Synthesis and biological evaluation of 1,3-diphenylprop-2-yn-1-ones as dual inhibitors of cyclooxygenases and lipoxygenases

Article abstract of DOI:10.1016/j.bmcl.2005.07.036

A new class of 1,3-diphenylprop-2-yn-1-ones possessing a p-MeSO₂ COX-2 phamacophore on the C-3 phenyl ring was designed for evaluation as dual inhibitors of cyclooxygenase (COX) and lipoxygenase (LOX). Among the group of compounds evaluated, 1-

Full text of DOI:10.1016/j.bmcl.2005.07.036

Bioorganic & Medicinal Chemistry Letters 15 (2005) 4842–4845
Synthesis and biological evaluation of 1,3-diphenylprop-2-yn-
1-ones as dual inhibitors of cyclooxygenases and lipoxygenases
P. N. Praveen Rao, Qiao-Hong Chen and Edward E. Knaus*
Faculty of Pharmacy and Pharmaceutical Sciences, University of Alberta, Edmonton, Alta., Canada T6G 2N8
Received 16 May 2005; revised 8 July 2005; accepted 11 July 2005
Available online 6 September 2005
Abstract—A new class of 1,3-diphenylprop-2-yn-1-ones possessing a p-MeSO2 COX-2 phamacophore on the C-3 phenyl ring was
designed for evaluation as dual inhibitors of cyclooxygenase (COX) and lipoxygenase (LOX). Among the group of compounds eval-
uated, 1-(4-fluorophenyl)-3-(4-methanesulfonylphenyl)prop-2-yn-1-one (11j) exhibited excellent COX-2 inhibitory potency (COX-2
IC50 = 0.1 lM) and selectivity (SI = 300), whereas 1-(4-cyanophenyl)-3-(4-methanesulfonylphenyl)prop-2-yn-1-one (11d) exhibited
an optimal combination of COX and LOX inhibition (COX-2 IC50 = 1.0 lM; COX-2 SI = 31.5; 5-LOX IC50 = 1.0 lM; 15-LOX
IC50 = 3.2 lM).
Ó 2005 Elsevier Ltd. All rights reserved.
The introduction of selective cyclooxygenase-2 (COX-2)
inhibitors, such as celecoxib (1) and rofecoxib (2), in the
late 1990s provided novel anti-inflammatory-analgesic
agents with reduced gastrointestinal side effects.1,2 How-
ever, the recent market withdrawal of rofecoxib and val-
decoxib due to their adverse cardiovascular side effects
clearly delineates the need to develop alternative anti-
inflammatory agents with reduced toxicity.3
and an anti-thrombotic effect.7 Nordihydroguaiaretic
acid (NDGA, 4), a natural dicatechol exhibiting in vivo
anti-inflammatory activity, is known to inhibit the
LOX isozymes (5-LOX, 12-LOX, and 15-LOX).8 As part
of our ongoing program to design novel anti-inflamma-
tory agents devoid of adverse side effects, we describe
herein the synthesis and biological evaluation of a novel
class of 1,3-diphenylprop-2-yn-1-ones possessing a p-
MeSO2 COX-2 pharmacophore on the C-3 phenyl ring
as dual inhibitors of COXs and LOXs.
