Discovery, synthesis, and structure-activity relationship development of a series of N -4-(2,5-dioxopyrrolidin-1-yl)phenylpicolinamides (VU0400195, ML182): Characterization of a novel positive allosteric modulator of the metabotropic glutamate receptor 4

Article abstract of DOI:10.1021/jm200956q

There is an increasing amount of literature data showing the positive effects on preclinical antiparkinsonian rodent models with selective positive allosteric modulators of metabotropic glutamate receptor 4 (mGlu₄). However, most of the data ge

Full text of DOI:10.1021/jm200956q

Article
pubs.acs.org/jmc
Discovery, Synthesis, and Structure−Activity Relationship Development
of a Series of N-4-(2,5-Dioxopyrrolidin-1-yl)phenylpicolinamides
(VU0400195, ML182): Characterization of a Novel Positive Allosteric
Modulator of the Metabotropic Glutamate Receptor 4 (mGlu4) with Oral
Efficacy in an Antiparkinsonian Animal Model
Carrie K. Jones,†,‡,§ Darren W. Engers,†,‡,# Analisa D. Thompson,†,‡ Julie R. Field,† Anna L. Blobaum,†,‡
Stacey R. Lindsley,†,‡ Ya Zhou,†,‡ Rocco D. Gogliotti,†,‡ Satyawan Jadhav,†,‡ Rocio Zamorano,†,‡
Jim Bogenpohl,∞ Yoland Smith,∞ Ryan Morrison,†,‡ J. Scott Daniels,†,‡ C. David Weaver,†,⊥
P. Jeffrey Conn,†,‡,⊥,# Craig W. Lindsley,†,∥,‡,⊥,# Colleen M. Niswender,*,†,‡ and Corey R. Hopkins*,†,∥,‡,#
‡
†Department of Pharmacology and Vanderbilt Center for Neuroscience Drug Discovery, Vanderbilt University Medical Center,
Nashville, Tennessee 37232, United States
§Tennessee Valley Healthcare System, U.S. Department of Veterans Affairs, Nashville, Tennessee 37212, United States
⊥
∥Department of Chemistry and Vanderbilt Institute of Chemical Biology, Vanderbilt University, Nashville, Tennessee 37232,
United States
#Vanderbilt Specialized Chemistry Center for Accelerated Probe Development (MLPCN), Nashville, Tennessee, 37232,
United States
∞Yerkes National Primate Research Center and Department of Neurology, Emory University, Atlanta, Georgia 30329, United States
S
* Supporting Information
ABSTRACT: There is an increasing amount of literature data showing the positive effects on pre-
clinical antiparkinsonian rodent models with selective positive allosteric modulators of metabotropic
glutamate receptor 4 (mGlu4). However, most of the data generated utilize compounds that have not
been optimized for druglike properties, and as a consequence, they exhibit poor pharmacokinetic
properties and thus do not cross the blood−brain barrier. Herein, we report on a series of N-4-(2,5-
dioxopyrrolidin-1-yl)phenylpicolinamides with improved PK properties with excellent potency and
selectivity as well as improved brain exposure in rodents. Finally, ML182 was shown to be orally active
in the haloperidol induced catalepsy model, a well-established antiparkinsonian model.
medical community nearly 200 years ago,7 there is still no
known cure for PD and, as important, there are very few
INTRODUCTION
■
Parkinson’s disease (PD) is a neurodegenerative disease that
palliative drugs that provide benefit over the time frame of the
affects the central nervous system and is present in nearly 1 in
300 adults.1 With the exception of Alzheimer’s disease (AD),
disease progression.
Because of the discovery that the loss of dopaminergic
PD is the most common neurodegenerative disorder. PD is part
neurons is the primary culprit for the motor disturbances in PD
of a larger group of conditions known as movement disorders
patients, the development of dopamine (DA) replacement
and is characterized by four major primary symptoms: tremor,
therapies has dominated the PD treatment landscape.8 The
which is present at rest; bradykinesia, loss of spontaneous
primary pharmaceutical used for the treatment of PD is
movement; rigidity, an increase in muscle tone; and disturbance
of posture, an inability to maintain an upright posture.1−4 The
levodopa (L-DOPA), since the use of dopamine itself proved
ineffective because it does not cross the blood−brain barrier
(BBB). However, it was also discovered that the use of L-DOPA
as a stand-alone treatment proved very difficult because of the
rapid decarboxylation of L-DOPA that releases vasoactive DA
major motor disturbances in PD patients are due to the loss of
mesencephalic dopaminergic neurons in the substantia nigra
which results in the decreased stimulation of the motor cortex
by the basal ganglia. In addition to the more prominent motor
disturbances, PD patients also suffer from significant nonmotor
symptoms, such as depression, sleep disorders, and cognitive
problems.1−6 Although the disease was first noted in the
Received: July 18, 2011
Published: October 3, 2011
© 2011 American Chemical Society
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Figure 1. Structures of recently reported mGlu4 PAMs.
prior to crossing the BBB, resulting in severe cardiovascular
events. This side effect can be mitigated by the coadministra-
tion of an amino acid decarboxylase inhibitor that significantly
increases the levels of DA in the CNS without the
cardiovascular side effects.3,4 Several other direct-acting DA
agonists have been introduced, as well other therapies for
increasing DA levels. Although the introduction of L-DOPA
has significantly improved the initial treatment of PD, DA-
replacement therapies have significant complications with long-
term use. For example, a “wearing-off” and “on−off” pheno-
menon has been noted in which DA-replacement therapies lose
efficacy over time, resulting in an ever-increasing dosage
cycle.9,10 Other consequences of DA-replacement include
dyskinesias (rocking movements, repetitive motor behaviors)
and psychotic and behavioral disturbances that often develop
after long-term usage.11 Because of these significant side effects
of DA replacement, alternative approaches toward the treat-
ment and reversal of PD have been investigated, including
invasive surgery and deep brain stimulation (DBS), along with
attempts to develop agents to manipulate other, potentially
druggable targets (e.g., antagonists of A2A adenosine receptors).
Because of the limitations of current therapies for PD, we
became interested in a potentially new target for the palliative
care, and potential disease modification, of PD. Because of
exceptionally high expression levels of metabotropic glutamate
receptor 4 (mGlu4) at the striatopallidal synapse of the basal
ganglia, we and others have targeted this receptor for
therapeutic intervention into PD.12−17
To this end, we started from a functional high-throughput
screening (HTS) initiated at Vanderbilt University, TN, and
discovered an interesting new lead compound, N-(4-(1,1,3,3-
tetraoxidobenzo[d][1,3,2]dithiazol-2-yl)phenyl)furan-2-carbox-
amide, 8 (Figure 2, Pubchem compound identification (CID),
Figure 2. Structure of initial HTS hit.
