An efficient synthesis and antimicrobial studies of bioactive 4H-1,4-benzothiazine and their sulfone derivatives

Article abstract of DOI:10.1080/10426507.2012.740703

4H-1,4-benzothiazines were prepared by condensation followed by oxidative cyclization of substituted 2-aminobenzenethiols with β-diketones in dimethylsulfoxide. On refluxing with 30% hydrogen peroxide in glacial acetic acid, 4H-1,4-benzothiazines yielded

Full text of DOI:10.1080/10426507.2012.740703

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Phosphorus, Sulfur, and Silicon and the
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An Efficient Synthesis and Antimicrobial
Studies of Bioactive 4H-1,4-
Benzothiazine and Their Sulfone
Derivatives
Naveen Gautam a , Yogesh Dixit a , Rahul Dixit a , Sudesh Kumar
Gupta a & Dinesh Chand Gautam a
a Department of Chemistry , University of Rajasthan , Jaipur ,
302004 , India
Accepted author version posted online: 01 Nov 2012.
To cite this article: Naveen Gautam , Yogesh Dixit , Rahul Dixit , Sudesh Kumar Gupta & Dinesh Chand
Gautam (2013) An Efficient Synthesis and Antimicrobial Studies of Bioactive 4H-1,4-Benzothiazine and
Their Sulfone Derivatives, Phosphorus, Sulfur, and Silicon and the Related Elements, 188:8, 1127-1136,
DOI: 10.1080/10426507.2012.740703
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Phosphorus, Sulfur, and Silicon, 188:1127–1136, 2013
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.740703
AN EFFICIENT SYNTHESIS AND ANTIMICROBIAL
STUDIES OF BIOACTIVE 4H-1,4-BENZOTHIAZINE
AND THEIR SULFONE DERIVATIVES
Naveen Gautam, Yogesh Dixit, Rahul Dixit, Sudesh Kumar
Gupta, and Dinesh Chand Gautam
Department of Chemistry, University of Rajasthan, Jaipur 302004, India
GRAPHICAL ABSTRACT
Abstract 4H-1,4-benzothiazines were prepared by condensation followed by oxidative cycliza-
tion of substituted 2-aminobenzenethiols with β-diketones in dimethylsulfoxide. On refluxing
with 30% hydrogen peroxide in glacial acetic acid, 4H-1,4-benzothiazines yielded 4H-1,4-
benzothiazine-1,1-dioxides. Structural evaluation has been done by spectral and elemental
analysis. All the synthesized compounds were evaluated for their antibacterial and antifungal
activity and all these have shown moderate to high activity against the test microbes.
Supplementary materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental
files: Additional text, figures and tables.
Keywords 4H-1,4-benzothiazine; heterocycles; sulfones and antimicrobial activity
INTRODUCTION
4H-1,4-benzothiazine and their analogs constitute an important class of bioactive het-
erocycles. Literature studies have shown their various chemotherapeutic importances.1–7
Many of their derivatives are in clinical use8 as antipsycotics, analgesics, diuretics, antitus-
sives and antihistamics, central nervous system depressants, antiinflammatories, anticancer,
tranquilizers, and antibiotic agents.
Received 26 July 2012; accepted 14 October 2012.
Authors are thankful to the Department of Chemistry and the Department of Botany, University of Rajasthan,
Jaipur (India) for providing laboratory facilities. Authors are also thankful to Central Drug Research Institute,
Lucknow (India) for providing IR, NMR, and Mass spectra. UGC Research Award Scheme, New Delhi is duly
acknowledged for financial support.
Address correspondence to Dr. Naveen Gautam, Department of Chemistry, University of Rajasthan, 692,
Mahaveer Nagar, Tonk Road, Jaipur- 302018, India. E-mail: ngautam70@yahoo.co.in
1127

