Synthesis, Spectral Characteristics, and Biological Activity of 1,3-Oxazepines and 1,3-Oxazepanes Derived from 6-Nitrobenzothiazol-2-amine

Article abstract of DOI:10.1134/S1070428020020244

Abstract: 1,3-Oxazepine and 1,3-oxazepane derivatives of 6-nitrobenzothiazol-2-amine were synthesized, and their spectral and antibacterial properties were studied. The condensation of 6-nitrobenzothiazol-2-amine with aromatic aldehydes gave the corresponding Schiff bases, whose subsequent intermolecular cyclization with maleic and succinic anhydrides led to the target 1,3-oxazepine and 1,3-oxazepane derivatives. The compositions and structures of the synthesized compounds were established by elemental analysis and FTIR and ¹H NMR spectroscopy. 2-(4-Hydroxy-3-methoxyphenyl)-3-(6-nitrobenzothiazol-2-yl)-1,3-oxazepane-4,7-dione and 2-(4-iso-propylphenyl)-3-(6-nitrobenzothiazol-2-yl)-1,3-oxazepane-4,7-dione showed the highest antibacterial activity against the gram-positive bacteria Klebsiellapneumonia and Bacillussubtilis, and the gram-negative bacteria Staphylococcusaureus provide to be highly sensitive to 2-(4-hydroxy-3-methoxyphenyl)-3-(6-nitrobenzothiazol-2-yl)-1,3-oxazepane-4,7-dione.

Full text of DOI:10.1134/S1070428020020244

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2020, Vol. 56, No. 2, pp. 327–331. © Pleiades Publishing, Ltd., 2020.
Synthesis, Spectral Characteristics, and Biological Activity
of 1,3-Oxazepines and 1,3-Oxazepanes Derived
from 6-Nitrobenzothiazol-2-amine
a
a,
b
b
a
S. K. Abbas , H. D. Hanoon *, Z. F. Abbas , K. A. Hussein , and S. M. Radhi
a
Department of Chemistry, College of Science, University of Kerbala, Kerbala, 56001 Iraq
b
Department of Biology, College of Science, University of Kerbala, 56001 Iraq
*
e-mail: haitham.alshebly@uokerbala.edu.iq
Received September, 14, 2019; revised December 08, 2019; accepted December 20, 2019
Abstract—1,3-Oxazepine and 1,3-oxazepane derivatives of 6-nitrobenzothiazol-2-amine were synthesized, and
their spectral and antibacterial properties were studied. The condensation of 6-nitrobenzothiazol-2-amine with
aromatic aldehydes gave the corresponding Schiff bases, whose subsequent intermolecular cyclization with ma-
leic and succinic anhydrides led to the target 1,3-oxazepine and 1,3-oxazepane derivatives. The compositions and
1
structures of the synthesized compounds were established by elemental analysis and FTIR and H NMR spec-
troscopy. 2-(4-Hydroxy-3-methoxyphenyl)-3-(6-nitrobenzothiazol-2-yl)-1,3-oxazepane-4,7-dione and 2-(4-iso-
propylphenyl)-3-(6-nitrobenzothiazol-2-yl)-1,3-oxazepane-4,7-dione showed the highest antibacterial activity
against the gram-positive bacteria Klebsiella pneumonia and Bacillus subtilis, and the gram-negative bacteria
Staphylococcus aureus provide to be highly sensitive to 2-(4-hydroxy-3-methoxyphenyl)-3-(6-nitrobenzothiazol-
2
-yl)-1,3-oxazepane-4,7-dione.
