Synthesis, anti-inflammatory evaluation, and docking studies of some new thiazole derivatives

Article abstract of DOI:10.1007/s00044-013-0861-4

A series of new 2-substituted-N-(1,3-thiazole-2-yl)acetamide 3-7 and N-(benzo[d]thiazol-2-yl)-2-(substituted)acetamide 10-13 derivatives have been synthesized and evaluated in vivo (rat paw edema) for their anti-inflammatory activities and in silico(docki

Full text of DOI:10.1007/s00044-013-0861-4

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-013-0861-4
ORIGINAL RESEARCH
Synthesis, anti-inflammatory evaluation, and docking studies
of some new thiazole derivatives
•
Pran Kishore Deb Rajwinder Kaur Balakumar Chandrasekaran
•
•
•
•
•
•
Madhu Bala Dilshad Gill Venkat Rao Kaki Raghuram Rao Akkinepalli
Raghuprasad Mailavaram
Received: 4 August 2013 / Accepted: 18 October 2013
Ó Springer Science+Business Media New York 2013
Abstract A series of new 2-substituted-N-(1,3-thiazole-2-yl)
acetamide 3–7 and N-(benzo[d]thiazol-2-yl)-2-(substituted)
acetamide 10–13 derivatives have been synthesized and eval-
uated in vivo (rat paw edema) for their anti-inflammatory
activities and in silico(docking studies) to recognize the
hypothetical binding motif of the title compounds with the
cyclooxygenase isoenzyme (COX-2) employing GLIDE soft-
ware (Schrodinger Inc.). The compounds, 10–13 were found to
have good anti-inflammatory activities [around 84–93 % of the
standard: indomethacin]. The binding mode of the title
compounds has been proposed based on the docking studies.
Further, the predicted ADME properties of all the tested com-
pounds were found to be in the ranges as predicted by QikProp
for 95 % of known oral drugs and alsosatisfy the Lipinski’s rule
of five.
Keywords Microwave-assisted synthesis ꢀ
Thiazole derivatives ꢀ Anti-inflammatory activity ꢀ
COX-2 docking studies ꢀ ADME prediction
Introduction
Nonsteroidal anti-inflammatory drugs (NSAIDs) are
important therapeutic agents for the treatment of pain and
inflammation of everyday life. Through their anti-inflam-
matory, antipyretic, and analgesic activities they represent a
choice of treatment in various inflammatory diseases such as
arthritis and rheumatisms (Stefano et al., 2001). NSAIDs are
competitive inhibitors of cyclooxygenase (COX), the
enzyme that catalyzes the first step of the biosynthesis of
prostaglandins (PGG2) from arachidonic acid which serves
as a precursor for the synthesis of PGs, prostacyclines, and
thromboxanes such as TXA2 that are collectively termed as
prostanoids (Vane et al., 1998). It is well established that
COX exists in two different isoforms, a constitutive form
(COX-1) and an inducible form (COX-2) (Xie et al., 1991).
The constitutive COX-1 isozyme is expressed in many tis-
sues and appears to be important for the maintenance of
various physiological functions such as cytoprotection of
gastric mucosa, regulation of renal blood flow, and platelet
aggregation (William and David, 1996). In contrast, COX-2
isozyme is not detected in most normal tissues, but its
expression is rapidly induced by stimuli such as mitogenes
and oncogenes, growth factors, hormones, and disorders of
water-electrolyte homeostasis linking its involvement to
pathological processes such as inflammation and various
cancer types (Harvey, 1996; Kawamori et al., 1998; Shigeru
et al., 2007). The classical NSAIDs act by reducing the
production of proinflammatory PGs at the sites of injury via
COX-2 inhibition. The side effects associated with these
P. K. Deb
Pharmaceutical Chemistry Division, School of Pharmacy,
International Medical University (IMU), No. 126, Jalan Jalil
Perkasa 19, Bukit Jalil, 57000 Kuala Lumpur, Malaysia
e-mail: prankishore1@gmail.com
R. Kaur ꢀ B. Chandrasekaran ꢀ M. Bala ꢀ D. Gill ꢀ V. R. Kaki
Pharmaceutical Chemistry Division, University Institute of
Pharmaceutical Sciences (UIPS) and Centre of Advanced Study
in Pharmaceutical Sciences (UGC-CAS), Panjab University
(PU), Chandigarh 14, India
R. R. Akkinepalli (&)
Medicinal Chemistry Division, University College
of Pharmaceutical Sciences, Kakatiya University,
Warangal 506 009, Andhra Pradesh, India
e-mail: raghumed@gmail.com
R. Mailavaram
Pharmaceutical Chemistry Division, Sri Vishnu College of
Pharmacy, Bhimavaram-2, Vishnupur, Andhra Pradesh, India
123

