Syntheses of 1,5-benzothiazepines: Part XXXVI - Syntheses and antimicrobial evaluation of 2-(2-chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2,5-dihydro-8- substituted-1,5-benzothiazepines

Article abstract of DOI:10.1080/10426500802048920

Six 5-substituted-2-aminobenzenethiols have been reacted with 3-(2-chlorophenyl)-1-(4-chlorophenyl)-2-propenone and 3-(2-chlorophenyl)-1-(2- thienyl)-2-propenone in dry ethanol saturated with dry HCl gas, to obtain twelve new compounds, 8-substituted-2-(2-chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2, 5-dihydro-1,5-benzothiazepines in satisfactory yields. The structures of the final products have been assigned by elemental microanalyses data for elements, C, H, and N and by IR, 1H NMR, and mass spectroscopies. The synthesized compounds have been evaluated for their relative antimicrobial activity against the gram-positive bacteria, Staphylococcus aureus, gram-negative bacteria, Pseudomonas aeruginosa and the fungus, Candida albicans. The compounds have been found to show little antibacterial activity, but interestingly, showed significant antifungal activity. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426500802048920

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Syntheses of 1,5-
Benzothiazepines: Part
XXXVI—Syntheses and
Antimicrobial Evaluation of
2-(2-Chlorophenyl)-4-(4-
chlorophenyl/2-thienyl)-2,5-
dihydro-8-substituted-1,5-
benzothiazepines
Seema Pant a , Priyanka Sharma a & Umesh C. Pant b
a Department of Chemistry , LBS Government PG
College , Kotputli, Jaipur, India
b Department of Chemistry , University of
Rajasthan , Jaipur, India
Published online: 03 Nov 2008.
To cite this article: Seema Pant , Priyanka Sharma & Umesh C. Pant (2008) Syntheses
of 1,5-Benzothiazepines: Part XXXVI—Syntheses and Antimicrobial Evaluation of
2-(2-Chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2,5-dihydro-8-substituted-1,5-
benzothiazepines, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:12,
2974-2983, DOI: 10.1080/10426500802048920
To link to this article: http://dx.doi.org/10.1080/10426500802048920
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Phosphorus, Sulfur, and Silicon, 183:2974–2983, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500802048920
Syntheses of 1,5-Benzothiazepines: Part
XXXVI—Syntheses and Antimicrobial Evaluation of
2-(2-Chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2,5-
dihydro-8-substituted-1,5-benzothiazepines
Seema Pant,1 Priyanka Sharma,1 and Umesh C. Pant2
1Department of Chemistry, LBS Government PG College, Kotputli,
Jaipur, India
2Department of Chemistry, University of Rajasthan, Jaipur, India
Six 5-substituted-2-aminobenzenethiols have been reacted with 3-(2-chlorophenyl)-
1-(4-chlorophenyl)-2-propenone and 3-(2-chlorophenyl)-1-(2-thienyl)-2-propenone
in dry ethanol saturated with dry HCl gas, to obtain twelve new compounds,
8-substituted-2-(2-chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2,5-dihydro-1,5-
benzothiazepines in satisfactory yields. The structures of the final products have
been assigned by elemental microanalyses data for elements, C, H, and N and by
IR, 1 H NMR, and mass spectroscopies. The synthesized compounds have been
evaluated for their relative antimicrobial activity against the gram-positive bac-
teria, Staphylococcus aureus, gram-negative bacteria, Pseudomonas aeruginosa
and the fungus, Candida albicans. The compounds have been found to show little
antibacterial activity, but interestingly, showed significant antifungal activity.
Keywords Antifungal; chlorophenyl; clentiazem; diltiazem
INTRODUCTION
Drug designing attempts to obtain improved versions of diltiazem have
resulted into the discovery of clentiazem,1 which has a chlorine atom
as a substituent in the fused benzene ring of 1,5-benzothiazepine
nucleus. Introduction of chlorine as a chlorophenyl substituent at
Received 5 January 2008; accepted 12 March 2008.
The authors gratefully acknowledge the financial assistance provided by the CSIR,
New Delhi, and the Sophisticated Analytical Instrument Facility (SAIF), Central Drug
Research Institute, Lucknow, for providing the elemental analyses and spectral data.
Thanks are also due to Principal, LBS Government PG College, Kotputli, Jaipur, the
Head, Department of Chemistry, University of Rajasthan, Jaipur, and Dr. Ramesh
Mishra, Department of Microbiology, S.M.S. Medical College, Jaipur, for providing the
facility to work.
Address correspondence to Umesh C. Pant, Department of Chemistry, University of
Rajasthan, Jaipur, India. E-mail: drumeshpant@yahoo.com
2974

