Benzodiazepinone derivatives as CRTH2 antagonists

Article abstract of DOI:10.1021/ml200019y

Multiple CRTH2 antagonists are currently evaluated in human clinical trials for asthma and chronic obstructive pulmonary disease (COPD). During our lead optimization for CRTH2 antagonists, an observation of an intramolecular hydrogen bond in ortho-phenyls

Full text of DOI:10.1021/ml200019y

LETTER
pubs.acs.org/acsmedchemlett
Benzodiazepinone Derivatives as CRTH2 Antagonists
Jiwen (Jim) Liu,* Alan C. Cheng, H. Lucy Tang, and Julio C. Medina
Amgen Inc., 1120 Veterans Boulevard, South San Francisco, California 94080, United States
S Supporting Information
b
ABSTRACT:
Multiple CRTH2 antagonists are currently evaluated in human clinical trials for asthma and chronic obstructive pulmonary disease
(COPD). During our lead optimization for CRTH2 antagonists, an observation of an intramolecular hydrogen bond in
ortho-phenylsulfonamido benzophenone derivatives led to the design and synthesis of conformationally constrained benzodiaze-
pinones as potent CRTH2 antagonists. The benzodiazepinones are 2 orders of magnitude more potent than the original flexible
bisaryl ethers in our binding assay. Selected benzodiazepinones, such as compound 6, were also potent in the human eosinophil
shape change assay. Analysis of the rigid conformations of these benzodiazepinones and ortho-phenylsulfonamido benzophenones
provided an explanation for the structureÀactivity relationship and revealed the possible bound conformations to CRTH2, which
may be useful for building a pharmacophore model of CRTH2 antagonists.
KEYWORDS: CRTH2, PGD2, antagonist, asthma, benzodiazepinones, pharmacophore
RTH2 (chemoattractant receptor-homologous molecule
expressed on Th2 cells), also known as DP2, is a G-protein-
signal of the sulfonamide NH is shifted downfield by 2À3 ppm
in CDCl3 and by 1À1.5 ppm in DMSO-d6 as compared to the
sulfonamide NH of the bisaryl ethers. It is likely that the
intramolecular hydrogen bond in compounds 2 and 4 locks these
moleculesintoa desired shape for bindingtothe CRTH2 receptor.
Even thoughthe methoxy next to the carbonyl may also contribute
to the improvement of the potency, its contribution should be
small based on the structureÀactivity relationship (SAR).24
Constraining flexible molecules to adopt desired binding
conformations is a very attractive tactic in lead optimization,
because it can improve binding affinity without increasing
molecule size. The observation of the intramolecular hydrogen
bond and improved potency encouraged us to design con-
strained molecules based on the conformation locked by the
intramolecular hydrogen bond. Benzodiazepinone derivatives
were among the molecules designed (Figure 1), and the benzo-
diazepinones were conveniently synthesized from the same
intermediate for the preparation of the ortho-phenylsulfonamido
benzophenones (Schemes 1 and 2).
C
coupled receptor, which has received increasing attention as a
promising new target for the treatment of asthma and other
allergic diseases.1À5 CRTH2 is selectively expressed on Th2 cells,
T cytotoxic type 2 (Tc2) cells, eosinophils, and basophils.6À8 Its
endogenous ligand is prostaglandin D2 (PGD2), which plays a key
role in mediating allergic reactions.9,10 Stimulation of CRTH2 by
PGD2 mediates multiple inflammatory responses, such as chemo-
taxis of eosinophils, basophils, and Th2 cells, eosinophil activation
and degranulation, cytokine production from Th2 cells, and
leukotriene production by mast cells.11À16 Therefore, blockade
of CRTH2 has the potential to be beneficial in the treatment of
allergic diseases triggered by PGD2.
