Discovery of selective biaryl ethers as PDE10A inhibitors: Improvement in potency and mitigation of Pgp-mediated efflux

Article abstract of DOI:10.1016/j.bmcl.2012.10.078

We report the discovery of a novel series of biaryl ethers as potent and selective PDE10A inhibitors. Structure-activity studies improved the potency and decreased Pgp-mediated efflux found in the initial compound 4. X-ray crystallographic studies revealed two novel binding modes to the catalytic site of the PDE10A enzyme.

Full text of DOI:10.1016/j.bmcl.2012.10.078

Bioorganic & Medicinal Chemistry Letters 22 (2012) 7371–7375
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of selective biaryl ethers as PDE10A inhibitors: Improvement
in potency and mitigation of Pgp-mediated efflux
Robert M. Rzasa a, , Essa Hu a, Shannon Rumfelt a, Ning Chen a, Kristin L. Andrews c, Samer Chmait c,
⇑
James R. Falsey a, Wenge Zhong a, Adrie D. Jones d, Amy Porter b, Steven W. Louie e, Xiaoning Zhao d,
James J. S. Treanor b, Jennifer R. Allen a
a Department of Medicinal Chemistry, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
b Department of Neuroscience, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
c Department of Molecular Structure and Characterization, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
d Department of Molecular Structure and Characterization, Amgen Inc., 1120 Veterans Boulevard, So San Francisco, CA 94080-1985, USA
e Department of Pharmacokenetics and Drug Metabolism, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
We report the discovery of a novel series of biaryl ethers as potent and selective PDE10A inhibitors.
Structure–activity studies improved the potency and decreased Pgp-mediated efflux found in the initial
compound 4. X-ray crystallographic studies revealed two novel binding modes to the catalytic site of the
PDE10A enzyme.
Received 21 August 2012
Revised 5 October 2012
Accepted 15 October 2012
Available online 22 October 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Phosphodiesterase
PDE10A
Inhibitors
Pgp-mediated efflux
Schizophrenia
Cyclic phosphodiesterases (PDE) are enzymes that regulate cel-
lular signaling by hydrolyzing the 30-50phosphodiester bond of sec-
ondary messengers cyclic adenosine mono phosphate (cAMP) and
cyclic guanosine mono phosphate (cGMP).1 Deregulation of PDEs
has been implicated in various diseases such as cardiovascular dis-
ease, neurodegenerative disorders, inflammation and cancer.1,2
PDE enzymes constitute a diverse, 11-membered family of iso-
zymes that differ in their substrate specificity and tissue distribu-
tion.3 Specifically, PDE10A is a dual specificity phosphodiesterase
that is predominantly expressed in the medium spiny neurons of
the striatum.4,5 Inhibition of PDE10A effectively increases the stri-
atal levels of cAMP/cGMP resulting in modulation of neuronal
activity.6 Evidence suggests inhibition of PDE10A can be a novel
mechanism for the treatment for neurological disorders such as
schizophrenia.7,8
effects associated with current treatments.9 To address the nega-
tive symptoms and minimize side effects associated with antipsy-
chotic medications, the development of PDE10A inhibitors as
antipsychotic drugs has attracted extensive research efforts over
the past several years.10 In particular, the alkaloid papaverine 1
(Fig. 1) has demonstrated in vivo efficacy in clinically relevant
animal models producing dose dependent inhibition in the
conditioned avoidance response (CAR) and phenycyclidine (PCP)-
induced hyperactivity models in rodents.6 Pfizer is currently
evaluating the PDE10A inhibitor MP-10 (2) in clinical trials.11
Recently, we disclosed our structure-activity relationships
investigation into a novel class of cinnolines as PDE10A inhibitors
exemplified by compound 3.10k As part of our on-going efforts to
develop a PDE10A inhibitor for the treatment of schizophrenia,
we identified compound 4 as a modestly potent and selective
PDE10A inhibitor (Fig. 2). Although compound 4 exhibited good
cellular permeability it also displayed high P-glycoprotein (Pgp)-
mediated efflux. It is well known in the literature that molecular
descriptors related to hydrogen bonding (hydrogen bond acceptor
count, hydrogen bond donor count, and topological polar surface
area) can have an instrumental effect in reducing passive perme-
ability and increasing efflux.12 Recognizing that Pgp susceptibility
is known to have a dramatic influence on compounds targeting
the CNS,13 we included permeability and efflux assays into our
Although current medications have demonstrated effectiveness
in treating positive symptoms of schizophrenia (delusions, halluci-
nations, disorganized behavior and speech) they are ineffective in
treating negative symptoms (apathy, anhedonia, social with-
drawal) and cognition disorders. In addition, diabetes, weight gain,
QT prolongation and extrapyramidal syndrome are common side
⇑
Corresponding author.
