
activity as ACE inhibitors and CCBs.
6.1.1.9. 4-((benzo[d]thiazol-2-ylamino)(2-hydroxynaphthalen-1-yl)
methyl)benzonitrile (4ai). White solid; mp ¼ 213e215 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d 10.31e10.20 (brs, 1H), 8.85 (d, 1H,
J ¼ 7.0 Hz), 7.89e7.78 (m, 3H), 7.76e7.65 (m, 3H), 7.46e7.33 (m, 5H),
7.31e7.17 (m, 3H), 7.03 (t, 1H, J ¼ 7.4 Hz). 13C NMR (75 MHz, DMSO-
d6): d 166.1,153.2,151.9,148.8,132.0,130.8,130.0,128.6,128.5,127.0,
126.5, 125.4, 123.2, 122.5, 121.2, 120.9, 118.8, 118.3, 117.8, 108.9, 53.0;
IR (KBr): nmax 3379, 3056, 2226, 1573, 1541, 1437, 1329, 1270, 1026,
751 cmꢂ1; ESI-MS: m/z: 408 (M þ H); HRMS Calcd. for C25H18N3OS:
408.1170, found:408.1163.
6.1.1.10. 1-((benzo[d]thiazol-2-ylamino)(2-bromo-5-fluorophenyl)
methyl)naphthalen-2-ol (4aj). white solid; mp ¼ 198e200 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d
9.92 (brs, 1H), 8.90 (d, 1H, J ¼ 7.4 Hz),
8.05 (d,1H, J ¼ 8.7 Hz), 7.80 (t, 2H, J ¼ 9.3 Hz), 7.66 (d,1H, J ¼ 7.7 Hz),
7.61e7.54 (m, 1H), 7.39e7.34 (m, 3H), 7.28 (t, 1H, J ¼ 7.4 Hz), 7.20 (t,
1H, J ¼ 7.6 Hz), 7.14e6.97 (m, 4H). 13C NMR (75 MHz, DMSO-d6):
d
165.0, 162.6, 159.4, 153.7, 152.0, 144.2, 144.1, 134.1, 134.0, 132.8,
130.6, 129.9, 128.5, 128.1, 126.5, 125.3, 122.4, 122.3, 121.0, 120.8,
118.5, 118.2, 116.9, 116.7, 116.6, 115.6, 115.3, 54.7; IR (KBr): nmax 3383,
1598, 1543, 1512, 1453, 1431, 1265, 812, 752 cmꢂ1; ESI-MS: m/z: 479
(M þ H); HRMS calcd. for C24H17BrFN2OS: 479.0204, found:
479.0190.
6.1.1.11. 1-((benzo[d]thiazol-2-ylamino)(phenyl)methyl) naphthalen-
2-ol (4ak). White solid: mp ¼ 200e202 ꢀC; 1H NMR (300 MHz,
DMSO-d6):
d
10.17 (brs, 1H), 8.78 (d, 1H, J ¼ 7.6 Hz), 7.94e7.74 (m,
3H), 7.66 (d,1H, J ¼ 7.6 Hz), 7.40e7.13 (m,10H), 7.0 (t,1H, J ¼ 7.4 Hz);
13C NMR (75 MHz, DMSO-d6):
d
166.3, 153.2, 152.1, 142.5, 132.1,
130.8, 129.6, 128.6, 128.6, 128.1, 126.2, 126.0, 125.4, 123.8, 122.4,
121.0, 120.9, 118.7, 118.4, 118.1, 53.1; IR (KBr): nmax 3376, 3060, 1598,
1547, 1514, 1444, 1331, 1263, 744 cmꢂ1; ESI-MS: m/z: 383 (M þ H);
HRMS calcd. for C24H19N2OS: 383.1218, found: 383.1206.
6.1.1.12. 1-((benzo[d]thiazol-2-ylamino)(2,4-dichlorophenyl)methyl)
naphthalen-2-ol (4al). White solid: mp ¼ 190e192 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d
10.02e9.91 (brs,1H), 8.88 (d,1H, J ¼ 7.0 Hz),
8.02 (d, 1H, J ¼ 8.5 Hz), 7.79 (t, 2H, J ¼ 9.3 Hz), 7.70e7.63 (m, 2H),
7.49 (d, 1H, J ¼ 2.1 Hz), 7.46e7.35 (m, 3H), 7.27 (t, 1H, J ¼ 7.6 Hz),
7.23e7.12 (m, 3H), 7.01 (t, 1H, J ¼ 7.6 Hz); 13C NMR (75 MHz, DMSO-
d6): d 165.2, 153.8, 152.1, 139.0, 133.0, 132.7, 131.8, 131.1, 130.7, 130.0,
128.7, 128.3, 126.6, 126.5, 125.5, 122.6, 122.4, 121.1, 120.9, 118.5,
118.3, 115.9, 52.3; IR (KBr): nmax 3378, 3068, 1592, 1542, 1438, 1371,
1331, 1268, 751 cmꢂ1; ESI-MS: m/z: 451 (M þ H); HRMS calcd. for
C24H17N2OSCl2: 451.0438, found: 451.0451.
6.1.1.13. 1-((benzo[d]thiazol-2-ylamino)(
3-chlorophenyl)methyl)
naphthalen-2-ol (4am). White solid: mp ¼ 193e194 ꢀC; 1H NMR
Fig. 8. a) Best predicted binding mode of 4as at tACE binding site. b) Best predicted
binding mode of lisinopril at tACE binding site. c) Best predicted binding mode of 4bn
at tACE binding site.