Multiple research groups have disclosed their efforts in identify-
ing CRTH2 antagonists.17À23 We also reported the discovery of
phenylacetic acid derivatives as CRTH2 and DP dual antagonists
and the optimization that led to the identification of AMG 009 and
AMG 853.24,25
During the optimization of our phenylacetic acid derivatives,
such as compounds 1 and 3, the bisaryl ether linker was studied
(Table 1). One of the linker replacements explored was carbonyl.
The resulting ortho-phenylsulfonamido benzophenones (2 and 4)
were significantly more potent than the corresponding bisaryl
ethers (1 and 3), as assessed by 3H-PGD2 displacement from the
CRTH2 receptors expressed on HEK 293 cells.26 The 1H NMR
spectra of the ortho-phenylsulfonamido benzophenones indicate
the existence of an intramolecular hydrogen bond between the
sulfonamide NH and the carbonyl oxygen, because the proton
Compounds 1 and 3 were prepared following our previously
reported route.24,25 The syntheses of compounds 2 and 4 are
shown in Scheme 1. FrieldelÀCrafts reaction of 2-nitrobenzoic
acid chloride with 4-methoxyphenylacetic acid methyl ester
yielded the 2-nitrobenzophenone, which was reduced to the
Received: February 11, 2011
Accepted: April 17, 2011
Published: April 17, 2011
r
2011 American Chemical Society
515
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ACS Medicinal Chemistry Letters
LETTER
Table 1
Scheme 2a
a (a) Glycine methyl ester, pyridine, 130 °C, overnight, 50%. (b) Sub-
stituted benzyl bromide, tBuOK, DMF, room temperature, overnight,
70%. (c) LiOH, water/MeOH/THF, room temperature, overnight, 90%.
Table 2
a Displacement of 3H-PGD2 from the CRTH2 receptors expressed on
HEK 293 cells. Assay run in buffer containing 0.5% bovine serum
albumin. See ref 26 for assay protocol. Values are the means of three
experiments, and the standard deviation is (30%.
a
CRTH2 IC50
compd
R
in buffer (μM)
in plasma (μM)
5
6
H
0.005
0.003
0.006
0.007
0.008
0.029
0.015
0.030
0.070
0.060
0.009
0.015
0.022
0.078
0.24
4-F
7
3,4-F
4-Cl
8
9
3-Cl
Figure 1. Compound design based on intramolecular hydrogen bond.
10
11
12
13
2,4-Cl
4-Me
4-CF3
4-OCF3
0.104
ND
Scheme 1a
ND
a Displacement of 3H-PGD2 from the CRTH2 receptors expressed on
HEK 293 cells. Assay run in buffer containing 0.5% bovine serum
albumin or in 50% plasma. See ref 26 for assay protocol. Values are the
means of three experiments, and the standard deviation is (30%.
various substituted benzyl bromides. Finally, the hydrolysis of the
methyl esters provided compounds 5À13.
The rigid benzodiazepinone derivatives were found to be
much more potent than the flexible compounds (Table 2).
The benzodiazepinone with an unsubstituted benzyl group (5)
had a CRTH2 binding IC50 of 5 nM in buffer and 60 nM in the
presence of 50% plasma. Fluorine and chlorine at the para
position of the benzyl group (6 and 8) further improved the
potency, especially in the presence of plasma. Compound 6 had
an IC50 of 9 nM in 50% plasma. More bulky substituents at the
para position of the benzyl group, such as trifluoromethyl (12)
and trifluoromethoxy (13), decreased the binding affinity. Ortho
substitution was found to be detrimental to the potency, as
indicated by compound 10. All of these benzodiazepinone
derivatives (5À13) are selective for the CRTH2 receptor over
the prostanoid D receptor (DP or DP1), the other GPCR for
PGD2 (DP binding IC50 >10 μM).
a (a) AlCl3, 4-methoxyphenylacetic acid methyl ester, ClCH2CH2Cl, ice
bath to room temperature, 2 h, 80%. (b) Iron, acetic acid, and water, 65
°C, 1 day, 90%. (c) Substituted benzenesulfonyl chlorides, 2,6-lutidine,
THF, 60 °C, 12 h. (d) NaOH, water/THF, room temperature, 2 h, 60%
two steps.