E-mail address: rrzasa@amgen.com (R.M. Rzasa).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.10.078

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R. M. Rzasa et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7371–7375
N
Further SAR investigations focusing on modifications to the D-
N
N
ring of compound 14 are shown in Table 3. In general, the addition
of alkyl groups in the 4-position of the piperidine D-ring decreased
potency. For instance, the methoxy analog 15 led to a >90-fold de-
crease in potency in addition to decreased microsomal stability.
The secondary alcohol 16 led to a 12-fold loss in potency while ter-
tiary alcohols 17 and 18 resulted in >21-fold and >690-fold loss in
enzyme inhibition, respectively. Although acid 19 showed a mod-
est 14-fold loss in activity and exhibited good passive permeability,
compound 19 displayed increased Pgp-mediated efflux, presume-
ably due to its high polar surface area (PSA 100 Å2).
N
N
OMe
N
OMe
OMe
N
N
N
MeO
OMe
N
O
HO
MeO
1
2
3
Figure 1. PDE10A inhibitors.
HO
R
Determination of the cocrystal structure of compound 7 bound
to human PDE10A provided insights into the potency and selectiv-
ity of this class of molecules (Fig. 3). Several important ligand-
protein interactions were observed. First, the hydroxyl moiety of
the piperidine displaces a water molecule in the lipophilic Q1
pocket of the catalytic site forming an H-bond with the backbone
carbonyl oxygen of Thr675 and a water mediated H-bond with
the conserved Gln716. This deep penetration into the catalytic site
may explain the high potency for compound 7. Second, the benz-
imidazole group occupies the Q2 selectivity pocket adjacent to
the sidechain of Met703 and the nitrogen on the benzimidazole
forms an H-bond with Tyr683. The occurrence of the small residue
Gly715, present only in PDE10A, allows these compounds access to
this pocket which may explain the high selectivity over other
PDEs.18 Lastly, the biaryl ether forms hydrophobic interactions
with the hydrophobic clamp as defined by residues Phe719,
D
N
N
SAR Strategy
O
O
X1
C
N
N
A
B
5
X2 X4
N
X3
N
H
N
H
N
H
Y
4
PDE10A IC50 = 422 nM
PDE3A IC50 = >30,000 nM
P
app = 23.4 x 10-6 cm/s
Efflux Ratio = 45.6
Figure 2. PDE10A SAR strategy.
screening paradigm. Thus, the goal of this investigation was not
only to improve PDE10A potency but to decrease Pgp susceptibility
of our newly identified lead molecule 4. In this report we describe
our SAR strategy into biaryl ethers 5 as potential PDE10A inhibitors
for the treatment of schizophrenia.