Lipoxygenases (LOXs), which are widely distributed in
both the plant and animal kingdoms, belong to a class
of non-heme iron-containing enzymes which catalyze
dioxygen incorporation into polyunsaturated fatty
acids, such as linoleic and arachidonic acid, to form
hydroperoxide products.4 Currently, LOXs are potential
targets in the treatment of diseases such as asthma, ath-
erosclerosis, cancer, and a variety of inflammatory
conditions. For example, leukotrienes formed via the 5-
lipoxygenase (5-LOX) pathway are known to contribute
to the pathophysiology of osteoarthritis, asthma, and
prostate cancer. Metabolites formed via the 15-lipoxyge-
nase (15-LOX) pathway have been implicated in the oxi-
dative modification of low-density lipoprotein (LDL),
ultimately leading to atherosclerosis.5,6 The dual COX/
5-LOX inhibitor ML-3000 (licofelone, 3) is a potent
anti-inflammatory agent with excellent gastrointestinal
tolerance, demonstrating platelet function inhibition
SO2Me
SO2NH2
N
N
O
F3C
O
Me
Rofecoxib (2)
Celecoxib (1)
OH
Me
Me
OH
Me
N
Me
HO
HO2C
ML-3000 (3)
OH
NDGA (4)
The synthetic strategies used to prepare the target substi-
tuted-1,3-diphenylprop-2-yn-1-ones (11a–11k, 16a and
16b) are shown in Schemes 1 and 2. The precursor,
*
Corresponding author. Tel.: +1 780 492 5993; fax: +1 780 492
1217; e-mail: eknaus@pharmacy.ualberta.ca
0960-894X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2005.07.036

P. N. Praveen Rao et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4842–4845
4843
R1
R1
Me
b
a
MeS
C
OH
MeS
Br
a
b, c
R2
CHO
R2
CHO
Me
6
R1
5
13a (R1 = OMe; R2 = OTBDMS)
13b (R1 = OTBDMS; R2 = OMe)
12a (R1 = OMe; R2 = OH)
12b (R1 = OH; R2 = OMe)
R2
+
MeS
OHC
c
8
R1
R3
7
R1
d
MeS
C
O
R2
H
MeS
C
R2
14a (R1 = OMe; R2 = OTBDMS)
OH
R3
14b (R1 = OTBDMS; R2 = OMe)
9 (R1 = H, OMe, F; R2 = H, Me, CF3, CN, OMe, F;
R1
R3 = H, OMe)
e
MeS
C
O
R2
d
R1
15a (R1 = OMe; R2 = OH)
15b (R1 = OH; R2 = OMe)
MeS
C
O
R2
R1
R3
10 (R1 = H, OMe, F; R2 = H, Me, CF3, CN, OMe, F;
MeO2S
C
O
R2
R3 = H, OMe)
e
R1
16a (R1 = OMe; R2 = OH)
16b (R1 = OH; R2 = OMe)
MeO2S
C
O
R2
Scheme 2. Reagents and conditions: (a) THF, NaH, TBDMSCl,
25 °C, 2–3 h; (b) 4-MeS-C6H4C„CH, THF, À78 °C, n-BuLi, À78 °C
to 25 °C over night; (c) acetone, MnO2, 25 °C, 2–3 h; (d) EtOH, KOH,
25 °C, 1 h; (e) 1,4-dioxane, aqueous OxoneÒ, 25 °C, 3–4 h.
R3
R1
H
H
H
H
H
H
R2 R3
R1 R2
R3
H
11a
11b
11c
11d
11e
11f
H
H
H
H
H
H
H
11g OMe
11h OH
H
H
f
H
Me
11i OMe OMe OMe
CF3
CN
OMe
OH
11j
H
F
F
F
H
H
Compounds 16a and 16b were prepared according to
Scheme 2. The tert-butyldimethylsilyloxy benzaldehyde
regioisomers (13) were prepared by the reaction of the
respective benzaldehyde (12) with tert-butyldimethylsilyl
chloride (TBDMSCl) in the presence of NaH10 (65–
70%). Subsequent condensation of 13 with 7 in the pres-
ence of n-BuLi, and then oxidation of the intermediate
alcohol using activated MnO2 afforded the 1,3-diphenyl-
prop-2-yn-1-ones 14 (45–54%). Deprotection of aryl
tert-butyldimethylsilyl (TBS) ethers (14) using KOH in
EtOH afforded the respective phenol (15, 45–52%)10,
which was then oxidized using aqueous OxoneÒ to
afford 16a and 16b (80–85%), as shown in Scheme 2.
