N-1 and C-3 substituted indole Schiff bases as selective COX-2 inhibitors: Synthesis and biological evaluation

Article abstract of DOI:10.1016/j.bmcl.2012.01.130

A group of N-1 and C-3 disubstituted-indole Schiff bases bearing an indole N-1 (R′ = H, CH₂Ph, COPh) substituent in conjunction with a C-3 -CHN-C₆H₄-4-X (X = F, Me, CF₃, Cl) substituent were synthesized and eval

Full text of DOI:10.1016/j.bmcl.2012.01.130

Bioorganic & Medicinal Chemistry Letters 22 (2012) 2154–2159
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
N-1 and C-3 substituted indole Schiff bases as selective COX-2 inhibitors:
Synthesis and biological evaluation
⇑
Jatinder Kaur, Atul Bhardwaj, Zhangjian Huang, Edward E. Knaus
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2N8
a r t i c l e i n f o
a b s t r a c t
A group of N-1 and C-3 disubstituted-indole Schiff bases bearing an indole N-1 (R0 = H, CH2Ph, COPh) sub-
stituent in conjunction with a C-3 –CH@N–C6H4–4-X (X = F, Me, CF3, Cl) substituent were synthesized and
evaluated as inhibitors of cyclooxygenase (COX) isozymes (COX-1/COX-2). Within this group of Schiff
bases, compounds 15 (R1 = CH2Ph, X = F), 17 (R1 = CH2Ph, X = CF3), 18 (R1 = COPh, X = F) and 20
(R1 = COPh, X = CF3) were identified as effective and selective COX-2 inhibitors (COX-2 IC50’s = 0.32–
Article history:
Received 13 January 2012
Revised 25 January 2012
Accepted 30 January 2012
Available online 6 February 2012
0.84
l
M range; COX-2 selectivity index (SI) = 113 to >312 range). 1-Benzoyl-3-[(4-trifluoromethylphe-
M; COX-2 IC50 = 0.32 M)
Keywords:
Inflammation
Cyclooxygenase-1 and -2
In vitro COX-2 inhibition
Indole
nylimino)methyl]indole (20) emerged as the most potent (COX-1 IC50 >100
and selective (SI >312) COX-2 inhibitor. Furthermore, compound 20 is a selective COX-2 inhibitor in con-
trast to the reference drug indomethacin that is a potent and selective COX-1 inhibitor (COX-1
IC50 = 0.13 lM; COX-2 IC50 = 6.9 lM, COX-2 SI = 0.02). Molecular modeling studies employing compound
l
l
20 showed that the phenyl CF3 substituent attached to the C@N spacer is positioned near the secondary
pocket of the COX-2 active site, the C@N nitrogen atom is hydrogen bonded (Nꢀ ꢀ ꢀNH = 2.85 Å) to the H90
residue, and the indole N-1 benzoyl is positioned in a hydrophobic pocket of the COX-2 active site near
W387.
Molecular modeling
Ó 2012 Elsevier Ltd. All rights reserved.
Nonsteroidal anti-inflammatory drugs (NSAIDs) have been
widely used for the relief of pain, fever and inflammation. NSAIDs
act by inhibiting the cyclooxygenase (COX) catalyzed biotransfor-
mation of arachidonic acid (AA) to prostaglandins (PGs), prostacy-
clin (PGI2), and thromboxane A2 (TXA2).1–3 Traditional NSAIDs
(aspirin, ibuprofen, naproxen and indomethacin), and selective
inhibitors of COX-2 (celecoxib, rofecoxib and valdecoxib), exert their
desirable therapeutic and unwanted side effects by suppressing the
functions of COX-1 and/or COX-2 isozymes.4–9 The COX-1 isoform,
that is expressed constitutively in most tissues, provides important
physiological maintenance actions such as synthesis of cytoprotec-
tive prostaglandins in the gastrointestinal tract, vascular homeosta-
sis,10 induction of labor pain, and the biosynthesis of proaggregatory
TXA2 in blood platelets.11 The use of non-selective NSAIDs (aspirin,
ibuprofen and indomethacin), based on their cytoprotective and
associated actions of the COX-1 isoform, is limited due to contrain-
dicated side effects that include gastrointestinal (GI), ulcerogenic,
hepatic and renal toxicity.12–22 Unlike COX-1, the COX-2 isoform is
induced by mitogenic and proinflammatory stimuli23 resulting in
peripheral inflammatory actions.24 Selective inhibition of COX-2
was found to be a safer way to reduce gastrointestinal toxicity.
Accordingly, selective COX-2 inhibitors provide effective treatment
of inflammatory disease states such as rheumatoid arthritis and
osteoarthritis. A number of selective COX-2 inhibitors such as cele-
coxib, rofecoxib and valdecoxib (see structures 1–3 in Fig. 1),25–28
have been developed and were approved for clinical use.
Unfortunately, the cardiovascular side effects of selective COX-2
inhibitors soon became evident since it was found that celecoxib29
and rofecoxib30 cause a significant decline in the urinary excretion
of the metabolite prostacyclin (PGI2 is a potent vasodilator, anti-
thrombotic), but not thromboxane A2 (TxA2 is prothrombotic). This
biochemical imbalance in PGI2/TxA2 production is considered to be
the major cause of adverse cardiovascular thrombotic events asso-
ciated with the use of highly selective COX-2 inhibitors.31–35 Ongo-
ing safety concerns pertaining to the use of non-selective NSAIDs
has provided a stimulus for the development of new COX-2 inhib-
itors with a greater safety profile.
Numerous investigations exploring the design of indole ring
based NSAIDs have been described that were targeted at improving
their COX-2 selectivity and safety profile. These studies encom-
passed modifications of the indole ring and side chains of the
highly ulcerogenic and selective COX-1 inhibitor indomethacin
(4).36–42 In continuation of our ongoing research work directed
towards the development of selective COX-2 inhibitors,43–45 we
have selected the indole ring as the template. A group of indole
based Schiff bases (9–11, 15–21; Fig. 1), employing focused substi-
tution at the N-1 and C-3 positions of the indole ring, were synthe-
sized. The COX-1/COX-2 inhibitory activities of this new class of
compounds were determined, and plausible binding interactions
⇑
Corresponding author. Tel.: +1 780 492 5993; fax: +1 780 492 1217.
