Tert-Butyl 1,5-bis(4-(benzo[d]isothiazol-3-yl)piperazin-1-yl)-1,5- dioxopentan-2-ylcarbamate urea/thiourea derivatives as potent H +/K+-ATPase inhibitors

Article abstract of DOI:10.1016/j.bmcl.2013.05.043

Amino acids are known to possess variable efficacy against ulceration. Considering the good antiulcer activity of amino acids, a series of urea/thiourea derivatives of glutamic acid conjugated benzisothiazole analogue 3a-u with various substituents on aryl ring were synthesized, spectroscopically characterized and evaluated for in vitro H⁺/K⁺-ATPase inhibition. Majority of the compounds possessed potency compared to that of omeprazole, a reference drug. In particular, methoxy derivatives 3p-u were the most active compounds possessing a significant 15-fold increase for para substituent thus, contributing positively to gastric H⁺/K ⁺-ATPase inhibition.

Full text of DOI:10.1016/j.bmcl.2013.05.043

Bioorganic & Medicinal Chemistry Letters 23 (2013) 4096–4098
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
tert-Butyl 1,5-bis(4-(benzo[d]isothiazol-3-yl)
piperazin-1-yl)-1,5-dioxopentan-2-ylcarbamate urea/thiourea
derivatives as potent H+/K+-ATPase inhibitors
Anamika Sharma a, R. Suhas b, K. V. Chandana c, Syeda Hajira Banu c, D. Channe Gowda a,
⇑
a Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, Karnataka, India
b Postgraduate Department of Chemistry, JSS College of Arts, Commerce and Science, Ooty Road, Mysore 570 025, Karnataka, India
c Postgraduate Department of Biochemistry, JSS College of Arts, Commerce and Science, Ooty Road, Mysore 570 025, Karnataka, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Amino acids are known to possess variable efficacy against ulceration. Considering the good antiulcer
activity of amino acids, a series of urea/thiourea derivatives of glutamic acid conjugated benzisothiazole
analogue 3a–u with various substituents on aryl ring were synthesized, spectroscopically characterized
and evaluated for in vitro H+/K+-ATPase inhibition. Majority of the compounds possessed potency com-
pared to that of omeprazole, a reference drug. In particular, methoxy derivatives 3p–u were the most
active compounds possessing a significant 15-fold increase for para substituent thus, contributing posi-
tively to gastric H+/K+-ATPase inhibition.
Received 13 April 2013
Revised 13 May 2013
Accepted 14 May 2013
Available online 24 May 2013
Keywords:
Benzisothiazole
Urea
Ó 2013 Elsevier Ltd. All rights reserved.
Thiourea
H+/K+-ATPase activity
Gastric and duodenal ulcers are commonly occurring diseases.
Ulcers are believed to result from an imbalance between the
aggressive (acid, pepsin) and defensive forces (bicarbonate, mu-
cous) in the stomach and duodenum. Reduction of acid secretion,
especially by antagonism of the H2 receptor, has proven to be a
useful means for promoting the healing of ulcers, particularly those
of the duodenal mucosa.1 Recently, agents have been identified
that completely suppress acid secretion by inhibition of the gastric
proton pump H+/K+-ATPase. Such inhibition leads to a profound
and prolonged achlorhydria, which results in ulcer healing rates
substantially more rapid than those achievable by H2 antagonists.
H+/K+-ATPase catalyzes the terminal step in gastric acid whereas
histamine is but one of three key messengers which stimulate acid
secretion (the other two being acetylcholine and gastrin). As a re-
sult, inhibition of H+/K+-ATPase can provide an intrinsically greater
reduction in gastric acid secretion.2–7 Although several efficient
drugs are available for their treatment with different mechanisms
of action there is always a need for new agents with even better
efficacy and safety profiles.8
varying results. Amino acids such as leucine, isoleucine and proline
augment the acid release10,11 where as amino acids including ser-
ine, tryptophan, arginine, glycine, tyrosine and glutamic acid12
have been shown to provide protection against gastric ulcers.
Although the mechanism of antiulcer action of individual amino
acids is not clear, their derivatives have been shown to have direct
in vitro H+/K+-ATPase inhibitory activity as well as in vivo efficacy
in pylorus ligation model.13
Small and simple heterocyclic structures often have surpris-
ingly varied biological properties. Compounds containing thiazole
nucleus and their derivatives were found to have pharmacological
activities like antiviral,14 antibacterial,15 analgesic, anti-inflamma-
tory and antiulcer.16 Urea/thiourea derivatives display a wide
range of biological activities including antibacterial, antifungal,
antithyroid, antiulcer, herbicidal and plant growth regulator prop-
erties.17–19
This apart, glutamic acid-heterocycle conjugate derived ureas
and thioureas were synthesized in our laboratory and evaluated
their antiglycation and urease inhibitory activities.20 Compounds
showed interesting bioactivity. The present investigation was
aimed at the evaluation of these compounds for H+/K+-ATPase
inhibitory properties since the groups present in the analogues
fit best within the framework of antiulcer properties also.
Hence, with this background and previous investigations from
our group,21–24 the present work was undertaken with a view to
evaluate the antiulcer efficacy of the title compounds. Synthesis
of the title compounds was carried out as reported in literature.20
Intraduodenal administration of amino acid solution has been
reported to significantly inhibit gastric acid secretion and gastrin
release, stimulated by intragastric perfusion of peptone.9 However,
studies conducted with individual amino acids have yielded
⇑
Corresponding author. Tel.: +91 821 2419664.
E-mail address: dchannegowda@yahoo.co.in (D. Channe Gowda).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.05.043