Med Chem Res
NSAIDs such as GI ulcer and renal function suppression are
due to the inhibition of COX-1 pathway (Allison et al., 1992;
Charles and Raymond, 1995). Thus the success of NSAIDs
in treatment of various inflammatory disorders depends on
the selective inhibition of COX-2 over COX-1 isoenzyme.
Moreover, recent studies indicating the role of COX-2
inhibitors in cancer chemotherapy especially colon cancer
(Taketo, 1998; Lisa and Dan, 2010) and neurological dis-
eases such as Parkinson (Van Gool et al., 2003) and Alz-
heimer’s (Paul et al., 2003) diseases still continues to attract
investigations on development of COX-2 inhibitors. As a
consequence, many selective COX-2 inhibitors have been
developed (Balakumar et al., 2010). However, the market
withdrawal of some COXIBs such as rofecoxib due to its
adverse cardiovascular side effects (Jean et al., 2005)
imposed a great challenge to the researchers to explore and
evaluate alternative templates with selective COX-2 inhib-
itory activity (Sara and Afshin, 2010).
recorded on Perkin Elmer FT-IR Spectrometer (Spectrum RX
I) using KBr pellet technique. Melting points were recorded in
open capillaries on LABINDIA melting point apparatus and
were uncorrected. Mass spectra (ESI) were recorded on
Waters Micromass Q-TOF Micro.
General procedure for the preparation of 2-chloro-N-
(1,3-thiazol-2-yl)acetamide (2) and N-(benzo[d]thiazol-
2-yl)-2-chloroacetamide (9)
Method A
To a solution of 2-amino-1,3-thiazole 1/2-amino-1,3-ben-
zothiazole 8 (0.10 mol) in freshly distilled THF, triethyl-
amine (0.10 mol) was added followed by dropwise
addition of chloroacetyl chloride (0.12 mol) at 0–5 °C and
allowed to stir for 30 min–3 h (Table 1). The reaction
mixture was poured into crushed ice and neutralized with
5 % HCl followed by extraction with EtOAc. The organic
phase was dried on anhydrous Na2SO4 and concentrated
under reduced pressure to get the pure compound 2-chloro-
N-(1,3-thiazol-2-yl)acetamide 2 and N-(benzo[d]thiazol-2-
yl)-2-chloroacetamide 9.
Recently, a series of 8/10-trifluoromethyl-substituted-
imidazo[1,2-c]quinazolines (Balakumar et al., 2010),
3-alkoxy-4-methanesulfonamido acetophenone derivatives
(Alka et al., 2012) cycloalkyl/aryl-3,4,5-trimethylgallates
(Mamta et al., 2013) have been reported from our labora-
tory as potent anti-inflammatory agents. The literature
reveals that thiazole derivatives are very potential for their
wide range of pharmacological activities including anti-
inflammatory, antiallergic, antibacterial, antitumor, anti-
hyperlipidemic activities (Afshin et al., 2007; Masakazu
et al., 1998; Michel et al., 1997; Jeffery et al., 1999; Pawan
and Sawhney, 1997; Rosaria et al., 2005; Franklin et al.,
2008, Prakash et al., 2008; Bharti et al., 2010; Balladka
et al., 2010). In continuation of our earlier effort, in the
present study, we report the synthesis and evaluation of
in vivo anti-inflammatory activity of a series of new
2-substituted-N-(1,3-thiazol-2-yl)acetamide (3–7) and N-
Method B
A mixture of 2-amino-1,3-thiazole 1/2-amino-1,3-benzo-
thiazole 8 (0.001 mol) in freshly distilled THF and trieth-
ylamine and chloroacetylchloride (0.001 mol) was heated
under microwave irradiation at 560 W for 10–20 s
(Table 1). The reaction mixture was worked up following
the same process as mentioned in Method A to get the pure
compound 2-chloro-N-(1,3-thiazol-2-yl)acetamide 2 and
N-(benzo[d]thiazol-2-yl)-2-chloroacetamide 9.
(benzo[d]thiazol-2-yl)-2-(substituted)acetamide
(10–13)
derivatives. Further, we propose the molecular interactions
and the binding mode of these target compounds using
COX-2 isoenzyme based on in silico docking studies.
2-Chloro-N-(1,3-thiazol-2-yl)acetamide (2) White solid,
Yield: 51 & 80 % (MW), M.P.: 161–162 °C, IR: 3,496,
3,089, 2,926, 1,676, 1,598 cm-1
;
1H NMR (CDCl3,
400 MHz) d 3.33 (s, 2H, –CH2), 7.11 (d, J = 6.8, 1H, Ar–
H), 7.23 (d, J = 6.8, 1H, Ar–H), 10.37 (s, 1H, –NH); 13C
NMR (CDCl3, 100 MHz) d 45.44 (Cl–CH2), 114.22 (C5-
1,3-thiazole), 130.66 (C4-1,3-thiazole), 159.93 (C2-1,3-
thiazole), 166.72 (C=O); ESIMS m/z 177.68 (M??1).
Experimental
Reactions were routinely monitored by thin layer chroma-
tography (TLC) on silica gel (pre-coated F254 103 Merck
plates) and visualized the products under UV light (254 nm).
N-(benzo[d]thiazol-2-yl)-2-chloroacetamide (9) Slight yel-
low solid, Yield: 70 & 95 % (MW), M.P.: 162–163 °C, IR:
1
The H was recorded on Bruker Avance II 400 MHz spec-
1
trometer for solutions in CDCl3/DMSO-d6 in parts per million
(d) downfield from tetramethylsilane as internal standard, and
J values were given in Hz. The 13C NMR spectra were
recorded at 100 MHz. The spin multiplicities are indicated by
the symbols, s (singlet), d (doublet), t (triplet), dd (double
doublet), m (multiplet), and br (broad). IR spectra were
3,505, 3,048, 2,920, 1,691, 1,646, 1,265 cm-1; H NMR
(CDCl3, 400 MHz) d 4.37 (s, 2H, –CH2–), 7.85 (m, 2H, Ar–
H), 7.42 (m, 2H, Ar–H), 12.63 (s, 1H, –NH); 13C NMR
(CDCl3, 100 MHz) d 47.68 (Cl–CH2), 120.20 (benzo
[d]thiazole), 122.54 (benzo[d]thiazole), 125.59 (benzo[d]
thiazole), 127.67 (benzo[d]thiazole), 132.33 (benzo
123

Med Chem Res
Table 1 Comparative data of conventional (Method A) and microwave-assisted (Method B) synthesis of compounds 2–7 and 9–13
N
O
N
O
R
R
S
N
S
N
H
H
(2-7)
(9-13)
Compounds
R
M.P.
Conventional (Method A)
Microwave-assisted (Method B)
(°C)
Time (h)
% Yield
Time (s) at 560 W
% Yield
2
3
Cl
160–162
140–142
30 min
8 h
51
35
10
50
80
75
4
5
148–151
160–162
8 h
8 h
49
57
50
50
80
80
6
7
162–164
158–160
8 h
8 h
60
57
45
50
85
85
9
Cl
161–162
210–212
3 h
2 h
70
70
20
30
95
85
10
11
12
13
190–193
146–148
120–122
2 h
4 h
4 h
75
65
65
30
50
50
87
88
85
M.P. melting point
[d]thiazole), 149.94 (benzo[d]thiazole), 167.64 (C=O), 175.
55 (C2-benzo[d]thiazole); ESIMS m/z 227.93 (M??1).
mixture was poured into crushed ice and neutralized with
5 % HCl followed by extraction with EtOAc. The organic
phase was dried on anhydrous Na2SO4 and concentrated
under reduced pressure. The residue was purified by col-
umn chromatography (EtOAc-Hexane 8:2) to afford the
desired compound 2-(substituted)-N-(1,3-thiazol-2-yl)acet-
amide (3–7) and N-(benzo[d]thiazol-2-yl)-2-(substituted)
acetamide (10–13) as a solid.
General procedure for the preparation of 2-
(substituted)-N-(1,3-thiazol-2-yl)acetamide (3–7)
and N-(benzo[d]thiazol-2-yl)-2-(substituted)acetamide
(10–13)
Method A
Method B
A mixture of compound 2/9 (0.10 mol) in freshly distilled
THF and triethylamine and appropriate amines (0.10 mol)
was heated under reflux for 2–8 h (Table 1). The reaction
A mixture of compound 2/9 (0.001 mol) in freshly distilled
THF and triethylamine and appropriate amines (0.001 mol)
123

