Synthesis, pharmacological evaluation and docking studies of N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs as COX-2 inhibitors

Article abstract of DOI:10.1016/j.bmcl.2011.12.062

The existing NSAIDs having number of toxicities emphasises the need for discovery of new non-toxic anti-inflammatory agents. In this Letter, we present the simple two step chemical synthesis, in vivo pharmacological screening and docking study of few N-(b

Full text of DOI:10.1016/j.bmcl.2011.12.062

Bioorganic & Medicinal Chemistry Letters 22 (2012) 820–823
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis, pharmacological evaluation and docking studies
of N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs
as COX-2 inhibitors
Nulgumnalli Manjunathaiah Raghavendra a, , Aitha Jyothsna a, Alapati Venkateswara Rao b,
⇑
C.V.S. Subrahmanyam a
a Department of Pharmaceutical Chemistry, Gokaraju Rangaraju College of Pharmacy, Osmania University, Hyderabad 500 090, Andhra Pradesh, India
b Department of Pharmacology, Gokaraju Rangaraju College of Pharmacy, Osmania University, Hyderabad 500 090, Andhra Pradesh, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The existing NSAIDs having number of toxicities emphasises the need for discovery of new non-toxic
anti-inflammatory agents. In this Letter, we present the simple two step chemical synthesis, in vivo phar-
macological screening and docking study of few N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide
analogs. Different amino benzothiazoles were chloroacetylated and further reacted with substituted
piperazines in presence of a base to get N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs
(A1–C4). These compounds were evaluated for anti-inflammatory activity by carragenan induced paw
oedema method. Promising compounds were screened for toxicity by evaluating the ulcerogenic poten-
tial. Molecular docking experiments were carried out against COX-2 enzyme using Surflex-Dock GeomX
programme of Sybyl software on Dell T-1500 workstation to confirm the mechanism of action of active
compounds among the series. In silico study reveal the binding interactions of N-(benzo[d]thiazol-2-yl)-
2-(piperazin-1-yl)acetamide analogs with COX-2 protein and is in agreement with the in vivo anti-
inflammatory activity.
Received 13 October 2011
Revised 28 November 2011
Accepted 12 December 2011
Available online 16 December 2011
Keywords:
Anti-inflammatory activity
Docking studies
Ulcerogenic activity
2-Amino benzothiazole
Piperazine
Computer aided drug design
Ó 2011 Elsevier Ltd. All rights reserved.
Non-steroidal anti-inflammatory drugs (NSAIDs) are one
amongst the most frequently prescribed classes of drugs. Both their
benefits and side effects arise due to inhibition of cycloxygenase
(COX) of which there are two isoenzymes, COX-1 and COX-2. Both
COX isoenzymes have a hydrophobic tunnel, through which the sub-
strate accesses the active site. The tunnel is larger in the COX-2 iso-
enzyme with a side pocket, a property exploited in the development
of specific COX-2 inhibitors.1 The premise of the initial, COX-2
hypothesis was that the gastrointestinal side effects arise due to
inhibition of COX-1, whereas their anti-inflammatory or analgesic
properties were COX-2 mediated.2,3 For the past 6–7 years, reports
mentioning risk of cardiovascular events with selective COX-2
inhibitors are increasing. In an early study of major gastrointestinal
events, an unexpected fivefold increase in the risk of acute myocar-
dial infarction (AMI) with rofecoxib was observed when compared
with naproxen.4 At the time, many suggested and aggressively pur-
sued the hypothesis that the increased frequency of events was a
spurious observation not due to any prothrombotic effects of rofec-
oxib, butthe cardioprotective properties ofnaproxen. However, sub-
sequent placebo-controlled studies of both rofecoxib, and celecoxib
in chemoprevention also reported an approximate twofold increase
in cardiovascular events with both drugs.5,6 Thus, there remains a
compelling need for effective NSAIDs with an improved safety
profile.
Substitutions at 2-position of benzothiazole have emerged in its
usage as a core structure in the diversified therapeutic applica-
tions.7–13 The studies of structure–activity relationship interest-
ingly reveal that change of the structure of substituent group at
C-2 position commonly results in the change of its bioactivity.
