A novel class of dual mPGES-1/5-LO inhibitors based on the α-naphthyl pirinixic acid scaffold

Article abstract of DOI:10.1016/j.bmcl.2011.01.049

Dual inhibition of microsomal prostaglandin E₂ synthase-1 (mPGES-1) and 5-lipoxygenase (5-LO) represents a promising strategy in the development of novel anti-inflammatory drugs targeting the arachidonic acid cascade. Herein, a class of α-naphthyl pirinixic acids is characterized as dual mPGES-1/5-LO inhibitors. Systematic structural variation was focused on the lipophilic backbone of the scaffold and yielded detailed structure-activity relationships (SAR) with compound 16 (IC₅₀ mPGES-1 = 0.94 μM; IC₅₀ 5-LO = 0.1 μM) showing the most favorable in vitro pharmacological profile.

Full text of DOI:10.1016/j.bmcl.2011.01.049

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1329–1333
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
A novel class of dual mPGES-1/5-LO inhibitors based on the
pirinixic acid scaffold
a-naphthyl
Martina Hieke a, , Christine Greiner b, , Theresa M. Thieme a, Manfred Schubert-Zsilavecz a, Oliver Werz b,
Heiko Zettl c,
⇑
a Goethe-University Frankfurt, Institute of Pharmaceutical Chemistry/ZAFES/LiFF, Max-von-Laue-Str. 9, D-60348 Frankfurt/M., Germany
b Friedrich-Schiller-University Jena, Institute of Pharmacy, Chair of Pharmaceutical/Medicinal Chemistry, Philosophenweg 14, D-07743 Jena, Germany
c ETH Zurich, Institute of Pharmaceutical Sciences, Wolfgang-Pauli-Str. 10, CH-8093 Zurich, Switzerland
a r t i c l e i n f o
a b s t r a c t
Article history:
Dual inhibition of microsomal prostaglandin E2 synthase-1 (mPGES-1) and 5-lipoxygenase (5-LO) repre-
sents a promising strategy in the development of novel anti-inflammatory drugs targeting the arachi-
Received 2 January 2011
Accepted 13 January 2011
Available online 18 January 2011
donic acid cascade. Herein, a class of
inhibitors. Systematic structural variation was focused on the lipophilic backbone of the scaffold and
yielded detailed structure-activity relationships (SAR) with compound 16 (IC50 mPGES-1 = 0.94 M;
IC50 5-LO = 0.1 M) showing the most favorable in vitro pharmacological profile.
a-naphthyl pirinixic acids is characterized as dual mPGES-1/5-LO
l
Keywords:
l
Inflammation
Arachidonic acid cascade
SAR
Ó 2011 Elsevier Ltd. All rights reserved.
mPGES-1
5-LO
Represented by the widely used cyclooxygenase (COX)-inhibit-
ing non-steroidal anti-inflammatory drugs (NSAIDs), agents inter-
fering with the arachidonic acid cascade have a long tradition in
the treatment of inflammatory diseases. However, especially the
long-term use of NSAIDs is under debate because of severe gastro-
intestinal and cardiovascular side effects.1 Therefore, the explora-
tion of alternative pharmacological approaches leading to safer
anti-inflammatory drugs is of urgent need.
One promising approach to circumvent COX-related side effects
while maintaining anti-inflammatory efficacy is the interference
with the microsomal prostaglandin E2 synthase (mPGES)-1. This
enzyme catalyzes the transformation of prostaglandin (PG) H2 to
pro-inflammatory PGE2 and is functionally coupled to COX-2 (see
Fig. 1).2 Because mPGES-1 (as well as COX-2) is mainly induced
after inflammatory stimulation, its inhibition would ideally not af-
fect the formation of house-keeping PGs. Recent studies with
mPGES-1 inhibitors showed analgesic and anti-inflammatory effi-
cacy in a variety of animal models.3,4
iron dioxygenase. Inhibition of 5-LO has shown to cause several
beneficial pharmacological effects, such as suppression of inflam-
mation and allergy-induced bronchoconstriction.5 However, as
many 5-LO inhibitors are lacking selectivity and/or show mecha-
nism-based side effects, zileuton is still the only compound being
approved so far.6
Based on the fact that COX-inhibiting NSAIDs increase the pro-
duction of chemotactic LTB4, a dual approach targeting both path-
ways of AA metabolism might be superior, in particular with
respect to reduced side effects.7 Indeed, compounds such as licofe-
lone (an inhibitor of mPGES-1, 5-LO and COX-1), which has
reached phase III clinical trials, show high anti-inflammatory po-
tency combined with a favorable safety profile.1,8
We previously identified novel dual inhibitors of mPGES-1 and
5-LO based on the core structure of pirinixic acid.9,10 Herein, we
present a novel class of
a-naphthyl-substituted pirinixic acid
derivatives as potent dual inhibitors of mPGES-1 and 5-LO. We fo-
cused on the structure–activity relationships (SAR) of the lipophilic
backbone of the lead structure (see Fig. 2) and explored a broad
variety of aliphatic and especially aromatic residues.
Besides PGs, leukotrienes (LTs) are the second major class of
lipid mediators derived from arachidonic acid and involved in
inflammatory and allergic processes (see Fig. 1). The central step
of LT biosynthesis is the initial conversion of arachidonic acid to
LTA4, which is catalyzed by 5-lipoxygenase (5-LO), a non-heme
Synthesis of compounds 3–24 was performed in a four step
reaction (Scheme 1) modified from d’Atri et al. and published pre-
viously.11,12 In brief, commercially available
a-bromonaphthyl
ethyl acetate was reacted with thiobarbituric acid in DMF/triethyl-
amine (i) and the resulting thioether derivative was chlorinated
with POCl3 (ii). The obtained 4,6-dichloro-substituted pyrimidine
was refluxed with amine building blocks in EtOH/triethylamine
⇑
Corresponding author. Tel.: +41 44 6339113; fax: +41 44 6331379.
E-mail address: heiko.zettl@pharma.ethz.ch (H. Zettl).
These authors contributed equally to this work.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.049

