Synthesis and Pharmacological Evaluation of Noncatechol G Protein Biased and Unbiased Dopamine D1 Receptor Agonists

Article abstract of DOI:10.1021/acsmedchemlett.9b00050

Noncatechol heterocycles have recently been discovered as potent and selective G protein biased dopamine 1 receptor (D1R) agonists with superior pharmacokinetic properties. To determine the structure-activity relationships centered on G protein or β-arrestin signaling bias, systematic medicinal chemistry was employed around three aromatic pharmacophores of the lead compound 5 (PF2334), generating a series of new molecules that were evaluated at both D1R G_s-dependent cAMP signaling and β-arrestin recruitment in HEK293 cells. Here, we report the chemical synthesis, pharmacological evaluation, and molecular docking studies leading to the identification of two novel noncatechol D1R agonists that are a subnanomolar potent unbiased ligand 19 (PW0441) and a nanomolar potent complete G protein biased ligand 24 (PW0464), respectively. These novel D1R agonists provide important tools to study D1R activation and signaling bias in both health and disease.

Full text of DOI:10.1021/acsmedchemlett.9b00050

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Letter
Synthesis and pharmacological evaluation of non-catechol G
protein biased and unbiased dopamine D1 receptor agonists
Pingyuan Wang, Daniel E. Felsing, Haiying Chen, Sweta R. Raval, John A. Allen, and Jia Zhou
ACS Med. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acsmedchemlett.9b00050 • Publication Date (Web): 05 Apr 2019
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ACS Medicinal Chemistry Letters
Synthesis and pharmacological evaluation of non-catechol G protein
biased and unbiased dopamine D1 receptor agonists
1
2
3
4
5
6
Pingyuan Wang,†,§ Daniel E. Felsing,‡,§ Haiying Chen,† Sweta R. Raval,‡ John A. Allen,*,†,‡ and Jia
Zhou*,†,‡
7
8
9
†Chemical Biology Program, Department of Pharmacology and Toxicology, ‡Center for Addiction Research, University of
Texas Medical Branch, Galveston, TX 77555, USA
ABSTRACT: Non-catechol heterocycles have recently been discovered as potent and selective G protein biased dopamine 1
receptor (D1R) agonists with superior pharmacokinetic (PK) properties. To determine the structure-activity relationships (SARs)
centered on G protein or -arrestin signaling
10
11
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bias, systematic medicinal chemistry was
employed
pharmacophores of the lead compound 5
(PF2334), generating series of new
around
three
aromatic
a
molecules that were evaluated at both D1R Gs-
dependent cAMP signaling and β-arrestin
recruitment in HEK293 cells. Here we report
the chemical synthesis, pharmacological
evaluation and molecular docking studies
leading to the identification of two novel non-
catechol D1R agonists that are
a sub-
nanomolar potent unbiased ligand 19
(PW0441) and a nanomolar potent complete G protein biased ligand 24 (PW0464), respectively. These novel D1R agonists provide
important tools to study D1R activation and signaling bias in both health and disease.
KEYWORDS: dopamine 1 receptor, biased agonism, functional selectivity, non-catechol, cAMP, β-arrestin
The dopamine (DA) (1, Figure 1) receptor family consists of
five G protein-coupled receptors (GPCRs) which play a
critical role in central nervous system (CNS) signaling.1
Numerous studies have revealed that dopamine receptors are
OH
HO
HO
HO
HO
HO
NH2
NH
O
HO
HO
NH
Cl
NH2
involved in the pathophysiology of human diseases including
3
neurologic and psychiatric illnesses,2,
addiction,4
3 (A77636)
2 (SKF81297)
1 (Dopamine)
4 (Dihydrexidine)
cardiovascular and endocrine diseases.5 Based on their
structure, biochemical and pharmacological characteristics, the
dopamine receptor family are divided into two subfamilies:
the D1-like family (D1 and D5) or the D2-like family (D2, D3
and D4).6 Canonical dopamine signaling by D1-like receptors
occurs via heterotrimeric Gs/olf proteins which activate
adenylyl cyclase to increase production of cyclic adenosine
monophosphate (cAMP).1, 6 In addition, D1-like receptors can
engage and couple to β-arrestin proteins, which control
receptor trafficking, desensitization and promote G protein-
O
N
N
N
NH
N
A
N
N
B
O
C
F
O
O
N
N
N
O
O
O
6 (PF6142)
7 (PF1119)
5 (PF2334)
Figure 1. Structures of previous representative catechol
(shown in red) and non-catechol D1R selective agonists.