A. Sharma et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4096–4098
4097
Synthesis of glutamic acid–benzisothiazole conjugate and their
urea/thiourea derivatives were accomplished according to the
steps illustrated in Scheme 1. Glutamic acid was conjugated to
3-(1-piperazinyl)-1,2-benzisothiazole using 1-ethyl-3-(3-dime-
thyllaminopropyl)carbodiimide (EDCI)/1-hydroxybenzotriazole
(HOBt) as coupling agent and N-methyl morpholine (NMM) as
base to get 1. The side chain benzyl group of 1 was deprotected
with 1 N NaOH/MeOH to get 2 which was conjugated again with
3-(1-piperazinyl)-1,2-benzisothiazole to get 3. Boc group of 3 was
deblocked using trifluoroacetic acid (TFA) and further reacted
with isocyanates and isothiocyanates to get urea and thiourea
derivatives respectively. All the derivatives were obtained in high
yield. The structures of all the newly synthesized compounds
were identified by IR, 1H NMR, 13C NMR, mass and elemental anal-
ysis. IR spectrum showed strong absorption bands at 3304–
3399 cmÀ1, 2029–2048 cmÀ1 and 1629–1642 cmÀ1 for –NH–, –
C@S, and –C@O groups, respectively. 1H NMR spectrum revealed
the appearance of peaks multiplets for the aromatic protons at d
7.21–7.93 and urea/thiourea NH protons at d 8.03–8.25 and
8.23–8.77, respectively. 13C NMR spectrum confirmed the car-
bonylic and thiocarbonylic structure due to peak appearance in
the range d 154.49–155.36 and d 180.62-180.86, respectively.
The physical and spectroscopical data of the compounds 1, 2, 3
and 3a–u have been provided in Tables 1 and 2, respectively (Sup-
plementary data).
All the synthesized compounds were evaluated for gastric
H+/K+-ATPase activity (assay procedure provided as Supplementary
data). The results are tabulated in Table 1. Omeprazole was used
as the reference compound. Glutamic acid earlier has been shown
to provide protection against gastric ulcers.12 Boc-Glu(OBzl)-OH
after conjugation with 3-(1-piperazinyl)-1,2-benzisothiazole re-
sulted in compound 1 which is also biologically inactive. Removal
of benzyl ester of c-carboxyl protection of 1 and further conjuga-
tion with another molecule of 3-(1-piperazinyl)-1,2-benzisothiaz-
ole showed no effective increase in activity. On the other hand, it
has been reported that the urea/thiourea structure was closely cor-
related with its potent antiulcer activity.25 This prompted us to
synthesize urea/thiourea derivatives of 3. Eventually, compounds
3a–u showed better activity compared with their precursors 1–3,
indicating that urea/thiourea derivatization seems to be in favor
of enhancing the inhibitory activity. As the H+/K+-ATPase inhibition
is associated with the modification of the mercapto groups in the
O
H
O
H
N
N
N
S
Boc
N
O
Boc
OH
O
+
HN
HCl.
N
N
EDCI/HOBt
N
NMM, 0 °C-rt
S
O
O
1
(i) 1N NaOH/MeOH, 2hr, 0 °C-rt
(ii) 1N HCl
O
N
H
N
N
S
Boc
HN
HCl
N
O
H
N
N
Boc
N
N
N
S
O
N
EDCI/HOBt
N
S
O
OH
NMM, 0 °C-rt
N
2
N
S
3
TFA, 45 min, rt
O
H
N
H
O
N
H2N
N
N
TFA.
N
N
Z
N
N
NMM, DMF
X
N
S
N
S
O
X-C6H4-N=C=Z
0 °C-rt
O
N
N
N
N
S
S
3a-u
where X = H, F, Cl, Br, OCH3
Z = O, S
Scheme 1. Urea/ thiourea derivatives of double 3-(1-piperazinyl)-1,2-benzisothiazole conjugated glutamic acid.

