Discovery of 6-(pyrimidin-5-ylmethyl)quinoline-8-carboxamide negative allosteric modulators of metabotropic glutamate receptor subtype 5

Article abstract of DOI:10.1016/j.bmcl.2018.04.053

Based on previous work that established fused heterocycles as viable alternatives for the picolinamide core of our lead series of mGlu₅ negative allosteric modulators (NAMs), we designed a novel series of 6-(pyrimidin-5-ylmethyl)quinoline-8-carboxamide mGlu₅ NAMs. These new quinoline derivatives also contained carbon linkers as replacements for the diaryl ether oxygen atom common to our previously published chemotypes. Compounds were evaluated in a cell-based functional mGlu₅ assay, and an exemplar analog 27 was >60-fold selective versus the other seven mGlu receptors. Selected compounds were also studied in metabolic stability assays in rat and human S9 hepatic fractions and exhibited a mixture of P450- and non-P450-mediated metabolism.

Full text of DOI:10.1016/j.bmcl.2018.04.053

Accepted Manuscript
Discovery of 6-(pyrimidin-5-ylmethyl)quinoline-8-carboxamide negative al-
losteric modulators of metabotropic glutamate receptor subtype 5
Andrew S. Felts, Alice L. Rodriguez, Ryan D. Morrison, Anna L. Blobaum,
Frank W. Byers, J. Scott Daniels, Colleen M. Niswender, P. Jeffrey Conn, Craig
W. Lindsley, Kyle A. Emmitte
PII:
S0960-894X(18)30365-2
https://doi.org/10.1016/j.bmcl.2018.04.053
BMCL 25800
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
20 January 2018
18 April 2018
21 April 2018
Please cite this article as: Felts, A.S., Rodriguez, A.L., Morrison, R.D., Blobaum, A.L., Byers, F.W., Daniels, J.S.,
Niswender, C.M., Conn, P.J., Lindsley, C.W., Emmitte, K.A., Discovery of 6-(pyrimidin-5-ylmethyl)quinoline-8-
carboxamide negative allosteric modulators of metabotropic glutamate receptor subtype 5, Bioorganic & Medicinal
Chemistry Letters (2018), doi: https://doi.org/10.1016/j.bmcl.2018.04.053
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Discovery of 6-(pyrimidin-5-ylmethyl)quinoline-8-
carboxamide negative allosteric modulators of
metabotropic glutamate receptor subtype 5
Leave this area blank for abstract info.
Andrew S. Felts, Alice L. Rodriguez, Ryan D. Morrison, Anna L. Blobaum, Frank W. Byers, J. Scott Daniels,
Colleen M. Niswender, P. Jeffrey Conn, Craig W. Lindsley, and Kyle A. Emmitte

Bioorganic & Medicinal Chemistry Letters
Discovery of 6-(pyrimidin-5-ylmethyl)quinoline-8-carboxamide negative
allosteric modulators of metabotropic glutamate receptor subtype 5
Andrew S. Feltsa,b, Alice L. Rodrigueza,b, Ryan D. Morrisona,b, Anna L. Blobauma,b, Frank W. Byersa,b, J.
Scott Danielsa,b, Colleen M. Niswendera,b,c, P. Jeffrey Conna,b, Craig W. Lindsleya,b,d, and Kyle A.
Emmittea,b,d,
a Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, TN 37232 USA
b
Department of Pharmacology, Vanderbilt University, Nashville, TN 37232 USA
c Vanderbilt Kennedy Center, Vanderbilt University Medical Center, TN 37232 USA
d Department of Chemistry, Vanderbilt University, Nashville, TN 37232 USA
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
Based on previous work that established fused heterocycles as viable alternatives for the
picolinamide core of our lead series of mGlu5 negative allosteric modulators (NAMs), we
designed a novel series of 6-(pyrimidin-5-ylmethyl)quinoline-8-carboxamide mGlu5 NAMs.
These new quinoline derivatives also contained carbon linkers as replacements for the diaryl
ether oxygen atom common to our previously published chemotypes. Compounds were
evaluated in a cell-based functional mGlu5 assay, and an exemplar analog 27 was more than 60-
fold selective versus the other seven mGlu receptors. Selected compounds were also studied in
metabolic stability assays in rat and human S9 hepatic fractions and exhibited a mixture of
P450- and non-P450-mediated metabolism.
Keywords:
Metabotropic glutamate receptor subtype 5 (mGlu5)
Negative allosteric modulator (NAM)
Central nervous system (CNS)
G protein-coupled receptor (GPCR)
Quinoline
2009 Elsevier Ltd. All rights reserved.
Glutamate is the major excitatory transmitter in the
mammalian central nervous system and activates both ionotropic
(iGlu) and metabotropic glutamate (mGlu) receptors. While the
iGlu receptors are ligand-gated ion-channels, the mGlu receptors
are a family of eight G protein-coupled receptors (GPCRs).
