2,3-Diarylbenzopyran derivatives as a novel class of selective cyclooxygenase-2 inhibitors

Article abstract of DOI:10.1016/S0960-894X(02)00952-6

A new series of cyclooxygenase-2(COX-2) inhibitors with naturally occurring flavone as the main skeleton has been synthesized and their biological activities were evaluated for cyclooxygenase inhibitory activity. Rational structural modifications were applied to potent COX-2 inhibitors to obtain the desired pharmacokinetic profiles for improved oral anti-inflammatory activity.

Full text of DOI:10.1016/S0960-894X(02)00952-6

Bioorganic & Medicinal Chemistry Letters 13 (2003) 413–417
2,3-Diarylbenzopyran Derivatives as a Novel Class of Selective
Cyclooxygenase-2 Inhibitors
Yung Hyup Joo,* Jin Kwan Kim, Seon-Hwa Kang, Min-Soo Noh, Jun-Yong Ha,
Jin Kyu Choi, Kyung Min Lim, Chang Hoon Lee and Shin Chung
Drug Discovery, AmorePacific Corporation R&D Center, 314-1 Bora-ri, Kiheung-eup, Yongin-si,
Kyounggi-do 449-729, South Korea
Received 30 September 2002; accepted 31 October 2002
Abstract—A new series of cyclooxygenase-2(COX-2) inhibitors with naturally occurring flavone as the main skeleton has been
synthesized and their biological activities were evaluated for cyclooxygenase inhibitory activity. Rational structural modifications
were applied to potent COX-2 inhibitors to obtain the desired pharmacokinetic profiles for improved oral anti-inflammatory
activity.
# 2002 Elsevier Science Ltd. All rights reserved.
Non-steroidal anti-inflammatory drugs (NSAIDs) have
been used over a century for the treatment of inflam-
mation, pain and inflammation-associated disorders.
Their anti-inflammatory activity results from inhibition
of cyclooxygenases (COXs), which convert arachidonic
acid into prostaglandins. However, inhibition of COXs
may lead to undesirable side effects such as life-threa-
tening gastrointestinal perforation, ulcer and bleeding
(PUB) as well as renal toxicity.1
and inflammation-associated disorders without disrupting
the bodily homeostasis maintained by COX-1. Indeed,
selective COX-2 inhibitors including celecoxib and
rofecoxibmanifested the therapeutic efficacy compar-
able to that of traditional NSAIDs but with improved
gastrointestinal safety.3
COX-2 inhibitors could be regarded to have evolved from
aspirin over a 100 years. The main theme in this century-
long evolution process has been in the improvement of
safety for chronic use. Even though COX-2 inhibitors
have shown an improved gastrointestinal safety profile,
they are not a perfect choice for long term use for arthritis.
Recently the cardiotoxicity issue echoed around COX-2
inhibitors. Even now there are enough reasons for dis-
covery of new classes of COX-2 inhibitors to meet the
unmet safety issues. Herein we report the synthesis and the
biological activity of 2,3-diarylbenzopyran derivatives as
a novel class of selective COX-2 inhibitors and also we
Nowadays, it is well established that there are at least
two isoforms of cyclooxygenases, COX-1 and COX-2.2
COX-1 is constitutively expressed in a variety of tissues
including the gastrointestinal tract, the kidneys, and the
platelets, and is known to be responsible for bodily
homeostasis. On the other hand, COX-2 is induced
upon inflammatory stimuli and responsible for aggra-
vation of inflammation. Thus, selective inhibition of
COX-2 should be useful for treatment of inflammation
Figure 1.
*Corresponding author. Tel.:+82-31-280-5912; fax:+82-31-281–8391; e-mail: yhjoo@pacific.co.kr
0960-894X/03/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00952-6

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Y. H. Joo et al. / Bioorg. Med. Chem. Lett. 13 (2003) 413–417
wish to discuss a rationale for the modification of ben-
zopyran structure together with an issue for translation
of in vitro activity into in vivo effect (Fig. 1).
one (10p) is presented in ref 6 in order to illustrate the
generality of Scheme 1. The benzothiopyran derivatives
11 were prepared via the reaction of diarylbenzopyran
10 with Lawesson’s reagent in toluene at reflux.