4098
A. Sharma et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4096–4098
Table 1
important role in the activity for electron withdrawing groups. As
the electronegativity decreases, increase in activity was signifi-
cantly observed.
Antiulcer activity of the synthesized compounds
H
N
H
N
N
S
From the above results, some broad generalizations could be
drawn. Due to electron releasing methoxy derivatives, an increase
in the activity was witnessed. Among electron withdrawing
groups, bromo derivative seems to be more active compared to
chloro and fluoro derivatives. Therefore, electron donating group
was found to be the most favorable which significantly contribute
in enhancing the antiulcer activity of the synthesized compounds.
In summary, the compounds presented in this Letter clearly dif-
fer in their corresponding antiulcer activity depending on the type
of substituent. In course of the study, derivatives possessing elec-
tron donating group such as methoxy is identified as exhibiting po-
tent antiulcer activity. These results make urea/thiourea
derivatives of benzisothiazole glutamic acid conjugate not only
interesting and simplified leads for further chemical optimization
but also potentially interesting for future scope to study their
mechanism of action and would be worthy of additional struc-
ture–activity relationship investigation.
Glu
N
N
N
Z
X
N
N
S
3a-u
For 1, 2, 3 refer Scheme
Entry
Z
X
Antiulcer activityaIC50
(lM)
1
2
3
—
—
—
O
S
—
—
—
H
Inactive
Inactive
Inactive
3a
3b
3c
3d
3e
3f
3g
3h
3i
94.0 0.52
90.0 0.66
44.0 0.82
50.0 0.79
48.0 0.97
46.0 0.84
60.0 0.99
56.0 0.75
54.0 0.63
52.0 0.81
80.0 0.53
74.0 0.74
78.0 0.67
72.0 0.99
70.0 0.57
19.0 0.74
17.0 0.89
11.0 0.73
10.0 0.58
6.2 0.52
5.4 0.64
Inactive
H
S
O
S
O
S
O
S
O
S
S
O
S
O
O
S
2-Br
3-Br
3-Br
4-Br
3-Cl
3-Cl
4-Cl
4-Cl
2-F
2-F
3-F
4-F
4-F
2-OCH3
2-OCH3
3-OCH3
3-OCH3
4-OCH3
4-OCH3
—
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.05.
043.
3j
3k
3l
3m
3n
3o
3p
3q
3r
3s
3t
3u
References and notes
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O
S
O
S
Boc-Glu(OBzl)-OH
Omeprazole
—
—
—
84.0 0.61
6. Konturek, S. J.; Cieszkowski, M.; Kwiecien, N.; Konturek, J.; Tasler, J.; Bilski, J.
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a
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9. Ikeda, M.; Shiratori, K.; Shimizu, K.; Watanabe, S.; Hayashi, N. Nihon Shokakibyo
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Among the derivatives, phenyl urea 3a and phenyl thiourea 3b
substituents displayed activity with IC50 = 94
l
M and IC50 = 90
lM
respectively which is less potent than omeprazole IC50 = 84
lM. It
can be inferred that compounds without substitution on the aryl
ring showed lesser activity. Therefore, the effect of substituents
on the phenyl ring was further investigated. When a methoxy
group was placed on the phenyl ring, derivatives exhibited highly
potent activity. Compound 3u bearing methoxy group at C4 re-
sulted as being most potent showing IC50 = 5.4 lM which is nearly
15-fold more potent than that of the reference standard. Ortho and
meta substituents were less active compared to para (p > m > o).
Further, the substitution of halogens (F, Cl and Br) for methoxy
yielded compounds 3c–o that resulted as being marginally active
antiulcer agents. Amongst, bromo derivatives were endowed with
significant antiulcer activity against H+/K+-ATPase compared to flu-
oro and chloro derivatives. The preferential order of halogens was
found to be Br > Cl > F. This revealed that electronegativity plays an