Discovery of a novel 2,3-dimethylimidazo[1,2-a]pyrazine-6-carboxamide M4 positive allosteric modulator (PAM) chemotype

Article abstract of DOI:10.1016/j.bmcl.2019.126812

This Letter details our efforts to discover structurally unique M₄ PAMs containing 5,6-heteroaryl ring systems. In an attempt to improve the DMPK profiles of the 2,3-dimethyl-2H-indazole-5-carboxamide and 1-methyl-1H-benzo[d][1,2,3]triazole-6-carboxamide cores, we investigated a plethora of core replacements. This exercise identified a novel 2,3-dimethylimidazo[1,2-a]pyrazine-6-carboxamide core that provided improved M₄ PAM activity and CNS penetration.

Full text of DOI:10.1016/j.bmcl.2019.126812

Journal Pre-proofs
Discovery of a novel 2,3-dimethylimidazo[1,2-a]pyrazine-6-carboxamide M4
positive allosteric modulator (PAM) chemotype
Kayla J. Temple, Julie L. Engers, Madeline F. Long, Katherine J. Watson,
Sichen Chang, Vincent B. Luscombe, Matthew T. Jenkins, Alice L. Rodriguez,
Colleen M. Niswender, Thomas M. Bridges, P. Jeffrey Conn, Darren W. Engers,
Craig W. Lindsley
PII:
S0960-894X(19)30781-4
DOI:
https://doi.org/10.1016/j.bmcl.2019.126812
BMCL 126812
Reference:
Bioorganic & Medicinal Chemistry Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
16 October 2019
4 November 2019
6 November 2019
Please cite this article as: Temple, K.J., Engers, J.L., Long, M.F., Watson, K.J., Chang, S., Luscombe, V.B., Jenkins,
M.T., Rodriguez, A.L., Niswender, C.M., Bridges, T.M., Jeffrey Conn, P., Engers, D.W., Lindsley, C.W., Discovery
of a novel 2,3-dimethylimidazo[1,2-a]pyrazine-6-carboxamide M4 positive allosteric modulator (PAM) chemotype,
Bioorganic & Medicinal Chemistry Letters (2019), doi: https://doi.org/10.1016/j.bmcl.2019.126812
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Discovery of a novel 2,3-dimethylimidazo[1,2-a]pyrazine-
6-carboxamide M4 positive allosteric modulator (PAM)
chemotype
Leave this area blank for abstract info.
Kayla J. Templea,b, Julie L. Engersa,b, Madeline F. Longa,b, Katherine J. Watsona,b, Sichen Changa,b, Vincent B. Luscombea,b
,
Matthew T. Jenkinsa,b, Alice L. Rodrigueza,b, Colleen M. Niswendera,b,d, Thomas M. Bridgesa,b, P. Jeffrey Conna,b,d, Darren W.
Engersa,b*, Craig W. Lindsleya,b,c*
This Work
Previous Work
Cl
N
O
O
O
R
R
N
Cl
N
N
N
N
N
N
H
H
N
N
= R
N
H
N
N
1a,
2,
VU6014364
VU6016265
19p,
hM4
VU6017405
132 nM
hM4 = 308 nM
rat CLHEP = 20 mL/min/kg
human CLHEP = 13 mL/min/kg
rat fu,plasma = 0.042
hM4 = 675 nM
=
rat CLHEP = 8.7 mL/min/kg
human CLHEP = 21 mL/min/kg
rat fu,plasma = 0.024
rat CLHEP = 40 mL/min/kg
human CLHEP = 13 mL/min/kg
rat fu,plasma = 0.009
human fu,plasma = 0.043
rat fu,brain= 0.032
human fu,plasma = 0.132
rat fu,brain= 0.053
human fu,plasma = 0.040
rat fu,brain= 0.034
rat brain:plasma Kp= 0.05
rat brain:plasma Kp,uu = 0.04
rat brain:plasma Kp< 0.05
rat brain:plasma Kp,uu < 0.11
0.29
rat brain:plasma Kp=
rat brain:plasma Kp,uu
1.09
=

Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com
Discovery of a novel 2,3-dimethylimidazo[1,2-a]pyrazine-6-carboxamide M4
positive allosteric modulator (PAM) chemotype
Kayla J. Templea,b, Julie L. Engersa,b, Madeline F. Longa,b, Katherine J. Watsona,b, Sichen Changa,b, Vincent
