Structure-activity relationship of thiopyrimidines as mGluR5 antagonists

Article abstract of DOI:10.1016/j.bmcl.2006.01.100

Structure-activity relationship investigations of the thiopyrimidine (1), an HTS hit with micromolar activity as a metabotropic glutamate receptor 5 (mGluR5) antagonist, led to compounds with sub-micromolar activity.

Full text of DOI:10.1016/j.bmcl.2006.01.100

Bioorganic & Medicinal Chemistry Letters 16 (2006) 2467–2469
Structure–activity relationship of thiopyrimidines as
mGluR5 antagonists
Lance G. Hammerland,a Martin Johansson,b Jonas Malmstro¨m,b Jan P. Mattsson,c
Alexander B. E. Minidis,b,* Karolina Nilsson,c Alecia Peterson,a David Wensbo,b
c,
c
*
¨
˚
Andreas Wallberg and Krister Osterlund
aNPS-Pharmaceuticals, 383 Colorow Drive, Salt Lake City, UT 84108, USA
bMedicinal Chemistry, Local Discovery CNS & Pain Control, Astra Zeneca R&D So¨derta¨lje, SE-151 85 So¨derta¨lje, Sweden
cMedicinal Chemistry, AstraZeneca R&D Mo¨lndal, SE-43183 Mo¨lndal, Sweden
Received 16 December 2005; revised 23 January 2006; accepted 23 January 2006
Available online 14 February 2006
Abstract—Structure–activity relationship investigations of the thiopyrimidine (1), an HTS hit with micromolar activity as a metab-
otropic glutamate receptor 5 (mGluR5) antagonist, led to compounds with sub-micromolar activity.
Ó 2006 Elsevier Ltd. All rights reserved.
The metabotropic glutamate receptors (mGluRs) are
G-protein-coupled receptors which have important roles
N
S
N
in modulating neuronal signaling in the central nervous
system.1 The mGluRs belong to family C of G-protein-
coupled receptors, of which there are eight subtypes
identified, divided into three major groups: Group I
includes mGluR1 and mGluR5, Group II mGluR2
and mGluR3, and Group III mGluR4, as well as
mGluR6–8.2
N
Cl
Figure 1. Thiopyrimidine (1), a weak mGluR5 antagonist HTS hit.
campaign targeting mGluR5, and a followup program
was initiated to investigate SAR around this novel
mGluR5 antagonist structure.
There are preclinical data supporting the use of metab-
otropic glutamate receptor 5 (mGluR5) antagonists in
the treatment of several CNS diseases and disorders3
like inflammatory and neuropathic pain,4 anxiety and
depression5 or drug addiction and drug withdrawal.6
Recent evidence also indicates mGluR5 as a potential
target for the treatment of gastroesophageal reflux dis-
ease, showing that mGluR5 antagonists inhibit transient
lower esophageal sphincter relaxations, the main mech-
anism behind gastroesophageal reflux.7
For this purpose, easy access to a variety of linker and
thioaryl groups was obtained by synthesizing scaffold 5
in two steps (Scheme 1) according to a literature
procedure.8
Elaboration of the thioaryl moiety (6–13) was achieved
by treating 5 with an array of commercially available
thiols in DMF, running the reaction overnight, followed
by removal of volatiles and chromatographic purifica-
tion. Amine as well as ether pyrimidine compounds
was obtained similarly to the thioethers by treatment
Our interest in thiopyrimidines as mGluR5 antagonists
started with the discovery of 1 (Fig. 1) as a weak antag-
onist (IC50 1250 nM) in a high-throughput screening
of 5 with the appropriate amine and alcohol,
respectively.
For synthesis of the bipyridyl core as illustrated by 23, a
regioselective Negishi cross-coupling, followed by reac-
tion with a thiol nucleophile, was employed (Scheme 2).
Compound 24 was synthesized in a similar fashion.9
Keywords: Thiopyrimidine; Metabotropic glutamate receptor;
mGluR5.