(300 MHz, DMSO-d6):
d 10.19 (brs, 1H), 8.4 (brs, 1H), 7.96 (brs, 1H),
7.77e7.64 (m, 2H), 7.52 (d, 1H, J ¼ 7.7 Hz), 7.45e7.30 (m, 3H),

350
P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
7.30e7.09 (m, 7H), 6.99 (t,1H, J ¼ 7.5 Hz); 13C NMR (75 MHz, DMSO-
J ¼ 7.4 Hz), 7.94e7.84 (brs, 1H), 7.79 (t, 2H, J ¼ 8.7 Hz), 7.66 (d, 1H,
J ¼ 7.6 Hz), 7.42e7.12 (m, 9H), 7.0 (t, 1H, J ¼ 7.9 Hz), 6.83 (d, 1H,
d6): d 166.1, 153.1, 151.9, 145.3, 132.8, 131.9, 130.9, 130.7, 129.9, 129.8,
128.6, 128.5, 126.5, 126.1, 125.6, 125.4, 124.8, 122.5, 121.1, 120.9,
118.3, 118.2, 118.0, 52.6; IR (KBr): nmax 3360, 3062, 1596, 1573, 1548,
1515, 1444, 1332, 1268, 749 cmꢂ1; ESI-MS: m/z: 417 (M þ H); HRMS
calcd. for C24H18N2OSCl: 417.0828, found: 417.0809.
J ¼ 8.7 Hz), 3.68 (s, 3H); 13C NMR (75 MHz, DMSO-d6):
d 166.2,157.7,
153.0,152.1, 134.1,132.1, 130.6,129.4,128.6,128.5,127.2, 126.1, 125.3,
123.8, 122.3, 120.9, 120.8, 118.7, 118.4, 118.0, 113.5, 54.9, 52.8; IR
(KBr): nmax 3313, 3052, 1541, 1442, 1264, 814, 749 cmꢂ1; ESI-MS: m/
z: 413 (M þ H); HRMS calcd. for C25H21N2O2S: 413.1323, found:
413.1319.
6.1.1.14. 1-((benzo[d]thiazol-2-ylamino)(p-tolyl)methyl) naphthalen-
2-ol (4an). White solid: mp ¼ 180e182 ꢀC; (300 MHz, DMSO-d6):
d
10.18e10.11 (brs, 1H), 8.78 (d, 1H, J ¼ 7.6 Hz), 7.91e7.73 (m, 3H),
6.1.1.20. 1-((benzo[d]thiazol-2-ylamino)(3,4,5-trimethoxyphenyl)
7.66 (d, 1H, J ¼ 7.4 Hz), 7.39e6.96 (m, 11H), 2.22 (s, 3H); 13C NMR
methyl) naphthalen-2-ol (4at). White solid; mp ¼ 170e172 ꢀC; 1H
(75 MHz, DMSO-d6):
d 166.2, 153.1, 152.1, 139.4, 135.1, 132.1, 130.7,
NMR (300 MHz, DMSO-d6): d 10.42e10.30 (brs, 1H), 8.63e8.37 (brs,
129.4, 128.6, 128.5, 126.1, 125.9, 125.4, 123.9, 122.4, 120.9, 120.8,
118.7, 118.3, 118.0, 52.9, 20.5; IR (KBr): nmax 3307, 1535, 1441, 1317,
1261, 744 cmꢂ1; ESI-MS: m/z: 397 (M þ H); HRMS calcd. for
1H), 7.98e7.87 (brs, 1H), 7.75e7.63 (m, 2H), 7.52e7.31 (m, 3H),
7.28e7.15 (m, 3H), 7.11e6.94 (m, 2H), 6.58 (s, 2H), 3.70 (s, 3H), 3.66
(s, 6H); 13C NMR (75 MHz, DMSO-d6):
d 166.3, 153.3, 152.4, 137.0,
C
25H21N2OS: 397.1374, found: 397.1373.
136.1, 132.0, 129.9, 129.1, 128.6, 128.1, 125.8, 125.1, 123.0, 122.2,
120.8, 120.1, 119.1, 118.8, 117.9, 103.6, 95.6, 59.8, 55.4, 54.3; IR (KBr):
nmax 3317, 2923, 2833, 1590, 1538, 1441, 1315, 1248, 1171, 1030, 813,
745 cmꢂ1; ESI-MS: m/z: 473 (M þ H).
6.1.1.15. 1-((benzo[d]thiazol-2-ylamino)(4-bromophenyl)methyl)
naphthalen-2-ol (4ao). White solid; mp ¼ 202e204 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d 10.24e10.16 (brs, 1H), 8.82 (d, 1H,
J ¼ 7.0 Hz), 7.89e7.75 (m, 3H), 7.67 (d, 1H, J ¼ 7.6 Hz), 7.49e7.36 (m,
6.1.1.21. 1-((benzo[d]thiazol-2-ylamino)(3-bromophenyl)naph-
4H), 7.30e7.12 (m, 6H), 7.02 (t, 1H, J ¼ 7.6 Hz); 13C NMR (75 MHz,
thalen-2-ol (4au). White solid; mp ¼ 201e203 ꢀC; 1H NMR
DMSO-d6): d 166.1,153.1,151.9,142.1,131.9,130.9,130.8,129.7,128.5,
128.2, 126.3, 125.3, 123.5, 122.4, 121.0, 120.8, 119.1, 118.3, 118.1, 52.6;
(300 MHz, DMSO-d6):
d 10.27e10.20 (brs, 1H), 8.84 (d, 1H,
J ¼ 7.4 Hz), 7.92e7.77 (m, 3H), 7.68 (d, 1H, J ¼ 7.6 Hz), 7.45e7.15 (m,
IR (KBr): nmax 3373, 1627, 1541, 1442, 1332, 1267, 1206, 1070, 749,
11H), 7.02 (t, 1H, J ¼ 7.6 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.0,
571 cmꢂ1
;
ESI-MS: m/z: 461 (M
þ
H); HRMS calcd. for
153.1, 151.9, 145.5, 131.9, 130.7, 130.2, 129.8, 129.0, 128.5, 126.4,
125.4, 125.1, 123.3, 122.4, 121.4, 121.0, 120.8, 118.3, 118.1, 118.0, 52.6;
C
24H18N2OSBr: 461.0323, found: 461.0320.
