Structure-activity relationships in a novel series of 7-substituted-aryl quinolines and 5-substituted-aryl benzothiazoles at the metabotropic glutamate receptor subtype 5

Article abstract of DOI:10.1016/j.bmc.2010.03.053

The metabotropic glutamate receptor subtype 5 (mGluR5) has been implicated in numerous neuropsychiatric disorders including addiction. We have discovered that the rigid diaryl alkyne template, derived from the potent and selective noncompetitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP), can serve to guide the design of novel quinoline analogues and pharmacophore optimization has resulted in potent mGluR5 noncompetitive antagonists (EC₅₀ range 60-100 nM) in the quinoline series.

Full text of DOI:10.1016/j.bmc.2010.03.053

Bioorganic & Medicinal Chemistry 18 (2010) 3026–3035
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Structure–activity relationships in a novel series of 7-substituted-aryl
quinolines and 5-substituted-aryl benzothiazoles at the metabotropic
glutamate receptor subtype 5
Peng Zhang a, Mu-Fa Zou a, Alice L. Rodriguez b, P. Jeffrey Conn b, Amy Hauck Newman a,
*
a Medicinal Chemistry Section, National Institute on Drug Abuse-Intramural Research Program, National Institutes of Health, 333 Cassell Drive, Baltimore, MD 21224, United States
b Department of Pharmacology, Vanderbilt Program in Drug Discovery, Vanderbilt University Medical Center, I215D Light Hall, 2215B Garland Avenue,
Nashville, TN 37232-0575, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The metabotropic glutamate receptor subtype 5 (mGluR5) has been implicated in numerous neuropsy-
chiatric disorders including addiction. We have discovered that the rigid diaryl alkyne template, derived
from the potent and selective noncompetitive mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine
(MPEP), can serve to guide the design of novel quinoline analogues and pharmacophore optimization
has resulted in potent mGluR5 noncompetitive antagonists (EC50 range 60–100 nM) in the quinoline
series.
Received 4 February 2010
Revised 18 March 2010
Accepted 23 March 2010
Available online 27 March 2010
Keywords:
Published by Elsevier Ltd.
Metabotropic glutamate receptor subtype 5
mGluR5
MPEP
MTEP
Drug abuse
1. Introduction
through Gq, and modulates the phosphatidylinositol signaling
pathway. Activation of the mGluR5 increases cytosolic calcium
Glutamate is the most abundant excitatory neurotransmitter in
the brain. It regulates the body homeostasis through ionotropic
(iGluRs) and metabotropic glutamate receptors (mGluRs). There
are at least eight subtypes of the mGluRs, which have been identi-
fied and partitioned into three groups based on their localization,
function, signaling pathway, and structural homology. mGluR5 be-
longs to group I, along with mGluR1. Accumulating evidence sug-
gests that mGluR5 antagonists have therapeutic potential in the
treatment of anxiety, depression, pain, gastro-esophageal acid re-
flux disease (GERD), Parkinson’s disease, epilepsy, and Fragile X
Syndrome (FXS).1 To date, several mGluR5 antagonists are being
tested in clinical trials for GERD, pain, and FXS.2 In addition,
mGluR5s have been implicated in drug abuse.3–6
concentrations, which initiates other signaling pathways.7
As a member of the G-protein coupled receptor (GPCR) family C,
mGluR5 has a seven-transmembrane alpha-helical domain (7TM)
and a large ‘bilobed’ N-terminal domain, which contains the orthos-
teric binding site.8 Competitive antagonists binding to the orthos-
teric site have at least two disadvantages including low brain
penetration and low selectivity across the different subtypes.1,9
MPEP (2-methyl-6-(phenylethynyl)pyridine) and MTEP (3-((2-
methyl-1,3-thiazol-4-yl)ethynyl)pyridine) are the two prototypic
noncompetitive mGluR5 antagonists, which bind to the allosteric
binding site located in the 7TM region.10 They are potent and selec-
tive over other mGluR subtypes.1 However, off-target actions (e.g.,
MPEP also acts as an inhibitor of the NMDA receptor and as a po-
sitive modulator of mGluR4, while MTEP is an inhibitor of cyto-
chrome P450)2 and potential for rapid metabolic degradation
(e.g., MTEP)2 have led to significant synthetic efforts to modify
and improve the pharmacological and drug-like profile of these
parent drugs.2,7,11–15 One approach has been to replace the ethyn-
ylpyridine moiety of MPEP (or ethynylthiazole moiety of MTEP)
with a quinoline (or benzothiazole) structure,16 toward the discov-
ery of new mGluR5 antagonists with a novel structural template.
Previous structure–activity relationship (SAR) studies exempli-
fied the challenge of optimizing the mGluR5 allosteric antagonists
mGluR5s are located on postsynaptic glutamatergic synapses of
the limbic cortex, hippocampus, amygdala, and basal ganglia
(including nucleus accumbens, striatum and olfactory tubercle).1
The mGluR5 functions as a dimer, coupled to phospholipase C
Abbreviations: mGluR, metabotropic glutamate receptor; iGluR, ionotropic
glutamate receptor; MPEP, 2-methyl-6-(phenylethynyl)pyridine; MTEP, 3-((2-
methyl-4-thiazolyl)ethynyl)pyridine.
* Corresponding author. Tel.: +1 443 740 2887; fax: +1 443 740 2111.
E-mail address: anewman@intra.nida.nih.gov (A.H. Newman).
0968-0896/$ - see front matter Published by Elsevier Ltd.
doi:10.1016/j.bmc.2010.03.053

P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
3027
S
X
'a'
N
N
CN
N
'b'
N
R
1, MPEP
2, MTEP
3; X=CHCH, R=H;
4; X=S, R=H;
5; X=CHCH, R=F
X
N
X
'a'
N
X
'a'
N
CN
R
CN
Z
'b'
'b'
Y
R
R
Structure I
X=S, CHCH;
R=Ph, 4'-F-Ph, 3'-Py
6; X=CHCH, R=H;
7; X=S, R=F
8a; X=CHCH, Y=CH, Z=CN, R=Ph;
8b; X=CHCH, Y=CH, Z=CN, R=4'-F-Ph;
8c; X=S, Y=N, Z=H, R=Ph;
8d; X=S, Y=CH, Z=F, R=3'-Py
Figure 1. mGluR5 antagonist structural templates.
with a parent structure that differs from the diaryl alkynes, as
binding affinities to the allosteric site are sensitive to small struc-
tural changes.16–19 Typically, chemical modification of the diary-
lalkynyl analogues of MPEP or MTEP are better tolerated at
mGluR5 than alternative templates.1,2,7,19–21
modifications, and designed a novel series of analogues as shown
in Structure I.
2. Chemistry
In our previous SAR studies of quinoline and benzothiazole ana-
logues, compounds 3 and 4 were discovered to bind with moderate
affinity to mGluR5 by introducing the 3-cyano group into the phe-
nyl rings at the 7-position of the quinoline or the 5-position of the
benzothiazole.16 The addition of a cyano group improved the bind-
One of the synthetic strategies toward the designed quinolines
(in Structure I) is shown in Scheme 1, starting from the boronic es-
ter 9a, which was made from commercially available 7-chloro-2-
methylquinoline, under Miyaura borylation conditions.16 5-Bro-
mo-2-hydroxybenzonitrile was coupled with 9a under modified
Suzuki coupling conditions to give 10, and the free hydroxyl group
of 10 was converted to the corresponding triflate 12 with trifluoro-
methanesulfonic anhydride in an overall 17% yield. Attempts to
introduce the aryl ring by treating the triflate 12 with various
substituted aryl boronic acids was undertaken using Suzuki cou-
pling conditions, but this strategy proved to be difficult as de-
scribed below. The same strategy was also applied to the
benzothiazole compounds starting from 9b. This strategy was
hampered by low yields in steps a to c. To improve the yield of
the phenolic intermediates (10 and 11), a protection–deprotection
strategy was applied as shown in Scheme 2. However, deprotection
of the MOM group in compound 16, or the benzyl group in
compounds 17 and 18, were either low yielding or incomplete.