4066845; ChemDiv ID, K906-0087). Although compound 8
did not possess favorable calculated properties for a CNS
probe compound (MW = 404.4, TPSA = 109.9), it represented a
submicromolar starting point for our mGlu4 hit-to-lead program.
The 1,1,3,3-tetraoxidobenzo[d][1,3,2]dithiazol-2-yl)phenyl)-
carboxamide compounds were synthesized as outlined
in Scheme 1. Commercially available mono-Boc protected
Scheme 1. Synthesis of 1,1,3,3-Tetraoxidobenzo[d][1,3,2]-
a
dithiazol-2-yl)phenyl)carboxamides 8a−l
Over the past several years, our laboratories and others have
added to the list of selective and novel tool compounds for the
study of mGlu4 via positive allosteric modulation (Figure 1).
Thus far, three disclosed mGlu4 PAMs (2,18 3,19 and 420) have
been shown to be CNS penetrant when dosed systemically,
with compounds 2 and 4 exhibiting efficacy in the haloperidol-
induced catalepsy assay.21,22 In addition to the aforementioned
in vivo tool compounds, there have been numerous in vitro
tools reported.23−25
Compound 3 possesses an acceptable balance of in vitro
pharmacological properties, as well as moderate stability in rat
liver microsomes (RLM). While compound 3 was able to cross
the blood−brain barrier with an acceptable brain/plasma ratio
(B/P = 1), its overall brain penetration was substantially
reduced compared to the aminopyridine 4. In this study, we
disclose a series of N-4-(2,5-dioxopyrrolidin-1-yl)phenyl-
picolinamide mGlu4 positive allosteric modulators that are
CNS penetrant and show oral efficacy in an antiparkinsonian
animal model.
a
Reagents and conditions: (a) 1,2-benzendisulfonyl dichloride, Et3N,
CH2Cl2; (b) 4.0 M HCL/dioxane, 99% (two steps); (c) RCOCL,
CH2CL2, DIEA, 49−87%; (d) RCO2H, EDCL, HOBt, dioxane/DMF,
27−74%. All library compounds were purified by mass-directed
preparative LC with a purity of >95%.
1,4-dianiline 5 was reacted with 1,2-dibenzenedisulfonyl
dichloride (Et3N, CH2Cl2), yielding 6. Next, the Boc group
was removed under acidic conditions (4.0 M HCl/dioxane),
and then the amides 8a−l were formed utilizing either the
carboxylic acids (EDCI, HOBt, dioxane/DMF) or acid
chlorides (DIEA, CH2Cl2).
The structure−activity relationship (SAR) surrounding this
set of compounds mirrored other series that we have reported
previously (Table 1).18,19,25 Namely, the 2-pyridylamide 8d was
RESULTS AND DISCUSSION
■
Although we have reported on several mGlu4 in vitro and in
vivo tool compounds, there still remains room for significant
improvement in an acceptable probe for the mGlu4 receptor.
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Table 1. Human mGlu4 Potency and %GluMax Response (As Normalized to Standard 1) for Selected Western Amide Analogues
a
a
compd
R
hEC50 (nM)
GluMax (% 1)
tPSA
cLogP
8a
8b
8c
8d
8e
8f
2-furan
phenyl
226 ± 61
402 ± 74
765 ± 133
136 ± 61
110.3 ± 5.8
65 ± 1.5
109.9
100.6
100.6
113.0
113.0
113.0
113.0
122.2
125.3
113.0
113.0
113.0
1.77
2.60
3.14
2.19
1.84
1.84
2.42
2.64
1.41
2.05
2.05
2.05
cyclohexyl
48.3 ± 3.3
99.7 ± 0.9
27.7 ± 2.7
22.3 ± 1.9
76.7 ± 8.1
22.0 ± 1.2
100.3 ± 4.9
122.3 ± 5.9
123 ± 1.2
39.7 ± 0.3
2-pyridyl
b
3-pyridyl
inactive
b
4-pyridyl
inactive
8g
8h
8i
6-fluoro-2-pyridyl
6-methoxy-2-pyridyl
4-pyrimidine
2-thiazole
1800 ± 1500
b
inactive
179 ± 36
353 ± 125
104 ± 34
8j
8k
8l
4-thiazole
b
5-thiazole
inactive
a
EC50 and maximal response when compared to glutamate (GluMax) are the average of at least three independent determinations performed in
triplicate (mean ± SEM). 1 is run as a control compound each day, and the maximal response generated in human mGlu4 CHO cells in the presence
of mGlu4 PAMs varies slightly in each experiment. Therefore, data were further normalized to the relative 1 response obtained in each day’s run.
b
Inactive compounds are defined as those in which the %GluMax did not surpass 2 × EC20 for that day’s run.
Table 2. Characteristics of Previously Reported mGlu4 Tool Compounds from Vanderbilt University
the most potent heterocyclic substituent (hEC50 = 136 nM).
Other aryl, cycloalkyl, and five-membered heterocycles also
showed submicromolar potency at both the human and rat
mGlu4 receptors. However, despite these modifications, the
molecular weight (MW) and polar surface area (TPSA)
remained suboptimal for the design of a CNS penetrant
probe compound. To confirm this prediction, we profiled 8d in
both in vitro and in vivo rat pharmacokinetic (PK) experiments
and assessed the extent of CNS penetration for this compound
(Table 2). While the compound displayed selectivity against
other mGlu subtypes (mGlu1−3,5,6−8), the extent of brain
penetration was poor (B/P = 0.085) following intraperitoneal
(ip) administration to rats.
molecule (MW < 400, TPSA < 90) (Table 3). To this end we
examined and evaluated the effect of removing the carbonyl
of the amide. Subsequent replacement of the carbonyl with a
methylene group (9b) or a cyclopropyl group (9c) effectively
reduced the TPSA (113−96) of the scaffold but with a cost of
10- to 40-fold reduction in mGlu4 potency. Likewise, the
addition of a substituent ortho to the amide on the internal
phenyl group (9a), or reversing the amide (9d), proved to alter
the TPSA but again with a significant reduction in the potency
for both compounds.
One area of diversification where we have had success with
other series is the 4-position of the internal phenyl group.