6
independent signaling.1, Agonists that activate receptors to
signal primarily via G proteins versus β-arrestin are known as
biased agonists,7 which may improve agonist efficacy and/or
reduce side effects induced by receptor ligands.8
Due to the fundamental role of the D1R in the CNS function
and disease, tremendous efforts for over 40 years have been
devoted to the discovery of selective D1R agonists for clinical
21-23
use.2,
While several selective D1R ligands have been
The dopamine 1 receptor (D1R) is the most abundant
dopamine receptor in mammalian brain, with particularly high
expression in the striatum (caudate, putamen and nucleus
accumbens) and the frontal cortex.9 The D1R enables DA
neurotransmission to control working memory and attention,10,
identified, none are currently FDA approved for the treatment
of CNS disorders, and development of clinically viable, drug-
like D1R selective agonists for CNS diseases remains elusive.
This is primarily due to the chemistry of all previous D1R
agonists, which possess a dihydroxyphenyl catechol or
catechol-like scaffolds, for example compounds 2, 3, and 4
(highlighted in red, Figure 1). Catechol-based D1R agonists
suffer from poor CNS penetration, negligible oral
bioavailability, rapid metabolism and therefore insufficient in
vivo efficacy.22 Most recently, a new generation of D1R non-
catechol agonists (compounds 5-7, Figure 1) with high
affinity, selectivity and superior PK (pharmacokinetic) profiles
11
13
15
voluntary movement,12,
reward,14,
and other
physiological processes. Hypofunction of the D1R has also
been observed in a variety of neurologic and psychiatric
disorders including Parkinson’s disease (PD),16 Alzheimer’s
disease (AD),17 attention deficit hyperactivity disorder
(ADHD),18 cognitive impairment in schizophrenia19 and
addiction.20 This suggests that selective activation of the D1R
is a promising therapeutic avenue for developing CNS
therapeutics.
25
were reported by Pfizer.24, In addition, previous catechol
D1R agonists typically display activation of both G protein-
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mediated and β-arrestin recruitment; however, a recent report
EtOH, 60 oC, 12 h, 94%; (h) (i) Cs2CO3, corresponding Cl-R,
120 C, 12 h. (ii) CF3COOH, CH2Cl2, rt, 1 h; (iii) K2CO3,
MeOH, rt, 12 h, 37-69% (three steps).
o
1
2
3
suggested select benzazepine derivatives exhibit G protein
bias;26 while non-catechol D1R agonists show minimal β-
26
arrestin recruitment (G protein biased agonists).22,
Accumulated studies suggest that the D1R-mediated β-arrestin
recruitment pathway may be involved in memory related
functions and cognitive processes.27-30 In addition, D1R-
mediated β-arrestin recruitment can cause D1R desensitization
that may limit the efficacy of some D1R agonists.22, 24, 31 To
accurately address the impact of D1R-mediated signaling by
β-arrestins versus G proteins, novel D1R chemical probes that
are biased and unbiased at these pathways are needed. Here
we report the synthesis, biological activity and docking studies
of novel non-catechol D1R ligands leading to our discovery of
G protein biased and the first unbiased non-catechol agonist.
These novel chemical probes provide important tools to study
D1R signaling mechanisms in health and disease and to
evaluate if balanced or biased D1R agonist activity is
preferred for the treatment of neurological and psychiatric
disorders.