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M. Hieke et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1329–1333
Figure 1. Schematic illustration of the arachidonic acid cascade. Targeted enzymes (mPGES-1 and 5-LO) are highlighted.
resulting in a nucleophilic substitution of one chlorine (iii). Finally,
ester hydrolysis with KOH in EtOH (iv) gave the desired carboxylic
acids.
Inhibition of mPGES-1 activity (transformation of PGH2 to PGE2)
was assessed in a cell-free assay using the mitochondrial fraction of
IL-1b-stimulated A549 lung epithelial adenocarcinoma cells (that
overexpress mPGES-1) and 20
nately, a cell-based test system that allows selective analysis of
l
M PGH2 as substrate.8 Unfortu-
Figure 2. General structure of the presented series of a-naphthyl pirinixic acids.
Scheme 1. Reagents and conditions: (i)
a-bromonaphtyl ethyl acetate, triethylamine, DMF, rt–80 °C, 24 h; (ii) POCl3 N,N-diethylaniline, reflux, 3.5 h; (iii) R-NH2,
triethylamine, ethanol, reflux, 4–96 h; (iv) KOH, ethanol, rt–80 °C, 1–24 h.

M. Hieke et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1329–1333
1331
Table 1
Inhibition of mPGES-1 and 5-LO by
a -naphthyl pirinixic acid derivatives
5-LO
O
H
IC50
PMNL
[l
M] or r.a. @ 10 lM (%)
N
N
S
R1
OH
Purified 5-LO
mPGES-1
IC50 M] or r.a. @ 10 lM (%)
Compound
N
R2
[l
Cl
R1
R2
1
2
H
Inactive
5.1
Inactive
5.0
Inactive
n.d.
1-Naphthyl
3
4
1-Naphthyl
1-Naphthyl
90.2% ( 5.8)
65.3% ( 3.0)
2.4
2.5
70.6% ( 15.2)
54.8% ( 8.2)
Cl
5
6
1-Naphthyl
1-Naphthyl
45.5% ( 11.7)
5.1
0.7
0.8
5.0
8.9
Cl
F
7
8
1-Naphthyl
1-Naphthyl
49.9% ( 4.5)
5.7
3.1
0.7
67.3% ( 2.9)
8.5
9
1-Naphthyl
1-Naphthyl
35.8% ( 8.8)
0.26
0.26
5.8
1.9
10
0.9
11
12
13
1-Naphthyl
1-Naphthyl
1-Naphthyl
42.3% ( 7.8)
2.5
1.8
0.5
44.2% ( 12.3)
68.9% ( 3.5)
2.9
6.1
1.9
14
15
1-Naphthyl
1-Naphthyl
49.1% ( 11.0)
36.7% ( 4.4)
4.4
0.5
19.0% ( 2.5)
4.2
N
16
17
1-Naphthyl
1-Naphthyl
0.94
1.9
0.1
0.5
2.3
5.0
(continued on next page)