E-mail address: eknaus@pharmacy.ualberta.ca (E.E. Knaus).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2012.01.130

J. Kaur et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2154–2159
2155
NH2
O
CH3
O
NH2
O
O
O
S
H3C
S
S
O
N
N
N
O
CH3
O
O
CF3
Valdecoxib (3)
X
Rofecoxib (2)
OH
Celecoxib (1)
O
H
O
N
H3C
CH3
3
N
1
N
O
R1
9-11 (R1= H,
15-17 (R1= CH2Ph, X = F, CH3, CF3)
18-21 (R1= COPh, X = F, CH3, CF3, Cl)
X
= F, CH3, CF3)
Cl
Indomethacin (4)
Figure 1. Chemical structures of some selective COX-2 inhibitors (1–3), a non-selective COX-2 inhibitor (4), and the target Schiff base derivatives of indole (9–11 and 15–21).
X
H
N
O
H
H2N
a
+
X
N
H
N
H
6; X = F
5
9; X = F
10; X = CH3
11; X = CF3
7; X = CH3
8; X = CF3
X
b
H
O
N
H
H2N
3
c
+
1
X
N
R1
N
R1
15; R1 = CH2Ph, X = F
6; X = F
12; R1 = CH2Ph
13; R1 = COPh
16; R1 = CH2Ph, X = CH3
17; R1 = CH2Ph, X = CF3
18; R1 = COPh, X = F
19; R1 = COPh, X = CH3
20; R1 = COPh, X = CF3
21; R1 = COPh, X = Cl
7; X = CH3
8; X = CF3
14;X = Cl
Scheme 1. Reagents and conditions: (a) p-toluenesulfonic acid, absolute ethanol, reflux, 8 h for compound 9; 4 h for compound 10; 12 h for compound 11; (b) benzyl
bromide, sodium hydride (NaH), dry THF, 25 °C, 10 min for compound 12; benzoyl chloride, sodium hydride (NaH), dry THF, 25 °C, 20 min for compound 13, (c) p-
toluenesulfonic acid, absolute ethanol, reflux, 20 min for compound 15; 10 min for compound 16; 3 h for compound 17; 30 min for compound 18; 10 min for compound 19;
1 h for compound 20; 40 min for compound 21.
of these compounds within the COX-1/COX-2 active sites were
explored using molecular modeling studies.
benzyl bromide and benzoyl chloride in the presence of sodium
hydride (NaH) in dry THF. The subsequent reaction of these N-
substituted-indole-3-carboxaldehydes (12–13) with a para-substi-
tuted-aniline (H2N–C6H4–4-X; X = F, Me, CF3, Cl) in the presence of
p-toluenesulfonic acid with absolute ethanol as solvent at 70–80 °C
with a reaction time from 10 min to 3 h furnished the target prod-
ucts 15–21 (18, 82%; 19, 85%; 20, 64%; 21, 89%; 22, 86%; 23, 83%;
24, 88%; isolated yield).
The synthetic methodologies used to synthesize the target com-
pounds 9–11 and 15–21 are shown in Scheme 1. Reaction of indole-
3-carboxaldehyde (5) with a para-substituted-aniline 6–8 (H2N–
C6H4–4-X; X = F, Me, CF3) in the presence of p-toluenesulfonic acid
in absolute ethanol at 70–80 °C with reaction times of 4–12 h fur-
nished compounds 9–11 (9, 80%; 10, 78%; 11, 72%; isolated yield).
The N-benzyl (12, 90%) and N-benzoyl (13, 87%) derivatives of
indole-3-carboxaldehyde were prepared by reaction of 5 with
In vitro COX-1/COX-2 isozyme inhibition studies (Table 1)
showed that the compounds (9–11 and 15–21) are more potent

2156
J. Kaur et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2154–2159
Table 1
In vitro COX-1 and COX-2 inhibition, COX-2 selectivity index (SI), and Eintermolecular data
X
H
N
3
1
N
R1
a
c
Compound
R1
X
IC50
(l
M)
COX-2 SIb
Eintermolecular
COX-1
COX-2
COX-1
COX-2
9
10
11
15
16
17
18
19
H
H
H
CH2Ph
CH2Ph
CH2Ph
COPh
COPh
COPh
COPh
F
68.4
62.3
78.2
91.1
81.5
95.5
>100
80.2
>100
86.1
0.13
0.35
7.7
17.2
30.4
11.6
0.71
17.5
0.84
0.43
12.4
0.32
6.53
6.9
4.0
2.0
6.7
128.3
4.7
113.6
>232
6.5
>312
13.2
0.02
0.14
110
ꢁ8.77
ꢁ9.01
ꢁ8.01
ꢁ8.09
ꢁ7.99
ꢁ7.80
ꢁ7.90
ꢁ8.10
ꢁ8.12
ꢁ7.61
—
ꢁ9.64
ꢁ10.01
ꢁ10.12
ꢁ13.52
ꢁ11.13
ꢁ12.21
ꢁ13.10
ꢁ12.01
ꢁ12.50
ꢁ13.01
—
CH3
CF3
F
CH3
CF3
F
CH3
CF3
Cl
20
21
Indomethacin
Aspirin
Celecoxib
2.4
0.07
—
—
—
—
a
The in vitro test compound concentration required to produce 50% inhibition of ovine COX-1 or human recombinant COX-2. The result (IC50, lM) is the mean of two
determinations acquired using the enzyme immuno assay kit (Catalogue No. 560131, Cayman Chemicals Inc., Ann Arbor, MI, USA) and the deviation from the mean is <10% of
the mean value.
b
In vitro COX-2 selectivity index (COX-1 IC50/COX-2 IC50).