4
5
6
7
8
9
First, we modified the pyridazin-3(2H)-one moiety of
compound 5 leading to compound 11, and its synthetic route is
described in Scheme 1. With starting material 4-
chlorofuro[3,2-c]pyridine (8) and 4-bromo-3-fluorophenol (9),
the intermediate 10 was obtained in the presence of Cs2CO3.24
Compound 11 was produced via C-N coupling reaction of 10
with pyridin-3-amine in a yield of 67%.32 Replacement the
pyridazin-3(2H)-one moiety of compound 5 with pyrimidine-
2,4(1H,3H)-dione led to compound 19. Further modification
of compound 19 by replacement of the furo[3,2-c]pyridine
with tricyclic ring, bicyclic ring and pyridine ring generated
compounds 20-24 (Scheme 1). Protection of compound 1233
with 2-(trimethylsilyl)ethoxymethyl group resulted in key
intermediate 13. The intermediate 15 was obtained by
protection of the starting material 4-bromo-3-methylphenol
(14) with a benzyl group. Treatment of intermediate 15 with
bis(pinacolato)diboron under palladium catalysis produced the
intermediate 16. Coupling of the intermediate 13 with 16
under the condition of Suzuki reaction provided the
intermediate 17. Deprotection of the benzyl group of 17 led to
intermediate 18. Compounds 19 ~ 24 were obtained by
reaction of intermediate 18 with corresponding heterocyclic
halides34-36 in the presence of Cs2CO3, followed by
deprotection of the 2-(trimethylsilyl)ethoxymethyl group.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
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35
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42
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59
60
The general premise of this report was to apply the scaffold
of the selective, high affinity, non-catechol G protein-biased
D1R agonist, compound 5,24 as the lead compound for further
structure−activity relationship (SAR) studies. We employed
systematic medicinal chemistry around three aromatic
substituents of compound 5: (A) head pyridazinone, (B)
middle phenyl, and (C) lower furopyridine (Figure 1; Ring C
highlighted in blue, ring B highlighted in cyan and ring A
highlighted in pink). The synthetic procedures of these newly
synthesized D1R agonists are depicted in Schemes 1-3.
As outlined in Scheme 2, compound 27 was designed by
substituting the phenoxyl group of compound 19 with
aminopyridine ring. The intermediate 26 was produced via C-
N coupling reaction of 12 with compound 25 in a yield of
67%. Further, the C-N coupling reaction of intermediate 26
with compound 8 afforded compound 27. Replacement of the
phenoxyl scaffold of compound 19 with indoline led to
compounds 33 and 34. The intermediate 29 was obtained by
protection of the starting material 5-bromoindoline (28) with a
Boc group. Treatment of intermediate 29 with
bis(pinacolato)diboron under palladium catalysis produced the
intermediate 30. Coupling of the intermediate 30 with 12
under the condition of Suzuki reaction provided the
intermediate 31, followed by Boc-deprotection leading to
intermediate 32. Coupling of 32 with corresponding
heterocyclic halides under the C-N condition produced
compounds 33 and 34, respectively.