Though literature survey reports many therapeutic applications of
2-substituted benzothiazoles, their investigation for anti-inflam-
matory activity is limited.8,14–17 Piperazines attached to benzimid-
azole and indole were found to have potent anti-inflammatory
activity.18 Prompted by recent literature developments and as a
part of our continuous search for biologically active compounds,
we worked on joining the two active moieties with an intention
of getting better biological activity.19,20 With this concept, we are
reporting the pharmacological activity of N-(benzo[d]thiazol-2-
yl)-2-(piperazin-1-yl)acetamide analogs for their anti-inflamma-
tory activity by carragenan induced paw oedema method. Selected
compounds were also evaluated for ulcerogenicity index. Molecular
modelling studies were performed in order to probe whether COX-2
was a possible target for the synthesised compounds (A1–C4).
As depicted in Scheme 1, commercially available substituted
amino benzthiazoles are treated with chloroacetylchloride to form
⇑
Corresponding author. Fax: +91 40 2304 1700.
E-mail address: nmraghava@yahoo.in (N.M. Raghavendra).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.12.062

N. M. Raghavendra et al. / Bioorg. Med. Chem. Lett. 22 (2012) 820–823
821
R1
N
n
O
Cl
O
N
S
N
S
N
S
N
NH2
NH
a
NH
b
R
R
R
Substituted benzo[d]
(A1-C4)
(A-C)
thiazol-2-amine
N-(benzo[d]thiazol-2-yl)
Substituted 2-chloro-N-(benzo[d]thiazol-
-2-(piperazin-1-yl)acetamide analogs
2-yl)acetamides
B4: R = OCH3, R1 = C6H5, n = 1
C1: R = NO2, R1 = H, n = 1
C2: R = NO2, R1 = C2H5, n = 1
C3: R = NO2, R1 = H, n = 2
C4: R = NO2, R1 = C6H5, n = 1
A3: R = H, R1 = H, n=2
A: R = H
A4: R = H, R1 = C6H5, n = 1
B: R = OCH3
C: R = NO2
B1: R = OCH3, R1 = H, n = 1
B2: R = OCH3, R1 = C2H5, n = 1
B3: R = OCH3, R1 = H, n = 2
A1: R = H, R1 = H, n = 1
A2: R = H, R1 = C2H5, n = 1
Scheme 1. Reagents and conditions: (a) ClCOCH2Cl, triethylamine, dioxane (15 °C for 20 min followed by 110 °C for 4 h); (b) substituted piperazine, triethylamine, dioxane
100 °C for 2–6 h.
corresponding substituted 2-chloro-N-(benzo[d]thiazol-2-yl)aceta-
mides (A–C).21,22 The 1H NMR signals at 3.5–4.4 due to CH2 of chloro
acetamide group, d 7–8.5 of benzothiazole; absence of primary ami-
no group IR signals at 3200–3300 cmÀ1, presence of C–Cl stretching
at 720 cmÀ1 and molecular weight determination from Mass spectra
confirms the structures of substituted 2-chloro N-(benzo[d]thiazol-
2-yl)acetamides (A–C). In the second step, substituted 2-chloro N-
(benzo[d]thiazol-2-yl)acetamides (A–C) were reacted with
substituted piperazines to yield N-(benzo[d]thiazol-2-yl)-2-(pip-
erazin-1-yl)acetamide analogs (A1–C4).23 Chemical synthesis and
characterisation of A4 is already reported in the literature.17 The
structures of the final compounds (A1–C4) were substantiated on
the basis of IR, NMR, and Mass spectral data.24
The anti-inflammatory activity of title compounds were evalu-
ated on Wistar rats at (30 mg/kg) by Winter’s method25 and data
is given in the Table 1. Compounds A1 and C4 were the most active
compounds in the series compared to naproxen. Compounds A2
and B4 showed moderate activity. The compound A1 having
N-benzo[d]thiazol-2-yl moiety attached to 2-(piperazin-1-yl)
acetamide (% DPV = 41.30) and the compound C4 having N-(5-
nitrobenzo[d]thiazol-2-yl) moiety attached to 2-(4-phenylpipera-
zin-1-yl)acetamide (% DPV = 34.78) were found to be the optimum
structural features amongst the series to show promising in vivo
Table 1
Percent inhibition of paw volumes of N-(benzo[d]thiazol-2-yl)-2-(pipierazinyl-1-
yl)acetamides analogs (A1–C4)
Compd
Anti-inflammatory activitya
Paw volume mean SEMc
% DPVd
Control
A1
A2
A3
A4
B1
B2
B3
B4
C1
C2
C3
C4
Naproxen
Rofecoxib
0.76 0.049
0.58 0.051
0.70 0.025
0.72 0.049
0.65 0.025
0.75 0.022
0.68 0.030
0.63 0.030
0.66 0.033
0.70 0.033
0.68 0.030
0.68 0.030
0.60 0.025
0.43 0.021
0.15 0.031
0
41.30*
13.04
8.60
23.91
2.17
17.39
17.39
21.70
12.30
17.39
17.39
34.78*
71.70***
81.01***
a
c
Percent inhibition of paw volumes of compounds at 2 h.