Calculated energy of intermolecular interactions during docking in the COX-1/COX-2 active site.
c
inhibitors of COX-2 (IC50 = 0.32–30.4
l
M
range) than COX-1
and the indole nucleus is positioned near the COX-2 hydrophobic
pocket in the vicinity of Y385, W387 and F518 residues. The phenyl
ring of the benzyl group is orientated towards the entrance of the
COX-2 active site secondary pocket lined by H90, R513, Q192 and
A516 residues. The F-atom is positioned near V116 where the mea-
sured distance between the F-atom and the –C@O group of V116 is
3.11 Å.
(IC50 = 62.3 to >100 M range). Structure–activity data acquired
l
showed that the indole N-substituent (R1) was a determinant of
COX-2 inhibitory potency and the COX-2 selectivity index where
the relative profile was –COPh > CH2Ph > H, irrespective of
whether the X-substituent was F, Me or CF3. The anilino X-substi-
tuent was also a determinant of COX-2 potency and COX-2 selec-
tivity index where the relative profile was CF3 > F > Me when the
R1-substituent was –COPh (18–21) or H (9–11). In comparison,
for compounds 15–17 possessing a R1 = benzyl substituent, the
relative profile with respect to the X-substituent was F > CF3 > Me.
Within the N1-benzoyl group of compounds 18–21, the halogeno
X-substituent was a determinant of COX-2 inhibitory potency
and selectivity where the relative profile was F (18) > Cl (21).
Among the ten compounds tested, compound 15 (R1 = CH2Ph,
A docking study for the compound 20 indicates that the phenyl
ring bearing the CF3 substituent, that is attached to the indole ring
via a C@N linker, is oriented toward the secondary pocket of the
COX-2 active site (Fig. 3) with the CF3 group in close proximity
of the Q192 residue (3.24 Å). The C@N nitrogen is hydrogen
bonded to the H90 residue (Nꢀ ꢀ ꢀNH = 2.85 Å), the benzoyl group
is positioned in the vicinity of the W387 residue that is part of
the COX-2 active site hydrophobic pocket, and the carbonyl oxygen
atom assumes a position close to V523 (3.11 Å). The energy associ-
ated with intermolecular interactions (Eintermolecular) obtained upon
computational analysis (docking) for all of the compounds within
the COX-1 and COX-2 active site is summarized in Table 1. The
comparison of Eintermolecular for compound 9, 11 (R1 = H) with 15,
17 (R1 = CH2Ph) and 18, 20 (R1 = COPh) supports the appreciable
interaction of compounds 15, 17, 18 and 20 within the COX-2 ac-
tive site. These favorable entry and binding interactions of com-
pound 15, 17, 18 and 20 within the COX-2 active site are
consistent with their experimentally observed potent COX-2 inhi-
bition. Compounds 15 and 20, which show only partial entry into
the COX-1 active site, did not show any significant interactions
with the COX-1 active site residues (data not shown).
X = F, COX-2 IC50 = 0.71
X = CF3, COX-2 IC50 = 0.84
X = F, COX-2 IC50 = 0.43
M and SI = >232), 20 (R1 = COPh and
X = CF3, COX-2 IC50 = 0.32 M and SI = >312), were identified as
l
M and SI = 128.3), 17 (R1 = CH2Ph and
and SI = 113.6), 18 (R1 = COPh,
lM
l
l
potent and selective COX-2 inhibitors. In contrast, indomethacin
and aspirin are selective COX-1 inhibitors. Accordingly, replace-
ment of the C-3 acetic acid moiety in indomethacin by a Schiff
base –CH@N–C6H4–4-X moiety (X = F, Me, CF3, Cl) constitutes a
drug design strategy that confers COX-2 inhibitory activity and
selectivity. In this regard, these Schiff base analogs of indometha-
cin possess a profile that is more similar to that of the selective
COX-2 inhibitor celecoxib.
To gain insight into the plausible mode of interaction(s) of the
compounds within the COX-1 and COX-2 isozymes, molecular
modeling (docking) experiments were performed using X-ray crys-
tal structure data for COX-1 and COX-2 obtained from the protein
data bank.46,47 Docking results for two of the lead compounds 15
and 20 are provided. Compound 15 assumes a favorable orienta-
tion within the COX-2 binding site (Fig. 2), wherein the C@N nitro-
gen atom shows hydrogen bonding with S530 (Nꢀ ꢀ ꢀHO = 2.80 Å),
In conclusion, a group of new N-1, C-3 substituted indole Schiff
bases were synthesized48 for evaluation53 as COX-1/COX-2 inhibi-
tors. Molecular modeling (docking) studies54 indicate appreciable
binding interactions within the COX-2, but not the COX-1, active
site that is enhanced by substituents at the indole N1-position
(PhCH2–, PhCO–). Compounds 15, 17, 18 and 20 were identified
as the most potent and selective COX-2 inhibitors. Within this

J. Kaur et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2154–2159
2157
Figure 2. Molecular modeling (docking) of compound 15 (carbon atoms in orange) in the binding site of COX-2 (pdb ID 6COX; Eintermolecular = ꢁ13.52 kcal/mol). Hydrogen
atoms of amino acid residues have been removed to improve clarity.
Figure 3. Molecular modeling (docking) of compound 20 (carbon atoms in orange) in the binding site of COX-2 (pdb ID 6COX; Eintermolecular = ꢁ12.50 kcal/mol). Hydrogen
atoms of amino acid residues have been removed to improve clarity.
group of compounds, a ‘lead-compound’ 1-benzoyl-3-[(4-trifluo-
romethylphenylimino)methyl]indole (20) was identified that
exhibited appreciable COX-2 inhibitory activity and selectivity
a drug design strategy that confers COX-2 inhibitory activity and
selectivity. The suitability of the imino compounds 9–11, 15–21
(–CH@N–R1; R1 = aryl) for oral administration has not been deter-
mined. Their hydrolysis to the respective aldehyde and amine,
which would be more difficult compared to when R1 is H, requires
acid or base catalysis. The Schiff base compounds described in this
study, unlike indomethacin having a pKa of 4.5, are not acidic.