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M. Hieke et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1329–1333
Table 1 (continued)
5-LO
O
H
N
IC50
PMNL
[l
M] or r.a. @ 10 lM (%)
N
S
R1
OH
Purified 5-LO
mPGES-1
IC50 [lM] or r.a. @ 10 lM (%)
Compound
N
R2
Cl
R1
R2
18
1-Naphthyl
1.6
0.17
2.3
NC
19
20
21
1-Naphthyl
1-Naphthyl
1-Naphthyl
1.45
0.94
0.4
0.4
0.6
2.0
3.1
5.2
O
O
38.8% ( 1.6)
N
H
22
1-Naphthyl
0.88
0.7
3.0
23
24
1-Naphthyl
1-Naphthyl
1.5
0.3
2.2
1.6
1.55
0.24
IC50 values were calculated based on the mean values of at least three determinations. Reference compounds were MK-886 for inhibition of mPGES-1 and BWA4C for
inhibition of 5-LO (both 3 M); r.a.: remaining activity.
l
interference with endogenous mPGES-1 activity in the cell
(i.e., the transformation of PGH2 to PGE2) is not available. The inhibi-
tion of 5-LO product formation was analyzed in a cell-based assay
using polymorphonuclear leukocytes (PMNL) as well as in a cell-free
assay using purified human recombinant 5-LO enzyme.10,13 The lat-
ter assay was chosen because a given test compound may suppress
5-LO product synthesis in intact cells without inhibiting 5-LO
directly, for example by interference with co-factors regulating
5-LO in the cell or with other enzymes involved in LT biosynthesis
(e.g., 5-lipoxygenase activating protein, LTA4 hydrolase, LTC4 syn-
thase). On the other hand many compounds inhibit 5-LO in cell-free
assays but fail in intact cells for several reasons.6 Therefore, we
performed the cell-based assay and the cell-free assay side by side.
Pirinixic acid itself (compound 1) is inactive on both mPGES-1
and 5-LO.9 As we have shown previously, the introduction of a
contrast, introduction of alkyl spacers between the central pyrim-
idine and an unsubstituted phenyl residue as in phenethyl-substi-
tuted 11 and phenpropyl-substituted 12 led to diminished
activities on both enzymes. Next, we examined bicyclic substitu-
ents such as 2-naphthyl (13), 6-quinolinyl (14) and 5-indanyl
(15). The 2-naphthyl-subsituted 13 was a potent dual mPGES-1/
5-LO inhibitor, whereas the 5-indanyl substituted compound (15)
displayed some selectivity for 5-LO. The introduction of an addi-
tional hydrogen-bond acceptor by using 6-quinolinyl (14) instead
of 2-naphthyl clearly diminished activity on both mPGES-1 and
5-LO. The most potent dual mPGES-1 and 5-LO inhibitors were ob-
tained among the series substituted with biphenyl (and analogue)
residues (16–24). In regard to 5-LO inhibition, SARs for these com-
pounds are very flat with all IC50 values (PMNL) in the triple digit
nanomolar range. Nanomolar inhibition of mPGES-1 was achieved
naphthyl residue in
well-balanced dual mPGES-1/5-LO inhibitor (2; IC50 mPGES-
1 = 5.1 M, IC50 5-LO = 5.0
M in PMNL).10 Based on the promising
in vitro pharmacology of compound 2, we replaced the 2,3-dimeth-
ylphenyl residue by a broad variety of aliphatic and aromatic sub-
structures (see Table 1). Introduction of aliphatic n-butyl (3) and
a
-position of the carboxylic acid leads to a
by introduction of 4-biphenyl (16; IC50 = 0.94
l
M), 4-phenoxyphe-
nyl (20; IC50 = 0.94 M) and 4-phenylbenzyl (22; IC50 = 0.88
l
lM)
l
l
residues. Interestingly, connection of the two phenyl residues by
an amide bond (21) clearly diminished mPGES-1 inhibition.
Regarding all presented derivatives, 4-phenylbenzyl-substituted
compound 16 showed the most favorable pharmacological profile
isobutyl (4) residues caused
a
complete loss of activity on
with mPGES-1 IC50 = 0.94
In summary, we were able to optimize the initial
substituted pirinixic acid towards potent, nanomolar
dual mPGES-1/5-LO inhibitors by introducing larger aromatic
substituents to the lipophilic backbone of the lead structure.
l
M and 5-LO IC50 = 0.1
l
M (in PMNL).
mPGES-1. Among the phenyl-substituted compounds 5–10, the
3,5-di-tert-butylphenyl-subsituted 10 showed clearly the most
favorable pharmacological profile with nanomolar activity on
a-naphthyl-
2
mPGES-1 (IC50 = 0.9 lM) and 5-LO (in PMNL IC50 = 0.26 lM). In

M. Hieke et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1329–1333
2. Koeberle, A.; Werz, O. Curr. Med. Chem. 2009, 16, 4274.
1333
Depending on the residues, we obtained compounds covering the
range of a slight preference for the inhibition of cellular leukotriene
biosynthesis to equipotent dual mPGES-1/5-LO inhibitors. SAR
studies revealed that lipophilic aromatic substructures are gener-
ally well tolerated whereas the introduction of polar atoms or
groups was detrimental for the activity on both enzymes. With
their high potency and interesting in vitro pharmacological profile,
3. Xu, D.; Rowland, S. E.; Clark, P.; Giroux, A.; Cote, B.; Guiral, S.; Salem, M.;
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Pharmacol. Exp. Ther. 2008, 326, 754.
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Reckel, S.; Hoernig, C.; Northoff, H.; Bernhard, F.; Dotsch, V.; Sautebin, L.;
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a-naphthyl pirinixic acid derivatives are highly attractive candi-
dates for further exploration in pharmacological assays and might
be an appealing alternative to the established NSAIDs circumvent-
ing COX-related side effects.
Acknowledgements
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We thank Daniela Müller for expert technical assistance and
Aureliasan GmbH (Tuebingen, Germany) for financial support.
References and notes
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