SEM = Standard error of mean.
DPV = Decrease in paw volume.
P <0.05.
d
*
***
P <0.0001.
Figure 1. Overlap of ball and stick form of A1 (magenta colour), C4 (cyano colour), naproxen (green colour) and rofecoxib (yellow colour) showing hydrogen bonding
interaction with amino acids in the active site of COX-2. PDB code 3NT1.

822
N. M. Raghavendra et al. / Bioorg. Med. Chem. Lett. 22 (2012) 820–823
anti-inflammatory activity. Sodium carboxy methyl cellulose (con-
trol) alone did not modify the responses to nociceptive stimuli in
the rat pedal oedema induced by fresh carrageenan administration.
The compounds A1 and C4 endowed with significant anti-
inflammatory activity were evaluated for acute gastric ulcerogenic
effect in Wistar rats.26 Six hours after the treatment with a dose of
90 mg/kg, they were sacrificed under deep ether anaesthesia and
their stomachs were removed and opened through great curvature
for examining lesions or bleedings. Compounds A1 (Ulcer Index
(UI) = 1.24) and C4 (UI = 1.21) were found to possess less ulcer
inducible capacity than naproxen (UI = 2.5).
To understand the mechanism of anti-inflammatory activity of
the compounds synthesised, molecular modelling and docking
studies were performed on X-ray crystal structure of COX-2 protein
(PDB code: 3NT1; resolution 1.73 Å)27 using Surflex-Dock GeomX
(SFXC) programme of Sybyl software on Dell Precision T-1500
workstation.28 Synthesised compounds (A1–C4) occupy the same
binding site as that of naproxen and rofecoxib (Fig. 1); naproxen
was found to have three hydrogen bonding interactions with
Arg120 (2.16, 2.52 and 1.92 Å) and one with Tyr355 (1.86 Å). Com-
pound A1 forms two hydrogen bonds one with NH of its piperazine
moiety and OH of Tyr385 (2.62 Å) and the other with NH of its
piperazine moiety and OH of Tyr385 (2.54 Å). Compound C4 forms
hydrogen bonding interaction with its carbonyl oxygen of amide
bond and Arg120 (1.60, 2.64 Å). Compound A1, C4, naproxen and
rofecoxib were having hydrophobic interactions with the amino
acid residues such as Met522, Val523, Leu352, Leu525, Phe529,
Ala527, Val116, Leu531, Leu359, and Val349 (Fig. 2). The rest of
the compounds except A2, B2, B3, and C2 were having inappropri-
ate penetration (crash score >À4.5 kcal/mol) into the binding site
resulting in the decreased forces of interaction with the amino acids
of the COX-2 protein. However, compounds A2, B2, B3, and C2 were
having low C-score, which can be attributed to their low in vivo
anti-inflammatory activity.