(COX-1 IC50 >100 lM; COX-2 IC50 = 0.32 lM; COX-2 SI >312).
Replacement of the C-3 acetic acid moiety in the potent, highly
ulcerogenic, and very selective COX-1 inhibitor indomethacin by a
Schiff base –CH@N–C6H4–4-X moiety (X = F, Me, CF3, Cl) constitutes

2158
J. Kaur et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2154–2159
40. Hu, W.; Guo, Z.; Chu, F.; Bai, A.; Yi, X.; Cheng, G.; Li, J. Bioorg. Med. Chem. 2003,
Acknowledgment
11, 1153.
41. Kalgutkar, A. S.; Marnett, A. B.; Crews, B. C.; Remmel, R. P.; Marnett, L. J. J. Med.
Chem. 2000, 43, 2860.
42. Bandgar, B. P.; Sarangdhar, R. J.; Viswakarma, S.; Ahamed, F. A. J. Med. Chem.
2011, 54, 1191.
We are grateful to the Canadian Institutes of Health Research
(MOP-14712) for financial support of this research.
43. Rahim, M. A.; Rao, P. N. P.; Bhardwaj, A.; Kaur, J.; Huang, Z.; Knaus, E. E. Bioorg.
Med. Chem. Lett. 2011, 21, 6074.
References and notes
44. Bhardwaj, A.; Huang, Z.; Kaur, J.; Knaus, E. E. ChemMedChem 2012, 7, 62.
45. Kaur, J.; Bhardwaj, A.; Huang, Z.; Knaus, E. E. ChemMedChem 2012, 7, 144.
46. Selinsky, B. S.; Gupta, K.; Sharkey, C. T.; Loll, P. J. Biochemistry 2001, 40, 5172.
47. Kurumbail, R. G.; Stevens, A. M.; Gierse, J. K.; McDonald, J. J.; Stegeman, R. A.;
Pak, J. Y.; Gildehaus, D.; Miyashiro, J. M.; Penning, T. D.; Seibert, K.; Isakson, P.
C.; Stallings, W. C. Nature 1996, 384, 644.
1. Hamberg, M.; Samuelsson, B. J. Biol. Chem. 1967, 242, 5336.
2. Miyamoto, T.; Ogino, N.; Yamamoto, S.; Hayaishi, O. J. Biol. Chem. 1976, 251,
2629.
3. Fletcher, B. S.; Kujubu, D. A.; Perrin, D. M.; Herschman, H. R. J. Biol. Chem. 1992,
267, 4338.
48. General: Melting points were measured in capillaries using a Thomas-Hoover
capillary apparatus and are uncorrected. 1H and 13C NMR spectra were
recorded on a Bruker AM 300 NMR spectrometer using CDCl3/DMSO-d6 as
solvent. 13C NMR spectra were acquired using the J modulated spin echo
technique where methyl and methine carbons appear as positive peaks and
methylene and quaternary carbon resonances appear as negative peaks. Mass
4. Brune, K.; Hinz, B. Arthritis Rheum. 2004, 50, 2391.
5. Marnett, L. J. Annu. Rev. Pharmacol. Toxicol. 2009, 49, 265.
6. Chakraborti, A. K.; Garg, S. K.; Kumar, R.; Motiwala, H. F.; Jadhavar, P. S. Curr.
Med. Chem. 2010, 17, 1563.
7. Harrak, Y.; Casula, G.; Basset, J.; Rosell, G.; Plescia, S.; Raffa, D.; Cusimano, M. G.;
Pouplana, R.; Pujol, M. D. J. Med. Chem. 2010, 53, 6560.
8. Ranatunge, R. R.; Augustyniak, M.; Bandarage, U. K.; Earl, R. A.; Ellis, J. L.;
Garvey, D. S.; Janero, D. R.; Letts, L. G.; Martino, A. M.; Murty, M. G.; Richardson,
S. K.; Schroeder, J. D.; Shumway, M. J.; Tam, S. W.; Trocha, A. M.; Young, D. V. J.
Med. Chem. 2004, 47, 2180.
9. Anzini, M.; Rovini, M.; Cappelli, A.; Vomero, S.; Manetti, F.; Botta, M.; Sautebin,
L.; Rossi, A.; Pergola, C.; Ghelardini, C.; Norcini, M.; Giordani, A.; Makovec, F.;
Anzellotti, P.; Patrignani, P.; Biava, M. J. Med. Chem. 2008, 51, 4476.
10. Smith, W. L.; DeWitt, D. L. Adv. Immunol. 1996, 62, 167.
11. Jouzeau, J. Y.; Terlain, B.; Abid, A.; Nedelec, E.; Netter, P. Drugs 1997, 53, 563.
12. Cryer, B. Am. J. Gastroenterol. 2005, 100, 1694.
spectra (MS) were recorded on
a Water’s Micromass ZQ 4000 mass
spectrometer using the ESI ionization mode. The purity of the compounds
was established using elemental analyses which were performed for C, H, N by
the Microanalytical Service Laboratory, Department of Chemistry, University of
Alberta. Compounds showed a single spot on Macherey-Nagel Polygram Sil G/
UV254 silica gel plates (0.2 mm) using a low, medium, and highly polar solvent
system, and no residue remained after combustion, indicating a purity >98%.
Column chromatography was performed on a Combiflash Rf system using a
gold silica column. All other reagents, purchased from the Aldrich Chemical Co.
(Milwaukee, WI), were used without further purification.