Med Chem Res
was heated under microwave irradiation at 560 W for
30–50 s (Table 1). The reaction mixture was worked up
following the same process as mentioned in Method A to
get the pure compound 3–7 and 10–13.
thiazole), 145.33 (C10-phenyl), 161.29 (C2-1,3-thiazole),
167.22 (C=O); ESIMS m/z 248.3 (M??1).
2-(4-Methoxyphenylamino)-N-(1,3-thiazol-2-yl)acetamide
(7) White solid, Yield: 57 & 85 % (MW), M.P.:
158–160 °C, IR: 3,348, 3,041, 2,898, 1,661, 1,515, 1,238,
2-Morpholino-N-(1,3-thiazol-2-yl)acetamide (3) White
solid, Yield: 35 & 75 % (MW), M.P.: 140–142 °C, IR:
1
1,033 cm-1; H NMR (CDCl3, 400 MHz) d 3.72 (s, 3H,
3,089, 2,928, 1,676, 1,598 cm-1
;
1H NMR (CDCl3,
–OCH3), 3.95 (s, 2H, –CH2), 4.13 (s, 1H, –NH), 6.60 (d,
J = 7.0, 1H, Ar–H), 6.78 (d, J = 7.2, 2H, Ar–H), 7.00 (d,
J = 7.2, 2H, Ar–H), 7.42(d, J = 7.0, 1H, Ar–H), 11.12 (s,
1H, –NH); 13C NMR (CDCl3, 100 MHz) d 55.26 (CH2),
56.38 (OCH3), 112.72 (C5-1,3-thiazole), 115.45 (C30&C50-
phenyl), 116.47 (C20&C60-phenyl), 131.66 (C4-1,3-thia-
zole), 138.76 (C40-phenyl), 154.24 (C10-phenyl), 162.11
(C2-1,3-thiazole), 167.46(C=O); ESIMS m/z 264.1
(M??1).
400 MHz) d 2.55 (t, J = 4.6, 4H, –CH2–), 3.19 (s, 2H,
–CH2), 3.70 (t, J = 4.4, 4H, –CH2–), 6.93 (d, J = 6.8, 1H,
Ar–H), 7.38 (d, J = 6.8, 1H, Ar–H), 10.37 (s, 1H, –NH);
13C NMR (CDCl3, 100 MHz) d 56.28 (CH2), 61.39 (CH2–
N–CH2), 64.23 (CH2–O–CH2), 114.53 (C5-1,3-thiazole),
130.91 (C4-1,3-thiazole), 160.84 (C2-1,3-thiazole), 166.33
(C=O); ESIMS m/z 228.2 (M??1).
2-(Phenylamino)-N-(1,3-thiazol-2-yl)acetamide (4) White
solid, Yield: 49 & 80 % (MW), M.P.: 148–151 °C, IR:
N-(benzo[d]thiazol-2-yl)-2-(1H-1,2,4-triazol-1-yl)acetam-
1
3,350, 3,030, 2,965, 1,669, 1,610, 1,590 cm-1; H NMR
ide (10) White solid, Yield: 70 & 85 % (MW), M.P.:
1
(CDCl3, 400 MHz) d 3.87 (s, 2H, –CH2), 4.12 (s, 1H, –NH),
7.01(d, J = 6.9, 1H, Ar–H), 7.23 (m, 3H, Ar–H), 7.42 (d,
J = 6.9, 1H, Ar–H), 7.51 (d, J = 7.2, 2H, Ar–H), 10.41
(s, 1H, –NH); 13C NMR (CDCl3, 100 MHz) d 54.28 (CH2),
111.18 (C5-1,3-thiazole), 112.61 (C30&C50-phenyl),
118.76 (C40-phenyl), 130.33 (C20&C60-phenyl), 131.89 (C4-
1,3-thiazole), 145.22 (C10-phenyl), 161.29 (C2-1,3-thia-
zole), 166.72 (C=O); ESIMS m/z 234.1 (M??1).
240 °C, IR: 3,045, 2,934, 1,668, 1,625, 1,267 cm-1; H
NMR (CDCl3, 400 MHz) d 4.01 (s, 2H, CH2), 7.39 (m, 2H,
Ar–H), 7.71 (d, J = 6.8, 1H, Ar–H), 7.88 (s, 1H, N=CH),
7.98 (s, 1H, N = CH), 8.75 (d, J = 7.0, 1H, Ar–H), 12.43
(s, 1H, NH); 13C NMR (CDCl3, 100 MHz) d 56.57 (CH2),
120.32 (benzo[d]thiazole), 122.63 (benzo[d]thiazole), 125.16
(benzo[d]thiazole), 127.39 (benzo[d]thiazole), 132.54 (benzo
[d]thiazole), 144.14 (C50-triazole), 148.11 (C30-triazole),
149.81 (benzo[d]thiazole), 169.33 (C2-benzo[d]thiazole),
175.44 (C=O); ESIMS m/z 260.4 (M??1).
2-(o-Toluidino)-N-(1,3-thiazol-2-yl)acetamide (5) White
solid, Yield: 57 & 80 % (MW), M.P.: 160–162 °C, IR:
1
3,345, 3,029, 2,964, 1,670, 1,620, 1,514 cm-1; H NMR
N-(benzo[d]thiazol-2-yl)-2-(1H-imidazol-1-yl)acetamide
(CDCl3, 400 MHz) d 2.2 (s, 3H, –CH3), 3.90 (s, 2H,
–CH2), 4.01 (s, 1H, –NH), 6.49 (d, J = 7.2, 1H, Ar–H),
6.97 (m, 4H, Ar–H), 7.41 (d, J = 7.2, 1H, Ar–H), 11.62
(s, 1H, –NH); 13C NMR (CDCl3, 100 MHz) d 18.22 (CH3),
55.11 (CH2), 113.32 (C5-1,3-thiazole), 118.11 (C20-phe-
nyl), 119.22 (C30-phenyl), 121.39 (C50-phenyl), 125.66
(C40-phenyl), 127.88 (C60-phenyl), 131.56 (C4-1,3-thia-
zole), 144.29 (C10-phenyl), 161.46 (C2-1,3-thiazole), 166.39
(C=O); ESIMS m/z 248.2 (M??1).
(11) White solid, Yield: 75 & 87 % (MW), M.P.: 230 °C,
IR: 3,042, 2,920, 1,662, 1,646, 1,260 cm-1 1H NMR
;
(CDCl3, 400 MHz) d 4.12 (s, 2H, CH2), 7.01 (d, J = 6.6,
1H, N–CH=CH), 7.32 (d, J = 7.0, 1H, N–CH=CH–), 7.45
(s, 1H, N=CH), 7.56 (m, 2H, Ar–H), 8.01 (d, J = 7.0, 1H,
Ar–H), 8.12 (d, J = 7.3, 1H, Ar–H), 11.98 (s, 1H, NH);
13C NMR (CDCl3, 100 MHz) d 39.47 (CH2), 119.23
(benzo[d]thiazole), 121.18 (C40-imidazole), 122.30 (benzo
[d]thiazole), 124.89 (benzo[d]thiazole), 126.93 (benzo[d]
thiazole), 128.49 (C50-imidazole), 132.36 (benzo[d]thia-
zole), 137.70 (C20-imidazole), 150.22 (benzo[d]thiazole),
168.91 (C2-benzo[d]thiazole), 175.12 (C=O); ESIMS
m/z 259.3 (M??1).
2-(p-Toluidino)-N-(1,3-thiazol-2-yl)acetamide (6) White
solid, Yield: 60 & 85 % (MW), M.P.: 162–164 °C, IR:
1
3,356, 3,123, 2,913, 1,664, 1,616, 1,521 cm-1; H NMR
(CDCl3, 400 MHz) d 2.24 (s, 3H, –CH3), 4.02 (s, 2H,
–CH2), 4.13 (s, 1H, –NH), 6.56 (d, J = 6.8, 2H, Ar–H),
7.00 (d, J = 7.1, 1H, Ar–H), 7.02 (d, J = 6.8, 2H, Ar–H),
7.42 (d, J = 7.1, 1H, Ar–H), 10.89 (s, 1H, –NH); 13C NMR
(CDCl3, 100 MHz) d 20.43 (CH3), 55.34 (CH2), 112.94
(C5-1,3-thiazole), 114.32 (C30&C50-phenyl), 129.11
(C40-phenyl), 130.18 (C20&C60-phenyl), 131.11 (C4-1,3-
N-(benzo[d]thiazol-2-yl)-2-(4-fluorophenylamino)acetam-
ide (12) White solid, Yield: 64 & 88 % (MW), M.P.:
146–148 °C, IR: 3,398, 3,048, 2,930, 1,675, 1,648, 1,380,
1
1,252 cm-1; H NMR (CDCl3, 400 MHz) d 4.01 (s, 2H,
CH2), 4.15 (s, 1H, NH), 7.02 (d, J = 6.9, 2H, Ar–H), 7.12
(d, J = 7.0, 2H, Ar–H), 7.45 (m, 2H, Ar–H), 7.73 (d, J =
123