The 2,3-diarylbenzopyran derivatives were synthesized
via the route outlined in Scheme 1. First, condensation
of 2-hydroxyacetophenone (1) and 4-(methylthio)-
benzaldehyde under basic condition gave chalcone 2,
which was followed by oxidative cyclization to afford
the desired flavone 3.4 Flavone 3 was subjected to bro-
mination by N-bromosuccinimide (NBS) to yield bro-
mide 4, which was then oxidized to methylsulfone
compound 5 by reaction with OXONE1. Alternatively,
compound 3 was subjected to the OXONE1 reaction
and then reaction with bis(trifluoroacetoxyiodo)benzene
(BTI) to give iodide compound 7. Haloflavone 5 or 7
was then coupled with an aromatic boronic acid by
Suzuki coupling5 to yield 2,3-diarylbenzopyran derivatives
10 with a pharmacophore for selective COX-2 inhibition.
A detailed procedure for synthesis of 2-{4-(methyl-
sulfonyl)phenyl}-3-(3-pyridinyl)-(4H)-1-benzopyran-4-
Another key functional moiety for selective COX-2
inhibition, aminosulfonyl group, was introduced as
illustrated in Scheme 2.
Compound 4 was converted to sulfoxide 12 using
OXONE1 or MCPBA, which was then subjected to in a
sequential manner (1) a Pummerer-type reaction,7 (2)
treatment with chlorine in AcOH, and (3) reaction with
NH4OH to yield sulfonamide 13. Then the Suzuki cou-
pling of sulfonamide 13 with boronic acid 8 or boronate
9 afforded the desired sulfonamide 14.
The benzopyran analogues synthesized in this study were
tested for their ability to inhibit COX-2 and COX-1 by
using freshly harvested mouse peritoneal macrophages
as described in the literature.8 The in vitro inhibitory
Scheme 1. Reagents and conditions: (a) 4-(methylthio)benzaldehyde, KOH, EtOH–H2O; (b) iodine/DMSO, reflux; (c) NBS,CHCl3; (d) oxone;
(e) BTI (=PhI(OCOCF3)2), I2; (f) ArB(OH)2(8) or ArBꢀ(OCH3)3Li+(9), Pd(PPh3)4, 2 M Na2CO3, EtOH–H2O–toluene; (g) Lawesson’s reagent,
toluene. Ar=substituted or unsubstituted aryl, heteroaryl.
Scheme 2. Reagents and conditions: (a) oxone or MCPBA; (b) TFAA, reflux; (c) Cl2, AcOH; (d) NH4OH; (e) arylboronic acid, Pd(PPh3)4,
2 M–Na2CO3, EtOH–H2O–toluene. Ar=substituted or unsubstituted aryl, heteroaryl.

Y. H. Joo et al. / Bioorg. Med. Chem. Lett. 13 (2003) 413–417
415
Table 1. In vitro COX-2 and COX-1 enzyme inhibitory activities of
benzopyran derivatives 10, 11 and 14
Table 2. In vitro COX-2 and COX-1 enzyme inhibitory activities of
benzopyran derivatives with N-heterocyclic substituents
Compd
Ar
COX-2
COX-1
Compd
COX-2
(IC50, mg/mL)a
COX-1a,b
(IC50, mg/mL)a (% inhibition
at 10 mg/mL)a
10p
10q
10r
10s
10t
15
0.5
24%b
0.94
44%b
13%b
0.5
13
<5
18
17
<5
12
10a
10b
10c
10d
10e
10f
10g
10h
10i
Phenyl
4-Fluorophenyl
2-Fluorophenyl
3-Fluorophenyl
4-Chorophenyl
3-Chlorophenyl
2,4-Dichlorophenyl
3,4-Dichlorophenyl
3,5-Dichlorophenyl
4-Methoxyphenyl
2-Methylphenyl
1-Naphthyl
0.35
0.08
0.03
0.21
0.14
0.15
0.16
0.12
7%b
0.21
0.37
1.62
0.14
0.04
0.03
0.08
0.24
0.06
0.04
0.05
0.07
0.16
0.12
0.39
76
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
61
aValues are means of at least two measurements.
b% Inhibition at 10 mg/mL.
