Synthesis and antioxidant studies of novel N-substituted benzyl/phenyl-2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H) -yl)acetamides

Article abstract of DOI:10.1007/s00044-012-0062-6

Two new series of twenty-two N-substituted benzyl/phenyl-2-(3,4-dimethyl-5, 5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)acetamides were synthesized by synergism of the dihydropyrazolo[4,3-c][1,2]benzothiazine 5,5-dioxide moiety with side chain of carboxamides. The routes of formation for these products have been discussed. All the compounds were characterized by NMR, mass and elemental analysis. Structures of compounds 6d and 6l have been elucidated by X-ray crystallography. The synthesized compounds were screened to the preliminary evaluation for their anti-oxidant activities and most of the compounds were found to possess moderate to significant radical scavenging activity. Furthermore, these compounds could be useful as a template for future development through modification or derivatization to design more potent biologically active compounds. Graphical Abstract: [Two series of novel carboxamides based upon pyrazolobenzothiazine ring system have been synthesized and evaluated for antioxidant activity. Many compounds were found to be good scavengers of superoxide anion radical. Moreover, the compounds may also possess the bioactivities of parent ring system and thus, are useful as template for further development of new bioactive molecules.][Figure not available: see fulltext.]

Full text of DOI:10.1007/s00044-012-0062-6

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2013) 22:794–805
DOI 10.1007/s00044-012-0062-6
ORIGINAL RESEARCH
Synthesis and antioxidant studies of novel N-substituted benzyl/
phenyl-2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c]
[1,2]benzothiazin-2(4H)-yl)acetamides
•
Matloob Ahmad Hamid Latif Siddiqui
•
•
John M. Gardiner Masood Parvez
•
Sana Aslam
Received: 27 November 2011 / Accepted: 12 April 2012 / Published online: 11 May 2012
Ó Springer Science+Business Media, LLC 2012
Abstract Two new series of twenty-two N-substituted
benzyl/phenyl-2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)acetamides were synthe-
sized by synergism of the dihydropyrazolo[4,3-c][1,2]
benzothiazine 5,5-dioxide moiety with side chain of
carboxamides. The routes of formation for these prod-
ucts have been discussed. All the compounds were
characterized by NMR, mass and elemental analysis.
Structures of compounds 6d and 6l have been elucidated
by X-ray crystallography. The synthesized compounds
were screened to the preliminary evaluation for their
anti-oxidant activities and most of the compounds were
found to possess moderate to significant radical scav-
enging activity. Furthermore, these compounds could be
useful as a template for future development through
modification or derivatization to design more potent
biologically active compounds.
Keywords 1,2-Benzothiazine ꢀ Pyrazolobenzothiazine ꢀ
Amide synthesis ꢀ Anti-oxidant activity
Introduction
A wide range of 1,2-benzothiazine-3-carboxamides 1,1-diox-
ides are known for their potent anti-inflammatory and analgesic
nature (Lomabardino et al., 1971). Anti-inflammatory and
analgesic drugs of this family are classified as oxicams in the
main category of non-steroidal anti-inflammatory drugs
(NSAID’s). Oxicams include piroxicam, sudoxicam, ampir-
oxicam, and meloxicam (Lomabardino et al., 1973; Turck
et al., 1995). These discoveries have led to the synthesis of a
variety of carboxamides using aliphatic (Lomabardino et al.,
1973), aromatic (Lomabardino and Wiseman, 1972; Zinnes
et al., 1973) and heterocyclic amines (Lomabardino et al.,
1971; Turck et al., 1995). Biological studies have revealed the
versatile bioactive nature of benzothiazine derivatives as anti-
allergic (Ikeda et al., 1992), anti-microbial (Giuseppe et al.,
1987; Zia-ur-Rehman et al., 2006), central nervous system
depressants and tranquilizers (Krapcho and Somerset, 1968;
Krapcho and Somerset, 1969a, b). Moreover, our previous
studies have shown N0-arylmethylidene-2-(3,4-dimethyl-5,
5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)acetohyd
razides are potent anti-oxidants and N0-[1-phenylethylidene]-
2H/2-methyl-1,2-benzothiazine-3-carbohydrazide 1,1-dioxides
are anti-microbial (Ahmad et al., 2010, 2011).
M. Ahmad
Institute of Chemistry, University of the Punjab,
Lahore 54590, Pakistan
M. Ahmad
Department of Chemistry, Govt. College University,
Faisalabad, Pakistan
H. L. Siddiqui (&) ꢀ S. Aslam
Institute of Chemistry, University of the Punjab,
Lahore 54590, Pakistan
e-mail: drhamidlatif@hotmail.com
Pyrazole-containing compounds include numerous
agents showing potent bioactivities including anti-bacte-
rial, anti-fungal (Iovu et al., 2003), anti-viral (Baraldi et al.,
1998), and anti-tumor efficacy (Riyadh, 2011). Some pyr-
azole derivatives have been reported to exhibit significant
anti-arrhythmic and sedative (Bruno et al., 1990),
J. M. Gardiner
School of Chemistry and Manchester Interdisciplinary
Biocentre, University of Manchester, Manchester M1 7DN, UK
M. Parvez
Department of Chemistry, University of Calgary,
2500 University Drive N.W, Calgary, AB T2N 1N4, Canada
123

Med Chem Res (2013) 22:794–805
795
hypoglycemic (Cottineau et al., 2002), and anti-inflam-
matory activities (Smith et al., 2001). Celecoxib (Fig. 1),
for example, is a pyrazole-containing anti-inflammatory
drug of recent significance due to its selective inhibition of
COX-2 enzyme (Silverstein et al., 2000).
ring expansion by sodium methoxide under anhydrous con-
ditions (Scheme 1). This provided a significantly improved
yield (80 %) over our prior stepwise process (62 %).
N-methylation of 1 with dimethylsulphate and cyclization
with hydrazine hydrate afforded 3,4-dimethyl-2,4-dihydropy-
razolo[4,3-c][1,2]benzothiazine 5,5-dioxide (3) (Scheme 2).
There are a number of literature reports of 4-hydroxy-2-
methyl-2H-1,2-benzothiazine-3-carboxamides 1,1-dioxides
showing as potent anti-inflammatory and analgesic agents.
With ready access to this novel pyrazole, we thus prepared
alkyl 3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothia-
zin-2(4H)-yl acetate (4) as a potential substrate for direct
conversion to respective carboxamide derivatives. However,
direct conversion of this ester (4) into respective anilides was
unsuccessful due to lower reactivity of ester toward anilines.
Therefore, ester (4) was hydrolyzed to 3,4-dimethyl-5,5-di-
oxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl acetic acid
(5), to approach amide derivatives by amine-carboxylate
coupling.
This precedent for broad bioactivity profiles for these
two different heterocyclic pharmacophores led us to per-
ceive that fusion of benzothiazine and pyrazole nuclei may
result in new bioactive molecules. The strategy envisioned
starting from the inexpensive raw material sodium saccharine
as a precursor to a common intermediate pyrazole-benzoa-
thiazine fused ring system, 3,4-dimethyl-5,5-dioxidopyraz-
olo[4,3-c][1,2]benzothiazin-2(4H)-yl acetic acid (5) which
could then function as a common scaffold to generate a
library of amide derivatives of the side chain carboxylate.
Herein, we report the synthesis of 5 and reaction with a range
of substituted benzylamines and anilines to afford two novel
series of twenty-two N-(substituted)benzyl-2-(3,4-dimethyl-
5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl) aceta-
mides (6a–l) and 2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,
3-c][1,2]benzothiazin-2(4H)-yl)-N-phenylacetamides (7a–j).
Structures of two representative compounds (6d and 6l) were
determined through XRD as well and preliminary evaluation
as antioxidants provides useful SAR information for further
development.
Finally, treatment of acid (5) with borane-THF complex
resulted in the formation of a reactive intermediate, tria-
cyloxyborane that reacted readily with substituted benzyl-
amines to form respective carboxamides (Huang et al.,
2007). Parallel synthesizer equipment was efficiently used
for the synthesis of libraries of these carboxamides, i.e.,
6a–l and 7a–j (Scheme 2). The yields of the carboxamides
(6a–l) were in the range of 60–75 %. It is worth men-
tioning here that the classical coupling agents DCC/HOBt
(Sheehan and Hess, 1955) and EDC/HOBt (Boger et al.,
1999) were also employed, however, provided lower yields
than use of borane-THF complex. Whereas, the yields
of anilides (7a–j) from reactions using anilines were in the
range of 15–20 % under the same reaction condi
tions which gave promising results using benzylamine
Results and discussion
Chemistry
One-pot synthesis of 3-acetyl-2H-1,2-benzothiazine 1,1-
dioxide (1) was carried out in DMSO by condensation of
sodium saccharine with monochloroacetone and subsequent
H3C
Fig. 1 Potent anti-
inflammatory drugs based upon
benzothiazine and pyrazole
nuclei
N
OH
S
O
CH3
S
NH
CH3
CF3
N
N
N
O
O
O
S
(Meloxicam)
H2N
O
(Celecoxib)
OH
Scheme 1 One-pot conversion
of sodium saccharine
to 3-acetyl-2H-1,2-
O
O
O
(i) and (ii)
Cl
NNa
benzothiazine 1,1-dioxide
NH
S
S
O
O
O
O
Sodium saccharine
(1)
(i) DMSO, 120 ºC, 1.5 hours (ii) NaOMe/ MeOH
123