3-[(4-Fluorophenylimino)methyl]indole
(9):
A
solution
of
indole-3-
13. Go, M. F. Gastrointest. Endosc. Clin. North. Am. 2006, 16, 83.
14. James, M. W.; Hawkey, C. J. Br. J. Clin. Pharmacol. 2003, 56, 146.
15. Lazzaroni, M.; Porro, G. B. Aliment. Pharmacol. Ther. 2004, 20, 48.
16. Naesdal, J.; Brown, K. Drug Saf. 2006, 29, 119.
17. Mounier, G.; Guy, C.; Berthoux, F.; Beyens, M. N.; Ratrema, M.; Ollagnier, M.
Therapie 2006, 61, 255.
carboxaldehyde (300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in
absolute ethanol (10 mL) was stirred at 70–80 °C for 15 min, a solution of p-
fluoroaniline (0.179 ml, 1.2 mmol) in absolute ethanol (2 mL) was added
slowly, and the reaction mixture was refluxed for 8 h. Removal of the solvent in
vacuo furnished a thick liquid which produced a brown precipitate on addition
of water. The precipitate was filtered off, washed with water, and dried to
18. Schneider, V.; Lévesque, L. E.; Zhang, B.; Hutchinson, T.; Brophy, J. M. Am. J.
Epidemiol. 2006, 164, 881.
afford 9 as a brown solid; 80% yield; mp 143–145 °C (lit49 mp 142–144 °C); 1
H
NMR (DMSO-d6): d 7.14–7.27 (m, 6H, phenyl hydrogens, indole H-5, H-6), 7.47
(d, J = 8.5 Hz, 1H, indole H-7), 7.99 (d, J = 2.4 Hz, 1H, CH@N), 8.35 (d, J = 7.3 Hz,
1H, indole H-4), 8.68 (s, 1H, indole H-2), 11.77 (br s, 1H, NH).
19. Zadrazil, J. Vnitr. Lek. 2006, 52, 686.
20. Adebayo, D.; Bjarnason, I. Postgrad. Med. J. 2006, 82, 186.
21. Chiroli, V.; Benedini, F.; Ongini, E.; Del Soldato, P. Eur. J. Med. Chem. 2003, 38, 441.
22. Fosslien, E. Ann. Clin. Lab. Sci. 1998, 28, 67.
3-[(4-Methylphenylimino)methyl]indole (10):
A
solution of indole-3-
carboxaldehyde (300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in
absolute ethanol (10 mL) was stirred at 70–80 °C for 15 min, a solution of p-
methylaniline (264 mg, 1.2 mmol) in absolute ethanol (2 mL) was added
slowly, and the reaction mixture was refluxed for 4 h. Removal of the solvent in
vacuo furnished a thick liquid which afforded a yellow precipitate on addition
of ether. The precipitate was filtered off, washed with hexane and dried to
furnish 10 as a yellow solid50; 78% yield; mp 170–172 °C; 1H NMR (DMSO-d6):
d 2.30 (s, 3H, CH3), 7.09–7.23 (m, 6H, phenyl hydrogens, indole H-5, H-6), 7.46
(d, J = 7.3 Hz, 1H, indole H-7), 7.96 (d, J = 2.2 Hz, 1H, CH@N), 8.35 (d, J = 7.3 Hz,
1H, indole H-4), 8.68 (s, 1H, indole H-2), 11.72 (br s, 1H, NH).
23. Herschman, H. R. Biochem. Biophys. Acta 1996, 1299, 125.
24. Dubois, R. N.; Abramson, S. B.; Crofford, L.; Gupta, R. A.; Simon, L. S.; Van de
Putta, L. B. A.; Lipsky, P. E. FASEB J. 1998, 12, 1063.
25. Prasit, P.; Wang, Z.; Brideau, C.; Chan, C.-C.; Charleson, S.; Cromlish, W.; Ethier,
D.; Evans, J. F.; Ford-Hutchinson, A. W.; Gauthier, J. Y.; Gordon, R.; Guay, J.;
Gresser, M.; Kargman, S.; Kennedy, B.; Leblanc, Y.; Leger, S.; Mancini, J.; O’Neill,
G. P.; Ouellet, M.; Percival, M. D.; Perrier, H.; Riendeau, D.; Rodger, I.; Tagari, P.;
Therien, M.; Vikers, P.; Wong, E.; Xu, L.-J.; Young, R. N.; Zamboni, R.; Boyce, S.;
Rupniak, N.; Forrest, M.; Visco, D.; Patrick, D. Bioorg. Med. Chem. Lett. 1999, 9,
1773.
26. Penning, T. D.; Talley, J. J.; Bertenshaw, S. R.; Carter, J. S.; Collins, P. W.; Docter,
S.; Graneto, M. J.; Lee, L. F.; Malecha, J. W.; Miyashiro, J. M.; Rogers, R. S.; Rogier,
D. J.; Yu, S. S.; Anderson, G. D.; Burton, E. G.; Cogburn, J. N.; Gregory, S. A.;
Koboldt, C. M.; Perkins, W. E.; Seibert, K.; Veenhuizen, A. W.; Zhang, Y. Y.;
Isakson, P. C. J. Med. Chem. 1997, 40, 1347.
27. Szabo, G.; Fischer, J.; Kis-Varga, A.; Gyires, K. J. Med. Chem. 2008, 51, 142.
28. Talley, J. J.; Brown, D. L.; Carter, J. S.; Graneto, M. J.; Koboldt, C. M.; Masferrer, J.
L.; Perkins, W. E.; Rogers, R. S.; Shaffer, A. F.; Zhang, Y. Y.; Zweifel, B. S.; Seibert,
K. J. Med. Chem. 2000, 43, 775.
29. Mcadam, B. F.; Catella-lawson, F.; Mardini, I. A.; Lawson, J. A.; Fitzgerald, G. A.
Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 272.
30. Catella-lawson, F.; Mcadam, B.; Morrison, B. W.; Kapoor, S.; Kujubu, D.; Antes,
L.; Lasseter, K. C.; Quan, H.; Gertz, B. J.; Fitzgerald, G. A. J. Pharmacol. Exp. Ther.
1999, 289, 735.
31. 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. Eng. J. Med. 2000, 343, 1520.
32. 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. Eng. J.
Med. 2005, 352, 1092.