Med Chem Res
7.1, 1H, Ar–H), 7.80 (d, J = 7.3, 1H, Ar–H), 11.12 (s, 1H,
–NH); 13C NMR (CDCl3, 100 MHz) d 54.91 (CH2), 115.34
(C20&C60-4-fluorophenyl), 118.96 (benzo[d]thiazole), 119.12
(C30&C50-4-fluorophenyl), 122.11 (benzo[d]thiazole), 124.84
(benzo[d]thiazole), 126.88 (benzo[d]thiazole), 132.29 (benzo
[d]thiazole), 146.32 (C10-4-fluorophenyl), 152.33 (benzo[d]
thiazole), 154.11 (C40-4-fluorophenyl), 169.21 (C2-benzo
[d]thiazole), 174.93 (C=O); ESIMS m/z 302.1 (M??1).
The synthesized compounds were tested for their anti-
inflammatory activity against carrageenan-induced paw
edema at dose of 10 mg/kg. The percentage inhibition of
edema was calculated using the formula given below:
Vc ꢁ Vt
ꢂ 100
Vc
where Vc is the increase in paw volume of control (in the
absence of test compound), and Vt is the increase in paw
volume after administration of the test compound.
The given data are of five animals (female wistar rats) per
group and divided into eleven (11) groups. Group 1 referred as
control (animals received carrageenan along with the vehicle
[0.5 % carboxymethylcellulose (CMC)]) and Group 2
received standard reference (indomethacin) along with the
vehicle prior to the administration of carrageenan. Group 3, 4,
5, 6, 7, 8, 9, 10 and 11 received the test compounds (3–7 and
10–13), respectively 1 h prior to the administration of carra-
geenan. All the test compounds were suspended in 0.5 % of
CMC and administered orally (10 mg/kg) 60 min prior to the
injection of 0.1 ml of freshly prepared carrageenan (1 %) in
physiological solution (154 mM NaCl) into the subplanter
tissue of hind paw of each rat. The equivalent volume of
carrageenan (1 %) in physiological solution was injected into
hindpaw ofthecontrol. Thevolumewasmeasuredthreetimes
using water plethysmometer prior to the administration of
carrageenan, 2 and 4 h after the injection. The increase in
volume of the paw was adopted as a measure of edema
(Winter et al., 1962). The antiedematous effects of the com-
poundswere estimated aspercentage inhibitionof the induced
inflammation in comparison with control. Statistical analysis
was carried out using a one-way analysis of variance
(ANOVA). In all cases, post hoc comparisons of the means of
individual groups were performed using Tukey’s test. A sig-
nificance level of p \ 0.001 denoted significance in all cases.
N-(benzo[d]thiazol-2-yl)-2-(4-methoxyphenylamino)acet-
amide (13) White solid, Yield: 65 & 85 % (MW), M.P.:
120–122 °C, IR: 3,389, 3,041, 2,920, 1,692, 1,646,
1
1,265 cm-1; H NMR (CDCl3, 400 MHz) d 3.82 (s, 3H,
OCH3), 4.11 (s, 2H, CH2), 5.50 (s, 1H, NH), 6.95 (d, J = 6.7,
2H, Ar–H), 7.51 (d, J = 6.8, 2H, Ar–H), 7.65 (m, 2H, Ar–H),
7.8 (d, J = 7.1, 1H, Ar–H), 7.91 (d, J = 7.3, 1H, Ar–H), 12.61
(s, 1H, NH); 13C NMR (CDCl3, 100 MHz) d 54.77 (CH2),
56.13 (OCH3), 116.52 (C20&C60-4-methoxyphenyl), 117.33
(C30&C50-4-methoxyphenyl), 119.14 (benzo[d]thiazole),
122.20 (benzo[d]thiazole), 123.11 (benzo[d]thiazole),
125.97 (benzo[d]thiazole), 132.67 (benzo[d]thiazole), 138.73
(C10-4-methoxyphenyl), 152.92 (benzo[d]thiazole), 152.11
(C40-4-methoxyphenyl), 169.33 (C2-benzo[d]thiazole), 174.74
(C=O); ESIMS m/z 314.2 (M??1).
Pharmacological evaluation: anti-inflammatory
activity-carrageenan-induced rat paw edema assay
The in vivo anti-inflammatory screening for the synthesized
compounds was performed by using the functional model of
carrageenan-induced rat paw edema and is presented as the
percentage inhibition of edema at the right hind paw in
comparison to the control (Table 2). Carrageenan-induced
edema is a nonspecific inflammation, but is highly sensitive
to NSAIDs. Indomethacin, a potent NSAID was used as a
reference standard. COX-2-mediated increase in prosta-
glandin E2 (PG-E2) production contributes to the severity of
the inflammatory and pain responses in this model. Wistar
rats (female) weighing between 190 and 260 g, obtained
from Central Animal House, Panjab University, Chandigarh,
India and were used in the present study. Animals were kept
in wire-mesh cages and maintained under constant envi-
ronmental food and water (ad libitum), in a constant light–
dark cycle. During the course of experiment, the general
behavior of animals was normal. All the experimental pro-
tocols were approved by the Institutional Animal Ethical
Committee (IACE), and experiments were conducted in
accordance with the standard guidelines. Carrageenan and
indomethacin were procured from Sigma Chemical, Co. For
statistical analysis, we have used GraphPad Prism 3.0 ver-
sion (GraphPad Software Inc (2007).
Molecular modeling study
Molecular modeling investigations were carried out using
Dell Precision work station T3400 running Intel Core2 Duo
Processor, 4 GB RAM, 250 GB hard disk, and NVidia
Quodro FX 4500 graphics card. Maestro 9.4, GLIDE v5.9
XP docking program, Schrodinger Inc. (Maestro version
and 9.4, 2013; Richard et al., 2004) was employed for the
docking studies.
Preparation of protein
PDB structure (www.rcsb.org) 1CX2 (Crystal structure of
COX-2) was downloaded, refined, and prepared using
Schrodinger protein preparation wizard tool (Glide), which
performs the following steps: assigning of bond orders,
addition of hydrogens, optimization of hydrogen bonds by
123