Based on their structure, function, and effects on downstream
signaling pathways, the mGlu receptors have been classified into
three groups. Group I receptors (mGlu1 and mGlu5), which are
found in postsynaptic locations, are coupled via Gq to the
activation of phospholipase C. On the other hand, group II
receptors (mGlu2-3), which are found both pre and
postsynaptically, and group III receptors (mGlu4, mGlu6-8), which
are found primarily in presynaptic locations, are coupled via Gi/o
to the inhibition of adenylyl cyclase activity. The orthosteric
glutamate binding site of the mGlu receptors is contained in the
extracellular domain; however, the allosteric binding sites that
have been discovered to date are found in the transmembrane
domain.1,2
overcoming this hurdle that has proven successful for a variety of
mGlu receptors has been the use of approaches focused on
compounds that interact with an allosteric site.3 Among these
efforts, the design and optimization of negative allosteric
modulators (NAMs) of mGlu5 has been pursued extensively.4
Likewise, preclinical and clinical studies have indicated many
potentially interesting therapeutic applications for mGlu5
NAMs.1-4 In fact, phase II clinical trials have been conducted
with small molecule mGlu5 NAMs in fragile X syndrome
(FXS),5,6 major depressive disorder (MDD),7 obsessive-
compulsive disorder (OCD),8 and Parkinson’s disease levodopa-
induced dyskinesia (PD-LID).9,10 Regrettably, in most instances,
the primary efficacy endpoints were not met;5-9 however, some
secondary efficacy endpoints have been noted in both MDD7 and
PD-LID.10
Small molecule mGlu5 NAM research has been a major focus
of our group and recently culminated in the identification of a
highly optimized mGlu5 NAM candidate for clinical evaluation,
VU0424238 (1) (Fig. 1),11 a member of a series of picolinamide
mGlu5 NAMs. We also recently reported on the discovery of an
additional backup series of heterocyclic mGlu5 NAMs
The design of drug-like orthosteric ligands that are highly
selective for a single mGlu receptor versus the other seven mGlu
family members can be quite challenging. One method for

Corresponding author. Present address: Dept. of Pharmaceutical Sciences, UNT System College of Pharmacy, University of North Texas Health Science
Center, 3500 Camp Bowie Blvd., Fort Worth, TX 76107; Tel.; +1 817 735 0241; fax: +1 817 735 2603. E-mail address: kyle.emmitte@unthsc.edu

exemplified by [1,2,4]triazolo[1,5-a]pyridine-8-carboxamide 2.12
The discovery of 2 was based on a hypothesis that an internal
hydrogen bond between the amide NH and the 1-nitrogen of the
heteroaryl core of 2 would help orient the molecule similarly to
the postulated conformation of VU0424238 (1), where an
analogous hydrogen bond between the amide NH and the
picolinamide nitrogen was assumed likely. The discovery of 2
and its analogs opened the door to investigate other heterocyclic
cores such as quinoline-8-carboxamides. In fact, we synthesized
compound 3, a quinoline analog of 2, and verified that it was
similarly potent versus mGlu5. Still, to further enhance the
novelty of such new compounds and explore new SAR, we also
sought to modify additional portions of the scaffold (Fig. 1).
Specifically, we chose to replace the oxygen linker that had been
constant across the chemotypes found in both 1 and 2 as well as
other related series13,14 by exchanging it with several carbon
linkers. This Letter describes our efforts toward that end.
halogen exchange of 5-bromopyrimidine was carried out at low
temperature, and the resultant organolithium intermediate was
treated with 6 in situ to yield secondary alcohol 7. Oxidation of 7
was accomplished with manganese oxide to provide ketone 8. A
palladium-catalyzed reaction with zinc cyanide gave nitrile 9, and
subsequent acidic hydrolysis with heating gave the penultimate
acid 10. Formation of amide analogs 11-14 was accomplished
with phosphorous oxychloride in pyridine, conditions that we
have employed successfully in the past.11-14
Scheme 1. Reagents and conditions: (a) H2C=CHBF3K, PdCl2(dppf), NEt3,
EtOH, 80 ºC, 100%; (b) O3, CH2Cl2, MeOH, -78 ºC, then Me2S, -78 ºC to rt,
77%; (c) 5-bromopyrimidine, n-BuLi, THF, ether, -100 ºC, then 6, -100 ºC to
rt, 81%; (d) MnO2, CH2Cl2, 100%; (e) Zn(CN)2, Pd(PPh3)4, DMF, microwave,
140 ºC, 20 min, 70%; (f) H2SO4, AcOH, sealed tube, 120 ºC, 64%; (g)
H2NR2, POCl3, pyridine, -15 ºC, 14% (10→11), 21% (10→12), 42%
(10→13), 14% (10→14).
Figure 1. Picolinamide mGlu5 NAM candidate VU0424238 (1),
[1,2,4]triazolo[1,5-a]pyridine-8-carboxamide mGlu5 NAM 2, quinoline-8-
carboxamide 3, and our plan for development of a new quinoline-8-
carboxamide mGlu5 NAM scaffold.