B. Luscombea,b, Matthew T. Jenkinsa,b, Alice L. Rodrigueza,b, Colleen M. Niswendera,b,d,e, Thomas M.
Bridgesa,b, P. Jeffrey Conna,b,d,e, Darren W. Engersa,b*, Craig W. Lindsleya,b,c,e*
aVanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University, Nashville, TN 37232, USA
bDepartment of Pharmacology, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
cDepartment of Chemistry, Vanderbilt University, Nashville, TN 37232, USA
dVanderbilt Kennedy Center, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
eVanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, TN 37232, USA
ARTICLE INFO
ABSTRACT
Article history:
Received
Revised
Accepted
Available online
This Letter details our efforts to discover structurally unique M4 PAMs containing 5,6-heteroaryl
ring systems. In an attempt to improve the DMPK profiles of the 2,3-dimethyl-2H-indazole-5-
carboxamide and 1-methyl-1H-benzo[d][1,2,3]triazole-6-carboxamide cores, we investigated a
plethora of core replacements. This exercise identified a novel 2,3-dimethylimidazo[1,2-
a]pyrazine-6-carboxamide core that provided improved M4 PAM activity and CNS penetration.
Keywords:
M4
Muscarinic acetylcholine receptor
Positive Allosteric modulator (PAM)
Structure Activity Relationship (SAR)
2019 Elsevier Ltd. All rights reserved.
Muscarinic acetylcholine receptor subtype 4 (M4) positive
allosteric modulators (PAMs) have garnered much attention as
potential drug targets as novel treatments for various neurological
disorders such as Parkinson’s disease,1 Huntington’s disease,2 and
schizophrenia (both the positive and negative symptom clusters).3-
5,6-heteroaryl ring systems lacking the β-amino carboxamide
moiety.
Our study began with modifications to the 3-methyl-1H-
indazole core of 1a (Table 1). First, we optimized our original
methylation protocol, which gave predominately the undesired
6
Recent efforts from our group have focused on eliminating the
Previous Work
Poor DMPK Profiles
This Work
classical β-amino carboxamide pharmacophore of many historical
M4 PAMs as this moiety engenders physiochemical and DMPK
properties that preclude candidate development.7-15 While our
endeavors to date have provided structurally distinct potent human
and rat M4 PAMs, the DMPK profiles of said compounds have
been rather lackluster. Previously, we reported several new M4
PAM chemotypes, two of which are depicted in Figure 1, analogs
1a & 2.16 These analogs exemplify new M4 PAM chemotypes that
possess activity, yet leave much to be desired in terms of
pharmacological profiles.
O
O
5
O
3
R
R
4
9
N
N
N
N
2N
N
H
H
NH
N
7
N
Het
8
1
1a,
2,
VU6014364
VU6016265
hM4 = 308 nM
hM4 = 675 nM
Cl = R
rat CLHEP = 20 mL/min/kg
human CLHEP = 13 mL/min/kg
rat fu,plasma = 0.042
rat CLHEP = 8.7 mL/min/kg
human CLHEP = 21 mL/min/kg
rat fu,plasma = 0.024
Cl
N
human fu,plasma = 0.043
rat fu,brain= 0.032
human fu,plasma = 0.132
rat fu,brain= 0.053
Various Heterocycles
rat brain:plasma Kp= 0.05
rat brain:plasma Kp,uu = 0.04
rat brain:plasma Kp< 0.05
rat brain:plasma Kp,uu < 0.11
In a new venture to identify novel M4 PAM chemotypes
possessing improved DMPK profiles, we elected to pursue a
scaffold hopping approach utilizing teh structures of 1a and 2 as a
starting point. In this Letter, we will discuss the scaffold hopping
exercise and the identification of fundamentally new M4 PAM
chemotypes. In general, we wished to explore a large selection
Figure1. Scaffold hopping concept from M4 PAMs 1a and 2 to generate
structurally unique M4 PAM chemotypes.