Figure 2. Hydrophobic amino acids (brown coloured space fill) enclosing the ball
and stick form of A1 (magenta colour), C4 (cyano colour), naproxen (green colour)
and rofecoxib (yellow colour) in the active site of COX-2. PDB code 3NT1.
the reward for hydrogen bonding, lipophilic contact, and rotational
entropy, along with an intercept terms reveal that compound C4
has more interactions with the protein than rofecoxib, naproxen
and A1. The C-score indicating the summary of all the forces of
interaction between the ligands and COX-2 enzyme, including the
crash score is in favour of naproxen, followed by A1, C4, rofecoxib
and the rest of the compounds amongst the series.
In conclusion, in vivo studies demonstrated that N-
(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs (A1
and C4), have promising anti-inflammatory activity and less toxicity
than naproxen. Molecular modelling and docking studies suggested
that compound A1 and C4 interacts with COX-2 enzyme more effi-
ciently than rofecoxib. Therefore, these two compounds can be fur-
ther developed to improve their anti-inflammatory activity.
Compounds A1 and C4 were having better hydrogen bonding,
complex (ligand–protein), and internal (ligand–ligand) energies
than naproxen, rofecoxib and other compounds of the series
(Table 2). Helmholtz free energies of interactions for protein–ligand
atom pairs prefers C4 over the rofecoxib and naproxen followed by
A1. Charge and van der Waals interactions between the protein
and the ligand suggests C4 and A1 are a superior ligand than na-
proxen to bind with COX-2. Scoring of compounds with respect to
Table 2
Surflex-Dock GeomX score (kcal/mol) of compounds
Compd
C-Scorea
Crash Scoreb
Polar Scorec
G scored
PMF scoree
D scoref
Chem scoreg
Naproxen
A1
C4
Rofecoxib
A2
B4
C2
A3
C1
B1
B2
A4
C3
9.16
6.48
6.23
6.13
5.95
5.78
5.36
5.15
5.14
4.52
4.35
4.25
4.02
3.39
À0.39
À3.12
À3.73
À2.91
À2.94
À4.53
À2.70
À5.72
À5.18
À5.62
À3.36
À6.52
À5.20
À3.56
2.98
0.00
1.06
0.00
1.01
0.00
0.52
0.58
0.00
0.42
0.22
0.00
1.06
0.91
À182
À281
À289
À268
À267
À309
À285
À341
À304
À289
À276
À337
À283
À254
À47.9
À30.5
À53.9
À48.8
À11.3
À35.3
À39.2
À26.1
À19.9
À23.0
À22.9
À24.5
À34.7
À29.6
À102
À130
À145
À140
À128
À141
À140
À152
À145
À138
À127
À157
À140
À123
À29.8
À25.8
À37.0
À35.3
À25.6
À27.6
À32.6
À28.4
À27.2
À27.8
À24.7
À39.4
À23.8
À23.3
B3
a
b
c
d
e
f
C-Score (Consensus-score) reports the output of total score.
Crash-score revealing the inappropriate penetration into the binding site.
Polar region of the ligand.
G-score showing hydrogen bonding, complex (ligand–protein), and internal (ligand–ligand) energies.
PMF-score indicating the Helmholtz free energies of interactions for protein–ligand atom pairs (Potential of Mean Force, PMF).
D-score for charge and van der Waals interactions between the protein and the ligand.
g
Chem-score points for hydrogen bonding, lipophilic contact, and rotational entropy, along with an intercept term.

N. M. Raghavendra et al. / Bioorg. Med. Chem. Lett. 22 (2012) 820–823
823
cmÀ1): 3270, 3030, 2901, 2878, 1685, 1600, 1567, 821; MS (API-ES) m/z for
Acknowledgments
C
15H20N4OS
(M+H)+
305.