*
Corresponding authors. Tel.: +46 31 7762788 (A.W.); e-mail: andreas.
wallberg@astrazeneca.com
0960-894X/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.01.100

2468
L. G. Hammerland et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2467–2469
H
NaO
O
a
NH2
NH
N
O
+
N
N
O
N
HCl
2
3
4
b
N
d
Cl
e
N
N
5
N
O
c
N
Ar2
N
N
S
N
Ar2
H
N
N
N
Ar2
N
N
Scheme 1. Versatile intermediate 5. Reagents and conditions: See Ref. 8c for compounds 2 and 3. (a) NaOEt, EtOH, reflux, 18 h; filter and wash:
54%. (b) POCl3, DCE, reflux; 93%. (c) Appropriate thiol, DMF, rt, o/n 2–90%. (d) Appropriate aniline, NEt3, THF, reflux, 8–48%. (e) Appropriate
phenol, t-BuOK, DME, 23–48%.
Cl
HS
Cl
a
Cl
Cl
N
S
N
Br
N
N
b
N
Br
23
Scheme 2. Synthesis of 23. Reagents: (a) 1—n-BuLi; 2—ZnCl2; 3—Pd(PPh3)4, 2,6-dibromopyridine, 34%. (b) NaH, DMF, 16%.
Table 1. In vitro potencies of thiopyrimidine mGluR5 antagonists
varying Ar2
N
R
N
R
NH2
NH
CN
HCl
N
X
Ar2
N
Scheme 3. Reagents and conditions: MeOH, cat. NaOEt, microwave
150 °C, 10 min; add NH4Cl to mixture, microwave 80 °C, 12 min, 78%.
N
a
FLIPR IC50 nM
Compound
X
Ar2
n
SEM
53
Variation of the lefthand pyridyl could be achieved by
synthesis of appropriate amidine derivatives (Scheme 3),
followed by the sequences shown in Scheme 1. We found
it advantageous to conduct the amidine synthesis in a
microwave reactor, thus decreasing reaction times from
1 to 2 days to less than half an hour.
6
S
4-Cl-Ph
3-Cl-Ph
320
620
3
1
3
3
3
3
3
3
1
1
1
3
1
3
7
S
8
S
3-Br-Ph
3-CF3-Ph
3-Me-Ph
4-CF3-Ph
2860
550
145
66
706
8
9
S
10
11
12
13
14
15
16
17
18
S
2300
210
S
S
3,4-Di-F-Ph 1520
3,4-Di-Cl-Ph 90
742
7
Removal of the methyl group from the hit 1 gave com-
pound 6 (Table 1), which was already fourfold more po-
tent (IC50 320 nM) compared to 1. On this basis, we
further investigated the SAR of the substitution pattern
on the phenyl group (Ar2), while keeping the remaining
parts of the molecule constant (Entries 7–13). Substitu-
ents in the meta position that gave compounds with a
potency better than 1 lM were chloro (7) (IC50
620 nM) and trifluoro methyl (9) (IC50 550 nM). Like-
wise, substituents in the para position such as trifluoro
methyl (11) (IC50 210 nM) lead to compounds in the same
potency range as 6. Disubstitution on the 3 and 4 posi-
tions gave compounds 12 (difluoro, IC50 1520 nM) and
1310 (dichloro, IC50 90 nM). Next, we turned our efforts
to replacement of the sulfur atom, since we anticipated
metabolic oxidation at this position. Unfortunately, oxy-
gen, nitrogen, N-acetyl, methylene, and hydroxymethyl-
S
O
NH
NAc
4-Cl-Ph
4-Cl-Ph
4-Cl-Ph
>10,000
>10,000
>10,000
>3000
>10,000
22
CHOH 4-Cl-Ph
CH2 4-Cl-Ph
0
2
MPEPb, for comparison
a Effect on glutamate-induced [Ca2+]i in a cell line expressing human
mGluR5d (splice variant of mGluR5 with a truncated C-terminal
domain) using a fluorescence imaging plate reader (FLIPR).
b 2-Methyl-6-(phenylethynyl)pyridine, see Ref. 12.