Scheme 1. Synthesis of compounds 11 and 19 - 24a
F
F
H
N
Br
N
Cl
F
Br
O
O
N
a
b
N
N
O
HO
8
9
O
O
11
10
O
N
O
N
Si
c
NH
N
O
O
Si
Br
O
Br
O
N
O
12
f
13
N
O
O
Br
Br
B
d
e
O
BnO
17
HO
BnO
BnO
g
14
16
15
Scheme 2. Synthesis of compounds 27, 33 and 34 a
O
O
N
Si
NH
N
O
h
N
O
O
O
R
HO
18
R =
O
H
N
O
N
F
N
N
N
N
N
F
O
S
S
N
N
N
24
19
20
21
23
22
aReagents and conditions: (a) Cs2CO3, DMSO, 18 h, 86%; (b)
Tris(dibenzylideneacetone)dipalladium(0), pyridin-3-amine,
o
K2CO3, XantPhos, 1,4-dioxane, 100 C, 12 h, 67%; (c) 2-
(trimethylsilyl)ethoxymethyl
chloride,
1,8-
Diazabicyclo[5.4.0]undec-7-ene, MeCN, 60 oC, 18 h, 64%; (d)
BnBr, K2CO3, DMF, rt, 12 h, 80%; (e) bis(pinacolato)diboron,
[1,1'-Bis(diphenylphosphino)ferrocene]dichloropalladium(II),
KOAc, 1,4-dioxane, 85 oC, 16 h, 71%; (f) [1,1'-
bis(diphenylphosphino)ferrocene]dichloropalladium(II),
o
K2CO3, 1,4-dioxane, 100 C, 12 h, 41%; (g) H2, Pd(OH)2/C,
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O
O
N
O
B
O
N
NH
1
2
3
4
5
6
7
8
O
B
NH
Br
O
O
c
d
a
b
NH
N
N
N
O
O
b
a
O
N
O
N
N
N
N
N
Br
Br
O
HN
H
H
Cbz
N
NH2 H2N
Cbz
Cbz
35
39
36
38
37
12
25
26
27
O
e
O
O
N
Si
HN
Si
O
N
NH
O
B
O
N
Br
g
e
O
N
f
c
d
O
N
O
O
O
N
N
N
H
N
N
H
N
Boc
N
N
R
Boc
9
31
Boc
28
Cbz
41
29
30
40
f
10
11
12
13
14
15
16
17
18
19
20
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23
24
25
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42
43
44
45
46
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R =
F
O
N
O
N
O
N
F
O
NH
NH
43
42
g
R =
F
O
N
O
N
O
N
aReagents and conditions: (a) NaBH3CN, AcOH, 0 C - rt, 4
h, 68%; (b) CbzCl, Et3N, CH2Cl2, 0 oC - rt , 12 h, 74%; (c) N-
bromosuccinimide, CH2Cl2, 0 oC ~ rt , 12 h, 94%; (d)
o
F
N
O
N
H
R
34
33
32
aReagents
bis(diphenylphosphino)ferrocene]tdichloropalladium(II),
and
conditions:
(a)
[1,1'-
bis(pinacolato)diboron,
[1,1'-Bis(diphenylphosphino)
ferrocene]dichloropalladium(II), KOAc, 1,4-dioxane, 70 oC,
48 h, 46%; (e) 13, [1,1'-Bis(diphenylphosphino)ferrocene]
dichloropalladium(II), K2CO3, 1,4-dioxane, 100 oC, 12 h,
38%; (f) Pd/C, H2, rt, 12 h, 96%; (g) (i) Pd(OAc)2, 4,5-
bis(diphenylphosphino)-9,9-dimethylxanthene, Cs2CO3, 1,4-
o
K2CO3, 1,4-dioxane, 100 C, 12 h, 67%; (b) compound 8,
tris(dibenzylideneacetone)dipalladium(0), 4,5-
bis(diphenylphosphino)-9,9-dimethylxanthene, K2CO3, 1,4-
dioxane, 100 oC, 12 h, 59%; (c) (Boc)2O, Et3N, CH2Cl2, rt, 12
h, 91%; (d) bis(pinacolato)diboron, bis(diphenylphosphino)
o
dioxane, 100 C, 12 h. (ii) CF3COOH, CH2Cl2, rt, 1 h; (iii)
K2CO3, MeOH, rt, 12 h, 17-24% (three steps).
o
ferrocene]tdichloropalladium(II), KOAc, 1,4-dioxane, 85 C,
16 h, 81%; (e) Pd(PPh3)4, Na2CO3, 1,4-dioxane, water, 100 oC,
12 h, 77%; (f) i) CF3COOH, CH2Cl2, rt, 1 h; ii) K2CO3,
MeOH,
rt,
12
h,
92%;
(g)
Pd(OAc)2,
4,5-
Previous studies of non-catechol D1R agonists suggested
that the head group (A) might interact with residues S188 and
L190 in ECL2 to influence the potency of G protein-mediated
cAMP signaling.24 To probe the steric availability and
flexibility around this region of the molecule, we introduced a
nitrogen linker to yield compound 11, which was found to
drastically decrease the cAMP potency (> 1,000 nM).