The 1,3-diphenylprop-2-yn-1-ones (10, 11, and 14–16)
are expected to be useful Michael acceptors useful for
the synthesis of heterocyles.10b
11k
f
Scheme 1. Reagents and conditions: (a) triethylamine, 2-methyl-3-
butyn-1-ol, [(C6H5)3P]2PdCl2, CuI, 70–75 °C, 5–6 h; (b) benzene, NaH,
100–110 °C, 1–1.5 h; (c) THF, À78 °C, n-BuLi, and then at À78 °C to
25 °C over night; (d) acetone, MnO2, 25 °C, 2–3 h; (e) 1,4-dioxane,
aqueous OxoneÒ, 25 °C, 3–4 h; (f) BBr3, CH2Cl2, À5 to 0 °C, 1 h.
1-ethynyl-4-methylsulfanylbenzene (7), was prepared in
two steps by Sonogashira coupling of 4-bromothioani-
sole (5) with 2-methyl-3-butyn-1-ol in the presence
of triethylamine, CuI, and [(C6H5)3P]2PdCl2 [dichlor-
obis(triphenylphosphine)palladium], which gave the
protected para-methylsulfanylphenylacetylene (6) in
good yield (70–75%). Subsequent removal of the isopro-
panol moiety using NaH afforded 7 in good yield
(40–55%, Scheme 1).9 The condensation of 1-ethynyl-
4-methylsulfanylbenzene (7) with a substituted benzal-
dehyde (8) in the presence of n-BuLi afforded the
1,3-diphenylprop-2-yn-l-ols 9 (40–58%). Subsequent oxi-
dation of the alcohols 9 using activated MnO2 afforded
the corresponding 1,3-diphenylprop-2-yn-l-ones 10
(44–56%) having a C-3 4-methylthiophenyl substituent.
OxoneÒ oxidation of 10 afforded the target 1,3-diphenyl-
prop-2-yn-1-ones 11a–11e,11g, and 11i–11k (72–85%)
possessing a C-3 4-MeSO2-C6H4-substituent, as shown
in Scheme 1.10 O-Demethylation of 11e and 11g using
boron tribromide afforded the respective phenol deriva-
tives 11f and 11h (50–55%), as shown in Scheme 1.
In vitro structure–activity relationships acquired for
these 1,3-diphenylprop-2-yn-1-ones (11, 16) showed that
they exhibit a broad range (potent-to-inactive) of COX/
LOX inhibitory activities (COX-2 IC50 = 0.1 to
>100 lM range; COX-1 IC50 = 1 to >100 lM range;
5-LOX IC50 = 0.3 to >10 lM range; 15-LOX
IC50 = 0.1 to >10 lM range; Table 1).
Compound 11a, having an unsubstituted C-1 phenyl
ring, exhibited moderate inhibition of COX-2 (COX-2
IC50 = 10 lM), but it did not inhibit either 5- or 15-
LOX at a concentration of 10 lM. In contrast 11c,
possessing a C-1 p-CF3-phenyl substituent, exhibited
COX-1 selectivity (COX-1 IC50 = 3.1 lM; COX-2
IC50 > 100 lM). Interestingly, introduction of a C-1
p-CN-phenyl substituent (11d) provided a dual COX

4844
P. N. Praveen Rao et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4842–4845
Table 1. In vitro COX-1/COX-2 and 5-LOX/15-LOX isozyme assay data for 1,3-diphenylprop-2-yn-1-ones 11a–11k, 16a, and 16b
R1
R2
R3
COX-1 IC50 (lM) COX-2 IC50 (lM) COX-2 SIb 5-LOX IC50 (lM) 15-LOX IC50 (lM)
a
a
a
a
Compound
11a
11b
H
H
H
H
H
H
H
H
H
H
1.0
>100
3.1
10.0
33.0
>100
1.0
—
>10
>10
>10
1.0
>10
>10
>10
3.2
3.5
0.32
>10
0.5
>10
1.0
3.2
0.1
0.3
3.2
—
H
Me
CF3
CN
OMe
OH
H
>3.0
—
11c
11d
H
H
31.5
31.5
3.5
31.5
1.0
—
11e
11f
H
31.5
10.0
10.0
>100
>100
0.1
>10
0.3
H
11g
11h
OMe
OH
>100
>100
>10
—
9.0
0.3
H
11i
11j
OMe OMe OMe >100
—
7.0
H
F
F
F
H
H
H
H
30.0
3.1
1.1
1.0
—
300
6.2
—
>10
0.4
11k
16a
0.5
30
OMe OH
OH OMe
>10
>10
—
16b
3.2
—
—
—
Luteolin
Caffeic acid
NDGA
Rofecoxib
—
—
—
—
—
—
3.0
>10
—
3.5
—
>100
0.5
>200
a Values are means of two determinations acquired using an ovine COX-1/COX-2 and potato 5-LOX/soyabean 15-LOX, assay kits (Catalog No.