796
Med Chem Res (2013) 22:794–805
Scheme 2 Synthesis of novel
N-substituted benzyl/phenyl-2-
(3,4-dimethyl-5,5
dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-
yl)acetamides
OH
S
O
N
NH
OH
S
O
(2)
O
(i)
(ii)
NH
N
N
S
O
O
O
N
O
O
(3)
(1)
(iv)
R
O
(iii)
H
N
OH
R
O
O
O
N
S
N
N
N
N
(v)
(vi or vii)
N
N
O
N
S
S
O
O
O
O
O
(6a-l & 7a-j)
(5)
(4)
(i) (CH3)2SO4/NaOH(aq);Acetone (ii) N2H4.H2O/EtOH (iii) alkyl chloroacetat/K2CO3; DMF
(iv) BrCH2COOH/K2CO3; DMF (v) NaOH(aq)/MeOH (vi) BH3-THF complex/Ar-CH2-NH2;
Toluene:THF mixture (vii) SOCl2; Ar-NH2/Toluene:THF mixture
Antioxidant studies
deriviatives. This may be due to better nucleophilicity of
benzylamines compared to that of anilines. Thus, the more
reactive intermediate acyl halide was prepared by using
thionyl chloride as acylating reagent followed by its reac-
tion with substituted anilines in the presence of triethyl
amine as a base. The resulting novel N-substitutedphenyl-
2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothia-
zin-2(4H)-yl)acetamides (7a–j) were isolated in 75–86 %
yields (Table 1). Unreacted benzylamines/anilines and
carboxylic acid 5 were removed by dissolving residue in
ethyl acetate and successively washing the solution with
1.0 N HCl and saturated NaHCO3, respectively.
Reactive oxygen species (ROS) and free radicals are
involved in a wide range of human diseases (Gutteridge,
1993). ROS, including super oxide anion, hydrogen per-
oxide, and hydroxyl radical are byproducts of a variety of
pathways of aerobic metabolism (Foroumadi et al., 2007).
These are unstable and react readily with a wide range of
biological substrates, such as lipids, DNA, and protein
molecules, consequently resulting in cell damage
(Braughler et al., 1986). The title compounds were sub-
jected to antioxidant activity (superoxide anion and DPPH
scavenging activity) and the results are described in
Table 3.
Compound 6k (%RSA = 81.51), having 2-methylben-
zyl group, compound 7f (%RSA = 79.09), bearing 2-bro
mophenyl, and compound 7j (%RSA = 78.32), with 2,4-
dimethoxyphenyl group were found to be excellent super-
oxide anion radical scavengers. There is a reasonable
structure–activity relationship among all the compounds.
First, substituted aniline-based amides were more active as
compared to the corresponding benzylamine derivatives.
Second, compounds having electron donating substituents
present at ortho and para positions were observed to be
better scavengers. Among halogen substituted compounds,
following relationship was present: Br [ Cl [ F.
X-ray studies
The heterocyclic thiazine rings in both structures adopt
half-chair conformation (Fig. 2), with atoms N1 and S1
˚
displaced by 0.263(4) and -0.417(4) A, respectively, in 6d
˚
and 0.235(4) and -0.460(4) A, respectively, in 6l from the
plane formed by atoms C1/C6/C7/C8; the puckering
parameters (Cremer and Pople, 1975), respectively, are:
˚
Q = 0.441(2) and 0.459(2) A, h = 118.7(3)° and 118.3(2)
and u = 203.0(3) and 200.1(3)°. In both structures, the
five-membered rings are essentially planar with maximum
˚
deviations being 0.0097(13) and 0.0112(13) A for C7 in 6d
During our previous work (Ahmad et al., 2010), we reported
the antioxidant studies of N0-arylmethylidene-2-(3,4-dimeth
yl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)acet
ohydrazides. The comparison of superoxide scavenging stud-
ies of previously reported hydrazides (–CONHN=CHAr) and
and 6l, respectively. Crystallographic parameters are
described in detail in Table 2. Crystallographic data have
been deposited with the Cambridge Crystallographic Data
Center (CCDC deposition numbers are: 6d = 817,158;
6l = 817,157).
123

Med Chem Res (2013) 22:794–805
797
Table 1 Characterization of N-substituted benzyl/phenyl-2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)acetamides
(6a–l and 7a–j)
Code name
R
Yield (%)
Analysis (%)
Calculated (found)
C
H
N
6a
6b
6c
6d
6e
6f
2-Chlorobenzyl
4-Chlorobenzyl
2-Flourobenzyl
4-Flourobenzyl
2-Bromobenzyl
3-Bromobenzyl
2-Methoxybenzyl
3-Methoxybenzyl
4-Methoxybenzyl
2,4-Dimethoxybenzyl
2-Methylbenzyl
4-Methylbenzyl
Phenyl
70
72
63
65
67
61
73
69
71
75
68
67
78
82
85
75
77
77
75
85
84
86
55.75 (55.73)
55.75 (55.74)
57.96 (57.95)
57.96 (57.92)
50.53 (50.54)
50.53 (50.50)
59.14 (59.14)
59.14 (59.15)
59.14 (59.13)
57.88 (57.86)
61.44 (61.43)
61.44 (61.45)
59.67 (59.65)
54.74 (54.75)
54.74 (54.76)
56.99 (56.97)
56.99 (56.98)
49.47 (49.45)
49.47 (49.46)
58.24 (58.22)
58.24 (58.21)
57.00 (57.01)
4.44 (4.43)
4.44 (4.46)
4.62 (4.63)
4.62 (4.61)
4.03 (4.01)
4.03 (4.05)
5.20 (5.19)
5.20 (5.22)
5.20 (5.21)
5.30 (5.31)
5.40 (5.42)
5.40 (5.39)
4.74 (4.76)
4.11 (4.14)
4.11 (4.12)
4.28 (4.27)
4.28 (4.29)
3.71 (3.71)
3.71 (3.70)
4.89 (4.87)
4.89 (4.88)
5.01 (5.02)
13.00 (13.01)
13.00 (12.99)
13.52 (13.49)
13.52 (13.53)
11.79 (11.78)
11.79 (11.80)
13.14 (13.15)
13.14 (13.15)
13.14 (13.11)
12.27 (12.25)
13.65 (13.66)
13.65 (13.63)
14.65 (14.63)
13.44 (13.42)
13.44 (13.41)
13.99 (14.01)
13.99 (13.97)
12.14 (12.13)
12.14 (12.15)
13.58 (13.60)
13.58 (13.60)
12.66 (12.65)
6g
6h
6i
6j
6k
6l
7a
7b
7c
7d
7e
7f
2-Chlorophenyl
4-Chlorophenyl
2-Flourophenyl
4-Flourophenyl
2-Bromophenyl
3-Bromophenyl
2-Methoxyphenyl
3-Methoxyphenyl
2,4-Dimethoxyphenyl
7g
7h
7i
7j
anion radical as compared to corresponding benzylamides and
hydrazides. For example: compound 7j (bearing 2-Cl phenyl
moiety) is more active than corresponding compounds 6a
(benzylamide) and 6e (hydrazide). Similar order of the activity
was observed in the compounds possessing common substit-
uents (i.e., 4-Cl, 4-F, 3-OMe, and 2,4-dimethoxy) in the cor-
responding benzylamide and hydrazides, respectively.
For DPPH radical scavenging activity, the compounds
of both the series of carboxamides (i.e., 6a–l and 7a–j)
were observed either weakly active or inactive. Among all
the compounds, methoxy substituted compounds were the
most active, e.g., 7j, which contains a 2,4-dimethoxy-
phenyl moiety, (%RSA = 39.78) was more active than 7h
(2-methoxyphenyl; %RSA = 26.89) and 7i (3-methoxy-
phenyl; %RSA = 20.18), however, the difference in
activity was not as high as required to accomplish a sat-
Fig. 2 ORTEP II diagram of compounds 6d and 6l, with the
numbering scheme. Displacement ellipsoids are drawn at the 50 %
probability level; H atoms are represented by circles of arbitrary radii
isfactorily structure–activity relationship.
A
similar
behavior was observed among the benzyl substituted
compounds (6a–l), i.e., compound 6j (2,4-dimethoxyben-
zyl; %RSA = 27.31) has nearly same activity to the
compounds 6g (2-methoxybenzyl; %RSA = 25.58) and 6i
(4-methoxybenzyl; %RSA = 23.69).
corresponding carboxamides (–CONHR; where R = –CH2Ar
and –Ar)-posed interesting discussion. Overall, it is observed
that anilides are the most potent scavengers of superoxide
123