1128
N. GAUTAM ET AL.
4H-1,4-benzothiazines structurally resemble 10H-phenothiazines in having a fold
along nitrogen sulfur axis. The molecular configurations of these compounds are between
planar and tetragonal folded symmetry. In the later configuration, the nitrogen and sulfur
atoms are in SP3 hybridization state, and the plane containing benzene rings are folded
along the axis passing through nitrogen and sulfur. Their nitrogen–sulfur axis is responsi-
ble for a number of pharmacological activities. Their pharmacological applications have
stimulated our interest to extend synthetic, structural, and antimicrobial studies of 4H-1,4-
benzothiazine in search of better medicinal agents.
The oxidation of sulfide linkage in benzothiazine leads to formation of the sulfones. It
was considered worthwhile to undertake structural investigation to understand the oxidation
behavior of benzothiazine and to study the change in spectral feature caused by conversion
of sulfide linkage into sulfones.
Kerby-Bauer9,10 procedure has been used for the study of antimicrobial activity of
newly synthesized 4H-1,4-benzothiazine and their sulfone derivatives.
RESULTS AND DISCUSSION
Substituted 4H-1,4-benzothiazines have been synthesized by condensation and
oxidative cyclization of 2-amino-3-fluoro/2-amino-3-isopropyl/2-amino-5-isopropyl ben-
zenethiol 1 with β-diketones 2 in dimethyl sulfoxide (DMSO). The reaction is believed to
proceed through the formation of an intermediate enaminoketone11,12 3. Under the above
experimental conditions, 2-amino-3-fluoro/2-amino-3-isopropyl/2-amino-5-isopropyl ben-
zenethiol 1 is readily oxidized to bis-(2-aminophenyl) disulfide 1a which cyclizes to 4H-
1,4-benzothiazines 4a–i by scission of sulfur–sulfur bond due to the high reactivity of the
α-position of enaminoketones system 3 toward nucleophilic attack. The synthesized substi-
tuted 4H-1,4-benzothiazines were converted into corresponding sulfones 5a–i by oxidation
under reflux conditions with 30% hydrogen peroxide in glacial acetic acid13–18 (Scheme 1).
The physical and analytical data of the synthesized compounds are given in Tables 1
and 2.
IR Spectra (Table 3)
All the 4H-1,4-benzothiazines 4a–i exhibit a single sharp peak in the region
3410–3250 cm−1 due to N-H stretching vibrations. The sharp bands observed in the region
1730–1670 cm−1 are attributed to C O stretching vibrations of carbonyl group. All the
4H-1,4-benzothiazines showed a peak in the region 1060–1005 cm−1 due to C-S-C defor-
mation vibrations. Compounds 4c and 4g showed two peaks in the regions 1270–1250 cm−1
and 1080–1060 cm−1 due to asymmetric and symmetric vibrations of OCH3 groups. Com-
pounds 4a–g exhibit two bands in the region 1470–1440 cm−1 and 1355–1330 cm−1 due to
CH-deformation vibrations of CH3 group. Compounds 4f–h showed a peak in the region
1390–1360 cm−1 due to isopropyl deformation vibrations. Compound 4a exhibits a single
sharp peak in the region 695 cm−1 due to C-Br stretching vibrations. Compounds 4d and
4f exhibit a peak in the region 1340–1330 cm−1 and 1130–1120 cm−1 due to asymmetric
and symmetric vibrations of CF3 group.
Further, in compounds 4a–e and 4i, bands due to C-F stretching vibrations appeared
in the region 1275–1260 cm−1
.