Syntheses of 1,5-Benzothiazepines: Part XXXVI
2975
various positions of 1,5-benzothiazepine nucleus has been found fruit-
ful to yield compounds possessing2−5 antiulcerous, antidepressive, an-
tihypertensive, anticancerous, and Ca2+ antagonist activity. These
have also been reported to possess antibacterial6 and antifungal6
activity. Antiulcerous,7 analgesic,8 vasodepressant,9 antibacterial,10
antifungal,11 etc., activity have been reported in 1,5-benzothiazepines
having chlorophenyl group along with different heterocyclic groups
at positions 2, 3, and 4. We have synthesized and reported12−17 dif-
ferent series of 1,5-benzothiazepines, having chlorophenyl group at
various positions. A series of benzopyranobenzothiazepines having a
chlorophenyl group18 and monochlorophenyl and dichlorophenyl sub-
stituents were studied to find out the effects of increased proportion
of chlorine on antimicrobial activity.19 Antimicrobial studies of 1,5-
benzothiazepines having heterocyclic substituents such as thienyl and
pyridyl have been reported recently.20 Synthesis and antimicrobial ac-
tivities of two series of 1,5-benzothiazepines are reported here to eval-
`
uate the effect of chlorine as chlorophenyl vis-a-vis thienyl by study-
ing 2-chlorophenyl with 4-chlorophenyl substituent and 2-chlorophenyl
along with thienyl.
RESULTS AND DISCUSSION
In order to have a substituent in the fused benzene ring and hav-
ing a chlorophenyl group as 2-chlorophenyl and 4-chlorophenyl
and heterocyclic group as thienyl in the thiazepine ring of 1,5-
benzothiazepine nucleus, the starting materials, 5-substituted-2-
aminobenzenethiols12−20 (4a–f), and other precursors, a ketone,
3-(2-chlorophenyl)-1-(4-chlorophenyl)-2-propenone21 (3a), and an
α,β-unsaturated heterocyclic carbonyl compound, 3-(2-chlorophenyl)-
1-(2-thienyl)-2-propenone22 (3b) were prepared. Equimolar quantities
of these reactants 4a–f and 3a or 3b were reacted to obtain the
title compounds, 2-(2-chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2,5-
dihydro-8-substituted-1,5-benzothiazepines (5a–l, Scheme 1).
It has been well established that such reactions12−18 take place in
two steps. In the first step, nucleophilic attack by the sulfhydryl elec-
trons of 5-substituted-2-aminobenzenethiols takes place on the acti-
vated β-carbon atom of the α,β-unsaturated carbonyl compounds to give
Michael-adduct type intermediates, which simultaneously undergo de-
hydrative cyclization to give final products in the second step. The for-
mation of the intermediate and/or cyclized product has been found to
depend significantly on the reaction conditions.23−25 We have found12−17
that the cyclized products were obtained in a single step in maximum

2976
S. Pant et al.
Cl
Cl
R
O
HC
C2H5OH
H3C
C
CH
CHO
40% NaOH
O
C
R
2a, 2b
1
3a, 3b
..
SH
X
Dry ethanol
+ Dry HCl gas
..
NH2
4a-f
Cl
Cl
..
CH
C
X
S
X
S
H
HC
CH
CH
..
..
NH2
NH
O
H
C
H
R
R
O
H
H
- H3O
Cl
Cl
H
C
H
X
S
C
X
S
CH
CH2
N
C
N
C
R
R
H
5a-l (i)
5a-l (ii)
X
5
X
R
5
g
h
i
R
F
Cl
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
4-ClC6H4
F
Cl
2-C4H3S
2-C4H3S
2-C4H3S
2-C4H3S
2-C4H3S
a
b
c
d
e
f
Br
Br
CH3
CH3
OCH3
j
OCH3
k
l
OC2H5
OC2H5 2-C4H3S
SCHEME 1