1,3-dimethylated indazole (Scheme 1). Instead, we chose to use
the methyl Meerwein salt, which provided the desired 2,3-
dimethylated indazole as the major product. With our optimal
conditions in hand, various commercial 5-bromo-3-substituted-

1H-indazoles could be readily alkylated at the 2-position with
either trimethyloxonium tetrafluoroborate or triethyloxonium
tetrafluoroborate (1d-h). To generate fluorinated analogs 1b and
1c, we first needed to synthesize indazoles 11 and 15 (Scheme 2).
Analog 11 could readily be synthesized by condensing hydrazine
with commercially available 2’-fluoroacetophenone 9 to yield
intermediate 10 which was then methylated to afford bromide 11.
compounds were >98% pure by LCMS (214 nm, 254 nm and
ELSD). After evaluating analogs 1 against human M4, it became
very clear that minor modifications to the 2,3-dimethylated
indazole core lead to a decrease in potency (Table 1).
This initial exercise led us to turn our attention to evaluating
new 5,6-heteroaryl ring systems as potential M4 PAM cores. The
bromide or carboxylic acid precursors (16 or 18) for several of
these cores were commercially available (19e, 19g, 19i, and 19l)
R
R
R
CO2H
CO2H
a
CO2H
Table 1. Structures and activities for analog 1.
N
N
N
N
N
N
H
Cl
N
3
6
4
5
R = Me (1:3)
O
R2
N
Cl
N
R1
N
R
H
R
R
N
Br
Br
Br
R4
b
N
N
N
R3
1
N
N
N
H
7
8
Cpd
R1
R2
R3
R4
hM4
R = cyclopropyl (8:1)
R = CF3 (36:1)
R= propyl (18:1)
R = Et (17:1)
EC50 (nM) a
[% ACh Max]
Scheme 1. Methylation conditions of 3-substituted indazoles. Reagents and
308
[64]
739
a
b
c
d
e
f
conditions: (a) MeI, K2CO3, DMF, rt; (b) Me3OBF4, EtOAc, rt.
CH3
CH3
CH3
Et
CH3
CH3
CH3
CH3
Et
H
H
F
H
R1
R2
R1
R1
R2
F
F
O
a
b
N
N
[68]
2540
[54]
N
N
R
R2
F
H
9
10
11
16d
1 = Br;
R
2 = F
1 = F; R2 = Br
R
O
H
H
H
H
H
H
H
H
H
H
Inactive
O
Br
F
O
Br
F
Br
F
N
c
N
d
584
F
N
H
F
CH3
CH3
CH3
CH3
F
F
[34]
F
12
13
14
CF3
CF2
Inactive
Inactive
Inactive
Br
F
e
N
g
h
N
F
15
Scheme 2. Synthesis of non-commercial fluorinated indazoles 11, 15, & 16d.
Reagents and conditions: (a) NH2NH2, 1-butanol, µW 180 °C, 1h; (b)
Me3OBF4, EtOAc, rt, 5h, 52-55% (over 2 steps); (c) LDA, THF, -78 °C, 1h,
then rt, 18h, 55%; (d) NH2NH2, 1-butanol, µW 180 °C, 1h; (e) Me3OBF4,
EtOAc, rt, 60% (over 2 steps).
a
Calcium mobilization assays with hM4/Gqi5-CHO cells performed in the
presence of an EC20 fixed concentration of acetylcholine, n =1 experiments
performed in triplicate.
