3-Aryl-5-phenoxymethyl-1,3-oxazolidin-2-ones as positive allosteric modulators of mGluR2 for the treatment of schizophrenia: Hit-to-lead efforts

Article abstract of DOI:10.1016/j.bmcl.2010.03.089

Hit to lead optimization of (5R)-5-hexyl-3-phenyl-1,3-oxazolidin-2-one as a positive allosteric modulator of mGluR2 is described. Improvements in potency and metabolic stability were achieved through SAR on both ends of the oxazolidinone. An optimized lea

Full text of DOI:10.1016/j.bmcl.2010.03.089

Bioorganic & Medicinal Chemistry Letters 20 (2010) 3129–3133
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
3-Aryl-5-phenoxymethyl-1,3-oxazolidin-2-ones as positive allosteric
modulators of mGluR2 for the treatment of schizophrenia: Hit-to-lead efforts
a
a
a
b
Edward J. Brnardic a, , Mark E. Fraley , Robert M. Garbaccio , Mark E. Layton , John M. Sanders ,
Chris Culberson b, Marlene A. Jacobson c, Brian C. Magliaro c, Pete H. Hutson c, Julie A. O’Brien d,
Sarah L. Huszar e, Jason M. Uslaner e, Kerry L. Fillgrove f, Cuyue Tang f, Yuhsin Kuo f, Sylvie M. Sur g,
George D. Hartman a
*
a Department of Medicinal Chemistry, Merck Research Laboratories, West Point, PA 19486, USA
b Department of WP Chemistry Modeling and Informatics, Merck Research Laboratories, West Point, PA 19486, USA
c Department of Psychiatry Research, Merck Research Laboratories, West Point, PA 19486, USA
d Department of In Vitro Sciences, Merck Research Laboratories, West Point, PA 19486, USA
e Department of Central Pharmacology, Merck Research Laboratories, West Point, PA 19486, USA
f Department of Drug Metabolism, Merck Research Laboratories, West Point, PA 19486, USA
g Department of Automated Biotechnology, Merck Research Laboratories, West Point, PA 19486, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Hit to lead optimization of (5R)-5-hexyl-3-phenyl-1,3-oxazolidin-2-one as a positive allosteric modulator
of mGluR2 is described. Improvements in potency and metabolic stability were achieved through SAR on
both ends of the oxazolidinone. An optimized lead compound was found to be brain penetrant and active
in a rat ketamine-induced hyperlocomotion model for antipsychotic activity.
Received 9 February 2010
Revised 22 March 2010
Accepted 26 March 2010
Available online 31 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
mGluR2
Metabotropic glutamate receptors
Positive allosteric modulator
Schizophrenia
Oxazolidinone
Hit to lead
Schizophrenia is a chronic, debilitating disorder affecting 1% of
the world population.1–3 Current treatments are the atypical anti-
psychotics which target dopamine D2 and serotonin 5-HT2A
receptors. These therapeutics are effective in treating the positive
symptoms (hallucinations, delusions) associated with schizophre-
nia, but demonstrate poor efficacy for the negative symptoms
(emotional blunting, social withdrawal) and do not improve cogni-
tive deficit seen in schizophrenic patients.4 In addition, some atyp-
ical antipsychotics cause significant weight gain, sedation and
extrapyramidal symptoms (EPS).5 An alternative strategy focuses
on glutamate, the primary excitatory neurotransmitter in the
mammalian CNS. Specifically, it is hypothesized that elevated glu-
tamate transmission in the forebrain is associated with schizophre-
nia symptomatology and a treatment that could reduce these
levels might be therapeutically beneficial for treating the dis-
ease.6,7 Glutamate levels in the brain are regulated by metabotro-
pic glutamate receptors (mGluRs), and importantly, activation of
mGluR2 has been shown to suppress glutamate release into the
synapse.8,9 In support of this hypothesis, LY2140023 (1, Fig. 1), a
S
O
O
O
H
O
N
H2N
OH
HN
OH
O
H
H3C
S
O
O
1
2
LY2140023
mGluR2 (h) FLIPR EC50 = 450 nM
MW = 247.34 g/mol
Dog CL = 36.5 ml/min/kg
Dog t1/2 = 1.3 h
Dog Vdss = 2.365 L/kg
Human Pgp BA/AB = 1.2; Papp = 40 x 10-6 cm/sec
Rat Pgp BA/AB = 0.9; Papp = 24 x 10-6 cm/sec
* Corresponding author.