N-(benzo[d]thiazol-2-yl)-2-(1,4-diazepan-1-
yl)acetamide (A3): Yield 30%, mp 227 °C; 1H NMR (400 MHz, DMSO-d6): d
1.25 (s, 1H), 1.96–2.10 (m, 2H, J = 7.3 Hz), 2.9–3.0 (m, 8H, J = 7.3 Hz), 3.45 (s,
We are thankful to DST (SR/FT/CS-079/2009) and AICTE (8023/
BOR/RID/RPS-102/2009-10) for providing molecular modelling
softwares and other financial assistance for this project. We also
thank Gokaraju Rangaraju Educational Society for providing labo-
ratory facilities and Laila Impex R&D Center, Vijaywada, Andhra
Pradesh, India for the spectral analysis.
2H), 7.3–7.8 (m, 4H, J = 7.4 Hz), 10.60 (br r, 1H); IR (KBr,
m
cmÀ1): 3323, 3049,
2883, 2823, 1697, 1600, 1529, 827; MS (API-ES) m/z for C14H18N4OS (M+H)+
291. N-(5-methoxybenzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide (B1):
Yield 26%, mp 119 °C; 1H NMR (400 MHz, DMSO-d6): d 1.3 (s, 1H), 3.82 (s,
8H), 3.88 (s, 3H), 4.29 (s, 1H), 7.11 (d, 1H, J = 7.4 Hz), 7.45 (d, 1H, J = 7.6 Hz),
7.69 (d, 1H, J = 7.5 Hz); IR (KBr,
m
cmÀ1): 3280, 3095, 2920, 2845, 1690, 1603,
1571, 823; MS (API-ES) m/z for C14H18N4O2S (M+H)+ 307. 2-(4-ethylpiperazin-
1-yl)-N-(5-methoxybenzo[d]thiazol-2-yl)acetamide (B2): Yield 23%, mp
212 °C; 1H NMR (400 MHz, DMSO-d6): d 1.2 (s, 3H), 2.0 (br r, 8H), 3.9 (s, 2H),
6.90 (d, 1H, J = 7.1 Hz), 7.1 (d, 1H, J = 7.5 Hz), 7.45 (d, 1H, J = 7.4 Hz), 7.5 (s, 1H);
Supplementary data
IR (KBr,
(API-ES) m/z for
m
cmÀ1): 3287, 3095, 2971, 2922, 2848, 1641, 1545, 1466, 821; MS
16H22N4O2S (M+H)+ 335. 2-(1,4-diazepan-1-yl)-N-(5-
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2011.12.062.
C
methoxybenzo[d]thiazol-2-yl)acetamide (B3): Yield 33%; mp 222 °C; 1H NMR
(400 MHz, DMSO-d6): d 0.8 (br r, 2H), 2.00 (q, 4H, J = 6.5 Hz), 2.9-3.04 (m, 4H),
3.45 (t, 2H), 3.89 (s, 3H), 7.01 (d, 1H, J = 7.3 Hz), 7.28 (d, 1H, J = 7.5 Hz), 7.68 (s,
m
cmÀ1): 3280, 3095, 2920, 2896, 2848, 1690, 1537, 1470, 820; MS
References and notes
1H); IR (KBr,
(API-ES) m/z for C15H20N4O2S (M+H)+ 321. N-(5-methoxybenzo[d]thiazol-2-yl)-
2-(4-phenylpiperazin-1-yl)acetamide (B4): Yield 36%, mp 199 °C; 1H NMR
(400 MHz, DMSO-d6): d 2.70 (s, 4H), 3.19 (s, 4H), 3.43 (s, 2H), 3.79 (s, 3H), 6.78
(t, 1H, J = 7.8 Hz), 6.96 (d, 2H, J = 7.3 Hz), 7.20 (t, 2H, J = 7.3 Hz), 7.58 (s, 1H),
1. Ravi, G. K.; Anna, M. S.; James, K. G.; Joseph, J. M.; Roderick, A. S.; Jina, Y.;
Daniel, G.; Julie, M. I.; Thomas, D. P.; Karen, S.; Peter, C. I.; William, C. S. Nature
1996, 384, 644.
2. Seibert, K.; Masferrer, J.; Zhang, Y.; Gregory, S.; Olson, G.; Hauser, S.; Leahy, K.;
Perkins, W.; Isakson, P. Agents Actions Suppl. 1995, 46, 41.