Hence, higher yields were obtained via the direct coupling condi-
ing affinity of 3 to 110 lM from the parent compound that only
displaced [3H]MPEP by 50% at 10 mM.17 Milbank et al. also pub-
lished this compound in their series of quinoline analogues and
showed that the addition of a 5-fluoro substitution (shown as
structure 5 in Fig. 1) further increased the potency ꢀ10-fold.14 Re-
cently, we discovered that addition of a cyano and/or fluoro group
in a series of MPEP and MTEP analogues (e.g., 6 and 7 in Fig. 1) also
resulted in an increase in potency.19 Thus, our strategy was to use
SAR derived from the MPEP and MTEP analogues to direct the de-
sign and synthesis of quinoline and benzothiazole analogues.
Among our previous SAR results, we demonstrated that an addi-
tional aryl ring appended to the 40-position of ring ‘b’ was well tol-
erated, shown as structure 8a–8d in Figure 1.19 Hence, using 3 and
4 as the parent structures, we incorporated additional aryl ring
Br
CN
OH
X
X
CN
N
O
N
B
a
b
O
OH
9a; X=CHCH;
10; X=CHCH;
11;
X=S
9b;
X=S
(HO)2B
S
X
CN
N
F
CN
N
c
OTf
12; X=CHCH;
13;
14
F
X=S
Scheme 1. Reagents and conditions: (a) Na2CO3, Pd(OAc)2, dioxane, H2O, 50 °C, overnight; (b) trifluoromethanesulfonic anhydride, pyridine, CH2Cl2, rt, 2–5 h; (c) K3PO4,
Pd(PPh3)4, dioxane, 85 °C, overnight.

3028
P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
Br
CN
OR
X
N
X
CN
O
10;
N
X=CHCH, R=OH;
B
c
b
a
16;
X=CHCH, R=OMOM;
O
17; X=CHCH, R=OBz;
15a; R=Bz;
15b;
R
11;
X=S, R=OH;
18; X=S, R=OBz;
9a; X=CHCH;
9b;
R=MOM
c
X=S
Scheme 2. Reagents and conditions: (a) Na2CO3, Pd(PPh3)4, DME, H2O, 80 °C, overnight; (b) CF3COOH, CH2Cl2, rt, 3 h; (c) H2, 40 psi, Pd/C, ethanol, overnight.
tion (step a in Scheme 1) with 5-bromo-2-hydroxybenzonitrile, on
a small scale (<2 mmol). The triflates 12 and 13, from the phenols
(step b in Scheme 1) also proceeded in low yield. Triflates 12 and
13 were also easily hydrolyzed under the coupling condition of
step c in Scheme 1, especially when these reactions were scaled
up (>2 mmol). Utilization of a weaker base such as KF was also
tried, but it did not improve the yield. Hence, only compound 14
was synthesized using this strategy.
Although the strategy in Scheme 2 was not successful toward
the synthesis of the designed final products, several 7-substituted
quinoline and 5-substituted benzothiazole analogues were ob-
tained using this synthesis, and evaluated for mGluR5 activity.
The targeted compounds with Structure I were successfully syn-
thesized by the strategy shown in Scheme 3. Selective bromination
of 3-chlorobenzonitrile by 1,3-dibromo-5,5-dimethylhydantoin
(DBH) gave 2-bromo-5-chlorobenzonitrile 19 as reported previ-
ously.22 Compound 19 was treated with various substituted aryl
boronic acids under the Suzuki coupling condition to give a set of
intermediates 20a–c, and final product 21. The desired compounds
22–26 were then synthesized by Suzuki–Miyaura coupling with
quinoline boronic ester 9a or benzothiazole boron ester 9b, which
were made according to our previously reported procedure.16
These novel quinolines and benzothiazoles, compound 14 and
22–26, were assessed for mGluR5 activity in a binding assay and
in a functional assay measuring mGluR5 activity via calcium mobi-
lization.19 The resulting SAR led us to the synthesis of 7-pyridyl-
quinolines, such as compound 32. The details will be discussed in
the SAR section. At the same time, alkyne 28 and quinoline 3014
were synthesized for comparison.
Alkyne 28 was synthesized following the procedure in Scheme 4,
in which, synthon 27 was prepared according to a literature proce-
dure.21 Compound 27 was coupled with 5-bromonicotinonitrile un-
der the Sonogashira coupling condition to give the target alkyne 28.
The corresponding quinolines were synthesized according to
Scheme 5, starting from either the commercially available 5-
bromonicotinonitrile 29a or 5-bromo-2-chloronicotinonitrile 29b,
which was made from a literature procedure.23 The Suzuki–Miya-
ura coupling reactions with boronic ester 9a gave the desired com-
pounds 30 and 31.
compound 32.
A Suzuki coupling reaction of 31 gave
All the compounds synthesized were purified by flash column
chromatography, analytically characterized as the free bases, and
then converted to the HBr salts for biological testing, unless other-
wise described in the experimental methods.
CN
Cl
CN
Br
Cl
CN
9a
N
a
b
Cl
21
19
R
(HO)2B
b
X
R=H, 4-F, 3-aza
O
N
B
O
X
N
Cl
CN
MeO
OMe
P
9a;
9b;
X=CHCH;
X=S
CN
R
R
c
22;
23;
X=CHCH, R=H;
20a; R=H;
20b;
1L
X=CHCH, R=4-F;
R=4-F;
20c; R=3-aza
24; X=CHCH,R =3-aza;
25;
X=S, R=H;
26; X=S, R=3-aza;
Scheme 3. Reagents and conditions: (a) DBH, H2SO4, TFA;22 (b) Na2CO3, Pd(PPh3)4, DME, H2O, 70 °C, overnight; (c) K3PO4, Pd(OAc)2, ligand 1L, dioxane, H2O, 105 °C, 16–20 h.
Br
CN
Si
N
N
N
CN
a
b
N
Br
Si
N
27
28
Scheme 4. Reagents and conditions: (a) Pd(PPh3)2Cl2, CuI, NEt3, rt, overnight;21 (b) Pd(PPh3)4, CuI, Et3N, DMF, TBAF, 70 °C.

P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
3029
Br
CN
O
Br
CN
R
9a
CN
R
N
a
b
N
H
N
N
29a;
30;
R=H;
31; R=Cl
R=H
29b; R=Cl
B(OH)2
CN
Cl
CN
N
N
c
N
N
31
32
Scheme 5. Reagents and conditions: (a) POCl3, PCl5, reflux overnight;23 (b) Na2CO3, PdCl2(dppf), dioxane, H2O, MW, 140 °C, 30 min; (c) K3PO4, Pd(OAc)2, ligand 1L, dioxane,
H2O, MW 140 °C, 90 min.