BIOACTIVE 4H-1,4-BENZOTHIAZINE AND THEIR SULFONE DERIVATIVES
1129
Scheme 1
The vibrational frequency corresponding to each substituent is shifted to higher
frequency in all the synthesized 4H-1,4-benzothiazine sulfones 5a–i. Sulfone deriva-
tives 5a–i exhibit a sharp intense peak in the region 1370–1350 cm−1 in chloroform
which can be assigned to the asymmetric stretching (v3) mode of sulfonyl group, while
in solid state, this absorption band splits into three bands and appears in the region
1375–1360 cm−1, 1325–1285 cm−1, and 1290–1260 cm−1. The asymmetric stretching
vibrations in the sulfones are strongly affected on passing from the solution to the crys-
talline state. The symmetric stretching vibrations (v1) give rise to high intensity doublet
in potassium bromide disc in the region 1185–1145 cm−1, whereas in solution it appears
at 1180–1140 cm−1. Hence, these frequencies are slightly affected due to the state of ag-
gregation. The bands appeared in the region 585–550 cm−1 can be attributed to bending
vibration (v2).17
1H NMR and 13C NMR Spectra (Tables 4 and 5)
All the synthesized 4H-1,4-benzothiazines and their sulfones (4a–i and 5a–i) exhibit
a singlet at δ 9.06–7.92 ppm due to the NH-proton. Aromatic protons show multiplets in
the region δ 8.10–6.98 ppm. A single sharp peak observed in the region δ 2.55–2.28 ppm
in compounds 4a–g and 5a–g can be assigned to CH3 group present at C3. Two singlets are
observed at δ 3.82–3.81 ppm and δ 3.85 ppm in compound 4c, 5c due to two OCH3 groups
present at ortho- and para-positions in benzoyl side chain at C2. Compounds 4g and 5g
exhibit a singlet at δ 3.82 and 3.85 ppm, respectively, due to OCH3 proton at ortho-position
in the benzoyl side chain at C2. The multiplets observed in the region δ 2.26–2.21 ppm are
attributed to C-H proton of isopropyl group in compounds 4f–h and 5f–h. Compounds 4f–h
and 5f–h also show a doublet at δ 1.48–1.40 ppm due to CH3 proton of isopropyl group.