Synthetic work on the aforementioned ether analogs had
employed nucleophilic aromatic substitution (SNAr) as the means
for joining the northern heteroaryl ring to the core of the
scaffold.11-14 Our plan to move to a carbon linker would thus
necessitate a substantially different synthetic approach (Scheme
1).15 Our first targets were a small set of ketone-linker containing
analogs 11-14. 6-Bromo-8-chloroquinoline 4 was converted to
vinyl analog 5 via a Suzuki cross-coupling reaction with
potassium vinyltrifluoroborate.16 Ozonolysis of 5 followed by
treatment with dimethyl sulfide afforded aldehyde 6. Metal-
Scheme 2. Reagents and conditions: (a) H2C=CHBF3K, PdCl2(dppf), NEt3, i-
PrOH, 100 ºC, 68% (8→15), 48% (22→23); (b) NaBH4, MeOH, THF, 0 ºC to
rt, 99%; (c) Et2NSF3, CH2Cl2, 40 ºC, 37% (16→17), 28% (8→22); (d) O3,
CH2Cl2, MeOH, -78 ºC, then Me2S, -78 ºC to rt, 24% (17→18) 29%
(23→24); (e) NaClO2, NaOAc, AcOH, H2O, H2NSO3H, dioxane, 94%
(18→19), 99% (24→25); (f) H2NR2, POCl3, pyridine, -15 ºC, 10% (19→20),
24% (19→21), 11-63% (25→26-36).
Monofluoromethylene
linker
analogs
20-21
and
difluoromethylene linker analogs 26-36 were prepared from

intermediate 8 (Scheme 2). Suzuki cross-coupling reaction with
potassium vinyltrifluoroborate as before afforded vinyl
intermediate 15. Reduction of the ketone was accomplished with
sodium borohydride to provide alcohol 16, which was treated
with diethylaminosulfur trifluoride (DAST) to yield 17.
Ozonolysis of 17 followed by treatment with dimethyl sulfide
afforded aldehyde 18, which was subsequently oxidized to
penultimate acid 19 with sodium chlorite. Conversion of 19 to
amides 20-21 was carried out as previously described.
Preparation of difluoromethylene linker analogs 26-36 was
analogous; however, the route sequence was modified such that
conversion of ketone 8 to difluoromethylene intermediate 22 was
the initial step in the synthesis.
coupling between 39 and 41 was used to join the northern
pyrimidine ring to the quinoline core and gave intermediate 42.
Ozonolysis of 42 followed by treatment with dimethyl sulfide
afforded ketone 43, which was reduced to alcohol 44 with
sodium borohydride. Alcohol 44 was methylated with potassium
bis(trimethylsilyl) amide and methyl iodide to yield 45.
Treatment of 45 with aqueous lithium hydroxide gave
penultimate acid 46, which was converted to analogs 47 and 48
as previously described. Intermediate 42 was also subjected to a
palladium catalyzed hydrogenation to afford reduced
intermediate 49, which was subsequently converted to analogs 51
and 52 utilizing previously outlined chemistry.
Ketone linker analogs 11-14 were the first compounds from
this work to be evaluated in our functional assay that measures
the inhibition of Ca2+ mobilization induced by an EC80
concentration of glutamate in HEK293A cells expressing rat
mGlu5 (Table 1).18 The heteroaryl amides were chosen as these
had proven effective for engendering mGlu5 potency in other
similar chemotypes.11,12,14 Interestingly, in this series, substitution
of the pyridin-2-yl amide proved critical for potency; both 12 and
13 were more than 10-fold more active than 11. The most potent
analog in this set was 4-methylthiazol-2-yl amide 14.
Table 1. mGlu5 activity of 6-ketoquinoline analogs
mGlu5 pIC50
(±SEM)a
mGlu5 IC50
(nM)a
% Glu max
(±SEM)a,b
12.5 ± 8.4c
1.5 ± 0.1
2.7 ± 1.0
1.3 ± 0.1
No.
< 5.0
> 10,000
417
11
12
13
14
6.38 ± 0.22
6.07 ± 0.45
6.77 ± 0.19
842
172
a Calcium mobilization rat mGlu5 assay; values are avg. of n ≥ 3
b Amplitude of response in the presence of 30 µM test compound as a
percentage of maximal response (100 µM glutamate); avg. of n ≥ 3
c Concentration response curve does not plateau
Scheme 3. Reagents and conditions: (a) H2C=CHBF3K, PdCl2(dppf), NEt3, n-
PrOH, sealed tube, 100 ºC, 53%; (b) Br2, CHCl3, 0 ºC, then DBU, 65%; (c)
bis(pinacolato)diboron, PdCl2(dppf), KOAc, DMSO, microwave, 120 ºC, 10
min, 99%; (d) PdCl2(dppf), 1M Na2CO3 (aq), microwave, 100 ºC, 10 min,
61%; (e) O3, CH2Cl2, MeOH, -78 ºC, then Me2S, -78 ºC to rt, 39%; (f)
NaBH4, MeOH, THF, 0 ºC to rt, 52%; (g) KN(SiMe3)2, MeI, DMF, PhMe, 0
ºC; 26%; (h) 1M LiOH (aq), dioxane, 99% (45→46), 99% (49→50); (i)
H2NR2, POCl3, pyridine, -15 ºC, 26% (46→47), 27% (46→48), 11%
(50→51), 8% (50→52); (j) H2 (1 atm), 10% Pd/C, MeOH, 96%.
Figure 2. Major metabolic pathway of compound 14 in rat whole blood at 37
ºC (1 h).