560101, 60401, and 760700, 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 (SI, COX-1 IC50/COX-2 IC50).
and LOX inhibitor with moderate COX-2 selectivity
(COX-2 IC50 = 1.0 lM; SI = 31.5) and a more potent
inhibition of 5-LOX (5-LOX IC50 = 1.0 lM; 15-LOX
IC50 = 3.2 lM), as shown in Table 1.11 Introduction
of a C-1 p-MeO-phenyl moiety (11e) provided moder-
ate COX inhibition (COX-1/2 IC50 = 31.5 lM),
whereas incorporation of a C-1 m-MeO-phenyl substi-
tuent (11g) increased both COX-2 inhibitory potency
and selectivity (COX-2 IC50 = 10 lM; SI > 10) com-
pared to the regioisomer 11e. Compound 11g also
exhibited selective inhibition of 5-LOX (5-LOX
IC50 = 9.0 lM), relative to 15-LOX. The C-1 4-
hydroxyphenyl compound 11f, an equipotent inhibitor
of 5- and 15-LOX (5-LOX IC50 = 0.3 lM; 15-LOX
IC50 = 0.32 lM), was about a 9-fold more potent inhibi-
tor of 5-LOX than the reference drug caffeic acid (5-LOX
IC50 = 3.0 lM). Incorporation of a C-1 3,4,5-trimeth-
oxyphenyl substituent (11i, R1 = R2 = R3 = OMe) led
to a complete loss of COX inhibitory activity, but 11i
selective and potent COX-2 inhibitor 11j [1-(4-fluor-
ophenyl)-3-(4-methanesulfonylphenyl)prop-2-yn-1-one]
within the COX-2 binding site (Fig. 1).10,12 The most
stable ligand–enzyme complex of 11j (Fig. 1) showed
that this ligand binds in the center of the COX-2 binding
site such that the C-3 p-MeSO2-phenyl substituent is
positioned in the vicinity of the COX-2 secondary pock-
et where it is surrounded by Phe518, Arg513, Gln192,
His90, Ser353, and Val523. One of the oxygen atoms
of the SO2Me group undergoes a hydrogen bonding
interaction with the backbone NH of Phe518
˚
(distance = 3.63 A), whereas the other oxygen atom
did exhibit selective inhibition of 5-LOX (IC50
=
7.0 lM). Within this class of compounds, 11j possessing
a C-1 p-fluorophenyl substituent was a potent and selec-
tive inhibitor of COX-2 (COX-2 IC50 = 0.1 lM;
SI = 300), being 5-fold more potent than rofecoxib
(COX-2 IC50 = 0.5 lM; SI > 200). On the other hand,
introduction of a C-1 difluorophenyl substituent (11k,
R1 = R2 = F) decreased both COX-2 inhibitory potency
and selectivity (COX-2 IC50 = 0.5 lM; SI = 6.0), but in-
creased 5-LOX inhibition (5-LOX IC50 = 0.4 lM).
Introduction of a methoxyphenol antioxidant moiety at
the C-1 position provided compounds 16a (R1 = OMe,
R2 = OH) and 16b (R1 = OH, R2 = OMe) that exhibited
moderate COX-1 selectivity, with preferential inhibition
of 15-LOX (Table 1). Compound 16a, which exhibited
potent inhibition of 15-LOX (15-LOX IC50 = 0.1 lM),
is 35-fold more potent than the reference drug NDGA
(15-LOX IC50 = 3.5 lM).