E-mail address: edward_brnardic@merck.com (E.J. Brnardic).
Figure 1. mGluR2/3 dual agonist LY2140023 1 and mGluR2 selective PAM lead 2.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.03.089

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E. J. Brnardic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3129–3133
R
O
O
O
ArBr, CuI, Cs2CO3
O
H3C
O
NH2
N
O
NH 1,2-diaminocyclohexane
O
dioxane, 125 o
5-70%
C
Et3N, 145 o
32%
C
H3C
H3C
H3C
3
4
5-13
Figure 2. Synthesis of 3-aryl-5-alkyl-1,3-oxazolidin-2-ones.
(5–13 b). Generally small electron withdrawing groups were pre-
ferred although only the 3-cyano (8 b) was found to give a signif-
icant improvement in potency over the unsubstituted phenyl
group (2). The 3-cyano substitution could be expected to offer im-
proved pharmacokinetic properties as well, by adding polarity and
reducing metabolism of the aryl ring.
With this initial optimization of the aryl ring, we turned our
attention to optimizing the hexyl chain. We were able to quickly
vary the side chain of our 1,3-oxazolidin-2-ones by reacting com-
mercially available epoxides with N-Boc aniline 14 (Fig. 3).
Analysis of SAR (Table 2) indicated that the n-hexyl chain (15)
was found to be optimal in length as the longer n-octyl chain
(16) and the shorter n-pentyl (17) and n-butyl (18) chains resulted
in a potency loss. Although the benzyl substitution (19) was not
well tolerated, the phenyl ether (20) maintained some potency
Table 1
Functional activity of N-aryl modifications (5–13)
R
O
4
O
N
3
2
Compd
R
mGluR2 (h) FLIPR EC50 (nM)
2 (a)
3 (b)
4 (c)
5
6
Me
F
>30,000
7150
640
640
3820
790
7
8
9
10
11
12
13
Cl
CN
>30,000
1760
590
250
640
1930
3300
1350
2700
4450
760
O
O
CH3
O
O
H3C
H3C
R
OCH3
OH
NH2
CO2Me
SO2Me
>30,00
>30,00
>30,00
>30,00
>30,00
1170
7810
5870
1220
>30,000
O
N
N
H
Et3N, 145 o
30-75%
C
R
14
15-21
EC50 for potentiation of an EC20 glutamate concentration.19
Figure 3. Synthesis of 3-aryl-5-alkyl-1,3-oxazolidin-2-ones from epoxides.
novel mGluR2/3 agonist prodrug, demonstrated efficacy against
both positive and negative symptoms in a four-week phase IIb
schizophrenia trial.10
Table 2
Functional activity of 3-aryl-5-alkyl-1,3-oxazolidin-2-ones from epoxides (15–21)
Toward this end we11 and others12–14 have focused on the
development of mGluR2 allosteric potentiators which offer selec-
tivity for mGluR2 as well as the reduced potential for tolerance
that can occur with orthosteric agonists following chronic dos-
ing.15 Herein we present the optimization of (5R)-5-hexyl-3-phe-
nyl-1,3-oxazolidin-2-one (2) derived from a high throughput
screening campaign.
O
O
N
R
Compound 2 was an attractive hit with CNS drug like proper-
ties:0 low molecular weight (247 g/mol), low polar surface area
(34 ÅA2), reasonable potency and not a substrate for Pgp efflux.