Phe686 and Ile682. The phenyl ring forms an edge-to-face p-inter-
The derivatives prepared in this study were evaluated for their
ability to inhibit purified recombinant human PDE10A and
screened for PDE3A selectivity.14,15 Compounds were evaluated
for in vitro metabolic stability using a human liver microsomal as-
say (HLM). Passive permeability was determined using parental
LLC-PK cells whereas Pgp-mediated efflux was determined using
LLC-PK cells transfected with human MDR1.16
The first derivatives examined in this study were compounds
with various A-ring modifications (Table 1). The preliminary data
for compound 4 are included for comparison. Gratifyingly, phenyl
analog 6 was 448-fold more potent against PDE10A versus com-
pound 4. Pyridine isomers 7 and 8 resulted in >4000-fold improve-
ment in potency at the expense of decreased microsomal stability.
Interestingly, diazines were also potent PDE10A inhibitors but
position of the nitrogen atoms in the A-ring was critical. In
comparison to compound 4, pyrimidine 9 displayed a >800-fold
improvement in potency whereas the pyridazine analog 10 re-
sulted in a 14-fold loss in potency. Pyrazine 11 showed the most
significant improvement in potency (>4500-fold, 11 vs 4). Diazines
were also more metabolically stable than their pyridine and phenyl
counterparts (9–11 vs 6–8). Unfortunately, while our initial efforts
to improve potency and maintain PDE3A selectivity were success-
ful in producing highly permeable compounds, high efflux re-
mained an issue.
Encouraged by these initial results, we proceeded with our
investigation by modifying the C-ring of compound 11 to mitigate
Pgp-mediated efflux (Table 2). We hypothesized the high efflux re-
sulted from the presence of the amino-benzimidazole moiety.17
Our strategy to lower efflux was to remove the hydrogen bond do-
nor present in the benzimidazole. In general, replacement of the
NH of the benzimidazole maintained cellular permeability and de-
creased efflux. We were pleased when the N-methyl benzimid-
azole 12 displayed equal potency and lower efflux (>10-fold) in
comparison to compound 11. Although benzoxazole 13 exhibited
an fivefold loss in potency, the compound showed a further
reduction in efflux (13 vs 11). Ultimately, the most significant
improvement in lowering efflux was achieved by replacing the
benzimidazole C-ring with a benzothiazole (14 vs 11).
action with Phe719 whereas the pyridyl group forms hydrophobic
interactions with Phe686 and Ile682.
In contrast, the X-ray crystallographic data of compound 16 in
PDE10A revealed an alternative binding orientation this series of
compounds may adopt within the active site (Fig. 4). The presence
of the hydroxyethyl group on the piperidine D-ring of compound
16 is sufficiently large to orient the ligand into a different binding
mode within the catalytic site of enzyme. The ligand does not ac-
cess the Q1 pocket but positions the 4-hydroxyethyl-piperidine to-
ward the water coordinated metal site. The N-1 nitrogen of the
pyrazine forms a direct hydrogen bond with Gln716. Similar to
the benzimidazole of compound 7, the benzothiazole occupies
the Q2 selectivity pocket with the N-3 nitrogen forming a hydro-
gen bond to Tyr683. The phenyl ring is positioned within the
hydrophobic clamp forming an edge-face interaction with
Phe719 and a face-edge interaction with Phe686.
The compounds required for this investigation were prepared
by a variety of routes using SNAr or metal-mediated coupling strat-
egies. Various routes were utilized in the preparation of the desired
analogs and the particular route employed was dictated by the
availability of appropriate starting materials. Pyridine 4, pyridazine
10, and pyrazines 11-13 were prepared in three steps as outlined in
Scheme 1. Nucleophilic displacement of the appropiate chloro het-
erocycle 20–2219 with 4-aminophenol and cesium carbonate at
90–100 °C selectively gave compound 23. Introduction of the 4-
(hydroxymethyl)piperidine group under palladium catalyzed or
nucleophilic displacement conditions smoothly provided aniline
24. Final displacement using 2-chlorobenzimidazole under micro-
wave heating gave compounds 4, 10 and 11. Likewise, treatment of
compound 24 with either 1-methyl-2-chlorobenzimidazole or 2-
chlorobenzoxazole gave compounds 12 and 13, respectively.