1130

1131

1132

BIOACTIVE 4H-1,4-BENZOTHIAZINE AND THEIR SULFONE DERIVATIVES
1133
Table 4 1H NMR and 13C NMR spectral data of 4H-1,4-benzothiazines 4a–i
1H NMR (DMSO-d6, 300 MHz), δ
Comp. No.
ppm
13C NMR (CDCl3, 300 MHz), δ ppm
4a
8.50 (s, >NH), 7.72–7.01 (m, J =
8.58 Hz, Ar-H), 2.34 (s, -CH3
proton at C3)
8.61 (s, >NH), 7.60–6.98 (m, J =
8.61 Hz, Ar-H), 2.40 (s, -CH3
proton at C3)
8.71 (s, >NH), 7.80–7.25 (m, J =
8.60 Hz, Ar-H), 2.38 (s, -CH3
proton at C3), 3.81 (s, OCH3
protons at ortho-position in
benzoyal side chain at C2), 3.85 (s,
OCH3 protons at para-position in
benzoyal side chain at C2)
9.01 (s, >NH), 7.25–6.98 (m, J =
8.57 Hz, Ar-H), 2.52 (s, -CH3
protons at C3)
113.1 (C-2), 138.2 (C-3), 148.8 (C-5), 112.7 (C-6),
120.9 (C-7), 126.1 (C-8), 187.7 (C of CO at C2),
128.2–136.5 (C of C6H4Br at C2), 16.9 (CH3 at C3)
113.6 (C-2), 138.4 (C-3), 148.5 (C-5), 113.2 (C-6),
120.2 (C-7), 125.9 (C-8), 187.3 (C of CO at C2),
116.4–165.5 (C of C6H4F at C2), 16.2 (CH3 at C3)
113.3 (C-2), 138.9 (C-3), 150.4 (C-5), 113.8 (C-6),
120.4 (C-7), 125.8 (C-8), 186.8 (C of CO at C2), 58.4
(C of OCH3 of –COC6H3 (OCH3)2 (o,p) at C2), 15.8
(CH3 at C3)
4b
4c
4d
4e
4f
114.2 (C-2), 135.8 (C-3), 148.4 (C-5), 112.6 (C-6),
121.2 (C-7), 124.9 (C-8), 188.8 (C of CO at C2),
129.2 (CF3 at C2), 16.8 (CH3 at C3)
8.25 (s, >NH), 8.02–7.10 (m, J =
8.55 Hz, Ar-H), 2.28 (s, -CH3
protons at C3)
113.2 (C-2), 139.4 (C-3), 150.5 (C-5), 112.4 (C-6),
121.4 (C-7), 125.9 (C-8), 188.6 (C of CO at C2),
128.4–135.9 (C of C6H5 at C2), 17.0 (CH3 at C3)
116.9 (C-2), 136.1 (C-3), 136.0 (C-5), 124.4 (C-6),
118.9 (C-7), 128.6 (C-8), 195.8 (C of CO at C2),
129.2 (CF3 at C2), 16.8 (CH3 at C3), 23.2 (CH of
isopropyl group at C5), 25.3 (CH3 of isopropyl group
at C5)
8.89 (s, >NH), 7.80–7.60 (m, J =
8.53 Hz, Ar-H), 2.52 (s, -CH3
protons at C3), 2.22 (m, J =
5.2 Hz, C-H proton of isopropyl
group), 1.40 (d, J = 4.1 Hz, CH3
protons of isopropyl group)
8.20 (s, >NH), 7.75–7.20 (m, J =
8.55 Hz, Ar-H), 2.30 (s, -CH3
proton at C3), 3.82 (s, OCH3
protons of COC6H4 (OCH3) group
at C2), 2.21 (m, J = 6.3 Hz, C-H
proton of isopropyl group), 1.45
(d, J = 4.4 Hz, CH3 protons of
isopropyl group)
4g
114.2 (C-2), 139.2 (C-3), 135.8 (C-5), 124.5 (C-6),
117.9 (C-7), 128.1 (C-8), 188.5 (C of CO at C2),
115.2–162.3 (C of C6H5 at C2), 55.2 (C of OCH3 of
–COC6H4 (OCH3) (o) at C2) 16.9 (CH3 at C3), 22.9
(CH of isopropyl group at C5), 25.2 (CH3 of
isopropyl group at C5)
4h
4i
8.10 (s, >NH), 7.80–7.75 (m, J =
8.51 Hz, Ar-H), 2.25 (m, J =
5.3 Hz, C-H proton of isopropyl
group), 1.42 (d, J = 4.5 Hz, CH3
protons of isopropyl group)
7.92 (s, >NH), 7.80–7.17 (m, J =
8.60 Hz,Ar-H)
110.2 (C-2), 142.4 (C-3), 116.2 (C-5), 123.2 (C-6),
138.5 (C-7), 128.1 (C-8), 188.2 (C of CO at C2),
126.9–137.2 (C of C6H5 at C2), 126.4–135.5 (C of
C6H5 at C3), 32.2 (CH of isopropyl group at C7),
25.2 (CH3 of isopropyl group at C7)
108.6 (C-2), 142.1 (C-3), 148.8 (C-5), 113.6 (C-6),
121.0 (C-7), 125.9 (C-8), 187.4 (C of CO at C2),
126.7–136.9 (C of C6H5 at C2), 126.9–134.2 (C of
C6H5 at C3)
Figure S1 (Supplemental Materials are available online) contains the 13C NMR spectrum
of 4a as a representative example.
13C NMR spectra of the synthesized 4H-1,4-benzothiazines 4a–i and their sulfones
5a–i are given in Tables 4 and 5, respectively.