Med Chem Res
Table 2 Anti-inflammatory data of compounds 3–7 and 10–13 on carrageenan-induced paw edema in rats
N
O
N
O
R
R
S
N
S
N
H
H
(3-7)
(10-13)
Treatment
R
Volume of paw edema (ml)
2 h
4 h
Control (carrageenan treated)
Indomethacinb
–
–
0.93 0.012
0.21 0.023a (77.42)
0.36 0.015a (61.29)
0.90 0.020
0.19 0.019a (78.89)
0.32 0.021a (64.44)
3
4
5
0.41 0.020a (55.91)
0.39 0.042a (58.06)
0.40 0.035a (55.55)
0.37 0.030a (58.88)
6
0.37 0.036a (60.22)
0.36 0.017a (61.29)
0.32 0.019a (65.59)
0.29 0.016a (68.81)
0.26 0.019a (72.04)
0.27 0.023a (70.97)
0.34 0.025a (62.22)
0.31 0.030a (65.55)
0.29 0.021a (67.77)
0.27 0.070a (70.00)
0.23 0.090a (74.44)
0.25 0.013a (72.22)
7
10
11
12
13
Values are expressed as mean S.E.M (n = 5) and analyzed by ANOVA
Values in parenthesis (percentage inhibition of edema), 10 mg/kg
a
Different from carragenan group (p \ 0.001)
Reference standard
b
flipping amino side chains, correction of charges, and
minimization of the protein complex. All the bound water
molecules, ligands and cofactors, were removed (prepro-
cess) from the proteins which were taken in.mae format.
The tool neutralized the side chains that are not close to the
binding cavity and do not participate in salt bridges. This
step is then followed by restrained minimization of
cocrystallized complex, which reorients side chain hydro-
xyl groups and alleviates potential steric clashes. The
complex obtained was minimized using OPLS_2005 force
123

Med Chem Res
field (George and Richard, 2001) with Polack-Ribiere
Conjugate Gradient (PRCG) algorithm. The minimization
was terminated either completion of 5,000 steps or after the
energy gradient converged below 0.05 kcal/mol.
with chloroacetyl chloride in the presence of tetrahydro-
furan (THF) using triehtylamine as base maintaining the
temperature between 0 and 5 °C with constant stirring
resulted in the formation of 2-chloro-N-(1,3-thiazol-
2yl)acetamide 2 in quantitative yield (Method A) (Naren-
dra et al., 2010). Similarly, the compound 2 was also
synthesized in good yields by irradiating 2-amino-1,3-thi-
azole 1 with chloroacetyl chloride in the presence of THF
using triehtylamine at 560 W hitherto unreported in the
literature (Method B). The compound 2 was characterized
based on a typical NH absorption at 3,496 cm-1, a strong
signal at 1,676 cm-1 of the carbonyl (C=O) group, H–Ar
absorption at 3,089 cm-1, and –CH2– absorption at
Preparation of ligands
Structures of the ligands (3–7 and 10–13) were sketched
using built panel of Maestro and taken in.mae format. Lig-
Prep is a utility of Schrodinger software suit that combines
tools for generating 3D structures from 1D (Smiles) and 2D
(SDF) representation, searching for tautomers, steric iso-
mers, and perform a geometry minimization of the ligands.
Molecular Mechanics Force Fields (OPLS_2005) with
default settings were employed for the ligand minimization.
1
2,926 cm-1. The H NMR spectrum showed characteristic
singlet at d 3.33 (2H, –CH2) ppm assignable to the two
methylene protons (attached to chlorine atom). A broad
singlet at d 10.37 ppm corresponding to amine proton
(–NH), and two doublets at d 7.11 and 7.23 ppm integrated
to one proton each and assignable to thiazole protons
confirmed the formation of compound 2. The 13C NMR
signal at d 45.44 and 166.72 ppm indicated the presence of
methylene carbon (attached to chlorine atom) and carbonyl
carbon (C=O), respectively. The thiazole carbons appeared
at d 114.22 ppm (C5, thiazole), d 130.66 ppm (C4, thia-
zole), and d 159.93 ppm (C2, thiazole) with good intensity
further confirmed the formation of the key intermediate
compound 2. The compound 2 on reaction with various
aryl amines in basic condition under reflux for 8 h resulted
in the formation of target compounds 3–7 in quantitative
yields. They were also synthesized in good yields by irra-
diating compound 2 with aryl amines under similar basic
condition at 560 W. Compounds 3–7 were characterized
based on a typical NH absorption at 3,240 cm-1, a strong
signal at 1,702 cm-1 of the carbonyl group and H–Ar
absorption at 3,030 cm-1 (except in compound 3 with
–CH2– absorption at 2,928 cm-1). Moreover, the appear-
ance of an additional new broad singlet of NH signal
around d 5 ppm (except in compound 3) along with the NH
signal of amide bond around d 10 ppm and aromatic pro-
tons of various aryl amines at around 7.5 ppm confirmed
the formation of target compounds (3–7). The downfield
shift of 13C NMR signal around d 55 ppm indicated the
attachment of aromatic substituents (except compound 3
with morpholine substituent) to methylene carbon. The
appearance of downfield shift of 13C NMR signal at d
61.39 and 64.23 ppm, respectively assignable to methylene
carbons of morpholine moiety confirmed the formation of
compound 3. Moreover, the appearance of aromatic car-
bons around d 111–140 ppm confirmed the formation of
target compounds (4–7). The 13C NMR signal at d 18.22,
20.43, and 56.38 ppm, respectively, assignable to methyl
carbon (–CH3) attached to ortho and para position of
aromatic moiety of compound 5 and 6 as well as methoxy
Docking studies
Docking studies were carried out using the above men-
tioned prepared protein (PDB: 1CX2) and ligands (3–7 and
10–13), by employing Glide XP docking program (Schro-
dinger Inc.) following the reported procedure (Maestro
version 9.4, and Glide v5.9, 2013; Richard et al., 2004).
Prediction of ADME properties
TheQikPropmoduleofSchrodingerisaquick,accurate, easy-
to-use absorption, distribution, metabolism, and excretion
(ADME) prediction program design to produce certain
descriptors related to ADME. QikProp predicts physically
significant descriptors and pharmaceutically relevant proper-
ties of organic molecules, either individually or in batches.
QikProp has two modes: normal mode and fast mode. In fast
mode, certain time-consuming calculations are omitted; some
properties are not predicted, and some have different values.
In the present study, QikProp was run in normal processing
modewithdefaultoptions(QikProp,version3.6,2013).Toset
up the calculation, pose viewer file (generated after docking
with Glide) was used to consider the receptor and source of
ligands. Afterchoosingthereceptorandligands, byusingpose
viewer file (pv.maegz), the program QikProp that generates
the descriptors were run with default options that were chosen
toproducereasonabledescriptors. The selectedpropertiesthat
are known to influence metabolism, cell permeation, and
bioavailability are presented in Table 3.
Results and discussion
Chemistry
As illustrated in Scheme 1, target compounds were syn-
thesized from 2-amino-1,3-thiazole 1 which on reaction
123