IR (KBr): nmax 3377, 3058, 1543, 1511, 1435, 1327, 1268, 747 cmꢂ1
;
6.1.1.16. 1-((benzo[d]thiazol-2-ylamino)(4-fluorophenyl)methyl)
naphthalen-2-ol (4ap). White solid; mp ¼ 178e180 ꢀC; 1H NMR
MS-ESI: m/z: 461 (M þ H); HRMS calcd. for C24H18BrN2OS:
461.0323, found: 461.0312.
(300 MHz, DMSO-d6):
d
1.22e10.13 (brs, 1H), 8.81 (d, 1H, J ¼ 7.4 Hz),
7.93e7.76 (m, 3H), 7.67 (d, 1H, J ¼ 7.7 Hz), 7.42e7.32 (m, 2H),
6.1.1.22. 1-((benzo[d]thiazol-2-ylamino)(3,4-dichlorophenyl)naph-
7.31e7.15 (m, 6H), 7.93e6.95 (m, 3H); 13C NMR (75 MHz, DMSO-d6):
thalen-2-ol (4av). White solid; mp
¼
212e214 ꢀC; 1H NMR
d
166.1, 162.2, 159.0, 153.1, 151.9, 138.4, 131.9, 130.7, 129.5, 128.5,
(300 MHz, DMSO-d6): 10.28e10.24 (brs, 1H), 8.87 (d, 1H,
d
127.9, 127.8, 126.2, 125.3, 123.5, 122.3, 120.9, 120.8, 118.3, 118.0,
114.8, 114.5, 52.6; IR (KBr): nmax 3308, 1537, 1436, 1319, 1286, 1060,
810, 746 cmꢂ1; ESI-MS: m/z: 401 (M þ H).
J ¼ 7.2 Hz), 7.93e7.79 (m, 3H), 7.69 (d, 1H, J ¼ 7.6 Hz), 7.53 (d, 1H,
J ¼ 8.3 Hz), 7.47e7.37 (m, 3H), 7.32e7.15 (m, 5H), 7.03 (t, 1H
J ¼ 7.7 Hz). 13C NMR (75 MHz, DMSO-d6):
d 166.0, 153.2,151.8, 144.0,
131.9, 130.8, 130.6, 130.2, 130.0, 128.6, 128.4, 127.7, 126.6, 126.5,
125.4,123.1,122.5,121.1,120.9,118.3,118.2,117.6, 52.3; IR (KBr): nmax
3379, 1577, 1540, 11461, 1328, 1268, 1205, 1028, 816, 747 cmꢂ1; ESI-
MS: m/z: 451 (M þ H); HRMS calcd. for C24H17Cl2N2OS: 451.0438,
found: 451.0439.
6.1.1.17. 1-((benzo[d]thiazol-2-ylamino)(3-phenoxyphenyl)methyl)
naphthalen-2-ol (4aq). White solid; mp ¼ 171e173 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d
10.16 (s, 1H), 8.78 (d, 1H, J ¼ 7.4 Hz),
7.89e7.73 (m, 3H), 7.66 (d, 1H, J ¼ 7.0 Hz), 7.43e7.16 (m, 9H),
7.06e6.93 (m, 4H), 6.87 (d, 2H, J ¼ 7.6 Hz), 6.79 (dd, 1H, J1 ¼ 7.6 Hz,
J2 ¼ 2.1 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.1, 156.5, 156.0,
6.1.1.23. 1-((benzo[d]thiazol-2-ylamino)(3-fluorophenyl)naphthalen-
2-ol (4aw). White Solid; 1H NMR (300 MHz, DMSO-d6):
153.1, 152.0, 145.0, 132.0, 130.7, 129.7, 128.6, 128.5, 126.2, 125.4,
123.0, 122.4, 121.3, 121.0, 120.8, 118.3, 118.1, 117.9, 116.6, 116.3, 52.7;
IR (KBr): nmax 3314, 3052, 1541, 1511, 1451, 1267, 814, 749 cmꢂ1; ESI-
MS: m/z: 475 (M þ H); HRMS calcd. for C30H23N2O2S: 475.1480,
found: 475.1471.
d
10.26e10.19 (brs, 1H), 8.84 (d, 1H, J ¼ 7.4 Hz), 7.90e7.78 (m, 3H),
7.68 (d, 1H, J ¼ 7.7 Hz), 7.43e7.17 (m, 7H), 7.07e6.96 (m, 4H). 13
C
NMR (75 MHz, DMSO-d6):
d 166.1, 163.7, 160.5, 153.1, 151.9, 145.8,
145.8, 131.9, 130.7, 130.0, 129.9, 129.7, 128.5, 126.3, 125.4, 123.4,
122.4, 122.1, 121.0, 120.8, 118.3, 118.1, 113.0, 112.8, 112.5, 52.7; IR
6.1.1.18. 1-((benzo[d]thiazol-2-ylamino)(naphthalen-2-yl)methyl)
(KBr): nmax 3387,1587,1536,1482,1439,1329,1244,1053, 749 cmꢂ1
;
naphthalen-2-ol (4ar). White solid; mp ¼ 190e192 ꢀC; 1H NMR
ESI-MS: m/z: 401 (M þ H); HRMS calcd. for C24H18FN2OS: 401.1123,
(300 MHz, DMSO-d6):
d 10.21e10.16 (brs, 1H), 8.91 (d, 1H,
found: 401.1118.