3-[(4-Trifluoromethylphenylimino)methyl]indole (11):
A solution of indole-3-
carboxaldehyde (300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in
absolute ethanol (10 mL) was stirred at 70–80 °C for 15 min, a solution of 4-
(trifluoromethyl)aniline (0.311 ml, 1.2 mmol) in absolute ethanol (2 mL) was
added slowly, and the reaction mixture was refluxed for 12 h. Removal of the
solvent in vacuo furnished a thick liquid which gave a light greenish precipitate
on washing with ether. The precipitate was filtered off and dried to give 11 as a
pale green solid; 72% yield; mp 148–150 °C; 1H NMR (DMSO-d6): d 7.14–7.27
(m, 6H, phenyl hydrogens, indole H-5, H-6), 7.47 (d, J = 6.1 Hz, 1H, indole H-7),
7.98 (s, 1H, CH@N), 8.35 (d, J = 7.3 Hz, 1H, indole H-4), 8.68 (s, 1H, indole H-2),
11.77 (br s, 1H, NH); 13C NMR (DMSO-d6):
d 111.3, 112.9, 119.2 (q,
1JCF = 274.0 Hz, CF3), 121.5, 123.5, 125.3, 126.2, 127.2, 128.6, 128.7, 136.9 (q,
2JCCF = 14.7 Hz, CCF3), 137.1, 156.4, 156.7 (CH@N); ESI-MS: 289 [MꢁH]+; Anal.
Calcd for C16H11F3N2: C, 66.66; H, 3.85; N, 9.72. Found: C, 66.62; H, 3.81; N,
9.74.
1-Benzylindole-3-carboxyaldehyde (12) and 1-Benzoylindole-3-carboxyaldehyde
(13): A solution of indole-3-carboxaldehyde (1 g, 1 mmol) was added the
solution of sodium hydride (1.5 mmol) in dry THF (10 mL) and the reaction
mixture was stirred for 5 min at 0 °C. Either benzyl bromide (1.76 g, 1.5 mmol),
or benzoyl chloride (1.45 g, 1.5 mmol)), was added, and the reaction was
stirred at 0 °C for 10–20 min to furnish the title compound 12 or 13. The 1H
NMR spectra for 12 and 13 were identical to that reported.51,52
33. Grosser, T.; Fries, S.; FitzGerald, G. A. J. Clin. Invest. 2006, 116, 4.
34. FitzGerald, G. A. N. Eng. J. Med. 2004, 351, 1709.
35. Baron, J. A.; Sandler, R. S.; Bresalier, R. S.; Lanas, A.; Morton, D. G.; Riddell, R.;
Iverson, E. R.; DeMets, D. L. Lancet 2008, 372, 1756.
36. Khanna, S.; Madan, M.; Vangoori, A.; Banerjee, R.; Thaimattam, R.; Basha, S. K. J.
S.; Ramesh, M.; Casturi, S. R.; Pal, M. Bioorg. Med. Chem. 2006, 14, 4820.
37. Kalgutkar, A. S.; Crews, B. C.; Saleh, S.; Prudhomme, D.; Marnett, L. J. Bioorg.
Med. Chem. 2005, 13, 6810.
38. Chowdhury, M. A.; Huang, Z.; Abdellatif, K. R. A.; Dong, Y.; Yu, G.; Velázquez, C.
A.; Knaus, E. E. Bioorg. Med. Chem. Lett. 2010, 20, 5776.
1-Benzyl-3-[(4-fluorophenylimino)methyl]indole (15):
A
solution of 1-
benzylindole-3-carboxaldehyde (300 mg, 1 mmol) and p-toluenesulfonic acid
(3 mg) in absolute ethanol (10 mL) was stirred at 70–80 °C for 15 min, a
solution of p-fluoroaniline (0.145 mL, 1.2 mmol) in absolute ethanol (2 mL)
was added slowly, and the reaction mixture was refluxed for 20 min. Removal
of the solvent in vacuo furnished a viscous liquid which formed a brown
precipitate on addition of water. The precipitate were filtered off, washed with
water and dried to afford 15 as a brown solid; 82% yield; mp 98–100 °C; 1H
NMR (DMSO-d6):
d 5.51 (s, 2H, Ph-CH2), 7.16–7.35 (m, 11H, phenyl and
39. Leblanc, Y.; Black, W. C.; Chan, C. C.; Charleson, S.; Delorme, D.; Denis, D.;
Gauthier, J. Y.; Grimm, E. L.; Gordon, R.; Guay, D.; Hamel, P.; Kargman, S.; Lau,
C. K.; Mancini, J.; Ouellet, M.; Percival, D.; Roy, P.; Skorey, K.; Tagari, P.; Vickers,
P.; Wong, E.; Xu, L.; Prasit, P. Bioorg. Med. Chem. Lett. 1996, 6, 731.
fluorophenyl hydrogens, indole H-5, H-6), 7.54 (d, J = 6.1 Hz, 1H, indole H-7),
8.15 (s, 1H, CH@N), 8.36 (d, J = 7.3 Hz, 1H, indole H-4), 8.69 (s, 1H, indole H-2);
2
13C NMR (DMSO-d6): d 49.4, 110.8, 114.3, 115.6 (d, JCCF = 21.8 Hz, ArCH),

J. Kaur et al. / Bioorg. Med. Chem. Lett. 22 (2012) 2154–2159
2159
121.2, 121.9, 122.2 (d, 3JCCCF = 7.6 Hz, Ar-CH), 122.9, 125.3, 127.1, 127.5, 128.5,
8.25.