798
Med Chem Res (2013) 22:794–805
Table 2 Crystallographic parameters for compounds 6d and 6l
Crystallographic parameters
6d
6l
CCDC numbers
Empirical formula
Formula weight
Temperature
817158
817157
C20 H19 F N4 O3 S
414.45
C21 H22 N4 O3 S
410.49
173(2) K
173(2) K
˚
0.71073 A
˚
0.71073 A
Wavelength
Crystal system
Space group
Orthorhombic
Orthorhombic
Pca21
˚
17.7329(6) A
Pbca
˚
17.8676(4) A
Unit cell dimensions: a
b
˚
12.3170(4) A
˚
8.6431(2) A
˚
8.7837(3) A
˚
26.4267(6) A
c
3
3
˚
1918.50(11) A
˚
4081.11(16) A
Volume
Z
4
8
Density (calculated)
Absorption coefficient
F(000)
1.435 Mg/m3
0.209 mm-1
1.336 Mg/m3
0.189 mm-1
864
1728
Crystal size
0.18 9 0.16 9 0.06 mm3
Colorless, prism
2.0 to 25.0°
0.16 9 0.14 9 0.04 mm3
Colorless, plate
2.7 to 25.0°.
Crystal habit
h Range for data collection
Reflections collected
Absorption correction
Max. and min. transmission
Goodness of fit
Final R indices [I [ 2r(I)]
R indices (all data)
Largest diff. peak and hole
3239
6640
Multi-scan method
0.9876 and 0.9634
1.084
Multi-scan method
0.9925 and 0.9704
1.062
R1 = 0.0331, wR2 = 0.0761
R1 = 0.0354, wR2 = 0.0798
R1 = 0.0448, wR2 = 0.0970
R1 = 0.0556, wR2 = 0.1042
-3
-3
˚
0.160 and -0.253 e A
˚
0.259 and -0.375 e A
Conclusion
recorded on a Gallenkamp melting point apparatus and are
uncorrected. Ultrasonic mediated reactions were carried
out in Clifton Ultrasonic Bath (2 9 T2A, 300 W, DU-4)
made by Nickel Electro Ltd, Weston-S-Mare Somerset,
England.
This study revealed that the compounds obtained by syn-
ergism of the dihydropyrazolo[4,3-c][1,2]benzothiazine
5,5-dioxide moiety with side chain carboxamides were
found to possess anti-oxidant activities and could be useful
as a template for future development through modification
or derivatization to design more potent biologically active
compounds. The new skeleton may also possess other
biological activities of the parent ring systems.
One-pot synthesis of 3-acetyl-4-hydroxy-2H-1,2-
benzothiazine 1,1-dioxide (1)
Sodium saccharin (10 g, 0.0488 mol) and monochloroac-
etone (4.3 mL, 0.054 mol) were mixed in DMSO and the
reaction mixture was stirred at 110°C for 3 h under inert
atmosphere maintained by nitrogen. A solution of sodium
methoxide in methanol was added to this mixture and
stirring was continued for another half hour. The reaction
mixture was cooled to room temperature and was poured in
ice cold 5 % HCl. The resulting precipitates were col-
lected, washed with excess water and dried. Yield: 80 %,
Brownish amorphous material, m.p:155–156 °C, IR (KBr):
Experimental
Chemistry
All the chemicals were purchased from Alfa Aesar and
were used without purification. However, solvents were
1
purified through distillation. H NMR spectra were recor-
ded on a Bruker DPX-400 instrument at 400 MHz.
Chemical shifts are reported in ppm referenced to the
residual solvent signal. FT-IR spectra were recorded on a
Thermo Nicolet IR 200 spectrometer. Melting points were
3467, 3210, 1598, 1586, 1345, 1187 cm-1 1H NMR
,
(CDCl3, 400 MHz): d 2.22 (3H, s, CCH3), 5.83 (1H, s,
SO2NH), 7.55 (1H, t, J = 7.4 Hz, ArH), 7.67 (1H, t,
J = 7.2 Hz, ArH), 7.98 (2H, t, J = 7.8 Hz, ArH), 14.95
123

Med Chem Res (2013) 22:794–805
799
J = 7.3 Hz, ArH), 7.66 (1H, t, J = 7.2 Hz, ArH), 7.96
(2H, t, J = 7.7 Hz, ArH), 12.22 (1H, s, OH). 13C NMR:
21.5, 38.7, 117.9, 122.5, 123.4, 124.4, 127.2, 129.2, 133.4,
136.7, 167.2. HRMS (ESI) calculated for C11H11NO4S:
254.0487 (M ? H)?, found: 254.0471.
Table 3 Percent radical scavenging activities (% RSA) of com-
pounds 6a–l and 7a–j
Code
name
R
% RSA
(Superoxide (DPPH)
anion)
% RSA
6a
6b
6c
6d
6e
6f
2-Chlorobenzyl
4-Chlorobenzyl
2-Flourobenzyl
4-Flourobenzyl
2-Bromobenzyl
3-Bromobenzyl
2-Methoxybenzyl
3-Methoxybenzyl
4-Methoxybenzyl
2,4-Dimethoxybenzyl
2-Methylbenzyl
4-Methylbenzyl
Phenyl
52.49
47.20
48.48
42.26
64.05
32.54
38.79
25.91
33.11
58.27
81.51
57.8
17.10
16.71
20.16
15.77
21.08
14.13
25.58
16.19
23.69
27.31
15.17
17.85
18.29
21.76
25.37
23.12
22.14
27.64
26.09
26.89
20.18
39.78
Synthesis of 3,4-dimethyl-2,4-dihydropyrazolo[4,3-
c][1,2]benzo thiazine 5,5-dioxide (3)
A mixture of 3-acetyl-4-hydroxy-2-methyl-2H-1,2-benzo-
thiazine 1,1-dioxide (2) (5.0 g, 19.8 mmol) and hydrazine
monohydrate (4.8 mL, 99.0 mmol) was irradiated with
ultrasonic waves for 10 min at 65 °C. Unreacted hydrazine
was removed under vacuum and the residue obtained was
poured over hydrochloric acid (20 mL, 10% v/v). Precipi-
tates obtained were filtered, washed with excess water and
cold ethanol. Brownish-yellow solid, yield; 83 %, m.p.:
230 °C, IR (KBr): 3359, 1599, 1322, 1142 cm-1, 1H NMR
(CDCl3, 400 MHz) d: 2.39 (3H, s, CCH3), 3.06 (3H, s,
NCH3), 7.53 (1H, t, J = 7.4 Hz, ArH), 7.66 (1H, t,
J = 7.2 Hz, ArH), 7.94 (2H, t, J = 7.8 Hz, ArH), 10.09
(1H, s, NH). 13C NMR: 8.6, 38.8, 121.8, 123.3, 124.2, 128.8,
129.3, 131.1, 132.9, 133.2, 134.5. HRMS (ESI) calculated
for C11H11N3O2S: 250.0650 (M ? H)?, found: 250.0650.
6g
6h
6i
6j
6k
6l
7a
7b
7c
7d
7e
7f
28.61
60.95
55.56
47.73
44.10
79.09
47.11
53.75
47.44
78.32
90.8
2-Chlorophenyl
4-Chlorophenyl
2-Flourophenyl
4-Flourophenyl
2-Bromophenyl
3-Bromophenyl
2-Methoxyphenyl
3-Methoxyphenyl
2,4-Dimethoxyphenyl
7g
7h
7i
Synthesis of methyl (3,4-dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2] benzothiazin-2(4H)-yl)acetate (4)
7j
Standard n-Propyl gallate
ND
92.60
A mixture of 3,4-dimethyl-2,4-dihydropyrazolo[4,3-c][1,2]
benzothiazine 5,5-dioxide (3) (5.0 g, 0.020 mol), anhy-
drous potassium carbonate (3.31 g, 0.024 mol), methyl
chloroacetate (2.60 g, 0.024 mol), and acetonitrile (30 mL)
was refluxed for a period of 10 h, followed by the removal
of solvent under vacuum. Residue obtained was washed
with cold water to provide a white crystalline product.
Yield: 80 %, m.p.: 180 °C, 1H NMR (CDCl3, 400 MHz): d:
2.32 (3H, s, CCH3), 3.04 (3H, s, NCH3), 3.79 (3H, s, OCH3),
4.91 (2H, s, NCH2), 7.51 (1H, t, J = 7.7 Hz, ArH), 7.63
(1H, t, J = 7.7 Hz, ArH), 7.90 (1H, d, J = 7.7 Hz, ArH),
7.97 (1H, d, J = 7.7 Hz, ArH). 13C NMR: 8.6, 38.7, 51.3,
52.4, 122.5, 123.4, 124.4, 127.7, 129.2, 131.5, 133.4, 134.4,
136.8, 167.6. HRMS (ESI) calculated for C14H15N3O4S:
322.0862 (M ? H)?, found: 322.0861.
Standard 3-tert-butyl-4-hydroxy anisole ND
ND not determined
(1H, s, OH). 13C NMR: 21.5, 69.2, 122.5, 123.4, 124.4,
127.2, 129.2, 133.4, 136.7, 167.2. HRMS (ESI) calculated
for C10H9NO4S: 240.0331 (M ? H)?, found: 240.0327.
Synthesis of 3-acetyl-4-hydroxy-2-methyl-2H-1,2-
benzothiazine 1,1-dioxide (2)
The reaction was carried out according to our previously
reported method [14]. A mixture of 3-acetyl-4-hydroxy-
2H-1,2-benzothiazine 1,1-dioxide (1) (5.0 g; 20.9 mmol),
aqueous sodium hydroxide (8.4 ml; 20 %), and acetone
(50 ml) was stirred at room temperature for 5 min. After
that dimethyl sulfate (5.9 ml) was added drop wise to the
mixture over a period of 5 min and the contents were
stirred for half an hour. White precipitates were obtained
by careful addition of dilute HCl (20 ml; 5 %) to the
resulting reaction mixture. These precipitates were filtered,
washed with water and dried. Yield: 88 %. White crystal-
line material, m.p: 151–152 °C, IR (KBr): 3470, 1598,
Synthesis of 3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]
benzothiazin-2(4H)-yl acetic acid (5)
Method A A mixture of methyl (3,4-dimethyl-5,5-dioxid-
opyrazolo[4,3-c][1,2] benzothiazin-2(4H)-yl) acetate (4)
(5.0 g, 0.0156 mol), NaOH aqueous solution (2.49 g/
10 mL H2O), and methanol (30 mL) was refluxed for a
period of 30 min. The solvent was removed under vacuum
and residue obtained was acidified with 5 % HCl. The
1586, 1345, 1187 cm-1, H NMR (CDCl3, 400 MHz): d:
2.23 (3H, s, CCH3), 3.09 (3H, s, NCH3), 7.55 (1H, t,
1
123