3. Garner, S.; Fidan, D.; Frankish, R.; Judd, M.; Shea, B.; Towheed, T.; Wells, G.;
Tugwell, P. Cochrane Database Syst. Rev. 2002, 4, CD003831.
4. Bombardier, C.; Laine, L.; Reicin, A.; Shapiro, D.; Burgos-Vargas, R.; Davis, B.;
Day, R.; Ferraz, M. B.; Hawkey, C. J.; Hochberg, M. C.; Kvien, T. K.; Schnitzer, T. J.
N. Engl. J. Med. 2000, 343, 1520.
7.62–7.69 (m, 2H, J = 7.5 Hz), 11.9 (s, 1H); IR (KBr,
m
cmÀ1): 3261, 3088, 2987,
2931, 2824, 1699, 1540, 1501, 813; MS (API-ES) m/z for C20H22N4O2S (M+Na)+
405. N-(5-nitrobenzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide (C1): Yield
45%, mp 268 °C; 1H NMR (400 MHz, DMSO-d6): d 1.3 (s, 1H), 2.62–2.67 (m, 4H,
J = 8.5 Hz), 2.50 (s, 4H), 3.40 (s, 2H), 7.90 (d, 1H, J = 7.3 Hz), 8.30 (d, 1H,
J = 7.8 Hz), 9.05 (s, 1); IR (KBr,
m
cmÀ1): 3343, 3088, 2937, 2821, 1701, 1573,
13H15N5O3S (M+H)+ 322. 2-(4-
1514, 1442, 848; MS (API-ES) m/z for
C
ethylpiperazin-1-yl)-N-(5-nitrobenzo[d]thiazol-2-yl)acetamide (C2): Yield
25%, mp 179 °C; 1H NMR (400 MHz, DMSO-d6): d 1.40 (t, 3H, J = 7.3 Hz), 3.10
(br r, 4H), 3.25 (q, 2H, J = 7.0 Hz), 3.40 (br r, 4H), 3.62 (s, 2H), 7.78 (d, 1H,
5. Bresalier, R. S.; Sandler, R. S.; Quan, H.; Bolognese, J. A.; Oxenius, B.; Horgan, K.;
Lines, C.; Riddell, R.; Morton, D.; Lanas, A.; Konstam, M. A.; Baron, J. A. N. Engl. J.
Med. 2005, 352, 1092.
6. Solomon, S. D.; McMurray, J. J. V.; Pfeffer, M. A.; Wittes, J.; Fowler, R.; Finn, P.;
Anderson, W. F.; Zauber, A.; Hawk, E.; Bertagnolli, M. N. Engl. J. Med. 2005, 352,
1071.
7. Priyanka; Neeraj, K. S.; Keshari, K. J. Int. J. Curr. Pharm. Res. 2010, 2, 1.
8. Hemendra, P. S.; Sharma, C. S.; Chandra, P. G. Am. Eurasian J. Sci. Res. 2009, 4,
222.
9. Hemlata, K.; Sunil, K.; Indu, S.; Saxena, K. K.; Ashok, K. Digest J. Nanomaterials
Biostruct. 2010, 5, 67.
10. Ameya, A.; Chavan, A.; Nandini, R. P. Molecules 2007, 12, 2467.
11. Nadeem, S.; Arpana, R.; Suroor, A. K.; Ehtaishamul, H.; Faiz, A.; Sharique, A.;
Waquar, A. Acta. Pharm. 2009, 59, 441.
12. AlSoud, Y. A.; Al-Sadoni, H.; Amajaour, H. A. S.; Al-Masoudi, N. A. Naturforsch.
2006, 62b, 523.