However, consistent with its high lipophilicity (cLog D >5), com-
pound 2 showed a modest pharmacokinetic profile in dog (plasma
CL = 36.5 ml/min/kg, t1/2 = 1.3 h). Interestingly, the stereochemical
configuration of C-5 proved critical for potency: the (S)-enantiomer
was much less active. Our strategy for potency optimization was
initially focused on substituting the N-phenyl ring followed by
modification of the hexyl side chain. The synthesis of these deriv-
atives involved the reaction of n-hexyl epoxide (3) with ethyl car-
bamate resulting in 5-hexyl-1,3-oxazaolidin-2-one16,17 (4) which
underwent copper-catalyzed Ullmann couplings18 to afford the
various substituted 3-aryl-5-alkyl-1,3-oxazaolidin-2-ones (5–13)
(Fig. 2).
Compd
15
R
mGluR2 (h) FLIPR EC50 (nM)
H3C
H3C
590
16
1200
17
18
790
H3C
H3C
1300
19
20
25,130
3500
O
Analysis of the SAR (Table 1) indicated that substitution at the
2-position (5–13 a) was not tolerated suggesting that co-planarity
of the aryl ring was preferred for potency. While substitution at the
4-position (5–13 c) did not lead to significant potency enhance-
ment, we found that substitution was optimal in the 3-position
O
21
360
Cl
EC50 for potentiation of an EC20 glutamate concentration.19

E. J. Brnardic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3129–3133
3131
O
O
O
O
O
O
N
N
O
N
O
CH3
O
O
H2, Pd(OH)2/C
H3C
H3C
N
N
O
O
O
N
H
Et3N, 145 oC
74%
MeOH, 55 o
95%
C
14
H3C
H3C
22
H3C
H3C
34
35
CH3
CH3
OH
mGluR2 (h) FLIPR EC50 = 82 nM
mGluR2 (h) FLIPR EC50 = >30,000 nM
Figure 5. Optimized oxazolidione 34 and enantiomer 35.
O
R
O
O
N
PS-PPh3, DIAD
O
N
O
DCM, 23 oC
5-80%
Analysis of the SAR (Table 3) indicated that substitution at the
2-position (24–33 a) was not tolerated but potency could be opti-
mized at both the 3- and 4-positions. In general, substitution at the
4-position (24–33 c) was preferred to that of the 3-position (24–33
b). Polar groups (28, 31, 32 and 33 a–c) were also not tolerated at
any position while bulky alkyl substituents, particularly in the 4-
position maximized potency. The optimal substitution was found
to be the tert-butyl in the 4-position (27 c).
HO
24-33
23
R
Figure 4. Synthesis of 5-phenoxymethyl-1,3-oxazolidin-2-ones (24–33).
Table 3
Functional activity of 5-phenoxymethyl-1,3-oxazolidin-2-ones (24–33)
Gratifyingly, the mGluR2 potentiation potency was found to be
additive when the optimal groups on each side of the 1,3-oxazoli-
din-2-one were combined. The enantiomers were resolved to pro-
duce lead compound 34 and its inactive enantiomer 35 (Fig. 5).
Although the reaction schemes in Figures 3 and 4 could be used
to synthesize compound 34 it was not optimal for large scale syn-
theses that were required for in vivo testing. A more straightfor-
ward synthesis involved reacting 4-tert-butyl phenol (36) with
(R)-epichlorohydrin to give the enantiomerically pure epoxide21
(37) (via attack at the terminal epoxide carbon and subsequent ref-
ormation of the epoxide) which in turn was reacted with 3-cya-
noisocyanate in the presence of samarium(III) iodide22 to afford
(34) in 38% overall yield (Fig. 6).