With the knowledge that ketones can be metabolically
unstable, we decided to study that possibility with 14. Incubation
of 14 in rat whole blood at 37 ºC for one hour showed near
complete conversion to a metabolite thought to be the result of
ketone reduction (Fig. 2). To verify this result, the secondary
alcohol 53 was prepared through sodium borohydride reduction
of 14. Indeed, alcohol 53 was confirmed as the major metabolite
from the rat whole blood stability study. To determine if alcohol
53 might be an active metabolite, it was also tested in the mGlu5
Synthesis of analogs with methoxy (47-48) and methyl (51-
52) substituents at the methylene linker employed an alternative
method for joining the northern heteroaryl ring to the quinoline
core (Scheme 3). Here, a Suzuki cross-coupling reaction between
potassium vinyltrifluoroborate and 5-bromopyrimidine 37 was
used to access vinyl intermediate 38. Bromination of the olefin,
followed by treatment with 1,8-diazabicycloundec-7-ene (DBU),
gave vinyl bromide 39. Meanwhile, a palladium-catalyzed
coupling of methyl 6-bromoquinoline-8-carboxylate 40 with
bis(pinacolato)diboron provided boronic ester 41.17 A Suzuki
functional assay; however, it was only a weak antagonist (IC50
>
10 μM). Finally, to verify if this metabolic event occurred in

vivo, a rat pharmacokinetics (PK) study was conducted with 14
using intravenous (IV) dosing (Table 2). Not surprisingly,
compound 14 was consumed quite rapidly with a corresponding
appearance of metabolite 53 in the plasma. With such data in
hand, we were keen to evaluate non-ketone carbon linkers.
substitution as all new pyridin-2-yl analogs (28-35) were less
potent than 5-fluoropyridin-2-yl derivative 26. Likewise,
increasing the size of the 4-substituent on the thiazol-2-yl amide
from methyl (27) to cyclopropyl (36) led to a 3.5-fold drop in
mGlu5 potency.
Table 2. Rat pharmacokinetics of 14 and metabolite 53a,b
Table 4. mGlu5 activity of quinoline difluoromethylene linker analogs
mGlu5
pIC50
mGlu5
IC50
% Glu
max
No.
Series
R
(±SEM)a
(nM)a
(±SEM)a,b
A
B
A
A
A
A
A
A
A
A
B
5-F
Me
6.41 ± 0.28
6.79 ± 0.31
5.96 ± 0.23
5.44 ± 0.21
5.79 ± 0.24
6.17 ± 0.26
< 4.5
392
161
4.5 ± 2.2
1.4 ± 0.3
2.7 ± 0.5
7.8 ± 6.2
7.1 ± 4.7
3.0 ± 0.6
―
26
27
28
29
30
31
32
33
34
35
36
Compound 14
half-life (min)
MRTc (min)
Clp (mL/min/kg)
VSS (L/kg)
a n=2 male Sprague-Dawley rats; dose = 1.0 mg/kg
b IV formulation: 10% ethanol, 90% PEG 400
c MRT = mean residence time
Metabolite 53
half-life (min)
MRTc (min)
Clp (mL/min/kg)
VSS (L/kg)
6-Me
6-Et
1100
30
19
171
107
94
3600
6-OMe
5-Me
5-CN
4-Me
4-OMe
4-CN
cyc-Pr
1610
3430
50
676
10
>30,000
>10,000
>30,000
>30,000
558
< 5.0
44 ± 12c
―
< 4.5
< 4.5
―
6.25 ± 0.27
3.0 ± 0.5
Table 3. mGlu5 activity of quinoline linker analogs
a Calcium mobilization rat mGlu5 assay; values are avg. of n ≥ 3
b Amplitude of response in the presence of 30 µM test compound as a
percentage of maximal response (100 µM glutamate); avg. of n ≥ 3
c Concentration response curve does not plateau
Table 5. Metabolic stability in rat and human S9 hepatic fractions
mGlu5
pIC50
mGlu5
% Glu
max
No.
Series
X
IC50
(±SEM)a
(nM)a
(±SEM)a,b
A
B
A
B
A
B
A
B
CHF
CHF
6.66 ± 0.23
6.42 ± 0.25
6.41 ± 0.28
6.79 ± 0.31
5.46 ± 0.30
5.76 ± 0.25
5.82 ± 0.23
6.23 ± 0.18
217
378
1.5 ± 0.3
1.7 ± 0.1
4.5 ± 2.2
1.4 ± 0.3
2.9 ± 0.1
1.8 ± 0.3
1.5 ± 0.2
1.4 ± 0.0
20
21
26
27
47
48
51
52
CF2
392
human S9
CF2
161
No.
+NADPH
–NADPH
% NADPH
dependent
CHOMe
CHOMe
CHMe
CHMe
3480
1750
1520
589
a
b
a
b
CLINT
CLHEP
17.3
CLINT
CLHEP
12.6
98.2
110
31.3
27%
43%
21
27
17.6
19.6
10.1
a Calcium mobilization rat mGlu5 assay; values are avg. of n ≥ 3
b Amplitude of response in the presence of 30 µM test compound as a
percentage of maximal response (100 µM glutamate); avg. of n ≥ 3
rat S9
No.