Syntheses of 1,5-Benzothiazepines: Part XXXVI
2977
yields in an acidic medium i.e. in methanol/ethanol saturated with
dry hydrogen chloride gas. Hence, the reactions of 5-substituted-2-
aminobenzenethiols (4a–f) with 3-(2-chlorophenyl)-1-(4-chlorophenyl)-
2-propenone (3a) and 3-(2-chlorophenyl)-1-(2-thienyl)-2-propenone (3b)
have been carried out in dry ethanol saturated with hydrogen chloride
to obtain 12 new compounds,
2-(2-chlorophenyl)-4-(4-chlorophenyl/2-thienyl)-2,5-dihydro-8-
substituted-1,5-benzothiazepines (5a–l, Scheme 1) in a single step in
58−68% yields. The structures of the final products were ascertained
by microanalysis data of C, H, N (Table I) and spectral analysis
comprising IR, 1H NMR (Table II) and mass spectra.
SPECTROSCOPIC STUDIES
The IR spectra of the final products did not show characteristic absorp-
tions for C = O and NH2 in the region 1690−1650 cm−1 and 3445−3200
cm−1, respectively. However, they showed an absorption band in the re-
gion 3150−3140 cm−1, which is due to secondary amino group. These
observations indicate that the reactions between, 3-(2-chlorophenyl)-
1-(4-chlorophenyl/2-thienyl)-2-propenone (3a, 3b) and 5-substituted-2-
aminobenzene-thiols (4a–f) had taken place negating the formation of
the intermediates.
The 1H NMR spectra showed12−17,20 two doublets at δ 6.70−6.95 (d,
1H, J 7Hz) and δ 7.94−8.20 (d, 1H, J 7Hz), integrating for one pro-
ton each, which may be assigned to C-2-H and C-3-H absorption peaks,
respectively. The downfield absorption of C-2-H may be accounted for
its attachment with an electronegative sulfur atom and electronegative
phenyl group. A broad singlet of one proton absorption at δ 4.07−4.13
(1H) may be assigned to NH. The formation of 2,5-dihydro structure
(an enamino form (5a–l, i), a more stable form rather than 2,3-dihydro
form (an imino structure (5a–l,ii), may be understood to take place
due to extended conjugation through p electrons of nitrogen with π
electrons (5a–l, i). The 1H NMR spectra of 5d and 5j showed a singlet
of three protons at δ 2.34 and 2.36 (s, 3H) assigned to methyl pro-
tons and also a singlet of three protons at δ 3.82 and 3.94 (s, 3H) in
compounds 5e and 5k respectively, assigned to methoxyl group pro-
tons. Compound 5f and 5l, showed a triplet at δ 1.34−1.44 (t, 3H, J
7Hz) and quartet at δ 4.03−4.10 (q, 2H, J
7Hz), due to methyl
and methylene protons of ethoxyl group. Absorption peaks as multi-
plets of aromatic protons were found at δ 6.90−8.15 (m, 11H) in com-
pounds 5a—f and at around δ 6.85−8.02 (m, 10H) in compounds 5g–l
(Table II).