Therefore, we evaluated the activity of a number of
substitutions similar to the 1,1,3,3-tetraoxidobenzo[d][1,3,2]-
dithiazol-2-yl group, in an attempt to reduce TPSA and
Next we turned our attention to compounds that would have
more favorable calculated properties for a CNS penetrant
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Table 3. Human mGlu4 Potency and Efficacy (As Normalized to Standard 1) for Bis-sulfonamide Scaffold Modifications
a
a
compd
X
Y
R2
hEC50 (nM)
GluMax (% 1)
tPSA
cLogP
9a
9b
9c
9d
CO
NH
NH
NH
CO
2-F
H
1100 ± 424
1800 ± 199
6400 ± 750
67.7 ± 2.7
110.0 ± 6.2
62.7 ± 8.4
30.7 ± 2.4
113
95.9
95.9
113
1.89
1.54
1.88
2.19
CH2
cyclopropyl
NH
H
b
H
inactive
a
EC50 and maximal response when compared to glutamate (GluMax) are the average of at least three independent determinations performed in
triplicate (mean ± SEM). 1 is run as a control compound each day, and the maximal response generated in human mGlu4 CHO cells in the presence
of mGlu4 PAMs varies slightly in each experiment. Therefore, data were further normalized to the relative 1 response obtained in each day’s run.
b
Inactive compounds are defined as those in which the % GluMax did not surpass 2 × EC20 for that day’s run.
ultimately improve brain penetration. The inclusion of an imide
group in lieu of the 1,1,3,3-tetraoxidobenzo[d][1,3,2]dithiazol-
2-yl moiety represented a net lowering of the MW by 60 Da
and the TPSA by approximately 30 Å2. The synthesis of the
imide compounds is shown in Scheme 2.
(15d, hEC50 = 370 nM). Although there was a ∼10-fold loss of
potency, 15d still showed <500 nM potency against hmGlu4.
The trans-isomer was also evaluated with similar potency to the
cis-15d (results not shown). Increasing the bulk of the saturated
six-membered ring resulted in interesting compounds. The
[2.2.1]-bridged oxo compound (15e, hEC50 = 1300 nM)
exhibited a 4-fold loss in potency; however, the unsaturated
[2.2.1]-bridged carbon analogue (15f, hEC50 = 291 nM) and
unsaturated [2.2.2]-analogue (15g, hEC50 = 287 nM) were
more potent than 15d. Reducing the ring size from six-
membered to a substituted three-membered ring resulted in an
equipotent compound (15h, hEC50 = 435 nM). Substitution of
Scheme 2. Synthesis of N-4-(2,5-Dioxopyrrolidin-1-yl)-
a
phenylpicolinamides
the five-membered imide led to a loss of activity (15i, hEC50
=
1400 nM), but it remained comparable to the initial five-
membered imide (15a). However, when the size of the
substituent was increased from the gem-dimethyl to cyclohexyl
(15j, hEC50 = 158 nM), there was a 10-fold increase in activity.
Other bulky substituents were evaluated (15k, hEC50 = 674
nM; 15l, hEC50 = 771 nM); however, these compounds lost
activity when compared to 15f.
With our best compounds evaluated for human potency, we
evaluated the in vitro potency of the compounds on the rat
mGlu4 receptor. Additionally, we compared compounds in
terms of their relative efficacy which we evaluated by assessing
the ability of a 30 μM concentration of each compound to shift
a glutamate concentration−response curve to the left
(represented as fold shift, FS) (Table 5). For examination of
compound activity at the rat receptor, we employ an assay in
which we measure the ability of the Gi/o-coupled mGlu4
receptor to couple to G protein-coupled inwardly rectifying
potassium (GIRK) channels.26 In contrast to the calcium
mobilization assay, we generally do not observe large increases
above the response elicited by saturating concentrations of
glutamate alone when GIRK activation is used to assess activity;
rather, compounds shift the glutamate concentration−response
curve to the left only. Compounds from the 1,1,3,3-
tetraoxidobenzo[d][1,3,2]dithiazol-2-yl)phenyl)carboxamide
series (8d−k) all possessed GluMax values comparable to that
of 1, and their efficacies in shifting the glutamate curve were
modest, between 3.3 and 7.3. However, moving from the
1,1,3,3-tetraoxidobenzo[d][1,3,2]dithiazol-2-yl)phenyl)-
carboxamide series to the imide series produced significant
divergence in compound efficacies. In particular, two
phthalimide compounds (15b and 15c) exhibited large
differences in efficacy (leftward fold shift values of 23.6 and
83.0, respectively). Compound 15c produced the largest
a
Reagents and conditions: (a) Boc2O, DMAP, THF, reflux, 99%;
(b) Pd/C, EtOAc, H2 (1 atm), room temp; (c) picolinoyl chloride HCl,
CH2CL2, pyridine, 84%; (d) 4.0 HCL/dioxane; (e) anhydride, toluene/
AcOH (3:1), microwave, 150 °C, 90 min. All library compounds were
purified by mass-directed preparative LC with purity of >95%.
Evaluation of the compound containing a sultam group
revealed a complete loss of activity (16) (Table 4). This core
phenyl group does not contain a halogen as do the other
compounds; however, the compound containing an internal
halogen was not attainable by synthesis. Next, a series of imide
compounds were investigated. The initial five-membered imide
compound was active (15a, hEC50 = 6200 nM); however, the
compound lost ∼20-fold activity compared to 8d. Potency
could be recovered by increasing the bulk of the right-hand
side by utilizing phthalimide (and substituted phthalimides)
(15b, hEC50 = 59.4 nM; 15c, hEC50 = 42 nM). However, an
initial metabolic stability assessment revealed that these
compounds suffered from extensive oxidative metabolism
(results not shown). Having demonstrated the phenyl moiety
of the phthalimide as the predominant metabolic soft spot, we
turned to saturated versions of the phthalimide (15d−l). The
initial compound was the direct saturated comparator to 15b
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Table 4. Human mGlu4 Potency and Efficacy (As Normalized
to Standard 1) for Selected Bis-sulfonamide Replacements
Table 5. Rat mGlu4 Receptor Potency and Efficacy (Fold
Shift) Data for Selected Compounds
a
a
a
compd
EC50 (nM)
GluMax (% 1)
fold shift
8d
165 ± 1
242 ± 36
201 ± 37
105 ± 15
66.8 ± 4
34.9 ± 5.2
645 ± 63
376 ± 23
246 ± 12
686 ± 32
397 ± 38
491 ± 57
536 ± 105
124.3 ± 3.6
103.3 ± 3.2
127.1 ± 4.5
115.2 ± 2.3
131.8 ± 3.9
137.4 ± 3.2
129.1 ± 2.8
120.3 ± 3.2
122.2 ± 4.5
105.1 ± 0.1
114.2 ± 1.5
137.8 ± 2.0
130.7 ± 3.9
5.2 ± 0.6
3.3 ± 0.3
4.7 ± 0.4
7.3 ± 0.8
23.6 ± 3.1
83.0 ± 16.8
8.3 ± 0.5
11.2 ± 0.8
5.2 ± 1.2
5.5 ± 0.5
4.8 ± 0.2
12.1 ± 1.0
16.7 ± 1.7
8i
8j
8k
15b
15c
15d
15f
15g
15h
15j
15k
15l
a
EC50 and maximal response when compared to glutamate (GluMax)
are the average of at least three independent determinations performed
in triplicate (mean ± SEM).
leftward shift of the glutamate response curve reported to date.