1134
N. GAUTAM ET AL.
Table 5 1H NMR and 13C NMR spectral data of 4H-1,4-benzothiazine sulfones 5a–i
1H NMR (DMSO-d6, 300 MHz), δ
13C NMR (CDCl3, 300 MHz), δ
Comp. No.
ppm
ppm
5a
8.55 (s, >NH), 7.75–7.05 (m, J =
8.60 Hz, Ar-H), 2.40 (s, -CH3
proton at C3)
8.65 (s, >NH), 7.64–7.00 (m, J =
8.65 Hz, Ar-H), 2.45 (s, -CH3
proton at C3)
8.76 (s, >NH), 7.84–7.30 (m, J =
8.64 Hz, Ar-H), 2.47 (s, -CH3
proton at C3), 3.82 (s, OCH3
protons at ortho-position in
benzoyal side chain at C2), 3.85 (s,
OCH3 protons at para-position in
benzoyal side chain at C2)
9.06 (s, >NH), 7.32–6.99 (m, J =
8.60 Hz, Ar-H), 2.55 (s, -CH3
protons at C3)
103.2 (C-2), 147.5 (C-3), 149.7 (C-5), 119.6 (C-6),
122.8 (C-7), 121.2 (C-8), 187.5 (C of CO at C2),
128.5–136.2 (C of C6H4Br at C2), 16.5 (CH3 at C3)
104.2 (C-2), 146.4 (C-3), 150.2 (C-5), 120.1 (C-6),
123.1 (C-7), 120.7 (C-8), 187.8 (C of CO at C2),
116.6–165.8 (C of C6H4F at C2), 15.8 (CH3 at C3)
105.2 (C-2), 150.9 (C-3), 151.6 (C-5), 121.3 (C-6),
124.6 (C-7), 122.6 (C-8), 186.2 (C of CO at C2), 58.2
(C of OCH3 of –COC6H3 (OCH3)2 (o,p) at C2), 15.5
(CH3 at C3)
5b
5c
5d
5e
5f
102.4 (C-2), 151.4 (C-3), 150.2 (C-5), 118.9 (C-6),
125.3 (C-7), 121.6 (C-8), 188.4 (C of CO at C2),
128.8 (CF3 at C2), 16.3 (CH3 at C3)
8.30 (s, >NH), 8.10–7.12 (m, J =
8.58 Hz, Ar-H), 2.32 (s, -CH3
protons at C3)
102.8 (C-2), 145.1 (C-3), 153.4 (C-5), 119.4 (C-6),
122.5 (C-7), 120.5 (C-8), 188.2 (C of CO at C2),
128.6–135.4 (C of C6H5 at C2), 16.7 (CH3 at C3)
103.9 (C-2), 146.8 (C-3), 137.6 (C-5), 131.6 (C-6),
120.6 (C-7), 125.8 (C-8), 195.1 (C of CO at C2),
128.5 (CF3 at C2), 16.4 (CH3 at C3), 23.5 (CH of
isopropyl group at C5), 25.3 (CH3 of isopropyl group
at C5)
8.94 (s, >NH), 7.86–7.65 (m, J =
8.55 Hz, Ar-H), 2.54 (s, -CH3
protons at C3), 2.25 (m, J =
5.5 Hz, C-H proton of isopropyl
group), 1.44(d, J = 4.2 Hz, CH3
protons of isopropyl group)
8.26 (s, >NH), 7.80–7.22 (m, J =
8.58 Hz, Ar-H), 2.32 (s, -CH3
proton at C3), 3.85 (s, OCH3
protons of COC6H4 (OCH3) group
at C2), 2.24 (m, J = 6.5 Hz, C-H
proton of isopropyl group), 1.48
(d, J = 4.6 Hz, CH3 protons of
isopropyl group)
5g
105.4 (C-2), 144.6 (C-3), 136.9 (C-5), 133.6 (C-6),
119.7 (C-7), 124.5 (C-8), 188.9 (C of CO at C2),
115.2–162.3 (C of C6H5 at C2), 55.2 (C of OCH3 of
–COC6H4 (OCH3) (o) at C2) 16.2 (CH3 at C3), 23.4
(CH of isopropyl group at C5), 25.2 (CH3 of
isopropyl group at C5)
5h
5i
8.14 (s, >NH), 7.83–7.79 (m, J =
8.55 Hz, Ar-H), 2.26 (m, J =
5.5 Hz, C-H proton of isopropyl
group), 1.45 (d, J = 4.7 Hz, CH3
protons of isopropyl group)
7.95 (s, >NH), 7.85–7.20 (m, J =
8.64 Hz,Ar-H)
100.4 (C-2), 156.4 (C-3), 118.6 (C-5), 132.21(C-6),
140.4 (C-7), 123.9 (C-8), 188.6 (C of CO at C2),
126.9–137.2 (C of C6H5 at C2), 127.1–134.9 (C of
C6H5 at C3), 32.5 (CH of isopropyl group at C7),
25.4 (CH3 of isopropyl group at C7)
96.6 (C-2), 155.2 (C-3), 151.3 (C-5), 130.5 (C-6), 123.0
(C-7), 122.8 (C-8), 187.1 (C of CO at C2),
126.3–136.5 (C of C6H5 at C2), 126.4–134.6 (C of
C6H5 at C3)
Antimicrobial Activity
Synthesized compounds were tested for their antifungal activity against Aspergillus
niger and Aspergillus flavus while antibacterial activity was tested against Staphylococcus
aureus and Peudomonas fluoroscence. The activity of these compounds was tested by
Kerby-Bauer procedure9,10 (filter paper disc method). This method allows for the rapid