J ¼ 7.4 Hz), 7.95 (d, 1H, J ¼ 7.9 Hz), 7.89e7.74 (m, 6H), 7.68 (d, 1H,
J ¼ 7.9 Hz), 7.53e7.40 (m, 3H), 7.38e7.15 (m, 6H), 7.02 (m, 1H); 13
C
NMR (75 MHz, DMSO-d6):
d
166.2, 153.1, 152.0, 140.1, 132.6, 132.1,
6.1.1.24. 1-((benzo[d]thiazol-2-ylamino)( 4-isopropylphenyl)naph-
131.7, 130.7, 129.6, 128.5, 128.4, 127.5, 127.3, 126.1, 126.0, 125.4,
125.3,124.9,123.8,123.6,122.3,120.9,120.8,118.5,118.3,118.0, 53.3;
IR (KBr): nmax 3313, 3052, 1541, 1442, 1264, 814, 749 cmꢂ1; ESI-MS:
m/z:433 (M þ H); HRMS Calcd. for C28H21N2OS: 433.1374, found:
433.1387.
thalen-2-ol (4ax). White solid; mp
¼
191e193 ꢀC; 1H NMR
(300 MHz, DMSO-d6): 10.17e10.09 (brs, 1H), 8.78 (d, 1 h,
d
J ¼ 7.6 Hz), 7.98e7.87 (brs, 1H), 7.79 (t, 2H, J ¼ 7.8 Hz), 7.66 (d, 1H,
J ¼ 7.6 Hz), 7.4e7.32 (m, 2H), 7.30e7.10 (m, 8H), 7.00 (t, 1H,
J ¼ 8.1 Hz), 2.89e2.74 (m, 1H), 1.14 (dd, 6H, J1 ¼ 7.0 Hz, J2 ¼ 1.5 Hz).
13C NMR (75 MHz, DMSO-d6):
d 166.2, 153.0, 152.1, 146.1, 139.6,
6.1.1.19. 1-((benzo[d]thiazol-2-ylamino)(4-methoxyphenyl)methyl)
132.1, 130.6, 129.3, 128.5, 128.4, 126.1, 126.0, 125.9, 125.3, 123.7,
122.3, 120.8, 120.8, 118.7, 118.4, 118.0, 53.0, 32.9, 23.8, 23.7; IR (KBr):
nmax 3314, 3055, 2957, 1540, 1450,1268,1060, 746 cmꢂ1; ESI-MS: m/
naphthalen-2-ol (4as). White solid; mp ¼ 190e192 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d 10.19e10.11 (brs, 1H), 8.79 (d, 1H,

P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
351
z: 425 (M þ H); HRMS calcd. for C27H25N2OS: 425.1687, found:
J ¼ 7.6 Hz), 7.91e7.72 (m, 4H), 7.44e7.16 (m, 7H), 7.15e7.02 (m, 4H);
13C NMR (75 MHz, DMSO-d6):
166.1, 153.2, 151.9, 147.7, 132.0,
425.1704.
d
130.8, 129.9, 128.6, 128.5, 127.4, 127.0, 126.7, 126.6, 126.5, 126.1,
125.4, 124.99, 124.96, 123.3, 122.5, 121.1, 120.9, 118.3, 118.2, 118.0,
52.9; IR (KBr): nmax 3380, 3059, 2867, 2599, 1574, 1541,1326, 1267,
1158, 1125, 1068, 749 cmꢂ1; ESI-MS: m/z: 451 (M þ H); HRMS calcd.
for C25H18ON2F3S: 451.10865, found: 451.10976.
6.1.1.25. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(3,4-dichlorophenyl)
methyl)naphthalen-2-ol (4ay). White solid; mp ¼ 208e210 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d
10.24 (s, 1H), 9.20 (d, 1H, J ¼ 7.7 Hz),
8.07e7.97 (brs, 1H), 7.86e7.79 (m, 2H), 7.66 (d, 1H, J ¼ 7.9 Hz), 7.55
(d, 1H, J ¼ 8.3 Hz), 7.48e7.40 (m, 2H), 7.36e7.14 (m, 5H), 7.0 (t, 1H,
7.9 Hz); 13C NMR (75 MHz, DMSO-d6):
d
166.6, 153.4, 148.5, 143.4,
6.1.1.31. 1-((benzo[d]thiazol-2-ylamino)(3,4-dimethoxyphenyl)
132.1, 132.0, 130.9, 130.3, 130.0, 128.8, 128.6, 128.4, 127.8, 126.7,
126.5, 125.6, 123.1, 122.6, 121.7, 119.8, 118.3, 117.6, 52.5; IR (KBr):
nmax 3352, 2935, 1590, 1544, 1254, 817, 738 cmꢂ1; ESI-MS: m/z: 485
(M þ H); HRMS calcd. for C24H16N2OSCl3: 485.0048, found:
485.0032.
methyl)naphthalen-2-ol (4be). White solid; mp ¼ 176e178 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d 10.21e10.11 (brs, 1H), 8.78 (d, 1H,
J ¼ 7.6 Hz), 7.95 (d, 1H, J ¼ 7.4 Hz), 7.77 (t, 2H, J ¼ 8.9 Hz), 7.64 (d, 1H,
J ¼ 7.4 Hz), 7.41e7.31 (m, 2H), 7.28e7.14 (m, 4H), 7.03e6.92 (m,2H),
6.83 (d, 1H, J ¼ 8.5 Hz), 6.73 (d, 1H, J ¼ 7.6 Hz), 3.68 (s, 3H), 3.60 (s,
3H); 13C NMR (75 MHz, DMSO-d6):
d 166.3, 153.1, 152.1, 148.5, 147.5,
6.1.1.26. 1-((6-chlorobenzo[d]thiazol-2-ylamino)(3,4-dichlorophenyl)
134.5, 132.2, 130.6, 129.4, 128.6, 128.5, 126.1, 125.5, 123.8, 122.4,
121.0, 120.9, 118.7, 118.5, 118.0, 111.7, 110.6, 55.5, 53.3; IR (KBr): nmax
3368, 2930, 2834, 1573, 1543, 1510, 1330, 1271, 752 cmꢂ1; ESI-MS:
m/z: 443 (M þ H); HRMS calcd. for C26H23O3N2S: 443.14239,
found: 443.14472.
methyl)naphthalen-2-ol (4az). White solid; mp ¼ 215e217 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d 10.28e10.23 (brs, 1H), 8.98 (d, 1H,
J ¼ 7.4 Hz), 7.9307.77 (m, 4H), 7.53 (d, 1H, J ¼ 8.5 Hz), 7.47e7.14 (m,
8H); 13C NMR (75 MHz, DMSO-d6):
d
166.6, 153.2, 150.8, 143.8,
132.6, 131.9, 130.7, 130.3, 130.0, 128.7, 128.6, 128.4, 127.7, 126.6,
126.5, 125.5, 124.9, 123.0, 122.6, 120.6, 119.1, 118.3, 117.5, 52.4; IR
(KBr): nmax 3360, 2865, 1598, 1545, 1446, 1254, 813, 740 cmꢂ1; ESI-
MS: m/z: 485 (M þ H); HRMS calcd. for C24H16N2OSCl3: 485.0048,
found: 485.0032.