Alternatively, pyridine analogs 7 and 8 were prepared in three
steps from 2-chlorobenzimidazole as shown in Scheme 2. Reaction
between 4-aminophenol and 2-chlorobenzimidazole 25 in the
absence of base gave selectively the nitrogen linked phenol 26.
Treatment of either 3-fluoro-2-nitropyridine or 3-bromo-4-chloro-
pyridine with compound 26 gave compounds 27 and 28, respec-
tively. Final displacement of the nitro group of 27 or copper

R. M. Rzasa et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7371–7375
7373
Table 1
Table 3
PDE10A inhibitory activity of A-ring modified analogs
PDE10A inhibitory activity of D-ring modified analogs
HO
R
N
N
O
O
N
N
X1
N
N
X2 X4
X3
N
H
Ar
S
N
H
N
H
c
PDE10Aa
422
PDE3Aa
HLMb
52
Papp
ERd
c
Compd.
R
PDE10Aa
0.199
PDE3Aa
>30,000
HLMb
62
Papp
ERd
1.1
Compd.
Ar
HO
14
8.0
10.5
2.3
4
>30,000
23.4
13.0
75.2
15.8
45.6
N
MeO
HO
HO
HO
HO
15
16
17
18
19
19.3
2.4
>30,000
>30,000
>30,000
>30,000
>30,000
166
98
1.3
1.1
6
7
8
0.941
0.097
0.075
>30,000
>30,000
>30,000
315
277
142
10.6
49.5
42.1
4.2
72
12.6
3.7
2.9
N
CF3
138
2.82
18
1.8
O
N
N
<14
35.3
12.8
a
b
c
9
0.521
>30,000
76
26.2
>92
IC50 values (nM) are the means of at least two independent experiments.
mL/(min mg).
N
Apparent permeability rates (10ꢀ6 cm/s) through porcine proximal tubule cells
(LLC-PK1 cell line).
Efflux ratio (ER).
10
11
N
N
6210
0.092
>30,000
>30,000
22
41
44.0
41.6
79.3
76.7
d
N
N
a
b
c
IC50 values (nM) are the means of at least two independent experiments.
mL/(min mg).
Apparent permeability rates (10ꢀ6 cm/s) through porcine proximal tubule cells
(LLC-PK1 cell line).
Efflux ratio (ER).
d
Table 2
PDE10A inhibitory activity of C-ring modified analogs
HO
N
O
N
N
N
Y
N
H
Figure 3. 2.0 Å Cocrystal of 7 (green) and human PDE10A (PDB ID code 4HEU). Key
hydrogen bond interactions are represented as black dash lines, red spheres
indicate water molecules (some water molecules have been omitted for clarity) and
purple spheres indicate zinc atoms.
c
Compd.
Y
PDE10Aa
PDE3Aa
HLMb
Papp
ERd
11
12
13
14
NH
NMe
O
0.092
0.056
0.513
0.199
>30,000
>30,000
>30,000
>30,000
41
15
54
62
41.6
39.4
23.7
8.0
76.7
6.0
3.4
lithium aluminum hydride reduction and demethylation with
sodium iodide gave phenol 31. Attempts to couple 4-(hydroxy-
methyl)piperidine to either 2-bromoanisole or 2-iodoanisole
directly failed to give the desired coupling product. In the case of
intermediate 32 commercially available 4,6-dichloro-5-methoxy-
pyrimidine 30 was treated with 4-(hydroxymethyl)piperidine. Re-
moval of the second chlorine atom by hydrogenation followed by
demethylation provided pyrimidine 32. Intermediates 31 and 32
were treated with 1-fluoro-4-nitrobenzene followed by reduction
of the nitro moiety giving intermediates 33 and 34 which, upon
reaction with 2-chlorobenzimidazole under microwave conditions,
provided compounds 6 and 9, respectively.
S
1.1
a
b
c
IC50 values (nM) are the means of at least two independent experiments.
mL/(min mg).