Keywords: benzothiazole, Schiff base, 1,3-oxazepine, spectral study, antibacterial activity
DOI: 10.1134/S1070428020020244
The benzothiazole ring is a structural unit of a
great number of biologically active compounds [1, 2],
including anticancer [3], anti-inflammatory [4], anti-
tumor [5], anti-diabetic [6], anticonvulsants [7], and
antimicrobial agents [8]. Benzothiazoles are also applied
in industry as antioxidants [9].
amine (2) by treatment with a mixture of sulfuric and
nitric acids. Amine 2 was then condensed with various
aromatic aldehydes to obtain Schiff bases 3a–3d. The
intermolecular cyclization of the latter with maleic
and succinic anhydrides gave 1,3-oxazepines 4a–4d
and 1,3-oxazepanes 5a–5d, respectively (Scheme 1).
The synthesized compounds were identified by their
Oxazepines are known to exhibit diverse biological
and pharmacological activities [10] including antifungal
1
elemental analyses and FTIR and H NMR spectra.
The antibacterial activity of compounds 4 and 5 in
DMSO solutions was evaluated using agar diffusion
assay against 4 pathogenic bacteria: 2 gram-positive
[
11], anti-inflammatory [12], antagonistic [13], anti-
epileptic [14], hypnotic muscle relaxant [15], and anti-
bacterial [16]. These compounds are synthesized by the
reactions of Schiff bases with phthalic, maleic, succinic,
and nitrophthalic anhydrides [17].
(
Klebsiella pneumonia and Bacillus subtilis) and
gram-negative (Staphylococcus aureus and Esche-
richia coli).
2
The goal of the present research was to synthesize
novel 1,3-oxazepine and 1,3-oxazepane derivatives and
evaluate their biological activity.
The inhibition zone diameters (IZDs) were measured
after 24-h incubation. The resulting data are presented in
the table. 1,3-Oxazepane 5d showed the highest activity
against Bacillus subtilis and Klebsiella pneumonia (IZD
25 and 28 mm, respectively) and compound 5b ranked
secondinactivityagainstKlebsiellapneumonia, Bacillus
subtilis, and Staphylococcus aureus (IZD 22, 22, and
The synthesis of the benzothiazolyl-substituted
1
,3-oxazepans and 1,3-oxazepins is outlined in the
scheme 1. The first step involved the conversion of
benzothiazol-2-amine (1) into 6-nitrobenzothiazol-2-
3
27

328
ABBAS et al.
Scheme 1.
S
O N
S
2
HNO3
NH2
NH2 + Ar CHO
H SO
2
4
N
N
1
2
abs. EtOH
O N
S
2
N
C Ar
H
N
3a–3d
O
O
O
O
O
O
O N
2
S
O N
2
S
H
H
N C Ar
N C Ar
O
O
O
N
N
O
O
O
4a–4d
5a–5d
CH3
Ar =
Cl (a),
OH (b),
OCH (c),
CH
(d).
3
CH3
H CO
OCH3
3
2
6 mm, respectively). The inhibition zone diameter
agents among all the synthesized compounds, while
for compounds 4b, 4d, 5a, 5b, 5c and 5d was statistically
reliably (P 0.05) larger compared to the positive control
compounds 5a and 5c were found to be less active.
EXPERIMENTAL
(Amikacin antibiotic). Escherichia coli proved to be
resistant to all the test compounds.