+NADPH
–NADPH
% NADPH
dependent
a
b
a
b
CLINT
CLHEP
51.8
CLINT
CLHEP
23.2
199
163
34.7
38.3
55%
49%
21
27
Table 3 presents the SAR for four new carbon linkers in the
context of the 5-fluoropyridin-2-yl and 4-methylthiazol-2-yl
amides, groups that had demonstrated activity in this series and
other favorable properties in related historical series.11,12,14 Both
the monofluoromethylene analogs 20-21 and difluoromethylene
analogs 26-27 demonstrated potency on par with ketone
comparators 13 and 14 (Table 1). On the other hand, larger
substituents on the methylene carbon in the form of methoxy (47-
48) and methyl (51-52) negatively impacted mGlu5 activity.
Analogs 20-21 and 47-52 were tested as racemates. With the
most potent compound (27) bearing the difluoromethylene linker,
we prepared and tested several additional amide derivatives with
that linker (Table 4). SAR here showed little tolerance for further
49.0
24.8
a CLINT = intrinsic clearance in units of mL/min/kg
b CLHEP = predicted hepatic clearance in units of mL/min/kg calculated
according to the formula: CLHEP = (QH × CLINT)/(QH + CLINT) where
QH = hepatic flow of 21 (human) or 70 (rat)19
We have previously demonstrated that an unsubstituted
pyrimidin-5-yl ether moiety is a potential site for aldehyde
oxidase (AO) and/or xanthine oxidase (XO)-mediated
metabolism.11,20-22 Since predicting human pharmacokinetics for
compounds that are largely metabolized by AO and/or XO can be
challenging due to their variable expression across preclinical
species,20,23 we were interested in profiling some of these new
compounds to understand what fraction of their metabolism was

mediated by P450 versus non-P450 mechanisms. Thus, we
evaluated 21 and 27 in metabolic stability assays in rat and
human liver S9 hepatic fractions both with and without the
addition of NADPH (Table 5).24 Since NADPH is required for
cytochrome P450-mediated oxidations, experiments that lack
NADPH provide an assessment of non-P450-mediated
metabolism. Whereas VU0424238 (1) was metabolized almost
exclusively by AO/XO,20 21 and 27 demonstrated a mixture of
P450- and non-P450-mediated metabolism. Interestingly, while
21 exhibited a higher percentage of P450-mediated metabolism
in rat S9 than in human S9 hepatic fractions, the profile for 27
was similar across species. Such results highlight how subtle the
SAR can be for P450 versus non-P450-mediated metabolism. Of
note, while these experiments do not conclusively identify
AO/XO as the specific mechanism for the non-P450 mediated
component of metabolism, our prior studies with related
unsubstituted pyrimidin-5-yl ethers20-22 suggest AO/XO
involvement.
it is worth noting that such trends may be somewhat general with
the potential to translate to other chemotypes designed to interact
with a variety of targets.
Acknowledgments
We thank NIMH (U19 MH097056), NIDA (R01 DA023947),
Seaside Therapeutics (VUMC33842) and The William K.
Warren Foundation for their support of our programs in the
development of negative allosteric modulators of mGlu5.
References and notes
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295.
3. Lindsley, C. W.; Emmitte, K. A.; Hopkins, C. R.; Bridges, T. M.;
Gregory, K. J.; Niswender, C. M.; Conn, P. J. Chem. Rev. 2016, 116,
6707.
Since analog 27 was the most potent analog in this series, we
chose to profile that compound further (Table 6). Thus,
selectivity was assessed versus the other seven mGlu receptors
utilizing fold-shift experiments that assess the effect of 10 μM 27
on the concentration response curves (CRC) of an orthosteric
agonist in cell lines expressing each individual mGlu receptor.25
Compound 27 was inactive versus the other seven mGlu receptor
subtypes, indicating a selectivity for mGlu5 of at least 60-fold.
An analogous fold-shift experiment was conducted in HEK293A
cells expressing human mGlu5, and not surprisingly, 10 μM 27
fully blocked the glutamate CRC in that cell line. This result was
consistent with prior studies on compounds from related
chemotypes where the difference between rat and human mGlu5
activity was negligible.11,14 The extent to which 27 was bound to
proteins was also assessed, and the compound was highly bound
in both rat (fu = 0.015) and human (fu = 0.014) plasma.26 Finally,
a P450 inhibition profile was determined for 27, and the
compound was a moderate inhibitor of CYP3A4 and CYP2C9
and a potent inhibitor of CYP1A2.26
4. Emmitte, K. A. Expert Opin. Ther. Pat. 2017, 27, 691.
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Niswender, C. M.; Daniels, J. S.; Jones, C. K.; Conn, P. J.; Lindsley, C.
W.; Emmitte, K. A. J. Med. Chem. 2017, 60, 5072.
12. Felts, A. S.; Rodriguez, A. L.; Morrison, R. D.; Bollinger, K. A.;
Venable, D. F.; Blobaum, A. L.; Byers, F. W.; Thompson Gray, A.;
Daniels, J. S.; Niswender, C. M.; Jones, C. K.; Conn, P. J.; Lindsley, C.
W.; Emmitte, K. A. Bioorg. Med. Chem. Lett. 2017, 27, 4858.