Br
CO2Me
CO2H
O
O
a
b
Het
17
Het
16
Het
18
X
N
Br
X
N
Br
Y
Br
Y
a
c
N
Br
Ts
N
N
N
Ts
H2N
N
b
N
H
N
When Y = N
Br
O
21
22
23
16h
R
c
N
Het
1, 19, 20
H
O
O
Br
e
N
Br
N
N
X
Ts
X
N
d
When Y = C
Br
Scheme 3. Synthesis of M4 PAM analogs 1, 19, and 20. Reagents and
conditions: (a) Pd(dppf)Cl2, Et3N, MeOH/DMF (1:1), CO, 80 °C, 18 h; (b)
NaOH, MeOH/H2O (5:1); (c) RNH2, HATU, DIEA, DMF.
24
16o
16p
X = C
X = N
Scheme 4. Synthesis of M4 PAM intermediate 16h, 16o, and 16p. Reagents
and conditions: (a) pTsCl, pyridine, 90 °C, 18h, 64-94%; (b) i. DIEA, DMF, 0
°C, 30 min; ii. 3-bromo-2-butanone, rt, 18h, 81%; (c) TFAA, THF, 0 °C then
60 °C, 3h, 71%; (d) i. NaH, DMF, 0 °C then rt, 30 min; ii. 3-bromo-2-butanone,
rt, 18h, 60 - 94 %; (c) TFAA, THF, 0 °C then 60 °C, 3h, 80 - 87%.
The synthesis of 15 began with treating 1-bromo-2,3,4-
trifluorobenzene, 12, with LDA followed by N-methoxy-N-
methylacetamide to afford the acetylated intermediate 13. This 2’-
fluoroacetophenone intermediate was condensed with hydrazine
followed by methylation with the Meerwein salt to give bromide
15. With the 5-bromoindazole intermediates in hand (16), we
utilized common Pd-catalyzed carbonylation conditions to
generate the methyl esters 17 (Scheme 3).
Following
saponification of the methyl ester to the carboxylic acid,
intermediates 18 underwent HATU coupling with 1-(2,5-
dichloropyridin-4-yl)azetidin-3-amine to afford analogs 1a-h. All

O
[94]
132
[89]
O
O
F
N
a
Br
Br
Br
b
c
F
N
N
N
Br
N
N
N
N
N
H
N
p
N
N
Br
N
N
25
26
27
N
16m
16n
N
O
O
N
a
F
Calcium mobilization assays with hM4/Gqi5-CHO cells performed in the
presence of an EC20 fixed concentration of acetylcholine, n =1 experiment
performed in triplicate.
Br
N
Br
e
f
N
O
N
d
Br
N
N
H
N
28
29
16f
while others were synthesized according to established protocols
(19a, 19b, 19c, 19j, and 19k).17-20 Intermediate 6-bromo- 2,3-
dimethylimidazo[1,2-a]pyrimidine (16h) was synthesized by first
tosylating 5-bromopyrimidin-2-amine (21) followed by alkylation
with 3-bromo-2-butanone utilizing DIEA as the base afforded
intermediate 23, which readily cyclized to 16h in the presence of
trifluoroacetic anhydride (Scheme 4). Intermediates 16o and 16p
were constructed in a similar manner; however, we found it was
Table 3. Structure and activities for analog 20.
Scheme 5. Synthesis of M4 PAM intermediates 16f, 16m and 16n. Reagents
and conditions: (a) i. LDA, THF, -78 °C, 4h; ii. N-methoxy-N-
methylacetamide, THF, -78 °C to rt, 18h, 60%; (b) NH2NH2, 1-butanol, µW
180 °C, 2h; (c) K2CO3, MeI, DMF, rt, 3h, 31% (16m – over 2 steps) and 19%
(16n – over 2 steps); (d) i. n-BuLi, Et2O, -78 °C, 2h; ii. N-methoxy-N-
methylacetamide, Et2O, -78 °C, 1.5h, 51%; (e) NH2NH2, 1-butanol, µW 180
°C, 2h; (f) K2CO3, MeI, DMF, rt, 18h, 19%.
Table 2. Structure and activities for analog 19.