800
Med Chem Res (2013) 22:794–805
N-(4-chlorobenzyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (6b)
resulting precipitates were washed with cold water to
afford a white crystalline product, yield: 94 %.
Method B A mixture of 3,4-dimethyl-2,4-dihydropy-
razolo[4,3-c][1,2]benzothiazine 5,5-dioxide (3) (5.0 g,
0.020 mol), anhydrous potassium carbonate (6.62 g,
0.048 mol), bromoacetic acid (3.31 g, 0.024 mol), and
anhydrous DMF (15 mL) was stirred for a period of 3.0 h
under nitrogen atmosphere. Contents of the flask were
cooled to room temperature and then poured over ice cold
10 % HCl. White precipitates formed were filtered, washed
with ice cold water and dried. Yield: 75 %, white crystal-
White crystalline powder; m.p.:178 °C; IR (KBr): 3288;
1
1656; 1339; 1158 cm-1; H NMR(DMSO-d6): 2.32 (s, 3H,
CCH3), 2.96(s, 3H, NCH3), 4.32 (d, 2H, J = 5.7 Hz, ArCH2),
4.99(s, 2H, NCH2), 7.36(dd, 2H, J1 = 8.4 Hz, J2 = 26.1 Hz,
ArH), 7.65 (t, 1H, J = 7.8 Hz, ArH), 7.80 (t, 1H, J = 7.8 Hz,
ArH), 7.90 (dd, 2H, J1 = 7.8 Hz, J2 = 14.7 Hz, ArH), 8.85
(brs, 1H, NH); 13C NMR: 8.8, 30.8, 41.1, 52.6, 122.3, 123.4,
124.4, 127.1, 127.9, 128.3, 129.0, 129.2, 131.5, 132.1, 133.3,
134.5, 135.7, 136.4, 138.0, 166.2; HRMS (ESI) calculated for
C20H19ClN4O3S: 431.0945 (M ? H)?, found: 431.0953.
1
line product, H NMR (CDCl3) (400 MHz) d: 2.30 (3H, s,
CCH3), 2.96 (3H, s, NCH3), 5.07 (2H, s, NCH2), 7.61 (1H,
t, J = 7.6 Hz, ArH), 7.76 (1H, t, J = 7.6 Hz, ArH),
7.86(2H, dd, J = 7.8, 16.7 Hz, ArH). 13C NMR: 8.6, 38.7,
52.4, 122.5, 123.4, 124.4, 127.7, 129.2, 131.5, 133.4,
134.4, 136.8, 167.6. HRMS (ESI) calculated for
C13H13N3O4S: 308.0705 (M ? H)?, found: 308.0701.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(2-
fluorobenzyl)acetamide (6c)
White powder; m.p.146 °C; IR (KBr): 3279; 1656; 1334;
1168 cm-1; 1H NMR(DMSO-d6): 2.32 (s, 3H, CCH3), 2.96
(s, 3H, NCH3), 4.37 (d, 2H, J = 5.7 Hz, ArCH2), 5.01 (s,
2H, NCH2),7.18–7.24 (m, 2H, ArH), 7.33–7.42 (m,
2H,ArH), 7.62 (t, 1H, J = 7.8 Hz, ArH), 7.77 (t, 1H,
J = 7.8 Hz, ArH), 7.90 (dd, 2H, J1 = 7.8 Hz,
J2 = 14.7 Hz, ArH), 8.84 (brs, 1H, NH); 13C NMR: 8.8,
30.7, 41.4, 52.5, 115.0, 115.3, 121.3, 122.3, 123.4, 124.4,
125.5, 127.9, 128.2, 129.8, 129.9, 131.4, 133.3, 134.5,
136.4, 166.2; HRMS (ESI) calculated for C20H19FN4O3S:
415.1240 (M ? H)?, found: 415.1224.
Synthesis of N-substitutedbenzyl-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamides (6a–l)
Borane-THF complex (1.1 mmol) was added to the solution
of 3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2] benzo-
thiazin-2(4H)-yl acetic acid (5) (3.3 mmol) in toluene:THF
(1:1) mixture and was added in it. The reaction mixture was
stirred for 30 min at room temperature to generate tria-
cyloxyborane as a reactive intermediate. The suitable ben-
zylamine (3.4 mmol) was then added to the mixture
followed which was reflux for 5 h. After completion of
reaction, as indicated by TLC, solvent was removed under
vacuum and the contents of the flask were dissolved in
EtOAc. The solution was dried (Na2SO4), filtered and ethyl
acetate removed under vacuum. Finally, the product was
purified through column chromatography using EtOAc:
n-hexane in (2:1) as eluent.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(4-
fluorobenzyl)acetamide (6d)
White crystals; m.p.178 °C; IR (KBr): 3269; 1662; 1335;
1
1156 cm-1; H NMR: 2.32 (s, 3H, CCH3), 2.96 (s, 3H,
NCH3), 4.31 (d, 2H, J = 6.0 Hz, ArCH2), 4.98 (s, 2H,
NCH2), 7.15 (t, 2H, J = 8.7 Hz, ArH), 7.32 (dd, 2H,
J1 = 5.7 Hz, J2 = 8.4 Hz, ArH), 7.62 (t, 1H, J = 7.8 Hz,
ArH), 7.77 (t, 1H, J = 7.8 Hz, ArH), 7.87 (dd, 2H,
N-(2-chlorobenzyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (6a)
J1 = 7.8 Hz, J2 = 14.4 Hz, ArH), 8.82 (brs, 1H, NH); 13
C
NMR: 8.8, 30.7, 41.6, 52.6, 114.9, 115.2, 121.2, 122.3,
123.4, 124.3, 125.4, 127.9, 129.0, 129.3, 129.4, 131.5,
133.3, 134.5, 135.1, 166.1; HRMS (ESI) calculated for
C20H19FN4O3S: 415.1240 (M ? H)?, found: 415.1250.
White crystalline solid; m.p.: 161 °C; IR (KBr): 3288;
1659; 1375; 1170 cm-1; 1H NMR (DMSO-d6): 2.34(s, 3H,
CCH3), 2.97(s, 3H, NCH3), 4.41 (d, 2H, J = 5.7 Hz,
ArCH2), 5.03 (s, 2H, NCH2), 7.32–7.36 (m, 2H, ArH),
7.43–7.48 (m, 2H, ArH), 7.62 (t, 1H, J = 7.8 Hz, ArH),
7.77 (t, 1H, J = 7.8 Hz, ArH), 7.91 (dd, 2H, J1 = 7.5 Hz,
J2 = 17.4 Hz, ArH), 8.83 (brs, 1H, NH); 13C NMR: 8.8,
30.9, 41.3, 52.5, 122.3, 123.4, 124.4, 127.2, 127.9, 128.9,
129.0, 129.2, 129.3, 131.5, 132.2, 133.3, 134.5, 135.8,
136.5, 166.3; HRMS (ESI) calculated for C20H19ClN4O3S:
431.0945 (M ? H)?, found: 431.0955.
N-(2-Bromobenzyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (6e)
White powder; m.p.169 °C; IR (KBr): 3282; 1660; 1335;
1
1170 cm-1; H NMR (DMSO-d6): 2.34 (s, 3H, CCH3),
123