It is also noted that moving away from the phthalimide
structures to the saturated imides led to a significant reduction
in efficacy and the largest fold shift value for the saturated
compounds was 16.7 (15l), with most of the compounds
tested exhibiting fold shifts of <10 (see Supporting Information
Figure 1 for graphs of human and rat potency and fold shift
experiments). The exceptions were 15f (11.2), 15k (12.1), and
15l (16.7).
Having identified several key compounds based on human
and rat potency as well as efficacy at the rat receptor, we
evaluated these compounds in a battery of pharmacokinetic
assays including an assessment of intrinsic clearance (CLint) in
hepatic microsomes. In addition to intrinsic clearance allowing
for the prediction of pertinent rat and human PK parameters
(CL and t1/2), intrinsic clearance assessments allow for a rank
ordering of compounds with respect to oxidative lability and a
subsequent predicted stability in our in vivo PK and efficacy
models (Table 6). Although two compounds based on the
phthalimide scaffold (15b and 15c) showed excellent in vitro
potency on mGlu4, these compounds have been previously
reported by Merck and thus were not further evaluated.27 The
three compounds based on the saturated imide scaffold
(15f,j,k) displayed elevated clearance in human liver micro-
somes, each predicted to be at hepatic blood flow in humans
(QH = 21 mL min−1 kg−1). Conversely, an assessment in RLM
indicated the compounds to possess moderate-to-high
predicted hepatic clearance (CLHEP), with compound 15k
predicting the best stability in rat (CLHEP = 30 mL min−1 kg−1).
Assessment of the compound’s affinity for plasma proteins was
also estimated (amount free and unbound, fu (in %)) in vitro in
cryopreserved plasma (Table 6). While compounds 15j and
15k were highly protein bound in both human and rat plasma
(fu < 1%), 15f displayed lower protein binding under the same
conditions (fu > 3%). In addition, 15f was also investigated for
nonspecific binding (NSB) in freshly prepared rat brain
homogenate employing rapid equilibrium dialysis and found
to display a decrease in NSB (fu > 7%) relative to binding to
plasma proteins. As a first-tier screen for potential drug−drug
interaction liability, the compounds were evaluated for their
inhibition of the cytochrome P450 (CYP450 or CYP) enzymes
utilizing a cocktail approach in human liver microsomes
a
EC50 and maximal response when compared to glutamate (GluMax)
are the average of at least three independent determinations performed
in triplicate (mean ± SEM). 1 is run as a control compound each day,
and the maximal response generated in human mGlu4 CHO cells in
the presence of mGlu4 PAMs varies slightly in each experiment.
Therefore, data were further normalized to the relative 1 response
obtained in each day’s run.
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clearance (CL), volume of distribution at steady state (Vss),
half-life (t1/2), and bioavailability (F) (Table 7). Although
Table 6. Predicted Hepatic Clearance, Plasma Protein
Binding, CYP450 Inhibition, and mGlu Selectivity Values
for Selected Compounds
Table 7. Rat in Vivo Pharmacokinetic Values for Selected
Compounds
15f
15j
15k
Intrinsic Clearance (mL min−1 kg−1
)
PK parameter (rat)
15f
15j
15k
human CLHEP
rat CLHEP
19.7
53.0
19.4
66.7
19.9
32.6
a
iv (1 mg/kg)
CL (mL min−1 kg−1
t1/2 (min)
)
36.9
40.4
493
18
48.3
93.8
57.2
5.5
5.4
Plasma Protein Binding (PPB)
329
109
0.58
3225
human fu (%)
rat fu (%)
4.1
0.62
0.02
0.17
1.4
MRT
3.2
7.6
0.5
Vss (L/kg)
BHB rat fu (%)
1.7
AUC0−24 (ng·h/mL)
454
346
CYP450 IC50 (μM)
b
po dose (10 mg/kg)
2C9
2D6
3A4
2C19
1A2
>30
>30
>30
>30
>30
>30
>30
>30
>30
>30
8.7
AUC0−24 (h·ng/mL)
Cmax (ng/mL)
Tmax (h)
4354
238
0.62
97
813
18.3
7
2685
553
0.5
>30
>30
17.6
8.9
F (%)
24.6
8.3
a
a
b
mGlu Selectivity
10% EtOH, 80% PEG-400, 10% saline. 10% Tween 80 in 0.5%
b
b
b
b
mGlu1,2,3
mGlu5
mGlu6
mGlu7
mGlu8
inactive
inactive
inactive
inactive
methylcellulose.
PAM, 2.1 FS
PAM, 3.1 FS
PAM, 2.9 FS
PAM 2.0 FS
all three compounds displayed modest stability (CLHEP
)
PAM, 2.1 FS
PAM, 5.8 FS
when assessed in rat liver microsomes, 15k proved to be a
lower clearance compound in vivo (5.4 mL min−1 kg−1). Both
15f and 15j demonstrated moderate clearance values (37 and
48 mL min−1 kg−1, respectively), values that correlated well
with their in vitro CLHEP values. Because of the exceptional
stability of 15k following intraveneous administration to the rat,
we evaluated this compound in both beagle dog and rhesus
monkey employing an iv cassette dosing paradigm. Compound
15k showed excellent stability in both dogs (CL, 7 mL min−1 kg−1)
and monkeys (3 mL min−1 kg−1) with each species diplaying a
t1/2 of ≥3 h. Although 15k showed superior stability com-
paratively, it unfortunately displayed an oral bioavailability of
less than 10%. Conversely, compound 15f demonstrated an
excellent oral bioavailability of 97%, whereas 15j displayed a
modest bioavailability of 25%.
b
inactive
Ago-PAM, 12.9 FS
PAM, 2.1 FS
b
b
inactive
inactive
a
Selectivity was assessed by incubating cells with either DMSO-
matched vehicle or a 10 μM final concentration of compound in the
presence of a full glutamate (or, in the case of mGlu7, L-AP4)
concentration−response curve. FS = fold shift of the glutamate
concentration−response curve. Compound 15f showed weak
potentiator activity on mGlu5, mGlu6, and mGlu7 (leftward shift of
the glutamate concentration−response). Inactive compounds showed
no ability to left-shift the glutamate response curve at 10 μM. No
antagonist activity was noted for any compound at any receptor tested.
b
designed to inform on the inhibition of the five major drug-
metabolizing and/or polymorphic CYPs (CYP2C9, 2D6, 3A4,
2C19, and 1A2). All compounds tested showed no significant
activity against CYP2D6 and CYP3A4 (>30 μM), and only 15k
showed moderate inhibition of 2C9, 2C19, and 1A2 (8.7, 17.6,
and 8.9 μM, respectively).