O
Cl
Het
O
Cl
HN
N
N
Het
HN
N
N
Cl
19
OMe
20
Cpd
Het
hM4
Cpd
Het
hM4
EC50 (nM) a
[% ACh Max]
EC50 (nM) a
[% ACh Max]
a
b
c
d
e
f
Inactive
Inactive
Inactive
Inactive
N
a
b
c
d
e
f
S
Inactive
Inactive
Inactive
Inactive
Inactive
Inactive
N
S
N
O
N
O
N
N
N
N
N
N
F
N
F
N
N
N
494
N
S
N
S
[37]
N
Inactive
N
N
N
N
N
N
N
N
N
N
N
N
>10000
[52]
849
g
h
i
N
N
N
>10000
[31]
g
h
i
N
1832
[95]
[99]
746
N
N
N
N
[62]
654
Inactive
N
j
N
N
1384
[51]
940
j
N
N
[73]
468
k
l
N
N
F3C
k
l
N
N
[53]
420
F3C
[38]
3882
[35]
1422
[55]
454
N
[35]
375
N
N
N
m
n
o
N
N
N
m
n
o
N
[68]
370
N
N
N
N
N
N
[86]
243
N
[57]
1153
N
N
N
N
N
N
N
N

(hM4 EC50 = 308 nM) by adding a nitrogen to the 5-position of the
5,6-ring (Figure 1) to yield 2,3-dimethyl-2H-pyrazolo[4,3-
b]pyridine 19f led to a complete loss of activity. Alternatively,
addition of a nitrogen at the 7-position afforded 2,3-dimethyl-2H-
pyrazolo[3,4-c]pyridine 19n (hM4 EC50 = 370 nM), which
displayed comparable potency to 1a.
[89]
430
[83]
p
a
Calcium mobilization assays with hM4/Gqi5-CHO cells performed in the
presence of an EC20 fixed concentration of acetylcholine, n =1 experiment
performed in triplicate.
These trends were also observed with the most potent core of
the series: 2,3-dimethylimidazo[1,2-a]pyridine 19o (hM4 EC50
=
243 nM). In comparison, when inserting a nitrogen at the 5-
position of the ring system to afford 2,3-dimethylimidazo[1,2-
b]pyridazine 19c, a complete loss of activity was observed.
Likewise, addition of a nitrogen at the 2-position to give 3-methyl-
[1,2,4]triazolo[4,3-a]pyridine 19g led to a >40-fold loss in
potency; however, addition of a nitrogen at the 8-position to yield
2,3-dimethylimidazo[1,2-a]pyrimidine 19h led to only a ~3.5-fold
loss in potency. On the other hand, addition of a nitrogen at the 7-
position gave 2,3-dimethylimidazo[1,2-a]
crucial that sodium hydride be substituted for DIEA to obtain high
yields. Pyrazolo[3,4-c]pyridines 16m and 16n were synthesized
from 2-bromo-5-fluoropyridine (25), which could be selectively
acetylated para to the pyridine nitrogen when LDA was employed
as a base to afford the 2’-fluoroacetophenone 26 (Scheme 5).
Alternatively, to synthesize 16f, 2-bromo-5- fluoropyridine could
be selectively acetylated ortho to the pyridine nitrogen when n-
BuLi was substituted as the base to give the 2’-fluoroacetophenone
28. Both intermediates 26 and 28 were condensed with hydrazine
Table 3. In vitro DMPK and rat PBL data for select analogs 19 and 20.