2978

Syntheses of 1,5-Benzothiazepines: Part XXXVI
2979
TABLE II Characteristic IR Absorptions (ν in cm−1), 1H NMR (CDCl3,
δ Values in ppm, J in Hz) Signals of 2-(2-Chlorophenyl)-4-(4-chloroph-
enyl/2-thienyl)-2,5-dihydro-8-substituted-1,5-benzothiazepines (5a–l)
Compd.
no.
NH
C-2-H
C-3-H
Aromatic
protons (m)
νNH (br, 1H) (d, 1H, J 7) (d, 1H, J 7) C-8-XH
5a
5b
5c
5d
5e
5f
3140
3150
3142
3145
3142
3140
4.12
4.11
4.12
4.10
4.09
4.13
6.85
6.90
6.80
6.70
6.95
6.72
8.15
8.12
8.02
7.95
8.20
8.15
—
—
—
6.90−8.09
7.00−8.00
6.95−8.00
6.95−7.80
7.02−8.15
6.95−8.02
2.34 (s, 3H)
3.82 (s, 3H)
1.37 (3H, t, J
7) 4.03 (2H, q,
J
7)
5g
5h
5i
5j
5k
5l
3140
3145
3142
3150
3141
3146
4.11
4.09
4.07
4.07
4.12
4.13
6.83
6.82
6.90
6.84
6.82
6.92
7.99
8.00
8.05
7.94
8.00
8.02
—
—
—
6.85−8.00
6.94−7.95
6.94−8.00
6.98−7.92
6.94−8.02
7.00−7.99
2.36 (s, 3H)
3.94 (s, 3H)
1.44 (3H, t, J
7) 4.10 (2H, q,
J
7)
The mass spectrum of 5b showed cluster of isotopic molecu-
lar ion peaks, m/z, 417, 419, 421, and 423 which corresponded to
[M]+, [M+2]+, [M+4]+, and [M+6]+, respectively, while compound
5h showed molecular ion peaks, m/z, [M]+ at 389, [M+2]+ at 391
and [M+4]+ at 393. The pattern of molecular ion peaks confirmed
the presence of three chlorine atoms in the 5b and two chlo-
rine atoms in 5h. The elemental analyses of the final products
were found to be satisfactory within the permissible limits of error
(Table I).
ANTIMICROBIAL ACTIVITY
All the synthesized compounds, 5a–l were screened for their relative
antibacterial activity against the gram-positive bacteria, Staphylococ-
cus aureus and the gram-negative bacteria, Pseudomonas aeruginosa
and antifungal activity against the fungus, Candida albicans by using
Plate Disc Method26−28 at the concentration of 100 µg/disc. Gatifloxin,
natilmicin, and fluconazole were used as reference compounds forS.
aureus, P. aeruginosa and C. albicans respectively. The zone of inhibi-
tion exhibited by test and reference compounds were measured in 40 h
incubation period and relative activity was calculated as activity index

2980
S. Pant et al.
(Table III).
Activity Index
Zone of inhibition exhibited by test compound
Zone of inhibition exhibited by the reference compound
=
(1)
EXPERIMENTAL
All the melting points are uncorrected. The purity of compounds was
checked by TLC on glass plates coated with silica gel ‘G’ using Solvent
system, benzene: ethanol: aq. ammonia (50%) (7:3:1). The IR spectra
were taken in KBr pellets on Shimadzu 8201 PC spectrophotometer.
NMR spectra were recorded on a Bruker DRX-300 (300 MHz FT NMR)
instrument using CDCl3 as solvent and TMS as internal standard. The
FAB mass spectra were recorded on JEOL-SX 102/DA-6000 Mass spec-
trometer/Data system using Argon/Xenon (6kV, 10 mA) as the FAB
gas. The accelerating voltage was 10 kV and spectra were recorded at
room temperature. m-Nitrobenzyl alcohol (NBA) was used as the ma-
trix. Microestimations for carbon, hydrogen, and nitrogen were carried
out in Elemental Analyzer, Carlo Erba 1108. The spectral analysis and
TABLE III Zone of Inhibitiona and Activity Indexb of 5a—lf Against
the Bacteria, Staphylococcus Aureusc and Pseudomonas Aeruginosad
and the Fungus, Candida Albicanse
Compd. no.
S. aureus
P. aeruginosa
C. albicans
5a
5b
5c
5d
5e
5f
5g
5h
5i
13 (0.52)
15 (0.68)
—
8 (0.33)
10 (0.42)
24 (1.00)
—
18 (0.75)
10 (0.42)
16 (0.67)
17 (0.71)
17 (0.71)
18 (0.75)
—
—
22 (1.57)
10 (0.71)
10 (0.71)
18 (1.29)
18 (1.29)
—
22 (1.57)
—
20 (1.43)
18 (1.29)
24 (1.71)
14 (0.56)
14 (0.56)
14 (0.56)
8 (0.36)
15 (0.68)
20 (0.91)
8 (0.36)
18 (0.81)
8 (0.36)
5j
5k
5l
12 (0.50)
aZone of Inhibitions is in mm.bValues in parentheses represent activity index.cZone
of Inhibition of Gatifloxin for S. aureus is 25 mm for 5a–f and 22mm for 5g–l.dZone of
Inhibition of Natilmicin for P. aeruginosa is 24 mm.eZone of Inhibition of Fluconazole
for C. albicans is 14 mm.f Concentration used for the test and reference compounds
were 100 µg/disc.