ene analogues (14–18) were all inactive. Altering the
position of the nitrogen in the pyridine ring (19–20)
(Table 2) was not tolerated, whereas introduction of
small substituents on the pyridine gave 21 (6-methyl-2-

L. G. Hammerland et al. / Bioorg. Med. Chem. Lett. 16 (2006) 2467–2469
2469
Table 2. In vitro potencies of thiopyrimidine mGluR5 antagonists
varying Ar1 and linker, using preferred Ar2
is crucial for activity. Further optimisation is neces-
sary to increase potency, for example, by variation
of the substituents on the 2-pyridine ring (Ar1) and
replacement of the sulfur linker atom, since the latter
is most likely the main cause of low metabolic stabil-
ity. The SAR we have developed for thiopyrimidines
could be of interest for other projects concerning
mGluR5 antagonists and possibly applicable to other
lead series.
Ar1
N
S
Ar2
N
Compound Ar1
Ar2
FLIPR
a
IC50 nM
n
SEM
19
20
21
22
3-Pyridyl
4-Pyridyl
4-Cl-Ph
4-Cl-Ph
>10,000
>10,000
1
1
3
3
6-Me-2-Pyridyl 3,4-Di-Cl-Ph 390
5-F-2-Pyridyl 3,4-Di-Cl-Ph 80
63
14
References and notes
a Effect on glutamate-induced [Ca2+]i in a cell line expressing human
mGluR5d (splice variant of mGluR5 with a truncated C-terminal
domain) using a fluorescence imaging plate reader (FLIPR).
1. Conn, P. J.; Pin, J.-P. Annu. Rev. Pharmacol. Toxicol.
1997, 37, 205.
2. Pin, J.-P.; Duvoisin, R. Neuropharmacology 1995, 34, 1.
3. (a) Mutel, V. Expert Opin. Ther. Patents 2002, 12, 1845;
(b) Sabbatini, F. M.; Micheli, F. Expert Opin. Ther.
Patents 2004, 14, 1593; (c) Spooren, W.; Gasparini, F.
Drug News Perspect. 2004, 17, 251.
4. (a) Varney, M. A.; Gereau, R. W. CNS Neurol. Disord.
2002, 1, 283; (b) Zhu, C. Z.; Wilson, S. G.; Mikusa, J. P.;
Wismer, C. T.; Gauvin, D. M.; Lynch, J. M.; Wade, C. L.;
Decker, M. W.; Honore, P. Eur. J. Pharmacol. 2004, 506,
107.
Cl
Cl
N
S
Cl
Cl
S
N
N
N
23
24
5. (a) Brodkin, J.; Busse, C.; Sukoff, S. J.; Varney, M. A.
Pharmacol. Biochem. Behav. 2002, 73, 359; (b) Spooren,
W. P. J. M.; Vassout, A.; Neijt, H. C.; Kuhn, R.;
Gasparini, F.; Roux, S.; Porsolt, R. D.; Gentsch, C.
J. Pharmacol. Exp. Ther. 2000, 295, 1267; (c) Tata-
rczynska, E.; Klodzinska, A.; Chojnacka-Wojcik, E.;
Palucha, A.; Gasparini, F.; Kuhn, R.; Pilc, A. Br. J.
Pharmacol. 2001, 132, 1423; (d) Busse, C. S.; Brodkin, J.;
Tattersall, D.; Anderson, J. J.; Warren, N.; Tehrani, L.;
Bristow, L. J.; Varney, M. A.; Cosford, N. D. P.
Neuropsychopharmacology 2004, 29, 1971.
Cl
Cl
Cl
Cl
N
S
N
N
N
N
N
25
26
Figure 2. Variation of core and linker. Only 24 showed modest
mGluR5 antagonist activity (FLIPR IC50 2370 nM, n = 3, SEM 628).
pyridyl) (IC50 390 nM) and 2211 (5-fluoro-2-pyridyl)
(IC50 80 nM). Replacement of the central pyrimidine
moiety with the two isomers of pyridine (Fig. 2) gave
one inactive compound (23) and one with micromolar
activity (24, IC50 2370 nM), while the reversed pyrimi-
dine 25 was inactive. Absence of a linker atom gave an
inactive compound (26). In conclusion, all three nitrogen
atoms in the pyridine and pyrimidine rings and the sulfur
linker appear to be crucial for effecting potency, which
can be reinforced by introducing lipophilic substituents
on the 3 and 4 positions of the phenyl group.