The combination of enhanced bioavailability, oral PK, and an
exceptionally low protein binding value indicated that
compound 15f possessed the characteristics to be a potential
tool compound that could be evaluated for brain exposure after
oral dosing (Table 8). The hydrochloride salt of 15f was dosed
Lastly, these compounds were evaluated for their selectivity
against the other mGlu receptors. For initial studies, 10 μM
compound was applied prior to a complete agonist
concentration−response curve (CRC) appropriate for each
receptor. This technique allows for the detection of potentiator
(leftward shift) or antagonist (rightward shift and/or decrease
in the maximal response) activity within a single experiment. By
use of this assay, all compounds were selective versus the group
II mGlus (2 and 3) and only 15f showed weak PAM activity
against a group I receptor (mGlu5, 2.1 FS). However, these
compounds did show varying selectivity against the other group
III receptors. Whereas 15j only showed weak activity against
mGlu6 (PAM, 2.1 leftward FS of the agonist CRC), 15f was
weakly active against both mGlu6 (PAM, 3.1 FS) and mGlu7
(PAM, 2.9 FS), and 15k showed activity against all three
receptors (mGlu6, PAM, 5.8 FS; mGlu7, mixed agonist/PAM
(Ago-PAM) activity, 12.9 FS; mGlu8, PAM, 2.1 FS); the
allosteric agonist activity against mGlu7 was equivalent to that
observed for mGlu4 (12.9 FS vs 12.1 FS).
Table 8. PO Pharmacokinetic Parameters of 15f (10 mg/kg,
10% Tween 80 in 0.5% Methylcellulose)
PK parameter
a
systemic, AUC, 0−6 h (nM·h)
8.58
8.48
800
a
HPV, AUC, 0−6 h (nM·h)
brain, AUC, 0−6 h (nM·h)
a
AUCbrain/AUCsys
0.93
1.01
AUCsys/AUCHPV
a
The predicted in vitro ADME properties of these compounds
were consistent with advancement for in vivo studies. Thus, the
hydrochlorides of these compounds (15f, 15j, 15k) were
synthesized and dosed intraveneously (1 mg/kg) and orally
(10 mg/kg) to determine pertinent PK parameters such as
po dose, vehicle: 10 mg/kg, 10% Tween 80 in 0.5% methylcellulose.
orally in a microsuspension (10% Tween-80 in 0.5% methyl-
cellulose), and plasma (systemic and hepatic portal) and brain
samples were collected for bioanalysis of parent compound up
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to 6 h following administration of the compound. The
compound showed similar levels in the systemic and HPV
plasma, indicating neglible hepatic first pass metabolism
(AUCsys/AUCHPV = 1.01). Compound 15f also displayed
exceptional CNS penetration, with compound exposures
reaching 800 nM·h (AUC0−6) and a corresponding brain/
plasma ratio that reached unity (0.93).
disease. This new class of N-4-(2,5-dioxopyrrolidin-1-yl)-
phenylpicolinamides (such as 15f, VU0400195 (ML182))29
was discovered utilizing a rational drug design approach based on
the 1,1,3,3-tetraoxidobenzo[d][1,3,2]dithiazol-2-yl)phenyl)-
carboxamides (8d) scaffold that possessed suboptimal properties.
A common feature in many of the reported mGlu4 PAMs is the
presence of a picolinamide moiety which this new scaffold also
possesses. However, these new compounds are structurally
distinct from previously reported structures because of the
presence of the 2,5-dioxopyrrolidin-1-yl moiety. The present
report represents only the second example of a potent and
selective, orally active mGlu4 PAM.20
Considering the promising PK results for 15f, we evaluated
the compound for selectivity against the other mGlu subtypes.
In these studies, a 10-point concentration−response of 15f was
applied prior to an EC20 concentration of agonist appropriate
for each receptor. As with our original fold shift-type studies,
15f was shown to be inactive against mGlu1,2,3,8 and was active
against mGlu5 (PAM, EC50 = 1.7 ± 0.8 μM, 64.3 ± 0.8%
GluMax), mGlu6 (PAM, EC50 > 10 μM, 45.8 ± 3.0% GluMax),
and mGlu7 (PAM, 2.9 ± 0.7 μM, 64.0 ± 1.4% GluMax) (see
Supporting Information Table 1). In addition, 15f was tested in
Ricerca’s lead profiling screen (binding assay panel of 68
GPCRs, ion channels and transporters screened at 10 μM) and
was found to be not significant with all the 68 assays conducted
(no inhibition of radioligand binding, >50% at 10 μM).
On the basis of the previous PK studies, 15f was chosen as a
potential tool compound for an in vivo proof-of-concept study
and was examined in a rat model of neuroleptic-induced
catalepsy. Here we evaluated the ability of 15f to reverse
haloperidol-induced catalepsy, a preclinical rodent model of
motor impairments associated with Parkinson’s disease. The D2
receptor antagonist haloperidol induced robust catalepsy
(Figure 3). As shown in Figure 3, 15f (0.1−56.6 mg/kg, po)
EXPERIMENTAL SECTION
■
General. All NMR spectra were recorded on a 400 MHz AMX
Bruker NMR spectrometer. 1H chemical shifts are reported in δ values
in ppm downfield with the deuterated solvent as the internal standard.