Med Chem Res
Table 3 Properties of tested compounds calculated by QikProp
Comp No.
QPlogPo/wa
QPlogSb
QPPCacoc
#metabd
Percent human
oral absorptione
Lipinski’s
rule of fivef
3
0.753
0.488
0.384
1.58
-2.507
-2.223
-2.045
-3.654
-5.036
-4.548
-3.049
-4.656
-3.228
317.043
297.565
319.565
408.183
603.636
527.28
3
3
3
3
3
3
3
4
3
76.122
74.078
74.019
82.927
94.375
89.575
71.714
84.089
80.941
0
0
0
0
0
0
0
0
0
4
5
6
7
3.016
2.376
0.736
2.337
1.3
10
11
12
13
a
182.19
267.979
390.352
Predicted log of the octanol/water partition coefficient, range 95 % of drugs (-2 to 6.5)
b
c
Predicted log of aqueous solubility S (mol/l), range 95 % of drugs (-6.5 to 0.5)
Caco2 cell permeability in nm/s, range 95 % of drugs (\25 poor, [500 great). Caco-2 cells are a model for the gut-blood barrier. QikProp
predictions are for nonactive transport.
d
Number of likely metabolic reactions. Range 95 % of drugs (1–8).
e
Predicted human oral absorption on 0–100 % scale ([80 % is high, and \25 % is poor)
f
Number of violations of Lipinski’s rule of five. The rules are: mol_MW \ 500, QPlogPo/w \ 5, donorHB B 5, accptHB B 10. Compounds
that satisfy these rules are considered druglike. (The ‘‘five’’ refers to the limits, which are multiples of 5.)
carbon (–OCH3) attached to para position of compound 7.
Further, molecular ion peak (ESI–MS) corresponding to its
molecular formula revealed the formation of all the
products.
127.67 (benzo[d]thiazole), 132.33 (benzo[d]thiazole), 149.94
(benzo[d]thiazole), 175.55 (C2-benzo[d]thiazole) ppm,
respectively, with good intensity further confirmed the for-
mation of the key intermediate compound 9. The compound 9
on reaction with various aryl amines in basic condition under
reflux for 2–4 h resulted in the formation of target compounds
10–13 in quantitative yields. They were also synthesized in
good yields by irradiating 9 with various aryl amines in the
presence of THF and triethylamine at 560 W. Compounds
10–13 were characterized based on a typical NH absorption at
3,505 cm-1, a strong signal at 1,702 cm-1 indicating car-
bonyl group and H–Ar absorption at 3,030 cm-1. Further, the
appearance of an additional new broad singlet of NH signal
aroundd6.5–7 ppm(compounds12 &13)andtypicaltriazole
and imidazole proton peak at d 7–8 ppm (compounds 10 &
11) along with the NH signal of amide bond around d 12 ppm
and aromatic protons of various aryl amines at around
7.5 ppm confirmed the formation of target compounds 10–13.
The downfield shift of 13C NMR signal around d 55 ppm
indicated the replacement of chlorine atom and attachment of
aromatic substituents to methylene carbon. The appearance of
downfield shift of 13C NMR signal at d 144.14 (C50-triazole),
148.11 (C30-triazole) ppm, respectively assignable to triazole
carbons confirmed the formation of compound 10. Similarly,
the appearance of 13C NMR signal at d 121.18 (C40-imidaz-
ole), 128.49 (C50-imidazole), 137.70 (C20-imidazole) ppm,
respectively assignable to imidazole carbons confirmed the
formation of compound 11. Moreover, the appearance of
additional aromatic carbon signals around d 115–150 ppm
confirmed the formation of target compounds 12 and 13. The
Similarly, the target compounds 10–13 were synthesized
following scheme-2, starting from 2-amino-benzo[d]thiazole
8 which on reaction with chloroacetyl chloride in the presence
of tetrahydrofuran (THF) using triehtylamine as a base
maintainingthetemperaturebetween0and5 °Cwithconstant
stirring resulted in the formation of N-(benzo[d]thiazol-2-yl)-
2-chloroacetamide 9 in quantitative yield (Method A)
(Guangfu et al., 2001). Similarly, the compound 9 was also
synthesized in good yields by irradiating 2-amino-
benzo[d]thiazole 8 with chloroacetyl chloride under similar
basic condition at 560 W hitherto unreported in the literature
(Method B). The compound 9 was characterized based on a
typical NH absorption at 3,505 cm-1, a strong signal at
1,691 cm-1 of the carbonyl (C=O) group, H–Ar absorption at
1
3,048 cm-1, and –CH2– absorption at 2,920 cm-1. The H
NMR spectrum showed characteristic singlet at d 4.37 (2H,
–CH2)ppmassignabletothetwomethylene protons(attached
to chlorine atom). A broad singlet at d 12.63 ppm corre-
sponding to amine proton (–NH) and two multiplets at d 7.85
and 7.42 ppm, respectively, integrated to two protons each
and assignable to aromatic protons confirmed the formation of
compound 9. The 13C NMR signal at d 47.68 and 167.64 ppm
indicated the presence of methylene carbon (attached to
chlorine atom) and carbonyl carbon (C=O), respectively. The
benzo[d]thiazole carbons appeared at d 120.20 (benzo[d]thi-
azole), 122.54 (benzo[d]thiazole), 125.59 (benzo[d]thiazole),
123