13. Bates, B. S.; Rodriguez, A. L.; Felts, A. S.; Morrison, R. D.; Venable, D.
F.; Blobaum, A. L.; Byers, F. W.; Lawson, K. P.; Daniels, J. S.;
Niswender, C. M.; Jones, C. K.; Conn, P. J.; Lindsley, C. W.; Emmitte,
K. A. Bioorg. Med. Chem. Lett. 2014, 24, 3307.
Table 6. Comparison of 27 to VU0424238 (1) and 2
1
pharmacology
11
2
27
mGlu5 IC50 (nM)
20
161
>60
selectivity vs. other mGlus
>900
>500
plasma protein bindinga
rat plasma fu
0.106
0.120
0.066
0.071
0.015
0.014
human plasma fu
14. Felts, A. S.; Rodriguez, A. L.; Morrison, R. D.; Venable, D. F.; Manka, J.
T.; Bates, B. S.; Blobaum, A. L.; Byers, F. W.; Daniels, J. S.; Niswender,
C. M.; Jones, C. K.; Conn, P. J.; Lindsley, C. W.; Emmitte, K. A. Bioorg.
Med. Chem. Lett. 2013, 23, 5779.
P450 inhibition (IC50 in μM)b
CYP3A4
CYP2D6
CYP2C9
CYP1A2
>30
>30
12.1
1.0
>30
>30
>30
15.1
5.9
26.5
5.3
15. For detailed synthetic procedures see Conn, P. J.; Lindsley, C. W.;
Emmitte, K. A.; Felts, A. S. US Patent 9,533,982, January 3, 2017.
Synthesis of compound 27 is presented here as an exemplar compound
from this series: 8-Chloro-6-vinylquinoline (5): 6-Bromo-8-
chloroquinoline 4 (1.49 g, 6.14 mmol), PdCl2(dppf) (100 mg, 0.122
mmol), potassium vinyltrifluoroborate (823 mg, 6.14 mmol) and
triethylamine (857 μL, 6.15 mmol) were dissolved in ethanol (61 mL) in
a round-bottom flask and heated to 80 ºC until the reaction was judged
complete by LCMS (~2 h). The reaction was cooled, filtered through
celite, and washed with 1:1 hexanes:ethyl acetate. The solvents were
removed in vacuo, and the crude material was purified by flash
chromatography on silica gel to afford 1.17 g (100%) of the title
compound as an off-white solid: 1H NMR (400 MHz, DMSO-d6) δ 8.96
(dd, J = 4.2, 1.6 Hz, 1H), 8.40 (dd, J = 8.3, 1.6 Hz, 1H), 8.19 (d, J = 1.8
Hz, 1H), 7.96 (d, J = 1.6 Hz, 1H), 7.63 (dd, J = 8.3, 4.2 Hz, 1H), 6.89
(dd, J = 17.7, 10.9 Hz, 1H), 6.10 (d, J = 17.6 Hz, 1H), 5.46 (d, J = 11.0
Hz, 1H); ES-MS [M+H]+: 190.0. 8-Chloroquinoline-6-carbaldehyde (6):
Intermediate 5 (4.08 g, 21.5 mmol) was dissolved in CH2Cl2 (108 mL)
and methanol (108 mL) and cooled to -78 ºC. Ozone was bubbled
through the reaction until disappearance of 5 was observed by TLC. Air
0.3
a
Fraction unbound (fu) as measured by an equilibrium dialysis assay
using rat or human plasma
b Assayed in pooled human liver microsomes in the presence of
NADPH with CYP-specific probe substrates
When compared to clinical candidate VU0424238 (1) or
backup analog 2, compound 27 does not offer as attractive of an
overall profile (Table 6), and significant room for optimization
within this series remains. Nonetheless, the work described
herein demonstrates that a variety of single carbon linkers,
including both sp2 and sp3 hybridized carbons, can be accessed
from common intermediates and function as competent isosteric
replacements for diaryl ethers. In addition, the utility of the
quinoline core is consistent with our previously published work
utilizing
nitrogen-containing
fused
heterocycles12
as
replacements for the picolinamide core of our lead series. Finally,

was bubbled through the reaction to remove excess ozone and dimethyl
sulfide (47.7 mL, 645 mmol) was added. The reaction was allowed to
warm to room temperature and stirred for 2 h. Water was added, and the
reaction was extracted with CH2Cl2 (3x). The combined organics were
dried over MgSO4, filtered, and concentrated in vacuo. Purification by
flash chromatography on silica gel afforded 3.19 g (77%) of the title
compound as a white solid: 1H NMR (400 MHz, DMSO-d6) δ 10.15 (s,
1H), 9.17 (dd, J = 4.12, 1.7 Hz, 1H), 8.70 (dd, J = 8.3, 1.6 Hz, 1H), 8.66
(d, J = 1.6 Hz, 1H), 8.26 (d, J = 1.7 Hz, 1H), 7.79 (dd, J = 8.3, 4.2 Hz,
1H); ES-MS [M+H]+: 192.1. (8-Chloroquinolin-6-yl)(pyrimidin-5-
yl)methanol (7): 5-Bromopyrimidine (2.65 g, 16.7 mmol) was dissolved
in THF (34 mL) and ether (34 mL) in an oven-dried round bottom flask