Health’s Psychoactive Drug Screening Program).24 An assay utiliz-
3. In vitro pharmacology
ing calcium fluorescence was employed to test functional activity
of compounds by measuring receptor-induced intracellular release
of calcium with a kinetic imaging plate reader that makes simulta-
neous measurements of calcium levels in each well of a 384-well
plate.19 The results of these in vitro tests for the designed quino-
All the compounds synthesized were assessed in a radioligand
displacement binding assay for mGluR5, using [3H]MPEP as the
radioligand in rat brain membranes or HEK293-T cells transfected
with cloned rat mGluR5 cDNA (National Institute of Mental
Table 1
In vitro data for quinolines, benzothiazoles and MPEP or MTEP-like alkynyl mGluR5 antagonistsa
S
S
'a'
N
'a'
N
'a'
'a'
CN
CN
R
N
N
CN
R
R
'b'
Y
'b'
R
'b'
Y
'b'
Y
A
B
C
D
Compound ID
Template
Y
R
mGluR5 binding affinity Ki SEM (nM)
mGluR5 function (Ca+2 flux) IC50 SEM (nM)
cLog Pb
1, MPEP
2, MTEP
3
4
6
7
8a
8b
8c
8d
10
13
14
16
17
18
21
22
23
A
C
B
D
A
C
A
A
C
C
B
D
D
B
B
D
B
B
B
B
D
D
A
B
B
B
CH
N
CH
H, 3-Hc
H, 3-Hc
H
H
H
3-CN-5-F
Ph
40-F-Ph
4-Ph
3-F-4-30-Py
4-OH
OTf
13 1d
3.54 1.39d
13.6 2.09d
29 5f
3.8
2.1
3.9
3.9
3.2
3.2
5.1
5.3
4.2
3.0
3.9
5.4
5.9
3.6
5.9
5.9
4.6
5.7
5.9
4.3
5.8
4.3
1.9
2.5
3.2
4.7
16e
110 20f
2100 580f
1.3 0.09d
0.9 0.2d
4.0 0.6d
3.0 0.5d
5.49 1.43d
11.4 3d
>10,000
862 200
4679 1185
596 109
1040 206
7134 2026
4720 913
97 20
NT
CH
CH
CH
CH
N
0.415 0.10d
0.813 0.11d
3.08 0.61d
7.19 1.53d
1.21 1.15d
3.43 0.51d
>10,000
CH
CH
7840 1250
>10,000
294+21
>10,000
>10,000
9150 1540
1250 261
692 64
1340 41
6890 1250
>10,000
4-F-Ph
4-OCH2OCH3
4-OBz
OBz
CH
CH
CH
CH
CH
CH
3-Hc-2-CN-4-Cl
4-Ph
4-40-F-Ph
4-30-Py
Ph
3-Py
H
H
4-Cl
4-Ph
64 16
24
25
26
730 190
483 98
>10,000
1.5 0.3
100 21
>10,000
28
N
N
N
N
13 2.3
68 5.3
3310 384
81 8.1
30g
31h
32
97 19
a
b
c
Methods for binding (http://pdsp.med.unc.edu/pdspw/binding.php)24 and functional assays have been previously published.19
Determined with ChemDraw Ultra 11.0.
3-H, no CN group on the 3-position of structure.
d
e
f
Data reported previously in the literature.19
Data reported previously in the literature.25
Data reported previously in the literature.16
g
h
Compound reported previously in the literature.14
Partial antagonist; NT = not tested.

3030
P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
In general, mGluR5 binding affinity (Ki) values were comparable
100
80
60
40
20
0
to functional potency (IC50) values in the calcium fluorescence as-
say. However, in the case of these two quinolines, 22 and 23, their
functional potencies were lower than expected (e.g., 22
(IC50 = 1250 nM) and 23 (IC50 = 692 nM) versus 3 (IC50 = 29 nM)).
Considering this and their high cLog P values (e.g., 22, cLog P = 5.7
and 23, cLog P = 5.9), we reasoned that addition of the third aro-
matic ring system may be problematic for future in vivo investiga-
tion. Hence, we introduced the heteroatom ‘N’ into the ring
systems of our target compound, including the 3rd additional aryl
ring and ring ‘b’, to give compounds 24, 30–32. This modification
lowered the cLog P values below 5. The corresponding alkyne
was also synthesized for comparison (e.g., 28 vs 6).
The cLog P value of alkyne 28 was decreased to 1.9; high bind-
ing affinity (Ki = 1.5 nM) and functional activity (IC50 = 13 nM)
were retained. The same trend was observed in quinoline 30
(Ki = 100 nM, IC50 = 68 nM) compared to its parent compound 3
(Ki = 110 nM, IC50 = 29 nM). Importantly, the additional heteroaryl
ring was well tolerated (32 vs 30) in both binding affinity (32
(Ki = 97 nM) vs 30 (Ki = 100 nM)), and functional activity (32
(IC50 = 81 nM) vs 30 (IC50 = 68 nM)).
On the other hand, the relatively low binding affinity of 24 im-
plied that the ‘N’ introduced to the third ring system was detri-
mental to the binding affinity (Ki = 730 nM) and the functional
activity (IC50 = 1340 nM), although its cLog P value is comparable
to compound 32 (4.3 vs 4.7). This suggested the 4–30-pyridyl sub-
stituent was not favored for the template B structure.
3D-Superimposition comparison of 8a and 32, shown in Fig-
ure 3,26 demonstrated that with the additional phenyl ring, alkyne
8a and quinoline 32 aligned quite well. Conversely, 3D-superimpo-
sition of 8d and 26, showed that the benzothiazole 26 did not align
well with alkyne 8d (Fig. 4),26 which may explain why the benzo-
thiazoles (template D) did not have comparable binding affinities
as seen in the quinoline series. However, although they only
showed moderate potencies, improved tolerability for the addi-
tional ring system was observed for compound 25 (Ki = 483 nM),
which showed ꢀ4-fold increase in binding affinity compared to
its parent structure 4 (Ki = 2100 nM). This corresponds to the trend
observed in the alkyne series (template C) 8c (Ki = 5.49 nM) versus
2, MTEP (Ki = 16 nM).19 Other aryl-substituted benzothiazoles,
such as 14, only showed low binding affinity (Ki = 4679 nM) and
compound 26 was completely inactive at mGluR5.
-10
-9
-8
-7
-6
-5
-4
Log 31, [M]
Figure 2. Compound 31 as a partial antagonist.
lines, benzothiazoles and related MPEP or MTEP analogues are
listed in Table 1.
All the compounds were full antagonists, thereby inducing a
complete inhibition of glutamate-induced mGluR5 activity, with
the exception of 31, which exhibited partial antagonist activity
reaching only 50% inhibition of the EC80 glutamate response
(Fig. 2).
All alkyne, quinoline and benzothiazole analogues were func-
tionally inactive (<50% inhibition at 10
subtypes and did not bind to NMDA receptors at a concentration of
10
M.24
lM) at all the other mGluR
l
4. Structure–activity relationships
For the MPEP analogues (template A) in Table 1, the aryl ring
systems introduced into the 4-position of ring ‘b’, were well toler-
ated (e.g., phenyl group in 8a (Ki = 4 nM) and 4-fluorophenyl group
in 8b (Ki = 3 nM) as compared to their parent structure
6
(Ki = 1.3 nM).19 As predicted, the same modification on the ring
‘b’ system of the quinoline analogues (template B), 22 (Ki = 97 nM)
and 23 (Ki = 64 nM) showed comparably high binding affinities to
their parent structure 3 (Ki = 110 nM), which demonstrated the
same SAR trend as the MPEP analogues.
Figure 3. 3D-superimposition of 8a (alkyne) and 32 (quinoline).26 Note: Compound 32 is shown in turquoise blue and 8a in orange on right side for clarity.
Figure 4. 3D-superimposition of 8d (alkyne) and 26 (benzothiazole).26 Note: Compound 8d is shown in turquoise blue and 26 in orange on right side for clarity.