Med Chem Res
Scheme 1 Synthesis of
N
2-(substituted)-N-(thiazol-2-
yl)acetamide derivatives.
Reagents and conditions:
(i) Method A, ClCH2COCl,
THF, triethyl amine, 0–5 °C,
30 min; (ii) Method B,
NH2
S
(1)
(i)
(ii)
ClCH2COCl, THF, triethyl
amine, MW 560 W, 10 s; (iii)
Method A, aryl amines, THF,
triethyl amine, reflux, 8 h; (iv)
Method B, Aryl amines, THF,
Triethyl amine, MW 560 W,
45–50 s
N
O
N
O
Cl
Cl
Compound No.
(3)
R
S
S
N
H
(2)
N
H
N
O
(2)
(4)
(5)
HN
HN
(iii)
(iv)
H3C
HN
(6)
(7)
CH3
N
O
R
HN
OCH3
S
N
H
(3-7)
Scheme 2 Synthesis of N-
(benzo[d]thiazol-2-yl)-2-
(substituted)acetamide
N
S
NH2
(i)
(8)
derivatives. Reagents and
conditions: (i) Method A,
ClCH2COCl, THF, Triethyl
amine, 0–5 °C, 3 h; (ii) Method
B, ClCH2COCl, THF, Triethyl
amine, MW 560 W, 20 s; (iii)
Method A, Aryl amines, THF,
Triethyl amine, reflux, 2–4 h;
(iv) Method B, Aryl amines,
THF, Triethyl amine, MW
560 W, 30–50 s
(ii)
N
O
N
O
Cl
Cl
S
S
N
N
(9)
H
H
(9)
Compound No.
(10)
R
N
(iv)
(iii)
N
N
N
N
(11)
(12)
(13)
F
N
O
HN
HN
R
OCH3
S
N
H
(10-13)
13C NMR signalatd 56.13 ppm assignableto methoxycarbon
(–OCH3) attached to para position of compound 13. Further,
molecular ion peak (ESI–MS) corresponding to its molecular
formula revealed the formation of the product.
Anti-inflammatory activity: Carrageenan-induced rat
paw edema assay
All the title compounds were screened for their in vivo
anti-inflammatory activity using the carrageenan-induced
rat paw edema model and exhibited protection against
carrageenan-induced edema (Table 2; Fig. 1a, b). The
protection ranged up to 72 %, while the reference drug
(indomethacin) showed 77 % at an equivalent dose.
Among all the tested compounds, N-(benzo[d]thiazol-2-
yl)-2-(substituted)acetamides 10–13 showed remarkable
anti-inflammatory activities compared to other derivatives.
In particular, compounds 12 and 13 with 4-fluoroaniline
and 4-methoxyaniline substituent showed better activity
compare to analogs 10 and 11 with triazole and imidazole
Under classical heating conditions, these reactions have
certain disadvantages like long reaction times (30 min–
8 h), high energy consumption and the need for large
amounts of solvents for work up and purification. The
MW-assisted reactions were carried out using a Catalyst
Microwave Reactor, under constant irradiation power and
by varying the temperature (the so-called ‘‘power con-
trol’’). The best results were obtained when we used 80 %
of the full power of the magnetron (560 W). The details of
the optimized conditions employed, under MW irradiation
as well as under classical heating are presented in Table 1.
123

Med Chem Res
Fig. 1 Treated groups versus paw edema (ml). a after 2 h, b after 4 h
moieties. It indicates that the presence of benzene ring
attached with thiazole moiety along with the presence of
NH group attached to the aromatic ring is essential for
showing the enhanced activity. Further it has been
observed that a fluoro group at a strategic position on the
heterocyclic ring enhances the activity of a molecule due to
its enhanced lipophilicity (William, 2008) as it can be
evident from the most active compound 12 (with 4-fluo-
roaniline group). The SAR of the title compounds was
drawn based on docking studies and their binding mode
analyses.
Leu352, Val523, the backbone of Ser353, and Tyr355.
Further sulphonamido group interacted with His90, Arg513,
and Gln192 by forming a hydrogen bond which is the key
point of interaction for COX-2 selectivity. In particular,
sulfonamide –NH2 was found to form hydrogen bonding
with the nitrogen atom of imidazole ring of His90 and oxy-
˚
gen atom of Ser353 at a distance of 2.505 and 3.19485 A,
respectively, whereas sulfonamide oxygen (=O) formed
hydrogen bond with the NH of Arg513. Pyrazole ring of SC-
558 is found to be located within the vicinity of Tyr355 and
Val349. Sulphonyl group of the ligand was located around
the residues of Gln192, Ser353, Phe518, Arg513, and
Val523. Bromophenyl moiety was surrounded by Gly526,
Val523, and Ala527. These residues were identified as cru-
cial and involved in the binding which perhaps contributing
to the selectivity of the ligand.
Molecular modeling studies
The final compounds 3–7 and 10–13 were evaluated in
silico (docking) to recognize their hypothetical binding
mode using the X-ray crystal structure of COX-2 (PDB ID:
1CX2) and also to rationalize their structure activity rela-
tionships. To investigate the ability of molecular docking
to reproduce an experimentally observed ligand-binding
mode, the cocrystallized ligand SC-558 (a selective COX-2
inhibitor) has been used as reference ligand (Fig. 2a). It
was docked back into its binding site (Fig. 2a) of the
crystal structure of the COX-2 using GLIDE docking
program (Schrodinger Inc.). The top docked conformations
(poses) closely resembled the cocrystallized conformation
with a root-mean-square deviation (RMSD) 0.50–0.90 of
nonhydrogen atomic positions of the ligand (SC-558).
The experimental binding mode of SC-558 was repro-
duced and as shown in the Fig. 2a; the trifluoromethyl group
(–CF3) formed strong hydrogen bonding interactions with
Earlier from the docking studies of the indomethacin, a
nonselective COX-1/2 inhibitor, it has been observed that
the carboxylate ion formed a salt bridge with the Arg120 in
COX-2 isoenzyme which gives a more generalized
anchoring point for all the classical NSAIDs, thus, limiting
their selectivity due to curtailed freedom of movement of
the ligand (Balakumar et al., 2010). The present docking
study also revealed the similar observation (Fig. 2b). The
acetyl CH2 of indomethacin formed a hydrogen bond with
˚
the phenolic OH group of Tyr355 at a distance of 3.256 A,
whereas the chlorophenyl group showed significant p-p
stacking interaction with the phenyl ring of Phe518.
Interestingly, all the thiazole as well as benzothiazole
derivatives 3–7 and 10–13 docked well into the binding
pocket of COX-2 (Fig. 2c–h). The NH group and fluoro
group at 4th position of the 4-fluoroaniline moiety of the
most active compound 12 were found to form moderate
˚
the exocyclic NH2 group of Arg120 at a distance of 2.087 A.
The same group (–CF3) was also found to be located in the
vicinity of Leu531, Val116, Val349, Leu359, and Tyr355.
The Val523 permits the location of the phenylsufonamide
group of the ligand (SC-558) in a cavity formed by Phe518,
˚
H-bond with the phenolic OH group of Tyr355 (3.108 A)
˚
and exocyclic NH2 group of Arg120 (3.810 A), respec-
tively (Fig. 2d, e), as compared to SC-558. Similarly, the
123