However, replacement of pyridazin-3(2H)-one moiety of
compound 5 with pyrimidine-2,4(1H,3H)-dione to yield
compound 19 resulted in a dramatically increased cAMP
potency from 10.3 ± 2.8 nM to 0.3 ± 0.1 nM, and retained
efficacy in the cAMP assay (Figure 3 and Table 1).
Interestingly, this substitution led to the restoration of -
arrestin recruitment, which increased the potency from 485 ±
102 nM to 35 ± 4 nM, and efficacy from 45 ± 4 to 86 ± 14 %
DA, in comparison to the lead compound (Figure 4 and Table
2). The reversal of G protein cAMP bias from compound 5 to
19 suggests that ECL2 interactions with this head group may
affect both potency and signaling bias.
bis(diphenylphosphino)-9,9-dimethylxanthene, Cs2CO3, 1,4-
dioxane, 100 oC, 12 h, 50-73%.
Compounds 42 and 43 were designed by adding a methyl
group on the compounds 33 and 34, respectively, and the
synthetic procedures are outlined in Scheme 3. 4-
Methylindoline (36) was obtained by hydrogenation of the
starting material 4-methyl-1H-indole (35). Protection of
intermediate 36 by CbzCl in the presence of Et3N led to
intermediate 37. Compound 38 was prepared by reacting
intermediate 37 with NBS. The boronate intermediate 39 was
synthesized from compound 38 under the palladium catalysis
condition, and was further converted into compound 40 under
palladium catalyzed cross-coupling reaction conditions. Cbz-
deprotection of compound 40 gave intermediate 41. Coupling
of 41 with corresponding heterocyclic halides under the
palladium catalyzed C-N condition led to the compounds 42
and 43. The detailed synthetic procedures and structural
characterization data are provided in the Supporting
Information (SI).
Table 1. EC50 values and Emax (Gs-cAMP) of D1R agonists
Gs-cAMP
cLogPa
Scheme 3. Synthesis of compounds 42 and 43a
Compounds
EC50 (nM)b
44 ± 14
4.7 ± 2.8
10 ± 3
Emax (% DA)b
1
-0.40
3.03
3.28
4.13
4.13
4.14
3.02
3.51
3.75
100
2
100 ± 3
90 ± 4
78 ± 6
66 ± 5
63 ± 1
107 ± 6
30 ± 2
7 ± 1
5
6
11 ± 3
7
81 ± 38
>1,000
11
19
20
21
0.3 ± 0.1
>1,000
>1,000
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22
23
24
27
33
34
42
43
2.83
2.37
2.97
2.27
3.18
3.01
3.23
3.28
580 ± 60
610 ± 86
5.3 ± 1.0
450 ± 100
410 ± 70
>1,000
5 ± 1
1
2
3
4
5
6
7
8
106 ± 17
104 ± 2
89 ± 2
61 ± 8
77 ± 2
96 ± 9
92 ± 4
360 ± 120
950 ± 190
9
acLogP: http://biosig.unimelb.edu.au/pkcsm/prediction. bThe
values are the mean ± S.E.M. of at least three independent
experiments.
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11
12
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19
20
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23
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Figure 3. Representative dose-response curve for D1R-
mediated cAMP increase from 1 (red), 2 (green), 5 (purple),
19 (PW0441, blue), 24 (PW0464, orange). Luminescence
counts/sec were normalized to 100% DA response (10 µM
DA).
Table 2. EC50 values and Emax (Arrestin-TANGO) of selected
D1R agonists
Arrestin-TANGO
Compounds
EC50 (nM)a Emax (% DA)a
1
1,400 ± 190 100
2
360 ±70
76 ± 6
5
490 ± 100
320 ± 50
45 ± 4
21 ± 2
6
7
1,100 ± 300 9 ± 2
19
24
35 ± 4
N.A.b
86 ± 14
N.A.b
aThe values are the mean ± S.E.M. of at least three
independent experiments. bN.A. is no activity
Figure 4. Representative dose-response curve for D1R-
mediated -arrestin recruitment from 1 (red), 2 (green), 5
(purple), 19 (PW0441, blue), 24 (PW0464, orange).