6.1.1.32. 1-((benzo[d]thiazol-2-ylamino)(3,4-difluorophenyl)methyl)
naphthalen-2-ol (4bf). White solid; mp ¼ 177e179 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d 10.38e10.13 (brs, 1H), 8.84 (d, 1H,
J ¼ 7.0 Hz), 7.94e7.78 (m, 3H), 6.8 (d, 1H, J ¼ 7.6 Hz), 7.46e7.16 (m,
8H), 7.02 (t, 2H, J ¼ 7.2 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.0,
6.1.1.27. 1-((4-methylbenzo[d]thiazol-2-ylamino)(3,4-
153.1, 151.8, 140.4, 131.9, 130.7, 129.8, 128.5, 128.5, 126.4, 125.3,
123.2, 122.6, 122.4, 121.0, 120.8, 118.3, 118.2, 117.8, 117.1, 116.9, 114.9,
114.7, 52.4; IR (KBr): nmax 3390, 3052, 1598, 1541, 1511, 1431, 1274,
754, 467 cmꢂ1; ESI-MS: m/z: 419 (M þ H); HRMS calcd. for
dichlorophenyl)methyl)naphthalen-2-ol
(4ba). White
solid;
mp ¼ 222e224 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d
10.26e10.16
(brs, 1H), 8.98 (d, 1H, J ¼ 7.9 Hz), 8.17e8.02 (brs, 1H), 7.86e7.77 (m,
2H), 7.58e7.40 (m, 4H), 7.03 (d, 1H, J ¼ 7.2 HZ), 6.91 (t, 1H,
C24H17ON2F2S: 419.10242, found: 419.10338.
J ¼ 7.7 Hz), 2.41 (s, 3H); 13C NMR (75 MHz, DMSO-d6):
d 165.1, 153.3,
150.6, 143.7, 132.1, 130.6, 130.2, 130.1, 129.8, 128.7, 128.5, 128.3,
127.9, 127.3, 126.6, 126.5, 126.1, 123.1, 122.5, 121.0, 118.3, 118.3, 118.1,
52.4, 17.9; IR (KBr): nmax 3340, 2923, 1585, 1545, 1516, 1252, 816,
6.1.1.33. 1-((benzo[d]thiazol-2-ylamino)(4-chlorophenyl)methyl)
naphthalen-2-ol (4bg). White solid; mp ¼ 214e216 ꢀC; 1H NMR
(300 MHz, DMSO-d6):
d 10.22e10.18 (brs, 1H), 8.82 (d, 1H,
739 cmꢂ1
;
ESI-MS: m/z: 465 (M
þ
H); HRMS calcd. for
J ¼ 7.4 Hz), 7.87e7.66 (m, 3H), 7.68 (d, 1H, J ¼ 7.4 Hz), 7.42e7.16 (m,
C
25H19Cl2N2OS: 465.0595, found: 465.0575.
10H), 7.02 (t, 3H, J ¼ 7.7 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.1,
153.1, 152.0, 141.6, 132.0, 130.8, 130.6, 129.7, 128.5, 128.0, 127.9,
126.3, 125.4, 123.5, 122.4, 121.0, 120.8, 118.3, 118.2, 52.6; IR (KBr):
nmax 3375, 3056, 1574, 1541, 1514, 1436, 1330, 1269, 749 cmꢂ1; ESI-
MS: m/z: 417 (M þ H); HRMS calcd. for C24H18ON2ClS: 417.08229,
found: 417.08458.
6.1.1.28. 1-((benzo[d]thiazol-2-ylamino)(2,4-dimethoxyphenyl)
methyl)naphthalen-2-ol (4bb). White solid; mp ¼ 174e176 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d 10.22e10.08 (brs, 1H), 8.81 (d, 1H,
J ¼ 7.2 Hz), 7.95 (d, 1H, J ¼ 8.5 Hz), 7.78 (t, 2H, J ¼ 8.9 Hz), 7.65 (d,1H,
J ¼ 7.7 Hz), 7.41e7.31 (m, 2H), 7.29e7.15 (m, 4H), 7.04e6.91 (m, 4H),
6.84 (d, 1H, J ¼ 8.5 Hz), 6.73 (d, 1H, 8.7 Hz), 3.68 (s, 3H), 3.60 (s, 3H);
6.1.1.34. 1-((benzo[d]thiazol-2-ylamino)(2,3-dichlorophenyl)methyl)
13C NMR (75 MHz, DMSO-d6):
d
166.1, 153.0, 152.0, 148.4, 147.4,
naphthalen-2-ol (4bh). White solid; mp ¼ 200e202 ꢀC; 1H NMR
134.5, 132.1, 130.5, 129.3, 128.5, 128.4, 126.0, 125.3, 123.8, 122.3,
120.8, 118.6, 118.4, 117.9, 111.6, 110.6, 55.4, 53.1; IR (KBr): nmax 3368,
2930, 2834, 1573, 1542, 1509, 1271, 752 cmꢂ1; ESI-MS: m/z: 443
(300 MHz, DMSO-d6): d 10.03e9.92 (brs, 1H), 8.93 (d, 1H,
J ¼ 6.6 Hz), 8.01 (d, 1H, J ¼ 8.5 Hz), 7.80 (t, 2H, 8.9 Hz), 7.66 (d, 2H,
J ¼ 7.7 Hz), 7.53 (d, 1H, J ¼ 7.7 Hz), 7.46e7.11 (m, 7H), 7.01 (t, 1H,
(M
443.14463.