O
O
N
O
R
2
4
3
Compd
R
mGluR2 (h) FLIPR EC50 (nM)
2 (a)
3 (b)
4 (c)
24
25
26
27
28
29
30
31
32
33
Me
>30,000
>30,000
>30,000
N/A
>30,000
3897
3440
360
580
350
4110
840
1180
>30,000
>30,000
>30,000
660
590
360
240
2190
360
780
>30,000
>30,000
>30,000
Compound 34 was demonstrated to achieve appreciable brain
penetration in rat with a CSF/plasmau ratio of 1 (100 mpk, IP,
Et
iPr
tBu
PEG400, 30 min: [Brain] 24
lM, [Plasma] 3.2
lM, [CSF] 200 nM:
OCH3
Cl
CF3
NH2
CONH2
2 h: [Brain] = 10.5 M, [Plasma] = 3.5
l
l
M, [CSF] = 118 nM). Based
on these exposures, we examined the ability of 34 to attenuate
ketamine-induced psychomotor activity, an assay sensitive to
clinically therapeutic antipsychotics (Fig. 7). Compound 34 pro-
duced robust inhibition of the ketamine response during the first
30 min of the experiment, similar in magnitude to the orthoster-
ic mGluR2/3 agonist LY268.23 During the second 30 min of the
experiment, the effect of compound 34 drifted towards partial
efficacy, presumably due to dropping compound levels. The ob-
served efficacy is believed to be driven by mGluR2 potentiation.
Intrinsic agonism was low with 34 relative to these exposures,
and is therefore not expected to have contributed to efficacy.
In addition, compound 34 showed no activity against other
mGluR’s and did not have binding affinity for D2 dopamine or
5-HT2A receptors.
>30,000
N/A
N/A
NHCOCH3
>30,000
EC50 for potentiation of an EC20 glutamate concentration.19
and gratifyingly we found that 4-chloro substitution (21) resulted
in an improvement over the n-hexyl side chain.
With this result in hand we focused our attention to varying the
substitution pattern on the phenyl ether. N-Boc aniline (14) was re-
acted with benzyl glycidyl ether to afford the benzyl protected 1,3-
oxazolidin-2-one alcohol (22). Subsequent removal of the benzyl
group under hydrogenation conditions afforded alcohol (23) which
allowed exploration of SAR around the phenyl ether via Mitsunobu
reactions using resin bound triphenylphosphine to facilitate purifi-
cation (Fig. 4).
In summary, we have described the improvement of HTS hit (2)
to lead compound (34) (Fig. 8). Compound 34 had improved po-
O
O
N
C
N
Cl
O
O
O
N
OH
O
SmI3
THF, 23 oC
38% over two steps
NaOH
N
O
H3C
H3C
H3C
H3C
H2O, 64 o
C
CH3
CH3
H3C
H3C
36
37
34
CH3
Figure 6. Optimized synthesis of 34.

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E. J. Brnardic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3129–3133
Response First 30 min
Response Second 30 min
3000
2000
1000
0
*
*
4000
3000
2000
1000
0
^
*
α
α
α
V
V
30
100
10
V
V
30
100
10
Cmpd 34
Ketamine
for assay description see reference #24
LY268
Cmpd 34
Ketamine
LY268
*
Figure 7. The influence of compound 34 and LY268 on the psychomotor activating effects of ketamine in rat. indicates significantly different from V–V. ^ indicates trend
towards increased locomotor activity versus V–V.
a
indicates significant decrease versus V-Ket.
O
O
O
N
O
N
N
O
H3C
H3C
H3C
2
34
CH3
mGluR2 (h) FLIPR EC50 = 450 nM (%max = 74%)
Agonism EC50 = 13.8 μM (%max = 19%)
MW = 247.34 g/mol
mGluR2 (h) FLIPR EC50 = 82 nM (%max = 74%)
Agonism EC50 = 4.9 μM (%max = 29%)
MW = 350.42 g/mol
Dog CL = 36.5 ml/min/kg
Dog CL = 17.7 ml/min/kg
Dog t1/2 = 1.3 h
Dog t1/2 = 1.1 h
Human Pgp BA/AB = 1.2; Papp = 40 x 10-6 cm/sec
Rat Pgp BA/AB = 0.9; Papp = 24 x 10-6 cm/sec
Human Pgp BA/AB = 2.9; Papp = 14 x 10-6 cm/sec
Rat Pgp BA/AB = 1.9; Papp = 20 x 10-6 cm/sec
Rat plasma protein binding = 97%
Figure 8. Comparison of 2 versus 34.