2-aminobenzophenone using iron. Sulfonamide formation fol-
lowed by ester hydrolysis afforded compounds 2 and 4.
The benzodiazepinone derivatives (5À13) were prepared
from the same 2-aminobenzophenone intermediate in Scheme 1.
Reaction of the 2-aminobenzophenone with glycine in pyridine
gave the benzodiazepinone (Scheme 2), which was alkylated with
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LETTER
Figure 2. Compound 14.
Figure 4. Overlap of quinazolinone 14 (blue) and benzophenone 2
(orange).
in plasma was 5 μM at 1 h, 0.8 μM at 2 h, and 0.4 μM at 8 h. This
compound could also achieve similar or greater exposures when
dosed either subcutaneously or intraperitoneally.
In summary, we designed and synthesized benzodiazepinone
derivatives as potent CRTH2 antagonists based on the observa-
tion of an intramolecular hydrogen bond in the ortho-phenylsul-
fonamido benzophenone derivatives. The benzodiazepinones
are 2 orders of magnitude more potent than the corresponding
bisaryl ethers. The SAR can be explained through analysis of the
low energy conformations. The identification of the possible
bound conformation could be useful for building a pharmaco-
phore model of CRTH2 antagonists.
Figure 3. Overlap of benzodiazepinone 6 (green) and benzophenone 2
(orange). An alternate possible symmetric overlay is shown as an insert.
’ ASSOCIATED CONTENT
S
Supporting Information. Detailed synthetic experimen-
b
While constraining the molecule conformation in the form of
benzodiazepinone resulted in dramatic improvement of the
potency, in the form of quinazolinone, it decreased the binding
potency (Figure 2). Quinazolinone 14 had a CRTH2 binding
IC50 of 11 μM in buffer. This interesting SAR prompted us to
analyze the rigid conformations to seek an explanation.
The strong binding of benzodiazepinone 6 to the CRTH2
receptor indicates that one of its low energy conformations may
be close to the bound conformation to the CRTH2 receptor.
This bound conformation should also overlap with one of the low
energy conformations of ortho-phenylsulfonamido benzophe-
none 2 if they share a binding pocket. It was gratifying to see
the calculated lowest energy conformation of benzodiazepinone
6 matches very well with that of benzophenone 2 (Figure 3).27
Therefore, these lowest energy conformations may be the bound
conformations. Other low energy conformations of the two com-
pounds do not overlap well, with the exception of the symmetric
overlay (the mirror image, shown as an insert in Figure 3).
On the other hand, none of the low energy conformations of
quinazolinone 14 matches those of benzophenone 2, which may
explain why the binding potency of 14 is low. Figure 4 shows the
overlap of the lowest energy conformations of compound 14 and 2.
As expected, there are many low energy conformations for the
flexible bisaryl ethers (1 and 3), and the closest overlay with the
lowest energy conformations of 2 and 6 only occurs at a higher
energy conformation (calculated to be about 3.5 kcal/mol from
the minimal energy conformation). Therefore, the low binding
affinity of the bisaryl ethers is likely due largely to the higher
conformational energy of the CRTH2-bound conformation.
Compound 6 was also evaluated for its CRTH2 functional
activity. It inhibited PGD2-mediated human eosinophil shape
change with a Kb of 2 nM.28 In addition, this compound has
favorable pharmacokinetics properties in mouse. When dosed
orally at 15 mg/kg, the measured concentration of compound 6
tal procedures and characterization for all compounds. This
material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: 650-244-2438. E-mail: jiwenl@amgen.com.
’ ACKNOWLEDGMENT
We thank Tod Martin and Dr. Alison Budelsky for the human
eosinophil shape change assay data and useful suggestions.
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