Syntheses of 1,5-Benzothiazepines: Part XXXVI
2981
elemental analysis were carried out at the Sophisticated Analytical
Instrumentation Facility, Central Drug Research Institute, Lucknow.
α, β - Unsaturated carbonyl compound, 3-(2-chlorophenyl)-1-(4-
chlorophenyl)-2-propenone21 (3a), α,β-unsaturated heterocyclic ketone,
3-(2-chlorophenyl)-1-(2-thienyl)-2-propenone22 (3b) and 5-substituted-
2-aminobenzenethiols12−20(4a–f) were prepared by literature reported
methods.
General Procedure for the Preparation of 2-(2-chlorophenyl)-
4-(4-chlorophenyl/2-thienyl)-2,5-dihydro-8-substituted-1,5-
benzothiazepines (5a-l)
Equimolar quantities of 5-substituted-2-aminobenzenethiols (4, 0.001
mol) and 3-(2-chlorophenyl)-1-(4-chlorophenyl/2-thienyl)-2-propenone
(3a/3b, 0.001 mol) were taken in dry ethanol (15 mL) saturated with
dry HCl gas. The reaction mixtures were refluxed till the color changed
from light brown to deep red and concentrated under reduced pressure
to obtain crude solid. The crude solid thus obtained was crystallized
from methanol to obtain title compounds (5a–l).
The microanalytical and spectral data of 5a–l are given successively
in the Tables I−II.
ANTIMICROBIAL ACTIVITY
The Plate Disc Method was used for determining the antibacterial and
antifungal activity given as follows:
The nutrient agar culture media needed for testing antibacterial ac-
tivity was prepared by mixing a mixture of agar-agar (15 g), NaCl (5
g), beef extract (1.5 g), yeast extract (1.5 g) and peptic digest of ani-
mal tissues (5 g) in one litre of distilled water. The pH of the culture
media was maintained at 7.4 0.2. For testing antifungal activity, the
sabouraud dextrose agar culture media was prepared by mixing myco-
logical peptone (10 g), dextrose (40 g), and agar-agar (15 g) in 1 L of
distilled water. The pH of the culture media was maintained at 5.6
0.2. The Petri plates containing the culture were inoculated with the
required bacterial suspension or by even streaking of fungal suspen-
sion. The density of bacterial or fungal suspension (approximately 108
bacteria or fungi/ml) was standardized by dilution with sterile saline or
broth to a density visually equivalent to McFarland standard or barium
sulfate standard. Filter paper discs of test and reference compounds of
dose 10◦0 µg/disc were placed onto these plates and incubated for 40
h at 37 C. The zone of inhibition was measured and compared with

2982
S. Pant et al.
standard reference drugs. The results have been reported as activity
index (Table III).
CONCLUSION
All the synthesized compounds showed only mild antibacterial activity.
Compound 5i showed the highest relative activity against the gram-
positive bacteria Staphylococcus aureus; whereas, compound 5c showed
meaningful activity index, equal to that of the reference compound
against the gram-negative bacteria, Pseudomonas aeruginosa.
Compounds 5b,5h, and 5j showed high activity against the fun-
gus, Candida albicans whereas; compound 5l showed significant
and most profitable activity (Table III).These observations lead
us to state that the 4-(2-thienyl)-substituted 2-(2-chlorophenyl)-1,5-
benzothiazepines were found to be more active than the compounds 4-
(4-chlorophenyl)-substituted 2-(2-chlorophenyl)-1,5-benzothiazepines,
`
i.e., 2-thienyl substituent at position 4 vis-a-vis 4-chlorophenyl sub-
stituent rendered more activity to the compounds.
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Syntheses of 1,5-Benzothiazepines: Part XXXVI
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