P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
3031
(CFCl3, 0). Infrared spectra were recorded as a KBr pellet using a Per-
kin–Elmer Spectrum RZ I FT-IR spectrometer or recorded as powder
using an Avatar 370 FT-IR thermo Nicolet spectrometer. Gas chro-
matography–mass spectrometry (GC/MS) data were acquired using
an Agilent Technologies (Santa Clara, CA) 6890N GC equipped with
an HP-5MS column (cross-linked 5% PH ME siloxane,
30 m ꢁ 0.25 mm i.d. ꢁ 0.25
lM film thickness) and a 5973 mass-
selective ion detector in electron-impact mode. Ultrapure grade he-
lium was used as the carrier gas at a flow rate of 1.2 mL/min. The
injection port and transfer line temperatures were 250 and 280 °C,
respectively, and the oven temperature gradient used was as fol-
lows: the initial temperature (100 °C) was held for 3 min and then
increased to 295 °C at 15 °C/min over 13 min, and finally maintained
at 295 °C for10 min. CombustionanalysiswasperformedbyAtlantic
Microlab, Inc. (Norcross, GA) and agrees within 0.5% of calculated
values. Melting point determination was conducted using a Tho-
mas-Hoover melting point apparatus and are uncorrected. Anhy-
drous solvents were purchased from Aldrich or J. T. Baker and were
used without further purification, except for tetrahydrofuran, which
was freshly distilled from sodium–benzophenone ketyl. All other
chemicals and reagents were purchased from Aldrich Chemical Co.,
Combi-Blocks, TCI, America., Matrix Scientific, Lancaster Synthesis,
Inc. (Alfa Aesar) and AK Scientific, Inc. The final products were con-
verted into HBr salts, typically by treating the free base with metha-
nolic HBr followed by precipitation from a combination of organic
solvents. On the basis of NMR, GC–MS, and combustion data, all final
compounds are >95% pure. Methods for binding affinity and func-
tional assay for mGluR5 have been previously reported.19
Figure 5. 3D-superimposition of quinoline analogues.26
The SAR results of other 7-aryl-substituted quinoline analogues
with structural template B also provided additional SAR for
mGluR5. In Figure 5,26 the small substitutions on the 4-position
of ring b in template B (e.g., OH in compound 10 and Cl in com-
pound 31) were not favored for binding or functional potency. This
also corresponded to our previously reported results.16 Compound
31 was observed to be a weak partial antagonist. Similar conver-
sions of functional efficacy from mGluR5 antagonists to partial
antagonists, or even to the positive allosteric modulators has been
reported recently.2,27,28 Hence, we provide additional evidence
suggesting that mGluR5 intrinsic activities are very sensitive to
small structural modifications.
The flexibility of this 4-position on ring ‘b’ in template B is also
limited to the size of the substitution. For example, compound 17
extends the phenyl ring away from the quinoline, which decreased
binding affinity (Ki = 1040 nM) ꢀ10-fold compared to compound
22 (Ki = 97 nM). A similar 15-fold decrease in potency was also ob-
served in the 6-aryl-substituted benzothiazole (18 (Ki = 7134 nM)
vs 25 (Ki = 483nM)) in template D.
6.1. General procedure A: coupling of heteroaryl bromides with
boronic ester or acid
To a suspension of boronic ester (0.6 equiv) or boronic acid
(1.2 equiv), heteroaryl bromide (1 equiv), and Na2CO3 or KF
(3 equiv) in a mixture of solvents DME/H2O (3/1, 4 mL for 1 mmol
scale reaction) was added Pd(PPh3)4 (5 mol %) under Argon. The
mixture was warmed to 70–80 °C for 3 h to overnight with TLC
monitoring. The solvent was then removed under reduced pres-
sure, and the residue was extracted with EtOAc. The organic layer
was dried over MgSO4 and concentrated to crude product, which
was then purified by flash column chromatography to give the
pure product.
In addition to these in vitro pharmacological results, computa-
tional toxicology analyses29 predicted that these quinoline com-
pounds would not show toxicity, adding promise to the
development of quinoline compounds as mGluR5 antagonist.
5. Summary
A series of quinoline and benzothiazole analogues of the parent
compounds 3 and 4 were synthesized as selective mGluR5 antago-
nists using the SAR results we obtained for MPEP and MTEP ana-
logues.19 As hypothesized, the mGluR5 binding affinity and
functional results of these analogues demonstrated overlapping
SAR between the quinolines and their corresponding MPEP ana-
logues. The additional ring modifications on ring ‘b’ were tolerated
in both alkyne and quinoline structures, with the alkynes showing
higher potencies, uniformly, than the quinolines. This suggests that
the SAR results of MPEP analogues can be used to direct the further
investigation of novel quinoline analogues. In vivo evaluation of
the lead compounds herein will provide valuable direction toward
future drug design.
6.2. General procedure B: coupling of heteroaryl chlorides with
boronic ester or acid
To a suspension of boronic ester (1 equiv) or boronic acid
(1.2 equiv), heteroaryl chloride (1 equiv.), biphenyl phosphine li-
gand (1L, 4 mol %) and K3PO4 (3 equiv) in a solvent mixture of diox-
ane/H2O (10/1, 4 mL for 1 mmol scale reaction) was added
Pd(OAc)2 (2 mol %) under Argon. The mixture was warmed to
105 °C and kept stirring overnight. Solvents were then removed
under reduced pressure, and the residue was extracted with EtOAc.
The organic layer was dried over MgSO4 and concentrated to dry-
ness. The crude product was purified by flash column chromatog-
raphy to give the pure product.
6. Experimental methods
Reaction conditions and yields were not optimized, and spectro-
scopic data refer to the free base unless otherwise described in each
compound. Microwave reactions were performed using a CEM Corp.
(Matthews, NC) Discover LabMate system using the standard 10 mL
reaction vessel. Flash chromatography was performed using silica
gel (EMD Chemicals, Inc.; 230–400 mesh, 60 Å). 1H and 13C NMR
spectra were acquired using a Varian Mercury Plus 400 spectrome-
ter. Chemical shifts are reported in parts-per-million (ppm) and ref-
erenced according to deuterated solvent for 1H spectra (CDCl3, 7.26;
(CD3)2SO, 2.50), 13C spectra (CDCl3, 77.2; (CD3)2SO, 39.5), 19F spectra
6.3. 2-Hydroxy-5-(2-methylquinolin-7-yl)benzonitrile (10)
A
suspension of 5-bromo-2-hydroxybenzonitrile (0.24 g,
1.2 mmol), 9a (0.3 g, 1.1 mmol), Na2CO3 (0.32 g, 3 mmol), and
Pd(OAc)2 (0.011 g, 5%) in a mixture of dioxane (4 mL) and water
(0.4 mL) was degassed and heated at 50 °C overnight, under Argon
protection. Solvent was removed under vacuum. The residue was
dissolved in methanol and filtered. The filtrate was concentrated
and purified by a flash chromatography eluting with EtOAc to pro-

3032
P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
vide the solid product (0.19 g) in 60% yield; 1H NMR (400 MHz,
DMSO-d6) d 8.24 (d, J = 8.4 Hz, 1H), 8.14 (s, 1H), 8.10 (s, 1H), 7.98
(m, 2H), 7.84 (d, J = 8.0 Hz, 1H), 7.39 (d, J = 8.0 Hz, 1H), 7.12 (d,
J = 8.8 Hz, 1H), 2.65 (s, 3H); 13C NMR (100 MHz, DMSO-d6) d
160.6, 160.2, 151.8, 136.7, 134.1, 132.2, 129.2, 126.0, 125.3,
125.3, 122.8, 117.6, 110.0, 100.4, 25.3; HBr salt precipitated from
MeOH; mp 225–226 °C; IR (powder) 3463, 2226 cmꢂ1; Anal.
(C17H12N2OꢃHBrꢃ1/2H2O) C, H, N.