and cooled to -100 ºC. n-Butyllithium (1.6M in hexanes) (10.4 mL, 16.6
mmol) was added dropwise while ensuring the internal reaction
temperature remained below -90 ºC. After addition the reaction was
stirred for 15 minutes at -100 ºC and intermediate 6 (3.19 g, 16.7 mmol)
was added dropwise as a solution in THF (34 mL) while ensuring the
internal reaction temperature remained below -90 ºC. The reaction was
then allowed to gradually warm to room temperature. The reaction was
quenched with water, and the mixture was extracted with ethyl acetate
(3x). The combined organics were dried over MgSO4, filtered, and
concentrated in vacuo. Purification by flash chromatography on silica gel
afforded 3.67 g (81%) of the title compound as a white solid: 1H NMR
(400 MHz, DMSO-d6) δ 9.09 (s, 1H), 8.99 (dd, J = 4.2, 1.6 Hz, 1H), 8.86
(s, 2H), 8.46 (dd, J = 8.4, 1.6 Hz, 1H), 8.06 (d, J = 1.4 Hz, 1H), 7.98 (d, J
= 1.7 Hz, 1H), 7.64 (dd, J = 8.3, 4.2 Hz, 1H), 6.58 (d, J = 4.2 Hz, 1H),
6.06 (d, J = 4.2 Hz, 1H); ES-MS [M+H]+: 272.1. (8-Chloroquinolin-6-
yl)(pyrimidin-5-yl)methanone (8): Intermediate 7 (3.67 g, 13.5 mmol)
was dissolved in CH2Cl2 (113 mL), and MnO2 (8.22g, 94.5 mmol) was
added. The reaction was stirred overnight, filtered, and concentrated in
vacuo to afford 3.63 g (100%) of the title compound as a white solid: 1H
NMR (400 MHz, DMSO-d6) δ 9.48 (s, 1H), 9.21 (s, 2H), 9.17 (dd, J =
4.2, 1.7 Hz, 1H), 8.68 (dd, J = 8.4, 1.7 Hz, 1H), 8.54 (d, J = 1.8 Hz, 1H),
8.29 (d, J = 1.8 Hz, 1H), 7.78 (dd, J = 8.3, 4.2 Hz, 1H); ES-MS [M+H]+:
270.1. 8-Chloro-6-(difluoro(pyrimidin-5-yl)methyl)quinoline (22): DAST
(1.7 mL, 13 mmol) was added to intermediate 7 (500 mg, 1.85 mmol)
dissolved in CH2Cl2 (12.5 mL) in a sealed vessel, and the reaction was
heated to 40 ºC overnight. An additional portion of DAST (500 µL, 6.5
mmol) was added, and the reaction was heated at 40 ºC for an additional
24 hours. The reaction was cooled and quenched by slow addition to ice.
The layers were separated, and the aqueous was extracted with CH2Cl2.
The combined organics were dried over MgSO4, filtered, and
H2O (1.4 mL). The reaction was stirred for 1.5 hours and concentrated to
approximately one-third its total volume. The resulting solution was
extracted with 3:1 CHCl3/IPA (3x), and the combined organics were
dried over MgSO4, filtered, and concentrated in vacuo to afford 22 mg
(99%) of the title compound as an off-white solid: 1H NMR (400 MHz,
DMSO-d6) δ 9.40 (s, 1H), 9.22-9.14 (m, 3H), 8.82 (d, J = 7.9 Hz, 1H),
8.71 (s, 1H), 8.59 (s, 1H), 7.95-7.86 (m, 1H); ES-MS [M+H]+: 302.2. 6-
(Difluoro(pyrimidin-5-yl)methyl)-N-(4-methylthiazol-2-yl)quinoline-8-
carboxamide (27): Intermediate 25 (7.0 mg, 0.023 mmol) and 4-
methylthiazol-2-amine (2.9 mg, 0.025 mmol) were dissolved in pyridine
(0.75 mL) in a flame-dried round-bottom flask. The reaction was cooled
to -15 ºC and phosphorus oxychloride (2.4 μL, 0.026 mmol) was added
while ensuring the temperature remained at -15 ºC. After stirring for 30
min at -15 ºC, and the reaction was quenched with ice-water and
neutralized with 10% aqueous K2CO3. The mixture was extracted with
EtOAc (3x), and the combined organics were dried over MgSO4, filtered,
and concentrated in vacuo. Purification by reverse-phase chromatography
afforded 5.8 mg (63%) of the title compound as a white solid. 1H NMR
(400 MHz, DMSO-d6) δ 9.41 (s, 1H), 9.28 (d, J = 2.8 Hz, 1H), 9.19 (s,
2H), 8.77 (d, J = 8.0 Hz, 1H), 8.74-8.64 (m, 2H), 7.87 (dd, J = 4.2, 8.2
Hz, 1H), 6.86 (s, 1H), 2.31 (s, 3H); ES-MS [M+H]+: 398.3; HRMS,
calc’d for C17H10F2N6O2 [M], 397.0811; found 397.0809.
16. Molander, G. A.; Rodríguez Rivero, M. Org. Lett. 2002, 4, 107.
17. Ishiyama, T.; Murata, M.; Miyaura, N. J. Org. Chem. 1995, 60, 7508.
18. For a detailed description of the mGlu5 functional assay, see reference 11.
19. Davies, B.; Morris, T. Pharm. Res. 1993, 10, 1093.
20. Crouch, R. D.; Blobaum, A. L.; Felts, A. S.; Conn, P. J.; Lindsley, C. W.
Drug Metab. Dispos. 2017, 45, 1245.