All reagents and solvents were obtained from
commercial sources and used as received. The FTIR
spectra were recorded on a Shimadzu FTIR-8400S
Thus, the newly synthesized compounds were
showed good activity against Bacillus subtilis, Klebsiella
pneumonia and Staphylococcus aureus: compounds 4b,
1
spectrophotometer in KBr discs. The H NMR spectra
5
b, and 5d proved to be the most effective antibacterial
were recorded on a Bruker DRX-400 spectrometer
Table 1. Results of antibacterial activity testing of compounds 4 and 5
Inhibition zone diameter, mma
LSD
at
0.05
Bacteria
antibiotic
Amikacin)
15 ± 2
4
a
4b
4c
4d
5a
5b
5c
5d
(
Bacillus subtilis
Escherichia coli
Staphylococcus
aureus
15 ± 2 20 ± 3.46 17 ± 2.64 19 ± 1 20 ± 2.64 22 ± 3 19 ± 1 25 ± 1
3.02
0
9 ± 3
0
0
9±3
0
0
9 ± 3
18 ± 4.35 1.49
1
6 ± 1
16 ± 1
9 ± 3 17 ± 2.64 11 ± 2.08 22 ± 3 16 ± 1 21 ± 1
18 ± 4.35 2.62
Klebsiella
pneumonia
2
0 ± 2.64 18 ± 2.51 22 ± 3
15 ± 2
22 ± 3 26 ± 2.64 21 ± 1 28 ± 5.29 18 ± 4.35 2.11
a
Results are expressed as mean ± standard deviation (n = 3).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 2 2020

SYNTHESIS, SPECTRAL CHARACTERISTICS, AND BIOLOGICAL ACTIVITY OF 1,3-OXAZEPINES
329
4
00 MHz in DMSO-d . The elemental analyses were
N-(4-Isopropylbenzylidene)-6-nitrobenzothiazol-
2-amine (3d). Yield 72%, mp 254‒255°C. IR spectrum,
6
obtainedonaEuroEA3000-Singleanalyzer.Themelting
points were determined on a Stuart electrothermal
melting point apparatus. TLC (EtOAc–n-hexane, 2 : 1
as eluent) was conducted on aluminium plates coated
with silica gel (0.2 mm, 60 F254), with visualization by
iodine vapor.
–
1
ν, cm : 3025 (Ar–H), 1654 (C=N), 1519, 1345 (NO ),
2
740 (C–S). Found, %: C 62.52; H 4.45; N 12.73; S 9.77.
C17H15N3O2S. Calculated, %: C 62.75; H 4.65; N 12.91;
S 9.85.
1
,3-Oxazepine derivatives 4a–4d (general proce-
dure). A mixture of 0.010 mol of Schiff base 3a−3d and
.0 g (0.010 mol) of maleic anhydride in 20 mL of dry
6
-Nitrobenzothiazol-2-amine (2). 2-Aminobenzo-
1
thiazole, 0.157 mol, was dissolved in 36 mL of sulfuric
acid under cooling (< 5°C) and vigorous stirring, after
which 19 mL of nitric acid was added dropwise so that
the temperature of the reaction mixture was maintained
at 20°C. After 3-h stirring, the reaction mixture poured
onto ice while being stirred continuously, and aqueous
ammonia was added until the solid product turned
slightly orange. It was filtered off, washed with excess
water, dried, and recrystallized from ethanol. Yield 80%,
mp 150‒152°C. IR spectrum, ν, cm : 3385, 3311 (NH ),
1
C 43.22; H 2.33; N 21.09; S 16.76. C H N O S.
Calculated, %: C 43.07; H 2.58; N 21.53; S 16.43.
benzene was refluxed for 13 h. The solvent was then
evaporated, and the colored product was washed with
ethanol.
2
-(4-Chlorophenyl)-2,3-dihydro-3-(6-nitrobenzo-
thiazol-2-yl)-1,3-oxazepine-4,7-dione (4a). Yield 68%,
mp 205‒207°C. IR spectrum, ν, cm–1: 3095 (Ar–H),
1703 (C=O lactone), 1523, 1336 (NO ), 744 (C–S),
2
1
659 (C–Cl). Н NMR spectrum, δ, ppm: 9.06 s (1H,
–
1
Ar–H), 8.71‒8.11 m (2H, Ar–H), 7.94‒7.90 m (4H, Ar–
H), 7.56‒7.35 m (1H, N–CH, oxazepine ring), 6.58 s
(1H, =CH, oxazepine ring), 6.27 s (1H, =CH, oxazepine
ring). Found, %: C 51.23; H 2.10; N 10.55; S 7.13.