þ
H); HRMS calcd. for
C
26H23O3N2S: 443.14239, found:
J ¼ 7.4 Hz); 13C NMR (75 MHz, DMSO-d6):
d 165.1, 153.8, 152.1, 142.6,
132.7, 131.7, 130.7, 130.0, 128.6, 128.6, 128.3, 127.2, 126.5, 125.4,
122.6, 122.4, 121.0, 120.8, 118.5, 118.3, 115.8, 53.3; IR (KBr): nmax
3350, 3014, 1597, 1538,1512, 1448, 1270, 1154, 810, 748, 586,
6.1.1.29. 1-((benzo[d]thiazol-2-ylamino)(2-chlorophenyl)methyl)
naphthalen-2-ol (4bc). White solid; mp ¼ 197e199 ꢀC; 1H NMR
482 cmꢂ1
;
ESI-MS: m/z: 451 (M
þ
H); HRMS calcd. for
(300 MHz, DMSO-d6):
d
9.99e9.93 (brs, 1H), 8.86 (d, 1H, J ¼ 7.4 Hz),
C24H17Cl2N2OS: 451.04332, found: 451.04577.
8.05 (d,1H, J ¼ 8.7 Hz), 7.78 (t, 2H, J ¼ 9.3 Hz), 7.64 (d, 2H, J ¼ 7.7 Hz),
7.47e7.12 (m, 10H), 6.99 (t, 1H, J ¼ 7.9 Hz); 13C NMR (125 MHz,
6.1.1.35. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(phenyl)methyl)
DMSO-d6):
d
165.3, 153.7, 152.2, 139.4, 132.7, 132.4, 130.6, 129.7,
naphthalen-2-ol (4bi). White solid; mp ¼ 214e216 ꢀC; 1H NMR
129.4, 128.6, 128.3, 126.4, 126.3, 125.4, 122.9, 122.3, 120.9, 120.8,
118.5, 118.2, 116.5, 52.7; IR (KBr): nmax 3456, 3381, 3066, 1571, 1528,
1438, 1319, 1270, 1040, 750 cmꢂ1; ESI-MS: m/z: 417 (M þ H); HRMS
calcd. for C24H18ON2ClS: 417.08229, found: 417.08426.
(300 MHz, DMSO-d6): d 10.19e10.11 (brs, 1H), 9.18 (d, 1H,
J ¼ 7.4 Hz), 8.02e7.89 (brs, 1H), 7.84e7.76 (m, 2H), 7.64 (d, 1H,
J ¼ 7.7 Hz), 7.42e7.15 (m, 10H), 6.98 (t, 1H, J ¼ 7.7 Hz); 13C NMR
(75 MHz, DMSO-d6):
d 166.9, 153.3, 148.7, 141.8, 132.1, 132.0, 129.6,
128.5, 128.4, 128.1, 126.3, 126.2, 126.0, 125.5, 123.7, 122.4, 121.5,
119.7, 118.3, 53.3; IR (KBr): nmax 3350, 3314, 3059, 2937, 1587, 1537,
1416, 1325, 1253, 815, 747, 697 cmꢂ1; ESI-MS: m/z: 417 (M þ H);
HRMS calcd. for C24H18N2ClOS: 417.08229, found: 417.08168.
6.1.1.30. 1-((benzo[d]thiazol-2-ylamino)(4-(trifluoromethyl)phenyl)
methyl)naphthalen-2-ol (4bd). White solid; mp ¼ 203e205 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d 10.20e10.13 (brs, 1H), 8.90 (d, 1H,

352
P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
6.1.1.36. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(p-tolyl)methyl)
(m, 4H), 6.97 (t, 1H, J ¼ 7.7 Hz), 6.66 (s, 2H), 3.62 (s, 6H), 3.61 (s, 3H);
13C NMR (75 MHz, DMSO-d6):
166.9, 153.4, 152.6, 148.7, 137.2,
naphthalen-2-ol (4bj). White solid; mp ¼ 219e221 ꢀC; 1H NMR
d
(300 MHz, DMSO-d6):
d
10.18e10.07 (brs, 1H), 9.23e9.11 (brs, 1H),
136.3, 132.2, 131.9, 129.6, 128.5, 126.3, 125.6, 123.6, 122.4, 121.5,
121.5, 119.7, 118.4, 118.3, 104.1, 59.9, 55.8, 54.0; IR (KBr): nmax 3366,
2932, 1593, 1542, 1509, 1414, 1328, 1131, 818 cmꢂ1; ESI-MS: m/z:
507 (M þ H); HRMS calcd. for C27H24O4N2ClS: 507.11398, found:
507.11452.
8.04e7.88 (brs, 1H), 7.83e7.74 (m, 2H), 7.63 (d, 1H, J ¼ 7.0 Hz),
7.41e7.31 (m, H), 7.30e7.20 (m, 4H), 7.17e7.05 (m, 4H), 6.98 (t, 1H,
J ¼ 7.9 Hz), 2.24 (s, 3H); 13C NMR (75 MHz, DMSO-d6):
d 167.1, 153.4,
148.8, 138.7, 135.5, 132.2, 132.0, 129.6, 128.8, 128.6, 128.5, 126.3,
126.0, 125.7, 123.8, 122.5, 121.6, 121.6, 119.8, 118.5, 118.4, 53.4, 20.6;
IR (KBr): nmax 3310, 2927, 1586, 1533, 1417, 1320, 1271, 1051, 883,
812, 679 cmꢂ1; ESI-MS: m/z: 431 (M þ H); HRMS calcd. for
6.1.1.42. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(4-(dimethylamino)
phenyl)methyl) naphthalen-2-ol (4bp). Pale yellow solid;
C
25H20ClN2OS: 431.09794, found: 431.09731.