Apparent permeability rates (10ꢀ6 cm/s) through porcine proximal tubule cells
(LLC-PK1 cell line).
Efflux ratio (ER).
d
mediated coupling of 28 with 4-(hydroxymethyl)piperidine
yielded compounds 7 and 8, respectively.
Compounds 6 and 9, wherein the A-ring was either benzene or
pyrimidine rings, were prepared as shown in Scheme 3. Intermedi-
ates 31 and 32 were prepared as follows: palladium catalyzed
coupling of ethyl isonipecolate to 2-bromoanisole 29 followed by
Pyrazines 14–19, with modifications to the D-ring, were
synthesized in three steps beginning with 2-chlorobenzothiazole

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R. M. Rzasa et al. / Bioorg. Med. Chem. Lett. 22 (2012) 7371–7375
HO
N
a
b or c
N
Cl
N
H
N
H
N
H
25
26
OH
Z
N
O
O
X1
X2
N
X1
X2
N
d or e
N
H
N
H
N
N
H
H
27 X1 = N, X2 = CH, Z = NO2
28 X1 = CH, X2 = N, Z = Br
7 X1 = N, X2 = CH
8 X1 = CH, X2 = N
Figure 4. 2.0 Å Cocrystal of 16 (cyan) with human PDE10A (PDB ID code 4HF4). Key
hydrogen bond interactions are represented as black dash lines, red spheres
indicate water molecules (some water molecules have been omitted for clarity) and
purple spheres indicate zinc atoms.
Scheme 2. Reagents and conditions: (a) 4-aminophenol, HCl, EtOH, reflux, 72%; (b)
3-fluoro-2-nitropyridine, K2CO3, DMSO, 60 °C, 42%; (c) 3-bromo-4-chloropyridine,
Cs2CO3, DMSO, 90 °C; (d) 4-(hydroxymethyl)piperidine, K2CO3, DMSO, 110 °C, 35%;
(e) 4-(hydroxymethyl)piperidine, Cu, CsOAc, DMSO, 150 °C (1%, 2 steps).
Z
Z
OH
Cl
O
a
b or c
X1
X2 X4
X1
X2 X4
X1
R
Z
X1
N
a or b
c or d
NH2
X3
X3
OMe
OH
20 X1 = X2 =CH, X4 = N, Z = Br
23
29 R = H, X1 = X3 = CH, Z = Br
30 R = Cl, X1 = X3 = N, Z = Cl
31 X1 = X3 = CH
32 X1 = X3 = N
21
22
X
X
1 = X2 = N, X4 = CH, Z = Cl
1 = X4 = N, X2 = CH, Z = Cl
OH
OH
OH
OH
N
N
N
N
O
O
X1
X1
d
e
O
O
N
X1
X2 X4
X1
X2
N
X4
X3
NH2
X3
N
H
N
H
Y
NH2
N
H
1 = X3 = CH
X
X
1 = X3 = CH
1 = X3 = N
33
34
6
9
X
X
24
4
X1 = X2 = CH, X4 = N, Y = NH
1 = X3 = N
X
X
X
1 = X2 = N, X4 = CH Y = NH
10
11
12
,
1 = X4 = N, X2 = CH, Y = NH
1 = X4 = N, X2 = CH, Y = NMe
Scheme 3. Reagents and conditions: (a) (i) ethyl isonipecolate, Pd2dba3, BINAP,
NaOtBu, toluene, 105 °C, 64%; (ii) LAH, THF, 0 °C; (iii) NaI, pyridine, 200 °C, W, 3 h,
(50%, 2 steps), (b) (iv) 4-(hydroxymethyl)piperidine, K2CO3, DMSO, rt, 86%; (v) Pd/C,
H-cube, 74%; (vi) LiI, pyridine, 200 °C, W, 3 h, (c) (vii) 1-fluoro-4-nitrobenzene,
l
13 X1 = X4 = N, X2 = CH, Y = O
l
Scheme 1. Reagents and conditions: (a) 4-aminophenol, Cs2CO3, DMSO, 90–100 °C,
63–91%; (b) 4-(hydroxymethyl)piperidine, Pd2(dba)3, Xantphos, NaOtBu, toluene,
Cs2CO3, DMSO, rt, 57%; (viii) Fe dust, AcOH, aq EtOH, 65 °C, (97%), (d) (ix) 1-fluoro-
4-nitrobenzene, Cs2CO3, DMSO, 80 °C, (62% 2 steps); (x) Pd/C, MeOH, H-cube, 48–
100 °C; (c) 4-(hydroxymethyl)piperidine, iPrOH,
benzimidazole, 2-chloro-1-methylbenzimidazole, or 2-chloro-benzoxazole, iPrOH,
W, 160 °C, 30 min, 5–35% (2 steps).