6. Chiamulera, C.; Epping-Jordon, M. P.; Zocchi, A.;
Marcon, C.; Cottiny, C.; Tacconi, S.; Corsi, M.; Orzi,
F.; Conquet, F. Nat. Neurosci. 2001, 4, 873.
7. Jensen, J.; Lehmann, A.; Uvebrant, A.; Carlsson, A.;
Jerndal, G.; Nilsson, K.; Frisby, C.; Blackshaw, L.-A.;
Mattsson, J. P. Eur. J. Pharmacol. 2005, 519, 154.
8. (a) Medwid, J. B.; Paul, R.; Baker, J. S.; Brockman, J. A.;
Du, M. T.; Hallet, W. A.; Hanifin, J. W.; Hardy, R. A.;
Tarrant, M. E.; Torley, L. W.; Wrenn, S. J. Med. Chem.
1990, 33, 1230; (b) Moffatt, J. S. J. Chem. Soc. 1950, 9,
1603(c) 2 is commercially available, 3 was made according
to Gabriel, S. Ber. Dtsch. Chem. Ges. 1904, 37, 3638.
9. Intermediate for regioisomer 24 was synthesized according
to Araki, K.; Mutai, T.; Shigemitsu, Y.; Yamada, M.;
Nakajima, T.; Kuroda, S.; Shimao, I. J. Chem. Soc. Perkin
Trans. 2 1996, 613.
Compounds 21 and 22 were tested for selectivity, both
as positive modulators and as antagonists, on the other
mGluRs (1–4 and 6–8) exhibiting complete selectivity in
all assays (>25 lM).
10. Analytical data for 13: 1H NMR (400 MHz, DMSO-d6): d
7.1 (d, J=5.4 Hz, 1 H) 7.5 (m, 1 H) 7.7 (dd, J=8.4, 2.1 Hz,
1 H) 7.8 (d, J=8.4 Hz, 1 H) 7.9 (dt, J=7.7, 1.8 Hz, 1 H) 8.1
(d, J=2.1 Hz, 1 H) 8.2 (d, J=7.8 Hz, 1 H) 8.7 (d, J=5.4 Hz,
1 H) 8.7 (m, 1H). HRMS calcd for C15H10N3Cl2S (M+H)
333.9972. Found 333.9981.
Compounds 13 and 22 both have rather high in vitro
clearance (13 90 and 120 lL/min/mg in human and
rat liver microsomes, respectively, and 22 140 and
90 lL/min/mg in human and rat liver microsomes,
respectively). Attempts to synthesize the presumed
metabolites, the corresponding sulfoxides and sulfones,
failed because of chemical instability of these species.
11. Analytical data for 22: 1H NMR (400 MHz, CDCl3): d
6.89 (d, J = 5.30 Hz, 1 H), 7.48–7.52 (m, 1 H), 7.54 (m, 1
H), 7.60 (d, J = 8.34 Hz, 1 H), 7.81 (d, J = 2.02 Hz, 1 H),
8.35 (m, 1 H), 8.60 (d, J = 5.30 Hz, 1 H), 8.66 (d,
J = 2.78 Hz, 1 H). HRMS calcd for C15H9N3Cl2SF
(M+H) 351.9878. Found 351.9868.
In summary, we have identified a novel structural
class of mGluR5 antagonists, the thiopyrimidines,
with mGluR5 potency better than 100 nM. We have
shown that a 4-thiopyrimidine as a core-linker system
12. Pagano, A.; Ruegg, D.; Litschig, S.; Stoehr, N.; Stierlin,
`
C.; Heinrich, M.; Floersheim, P.; Prezeau, L.; Carroll, F.;
Pin, J.-P.; Cambria, A.; Vranesic, I.; Flor, P. J.; Gasparini,
F.; Kuhn, R. J. Biol. Chem. 2000, 275, 33750.