mp ¼ 205e207 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d 10.20e10.03
(brs, 1H), 9.23e9.07 (brs, 1H), 8.07e7.93 (brs, 1H), 7.77 (t, 2H,
J ¼ 8.9 Hz), 7.62 (d, 1H, J ¼ 7.9 Hz), 7.35 (t, 1H, J ¼ 7.9 Hz), 7.25 (t, 3H,
J ¼ 7.6 Hz), 7.18e7.03 (m, 3H), 6.96 (t, 1H, J ¼ 7.7 Hz), 6.64 (d, 2H,
6.1.1.37. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(4-bromophenyl)
methyl)naphthalen-2-ol (4bk). White solid; mp ¼ 223e225 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d
10.22e10.16 (brs, 1H), 9.18 (d, 1H,
J ¼ 8.9 Hz), 2.82 (S, 6H); 13C NMR (75 MHz, DMSO-d6):
d 167.0,
J ¼ 7.6 Hz), 8.02e7.88 (brs, 1H), 7.84e7.77 (m, 2H), 7.65 (d, 1H,
J ¼ 7.7 Hz), 7.48 (d, 2H, J ¼ 8.5 Hz), 7.39 (t, 1H, J ¼ 7.7 Hz), 7.32e7.15
(m, 6H), 6.99 (t, 1H, J ¼ 7.9 Hz); 13C NMR (75 MHz, DMSO-d6):
153.3, 149.1, 148.9, 132.2, 131.8, 129.3, 128.7, 128.6, 128.4, 126.9,
126.0, 125.5, 124.0, 122.3, 121.4, 121.4, 119.7, 118.6, 118.4, 112.2, 53.5,
40.1; IR (KBr): nmax 3353, 3321, 2851, 1587, 1533, 1433, 1269,
811 cmꢂ1; HRMS calcd. for C26H22N3ONaSCl: 482.1069, found:
482.1089.
d
166.8, 153.3, 148.7, 141.5, 132.0, 130.9, 129.8, 128.5, 128.3, 126.4,
125.5, 123.5, 122.5, 121.6, 119.7, 119.3, 118.3, 117.9, 52.9; IR (KBr):
nmax 3343, 3297, 1711, 1586, 1528, 1416, 881, 814, 744, 498 cmꢂ1
;
ESI-MS: m/z: (M þ H); HRMS calcd. for C24H17BrClN2OS: 494.9933,
6.2. In vitro angiotensin converting enzyme inhibition assay
found: 494.9948.
ACE inhibition assay was performed using the method described
by Jimsheena et al. [27,28]. Rabbit lung acetone powder (Sigma
Aldrich, USA) was used as a source of ACE enzyme. 1 g of rabbit lung
acetone powder was suspended in 10 mL of 0.05 M sodium borate
buffer pH 8.2 containing 0.3 M NaCl and 0.5% Triton X-100 at 4 ꢀC
for 24 h followed by centrifugation at 15,000 rpm for 60 min at 4 ꢀC.
Supernatant was used as a source of ACE enzyme for this assay. ACE
inhibition activity was assayed by monitoring the release of hip-
puric acid (HA) from the hydrolysis of the substrate hippuryl-
6.1.1.38. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(3-phenoxyphenyl)
methyl)naphthalen-2-ol (4bl). White solid; mp ¼ 208e210 ꢀC; 1H
NMR (300 MHz, DMSO-d6): d 10.28e10.14 (brs, 1H), 9.23e9.12 (brs,
1H), 8.02e7.88 (brs, 1H), 7.84e7.78 (m, 2H),7.64 (d, 1H, J ¼ 7.2 Hz),
7.46e7.28 (m, 9H), 7.07e6.95 (m, 4H), 6.90 (d, 2H, J ¼ 7.7 Hz), 6.82
(d, 1H, J ¼ 7.7 Hz); 13C NMR (75 MHz, DMSO-d6):
d 166.8, 156.6,
156.1, 153.4, 148.7, 144.4, 132.1, 129.7, 128.5, 126.3, 125.5, 123.7,
123.0, 122.4, 121.7, 121.6, 121.4, 119.7, 118.3, 118.1, 117.9, 116.8, 116.5,
53.1; IR (KBr): nmax 3332, 2938, 1588, 1545, 1485, 1249, 1165, 884,
744, 491 cmꢂ1; ESI-MS: m/z: 509 (M þ H); HRMS calcd. for
histidyl-leucine (HHL) (SigmaeAldrich, USA). 7
solution was preincubated with test and standard drug solution at
M concentration for 10 min at 37 ꢀC. Final volume was adjusted
ml of ACE enzyme
C
30H22ClN2O2S: 509.10850, found: 509.10754.
1 m
using 0.05 M sodium borate buffer (pH 8.2) containing 0.3 M NaCl
to get equal concentration. The enzyme reaction was then initiated
by adding 50 ml of 5 mM substrate (HHL) followed by incubation at
6.1.1.39. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(naphthalen-2-yl)
methyl)naphthalen-2-ol (4bm). White solid; mp ¼ 236e238 ꢀC; 1H
NMR (300 MHz, DMSO-d6):
d
10.25e10.14 (brs, 1H), 9.36e9.27 (brs,
37 ꢀC for 30 min. The reaction was then arrested by the addition of
0.1 mL of 1 M HCl. Hippuric acid produced in the reaction was then
reacted with0.2 mL of pyridine (SD Fine chemical, India) and 0.1 mL
of Benzenesulfonyl chloride(BSC) (SD Fine chemical, India)to
develop yellow colour. The solution was mixed by inversion for
1 min and cooled on ice. The yellow colour developed was
measured at 410 nm. The decreased concentration of HA in the test
reaction compared with the control. ACE inhibition was expressed
as percentage inhibition and calculated from the equation: Inhibi-
tion% ¼ 100 ꢂ [T/C] ꢁ 100, where T ¼ absorbance of test reaction
and C ¼ absorbance of control reaction. The therapeutic drug Lisi-
nopril was used as reference ACE inhibitor. The inhibitory con-
centration 50% (IC50) was calculated by nonlinear regression. The
doseeresponse curve was obtained by plotting the percentage in-
hibition versus the concentrations.