lW, 160 °C, 30 min; (d) 2-chloro-
84%, (e) 2-chlorobenzimidazole, iPrOH, 120–160 °C,
lW, 17–42%.
l
HO
N
S
a
b
N
Cl
(Scheme 4). Treatment of 2-chlorobenzothiazole 35 with
4-aminophenol gave compound 36 which was reacted with 2,3-
dichloropyrazine under basic conditions to yield compound 37.
Subsequent chloride displacement with a variety of substituted
piperidines provided compounds 14–19.
S
N
H
35
36
R
N
In summary, a series of potent and selective biaryl ether
PDE10A inhibitors was discovered. Structure-activity relationship
studies resulted in >10,000-fold improvement in potency while
maintaining PDE3A selectivity. The issue of high Pgp-mediated ef-
flux was addressed by removing a hydrogen bond donor from the
benzimidazole C-ring. X-ray crystallographic data suggested that
compounds of this series may adopt one of two different binding
modes depending on the substitutent present in the 4-position of
the D-ring. The bicyclic C-ring in this series of inhibitors occupies
the unique Q2 pocket resulting in high selectivity among other
PDEs.
Cl
O
O
N
c
N
N
N
N
N
S
S
N
H
N
H
37
14-19
Scheme 4. Reagents and conditions: (a) 4-aminophenol, NMP, 160 °C, 71%; (b) 2,3-
dichloropyrazine, Cs2CO3, DMSO, 80 °C, 66%; (c) 4-substituted piperidine, DMSO,
60 °C, 34–73%.

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7375
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Acknowledgments
The authors would like to thank Dr. Andreas Reichelt, Dr. Lewis
Pennington and Dr. Markian Stec for their insightful discussions
and suggestions. The authors also thank the Advanced Light Source
staff at beamline 5.0.2 for their support. The Advanced Light Source
is supported by the Director, Office of Science, Office of Basic
Energy Sciences, Materials Sciences Division, of the U.S. Depart-
ment of Energy under Contract DE-AC03-76SF00098 at Lawrence
Berkeley National Laboratory.
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System from LABCYTE. 10 lL of PDE enzyme in IMAP reaction buffer (10 mM
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Tris–HCL, pH 7.2, 10 mM MgCl2, 0.05% NaN3, and 0.01% Tween-20) was added
into the assay wells. The PDE enzyme concentration used was based on each lot
of enzyme activity, to ensure enzyme reaction falls in a linear range under
assay condition. 0.2 nM of PDE3 or 8 pM PDE10 were used in the assay system.