Med Chem Res
Fig. 2 a Superimposition of redocked SC-558 (cyan color) with its
original position (yellow color) as cocrystal in the binding site of the
crystal structure of COX-2 (PDB ID: 1CX2) isoenzyme (rmsd-
0.50–0.90) showing H-bond interactions with the amino acid residues
His90, Arg120, Tyr355, and Arg513, respectively. b Binding orientation
of indomethacin within the binding site of COX-2 showing salt bridge
formation between the carboxylate ion and Arg120. c Superimposition of
compounds 3–7, 10–13, and SC-558 original position (yellow color) and
orientation in the binding site of the crystal structure of COX-2.
d Superimposition ofcompound12 and SC-558 with their orientations in
the binding site of the crystal structure of COX-2. e Hypothetical binding
motif of compound 12 showing H-bonding interaction between F atom
and N–H of fluoroaniline moiety with N–H of Arg120 and OH of Tyr355
˚
at a distance 3.810 and 3.108 A, respectively. f Hypothetical binding
orientation of compound 13 showing H-bonding interaction between OH
and N–H of p-anisidinemoiety with N–H ofArg120 and OH of Tyr355 at
˚
a distance 3.846 and 2.288 A, respectively. g Binding orientation of
compound 10 in the binding site of the crystal structure of COX-2.
h Superimposition of compounds 3, 7, and SC-558 original position
(yellow color) and orientation in the binding site of the crystal structure of
COX-2 (Color figure online)
123

Med Chem Res
compound 13 showed significant H-bond between the
H-atom of N–H group and O-atom at 4th position of the
4-methoxyaniline group with the phenolic OH group of
Tyr355 and exocyclic NH2 group of Arg120 at a distance
2-(substituted)acetamide 10–13 derivatives have been syn-
thesized and evaluated in vivo (rat paw edema) for their anti-
inflammatory activities and in silico (docking studies) to
recognize the hypothetical binding motif of the title com-
pounds with the cyclooxygenase isoenzyme (COX-2)
employing GLIDE software (Schrodinger Inc.). The
microwave-assisted synthesis of these compounds was
found be economic, less time consuming with better yield as
compared to classical heating conditions. Among all
the tested compounds, N-(benzo[d]thiazol-2-yl)-2-(substi-
tuted)acetamides 10–13 showed remarkable anti-inflam-
matory activity compared to other derivatives (around
84–93 % of the standard: indomethacin). In particular,
compounds 12 and 13 with 4-fluoroaniline and 4-methoxy-
aniline substituent showed better activity compared to ana-
logs 10 and 11 with triazole and imidazole moieties. The
binding mode of the title compounds has been proposed
based on the docking studies. The predicted ADME prop-
erties of all the tested compounds were in the ranges as
predicted by QikProp for 95 % of known oral drugs and also
satisfy the Lipinski’s rule of five which signifies a good
absorption and hence, good bioavailability so that the
observed differences in bioactivity of these compounds may
be attributable to the differences in their chemical structures.
Further, evaluation of these active compounds for their
in vitro COX-2 binding studies is under progress.
˚
2.288 and 3.846 A, respectively (Fig. 2f). The thiazole and
benzothiazole moieties of all the target compounds were
found to be aligned similar to the bromophenyl ring of
SC558, and the benzene ring of the benzothiazole moiety
showed significant p–p stacking interaction with Phe518
(Fig. 2c–g) similar to indomethacin which probably
account for their better anti-inflammatory efficacy com-
pared to other analogs 3–7 of the series. Whereas in case of
compounds 10 and 11, the N-atom of triazole and imid-
azole moiety formed significant H-bond with the exocyclic
˚
NH2 group of Arg120 at a distance 2.245 and 1.959 A,
respectively, (Fig. 2g) but there was no H-bond formation
with Tyr355 due to lack of aromatic NH group which
probably causes decrease in their activities compared to
other benzothiazole derivatives.
The thiazole derivatives (4–7, except compound 3), on
the other hand, were found to have different orientations
compared to benzothiazole derivatives where the aromatic
ring attached to amino moiety was found to be aligned with
phenylsulfonamido group of SC558. Hence they were
unable to form any hydrogen bond with Arg120, but
showed significant hydrogen bond formation with other
important amino acid residues such as His90 and Arg513
(Fig. 2h). Moreover, these derivatives could not form any
p–p stacking interaction with Phe518 which might be the
reason for their overall decrease in activity as compared to
benzothiazole derivatives 10–13. Further, none of the
compounds showed any kind of salt bridge formation like
nonselective indomethacin. Hence it can be deduced that in
silico docking, studies can enable us to get an insight and
further guide us to rationally design novel and potent anti-
inflammatory agents in future.
Acknowledgments The author PKD is thankful to CSIR, New
Delhi for awarding the Senior Research Fellowship [Sanction No.
09/135/(0534)/2008/EMR-I (18/03/2008)]. The authors thankfully
acknowledge the Chairman, UIPS, Chandigarh for providing the
facilities. Authors are also thankful to Dr. Kanwaljit Chopra, Phar-
macology Division and Dr. Maninder Karan Vasisht, Pharmacognosy
Division, UIPS, PU for valuable help during pharmacological studies.
Authors profusely thank to Avtar Singh, SAIF (CIL), PU for carrying
out the NMR studies. Author PKD is thankful to Pharmaceutical
Chemistry Division, School of Pharmacy, IMU, Malaysia for pro-
viding the facilities to carry out the docking studies. Authors are also
thankful to Mr. Raghurangaswamy, Executive Director, Schrodinger,
India for providing the evaluation license (14 Jun–16 July, 2013) to
carry out the molecular modeling studies.
Prediction of ADME properties
The expected ADME properties of the tested compounds
were evaluated with QikProp module of Schrodinger
(Table 3). The selected properties are known to influence
metabolism, cell permeation, and bioavailability. Almost
all the predicted properties of the tested compounds were in
the ranges as predicted by QikProp for 95 % of known oral
drugs and also satisfy the Lipinski’s rule of five to be
considered as druglike potential.
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