Luminescence counts/sec were normalized to 100% DA
response (10 µM DA).
Gray and Allen et al. previously suggested the lower
heterocycle (C) in compound 5 orients the compound into a
unique binding mode, responsible for enabling G protein
bias.24 Thus, we further probed the steric and electronic
components around the lower scaffold of the molecule to
probe the SAR influencing signaling bias of these non-
catechol agonists. Increasing the size and/or aromaticity of the
heterocycle, i.e. compounds 20-22, detrimentally affected both
cAMP potency (> 500 nM) and efficacy (< 30% DA),
suggesting that the space in the orthosteric binding pocket for
the heterocycle is sterically limited (Table 1). In addition, all
of the newly synthesized compounds exhibit cLogP < 5,
similar to compound 5, suggesting these novel ligands may
have a favorable PK profile (Table 1). Interestingly, when we
broke the furan ring into a linear substituted amide, or
difluoroether moiety yielding compounds 23 and 24, these
molecules retained their cAMP full agonism, and compound
24 was similarly potent (5.3 ± 1.0 nM) to compound 5 (10.3 ±
2.8 nM). Additionally, compound 24 was found to elicit
complete G protein bias, showing no activity for D1R-
mediated β-arrestin recruitment (Figure 4 and Table 2).
Table 3. D1R affinity values of selected D1R agonists
Compounds
Ki (nM)a
2
15 ± 2
5
51 ± 13b
2.4 ± 0.1
51 ± 4
19
24
aThe values are the mean ± S.E.M. of at least three
independent experiments. bData are taken from reference.24
Following the discovery of the potent unbiased agonist 19
and complete G protein biased ligand 24, we formally
determined binding affinities at the orthosteric D1R binding
pocket using competition radioligand binding (see SI). Both
compounds 19 and 24 displayed relevant affinities of 2.4 ± 0.1
nM and 51 ± 4 nM, respectively (Table 3) indicating the
ligands are high affinity orthosteric site D1R agonists. In
addition, we further confirmed G protein signaling bias of
select molecules using the method of Kenakin, resulting in
bias factors of 1.0 for 2, 0.94 for 5 and 1.28 for 19, indicating
these ligands are not biased. Bias factors could not be
calculated for 24 due to the complete inactivity of this agonist
for D1R-mediated β-arrestin recruitment, consistent with its
complete G protein bias. Lastly, the selectivity of 19 and 24
for G protein-mediated cAMP activity at other DA receptors
was performed (Figure S1, Table S1). Neither ligand had
detectable activity at D2R or D4R, but both showed similar
Compounds 27, 33, 34, 42 and 43 were synthesized to probe
the impact of flexibility and aromaticity of the middle
aromatic ring (B). Unfortunately, all five compounds
substantially lost potency in the cAMP assay (decreased ≥ 500
nM) (Table 1), suggesting that modifications on this portion
of the molecule are neither amenable for D1R G protein
activation, nor β-arrestin recruitment.