(0.06 g, 0.05 mmol) in dioxane (5 mL) was degassed and heated
at 85 °C overnight, under Argon protection. Solvent was removed
under vacuum. The residue was extracted with CH2Cl2 and washed
with brine. The organic layer was dried over magnesium sulfate
and concentrated to give a crude product. It was purified by flash
chromatography eluting with hexane/EtOAc (6:1, 4:1) to give the
product (50 mg) in 25% yield; mp 101–103 °C; 1H NMR
(400 MHz, CDCl3) d 8.18 (s, 1H), 8.04 (s, 1H), 7.93 (dd, J = 8.4,
8.8 Hz, 2H), 7.60 (m, 4H), 7.22 (dd, J = 8.4, 8.8 Hz, 2H), 2.89 (s,
3H); 13C NMR (100 MHz, CDCl3) d 168.7, 154.4, 143.4, 140.8,
136.9, 136.1, 132.6, 131.9, 130.9, 130.8, 130.8, 123.9, 122.4,
120.9, 118.8, 116.2, 116.0, 112.1, 20.5; 19F NMR (376 MHz, CDCl3)
d ꢂ113.3; IR (powder) 2232 cmꢂ1; GC–MS (EI) m/z 344 (M+); Anal.
(C21H13FN2S) C, H, N. HBr salt precipitated from MeOH. Anal.
(C21H13FN2SꢃHBr) C, H, N.
6.4. 2-Hydroxy-5-(2-methylbenzo[d]thiazol-5-yl)benzonitrile
(11)
A
suspension of 5-bromo-2-hydroxybenzonitrile (0.24 g,
1.2 mmol), 9b (0.3 g, 1 mmol), Na2CO3 (0.32 g, 3 mmol), and
Pd(OAc)2 (0.011 g, 5%) in a mixture of dioxane (4 mL) and water
(0.4 mL) was degassed and heated at 50 °C overnight, under Argon
protection. Solvent was removed under vacuum. The residue was
dissolved in methanol and filtered. The filtrate was concentrated
and purified using a flash chromatography eluting with EtOAc to
provide the solid product (0.11 g) in 40% yield; mp 195–197 °C
(dec); 1H NMR (400 MHz, DMSO-d6) d 11.2 (br, 1H), 8.15 (s, 1H),
8.06 (d, J = 8.4 Hz, 1H), 8.01 (s, 1H), 7.90 (d, J = 8.8 Hz, 1H), 7.66
(d, J = 8.8 Hz, 1H), 7.12 (d, J = 8.8 Hz, 1H), 2.80 (s, 3H); 13C NMR
(100 MHz, DMSO-d6) d 168.7, 160.4, 154.4, 137.2, 134.8, 134.0,
132.0, 131.9, 123.9, 123.1, 120.0, 117.6, 117.5, 100.2, 20.5; IR (pow-
der) 3096, 2232 cmꢂ1; Anal. (C15H10N2OSꢃ5/8H2O) C, H, N.
6.8. 2-Benzoxy-5-bromobenzonitrile (15a)
A
suspension of 5-bromo-2-hydroxybenzonitrile (10 g,
50 mmol), benzyl bromide (6 mL, 50 mmol), and K2CO3 (7.6 g,
55 mmol) in acetone (100 mL) was refluxed for 5 h. The reaction
mixture was filtered. The filtrate was concentrated and solidified
to give crude product. It was washed with hexane to give the pure
product (12 g) in 83% yield; mp 74–76 °C. 1H NMR (400 MHz,
CDCl3) d 7.68 (s, 1H), 7.57 (d, J = 9.2 Hz, 1H), 7.44–7.33 (m, 5H),
6.88 (d, J = 9.2 Hz, 1H) 5.21 (s, 2H); 13C NMR (100 MHz, CDCl3) d
159.6, 137.3, 136.2, 135.3, 129.3, 129.1, 128.7, 128.1, 127.2,
6.5. 2-Cyano-4-(2-methylquinolin-7-yl)phenyl triflate (12)
115.2, 114.9, 112.9, 104.5, 71.2; IR (powder) 2232, 1135 cmꢂ1
;
GC–MS (EI) m/z 287, 289 (M+).
To a suspension of 10 (0.6 g, 1.7 mmol) in 8 mL CH2Cl2 on an ice
bath, pyridine (0.6 mL, 7.4 mmol) and trifluoromethanesulfonic
anhydride (0.6 mL, 3.4 mmol) were added successively. The reac-
tion mixture was stirred at rt for 2 h. The reaction mixture was ex-
tracted with CH2Cl2. The organic layer was concentrated and
purified by flash chromatography eluting with hexane/EtOAc
(4:1) to give the product as syrup (0.2 g) in 30% yield. 1H NMR
(400 MHz, CDCl3) d 8.23 (s, 1H), 8.10 (d, J = 8.8 Hz, 1H), 8.10 (s,
1H), 8.05 (d, J = 8.8 Hz, 1H), 7.92 (d, J = 8.8 Hz, 1H), 7.67 (d,
J = 8.8 Hz, 1H), 7.62 (d, J = 8.4 Hz, 1H), 7.37 (d, J = 8.4 Hz, 1H),
2.79 (s, 3H); 13C NMR (100 MHz, CDCl3) d 162.1, 159.5, 149.2,
145.5, 134.8, 133.5, 129.5, 129.2, 126.8, 126.5, 123.8, 123.6,
123.5, 109.8, 29.5; GC–MS (EI) m/z 392 (M+).
6.9. 5-Bromo-2-methoxymethoxylbenzonitrile (15b)
To
a suspension of 5-bromo-2-hydroxybenzonitrile (1 g,
5 mmol) and K2CO3 (0.76 g, 5.5 mmol) in DMF (10 mL) was added
methoxymethyl chloride (4.18 mL, 5.5 mmol). The reaction mix-
ture was kept at rt overnight and extracted with ether. The organic
layer was concentrated to give the product (0.93 g) in 77% yield;
mp 65–67 °C; 1H NMR (400 MHz, CDCl3) d 7.68 (m, 1H), 7.65 (m,
1H), 7.16 (m, 1H), 5.29 (s, 2 H), 3.53 (s, 3H); 13C NMR (100 MHz,
CDCl3) d 158.5, 137.5, 135.9, 116.9, 115.1, 113.9, 104.9, 95.2,
57.0; IR (powder) 2236, 1129 cmꢂ1; GC–MS (EI) m/z 241, 243 (M+).
6.10. 2-Methoxymethoxy-5-(2-methylquinolin-7-yl)benzo-
nitrile (16)
6.6. 2-Cyano-4-(2-methylbenzo[d]thiazol-5-yl)phenyl triflate
(13)
Prepared by following the general procedure A using 9a (0.27 g,
1 mmol) and 15b (0.24 g, 1 mmol), eluting with hexane/EtOAc
(4:1) to give the product (0.18 g) in 59% yield; mp 97–99 °C; 1H
To a solution of 11 (0.4 g, 1.5 mmol) in 20 mL CH2Cl2 on an ice
bath, pyridine (0.3 mL, 3.7 mmol) and trifloromethanesulfonic
anhydride (0.3 mL, 1.7 mmol) were added successively. The reac-
tion mixture was stirred at rt for 5 h and then extracted with
CH2Cl2. The organic layer was concentrated and purified by flash
chromatography eluting with hexane/EtOAc (4:1) to give the prod-
uct as a solid (0.1 g) in 18% yield; mp 87–89 °C (dec); 1H NMR
(400 MHz, CDCl3) d 8.10 (d, J = 1.6 Hz, 1H), 8.00 (d, J = 2.0 Hz, 1H),
7.96 (s, 1H), 7.94 (s, 1H); 7.59 (d, J = 8.4 Hz, 1H), 7.53 (dd, J = 8.4,
2.0 Hz, 1H), 2.87 (s, 3H); 13C NMR (100 MHz, CDCl3) d 169.2,
163.8, 159.1, 149.8, 143.8, 142.3, 138.4, 135.5, 133.5, 133.0,
123.9, 123.4, 122.6, 121.1, 20.28; 19F NMR (376 MHz, CDCl3) d
ꢂ72.9; IR (powder) 2232 cmꢂ1; GC–MS (EI) m/z 398 (M+); Anal.