J = 7.3 Hz), 8.25 (d, 1H, J = 7.3 Hz), 8.75 (s, 1); IR (KBr,
m
cmÀ1): 3402, 3170,
2876, 2831, 1705, 1573, 1506, 1442, 819; MS (API-ES) m/z for C15H19N5O3S
(M+H)+ 350. 2-(1,4-diazepan-1-yl)-N-(5-nitrobenzo[d]thiazol-2-yl)acetamide
(C3): Yield 38%, mp 229 °C; 1H NMR (400 MHz, DMSO-d6): d 1.1–1.3 (m, 2H,
J = 7.9 Hz), 2.0 (br r, 1H), 2.93–3.0 (m, 4H, J = 7.8 Hz), 3.6 (s, 4H), 3.85 (s, 2H),
7.69 (d, 2H, J = 7.5 Hz), 8.15 (d, 1H, J = 7.5 Hz), 8.8 (s, 1H); IR (KBr,
3394, 3170, 2918, 2878, 1708, 1573, 1500, 1448, 827; MS (API-ES) m/z for
m
cmÀ1):
C
14H17N5O3S
(M+H)+
334.
N-(5-nitrobenzo[d]thiazol-2-yl)-2-(4-
phenylpiperazin-1-yl)acetamide (C4): Yield 72%, mp 230 °C; 1H NMR
(400 MHz, DMSO-d6): d 2.80 (br r, 4H), 3.12 (s, 2H), 3.20 (br r, 4H), 6.9–7.1
(m, 3H, J = 7.0 Hz), 7.3–7.4 (m, 2H, J = 7.5 Hz), 8.1 (d, 2H, J = 7.3 Hz), 8.5 (s, 1H);
IR (KBr,
m
cmÀ1): 3311, 3040, 2916, 2864, 1651, 1570, 1516, 1442, 852; MS
(API-ES) m/z for C19H19N5O3S (M+H)+ 398.
25. Winter, C. A.; Risley, E. A.; Nuss, G. W. Proc. Soc. Exp. Biol. Med. 1962, 111, 544.
26. Meddhi, B.; Prakash, A. Practical Manual of Experimental and Clinical
Pharmacology. Jaypee brothers medical publishers (P) Ltd; New Delhi, 2010.
27. Duggan, K. C.; Walters, M. J.; Musee, J.; Harp, J. M.; Kiefer, J. R.; Oates, J. A.;
Marnett, L. J. J. Biol. Chem. 2010, 45, 34950.
13. Gajdos, P.; Magdolen, P.; Zahradnik, P.; Foltinova, P. Molecules 2009, 14, 5382.
14. Velingkar, V. S.; Ahire, D. C.; Kolhe, N. S.; Shidore, M. M.; Pokharna, G. Int. J.
Pharm. Sci. Res. 2011, 2, 197.
15. Paramashivappa, R.; Phani Kumar, P.; Subba Rao, P. V.; Srinivasa Rao, A. Bioorg.
Med. Chem. Lett. 2003, 13, 657.
28. Molecular modelling and docking simulations: The X-ray crystal structure of
COX-2-naproxen complex (PDB code: 3NT1; resolution 1.73 Å) was optimized
by deleting the identical B chain of the protein and retaining respective A chain
for docking studies. Mislabelled atom types from the pdb file were corrected,
subsequently, proline F angles were fixed at 70°, side chain amides were
checked to maximize potential hydrogen bonding, side chains were checked
for close van der Waals contacts, and essential hydrogens were added. The
model was checked for conformational problems using the module ProTable
from Sybyl. Ramachandran plot29 of the backbone torsion angles PHI and PSI,
local geometry and the location of buried polar residues/exposed non-polar
residues were examined. The protein and synthesised compounds, including
naproxen and rofecoxib were subjected to energy minimization following the
gradient termination of the Powell method for 3000 iterations using Kollman
united force field with non-bonding cut-off set at 9.0 and the dielectric
constant set at 4.0.30,31 The synthesised compounds and the standard
compounds tested in this study were docked to COX-2 (PDB code: 3NT1)
using Surflex-Dock GeomX programme in Sybyl software by incremental
construction approach of building the structure in the active site so as to favour
the binding affinity.32,33 Finally, the docked ligands were ranked based on a
variety of scoring functions that have been compiled into the single consensus
score (C-score).34,35
16. Shashank, D.; Vishawanth, T.; Arif Pasha, Md.; Balasubramaniam, V.; Nagendra,
A.; Perumal, P.; Suthakaran, R. Int. J. Chem. Tech. Res. 2009, 1, 1224.