C H ClN O S. Calculated, %: C 51.99; H 2.42;
2
525, 1342 (NO ), 1284 (C–N), 744 (C–S). Found, %:
2
7
5
3
2
1
8
10
3
5
Schiff bases 3a−3d (general procedure). A
mixture of 2.3 g (0.010 mol) amine 2 and 0.011 mol
corresponding aromatic aldehyde in 30 mL of absolute
ethanol was refluxed on water bath for 5 h, then poured
into an ice-cold water. The solid product was filtered off
and recrystallized from ethanol.
N 10.11; S 7.71.
2,3-Dihydro-2-(4-hydroxy-3-methoxyphenyl)-3-
(
(
6-nitrobenzothiazol-2-yl)-1,3-oxazepine-4,7-dione
4b). Yield 70%, mp 246‒249°C. IR spectrum, ν, cm :
–1
3
1
348 (OH), 3022 (Ar–CH), 1710 ν(C=O lactone), 1529,
338 (NO ), 1130, 1040 (C–O–C), 752 (C–S). Found, %:
2
N-(4-Chlorobenzylidene)-6-nitrobenzothiazol-2-
amine (3a). Yield 76%, mp 215‒217°C. IR spectrum,
ν, cm : 3066 (Ar–H), 1626 (C=N), 1564, 1361 (NO ),
7
1
H 2.54; N 13.22; S 10.09.
-Methoxy-4-[(6-nitrobenzothiazol-2-ylimino)-
methyl]phenol (3b). Yield 79%, mp 233‒234°C. IR
C 53.99; H 3.35; N 9.27; S 7.21. C H N O S. Cal-
1
9
13
3
7
culated, %: C 53.39; H 3.07; N 9.83; S 7.50.
,3-Dihydro-2-(2,5-dimethoxyphenyl)-3-(6-
nitrobenzothiazol-2-yl)-1,3-oxazepine-4,7-dione (4c).
–1
2
2
50 (C–S), 684 (C–Cl). Found, %: C 52.77; H 2.26; N
3.10; S 10.23. C H ClN O S. Calculated, %: C 52.92;
1
4
8
3
2
–1
Yield 65%, mp 285‒287°C. IR spectrum, ν, cm : 3099
(
1
1
Ar–H), 1701 (C=O lactone), 1518, 1340 (NO ), 1130,
043 (C–O–C), 746 (C–S). Н NMR spectrum, δ, ppm:
0.30s(1H,Ar–H),9.06‒7.42m(6H,Ar–H),7.26‒7.04m
2
2
1
–
1
spectrum, ν, cm : 3396 (OH), 3079 (Ar–H), 1656
(1H, N–CH, oxazepine ring), 6.59 d (1H, =CH, oxaze-
(C=N), 1519, 1338 (NO ), 1126, 1035 (C–O–C), 738
2
pine ring), 6.30 s (1H, =CH, oxazepine ring), 3.86 s (3H,
OCH ), 3.74 s (3H, OCH ). Found, %: C 54.12; H 3.16;
(C–S). Found, %: C 54.88; H 3.11; N 12.64; S 9.63.
3
3
C H N O S. Calculated, %: C 54.71; H 3.37; N 12.76;
S 9.74.
15
11
3
4
N 9.83; S 7.05. C H N O S. Calculated, %: C 54.42;
20 15 3 7
H 3.43; N, 9.52; S 7.26.
N-(2,5-Dimethoxybenzylidene)-6-nitrobenzo-
thiazol-2-amine (3c). Yield 82%, mp 199‒202°C. IR
2,3-Dihydro-2-(4-isopropylphenyl)-3-(6-nitro-
benzothiazol-2-yl)-1,3-oxazepine-4,7-dione(4d).Yield
–
1
–1
spectrum, ν, cm : 3099 (Ar–H), 1658 (C=N), 1521,
340 (NO ), 1134, 1043 (C–O–C), 746 (C–S). Found,
63%, mp185‒187°C. IRspectrum,ν, cm :3093(Ar–H),
1
1712 (C=O lactone), 1518, 1346 (NO ), 744 (C–S).