Med Chem Res (2013) 22:794–805
801
2.96 (s, 3H, NCH3), 4.37 (d, 2H, J = 5.4 Hz, ArCH2), 5.03
(s, 2H, NCH2), 7.25–7.30 (m, 1H, ArH), 7.40–7.44 (m,
1H,ArH), 7.62 (t, 2H, J = 7.8 Hz, ArH), 7.77 (t, 1H,
J = 7.8 Hz, ArH), 7.87 (dd, 2H, J1 = 7.8 Hz,
J2 = 18.0 Hz, ArH), 8.85 (brs, 1H, NH); 13C NMR: 8.8,
30.7, 42.8, 52.5, 115.2, 122.3, 122.5, 123.4, 124.4, 127.8,
128.7, 129.2, 129.8, 130.4, 131.4, 132.5, 134.6, 137.3,
141.8, 166.3; HRMS (ESI) calculated for C20H19BrN4O3S:
475.0439 (M ? H)?, found: 475.0427.
2H, J1 = 7.8 Hz, J2 = 16.5 Hz, ArH), 8.81 (brs, 1H, NH);
13C NMR: 8.8, 30.7, 42.2, 52.6, 55.0, 112.3, 113.0, 119.5,
122.3, 123.4, 124.3, 127.9, 128.8, 129.0, 129.4, 131.5,
133.3, 134.5, 136.4, 159.3, 166.1; HRMS (ESI) calculated
for C21H22N4O4S: 427.1440 (M ? H)?, found: 427.1439.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(4-
methoxybenzyl)acetamide (6i)
N-(3-bromobenzyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (6f)
Dirty yellow powder; m.p.178 °C; IR (KBr): 3341; 1658;
1337; 1155 cm-1 1H NMR (DMSO-d6): 2.33 (s, 3H,
;
CCH3), 2.97 (s, 3H, NCH3), 3.74 (s, 3H, OCH3), 4.26 (d,
2H, J = 6.0 Hz, ArCH2), 4.96 (s, 2H, NCH2), 6.89 (d, 2H,
J = 8.7 Hz, ArH), 7.22 (d, 2H, J = 8.7 Hz, ArH), 7.62 (t,
1H, J = 7.8 Hz, ArH), 7.77 (t, 1H, J = 7.8 Hz, ArH), 7.88
(dd, 2H, J1 = 7.8 Hz, J2 = 14.7 Hz, ArH), 8.73 (brs, 1H,
NH); 13C NMR: 8.8, 30.7, 41.8, 52.6, 55.1, 113.8, 114.0,
122.3, 123.4, 124.3, 127.6, 127.9, 128.8, 129.0, 130.8,
131.4, 133.3, 134.5, 136.4, 158.3, 165.9; HRMS (ESI)
calculated for C21H22N4O4S: 427.1440 (M ? H)?, found:
427.1432.
White powder; m.p.123 °C; IR (KBr): 3289; 1655; 1335;
1
1156 cm-1; H NMR(DMSO-d6): 2.33 (s, 3H, C–CH3),
2.96 (s, 3H, N–CH3), 4.34 (d, 2H, J = 6.0 Hz, Ar–CH2),
5.00 (s, 2H, N–CH2), 7.31 (d, 2H, J = 5.4 Hz, ArH), 7.47–
7.52 (m, 2H, ArH), 7.62 (t, 1H, J = 7.8 Hz, ArH), 7.77 (t,
1H, J = 7.8 Hz, ArH), 7.91 (dd, 2H, J1 = 7.8 Hz,
J2 = 18.9 Hz, ArH), 8.86 (brs, 1H, NH); 13C NMR: 8.8,
30.7, 41.7, 52.6, 121.7, 122.3, 123.4, 124.3, 126.4, 127.9,
129.0, 129.8, 129.9, 130.5, 131.5, 133.3, 134.5, 136.5,
141.8, 166.3; HRMS (ESI) calculated for C20H19BrN4O3S:
475. 0439 (M ? H)?, found: 475.0428.
N-(2,4-dimethoxybenzyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (6j)
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(2-
methoxybenzyl)acetamide (6g)
White powder; m.p. 201 °C; IR (KBr): 3285; 1657; 1337;
1
1156 cm-1; H NMR (DMSO-d6): 2.09 (s, 3H, CCH3),
2.96 (s, 3H, NCH3), 3.75 (s, 3H, OCH3), 3.80 (s, 3H,
OCH3), 4.21 (d, 2H, J = 5.4 Hz, ArCH2), 4.96 (s, 2H,
NCH2), 6.49 (dd, 1H, J1 = 2.2 Hz, J2 = 8.2 Hz, ArH),
6.57 (d, 1H, J = 2.1 Hz, ArH), 7.13 (d, 1H, J = 8.4 Hz,
ArH), 7.62 (t, 1H, J = 7.5 Hz, ArH), 7.77 (t, 1H,
J = 7.5 Hz, ArH), 7.90 (dd, 2H, J1 = 7.8 Hz,
J2 = 14.4 Hz, ArH), 8.52 (brs, 1H, NH); 13C NMR: 8.8,
30.7, 37.3, 52.5, 55.2, 55.4, 98.3, 118.3, 122.3, 123.4,
124.4, 127.9, 129.0, 129.3, 130.0, 131.4, 133.3, 134.5,
136.3, 157.8, 159.9, 166.2; HRMS (ESI) calculated for
C22H24N4O5S: 457.1546 (M ? H)?, found: 457.1540.
White powder; m.p.121 °C; IR (KBr): 3261; 1661; 1335;
1
1156 cm-1; H NMR (DMSO-d6): 2.34 (s, 3H, CCH3),
2.96 (s, 3H, NCH3), 3.81 (s, 3H, OCH3), 4.30 (d, 2H,
J = 5.7 Hz, ArCH2), 4.99 (s, 2H, NCH2), 6.91 (t, 1H,
J = 7.5 Hz, ArH), 6.99 (d, 1H, J = 8.1 Hz, ArH), 7.24–
7.30 (m, 2H, ArH), 7.62 (t, 1H, J = 7.8 Hz, ArH), 7.77 (t,
1H, J = 7.8 Hz, ArH), 7.90 (dd, 2H, J1 = 7.8 Hz,
J2 = 16.5 Hz, ArH), 8.56 (brs, 1H, NH); 13C NMR: 8.8,
30.7, 37.6, 52.6, 55.3, 110.6, 120.1, 122.3, 123.4, 124.3,
126.1, 127.9, 128.2, 128.4, 129.0, 131.4, 133.3, 134.5,
136.4, 156.8, 166.1; HRMS (ESI) calculated for
C21H22N4O4S: 427.1440 (M ? H)?, found: 427.1435.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(2-
methylbenzyl)acetamide (6k)
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(3-
methoxybenzyl)acetamide (6h)
White powder; m.p.190 °C; IR (KBr): 3292; 1661; 1335;
1
1156 cm-1; H NMR (DMSO-d6): 2.34 (s, 3H, ArCH3),
White powder; m.p.152 °C; IR (KBr): 3286; 1662; 1337;
2.35 (s, 3H, CCH3), 2.98 (s, 3H, NCH3), 4.30 (d, 2H,
J = 5.7 Hz, ArCH2), 4.99 (s, 2H, NCH2), 6.92 (t, 1H,
J = 7.5 Hz, ArH), 7.04 (d, 1H, J = 8.0 Hz, ArH), 7.25–
7.30 (m, 2H, ArH), 7.64 (t, 1H, J = 7.8 Hz, ArH), 7.79 (t,
1H, J = 7.8 Hz, ArH), 7.89–7.96 (dd, 2H, J1 = 7.8 Hz,
J2 = 16.5 Hz, ArH), 8.59 (brs, 1H, NH); 13C NMR: 8.8,
1
1168 cm-1; H NMR (DMSO-d6): 2.32 (s, 3H, CCH3),
2.97 (s, 3H, NCH3), 3.75 (s, 3H, OCH3), 4.31 (d, 2H,
J = 6.0 Hz, ArCH2), 4.99 (s, 2H, NCH2), 6.85–6.94 (m,
3H, ArH), 7.24 (t, 1H, J = 8.1 Hz, ArH), 7.62 (t, 1H,
J = 7.8 Hz, ArH), 7.77 (t, 1H, J = 7.8 Hz, ArH), 7.88 (dd,
123