A molecular modeling (docking) experiment was carried
out to investigate the binding interactions of the most
Figure 1. Docking of 11j in the binding site of murine COX-2.
Hydrogen atoms of the amino acid residues are not shown for clarity.

P. N. Praveen Rao et al. / Bioorg. Med. Chem. Lett. 15 (2005) 4842–4845
4845
Hawkey, C. J.; Hochberg, M. C.; Kvien, T. K.; Schnitzer,
T. J. N. Engl. J. Med. 2000, 343, 1520.
undergoes a favorable hydrogen bonding interaction
˚
with the NH2 of Gln192 (distance = 2.70 A). The methyl
´
3. (a) Dogne, J. M.; Supuran, C. T.; Pratico, D. J. Med.
group of the p-SO2Me moiety is within van der WaalÕs
Chem. 2005, 48, 2251; (b) BextraÒ (valdecoxib) sales
suspended published by Pfizer on April 12, 2005, available
at http://www.bextra.com.
˚
contact range (distance <4 A) of the aromatic ring of
Phe518. It is notable that, the prop-2-yn-1-one carbonyl
oxygen atom (C„C–C@O) is hydrogen bonding to the
OH of Tyr355 close to the entrance of the COX-2 sec-
4. Brash, A. R. J. Biol. Chem. 1999, 274, 23679.
5. (a) Marcouiller, P.; Pelletier, J. P.; Guevremont, M.;
Martel-Pelletier, J.; Ranger, P.; Laufer, S.; Reboul, P.
J. Rheumatol. 2005, 32, 704; (b) Ramires, R.; Caiaffa,
M. F.; Tursi, A.; Haeggstrom, J. Z.; Macchia, L.
Biochem. Biophys. Res. Commun. 2004, 324, 815.
6. (a) Pommery, N.; Taverne, T.; Telliez, A.; Goossens, L.;
Charlier, C.; Pommery, J.; Goossens, J. F.; Houssin, R.;
Durant, F.; Henichart, J. P. J. Med. Chem. 2004, 47, 6195;
(b) Zhao, L.; Funk, C. D. Trends Cardiovasc. Med. 2004,
14, 191.
7. (a) Bias, P.; Buchner, A.; Klesser, B.; Laufer, S. Am. J.
Gastroenterol. 2004, 99, 611; (b) Tries, S.; Neupert, W.;
Laufer, S. Inflamm. Res. 2002, 51, 135; (c) Tries, S.;
Laufer, S.; Radziwon, P.; Breddin, H. K. Inflamm. Res.
2002, 51, 129.
8. (a) Fitzpatrick, L. R.; Bostwick, J. S.; Renzetti, M.;
Pendleton, R. G.; Decktor, D. L. Agents Actions 1990, 30,
393; (b) Whitman, S.; Gezginci, M.; Timmermann, B. N.;
Holman, T. R. J. Med. Chem. 2002, 45, 2659.
9. Stiegman, A. E.; Graham, E.; Perry, K. J.; Khundkar, L.
R.; Cheng, L. T.; Perry, J. W. J. Am. Chem. Soc. 1991,
113, 7658.
˚
ondary pocket (distance = 2.01 A) and it is positioned
˚
about 4.38 A from the guanidine side chain (NH2) of
Arg120. The C-1 p-fluorophenyl substituent is oriented
in a region comprised of Ala527, Ser530, Leu531,
Leu359, Val349, and Ile345. The distance between the
OH of Ser530 and fluorine atom of the p-fluorophenyl
˚
substituent was about 4.53 A, and the fluorine atom is
within van der WaalÕs contact range of the methyl side
˚
chain of Ile345 (distance <3.5 A).