(C16H9F3N2O3S2) C, H, N.
NMR (400 MHz, CDCl3)
d 8.18 (d, J = 2.4 Hz, 1H), 8.08 (d,
J = 8.4 Hz, 1H), 7.94 (d, J = 2.4 Hz, 1H), 7.91 (dd, J = 8.8, 2.4 Hz,
1H), 7.88 (d, J = 8.8 Hz, 1H), 7.67 (dd, J = 8.4, 2.0 Hz, 1H), 7.37 (d,
J = 8.4 Hz, 1H), 7.32 (d, J = 8.4 Hz, 1H), 5.35 (s, 2H), 3.57 (s, 3H),
2.78 (s, 3H); 13C NMR (100 MHz, CDCl3) d 160.2, 158.9, 148.3,
139.6, 136.1, 134.8, 133.4, 132.4, 128.6, 126.3, 126.0, 124.7,
122.6, 115.7, 103.7, 95.1, 57.0, 25.6; IR (powder) 2232,
1258 cmꢂ1; GC–MS (EI) m/z 304 (M+); Anal. (C19H16N2O2ꢃ1/4H2O)
C, H, N.
6.11. 2-Benzoxy-5-(2-methylquinolin-7-yl)benzonitrile (17)
Prepared by following the general procedure A using 9a (0.27 g,
1 mmol) and 15a (0.35 g, 1.1 mmol), eluting with hexane/EtOAc
(4:1) to give the solid product (0.14 g) in 40% yield. HBr salt precip-
itated from MeOH/acetone. mp 190–191 °C; 1H NMR (400 MHz,
DMSO-d6) d 8.86 (m, 1H), 8.31 (m, 3H), 8.17 (dd, J = 7.2, 9.2 Hz,
2H), 7.82 (d, J = 8.8 Hz, 1H), 7.54 (d, J = 9.2 Hz, 1H), 7.52 (m, 2H),
6.7. 2-(4-Fluorophenyl)-4-(2-methylbenzo[d]thiazol-5-yl)ben-
zonitrile (14)
A suspension of 13 (0.4 g, 0.75 mmol), 4-fluorophenylboronic
acid (0.135 g, 1 mmol), K3PO4 (0.64 g, 3 mmol), and Pd(PPh3)4

P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
3033
7.43 (dd, J = 8.0, 7.2 Hz, 2H), 7.37 (d, J = 6.4 Hz, 1H), 5.37 (s, 2H),
2.84 (s, 3H); 13C NMR (100 MHz, DMSO-d6) d 160.6, 159.5, 136.6,
134.6, 133.3, 132.0, 130.2, 129.3, 129.0, 128.3, 127.7, 126.5,
124.1, 116.7, 115.2, 102.6, 71.2, 22.8; IR (powder) 2349,
1135 cmꢂ1; GC–MS (EI) m/z 350 (M+); Anal. (C24H18N2OꢃHBrꢃ2/
3H2O) C, H, N.
1H NMR (400 MHz, CDCl3 d 8.15 (s, 1H), 8.12 (d, J = 8.0 Hz, 1H),
7.91 (d, J = 8.4 Hz, 1H), 7.79 (s, 1H), 7.69 (dd, J = 8.4, 8.8 Hz, 2H),
7.59 (d, J = 8.8 Hz, 1H), 7.36 (d, J = 8.4 Hz, 1H), 2.78 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 160.4, 152.7, 147.8, 143.6, 138.2, 136.3,
133.6, 133.7, 131.8, 129.1, 128.4, 126.0, 123.3, 117.5, 113.2, 25.6;
IR (powder) 2232 cmꢂ1; GC–MS (EI) m/z 278 (M+); HBr salt precip-
itated from MeOH/acetone/ether. Anal. (C17H11ClN2ꢃHBrꢃ1/3H2O) C,
H, N.
6.12. 2-Benzoxy-5-(2-methylbenzo[d]thiazol-5-yl)benzonitrile
(18)
6.18. 5-(2-Methylquinolin-7-yl)-2-phenylbenzonitrile (22)
Prepared by following the general procedure A using 9b (0.48 g,
1.8 mmol) and 15a (0.65 g, 2.7 mmol), eluting with hexane/EtOAc
(5:2) to give the solid product (0.6 g) in 94% yield; mp 102–
103 °C; 1H NMR (400 MHz, CDCl3) d 8.06 (s, 1H), 7.89 (s, 1H),
7.86 (d, J = 9.2 Hz, 1H), 7.76 (d, J = 7.2 Hz, 1H), 7.5–7.4 (m, 5H),
7.36 (d, J = 7.2 Hz, 1H), 7.12 (d, J = 9.2 Hz, 1H), 5.29 (s, 2H), 2.87
(s, 3H); 13C NMR (100 MHz, CDCl3) d 168.5, 159.9, 154.3, 137.2,
135.8, 135.3, 134.4, 133.3, 132.6, 129.0, 128.5, 127.2, 123.8,
122.2, 120.5, 116.6, 113.7, 103.2, 71.1, 20.5; IR (powder) 2232,
1170 cmꢂ1; GC–MS (EI) m/z 356 (M+); Anal. (C22H16N2OS) C, H, N.
Prepared by following the general procedure B using 9a (0.4 g,
1.5 mmol) and 20a (0.26 g, 1.2 mmol), eluting with hexane/EtOAc
(4:1) to provide the product (0.16 g) in 42% yield. 1H NMR
(400 MHz, CDCl3) d 8.29 (s, 1H), 8.14 (s, 1H), 8.11 (d, J = 8.4 Hz,
1H), 8.03 (d, J = 8.4 Hz, 1H), 7.91 (d, J = 8.4 Hz, 1H), 7.76 (d,
J = 8.4 Hz, 1H), 7.67–7.46 (m, 6H), 7.35 (d, J = 8.8 Hz, 1H), 2.79 (s,
3H); 13C NMR (100 MHz, CDCl3) d 160.05, 148.06, 144.49, 140.06,
135.90, 132.45, 131.64, 128.81, 126.72, 124.54, 122.58, 118.66,
111.94, 24.87. GC–MS (EI) m/z 320 (M+). HBr salt precipitated from
MeOH/acetone. Mp 273–274 °C (dec); IR (powder) 2220 cmꢂ1
Anal. (C23H16N2ꢃHBrꢃ5/4H2O) C, H, N.
;
6.13. 2-Bromo-5-chloro-benzonitrile (19)22
Yield: 4.45 g (76%). 1H NMR (400 MHz, CDCl3 d 7.64 (s, 1H), 7.63
(d, J = 10.8 Hz, 1H), 7.44 (d, J = 10.8 Hz, 1H); GC–MS (EI) m/z 217
(M+).
6.19. 5-(2-Methylquinolin-7-yl)-2-(4-fluorophenyl)benzonitrile
(23)
Prepared by following the general procedure B using 9a (0.28 g,
1.1 mmol) and 20b (0.27 g, 1 mmol), eluting with hexane/EtOAc
(4:1, 2.5:1) to give the product (0.16 g) in 42% yield. HBr salt pre-
cipitated from MeOH/acetone; mp 192–193 °C; 1H NMR (400 MHz,
DMSO-d6) d 8.95 (d, J = 6.4 Hz, 1H), 8.48 (s, 1H), 8.40 (s, 1H), 8.36
(d, J = 8.0 Hz, 1H), 8.27 (m, 2H), 7.88 (d, J = 7.6 Hz, 1H), 7.83 (d,
J = 9.2 Hz, 1H), 7.72 (m, 2H), 7.42 (m, 2H), 2.79 (s, 3H); 13C NMR
(100 MHz, DMSO-d6) d 165.2, 162.0, 159.8, 144.3, 138.8, 133.3,
132.9, 131.9, 131.8, 131.7, 130.4, 127.0, 124.5, 118.9, 116.7,
116.4, 112.1, 22.8; 19F NMR (376 MHz, DMSO-d6) d ꢂ113.0; IR
6.14. 5-Chloro-2-phenylbenzonitrile (20a)
Prepared by following the general procedure A using 19 (1 g,
5 mmol) and phenyl boronic acid (0.67 g, 5.5 mmol), eluting with
hexane/EtOAc (6:1) to give the product (0.52 g) in 50% yield; mp
87–89 °C; 1H NMR (400 MHz, CDCl3) d 7.75 (s, 1H), 7.64 (d,
J = 8.4 Hz, 1H), 7.48 (m, 6H); 13C NMR (100 MHz, CDCl3) d 144.2,
137.2, 133.9, 133.4, 131.6, 129.3, 129.1, 128.9, 117.7, 112.9; IR
(powder) 2226 cmꢂ1; GC–MS (EI) m/z 213 (M+).