1H), 8.13e7.96 (brs, 1H), 7.88e7.76 (m, 6H), 7.66 (d, 1H, J ¼ 7.4 Hz),
7.55e7.21 (m, 8H), 6.99 (t, 1H, J ¼ 7.7 Hz); 13C NMR (75 MHz, DMSO-
d6): d 167.0, 153.5, 148.8, 139.6, 132.7, 132.3, 132.1, 131.8, 129.7, 128.6,
128.5, 127.7, 127.6, 127.3, 126.3, 125.6, 125.5, 125.0, 124.0, 123.7,
122.4,121.7,121.6, 119.8,118.5,118.4, 53.7; IR (KBr): nmax 3320, 3052,
2930, 1585, 1533, 1416, 1268, 816, 660, 478 cmꢂ1; ESI-MS: m/z: 467
(M þ H); HRMS calcd. for C28H19N2ONaSCl: 489.0804, found:
489.0822.
6.1.1.40. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(4-methoxyphenyl)
methyl)naphthalen-2-ol (4bn). White solid; mp ¼ 211e213 ꢀC; 1H
NMR (300 MHz, DMSO-d6): d 10.22e10.08 (brs, 1H), 9.24e9.10 (brs,
1H), 8.05e7.93 (brs, 1H), 7.79 (m, 2H), 7.63 (d, 1H, J ¼ 7.742 Hz),
7.42e7.13 (m, 7H), 6.98 (t, 1H, J ¼ 7.9 Hz), 6.85 (d, 2H, J ¼ 8.7 Hz),
3.69 (s, 3H); 13C NMR (75 MHz, DMSO-d6):
d 166.9, 157.8, 153.3,
148.8, 133.4, 132.1, 131.9, 129.5, 128.6, 128.4, 127.3, 126.1, 125.5,
123.8, 122.4, 121.5, 121.5, 119.7, 118.4, 113.5, 54.9, 53.2; IR (KBr): nmax
3315, 3066, 2925, 2830, 1583, 1510, 1433, 1319, 1250, 1173, 1032,
821, 668, 588 cmꢂ1; ESI-MS: m/z: 447 (M þ H); HRMS calcd. for
6.3. Ex-vivo model for measuring aortic contraction
All the experiments were approved by the Institutional Animal
Ethics Committee (IAEC, IICT, Hyderabad). Experiments were per-
formed on male SpragueeDawley rats that were 8e10 weeks old
and weighed 180e200 g. Aortic contraction was determined by
measuring isometric tension from a rat aortic ring [29]. The rats
were sacrificed by cervical dislocation and under xylazine and ke-
tamine anaesthesia. The thoracic aorta (from the arch of aorta to the
diaphragm) was quickly excised and placed in 37 ꢀC oxygenated
(95% O2 e 5% CO2) calcium free Krebs e Hensleit buffer (KHB). Aorta
C
25H20O2N2ClS: 447.09285, found: 447.09345.
6.1.1.41. 1-((4-chlorobenzo[d]thiazol-2-ylamino)(3,4,5-
trimethoxyphenyl)methyl) naphthalen-2-ol (4bo). White solid;
mp ¼ 215e217 ꢀC; 1H NMR (300 MHz, DMSO-d6):
d 10.27e10.10
(brs, 1H), 9.32e9.17 (brs, 1H), 8.18e8.04 (brs, 1H), 7.79 (t, 2H,
J ¼ 8.3 Hz), 7.63 (d, 1H, J ¼ 7.9 Hz), 7.42 (t, 1H, J ¼ 7.5 Hz), 7.31e7.13

P.K. Kalavagunta et al. / European Journal of Medicinal Chemistry 83 (2014) 344e354
353
was cut into 5-mm segments and was cleared of adhering fat and
Appendix A. Supplementary data
adventitial tissues. Due care was taken to keep the endothelium
intact. The composition of calcium free KHB (mM) was NaCl : 118,
KCl : 4.7, MgSO4 : 1.2, KH2PO4 : 1.2, NaHCO3 : 25 and Glucose : 5.5
(pH 7.4). Each ring was suspended by stainless steel hooks in a
water-jacketed organ bath, filled with 25 mL of oxygenated KHB
maintained at 37 ꢀC. Response from isometric tension was
measured using an isometric force transducer (AD Instruments,
Australia). A resting tension of 1 g was applied to aortic rings, which
were then allowed to equilibrate for about 30 min. Once the tissue
was stabilized, contraction was evoked by adding phenylephrine
1 mM to the organ bath during which the buffer was changed every
15 min. After the initial contraction by epinephrine, concen-
trationeresponse curve was measured with the cumulative con-
centration of calcium (10ꢂ3 to 10ꢂ1 M). Similarly, the same
cumulative concentrationeresponse curve with calcium was pre-
pared in presence of 100 mM test drugs (4as and 4bn) and standard
drug (Nifedipine).
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.ejmech.2014.06.035.
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Acknowledgements
Authors are thankful to Dr. M. Lakshmikantam, Director, Dr. V. J.
Rao, Head, C P C Division, IICT, Hyderabad for their continuous
support, encouragement and assistance. S.K.B is thankful to CSIR
(SMiLE project) and Department of Biotechnology (DBT) for
providing Ramalingaswami Fellowship. A. J, K. P. K. (SRF) & P.K.B.
(SRF) were thankful to CSIR for financial assistance. We also thank
Rene Thomsen, Molegro, Denmark for providing evaluation copy of
Molegro Virtual Docker Software.

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