802
Med Chem Res (2013) 22:794–805
21.2, 30.6, 42.2, 51.9, 115.1, 121.9, 122.5, 123.4, 124.4,
127.8, 128.8, 129.2, 129.9, 130.4, 131.1, 132.5, 134.1,
136.8, 141.2, 165.8; HRMS (ESI) calculated for
C21H22N4O3S: 411.1491(M ? H)?, found: 411.1491.
J = 7.8 Hz, ArH), 7.31 (t, 2H, J = 7.8 Hz, ArH), 7.60–
7.67 (m, 3H, ArH), 7.79 (t, 1H, J = 7.8 Hz, ArH), 7.88
(dd, 2H, J1 = 7.8 Hz, J2 = 16.2 Hz, ArH), 10.49 (s, 1H,
NH); 13C NMR: 8.9, 30.7, 53.1, 119.2, 122.3, 122.5, 123.4,
123.8, 124.4, 127.9, 128.9, 129.1, 129.8, 131.5, 133.3,
134.7, 136.6, 138.5, 164.8; HRMS (ESI) calculated for
C19H18N4O3S: 383.1178 (M ? H)?, found: 383.1172.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(4-
methylbenzyl)acetamide (6l)
N-(2-Chlorophenyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (7b)
White crystalline solid; m.p.150 °C; IR (KBr): 3281; 1656;
1336; 1157 cm-1 1H NMR (DMSO-d6): 2.31 (s, 3H,
;
ArCH3), 2.32 (s, 3H, CCH3), 2.98 (s, 3H, NCH3), 4.33 (d,
2H, J = 6.0 Hz, ArCH2), 4.95 (s, 2H, NCH2), 7.28 (t, 2H,
J = 8.7 Hz, ArH), 7.32 (dd, 2H, J1 = 5.7 Hz,
J2 = 8.4 Hz, ArH), 7.63 (t, 1H, J = 7.8 Hz, ArH), 7.72 (t,
1H, J = 7.8 Hz, ArH), 7.87 (dd, 2H, J1 = 7.8 Hz,
J2 = 14.4 Hz, ArH), 8.79 (brs, 1H, NH); 13C NMR: 8.7,
24.8, 30.4, 41.8, 51.9, 115.2, 122.4, 122.7, 123.3, 124.6,
127.3, 128.8, 129.2, 129.9, 130.5, 131.2, 132.1, 133.9,
136.7, 141.4, 165.3; HRMS (ESI) calculated for
C21H22N4O3S: 411.1491 (M ? H)?, found: 411.1475.
White powder; m.p. 217 °C; IR (KBr): 3282; 1660; 1335;
1
1170 cm-1; H NMR (DMSO-d6): 2.33 (s, 3H, CCH3),
2.96 (s, 3H, NCH3), 5.07 (s, 2H, NCH2), 7.27–7.31 (m, 1H,
ArH), 7.35–7,41 (m, 2H, ArH), 7.57 (t, 2H, J = 7.8 Hz,
ArH), 7.71 (t, 1H, J = 7.8 Hz, ArH), 7.82 (dd, 2H,
J1 = 7.8 Hz, J2 = 18.0 Hz, ArH), 10.43 (s, 1H, NH); 13C
NMR: 8.8, 30.7, 52.5, 115.2, 122.3, 122.5, 123.4, 124.4,
127.8, 128.7, 129.2, 129.8, 130.4, 131.4, 132.5, 134.6,
137.3, 141.8, 166.3; HRMS (ESI) calculated for
C19H17ClN4O3S: 417.0788 (M ? H)?, found: 417.0775.
Synthesis of a series of 2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-yl)-N-
phenyl acetamides (7a–j)
N-(4-chlorophenyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (7c)
Procedure Thionyl chloride was added to the solution of
3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-
2(4H)-yl acetic acid (5) (3.3 mmol) in toluene under inert
atmosphere. The reaction mixture was refluxed for 30 min
to generate the respective acyl halide as a reactive inter-
mediate. Unreacted thionyl chloride was removed from the
reaction mixture by evaporation under a continuous stream
of nitrogen gas. Respective anilines and triethyl amine
were then added to the mixture was refluxed for 1 h along
with continuous monitoring by mass spectrometry. Subse-
quently, the solvent was removed under vacuum and the
contents of the flask were dissolved in EtOAc. In order to
remove the impurities, the mixture was consecutively
washed with excess water, 1.0 N HCl and saturated
NaHCO3 solution. The solution was dried (Na2SO4), fil-
tered and the ethyl acetate removed in vacuo. Finally the
product was purified through column chromatography
using EtOAc: n-Hexane (2:1) as eluent.
White crystalline powder; m.p. 227 °C; IR (KBr): 3288;
1656; 1339; 1158 cm-1; 1H NMR (DMSO-d6): 2.36 (s, 3H,
CCH3), 2.98 (s, 3H, NCH3), 5.15 (s, 2H, NCH2), 7.38 (d,
2H, J = 7.8 Hz, ArH), 7.62 (t, 3H, J = 8.4 Hz, ArH), 7.77
(t, 1H, J = 7.8 Hz, ArH), 7.92–7.96 (dd, 2H, J1 = 8.1 Hz,
J2 = 15.0 Hz, ArH), 10.64 (s, 1H, NH); 13C NMR: 8.8,
30.8, 53.1, 120.8, 122.1, 123.3, 124.4, 127.8, 127.9, 128.8,
129.1, 129.2, 129.4, 131.5, 133.3, 134.8, 135.7, 137.5,
165.0; HRMS (ESI) calculated for C19H17ClN4O3S:
417.0788 (M ? H)?, found: 417.0790.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(2-
fluorophenyl)acetamide (7d)
Light yellow; m.p. 222 °C; IR (KBr): 3282; 1660; 1335;
1
1170 cm-1; H NMR (DMSO-d6): 2.33 (s, 3H, CCH3),
2.97 (s, 3H, NCH3), 5.06 (s, 2H, NCH2), 7.21–7.24 (m, 1H,
ArH), 7.29–7.35 (m, 2H, ArH), 7.47 (t, 2H, J = 7.8 Hz,
ArH), 7.65 (t, 1H, J = 7.8 Hz, ArH), 7.79 (dd, 2H,
J1 = 7.8 Hz, J2 = 18.0 Hz, ArH), 10.41 (s, 1H, NH); 13C
NMR: 8.8, 30.6, 42.4, 51.8, 116.1, 121.2, 122.7, 123.7,
124.1, 127.0, 128.1, 129.5, 129.9, 130.4, 131.0, 131.8,
133.1, 137.5, 141.1, 165.9; HRMS (ESI) calculated for
C19H17FN4O3S: 401.1084 (M ? H)?, found: 401.1086.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-phenylacetamide (7a)
White powder; m.p. 227 °C; IR (KBr): 3282; 1660; 1335;
1
1170 cm-1; H NMR (DMSO-d6): 2.37 (s, 3H, CCH3),
2.98 (s, 3H, NCH3), 5.15 (s, 2H, NCH2), 7.09 (t, 1H,
123