19m
19n
20n
19o
19p
20p
Property
VU6016371
VU6016376
VU6016377
VU6017410
VU6017405
VU6017406
MW
391.25
1.71
391.25
1.17
386.84
1.06
390.27
3.08
391.25
1.69
386.84
1.03
xLogP
TPSA
75.9
75.9
85.2
62.5
75.4
84.7
In vitro PK parameters
CLINT (mL/min/kg), rat
CLHEP (mL/min/kg), rat
CLINT (mL/min/kg), human
CLHEP (mL/min/kg), human
Rat fuplasma
85
38
59
32
33
23
130
46
96
40
83
38
28
26
28
39
33
25
12
12
12
14
13
11
0.011
0.039
0.021
0.022
0.014
0.030
0.022
0.017
0.032
0.013
0.030
0.027
0.009
0.040
0.034
0.017
0.045
0.021
Human fuplasma
Rat fubrain
Kp, brain:plasma
<0.24
<0.45
0.30
0.41
0.67
0.97
0.10
0.21
0.29
1.09
<1.08
<1.33
Kpuu, brain:plasma
19p (hM4 EC50 = 132 nM) which was 2-fold more potent than 19o.
Of these compounds, 19m, 19n, 20n, 19o, 19p, and 20p were
advanced into a battery of in vitro DMPK assays (Table 4) and our
standard rat plasma:brain level (PBL) IV cassette paradigm. In
regard to physicochemical properties, all six analogs possess
molecular weights less than 400 Da, with two having attractive
CNS xLogPs (3.11 and 3.08). The new 5,6-ring systems evaluated
displayed moderate predicted hepatic clearance based on
microsomal CLint in both human (CLheps of 12 – 14 mL/min/kg)
and rat (CLheps of 23 - 46 mL/min/kg). When compared to cores
1a and 2 (Figure 1), the human clearance values of our new
scaffolds were comparable; however, rat clearance values were
slightly higher.
All compounds evaluated (rat fus 0.009 – 0.022; rat fus brain
0.021 – 0.034; human fus 0.014 – 0.045) were more bound to
plasma proteins when compared to 1a or 2. While 1a and 2 proved
to have limited CNS penetration (rat brain:plasma Kp ≤ 0.05, Kp,uu
< 0.11), all six novel 5,6-ring systems examined showed improved
CNS penetration with 19p (Kp = 0.29, Kp,uu = 1.09), 20p (Kp <1.08,
Kp,uu < 1.33), and 20n (Kp = 0.67, Kp,uu = 0.97) being superior.
Interestingly, these analogs incorporated a nitrogen at the 7-
position of the 5,6-ring system.
followed by methylation with potassium carbonate and methyl
iodide. It should be noted that we did not utilize the methyl
Meerwein salt in this instance as it predominately yielded the
trimethyl tertiary amine salt. With the commercial and in-house
generated intermediates in hand, final analogs 19 and 20 were
readily synthesized according to Scheme 3. Amino azetidines of
19 and 20 were chosen for this exercise based on past studies.
Select analogs 19 and 20 were screened against human M4
(hM4) to determine potency, with results highlighted in Tables 2
& 3. This exercise resulted in several analogs that possess M4
PAM functional potencies less than 500 nM in both human and rat:
19k (hEC50 = 468 nM; rEC50 = 378 nM), 19n (hEC50 = 370 nM;
rEC50 = 331 nM), 19o (hEC50 = 243 nM; rEC50 = 433 nM), 19p
(hEC50 = 132 nM; rEC50 = 233 nM), 20n (hEC50 = 454 nM; rEC50
= 339 nM), and 20p (hEC50 = 430 nM; rEC50 = 295 nM).
Interestingly, changing the 2-chloro substituent of 1-(2,5-
dichloropyridin-4-yl)azetidin-3-amine to a methoxy substituent
typically led to a 2-9 fold decrease in potency with one analog
ranked as inactive (19i vs. 20i). In previous series, these two
amines often gave similar potency profiles.
Benzothiazoles, benzoisothiazoles and benzoisoxaoles were
generally not tolerated (19a, 19b, 19e, 202a, 20b, 20e). It was also
noted that placement of an additional nitrogen within the 5,6-ring
systems was crucial for activity or lack thereof. For example,
modification of the original 2,3-dimethyl-2H-indazole core of 1a
In summary, a scaffold hopping exercise based on M4 PAMs 1a
and 2 identified two novel cores: a 2,3-dimethyl-2H-pyrazolo[3,4-
c]pyridine-5-carboxamide core (19n & 20n) and a 2,3-
dimethylimidazo[1,2-a]pyrazine-6-carboxamide core (19p).