10j
10k
10l
over COX-1, replicating the observations in other clas-
ses of COX-2 inhibitors with pharmacophore of
1,2-diaryl alkene type.9
10m
11a
11b
11c
11h
11j
14a
14b
14c
14j
2-Benzo[b]thiophenyl
Phenyl
4-Fluorophenyl
2-Fluorophenyl
3,4-Dichlorophenyl
4-Methoxyphenyl
Phenyl
When the benzopyran derivatives were evaluated
against carrageenan-induced rat paw edema model,
there were no meaningful anti-inflammatory effects
observed. Pharmacokinetic evaluation for some of the
benzopyran derivatives suggested that their oral bio-
availability is very poor. The benzopyran COX-2 inhib-
itors in Table 1 have three aromatic groups and tend to
be highly lipophilic. If oral anti-inflammatory activity is
to be pursued for the benzopyran derivatives, there
should be some structural variation to overcome the
issue of poor bioavailability.
4-Fluorophenyl
2-Fluorophenyl
4-Methoxyphenyl
4-Methylthiophenyl
3,4-Methylenedioxyphenyl
Celecoxib0.01
67
60
84
90
14n
14o
75
aValues are means of at least two measurements.
b% Inhibition at 3 mg/mL.
A nitrogen-containing aromatic group such as pyridine
would be a reasonable choice for reducing overt lipo-
philicity of an aromatic group. The substitution of the
phenyl moiety with a pyridinyl group on the 3-position
of benzopyran tended to show reduction of COX-2
inhibitory potency when compared to 10a (see Tables 1
and 2). However, their solubility increased to the level
of 100–200 mg/mL in 1% aqueous DMSO solution to
meet a premise for pharmacokinetic purpose. Among
them, the 3-pyridinyl compounds 10p, 10r, and 15
showed in vitro COX-2 inhibitory activity similar to
that of the corresponding phenyl-containing parent
COX-2 inhibitor 10a (Fig. 2).
activities against COX-2 and COX-1 are summarized in
the Table 1.
Methylsulfone compounds 10 and thiobenzopyran
compounds 11 showed moderate to good COX-2 inhib-
itory activities. No meaningful COX-1 inhibition was
observed for these COX-2 inhibitors at 10 mg/mL.
Introduction of a halogen atom on the 3-aryl ring often
resulted in improved COX-2 potency, however, a big
steric bulk on the 3-aryl ring appeared to be inap-
propriate for COX-2 activity as in 3,5-dichlorophenyl
derivative 10i and 1-naphthyl derivative 10l. 10c showed
COX-2 inhibitory potency comparable to that of cel-
ecoxib. Sulfonamide derivatives 14 showed some
improvement in COX-2 inhibitory potency from the cor-
responding methylsulfone derivatives 10, however, the
improvement was not significant. Instead sulfonamide
derivatives 14 showed a decreased COX-2 selectivity
Assessment of the anti-inflammatory activity of 10p by
carrageenan-induced rat paw edema10 in Sprague–
Dawley (SD) rats exhibited a modest oral activity (18%
inhibition at 3 mg/kg, 25% inhibition at 10 mg/kg, 41%
inhibition at 30 mg/kg body weight) compared to cel-
Figure 2.