(powder) 2226 cmꢂ1
;
GC–MS (EI) m/z 338 (M+); Anal.
6.15. 5-Chloro-2-(4-fluorophenyl)benzonitrile (20b)
(C23H15FN2ꢃHBrꢃ7/4H2O) C, H, N.
Prepared by following the general procedure A using 19 (0.54 g,
2.5 mmol) and 4-fluorophenyl boronic acid (0.27 g, 2.7 mmol). The
crude product was solidified by adding MeOH and filtered to give
the pure product (0.22 g) in 40% yield; mp 101–102 °C; 1H NMR
(400 MHz, CDCl3) d 7.74 (s, 1H), 7.62 (d, J = 8.4 Hz, 1H), 7.51 (dd,
J = 8.8, 8.8 Hz, 2H), 7.43 (d, J = 8.8 Hz, 1H), 7.19 (dd, J = 8.4,
8.8 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 158.3, 139.2, 130.6,
130.5, 130.2, 129.5, 127.6, 126.9, 126.8, 124.4, 119.7, 112.4,
6.20. 5-(2-Methylquinolin-7-yl)-2-(pyridin-3-yl)benzonitrile
(24)
Prepared by following the general procedure B using 9a (0.36 g,
1.33 mmol) and 20c (0.28 g, 1.3 mmol), eluting with EtOAc to pro-
vide the product (0.14 g) in 33% yield. 1H NMR (400 MHz, CDCl3) d
8.86 (s, 1H), 8.74 (d, J = 6.0 Hz, 1H), 8.30 (s, 1H), 8.18 (s, 1H), 8.11
(d, J = 8.4 Hz, 1H), 8.08 (d, J = 6.0 Hz, 1H), 8.02 (d, J = 8.4 Hz, 1H),
7.93 (d, J = 8.8 Hz, 1H), 7.76 (d, J = 8.8 Hz, 1H), 7.68 (d, J = 8.8 Hz,
1H), 7.48 (m, 1H), 7.36 (d, J = 8.4 Hz, 1H), 2.80 (s, 3H); 13C NMR
112.2; 19F NMR (376 MHz, CDCl3)
d
ꢂ112.8; IR (powder)
2226 cmꢂ1; GC–MS (EI) m/z 231 (M+).
(100 MHz, CDCl3)
d 160.18, 149.98, 149.31, 141.06, 138.90,
6.16. 5-Chloro-2-(pyridin-3-yl)benzonitrile (20c)
136.08, 132.65, 131.93, 130.71, 128.64, 126.9, 126.28, 124.45,
123.43, 122.73, 112.26, 25.48; GC–MS (EI) m/z 321 (M+); Anal.
(C22H15N3ꢃ1/2H2O) C, H, N. HBr salt precipitated from acetone.
Mp 171–172 °C; IR (powder) 2220 cmꢂ1; Anal. (C22H15N3ꢃ2HBrꢃ3/
2H2O) C, H, N.
Prepared by following the general procedure A using 19 (0.44 g,
2 mmol) and 3-pyridylboronic acid (0.27 g, 2.2 mmol), eluting with
hexane/EtOAc (1:1) to give the product (0.35 g) in 75% yield; mp
137–139 °C. 1H NMR (400 MHz, CDCl3) d 8.76(s, 1H), 8.73 (d,
J = 7.2 Hz, 1H), 7.95 (d, J = 7.6 Hz, 1H), 7.80 (s, 1H), 7.69 (d,
J = 7.6 Hz, 1H), 7.48 (m, 2H); 13C NMR (100 MHz, CDCl3) d 150.4,
149.4, 140.5, 136.2, 135.1, 133.8, 133.7, 133.1, 131.5, 123.7,
117.1, 113.3; IR (powder) 2232 cmꢂ1; GC–MS (EI) m/z 214 (M+).
6.21. 2-Phenyl-4-(2-methylbenzo[d]thiazol-5-yl)benzonitrile
(25)
Prepared by following the general procedure B using 9b (0.38 g,
1.38 mmol) and 20a (0.26 g, 1.26 mmol), eluting with hexane/
EtOAc (4:1) to give the solid product (0.1 g) in 24% yield. 1H NMR
(400 MHz, CDCl3) d 8.19 (s, 1H), 8.05 (s, 1H), 7.94 (dd, J = 7.2,
7.2 Hz, 2H), 7.65–7.47 (m, 7H), 2.89 (s, 3H); 13C NMR (100 MHz,
CDCl3) d 168.4, 154.2, 140.4, 137.7, 136.8, 132.4, 131.6, 130.7,
128.7, 123.7, 122.1, 120.7, 118.7, 111.9, 20.31; GC–MS (EI) m/z
6.17. 5-Chloro-2-(2-methylquinolin-7-yl)benzonitrile (21)
Prepared by following the general procedure A using 9a (0.19 g,
0.7 mmol) and 19 (0.2 g, 0.7 mmol), eluting with hexane/EtOAc
(4:1) to provide the product (0.1 g) in 36% yield; mp 98–100 °C;

3034
P. Zhang et al. / Bioorg. Med. Chem. 18 (2010) 3026–3035
326 (M+). HBr salt precipitated from MeOH/acetone; mp 234–
(400 MHz, CDCl3) d 9.19 (s, 1H), 8.91 (s, 1H), 8.28 (d, J = 2.0 Hz,
1H), 8.26 (s, 1H), 8.12 (d, J = 8.4 Hz, 1H), 7.95 (d, J = 8.4 Hz, 1H),
7.70 (d, J = 8.4 Hz, 1H), 7.38 (dd, J = 8.4, 2.0 Hz, 1H), 2.81 (s, 3H);
13C NMR (100 MHz, CDCl3) d 162.1, 160.5, 151.8, 151.2, 137.5,
136.3, 129.1, 127.9, 124.5, 123.5, 110.2, 100.5, 25.9; GC–MS (EI)
m/z 245 (M+); Anal. (C16H11N3) C, H, N. HBr salt precipitated from
MeOH/acetone. Anal. (C16H11N3ꢃ2HBrꢃ3/4H2O) C, H, N.
235 °C (dec); IR (powder) 2226 cmꢂ1; Anal. (C21H14N2SꢃHBr) C, H,
N.
6.22. 2-(Pyridin-3-yl)-4-(2-methylbenzo[d]thiazol-5-yl)benzo-
nitrile (26)
Prepared by following the general procedure B using 9b (0.3 g,
1.1 mmol) and 20c (0.21 g, 1 mmol), eluting with EtOAc and
MeOH/NH4OH (trace amount) to give the product (0.18 g) in 55%
yield. 1H NMR (400 MHz, CDCl3) d 8.84 (s, 1H), 8.73 (d, J = 6.4 Hz,
1H), 8.19 (d, J = 2.0 Hz, 1H), 8.09 (d, J = 2.0 Hz, 1H), 8.00 (m, 1H),
7.97 (s, 1H), 7.95 (s, 1H), 7.65 (d, J = 8.4 Hz, 1H), 7.61 (m, 1H),
7.49 (dd, J = 8.0, 4.8 Hz, 1H), 2.89 (s, 3H); 13C NMR (100 MHz,
CDCl3) d 168.5, 154.2, 150.0, 149.3, 141.4, 140.5, 136.1, 133.6,
132.6, 131.9, 130.7, 123.4, 122.2, 120.7, 118.2, 112.2, 20.3; GC–
MS (EI) m/z 327 (M+). HBr salt precipitated from MeOH/acetone.