4
136.1, 136.9, 137.2, 149.3 (d, JCCCCF = 2.1 Hz), 154.9 (CH@N), 159.6 (d,
1-Benzoyl-3-[(4-trifluoromethylphenylimino)methyl]indole (20):
A
solution of
1JCF = 239.1 Hz, ArC-F); ESI-MS: 329 [MꢁH]+; Anal. Calcd for C22H17FN2: C,
the aldehyde 13 (300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in
absolute ethanol (10 mL) was stirred at 70–80 °C for 15 min, a solution of 4-
(trifluoromethyl)aniline (0.232 ml, 1.2 mmol) in absolute ethanol (2 mL) was
added slowly, and the reaction mixture was refluxed for 1 h. On cooling, a
cream colored solid separated, the solid was filtered off, washed with water,
and dried to give 20 as a pale yellow solid; 83% yield; mp 150–152 °C; 1H NMR
(DMSO-d6): d 7.39–7.53 (m, 4H, Ar-H), 7.61–7.77 (m, 7H, Ar-H), 8.18 (s, 1H,
CH@N), 8.34 (d, J = 8.52 Hz, 1H, indole H-7), 8.50 (d, J = 9.15 Hz, 1H, indole H-
4), 8.81 (s, 1H, indole H-2); 13C NMR (DMSO-d6): 13C NMR: d 112.7, 114.8,
80.47; H, 5.22; N, 8.53. Found: C, 80.45; H, 5.20; N, 8.50.
1-Benzyl-3-[(4-methylphenylimino)methyl]indole (16):
A
solution of 1-
benzylindole-3-carboxaldehyde (300 mg, 1 mmol) and p-toluenesulfonic acid
(3 mg) in absolute ethanol (10 mL) was stirred at 70–80 °C for 15 min, a
solution of p-methylaniline (0.163 mg, 1.2 mmol) in absolute ethanol (2 mL)
was added slowly, and the reaction mixture was refluxed for 10 min. Removal
of the solvent in vacuo furnished a viscous liquid which produced a yellow
precipitate on trituration with ether. The precipitate was filtered off, washed
with hexane and dried to afford 16 as a yellow solid; 85% yield; mp 108–
110 °C; 1H NMR (DMSO-d6): d 2.30 (s, 3H, CH3), d 5.51 (s, 2H, PhCH2), 7.11–7.35
(m, 11H, indole H-5, H-6, phenyl hydrogens), 7.55 (d, J = 7.3 Hz, 1H, indole H-
7), 8.17 (s, 1H, CH@N), 8.36–8.39 (d, J = 6.1 Hz, 1H, indole H-4), 8.72 (s, 1H,
indole H-2); 13C NMR (DMSO-d6): d 20.5, 49.4, 110.8, 114.2, 114.7, 120.5, 121.2,
121.9, 123.0, 125.4, 127.1, 127.5, 128.6, 129.5, 133.8, 136.9, 137.2, 142.3, 154.0
(CH@N); ESI-MS: 325 [MꢁH]+; Anal. Calcd for C23H20N2: C, 85.15; H, 6.21; N,
8.63. Found: C, 85.12; H, 6.20; N, 8.61.
1
115.8, 120.0 (q, JC,F = 238.0 Hz, CF3), 121.3, 121.4, 122.4, 124.8, 126.0, 127.0,
2
128.8, 129.3, 129.7, 132.7, 135.9, 136.3 (q, JCCF = 14.2 Hz, CCF3), 152.1, 157.4
(CH@N), 168.4 (C@O); ESI-MS: 393 [MꢁH]+; Anal. Calcd for C23H15F3N2O: C,
70.40; H, 3.85; N, 14.53. Found: C, 70.42; H, 3.84; N, 14.51.
1-Benzoyl-3-[(4-chlorophenylimino)methyl]indole (21):
aldehyde 13 (300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in absolute
ethanol (10 mL) was stirred at 70–80 °C for 15 min, solution of p-
A
solution of the
a
chloroaniline (0.184 mg, 1.2 mmol) in absolute ethanol (2 mL) was added
slowly, and the reaction mixture was refluxed for 40 min. On cooling, the
cream coloured solid that separated was filtered off, washed with hexane, and
dried to afford 21 as a pale yellow solid; 88% yield; mp 161–163 °C; 1H NMR
(DMSO-d6): d 7.26–7.29 (m, 2H, Ar-H), 7.43–7.51 (m, 4H, Ar-H), 7.61–7.85 (m,
5H, Ar-H), 8.11 (s, 1H, CH@N), 8.34 (d, J = 8.55 Hz, 1H, indole H-7), 8.50 (d,
J = 8.52 Hz, 1H, indole H-4), 8.79 (s, 1H, indole H-2); 13C NMR (DMSO-d6): d
115.7, 119.2, 122.4, 122.6, 124.7, 125.8, 127.1, 128.7, 129.0, 129.2, 129.8, 132.4,
133.3, 135.2, 136.3, 150.7, 155.9 (CH@N), 168.2 (C@O); ESI-MS: 359 [MꢁH]+,
361 [MꢁH]+; Anal. Calcd for C22H15ClN2O: C, 73.64; H, 4.21; N, 7.81. Found: C,
73.61; H, 4.24; N, 7.80.
1-Benzyl-3-[(4-trifluoromethylphenylimino)methyl]indole (17): A solution of 12
(300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in absolute ethanol
(10 mL) was stirred at 70–80 °C for 15 min,
a
solution of 4-
(trifluoromethyl)aniline (0.191 ml, 1.2 mmol) in absolute ethanol (2 mL) was
added slowly, and the reaction mixture was refluxed for 3 h. Removal of the
solvent in vacuo furnished a thick liquid which gave a light brown precipitate
on addition of water. The precipitate was filtered off, washed with water and
dried to yield 17 as a pale brown solid; 64% yield; mp 110–112 °C; 1H NMR
(DMSO-d6): d 5.53 (s, 2H, PhCH2), 7.19–7.39 (m, 9H, 4-trifluoromethylphenyl
H-2, H-6, benzyl C6H5CH2, indole H-5, H-6), 7.57 (d, J = 6.1 Hz, 1H, indole H-7),
7.71 (d, J = 7.9 Hz, 2H, 4-trifluoromethylphenyl H-3, H-5), 8.23 (s, 1H, CH@N),
8.37 (d, J = 6.7 Hz, 1H, indole H-4), 8.72 (s, 1H, indole H-2); 13C NMR (DMSO-
49. Scola, D. A.; Lopiekes, D. V.; Dlpletro, H. R. J. Chem. Eng. Data 1969, 14, 111.
50. Lulukyan, K. K.; Mkrtchyan, N. D.; Agbalyan, S. G. Armyanskii Khim. Zh. 1985, 38,
701.
