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B. Cote et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6816–6820
6819
Table 5. Comparative data on potency and selectivity of mPGES-1
inhibitors 1 and 3
HO
O
N
H2N
a
Enzyme or cell assay
IC50 (lM)
1
3
b
a
Human mPGES-1
Rat mPGES-1
0.003
0.13
N/A
>1
0.001
>30
0.0009
>30
3.0
Guinea pig mPGES-1
Human mPGES-2
TX synthase
18
19
17
0.95
5.8
A549 cells, PGE2, 50% FBS
A549 cells, PGF2a, 50% FBS
Human whole blood, PGE2
Human whole blood, TXB2
Human JAK2
0.42
>50
1.3
Cl
Cl
>50
>40
>40
N/A
N/A
O
O
d
e
c
>40
0.1
Human JAK3
>10
a Values are means of at least two experiments.
21
20
Cl
Cl
presented in Table 5 for the indole carboxylic acid 1 and
the phenanthrene imidazole 3. Both compounds have
similar intrinsic mPGES-1 activity with IC50s of 0.003
and 0.001 lM, respectively. They are selective against
mPGES-216 and thromboxane synthase. Compound 3
is 14-fold more potent than the initially reported inhib-
itor 1 with an IC50 of 0.42 lM in the A549 whole cell as-
say (50% FBS). Most importantly, the phenanthrene
imidazole 3 is the first reported mPGES-1 inhibitor to
demonstrate potency in a human whole blood (HWB)
assay. When freshly collected blood was stimulated with
LPS, compound 3 selectively inhibited the production of
PGE2 with an IC50 of 1.3 lM with no concomitant
TXB2 inhibition. It is worth mentioning that this
HWB IC50 is comparable to the ones of marketed cox-
ibs.17 With this markedly improved potency and a suit-
able pharmacokinetic profile,18 compound 3 may serve
as a good tool for in vivo proof-of-concept studies.19
Gram quantities of this new potent mPGES-1 inhibitor
were prepared according to Scheme 2.
Br
Br
NC
NC
N
N
f
N
H
N
H
3
22
Scheme 2. Reagents and conditions: (a) H2NOHHCl, EtOH, reflux,
59%, pyridine; (b) PPA, 100 ꢁC, concd HCl, MeOH, reflux, 92%; (c)
CuCl2, t-BuONO, MeCN, 65 ꢁC, 52%; (d) CrO3, AcOH, 100 ꢁC, 88%;
(e) 2,6-dibromobenzaldehyde, NH4OAc, AcOH, 100 ꢁC, 85%; (f)
CuCN, DMF, 80 ꢁC, 80%.
zyme activity was also observed for mice. To
demonstrate in vivo efficacy, a LPS-induced hyperalge-
sia model in guinea pig was therefore developed7 know-
ing the ability of compound 3 to inhibit this enzyme
(guinea pig IC50 = 0.9 nM). When orally dosed at 30
and 100 mg/kg, inhibitor 3 prevented the hyperalgesic
response in guinea pig in a dose-dependent manner with
a complete blockade of hyperalgesia at 100 mg/kg.21
This constitutes the first reported example of in vivo effi-
cacy for a selective mPGES-1 inhibitor in a pre-clinical
model. A full description of this in vivo pharmacological
profile will be published elsewhere.7
The synthesis of 3 starts with commercially available 3-
acetylphenanthrene 17. This methyl ketone was refluxed
in ethanol in the presence of hydroxylamine hydrochlo-
ride to afford the corresponding oxime 18 in 59% yield.
Phenanthreneamine 19 is obtained by a Beckmann rear-
rangement with polyphosphoric acid at 100 ꢁC followed
by amide hydrolysis under acidic conditions in an over-
all yield of 92%. Conversion of the amine to the aryl
chloride 20 was performed with tert-butyl nitrite in the
presence of copper (II) chloride in 52% yield.20 Phenan-
threne 20 was then treated with chromium (VI) oxide in
acetic acid at 100 ꢁC to afford the corresponding qui-
none 21 in 88% yield. The core of the molecule was
assembled using the same transformation described
above and phenanthrene imidazole 22 was obtained in
85% yield. Finally, the cyano groups were incorporated
by reacting the dibromo precursor 22 with CuCN in
DMF at 80 ꢁC to afford the phenanthrene imidazole bis-
nitrile 3 in 80% yield.
In summary, phenanthrene imidazole 3 (MF63) has been
identified as a new potent, selective, and orally active
mPGES-1 inhibitor. This new series was developed by
lead optimization of an internal HTS hit. Compound 3
shows in vitro superiority over the previously reported in-
dole carboxylic acid 1, both in the A549 whole cell assay
(50% FBS, IC50 = 0.42 lM) and in the human whole
blood assay (IC50 = 1.3 lM). Finally, in a guinea pig
hyperalgesia model, inhibitor 3 demonstrated a signifi-
cant analgesic effect.
References and notes
As disclosed in Table 5, the mPGES-1 inhibitor 3 is not
active against the rat enzyme which precluded the use of
well-established rat inflammatory pain models. This ma-
jor discrepancy between the human and the rodent en-
1. Funk, C. D. Science 2001, 294, 1871.
2. (a) Portanova, J. P. et al. J. Exp. Med. 1996, 184, 883; (b)
Pulichino, A. M. et al. J. Pharmacol. Exp. Ther. 2006,
319, 1043; (c) Murata, T. et al. Nature 1997, 388, 678.