BIOACTIVE 4H-1,4-BENZOTHIAZINE AND THEIR SULFONE DERIVATIVES
1135
determination of the efficiency of a drug by measuring the diameter of the zone of inhibition
that results from diffusion of the agent into the medium surrounding the disc.
The antifungal and antibacterial activities were determined by measuring the inhi-
bition zone around the disc. The antimicrobial activity of 4H-1,4-benzothiazine and their
sulfone derivatives was measured in terms of activity index.
From the antimicrobial activity data (Table S1 Supplemental Materials are available
online), it may be concluded that synthesized compound showed good and moderate activity
against the microbes.
CONCLUSIONS
The structures proposed for the synthesized compounds were well supported by
elemental analysis and spectroscopic data. All these synthesized 4H-1,4-benzothiazines
and their sulfone derivatives are novel and showed good and moderate antifungal and
antibacterial activities against the respective S. aureus, P. fluoroscence (bacteria) and A.
niger, A. flavus (fungi). Hence, these compounds can be use as an antifungal and antibacterial
drugs after that studyandanalysis of their biomedical aspects. Further biomedical researches
are required.
EXPERIMENTAL
All the melting points are uncorrected. The purity of synthesized compound has
been checked by thin layer chromatography. IR spectra were recorded in KBr on SHI-
MADZU 8400S FTIR spectrophotometer. The NMR spectra (1H NMR and 13C NMR)
have been recorded at 300 MHz on JEOL AL 300 FT NMR using TMS as internal stan-
dard in CDCl3/DMSO-d6. Mass spectra were recorded on JEOL SX 102/DA 600 using
Argon/Xenon as FAB (Fast Atom Bombarding) gas.
Synthesis of Substituted 4H-1,4-benzothiazines 4a–i
To a stirred suspension of β-diketone (2; 0.01 mol) in dimethyl sulfoxide (5 mL)
was added 2-amino-3-fluoro/2-amino-3-isopropyl/2-amino-5-isopropyl benzenethiol (1;
0.01 mol) and the resulting mixture was refluxed for 4 h. The reaction mixture was concen-
trated and cooled down to room temperature and filtered. The product obtained was washed
with petroleum ether and crystallized from methanol.
Synthesis of Sulfone Derivatives of 4H-1,4-benzothiazines 5a–i
To a solution of substituted 4H-1,4-benzothiazine (4; 0.01 mol) in 20 mL of glacial
acetic acid, 5 mL of 30% hydrogen peroxide was added and refluxed for 15 min. Heating
was stopped and portion of 30% hydrogen peroxide (5 mL) was added. The reaction mixture
was again refluxed for 3–4 h. The contents were poured in a beaker containing crushed ice.
The yellowish residue obtained was filtered and washed with water and recrystallized with
ethanol.

1136
N. GAUTAM ET AL.
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