Data are reported as follows: chemical shift, multiplicity (s = singlet,
d = doublet, t = triplet, q = quartet, br = broad, m = multiplet),
integration, coupling constant (Hz). Low resolution mass spectra were
obtained on an Agilent 1200 series 6130 mass spectrometer with
electrospray ionization. High resolution mass spectra were recorded on
a Waters Q-TOF API-US plus Acquity system with electrospray
ionization. Analytical thin layer chromatography was performed on
EM reagent 0.25 mm silica gel 60-F plates. All samples were of ≥95%
purity as analyzed by LC−UV/vis-MS. Analytical HPLC was
performed on an Agilent 1200 series with UV detection at 214 and
254 nm along with ELSD detection. LC/MS parameters were as
follows: method 1 = (J-Sphere80-C18, 3.0 mm × 50 mm, 4.1 min
gradient, 5% [0.05% TFA/CH3CN]/95% [0.05%TFA/H2O] to 100%
[0.05%TFA/CH3CN]; method 2 = (Phenomenex-C18, 2.1 mm ×
30 mm, 2 min gradient, 7% [0.1%TFA/CH3CN]/93% [0.1%TFA/
H2O] to 100% [0.1%TFA/CH3CN]; method 3 = (Phenomenex-C18,
2.1 mm × 30 mm, 1 min gradient, 7% [0.1%TFA/CH3CN]/93%
[0.1%TFA/H2O] to 95% [0.1%TFA/CH3CN]. Preparative purifica-
tion was performed on a custom HP1100 purification system16 with
collection triggered by mass detection. Solvents for extraction, washing,
and chromatography were HPLC grade. All reagents were purchased
from Aldrich Chemical Co. and were used without purification.
tert-Butyl (4-(1,1,3,3-Tetraoxidobenzo[d][1,3,2]dithiazol-2-
yl)phenyl)carbamate (6). A solution of N-Boc-p-phenylenediamine
5 (0.68 g, 3.26 mmol, 1.0 equiv) and Et3N (0.51 mL, 7.19 mmol,
2.2 equiv) in dry DCM (29 mL) was added via syringe pump (8 mL/
h) to a refluxing solution of 1,2-benzenedisulfonyl dichloride (0.90 g,
3.27 mmol, 1.005 equiv) in DCM (135 mL). After the complete
addition, the solution was maintained at reflux for an additional 2 h.
The heat was removed, and after 16 h at room temperature, the
solvent was removed under reduced pressure. The residue of the crude
reaction mixture was redissolved in DCM (75 mL), washed with
saturated NaHCO3 (aqueous, 75 mL), brine (75 mL), and dried
(MgSO4). After the filtration and concentration under reduced
pressure, analytical LCMS confirmed the product (6). The material
Figure 3. Reversal of haloperidol-induced catalepsy in rats by 15f
after oral dosing. Catalepsy was measured in haloperidol
treated (0.75 mg/kg) rats after oral administration of compound
(0.1, 0.3, 1, 3, 10, 30, and 56.6 mg/kg) after 30 min. An adenosine A2A
antagonist from Neurocrine Biosciences28 was used as a positive
control at 56.6 mg/kg, po.
1
was taken through to the deprotection step. H NMR (400 MHz,
CDCl3): δ 8.11−8.08 (m, 2 H), 7.99−7.96 (m, 2 H), 7.59−7.55 (m,
4 H), 6.66 (br s, 1 H), 1.54 (s, 9 H).
produced a reversal of haloperidol-induced catalepsy (F(8,89)
=
2-(4-Aminophenyl)benzo[d][1,3,2]dithiazole 1,1,3,3-Tetra-
oxide (7). To a solution of 6 (3.26 mmol, 1.0 equiv) in DCM
(100 mL) at 0 °C was added dropwise 4 N HCl in dioxane (20 mL).
After 15 min, the ice bath was removed. Once the starting material was
no longer evident by TLC, the solvent was removed affording the HCl
salt (7), which was taken through to the amide formation step. LCMS:
tR = 3.319 min, m/z = 311.0 [M + H]+. 1H NMR (400 MHz, DMSO-
d6) δ 8.55−8.51 (m, 2 H), 8.21−8.17 (m, 2 H), 7.17−7.15 (m, 2 H),
6.75−6.73 (m, 2 H).
5.8697, p < 0.0001), significant at doses of 0.1−56.6 mg/kg,
compared with the vehicle control. The effects of 15f were
equally efficacious compared to those observed using an
adenosine A2A antagonist from Neurocrine Bioscience (com-
pound 23)28 as a positive control, administered at a dose of
56.6 mg/kg, po.
N-(4-(1,1,3,3-Tetraoxidobenzo[d][1,3,2]dithiazol-2-yl)-
phenyl)picolinamide (8d). To a solution of the HCl salt (7)
(1.0 equiv) in DCM/DIEA (4:1) (1 mL, 0.1 M) was added picolinyl
acid chloride (1.0 equiv). After 12 h at room temperature, the desired
CONCLUSION
■
We have discovered and characterized a new mGlu4 PAM in vivo
tool compound with activity in a preclinical model of Parkinson’s
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analogue 8d was obtained as an tan solid (49%). Analytical LCMS:
130.6, 127.7, 126.0, 125.6, 123.1, 121.34, 121.31, 120.2, 119.9, 52.4,
52.1, 46.9, 45.7, 45.3, 44.9. HRMS calcd for C21H17N3O3Cl [M + H]+,
394.0958; found 394.0959.
1
tR = 3.074 min, >98% (214 nm), m/z = 416.1 [M + H]+; H NMR
(400 MHz, DMSO-d6) δ 11.08 (br s, 1 H), 8.79 (d, 1 H, J = 4.0 Hz),
8.60−8.59 (m, 2 H), 8.24−8.21 (m, 5 H), 8.11 (t, 1 H, J = 8.0 Hz),
7.73 (t, 1 H, J = 4.8 Hz), 7.59 (d, 2 H, J = 8.4 Hz); 13C NMR (125
MHz, DMSO-d6) δ 163.5, 149.8, 148.9, 142.1, 138.7, 136.8, 134.0,
133.0, 127.7, 123.8, 123.1, 122.4, 119.1. HRMS calcd for
C18H13N3O5NaS2 [M + Na+], 438.0194; found 438.0194.
Bis(tert-butyl-2-chloro-4-nitrophenyl)carbamate (11). To a
solution of 2-chloro-4-nitroaniline 10 (5.0 g, 29 mmol) and DMAP
(50 mg, 0.41 mmol) in dry THF (250 mL) was added Boc2O (16.0 g,
73.3 mmol). The mixture was heated to reflux. After 1 h, the solvent
was removed. The residue was redissolved in EtOAc/0.5 N HCl
(aqueous), and the organic layer was separated. The aqueous layer was
extracted with EtOAc (3 × 50 mL), and the collected organic layers
were washed with brine (100 mL). The solution was dried (MgSO4),
filtered, and concentrated to afford bis(tert-butyl-2-chloro-4-
nitrophenyl)carbamate 11. LCMS: tR = 3.74 min, >98% at 254 nM,
m/z = 767.2 [2M + Na]+.