Med Chem Res (2013) 22:794–805
803
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(4-
fluorophenyl)acetamide (7e)
2.98 (s, 3H, NCH3), 3.86 (s, 3H, OCH3), 5.26 (s, 2H,
NCH2), 6.91 (t, 1H, J = 7.5 Hz, ArH), 7.09 (t, 2H,
J = 6.9 Hz, ArH), 7.65 (t, 1H, J = 7.5 Hz, ArH), 7.80 (t,
1H, J = 7.5 Hz, ArH), 7.89 (d, 1H, J = 7.8 Hz, ArH),
7.98 (t, 2H, J = 7.2 Hz, ArH), 9.65 (s, 1H, NH); 13C
NMR: 8.8, 30.7, 53.1, 55.7, 111.2, 120.3, 121.5, 122.4,
123.5, 124.4, 124.8, 126.6, 127.8, 129.1, 131.5, 133.3,
134.7, 136.6, 149.4, 165.1; HRMS (ESI) calculated for
C20H20N4O4S: 413.1284 (M ? H)?, found: 413.1281.
White powder; m.p. 237 °C; IR (KBr): 3288; 1656; 1339;
1
1158 cm-1; H NMR: 2.37 (s, 3H, CCH3), 2.97 (s, 3H,
NCH3), 5.10 (s, 2H, NCH2), 7.19 (d, 2H, J = 7.8 Hz, ArH),
7.62 (d, 2H, J = 7.8 Hz, ArH), 7.77 (t, 2H, J = 7.8 Hz,
ArH), 7.92 (dd, 2H, J1 = 8.1 Hz, J2 = 15.5 Hz, ArH),
10.57 (s, 1H, NH); 13C NMR: 8.8, 30.7, 52.6, 114.9, 115.2,
121.2, 122.3, 123.4, 124.3, 125.4, 127.9, 129.0, 129.4,
131.5, 133.3, 134.5, 135.1, 136.3, 166.1; HRMS (ESI)
calculated for C19H17FN4O3S: 401.1084 (M ? H)?, found:
401.1081.
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(3-
methoxyphenyl)acetamide (7i)
White powder; m.p. 185 °C; IR (KBr): 3286; 1662; 1337;
1
1168 cm-1; H NMR (DMSO-d6): 2.36 (s, 3H, CCH3),
N-(2-bromophenyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (7f)
2.97 (s, 3H, NCH3), 3.75 (s, 3H, OCH3), 5.14 (s, 2H,
NCH2), 6.87 (d, 1H, J = 7.5 Hz, ArH), 7.12 (t, 2H,
J = 7.8 Hz, ArH), 7.25 (t, 1H, J = 8.1 Hz, ArH), 7.54 (t,
1H, J = 7.8 Hz, ArH), 7.71 (t, 1H, J = 7.8 Hz, ArH), 7.82
(dd, 2H, J1 = 7.8 Hz, J2 = 15.5 Hz, ArH), 10.41 (s, 1H,
NH); 13C NMR: 8.8, 30.7, 52.7, 55.1, 107.3, 113.4, 120.5,
122.1, 123.4, 124.1, 126.8, 128.8, 129.2, 130.1, 131.2,
132.7, 134.8, 135.9, 159.7, 166.3; HRMS (ESI) calculated
for C20H20N4O4S: 413.1284 (M ? H)?, found: 413.1278.
Off white powder; m.p. 205 °C; IR (KBr): 3276; 1671;
1337; 1168 cm-1 1H NMR (DMSO-d6): 2.38 (s, 3H,
;
CCH3), 2.97 (s, 3H, NCH3), 5.25 (s, 2H, NCH2), 7.14 (t,
1H, J = 7.8 Hz, ArH), 7.36 (t, 1H, J = 7.8 Hz, ArH), 7.66
(t, 3H, J = 7.5 Hz, ArH), 7.78 (t, 1H, J = 7.5 Hz, ArH),
7.89 (d, 1H, J = 7.8 Hz, ArH), 7.96 (d, 1H, J = 7.8 Hz,
ArH), 9.92 (s, 1H, NH); 13C NMR: 8.8, 30.7, 52.9, 122.5,
123.5, 124.4, 127.3, 127.4, 127.8, 128.1, 129.1, 129.8,
131.5, 132.8, 133.3, 134.7, 135.5, 136.6, 165.4; HRMS
(ESI) calculated for C19H17BrN4O3S: 461.0283 (M ? H)?,
found: 461.0285.
N-(2,4-dimethoxyphenyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (7j)
White powder; m.p. 203 °C; IR (KBr): 3277; 1657; 1343;
1
1147 cm-1; H NMR (DMSO-d6): 2.42 (s, 3H, CCH3),
N-(3-bromophenyl)-2-(3,4-dimethyl-5,5-
dioxidopyrazolo[4,3-c][1,2]benzothiazin-2(4H)-
yl)acetamide (7g)
3.03 (s, 3H, NCH3), 3.80 (s, 3H, OCH3), 3.90 (s, 3H,
OCH3), 5.26 (s, 2H, NCH2), 6.52 (d, 1H, J = 9.0 Hz,
ArH), 6.70 (d, 1H, J = 2.4 Hz, ArH), 7.68 (t, 1H,
J = 7.8 Hz, ArH), 7.80 (t, 2H, J = 9.0 Hz, ArH), 7.97 (dd,
2H, J1 = 7.8 Hz, J2 = 19.8 Hz, ArH), 9.59 (s, 1H, NH)
13C NMR: 8.8, 30.7, 37.3, 52.9, 55.3, 55.8, 98.9, 104.1,
119.7, 122.3, 123.1, 123.4, 124.4, 127.9, 129.1, 131.5,
133.3, 136.5, 151.2, 156.9, 164.7; HRMS (ESI) calculated
for C21H22N4O5S: 443.1389 (M ? H)?, found: 443.1377.
Dirty yellow; m.p. 204 °C; IR (KBr): 3280; 1651; 1337;
1
1150 cm-1; H NMR (DMSO-d6): 2.41 (s, 3H, CCH3),
3.01 (s, 3H, NCH3), 5.25 (s, 2H, NCH2), 7.28–7.32 (m, 2H,
ArH), 7.48 (d, 1H, J = 7.2 Hz, ArH), 7.63 (t, 1H,
J = 7.5 Hz, ArH), 7.77 (t, 1H, J = 7.5 Hz, ArH), 7.88 (t,
2H, J = 7.2 Hz, ArH), 7.96 (d, 1H, J = 3.9 Hz, ArH)
10.69 (s, 1H, NH); 13C NMR: 8.8, 30.7, 52.6, 121.7, 122.3,
123.4, 124.3, 126.4, 127.9, 129.0, 129.8, 129.9, 130.5,
131.5, 133.3, 134.5, 136.5, 141.8, 165.3; HRMS (ESI)
calculated for C19H17BrN4O3S: 461.0283 (M ? H)?,
found: 461.0278.
X-ray crystallography
The crystals of 6d and 6l suitable for X-ray crystallo-
graphic study were coated with Paratone 8277 oil (Exxon)
and mounted on glass fibers. All measurements were made
on a Bruker APEX2 CCD installed on a Nonius Kappa
Goniometer diffractometer with graphite monochromated
Mo-Ka radiation. The data were collected (Otwinowski
and Minor, 1997) using x and u scans. The data were
corrected for Lorentz and polarization effects and for
absorption using multi-scan method (Hooft, 1998). The
2-(3,4-Dimethyl-5,5-dioxidopyrazolo[4,3-
c][1,2]benzothiazin-2(4H)-yl)-N-(2-
methoxyphenyl)acetamide (7h)
White powder; m.p. 189 °C; IR (KBr): 3259; 1671; 1337;
1
1157 cm-1; H NMR (DMSO-d6): 2.36 (s, 3H, CCH3),
123