6.27. 2-Chloro-5-(2-methylquinolin-7-yl)nicotinonitrile (31)
Prepared by following the general procedure A using 9a (0.11 g,
0.4 mmol) and 29 (0.1 g, 0.4 mmol), eluting with hexane/EtOAc
(4:1, 1:1) to provide the product (70 mg) in 65% yield; mp 187–
189 °C (dec); 1H NMR (400 MHz, CDCl3) d 8.96 (s, 1H), 8.32 (s,
1H), 8.24 (s, 1H), 8.12 (d, J = 8.0 Hz, 1H), 7.95 (d, J = 8.4 Hz, 1H),
7.66 (d, J = 8.4 Hz, 1H), 7.39 (d, J = 8.0 Hz, 1H), 2.79 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 165.3. 152.8, 141.5, 140.0, 139.9, 134.3,
Mp
264–266 °C(dec);
IR
(powder)
2220 cmꢂ1
;
Anal.
131.7, 129.8, 128.5, 120.5, 115.4, 30.3; IR (powder) 2232 cmꢂ1
;
(C20H13N3Sꢃ2HBrꢃH2O) C, H, N.
GC–MS (EI) m/z 279 (M+); Anal. (C16H10ClN3ꢃ1/8H2O) C, H, N. HBr
salt precipitated from MeOH/acetone. Anal. (C16H10ClN3ꢃHBrꢃ5/
4H2O) C, H, N.
6.23. 2-Methyl-6-((trimethylsilanyl)ethynyl)pyridine (27)21
Yield: 2.35 g (71%). 1H NMR (400 MHz, CDCl3) d 7.54 (m, 1H),
7.30 (m, 1H), 7.10 (m, 1H), 2.55 (s, 3H), 0.26 (s, 9H). GC–MS (EI)
m/z 189 (M+).
6.28. 5-(2-Methylquinolin-7-yl)-2-phenylnicotinonitrile (32)
To a microwave reaction vessel was added 31 (0.28 g, 1 mmol),
phenylboronic acid (0.13 g, 1.05 mmol), Pd(OAc)2 (0.045 g,
0.20 mmol, 3 mol %), ligand 1L (0.17 g, 0.40 mmol, 6 mol %),
K3PO4 (0.64 g, 3 mmol), dioxane (5 mL). The reaction mixture
was degassed, protected under Argon, and reacted under micro-
wave condition at 140 °C for 90 min, followed the same work-up
procedure in general procedure B, eluting with hexane/EtOAc
(4:1, 2.5:1) to provide the product (70 mg) in 30% yield; mp
105–107 °C (dec); 1H NMR (400 MHz, CDCl3 d 9.26 (t, J = 2.8 Hz,
1H), 8.40 (t, J = 2.8 Hz, 1H), 8.32 (s, 1H), 8.12 (dd, J = 8.0, 2.8 Hz,
1H), 8.02 (m, 2H), 7.96 (dd, J = 8.0, 2.8 Hz, 1H), 7.55 (dt, J = 8.4,
2.0 Hz, 1H), 7.56 (m, 3H), 7.38 (dd, J = 6.8, 2.8 Hz, 1H), 2.80 (s,
3H); 13C NMR (100 MHz, CDCl3) d 160.7, 159.9, 151.5, 148.2,
140.2, 137.0, 136.2, 134.4, 130.6, 129.7, 129.2, 129.1, 129.0,
127.3, 126.7, 124.4, 123.3, 117.9, 107.8, 25.7; IR (powder)
2226 cmꢂ1; GC–MS (EI) m/z 321 (M+); Anal. (C22H15N3ꢃ1/8H2O) C,
H, N. HBr salt precipitated from MeOH/acetone. Anal.
(C22H15N3ꢃ2HBrꢃH2O) C, H, N.
6.24. 5-((6-Methylpyridin-2-yl)ethynyl)nicotinonitrile (28)
To a suspension of 5-bromonicotinonitrile (0.5 g, 2.5 mmol), 27
(0.5 g, 2.6 mmol), CuI (0.05 g, 0.25 mmol), Et3N (1.47 mL) and
Pd(PPh)4) (0.15 g) in degassed DMF (8 mL) was added tributylam-
monium fluoride (TBAF, 2.64 mL, 2.6 mmol) in THF (1.0 M) drop-
wise at 55 °C for 30 min. The reaction mixture was kept at 70 °C
overnight, then extracted with ether and washed with brine. The
organic layer was dried over magnesium sulfate and concentrated
to give the crude product. It was purified by flash chromatography
eluting with hexane/EtOAc (1:1) to provide the pure product
(0.3 g) in 52% yield; mp 162–164 °C; 1H NMR (400 MHz, CDCl3) d
8.99 (s, 1H), 8.83 (s, 1H), 8.13 (d, J = 2.0 Hz, 1H), 7.64 (m, 1H),
7.41 (d, J = 7.6 Hz, 1H), 7.21 (d, J = 8.0 Hz, 1H), 2.61 (s, 3H); 13C
NMR (100 MHz, CDCl3) d 155.6, 151.3, 149.0, 144.4, 141.7, 136.9,
133.4, 126.7, 125.1, 124.0, 114.7, 20.59; IR (powder) 2226 cmꢂ1
;
GC–MS (EI) m/z 219 (M+); Anal. (C14H9N3) C, H, N.
Acknowledgements
6.25. 5-Bromo-2-chloronicotinonitrile (29b)23
This work was funded by the NIDA-Intramural Research Pro-
gram and an NRSA Fellowship F32 NS049865 awarded by NINDS
to A.L.R. mGluR5 binding data, and a functional screens across all
mGluRs were provided by the National Institute of Mental Health’s
Psychoactive Drug Screening Program, Contract no. NO1MH32004
(NIMH PDSP). The NIDA Addiction Treatment Discovery Program
provided the computational toxicology data, thanks to Dr. Rik
Kline.
A solution of 5-bromo-2-hydroxynicotinonitrile (0.2 g, 1 mmol)
and PCl5 (0.21 g, 1 mmol) in POCl3 (3 mL) was refluxed overnight.
Aqueous NaOH solution (1 M) was added slowly to quench the
reaction with an ice bath. Product was extracted with ether. The
solvent was removed to give crude product, which was used in
the followed reaction without further purification. 1H NMR
(400 MHz, CDCl3) d 8.67 (s, 1H), 8.12 (s, 1H); GC–MS (EI) m/z
216, 218 (M+).
Supplementary data
6.26. 5-(2-Methylquinolin-7-yl)nicotinonitrile (30)14
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2010.03.053.
A suspension of 5-bromonicotinonitrile (0.09 g, 0.5 mmol), 9a
(0.2 g, 0.5 mmol), Na2CO3 (0.16 g, 1.5 mmol), and PdCl2(dppf)
(0.02 g) in DME (4.5 mL) and H2O (0.75 mL) was degassed and re-
acted under microwave condition at 140 °C for 30 min. Solvent was
removed under vacuum. The residue was extracted with EtOAc and
washed with brine. The organic layer was dried over magnesium
sulfate and evaporated to give the crude product. It was purified
by flash chromatography eluting with hexane/EtOAc (1:1) to give
the product (0.1 g) in 80% yield; mp 195–196 °C; 1H NMR
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