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potency and efficacy at the D5R and D1R, consistent with the
dual D1R/D5R agonist activity of non-catechol ligands.24
1
2
3
To probe which amino acid residues our leads are mostly
likely to interact with, we docked compounds 19 and 24 in an
4
5
established D1R homology model based on the 2-adrenergic
37
receptor24,
using the Schrödinger Drug Discovery Suite
program (Figures 5A & 5B). The docking results indicated
that the new compounds have energetically favorable
interactions and readily dock into the orthosteric ligand-
binding site. To further characterize the binding pose,
compounds 19 and 24 were compared in our theoretical
investigation. As shown in Figures 5A and 5B, both
compounds 19 and 24 do not form significant interactions with
D1R Ser198 or Ser202 in the transmembrane 5 (TM5). These
TM5 residues are known to form hydrogen bonds with
catechol-based ligands and the lack of such interactions
suggest non-catechol agonists form a unique binding mode
versus catechols.24 Interestingly, residue Ser107 in the TM3
does form a hydrogen bond interaction with the O atom on the
furo[3,2-c]pyridine ring of 19. The furo[3,2-c]pyridine ring of
19 forms π-π stacking interactions with residues Phe288 and
Phe289 in the TM6. Moreover, the O atom between benzene
ring and furo[3,2-c]pyridine ring of 19 forms a hydrogen bond
with Asn292 in the TM6. This binding mode may explain the
significant activity loss when changing phenoxyl into the
aminopyridine ring or indoline ring. In addition, another
similar π-π stacking interaction between pyrimidinedione ring
and Phe313 is also formed. Meanwhile, the pyrimidinedione
ring points into the ECL2 chain, leading to hydrophobic
interactions with the hydrophobic residues of Leu190, Ser189,
Ser188 and Asp187 in the ECL2 (Figures S2 and S3). Its
analog 24 displayed a similar binding pose as 19, but notably
without a π-π interaction with Phe288 and no H-bond with
Ser107 in TM3 due to lack of the aromatic furan ring. This
may explain the decreased binding affinity of 24 with D1R
compared to 19.
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Figure 5. Putative binding modes and molecular docking of
compound 19 and 24 with D1R. (A) Docking of compound 19
(purple) into the binding pocket of D1R. Important residues
are drawn in sticks. Hydrogen bonds are shown as dashed
black lines, while π-π interactions are shown in dashed cyan
lines. (B) Docking of compound 24 (green) into the binding
pocket of D1R. Important residues and key interactions are
presented in a similar fashion.
As shown in Figures 5A and 5B, compound 19 forms a
hydrogen bond with Ser107 on the TM3 and it displays both G
protein and β-arrestin activities (unbiased D1R agonist).
However, compound 24 without that Ser107 TM3 hydrogen
bond shows no β-arrestin activity (biased D1R agonist). This
suggests non-catechol ligands which engage Ser107 in TM3 of
the D1R may be important for β-arrestin activity.
Interestingly, recent studies by McCorvy et al. indicate ligand
interactions with TM5 serine residues and ECL2 are very
important for G protein and β-arrestin signaling activity at
39
related GPCRs.38,
19 and 24 do not form significant
interactions with D1R Ser198 or Ser202 in the transmembrane
5 (TM5) but are in close proximity to form hydrophobic
interactions with ECL2 residues, further supporting the
concept that ligand interactions with ECL2 and TMs drive
D1R biased signaling. However, to mechanistically
understand the key ligand-D1R interactions and receptor
conformations controlling biased signaling, future D1R
biochemical (e.g. receptor mutagenesis) and biophysical
studies are required. Taken together, the radioligand binding
and ligand docking studies indicate 19 and 24 are both
orthosteric site agonists at the D1R. These modeling studies
also provide
a foundation to further study structural
mechanisms by which 19 and 24 promote D1R biased and
balanced signaling.
In summary, a series of non-catechol heterocycles have
been designed, synthesized, and pharmacologically evaluated
as D1R orthosteric agonists. We probed the steric and
electronic components around three aromatic regions of the
lead compound 5. The findings demonstrate that both the head
(A) and lower (C) aromatic regions have significant impact on
the potency and efficacy of G protein cAMP signaling and -
arrestin recruitment; these regions are amenable for further
medicinal chemistry efforts. However, changing the middle
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(B) aromatic ring into the indoline ring is not tolerated. These
therapeutics for neurological and psychiatric disorders. Chem.
Rev. 2013, 113, 123-178.
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5
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studies culminated with the discovery of the first potent non-
catechol D1R unbiased agonist 19 (PW0441) and a complete
G protein biased agonist 24 (PW0464). Further studies to
discover a D1R -arrestin biased agonist and testing of lead
molecules 19 and 24 for in vivo efficacy in preclinical models
of neurological and neuropsychiatric diseases are currently
underway.
3.