N-(3-Chloro-4-(1,3-dioxo-2-azaspiro[4.5]decan-2-yl)phenyl)-
picolinamide (15j). Following the general procedure, N-(3-chloro-4-
(1,3-dioxo-2-azaspiro[4.5]decan-2-yl)phenyl)picolinamide was obtained.
LCMS: tR = 1.439 min, >98% at 254 nM, m/z = 398.2 [M + H]+.
1H NMR (400 MHz, DMSO-d6) δ 11.01 (br s, 1 H), 8.76 (d, 1 H, J =
4.4 Hz), 8.24 (d, 1 H, J = 2.0 Hz), 8.17 (d, 1 H, J = 8.0 Hz), 8.08 (ddd,
1 H, J = 8.0, 8.0, 2.0 Hz), 7.99 (dd, 1 H, J = 8.4, 2.0 Hz), 7.70 (ddd,
1 H, J = 7.6, 4.8, 1.2 Hz), 7.39 (d, 1 H, J = 8.4 Hz), 2.86 (d, 1 H, J =
18.0 Hz), 2.78 (d, 1 H, J = 18.4 Hz), 1.77−1.60 (m, 7 H), 1.46−1.24
(m, 3 H); 13C NMR (125 MHz, DMSO-d6) δ 181.6, 175.1, 163.4,
149.7, 148.9, 140.7, 138.7, 131.7, 131.7, 131.1, 127.7, 125.8, 123.1,
121.3, 120.1, 45.3, 39.3, 34.0, 32.5, 25.1, 22.0, 21.9. HRMS calcd for
C21H21N3O3Cl [M + H]+, 398.1271; found 398.1271.
N-(3-Chloro-4-(2,5-dioxo-3-phenylpyrrolidin-1-yl)phenyl)-
picolinamide (15k). Following the general procedure, N-(3-chloro-
4-(2,5-dioxo-3-phenylpyrrolidin-1-yl)phenyl)picolinamide was obtained
as a mixture of diastereomers (dr 2:1). Major diastereomer, LCMS:
Bis(tert-butyl-4-amino-2-chlorophenyl)carbamate (12). To
a solution of bis(tert-butyl-2-chloro-4-nitrophenyl)carbamate 11
(29.0 mmol) in EtOAc (120 mL) was added 5% Pd/C (150 mg),
and an H2 atmosphere was applied. After 12 h, TLC confirmed loss of
starting material. The reaction mixture was filtered through Celite and
concentrated to afford bis(tert-butyl-4-amino-2-chlorophenyl)-
carbamate which was used without further purification. 1H NMR
(400 MHz, CDCl3) δ 6.94 (d, 1 H, J = 8.4 Hz), 6.72 (d, 1 H, J =
2.8 Hz), 6.53 (dd, 1 H, J = 8.4, 2.8 Hz), 3.75 (br s, 2 H), 1.41 (s, 18 H).
Bis(tert-butyl-2-chloro-4-(picolinamido)phenyl)carbamate
(13). A solution of bis(tert-butyl-4-amino-2-chlorophenyl)carbamate
12 (29.0 mmol) in DCM (25 mL) at 0 °C was subjected to DIEA
(10.2 mL, 72.5 mmol) followed by picolinoyl chloride hydrochloride
(5.68 g, 31.9 mmol). After 12 h, the mixture was added to EtOAc/
H2O (1:1, 120 mL). The organic layer was washed with water (2 ×
50 mL), brine (50 mL) and dried (MgSO4). The mixture was filtered
and concentrated to provide bis(tert-butyl-2-chloro-4-(picolinamido)-
1
tR = 1.370 min, >98% at 254 nM, m/z = 406.2 [M + H]+. H NMR
(400 MHz, DMSO-d6) δ 11.03 (br s, 1 H), 8.76 (d, 1 H, J = 4.8 Hz),
8.28 (d, 1 H, J = 2.4 Hz), 8.17 (d, 1 H, J = 8.0 Hz), 8.08 (ddd, 1 H, J =
7.6, 7.6, 1.6 Hz), 8.01 (dd, 1 H, J = 8.8, 2.4 Hz), 7.72−7.68 (m, 1 H),
7.52−7.30 (m, 6 H), 4.36 (dd, 1 H, J = 9.6, 5.2 Hz), 3.42 (dd, 1 H, J =
18.4, 9.6 Hz), 2.97 (dd, 1 H, J = 18.4, 5.2 Hz); 13C NMR (125 MHz,
DMSO-d6, mixture of diasteromers) δ 177.1, 175.4, 175.1, 163.3,
149.5, 148.7, 140.8, 140.7, 138.9, 138.5, 137.9, 131.8, 131.7, 131.2,
130.9, 129.3, 129.1, 128.7, 128.4, 127.9, 127.7, 126.0, 125.9, 123.2,
121.4, 121.3, 120.24, 120.15, 46.5, 46.2, 37.7, 37.5. HRMS calcd for
C22H17N3O3Cl [M + H]+, 406.0958; found 406.0958.
ASSOCIATED CONTENT
■
S
* Supporting Information
Experimental procedures, spectroscopic data, and NMR data
for selected compounds and biological procedures. This
material is available free of charge via the Internet at http://
pubs.acs.org. VU0400195, 20f, has been declared an MLPCN
mGlu4 probe (ML 182, CID 46869947, MLS 003171619) and
is available from BioFocus, South San Francisco, CA.
1
phenyl)carbamate 13. H NMR (400 MHz, CDCl3) δ 10.17 (br s,
1 H), 8.63 (d, 1 H, J = 4.0 Hz), 8.32 (d, 1 H, J = 8.0), 8.05 (d, 1 H, J =
2.4 Hz), 7.96 (ddd, 1 H, J = 8.0, 8.0, 1.2), 7.66 (dd, 1 H, J = 8.4, 2.4),
7.55−7.52 (m, 1 H), 7.20 (d, 1 H, J = 8.8 Hz), 1.40 (s, 18 H).
N-(4-Amino-3-chlorophenyl)picolinamide (14). To a solution
of bis(tert-butyl-2-chloro-4-(picolinamido)phenyl)carbamate 13 (29.0
mmol) in DCM (300 mL) at 0 °C was added dropwise 4 N HCl in
dioxane (50 mL). After 15 min, the ice bath was removed. Once the
starting material was no longer evident by TLC, the solvent was
removed, affording the HCl salt. The crude material was redissolved
with EtOAc (100 mL) and washed with NaHCO3 (aqueous). The
organic layer was dried (MgSO4), filtered, and concentrated to afford
N-(4-amino-3-chlorophenyl)picolinamide 14. LCMS: tR = 1.15 min,
>98% at 254 nM, m/z = 248.0 [M + H]+.