receptor allosteric modulator with potential antipsychotic
properties. Neuropsychopharmacology. 201;35:855-869.
Brady A, Jones CK, Bridges TM, et al. Centrally active allosteric
potentiators of the M4 muscarinic acetylcholine receptor reverse
amphetamine-induced hyperlocomotor activity in rats. J Pharm Exp
Ther. 2008;327;941-953.
Analog 19p exhibited a 2.5 to 5-fold improvement in rat M4 PAM
activity when compared to 1a or 2, respectively. While this analog
displayed a 2-fold increase in rat CLhep and was more bound to rat
plasma proteins than 1a, all other protein binding values were
similar. Moreover, 19p possessed improved brain:plasma Kp and
Kp,uu values in relation to 1a. Although this endeavor did not
deliver M4 PAMs with the desired DMPK profiles to advance as
potential development candidates, it did garner insights to further
our goals, which will be disclosed in due course.
9.
10. Byun NE, Grannan M, Bubser M, et al. Antipsychotic drug-like
effects of the selective M4 muscarinic acetylcholine receptor
positive
allosteric
modulator
VU0152100.
Neuropsychopharmacology. 2014;39:1578-1593.
11. Bubser M, Bridges TM, Dencker D, et al. Selective activation of M4
muscarinic acetylcholine receptors reverses MK-801-induced
behavioral impairments and enhances associative learning in
rodents. ACS Chem Neurosci. 2014;5:920-942.
Acknowledgments
12. Melancon BJ, Wood MR, Noetzel MJ, et al. Optimization of M4
positive allosteric modulators (PAMs): The discovery of
BU0476406, a non-human primate in vivo tool compound for
translational pharmacology. Bioorg Med Chem Lett. 2017;27:2296-
2301.
13. Wood MR, Noetzel J, Melancon BH, et al. Discovery of
VU0467485/AZ13713945: An M4 PAM evaluated as a preclinical
candidate for the treatment of Schizophrenia. ACS Med Chem Lett.
2017;8:233-238.
We thank the NIH for funding via the NIH Roadmap Initiative
1x01 MH077607 (C.M.N.), the Molecular Libraries Probe Center
Network (U54MH084659 to C.W.L.) and U01MH087965
(Vanderbilt NCDDG). We also thank William K. Warren, Jr. and
the William K. Warren Foundation who funded the William K.
Warren, Jr. Chain in Medicine (to C.W.L.).
14. Long MF, Engers JL, Chang S, et al. Discovery of a novel 2,4-
dimethylquinolin-6-carboxamide M4 positive allosteric modulator
(PAM) chemotype via scaffold hopping. Bioorg Med Chem Lett.
2017;27:4999-5001.
15. Temple KJ, Engers JL, Long MF, et al. Discovery of a novel 3,4-
dimethylcinnoline carboxamide M4 positive allosteric mosulator
(PAM) chemotype via scaffold hopping. Bioorg Med Chem Lett.
2019, 19, article 126678.
16. Temple KJ, Long MF, Engers JL, et al. Development of structurally
distinct tricyclic M4 positive allosteric modulator (PAM). Bioorg
Med Chem Lett. Manuscript submitted.
17. Fink DM, Strupczewski JT. Preparation of 6-fluorobenziothiazoles
via a regioselective nucleophilic aromatic substitution reaction.
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Synthesis and antiprotozoal activity of nitazoxanide-N-
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References and notes
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6.
7.
8.
Highlights
 Discovery of two novel tricyclic-based M4
PAMs
 Utility of scaffold hopping to improve
potency/properties/DMPK
 Balanced human and rat M4 PAM potency
 Rare 8,9-dimethyl-8H-pyrazolo[3,4-
h]quinazoline and 1-methyl-1H-
[1,2,3]triazolo[4,5-h]quinazoline cores