17. Papadopoulou, C.; Geronikaki, A.; Hadjipavlou-Litina, D. I. L. Farmaco 2005, 60,
969.
18. Terzioglu, N.; Van Rijn, R. M.; Bakker, R. A.; De Esch, J. P.; Leurs, R. Bioorg. Med.
Chem. Lett. 2004, 14, 5251.
19. Raghavendra, N. M.; Thampi, P. P.; Gurubasavarajaswamy, P. M.; Sriram, D.
Chem. Pharm. Bull. 2007, 55, 1615.
20. Raghavendra, N. M.; Thampi, P. P.; Gurubasavarajaswamy, P. M.; Sriram, D.
Arch. Pharm. 2007, 340, 635.
21. Srivastava, S. D.; Sen, J. P. Indian J. Chem. 2008, 47B, 1583.
22. Pratibha, A.; Anupam, M.; Shreeya, P. Indian J. Chem. 1999, 38B, 1289.
23. Synthesis of N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs
(A1–C4):
A mixture of equimolar quantities of substituted 2-chloro-N-
(benzo[d]thiazol-2-yl)acetamides (A–C), various piperazine derivatives,
dioxane (10 ml) and triethylamine (0.2 ml) were heated at 100 °C with
stirring for 2–6 h. The reaction was monitored by TLC using mobile phase
petroleum ether/ethyl acetate (2:8). The excess of ethanol was removed by
distillation. To the residue add warm distilled water. The solid thus obtained is
filtered, washed with 5% NaHCO3 to remove excess acidic impurities, filtered,
washed and dried. The product obtained was recrystallized and further
purified by flash chromatograph.
29. Edsall, J. T.; Flory, P. J.; Kendrew, J. C.; Liquori, A. M.; Nemethy, G.;
Ramachandran, G. N.; Scheraga, H. A. J. Biol. Chem. 1966, 241, 1004.
30. Purcell, W.; Singer, J. A. J. Chem. Eng. Data. 1967, 12, 235.
31. Cieplak, P.; Cornell, W. D.; Bayly, C.; Kollman, P. A. J. Comput. Chem. 1995, 16,
1357.
24. Spectral data of N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide analogs
(A1–C4): N-(benzo[d]thiazol-2-yl)-2-(piperazin-1-yl)acetamide (A1): Yield
22%, mp 196 °C; 1H NMR (400 MHz, DMSO-d6): d 0.9 (br r, 1H), 1.2 (br r, 8H),
3.36 (s, 2H), 7.35 (d, 2H, J = 7.50 Hz), 7.67 (d, 2H, J = 7.50 Hz), 7.9 (br r, 1H); IR
(KBr,
m
cmÀ1): 3282, 3060, 2872, 2848, 1690, 1600, 1533, 842; MS (API-ES) m/z
32. Leach, A. R.; Kuntz, I. J. Comput. Chem. 1992, 13, 730.
for C13H16N4OS (M+H)+ 277. N-(benzo[d]thiazol-2-yl)-2-(4-ethylpiperazin-1-
yl)acetamide (A2): Yield 28%, mp 132 °C; 1H NMR (400 MHz, DMSO-d6): d 1.12
(t, 3H, J = 7.0 Hz), 2.3 (q, 2H, J = 6.8 Hz), 2.7 (br r, 8H), 3.33 (s, 2H), 5.5 (br r, 1H),
33. Rarey, M.; Kramer, B.; Lengauer, T. J. Comput.-Aided Mol. Des. 1997, 11, 369.
34. Rarey, M.; Kramer, B.; Lengauer, T.; Klebe, G. A. J. Mol. Biol. 1996, 261, 470.
35. Jones, G.; Willett, P.; Glen, R.; Leach, A. R.; Taylor, R. J. Mol. Biol. 1997, 267, 727.
7.0 (d, 1H, J = 7.4 Hz), 7.15 (t, 1H, J = 7.5 Hz), 7.58 (d, 2H, J = 7.3 Hz); IR (KBr,
m