804
Med Chem Res (2013) 22:794–805
structures were solved by the direct methods (Altomare
et al., 1993) and expanded using Fourier techniques
(Beurskens et al., 1994). The non-hydrogen atoms were
refined anisotropically (Sheldrick, 2008). The H-atoms
were included at geometrically idealized positions and
were not refined. The weighting schemes were based on
counting statistics and the final difference Fourier maps
were essentially featureless. Details of crystal data and
structure refinement have been provided in Table 1. The
figures were plotted with the aid of ORTEP-3 for Windows
(Farrugia, 1997). The crystals of 6d were racemic twins
with a BASF parameter = 0.54(8). Therefore, an absolute
configuration of 6d could not be determined. Crystallo-
graphic data have been deposited with the Cambridge
Crystallographic Data Center (CCDC deposition numbers
are: 6d = 817158; 6l = 817157.
butyl-4-hydroxy anisole. The results are presented in
Table 3.
Acknowledgments The authors (MA and HLS) are grateful to
Higher Education Commission, Pakistan for financial assistance and
for funding the research visit of MA to the University of Manchester.
We are also thankful to School of Chemistry, University of Man-
chester, Manchester, UK, and International Centre for Chemical and
Biological Sciences, HEJ Research Institute of Chemistry, University
of Karachi, Karachi and Institute of Chemistry, University of the
Punjab for research facilities, spectral measurements and antioxidant
studies.
References
Ahmad M, Siddiqui HL, Zia-ur-Rehman M, Parvez M (2010) Anti-
oxidant and antibacterial activities of novel N0-arylmethylidene-
2-(3,4-dimethyl-5,5-dioxidopyrazolo[4,3-c][1,2]benzothiazin-2
(4H)-yl) acetohydrazides. Eur J Med Chem 45:698–704
Ahmad N, Rehman MZ, Siddiqui HL, Fasih Ullah M, Parvez M (2011)
Microwave assisted synthesis and structure–activity relationship
of 4-hydroxy-N0-[1-phenylethylidene]-2H/2-methyl-1,2-benzothia
zine-3-carbohydrazide 1,1-dioxides as anti-microbial agents. Eur J
Med Chem 46:2368–2377
Antioxidant studies
Superoxide anion radical scavenging activity
Altomare A, Cascarano G, Giacovazzo C, Guagliardi A (1993)
Completion and refinement of crystal structures with SIR92.
JAppl Cryst 26:343–350
Compounds were assessed by the method reported in lit-
erature (Gaulejac et al., 1999). The reaction mixture
comprises of 40 lL of 280 lM b-nicotinamide adenine
dinucleotide reduced form (NADH), 40 lL of 80 lM nitro
blue tetrazolium (NBT), 20 lL of 8 lM phenazine
methosulphate (PMS), 10 lL of 1 mM sample and 90 lL
of 0.1 M phosphate buffer (pH 7.4). The reagents were
prepared in buffer and the sample in DMSO. The reactions
were performed in 96-well microtitre plate at room tem-
perature and absorbance was measured at 560 nm. The
formation of superoxide was monitored by measuring the
formation of water soluble blue formazan dye. A lower
absorbance of reaction mixture indicates the higher scav-
enging activity of sample. Percent Radical Scavenging
Activity was determined in comparison with control using
the formula given below. The results are presented in
Table 2.
Baraldi PG, Manfredini S, Romagnoli R, Stevanato L, Zaid AN,
Manservigi R (1998) Synthesis and anti-HSV-1 activity of 6
substituted pyrazolo[3,4-d]pyridazin-7-one nucleosides. Nucleo-
sides Nucleotides 17(12):2165–2171
Beurskens PT, Admiraal G, Beurskens G, Bosman WP, de Gelder R,
Israel R, Smits JMM (1994) The DIRDIF-94 program system.
Technical Report of the Crystallography Laboratory, University
of Nijmegen, Nijmegen
Boger DL, Miyazaki S, Kim SH, Wu JH, Castle SL, Loiseleur O, Jin
Q (1999) Total synthesis of the vancomycin aglycon. J Am
Chem Soc 121:10004–10011
Braughler JM, Duncan LA, Chase RL (1986) The involvement of iron
in lipid peroxidation. Importance of ferric to ferrous ratios in
initiation. J Biol Chem 261:10282–10289
Bruno O, Bondavalli F, Ranise A, Schenone P, Losasso C, Cilenti L,
Matera C, Marmo E (1990) 3,5-Diphenyl-1H-pyrazole deriva-
tives. V–1-acetyl-4-hydroxy-3,5-diphenyl-2-pyrazoline esters,
4-hydroxy-3,5-diphenyl-1H-pyrazole esters and N-substituted
4-(3-amino-2-hydroxy-1-propoxy)-1-methyl-3,5-diphenyl-1H-pyr-
azoles with antiarrhythmic, sedative and platelet antiaggregating
activities. Farmaco 45(2):147–166
%RSA ¼ 100 ꢁ ðOD test compound=OD controlÞ ꢂ 100
Cottineau B, Toto P, Marot C, Pipaud A, Chenault J (2002) Synthesis
and hypoglycemic evaluation of substituted pyrazole-4-carbox-
ylic acids. Bioorg Med Chem Lett 12:2105–2108
Cremer D, Pople JA (1975) General definition of ring puckering
coordinates. J Am Chem Soc 97:1354–1358
DPPH radical scavenging activity
Farrugia LJ (1997) ORTEP-3 for windows—a version of ORTEP-III
with a graphical user interface (GUI). J Appl Cryst 30:565
Foroumadi A, Samzadeh-Kermani A, Emami S, Dehghan G, Sorkhi M,
Arabsorkhi F, Heidari MR, Abdollahi M, Shafiee A (2007)
Synthesis and antioxidant properties of substituted 3-benzylidene-
7-alkoxychroman-4-ones. Bioorg Med Chem Lett 17:6764–6769
Gaulejac NSC, Glories Y, Vivas N (1999) Free radical scavenging
effect of anthocyanins in red wines. Food Res Int 32:327–333
Giuseppe M, Arnaldo F, Patrizia T (1987) Derivatives of pyrido-
benzothiazine with high anti-microbial activity. US Patent
4,668,784, 26 May 1987
Compounds were assessed for DPPH radical scavenging
activity using the procedure of Shaheen et al. (2005). The
reaction mixture containing 5 lL of test sample (0.5 mM
in DMSO) and 95 lL of DPPH (300 mmol in EtOH) was
taken in a 96-well micro titer plate and incubated at 37 °C
for 30 min. The absorbance was measured at 515 nm.
Percent radical scavenging activity was determined by
comparison with DMSO containing control, i.e., 3-tert-
123

Med Chem Res (2013) 22:794–805
805
Gutteridge JMC (1993) Free radicals in disease processes:
a
Riyadh SM (2011) Enaminones as building blocks for the synthesis of
substituted pyrazoles with antitumor and antimicrobial activities.
Molecules 16:1834–1853
Shaheen F, Ahmad M, Khan MTH, Jalil S, Ejaz A, Sultankhodjaev
MN, Arfan M, Choudhary MI, Rahman A (2005) Alkaloids of
aconitum laeve and their anti-inflammatory, antioxidant and
tyrosinase inhibition activities. Phytochemistry 66:935–940
Sheehan JC, Hess GP (1955) A new method of forming peptide
bonds. J Am Chem Soc 77:1067–1068
compilation of cause and consequence. Free Radic Res Commun
19:141–158
Hooft R (1998) Collect. Nonius BV, Delft
Huang Z, Reilly JR, Buckle RN (2007) An efficient synthesis of
amides and esters via triacyloxyboranes. Synlett 7:1026–1030
Ikeda T, Kakegawa H, Miyataka H, Matsumoto H, Satoht T (1992)
Anti-allergic and anti-inflammatory actions of 20-(tetrazole-5-yl)-
4-hydroxy-2-methyl-2H-1,2-benzothiazine-3-carboxanilide 1,1-
dioxide. Bioorg Med Chem Lett 2:709–714
Iovu M, Zalaru C, Dumitrascu F, Draghici C, Moraru M, Criste E
(2003) New substituted 2-(pyrazol-1-yl)-dialkylacetanilides with
potential local anesthetic and antiarrhythmic action. Part II. IL
Farmaco 58:301–307
Krapcho J, Somerset NJ (1968) Therapeutically active benzothia-
zines. US Patent 3, 401,166, 10 Sept 1968
Krapcho J, Somerset NJ (1969) Hydroxyalkylene-substituted ben-
zoxazines and benzothiazines. US Patent 3,459,748, 5 Aug 1969
Krapcho J, Somerset NJ (1969) Substituted benzoxazines and
benzothiazines. US Patent 3,455,915, 15 July 1969
Lomabardino JG, Wiseman ED (1972) Sudoxicam and related
N-heterocyclic carboxamides of 4-hydroxy-2H-1,2-benzothi-
azine 1,1-dioxide. Potent nonsteroidal antiinflammatory agents.
J Med Chem 15:848–849
Sheldrick GM (2008) A short history of SHELX. Acta Cryst
A64:112–122
Silverstein FE, Faich G, Goldstein JL, Simon LS, Pincus T, Whelton
A, Makuch R, Eisen G, Agrawal NM, Stenson WF, Burr AM,
Zhao WW, Kent JD, Lefkowith JB, Verburg KM, Geis GS
(2000) Gastrointestinal toxicity with celecoxib vs nonsteroidal
anti-inflammatory drugs for osteoarthritis and rheumatoid arthri-
tis: the CLASS study: a randomized controlled trial. J Am Med
Assoc 284:1247–1255
Smith SR, Denhardt G, Terminelli C (2001) The anti-inflammatory
activities of cannabinoid receptor ligands in mouse peritonitis
models. Eur J Pharmacol 432:107–119
Turck D, Busch U, Heinzel G, Narjes H, Nehmiz G (1995) Effect of
food on the pharmacokinetics of meloxicam after oral admin-
istration. Clin Drug Invest 9:270–276
Lomabardino JG, Wiseman EH, McLamore WM (1971) Synthesis and
antiinflammatory activity of some 3-carboxamides of 2-alkyl-4-
hydroxy-2H-1,2-benzothiazine 1,1-dioxide. J Med Chem 14:
1171–1175
Lombardino JG, Wiseman EH, Chiaini J (1973) Potent antiinflam-
matory N-heterocyclic 3-carboxamides of 4-hydroxy-2-methyl-
2H-1,2-benzothiazine 1,1-dioxide. J Med Chem 16:493–496
Otwinowski Z, Minor W (1997) Processing of X-ray diffraction data
collected in oscillation mode. Methods Enzymol 276:307–326
Zia-ur-Rehman M, Choudary JA, Ahmad S, Siddiqui HL (2006)
Synthesis of potential biologically active 1,2-benzothiazin-3-yl-
quinazolin-4(3H)-ones. Chem Pharm Bull 54:1175–1178
Zinnes H, Lindo NA, Sircar JC, Schwartz ML, Shavel J Jr (1973) 1,2-
Benzothiazines. 6. 3-Carbamoyl-4-hydroxy-2H-1,2-benzothi-
azine 1,1-dioxides as antiinflammatory agents. J Med Chem
16:44–48
123