416
Y. H. Joo et al. / Bioorg. Med. Chem. Lett. 13 (2003) 413–417
ecoxib(38% inhibition at 3 mg/kg). However, 10p failed
to show any appreciable oral anti-inflammatory activity
at 3 mg/kg/day, QD (daily once), when evaluated by a
subchronic inflammatory animal model of adjuvant-
induced arthritis.11 It was perceived that such a poor
anti-inflammatory effect by 10p would be from its rapid
degradation in the body after oral intake. Indeed 10p
was metabolized very fast in the SD rat with a plasma
clearance half-life of 0.5 h. It has been well-documented
that the 40-position of flavonoid A ring is highly sus-
ceptible to hydroxylation by CYP 450 isozymes.12
However, owing to the presence of 40- methylsulfonyl
group, the A ring metabolism of compound 10p must be
structurally hindered. Furthermore, reduced electron
density in the pyridine ring makes the pyridine moiety
of 10p resistant to metabolic degradation by CYP 450
isozymes. Therefore, it is likely that the metabolic event
should occur in the B ring of flavonoid in this specific
case. In order to extend the plasma clearance half-life,
was designed and prepared compound 15, in which the
6-position of the flavone B ring is substituted with
fluorine atom. Indeed, the effect of the substitution at
the 6-position by fluorine atom showed up as a sig-
nificant increase in plasma clearance half-life: T1/2=7.4
h; Tmax=5.0 h; and Cmax=6.9 mg/mL at 10 mg/kg, po
Compound 15 showed a modest anti-inflammatory
effect by carrageenan-induced rat paw edema, compar-
able to that of 10p (20% inhibition at 3 mg/kg po, 26%
inhibition at 10 mg/kg po, 41% inhibition at 30 mg/kg
po). As noted previously compound 10p failed to show
any notable anti-inflammatory effect at 3 mg/kg/day,
QD (daily once) by adjuvant-induced arthritis, possibly
due to its very short plasma clearance half-life. How-
ever, the extended plasma clearance half-life of com-
pound 15 allowed to show a modest oral activity against
adjuvant-induced arthritis by the therapeutic model:
63% inhibition at 3 mg/kg/day, QD (n=7 per group)
for 15; 51% inhibition at 0.3 mg/kg/day, QD for posi-
tive comparator celecoxib.
Zhang, Y. Y.; Seibert, K. J. Med. Chem. 2000, 43, 1661. (b)
Talley, J. J.; Brown, D. L.; Carter, J. S.; Graneto, M. J.;
Koboldt, C. M.; Masferrer, J. L.; Perkin, W. E.; Rogers, R. S.;
Shaffer, A. F.; Zhang, Y. Y.; Zweifel, B. S.; Seibert, K. J. Med.
Chem. 2000, 43, 775. (c) Shin, S. S.; Noh, M.; Byun, Y. J.;
Choi, J. K.; Kim, J. Y.; Lim, K. M.; Ha, J.; Kim, J. K.; Lee,
C. H.; Chung, S. Bioorg. Med. Chem. Lett. 2001, 11, 165. (d)
Hashimoto, H.; Imamura, K.; Haruta, J.; Wakitani, K.
J. Med. Chem. 2002, 45, 1511.
4. (a) Iqbal, J.; Fatma, W.; Shaida, W. A.; Rahman, W.
J. Chem. Research(S) 1982, 92. (b) Makrandi, J. K. Seema.
Chem. & Ind 1989, 607.
5. (a) Miyaura, N.; Yanagi, T.; Suzuki, A. Synth. Commun.
1981, 11, 513. (b) Hoshino, Y.; Miyaura, N.; Suzuki, A. Bull.
Chem. Soc. Jpn. 1988, 61, 3008. (c) Watanabe, T.; Miyaura,
N.; Suzuki, A. Synlett 1992, 207.