AUTHOR INFORMATION
■
Corresponding Author
*For C.M.N.: phone, 615-343-4303; fax, 615-343-3088; e-mail,
colleen.niswender@vanderbilt.edu. For C.R.H.: phone, 615-
936-6892; fax, 615-936-4381; e-mail, corey.r.hopkins@
vanderbilt.edu.
General Cyclic Imide Formation. To a solution of N-(4-amino-
3-chlorophenyl)picolinamide 14 (1.0 equiv) in toluene/acetic acid
(3:1) was added the desired anhydride (1.25 equiv), and the mixture
was heated to 150 °C in the microwave for 90 min. After LCMS
confirmed the product, the mixture was added to EtOAc/NaHCO3
(saturated) (1:1). The organic layer was separated, washed with brine,
and dried (MgSO4). After the organic layer was filtered and con-
centrated, the material was purified by LC (Gilson) or crystallization.
N-(3-Chloro-4-((1R,2S,3R,4S-bicyclo[2.2.1]hept-5-ene-1,3-
dioxo-1H-isoindol-1-yl)phenyl)picolinamide (15f). Following
the general procedure, N-(3-chloro-4-((1R,2S,3R,4S-bicyclo[2.2.1]-
hept-5-ene-1,3-dioxo-1H-isoindol-1-yl)phenyl)picolinamide was ob-
tained (mixture of diastereomers). LCMS: tR = 1.367 min, >98% at
254 nM, m/z = 394.0 [M + H]+. 1H NMR (400 MHz, MeOD) δ 8.81
(d, 1 H, J = 4.4 Hz), 8.40 (s, 1 H), 8.31−8.28 (m, 1 H), 8.20 (d, 1 H,
J = 2.4 Hz), 7.84 (m, 1 H), 7.79 (d, 1 H, J = 2.4 Hz), 7.05 (d, 1 H, J =
8.4 Hz), 6.31 (s, 2 H), 3.61−3.56 (m, 2 H), 3.44−3.42 (m, 2 H),
1.79−1.76 (m, 1 H), 1.71−1.68 (m, 1 H); 13C NMR (125 MHz,
DMSO-d6, mixture of diastereomers) δ 176.5, 176.4, 163.44, 163.42,
149.8, 149.7, 148.9, 140.7, 140.4, 138.7, 135.3, 135.0, 131.7, 131.2,
ACKNOWLEDGMENTS
■
The authors warmly acknowledge Emily L. Days, Tasha
Nalywajko, Cheryl A. Austin, and Michael Baxter Williams for
their critical contributions to the HTS portion of the project;
Matt Mulder, Chris Denicola, Nathan Kett, and Sichen Chang
for the purification of compounds utilizing the mass-directed
HPLC system; and Katrina Brewer for technical assistance with
the PK assays. The dog cassette in vivo experiment was
performed at Calvert Labs, and the rhesus in vivo experiment
was performed at the Yerkes Primate Center at Emory
University, GA. This work was supported by the National
Institute of Mental Health, National Institute of Neurological
Disorders and Stroke, the Michael J. Fox Foundation, the
Vanderbilt Department of Pharmacology, and the Vanderbilt
Institute of Chemical Biology. In addition, the authors thank
the NIH/MLPCN (Grant 5U54MH084659-02) for support of
this research. Vanderbilt is a member of the MLPCN and
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Article
(17) Hopkins, C. R.; Lindsley, C. W.; Niswender, C. M. mGluR4
positive allosteric modulation as potential treatment of Parkinson’s
disease. Future Med. Chem. 2009, 1, 501−513.
houses the Vanderbilt Specialized Chemistry Center for
Accelerated Probe Development.
(18) Engers, D. W.; Niswender, C. M.; Weaver, C. D.; Jadhav, S.;
Menon, U. N.; Zamorano, R.; Conn, P. J.; Lindsley, C. W.; Hopkins,
C. R. Synthesis and evaluation of a series of heterobiarylamides that
are centrally penetrant metabotropic glutamate receptor 4 (mGluR4)
positive allosteric modulators (PAMs). J. Med. Chem. 2009, 52, 4115−
4118.
(19) Engers, D. W.; Field, J. R.; Le, U.; Zhou, Y.; Bolinger, J. D.;
Zamorano, R.; Blobaum, A. L.; Jones, C. K.; Jadhav, S.; Weaver, C. D.;
Conn, P. J.; Lindsley, C. W.; Niswender, C. M.; Hopkins, C. R.
Discovery, synthesis, and structure−activity relationship development
of a series of N-(4-acetamido)phenylpicolinamides as positive
allosteric modulators of metabotropic glutamate receptor 4 (mGlu4)
with CNS exposure in rats. J. Med. Chem. 2011, 54, 1106−1110.
(20) East, S. P.; Bamford, S.; Dietz, M. G. A.; Eickmeier, C.; Flegg,
A.; Ferger, B.; Gemkow, M. J.; Heilker, R.; Hengerer, B.; Kotey, A.;
ABBREVIATIONS USED
■
SAR, structure−activity relationship; mGluR, metabotropic
glutamate receptor; PAM, positive allosteric modulator; HTS,
high-throughput screening; CLint, intrinsic clearance; PPB,
plasma protein binding; AUC, area under the curve; GPCR,
G-protein-coupled receptor; 1, N-phenyl-7-(hydroxyimino)-
cyclopropa[b]chromen-1a-carboxamide; CNS, central nervous
system; PD, Parkinson’s disease; GIRK, G-protein-coupled
inwardly rectifying potassium channel; CYP, cytochrome P450;
TPSA, topological polar surface area; CLHEP, predicted hepatic
clearance; B/P, brain/plasma ratio; CRC, concentration−
response curve; fu, amount free and unbound (in %); DA,
dopamine; PK, pharmacokinetics; BBB, blood−brain barrier;
MW, molecular weight; FS, fold shift; RLM, rat liver
microsome
Loke, P.; Schanzle, G.; Schubert, H.-D.; Scott, J.; Whittaker, M.;
̈
Williams, M.; Zawadzki, P.; Gerlach, K. An orally bioavailable positive
allosteric modulator of the mGlu4 receptor with efficacy in an animal
model of motor dysfunction. Bioorg. Med. Chem. Lett. 2010, 20, 4901−
4905.
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