21. Crouch, R. D.; Morrison, R. D.; Byers, F. W.; Lindsley, C. W.; Emmitte,
K. A.; Daniels, J. S. Drug Metab. Dispos. 2016, 44, 1296.
22. Morrison, R. D.; Blobaum, A. L.; Byers, F. W.; Santomango, T. S.;
Bridges, T. M.; Stec, D.; Brewer, K. A.; Sanchez-Ponce, R.; Corlew, M.
M.; Rush, R.; Felts, A. S.; Manka, J.; Bates, B. S.; Venable, D. F.;
Rodriguez, A. L.; Jones, C. K.; Niswender, C. M.; Conn, P. J.; Lindsley,
C. W.; Emmitte, K. A.; Daniels, J. S. Drug Metab. Dispos. 2012, 40,
1834.
23. Kitamura, S.; Sugihara, K.; Ohta, S. Drug-metabolizing ability of
molybdenum hydroxylases. Drug Metab. Pharmacokinet. 2006, 21, 83.
24. For a detailed description of the S9 metabolic stability assays, see
reference 21.
25. For a detailed description of the mGlu fold-shift assays employed to
assess selectivity, see reference 11.
concentrated in vacuo. Purification by flash chromatography on silica gel
afforded 152 mg (28%) of the title compound as a yellow solid: 1H NMR
(400 MHz, DMSO-d6) δ 9.39 (s, 1H), 9.19 (dd J = 4.3, 1.7 Hz, 1H), 9.17
(s, 2H), 8.75-8.69 (m, 2H), 8.67 (dd, J = 8.4, 1.6 Hz, 1H), 7.83 (dd, J =
8.4, 4.3 Hz, 1H); ES-MS [M+H]+: 291.9. 6-(Difluoro(pyrimidin-5-
yl)methyl)-8-vinylquinoline (23): Intermediate 22 (152 mg, 0.521 mmol),
PdCl2(dppf) (17 mg, 0.021 mmol), potassium vinyltrifluoroborate (84
mg, 0.63 mmol), and triethylamine (73 μL, 0.52 mmol) were dissolved in
isopropanol (3.5 mL) in a round-bottom flask and heated to 100 ºC until
the reaction was judged complete by LCMS (~2 h). The reaction was
cooled, filtered through celite, and washed with 5% methanol in CH2Cl2.
The solvents were removed in vacuo, and the crude material was purified
by flash chromatography on silica gel to afford 71 mg (48%) of the title
compound as a pale-yellow solid: 1H NMR (400 MHz, DMSO-d6) δ 9.38
(s, 1H), 9.18 (s, 2H), 9.04 (dd, J = 4.2, 1.7 Hz, 1H), 8.50 (dd, J = 8.3, 1.6
Hz, 1H), 8.27-8.17 (m, 2H), 7.93 (dd, J = 18.0, 11.3 Hz, 1H), 7.66 (dd, J
= 8.3, 4.2 Hz, 1H), 6.21 (d, J = 18.0 Hz, 1H), 5.56 (d, J = 11.3 Hz, 1H);
ES-MS [M+H]+: 284.0. 6-(Difluoro(pyrimidin-5-yl)methyl)quinoline-8-
carbaldehyde (24): Intermediate 23 (71 mg, 0.25 mmol) was dissolved in
CH2Cl2 (2.5 mL) and cooled to -78 ºC. Ozone was bubbled through the
reaction until disappearance of 23 was observed by TLC. Air was
bubbled through the reaction to remove excess ozone and dimethyl
sulfide (556 µL, 7.52 mmol) was added. The reaction was allowed to
warm to room temperature and stirred for 2 h. The reaction was
26. For a detailed description of the equilibrium dialysis plasma protein
binding assays and cytochrome P450 cocktail inhibition assay in pooled
human liver microsomes, see reference 11.
 New negative allosteric modulators of metabotropic
glutamate receptor subtype 5
 Quinoline-8-carboxamides are functional as a
picolinamide replacement
 Certain carbon-based linkers are alternatives to an
ether linker
concentrated in vacuo, and purification by flash chromatography on silica
gel afforded 21 mg (29%) of the title compound as a yellow solid: 1H
NMR (400 MHz, CDCl3) δ 9.52 (s, 1H), 7.63 (s, 1H), 7.48 (d, J = 3.6 Hz,
1H), 7.26 (s, 2H), 6.71 (d, J = 8.2 Hz, 1H), 6.66-6.60 (m, 2H), 5.98 (dd, J
= 8.4, 4.3 Hz, 1H); ES-MS [M+H]+: 286.0. 6-(Difluoro(pyrimidin-5-
yl)methyl)quinoline-8-carboxylic acid (25): Intermediate 24 (21 mg,
0.074 mmol) was dissolved in dioxane (1.5 mL) and a solution of sodium
acetate (21 mg, 0.26 mmol) in AcOH (484 µL) and H2O (484 µL) was
added followed by a solution of sulfamic acid (14 mg, 0.15 mmol) in
H2O (1.1 mL) and a solution of sodium chlorite (17 mg, 0.18 mmol) in