Vaughan Iii, T. B.; Katznelson, L. Psychological effects of
Dopamine Agonist Treatment in Patients with
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A.; Lust, R. M.; Clemens, S. The dopamine D3 receptor
knockout mouse mimics aging-related changes in autonomic
function and cardiac fibrosis. PLoS One 2013, 8, e74116.
The Supporting Information is available free of charge on the
ACS Publications website.
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Beaulieu, J. M.; Espinoza, S.; Gainetdinov, R. R.
Synthetic procedures for the preparation of new compounds,
analytical data, and experimental procedures for in vitro
assays as well as molecular docking studies (PDF).
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AUTHOR INFORMATION
Corresponding Authors
*Tel: 409-772-9748. Fax: 409-772-9648. E-mail:
jizhou@utmb.edu
8.
Allen, J. A.; Yost, J. M.; Setola, V.; Chen, X.;
Sassano, M. F.; Chen, M.; Peterson, S.; Yadav, P. N.; Huang,
X. P.; Feng, B.; Jensen, N. H.; Che, X.; Bai, X.; Frye, S. V.;
Wetsel, W. C.; Caron, M. G.; Javitch, J. A.; Roth, B. L.; Jin, J.
Discovery of beta-arrestin-biased dopamine D2 ligands for
probing signal transduction pathways essential for
antipsychotic efficacy. Proc. Natl. Acad. Sci. U S A, 2011, 108,
18488-18493.
*Tel: 409-772-9621. Fax: 409-747-7050. E-mail:
joaallen@utmb.edu
Author Contributions
§These two authors contributed equally and should be
considered as co-first authors.
Funding
9.
Klein, M. O.; Battagello, D. S.; Cardoso, A. R.;
This work was supported by grants from the National
Institutes of Health (P50 DA033935, P30 DA028821), and
T32 DA07287 (to DEF), Pharmaceutical Research and
Manufacturers of America Foundation (PhRMA Research
Starter Grant RSGPT18) (to JAA), and the Center for
Addiction Research at the University of Texas Medical
Branch.
Hauser, D. N.; Bittencourt, J. C.; Correa, R. G. Dopamine:
Functions, Signaling, and Association with Neurological
Diseases. Cell. Mol. Neurobiol. 2018, 39, 31-59.
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Sawaguchi, T.; Goldman-Rakic, P. S. D1 dopamine
receptors in prefrontal cortex: involvement in working
memory. Science 1991, 251, 947-950.
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White, N. M.; Packard, M. G.; Seamans, J. Memory
enhancement by post-training peripheral administration of low
doses of dopamine agonists: possible autoreceptor effect.
Behav. Neural. Biol. 1993, 59, 230-241.
Notes
The authors declare no competing financial interest.
12.
Jackson, D. M.; Westlind-Danielsson, A. Dopamine
ACKNOWLEDGMENT
receptors: molecular biology, biochemistry and behavioural
aspects. Pharmacol. Ther. 1994, 64, 291-370.
We sincerely thank Dr. Scot Mente for the assistance with and
for providing the D1R homology model.
13.
Gershanik, O.; Heikkila, R. E.; Duvoisin, R. C.
Behavioral correlations of dopamine receptor activation.
Neurology 1983, 33, 1489-1492.
ABBREVIATIONS
14.
Dichter, G. S.; Damiano, C. A.; Allen, J. A. Reward
AD, Alzheimer’s disease; ADHD, attention deficit
hyperactivity disorder; CNS, central nervous system; cAMP,
circuitry dysfunction in psychiatric and neurodevelopmental
disorders and genetic syndromes: animal models and clinical
findings. J. Neurodev. Disord. 2012, 4, 19.
cyclic adenosine monophosphate; D1R, dopamine
1
receptor; DA, dopamine; GPCR, G protein-coupled receptor;
PD, Parkinson’s disease; PK, pharmacokinetic; SAR,
structure-activity relationship; TM, transmembrane.
15.
Di Chiara, G. The role of dopamine in drug abuse
viewed from the perspective of its role in motivation. Drug
Alcohol Depend. 1995, 38, 95-137.
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Gerfen, C. R.; Engber, T. M. Molecular
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