6. Chavez-Noriega, L. E.; Schaffhauser, H.; Campbell, U. C. Curr. Drug Targets CNS
Neurol. Disord. 2002, 1, 261.
7. Conn, P. J.; Tamminga, C.; Schoepp, D. D.; Lindsley, C. Mol. Interventions 2008, 8,
99.
tency and dog clearance. Importantly, 34 was shown to be brain
penetrant and to demonstrate efficacy similar to an mGluR 2/3
agonist in an in vivo assay predictive of antipsychotic potential.
8. Schoepp, D. D. J. Pharmacol. Exp. Ther. 2001, 299, 12.
9. Moghaddam, B.; Adams, B. W. Science 1998, 281, 1349.
10. Patil, S. T.; Zhang, L.; Martenyi, F.; Lowe, S. L.; Jackson, K. A.; Andreev, B. V.;
Avedisova, A. S.; Bardenstein, L. M.; Gurovich, I. Y.; Morozova, M. A.; Mosolov,
S. N.; Neznanov, N. G.; Reznik, A. M.; Smulevich, A. B.; Tochilov, V. A.; Johnson,
B. G.; Monn, J. A.; Scheopp, D. D. Nat. Med. 2007, 13, 1102.
11. Cube, R. V.; Vernier, J. M.; Hutchinson, J. H.; Gardner, M. F.; James, J. K.; Rowe, B.
A.; Schaffhauser, H.; Daggett, L.; Pinkerton, A. B. Bioorg. Med. Chem. Lett. 2005,
14, 2389. and references cited therein.
12. Sandeep, T. P.; Zhang, L.; Martenyi, F.; Lowe, S. L.; Jackson, K. A.; Andreev, B. V.;
Avedisova, A. S.; Bardenstein, L. M.; Gurovich, I. Y.; Morozova, M. A.; Mosolov,
S. N.; Neznanov, N. G.; Reznik, A. M.; Smulevich, A. B.; Tochilov, V. A.; Johnson,
B. G.; Monn, J. A.; Schoepp, D. D. Nat. Med. 2007, 13, 1102. and references cited
therein.
13. Duplantier, A. J.; Efremov, I.; Candler, J.; Doran, A. C.; Ganong, A. H.; Haas, J. A.;
Hanks, A. N.; Kraus, K. G.; Lazzaro, J. T.; Lu, J.; Maklad, N.; McCarthy, S. A.;
O’Sullivan, T. J.; Rogers, B. N.; Siuciak, J. A.; Spraklin, D. K.; Zhang, L. B. Bioorg.
Med. Chem. Lett. 2009, 19, 2524.
14. Fraley, M. E. Exp. Opin. Ther. Patent 2009, 19, 1259.
15. Pin, J. P.; Parmentier, M. L.; Prezeau, L. Mol. Pharmacol. 2001, 60, 881.
16. Iwakura, Y.; Izawa, S. I. J. Org. Chem. 1964, 29, 379.
Acknowledgments
We thank Ziqiang Wang for chiral separations of intermediates
to give 34 and 35.
Supplementary data
Supplementary data (further experimental details and com-
pounds in this series are available in Ref. 25) associated with this
article can be found, in the online version, at doi:10.1016/
j.bmcl.2010.03.089.
References and notes
1. Regier, D. A.; Narrow, W. E.; Rae, D. S.; Manderscheid, R. W.; Locke, B. Z.;
Goodwin, F. K. Arch. Gen. Psychiatry 1993, 50, 85.
2. Tandon, R.; Keshavan, M. S.; Nasrallah, H. A. Schizophr. Res. 2008, 100, 4.
3. Tandon, R.; Keshavan, M. S.; Nasrallah, H. A. Schizophr. Res. 2008, 102, 1.
4. Murphy, B. P.; Chung, Y. C.; Park, T. W.; McGorry, P. D. Schizophr. Res. 2006, 88,
5.