Enzyme was pre-incubated with inhibitors for 60 min at room temperature
before addition of 10
cAMP in the reaction. Enzyme reaction was allowed to proceed at room
temperature for 90 min, and the reaction is stopped by 55 l addition of
lL of substrate addition, which results in 100 nM of FAM-
l
binding reagent according to manufacturer’s recommendation. The mixture is
further incubated at room temperature for additional 4 hours, and signal was
read on an Envision multimode reader (PerkinElmer). Fluorescence signals
were measured at 520 and 485 nm. The signal ratio at 520/485 nm
corresponded to the generation of reaction product of AMP, and it was used
in all data analysis. Values from DMSO-treated wells were normalized to
POC = 100, and no-enzyme wells were normalized to POC = 0. IC50 values were
determined by using the Genedata Screener V9.0.1.The curve fitting algorithm
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M.; DeCarr, L.; Gre-Willse, A.; Hoover-Litty, H.; Kumarasinghe, E. S.; Li, Y.;
Liang, S. X.; Livingston, J. N.; Lowinger, T.; MacDougall, M.; Ogutu, H. O.;
Olague, A.; Otto-Morgan, R.; Schoenleber, R. W.; Tersteegen, A.; Wickens, P.;
Zhang, Z.; Zhu, J.; Zhu, L.; Sweet, L. Bioorg. Med. Chem. Lett. 2007, 17, 2869; (c)
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L.; Malamas, M. S.; Brandon, N. J.; Kronbach, T. J. Med. Chem. 2010, 53, 4399; (d)
Helal, C. J.; Kang, Z.; Hou, X.; Pandit, J.; Chappie, T. A.; Humphrey, J. M.; Marr, E.
S.; Fennell, K. F.; Chenard, L. K.; Fox, C.; Schmidt, C. J.; Williams, R. D.; Chapin, D.
S.; Siuciak, J.; Lebel, L.; Menniti, F.; Cianfrongna, J.; Fronseca, K. R.; Nelson, F. R.;
O’Connor, R.; MacDougall, M.; McDowell, L.; Liras, S. J. Med. Chem. 2011, 54,
4536; (e) Kehler, J.; Ritzen, A.; Langgård, M.; Petersen, S. L.; Farah, M. M.;
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Lett. 2011, 21, 3738; (f) Gage, J. L.; Onrust, R.; Johnston, D.; Osnowski, A.;
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T.-M.; Rindgen, D.; Bleickardt, C.; Hodgson, R. Bioorg. Med. Chem. Lett. 2012, 22,
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M.; McElroy, W.; Tan, Z.; Tulshian, D.; McKittrick, B.; Greenlee, W. J.; Hruza, A.;
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used for dose response data analysis in Genedata Screener is
a custom
implementation of robust curve-fitting algorithm called ROUT (Robust
a
regression with outlier detection) and uses a four-parameter logistical (4PL)
Hill model.
16. For a detailed description of assays performed in this study see: Hu, E.; Ma, J.;
Biorn, C.; Lester-Zeiner, D.; Cho, R.; Rumfelt, S.; Kunz, R. K.; Nixey, T.;
Michelson, K.; Miller, S.; Shi, J.; Wong, J.; Hill Della Puppa, G.; Able, J.; Taljeda,
S.; Hwang, D.-R.; Hitchcock, S. A.; Porter, A.; Immke, D.; Allen, J. R.; Treanor, J.;
Chen, H. J. Med. Chem. 2012, 55, 4776.
17. For
a similar strategy of masking the NH of a benzimidazole to reduce
Pgp susceptibility see: Bergman, J. M.; Roecker, A. J.; Mercer, S. P.; Bednar,
R. A.; Reiss, D. R.; Ransom, R. W.; Harrell, C. M.; Pettibone, D. J.; Lemaire,
W.; Murphy, K. L.; Li, C.; Prueksaritanont, T.; Winrow, C. J.; Renger, J. J.;
Koblan, K. S.; Hartman, G. D.; Coleman, P. J. Bioorg. Med. Chem. Lett. 2008,
18, 1425.
18. All compounds reported in this investigation showed selectivity against
PDE2A, PDE3A and PDE4D at IC50 >10
13 (PDE4D IC50 7.4 M).
lM with the exception of compound
l
19. For the preparation of 3,4-dichloropyridazine 21 see: Yanai, M.; Kinoshita, T.
Yakugaku Zasshi 1965, 85, 344.