6. Selected compounds were prepared as follows.
3-Bromo-2-(4-(methylthio)phenyl)-4H-1-benzopyran-4-one(4). A
solution of (4-(methylthio)phenyl)-4H-1-benzopyran-4-one
(0.50 g,1.86 mmol) and NBS (0.36 g, 2.05 mmol) in CHCl3 (30
mL) was heated to reflux for 5 h. The resulting mixture was
washed with saturated NaHCO3, brine and dried over anhy-
drous MgSO4, and filtered, and concentrated under reduced
pressure. The residue was subjected to flash chromatography
(SiO2, hexane/ethyl acetate, 4:1) to yield the title compound as
a pale yellow solid (0.6 g, 93%). Mp; 162–163 ꢁC (CH2Cl2/
petroleum ether): 1H NMR (CDCl3 , 300 MHz) d 8.30–8.27
(1H, m), 7.84–7.80 (2H, m), 7.74–7.69 (1H, m), 7.51–7.43(2H,
m), 7.38–7.34 (2H, m), 2.55 (3H, s): IR (KBr); 1658, 1611,
1463, 1331, 1065, 753 cmꢀ1: MS(EI); 346 (M+), 348 (M++2):
HRMS(EI); calcd for C16H11O2SBr 345.9663, found 345.9669.
3-Bromo-2-(4-(methylsulfonyl)phenyl)-4H-1-benzopyran-4-one(5).
To a solution of 3-bromo-2-(4-(methylthio)phenyl)-4H-1-ben-
zopyran-4-one (0.6 g, 1.73 mmol) in MeOH (10 mL) and THF
(10 mL) was added a solution of OXONE1 (1.59 g, 2.59
mmol) in H2O (10 mL) dropwise at 0 ꢁC. The resulting mixture
was stirred for 3 h. And the solution was extracted two times
with CH2Cl2 (20 mL per each), and the organic layer was washed
with brine and dried over anhydrous MgSO4. The resulting
solution was filtered and concentrated under reduced pressure.
Recrystallization (CH2Cl2/petroleum ether) of the resulting resi-
due yielded the title compound as a solid (0.59 g, 90%). Mp 211–
213 ꢁC (CH2Cl2/petroleum ether): 1H NMR (CDCl3, 300MHz)
d 8.34–8.30 (1H, m), 8.15–8.05 (4H, m), 7.80–7.74 (1H, m), 7.54–
7.49 (2H, m), 3.15 (3H, s): IR (KBr); 1646, 1310, 1146, 1075
cmꢀ1: MS(EI); 378 (M+), 380(M+ + 2): HRMS(EI); calcd for
C16H11O4SBr 377.9561, found 377.9561.
In summary, we prepared a class of selective COX-2
inhibitors having the central scaffold with naturally
occurring flavonoids. In order to improve the inap-
propriate pharmacokinetic properties of the benzopyran
COX-2 inhibitors, rational considerations were applied
for the modification of the benzopyran scaffold as well
as the pendant 3-position aromatic group. Bioavail-
ability was improved by modification of the 3-position
aromatic pendant. In the meantime the extension of
plasma clearance half-life became possible by modulat-
ing the metabolically susceptible flavone ring. Com-
pound 15 is an orally potent COX-2 inhibitor obtained
through such rational structural modifications.
2-(4-(Methylsulfonyl)-phenyl)-3-(3-pyridinyl)-4H-1-benzopyran-
solution of 3-bromo-2-(4-(methyl-
4-one(10p). To
a
sulfonyl)phenyl)-4H-1-benzopyran-4-one (2.5 g, 6.6 mmol),
lithium trimethoxy-3-pyridinylboronate (1.62 g, 8.5 mmol) in
toluene (100 mL) and ethanol (100 mL) was added 2 M aqu-
eous sodium carbonate (6 mL) and then tetrakis (triphenyl-
phosphine) palladium (0.38 g, 0.33 mmol) and was stirred at
100 ꢁC for 27 h. After being concentrated under reduced pres-
sure, it was dissolved in CH2Cl2 (50 mL) and washed with
water, brine. The organic layer was dried over anhydrous
MgSO4. And the resulting solution was filtered and con-
centrated under reduced pressure. The residue was subjected
to flash chromatography (SiO2, CH2Cl2/ethyl acetate, 1:4) to
yield the title compound as a pale yellow solid (1.04 g, 42%).
References and Notes
Mp 220–221 ꢁC (CH2Cl2/petroleum ether): H NMR (CDCl3,
1
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