5. Lieberman, J. A.; Stroup, T. S.; McEvoy, J. P.; Swartz, M. S.; Rosenheck, R. A.;
Perkins, D. O.; Keefe, R. S.; Davis, S. M.; Davis, C. E.; Lebowitz, B. D.; Severe, J.;
Hsiao, J. K. N. Eng. J. Med. 2005, 353, 1209.
17. Fujimoto, Y.; Suzuki, Y.; Tanaka, Y.; Tominaga, T.; Takeda, H.; Sekine, H.;
Morito, N.; Miyaoka, Y. Heterocycles 1977, 6, 1604.
18. Mallesham, B.; Rajesh, B. M.; Reddy, P. R.; Srinivas, D.; Trehan, S. Org. Lett. 2003,
5, 963.
19. CHOdhfr-cells co-expressing human mGluR2 receptors and the promiscuous
G-protein
bottomed, poly-
G
a
16 (see Ref. 20) were plated (40 K cells per well) in clear-
D
-lysine-coated 384-well plates (BD Biosciences, Franklin
Lakes, NJ) in glutamate/glutamine-free medium using a Multidrop384 cell
dispenser (Thermo Electron Corporation, Waltham, MA). The plated cells were

E. J. Brnardic et al. / Bioorg. Med. Chem. Lett. 20 (2010) 3129–3133
3133
grown overnight at 37 °C in the presence of 6% CO2. The next day, the cells
L of assay buffer [Hanks’ balanced salt solution
(Invitrogen) containing 20 mM HEPES (Invitrogen), 2.5 mM probenecid (Sigma
Chemical Co., St. Louis, MO), and 0.1% bovine serum albumin (Sigma)] using an
EMBLA cell washer (Molecular Devices Corp., Sunnyvale, CA). The cells were
20. Schaffhauser, H.; Rowe, B. A.; Morales, S.; Chaves-Noriega, L. E.; Yin, R.; Jachec,
C.; Rao, S. P.; Bain, G.; Pinkerton, A. B.; Vernier, J.; Bristow, L. J.; Varney, M. A.;
Daggett, L. P. Mol. Pharmacol. 2003, 64, 798.
21. Jin, C. Z.; Hagasawa, H.; Shimamura, M.; Uto, Y.; Inayama, S.; Takeuchi, Y.; Kirk,
K. L.; Hori, H. Bioorg. Med. Chem. 2004, 12, 4917.
were washed with 3 ꢀ 100
l
incubated with 2
l
M Fluo-4AM and 0.02% Pluronic acid (Molecular Probes,
22. Wu, H. Y.; Ding, J. C.; Liu, Y. K. J. Indian Chem. Soc. 2003, 80, 36.
23. Schoepp, D. D.; Marek, G. J. Curr. Drug Targets CNS Neurol. Disord. 2002, 1, 215.
24. Adult male Wistar Hannover rats weighing 200–250 g were transported to the
testing room, administered compound 34 (30 or 100 mg/kg; ip), LY379268
(10 mg/kg; ip) or vehicle (PEG 400) and placed in locomotor activity monitors
(43.2 cm ꢀ 43.2 cm Med Associates activity chamber; each apparatus was
housed in a sound attenuating chamber). After habituation to the activity
monitors for 30 min, animals were given an injection of ketamine (37.5 mg/kg;
s.c.) and monitored for an additional 60 min.
Eugene, OR) for 1 h at 37 °C and 6% CO2. The extracellular dye was removed by
washing as described above. Ca2+ flux was measured using FLIPR384
fluorometric imaging plate reader (Molecular Devices Corp., Sunnyvale, CA).
Compounds were serially diluted in 100% DMSO and then diluted in assay
buffer to a 3ꢀ stock at 2% DMSO. This stock was then applied to the cells for a
final DMSO concentration of 0.67%. For potency determination, the cells were
preincubated with various concentrations of compound for 5 min and then
stimulated for 3 min with an EC20 concentration of glutamate to measure
potentiation. The peak of the calcium response was used to construct
concentration–response curves.
25. Brnardic, E.; Fraley, M.; Garbaccio, R.; Layton, M.; PCT Int. Patent Appl. WO
2009/094265.