51. Lee, S.; Park, S. B. Org. Lett. 2009, 11, 5214.
52. Ohno, K.; Mohri, S.-i.; Takahashi, M.; Tamura, Y. J. Chem. Soc., Perkin Trans. 1
1984, 405.
1
d6): d 49.8, 110.9, 111.3, 112.9, 114.4, 119.1 (q, JC,F = 269.2 Hz, CF3), 121.0,
123.5, 125.3, 126.1, 127.2, 127.6, 127.7, 128.5, 129.0, 136.9 (q, 2JCCF = 15.2 Hz),
137.1, 152.1, 156.7 (CH@N); ESI-MS: 379 [MꢁH]+; Anal. Calcd for C23H17F3N2:
C, 73.01; H, 4.53; N, 7.40. Found: C, 73.00; H, 4.54; N, 7.41.
1-Benzoyl-3-[(4-fluorophenylimino)methyl]indole (18): A solution of 13 (300 mg,
1 mmol) and p-toluenesulfonic acid (3 mg) in absolute ethanol (10 mL) was
53. The ability of the test compounds 9–11 and 15–21 listed in Table 1 to inhibit
ovine COX-1 and human recombinant COX-2 (IC50 value, lM) was determined
stirred at 70–80 °C for 15 min,
a
solution of 4-(fluoro)aniline (0.136 ml,
using an enzyme immuno assay (EIA) kit (Catalog No. 560131, Cayman
Chemical, Ann Arbor, MI, USA) according to a previously reported method
(Uddin, M. J.; Rao, P. N. P.; McDonald, R.; Knaus, E. E. J. Med. Chem. 2004, 47,
6108).
1.2 mmol) in absolute ethanol (2 mL) was added slowly, the reaction mixture
was refluxed for 30 min. On cooling, a cream colored solid separated, the solid
was filtered off, washed with water, and dried to furnish 18 as a pale yellow
solid; 89% yield; mp 120–121 °C; 1H NMR (DMSO-d6): d 7.20–7.51 (m, 6H, Ar-
H), 7.61–7.85 (m, 5H, Ar-H), 8.08 (s, 1H, CH@N), 8.33 (d, J = 7.32 Hz, 1H, indole
H-7), 8.53 (d, J = 7.32 Hz, 1H, indole H-4), 8.78 (s, 1H, indole H-2); 13C NMR
54. Crystal coordinates from the X-ray crystal structure of COX-1 (ovine, 1EQG,
ibuprofen bound in the active site) and COX-2 (murine, 6COX, SC558 bound in
the active site) were obtained from the protein data bank. Compounds were
constructed using the builder toolkit of the software package ArgusLab 4.0.1
(Mark, A. ArgusLab, Version 4.0.1; Thompson Planaria Software LLC: Seattle,
WA) and energy minimized using the semi-empirical quantum mechanical
method PM3. The monomeric structure of the enzyme was chosen and the
active site was defined around the ligand. The molecule to be docked in the
active site of the enzyme was inserted in the work space carrying the structure
of the enzyme. The docking program implements an efficient grid based
docking algorithm which approximates an exhaustive search within the free
volume of the binding site cavity. The conformational space was surveyed by
the geometry optimization of the flexible ligand (rings are treated as rigid) in
combination with the incremental construction of the ligand torsions. Thus,
docking occurred between the flexible ligand parts of the compound and
enzyme. The ligand orientation was determined by a shape scoring function
based on Ascore and the final positions were ranked by lowest interaction
energy values. The Einteraction is the sum of the energies involved in H-bond
interactions, hydrophobic interactions and van der Waal’s interactions. H-bond
and hydrophobic interactions between the compound and enzyme were
explored by distance measurements.
2
(DMSO-d6): d 115.6, 115.8 (d, JCCF = 22.2 Hz, ArCH), 119.3, 122.4, 122.5 (d,
3JCCCF = 7.6 Hz, ArCH), 124.6, 125.7, 127.1, 128.7, 129.2, 132.3, 133.3, 134.8,
136.3, 148.2 (d, 4JCCCCF = 3.2 Hz, ArCH), 155.1 (CH@N), 160.2 (d, 1JCF = 240.1 Hz,
ArC-F), 168.2 (C@O); ESI-MS: 343 [MꢁH]+; Anal. Calcd for C22H15FN2O: C,
77.18; H, 4.42; N, 8.18. Found: C, 77.17; H, 4.45; N, 8.15.
1-Benzoyl-3-[(4-methylphenylimino)methyl]indole (19):
aldehyde 13 (300 mg, 1 mmol) and p-toluenesulfonic acid (3 mg) in absolute
ethanol (10 mL) was stirred at 70–80 °C for 15 min, solution of p-
A solution of the
a
methylaniline (0.154 mg, 1.2 mmol) in absolute ethanol (2 mL) was added
slowly, and the reaction mixture was refluxed for 10 min. On cooling, a light
yellow solid separated, the solid was filtered off, washed with hexane, and
dried to provide 19 as a pale yellow solid; 86% yield; mp 132–133 °C; 1H NMR
(DMSO-d6): d 2.30 (s, 3H, CH3), 7.15–7.19 (m, 4H, Ar-H), 7.22–7.85 (m, 7H, Ar-
H), 8.07 (s, 1H, CH@N), 8.31 (d, J = 8.55 Hz, 1H, indole H-7), 8.53 (d, J = 9.15 Hz,
1H, indole H-4), 8.77 (s, 1H, indole H-2); 13C NMR (DMSO-d6): d 20.5, 115.7,
119.5, 120.7, 122.5, 124.6, 125.7, 127.3, 128.7, 129.2, 129.6, 132.3, 133.4, 134.4,
134.9, 136.3, 149.3, 154.1 (CH@N), 168.2 (C@O); ESI-MS: 339 [MꢁH]+; Anal.
Calcd for C23H18N2O: C, 81.63; H, 5.36; N, 8.28. Found: C, 81.61; H, 5.39; N,