In summary, structure–activity studies show that (i) the
1,3-diphenylprop-2-yn-1-one structure is a suitable tem-
plate to design dual inhibitors of COX and LOX; (ii)
COX/LOX inhibition was sensitive to substituents pres-
ent on the C-1 phenyl ring, with 11j [1-(4-fluorophenyl)-
3-(4-methanesulfonylphenyl)prop-2-yn-1-one] exhibit-
ing potent and selective COX-2 inhibition (COX-2
IC50 = 0.1 lM; SI = 300); and (iii) an optimal combina-
tion of COX and LOX inhibition was obtained for 1-(4-
cyanophenyl)-3-(4-methanesulfonylphenyl)prop-2-yn-1-
one (11d, COX-2 IC50 = 1.0 lM; SI = 31.5; 5-LOX
IC50 = 1.0 lM; 15-LOX IC50 = 3.2 lM). Further studies
are in progress to extend these structure–activity data
and to determine anti-inflammatory activity of potential
lead compounds.
10. (a) Rao, P. N. P.; Uddin, M. J.; Knaus, E. E. J. Med.
Chem. 2004, 47, 3972; (b) Weiss, K. L.; Alshafie, G.;
Chapman, J. S.; Mershon, S. M.; Abou-Issa, H.; Clagett-
Dame, M.; Curley, R. W. Bioorg. Med. Chem. Lett. 2001,
11, 1583; (c) Jiang, Z. Y.; Wang, Y. G. Chem. Lett. 2003,
32, 568.
11. Analytical data for 11d. Yield, 85%; white solid; mp 183–
185 °C; IR (film): 2220 (C„N), 2200 (C„C), 1640
(C@O), 1311, 1150 (SO2) cmÀ1 1H NMR (CDCl3): d
;
Acknowledgments
3.11 (s, 3H, SO2CH3), 7.84 (d, J = 8.2 Hz, 2H, metha-
nesulfonylphenyl H-2, H-6), 7.88 (d, J = 8.5 Hz, 2H,
cyanophenyl H-3, H-5), 8.03 (d, J = 8.2 Hz, 2H, metha-
nesulfonylphenyl H-3, H-5), 8.29 (d, J = 8.5 Hz, 2H,
cyanophenyl H-2, H-6). Anal. Calcd for C17H11NO3S:
C, 66.01; H, 3.58; N, 4.58. Found: C, 65.82; H, 3.44; N,
4.40.
We are grateful to the Canadian Institutes of Health
Research (CIHR) (MOP-14712) for financial support
of this research and to Rx&D-HRF/CIHR for a post-
doctoral fellowship (to Q.H.C.).
References and notes
12. Analytical data for 11j. Yield, 81%; yellow solid; mp 142–
144 °C; IR (film): 2200 (C„C), 1647 (C@O), 1309, 1154
1
(SO2) cmÀ1; H NMR (CDCl3): d 3.10 (s, 3H, SO2CH3),
1. Silverstein, F. E.; Faich, G.; Goldstein, J. L.; Simon, L. S.;
Pincus, T.; Whelton, A.; Makuch, R.; Eisen, G.; Agrawal,
N. M.; Stenson, W. F.; Burr, A. M.; Zhao, W. W.; Kent, J.
D.; Lefkowith, J. B.; Verburg, K. M.; Geis, G. S. JAMA
2000, 284, 1247.
3
3
7.19 (dd, JHH = 8.5, JFH = 8.5 Hz, 2H, fluorophenyl H-
3, H-5), 7.85 (d, J = 8.2 Hz, 2H, methanesulfonylphenyl
H-2, H-6), 8.01 (d, J = 8.2 Hz, 2H, methanesulfonylphenyl
3
4
H-3, H-5), 8.23 (dd, JHH = 8.5, JFH = 5.5 Hz, 2H,
fluorophenyl H-2, H-6). Anal. Calcd for C16H11FO3S: C,
63.57; H, 3.67. Found: C, 63.43; H, 3.47.
2. Bombardier, C.; Laine, L.; Reicin, A.; Shapiro, D.;
Burgos-Vargas, R.; Davis, B.; Day, R.; Ferraz, M. B.;