2
2
%
: C 55.59; H 3.46; N 12.12; S 9.55. C H N O S.
Found,%:C59.23;H3.97;N9.15;S7.08.C H N O S .
1
6
13
3
4
21 17
3
5 2
Calculated, %: C 55.97; H 3.82; N 12.24; S 9.34.
Calculated, %: C 59.57; H 4.05; N 9.92; S 7.57.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 56 No. 2 2020

330
ABBAS et al.
1
,3-Oxazepane derivatives 5a–5d (general proce-
Amikacin was used as a positive control. The turbidity of
the inoculating media for each test bacteria was adjusted
with saline to match the McFarland standard 0.5 (1.5 ×
108 cell mL ). A 100-μL portion of the prepared
solution of each bacterial strain was plated on Muller−
Hiton agar, and the plates were left to stand for 15 min
to allow the bacterial solution to be absorbed. Wells
were then made using a sterile 6-mm cork borer, and
dure). A solution of 1.0 g (0.010 mol) of succinic
anhydride in 10 mL of dry benzene was added dropwise
to 20 mL of a hot dry benzene solution of 0.010 mol of
compound 3a–3d. The reaction mixture was refluxed for
–
1
1
3 h. The reaction progress was monitored by TLC. The
solid product was filtered off and washed with ethanol.
-(4-Chlorophenyl)-3-(6-nitrobenzothiazol-2-yl)-
,3-oxazepane-4,7-dione (5a). Yield 71%, mp 282‒
2
1
00-μL portions of 100 mg/mL solutions of each of
1
2
–
1
the test compounds in DMSO (prepared in advance
by dissolving the required weight in 2 mL of DMSO)
were introduced in the wells (three replicates were used
in each case). After incubation at 37°C for 24 h, the
diameter of the inhibition zone around each well was
measured.
85°C. IR spectrum, ν, cm : 3047 (Ar–H), 1707 (C=O
lactone), 1558, 1363 (NO ), 759 (C–S), 636 (C–Cl). Н
NMRspectrum, δ, ppm:10.65s(1H,Ar–H), 9.80‒8.71m
2H, Ar–H), 8.26‒7.25 m (4H, Ar–H), 7.55‒7.45 m
1H, N–CH, oxazepine ring), 2.81‒2.60 m (2H, -CH2,
1
2
(
(
oxazepine ring), 1.15‒1.10 m (2H, -CH , oxazepine
2
ring). Found, %: C 51.33; H 2.37; N 10.75; S 7.22.
C H ClN O S. Calculated, %: C 51.47; H 2.89;
N 10.06; S 7.67.
Statistical analysis. Completely randomized design
(CRD) was employed and the Fisher's least significant
difference (LSD) method was used for post-hoc
comparisons, statistical significance was set at P 0.05.
18
12
3
5
2
-(4-Hydroxy-3-methoxyphenyl)-3-(6-nitro-
benzothiazol-2-yl)-1,3-oxazepane-4,7-dione
Yield 66%, mp 220-222°C. IR spectrum, ν, cm : 3304
(5b).
CONFLICT OF INTEREST
The authors declare no conflict of interest.
SUPPLEMENTARY MATERIALS
–
1
(
OH), 3037 (Ar–H), 1693 (C=O lactone), 1527, 1329
1
(NO ), 1195, 1089 (C–O–C), 740 (C–S). Н NMR spec-
2
Supplementary materials are available for this article
at https://doi.org/10.1134/S1070428020020244 and are
accessible for authorized users.
trum, δ, ppm: 12.80 s (1H, OH), 9.76 s (1H, Ar–H),
9
7
.04‒8.35 m (2H, Ar–H), 8.27‒7.67 m (4H, Ar–H),
.45‒6.94 m (1H, N–CH, oxazepane ring), 3.83 s (3H,
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