Synthesis and preliminary biological evaluation of potent and selective 2-(3-alkoxy-1-azetidinyl) quinolines as novel PDE10A inhibitors with improved solubility

Article abstract of DOI:10.1016/j.bmc.2014.10.013

We report the discovery of a novel series of 2-(3-alkoxy-1-azetidinyl) quinolines as potent and selective PDE10A inhibitors. Structure-activity studies improved the solubility (pH 7.4) and maintained high PDE10A activity compared to initial lead compound 3, with select compounds demonstrating good oral bioavailability. X-ray crystallographic studies revealed two distinct binding modes to the catalytic site of the PDE10A enzyme. An ex vivo receptor occupancy assay in rats demonstrated that this series of compounds covered the target within the striatum.

Full text of DOI:10.1016/j.bmc.2014.10.013

Bioorganic & Medicinal Chemistry 22 (2014) 6570–6585
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis and preliminary biological evaluation of potent and
selective 2-(3-alkoxy-1-azetidinyl) quinolines as novel PDE10A
inhibitors with improved solubility
a
b
b
a
Robert M. Rzasa a, , Michael J. Frohn , Kristin L. Andrews , Samer Chmait , Ning Chen ,
Jeffrey G. Clarine e, Carl Davis e, Heather A. Eastwood b, Daniel B. Horne a, Essa Hu a, Adrie D. Jones c,
Matthew R. Kaller a, Roxanne K. Kunz a, Silke Miller d, Holger Monenschein a, Thomas Nguyen a,
Alexander J. Pickrell a, Amy Porter d, Andreas Reichelt a, Xiaoning Zhao c, James J. S. Treanor d,
Jennifer R. Allen a
⇑
a Department of Medicinal Chemistry, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
b Department of Molecular Structure and Characterization, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
c Department of Molecular Structure and Characterization, Amgen Inc., 1120 Veterans Boulevard, So San Francisco, CA 94080-1985, USA
d Department of Neuroscience, Amgen Inc., One Amgen Center Drive, Thousand Oaks, CA 91320-1799, USA
e Department of Pharmacokinetics 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 2-(3-alkoxy-1-azetidinyl) quinolines as potent and selective
PDE10A inhibitors. Structure–activity studies improved the solubility (pH 7.4) and maintained high
PDE10A activity compared to initial lead compound 3, with select compounds demonstrating good oral
bioavailability. X-ray crystallographic studies revealed two distinct binding modes to the catalytic site
of the PDE10A enzyme. An ex vivo receptor occupancy assay in rats demonstrated that this series of
compounds covered the target within the striatum.
Received 11 July 2014
Revised 1 October 2014
Accepted 12 October 2014
Available online 22 October 2014
Keywords:
Phosphodiesterase
PDE10A
Ó 2014 Elsevier Ltd. All rights reserved.
Inhibitors
Azetidine
Schizophrenia
1. Introduction
for the treatment of erectile dysfunction and pulmonary hyperten-
sion,3 and the recent approval of the first PDE4 inhibitor (roflumi-
Cyclic nucleotide phosphodiesterases (PDEs) constitute a family
of bimetallic hydrolase enzymes that regulate cell signaling medi-
ated by the ubiquitous second messengers, cyclic adenosine mono-
phosphate (cAMP) and cyclic guanosine monophosphate (cGMP).
Specifically, PDEs modulate intracellular levels of cAMP or cGMP
by hydrolyzing the 30A50 phosphodiester bond producing AMP
and GMP, respectively. This 11-membered family of enzymes con-
sists of 21 gene variants that differ in their structure, regulation,
localization and substrate specificity.1 Decreased intracellular
cAMP or cGMP levels as a result of upregulation of PDEs have been
implicated in various diseases such as cardiovascular disease, neu-
rodegenerative disorders, inflammation and cancer.2 With the suc-
cess of PDE5 inhibitors (sildenafil, vardenafil, tadalafil and avanafil)
last) for the treatment of chronic obstructive pulmonary disease,
considerable interest has been given to this family of enzymes.
Phosphodiesterase 10A (PDE10A) is predominantly expressed in
the medium spiny neurons of the striatum and regulates the intra-
cellular concentrations of both cAMP and cGMP.4,5 Modulation of
neuronal activity through the inhibition of PDE10A effectively
increases the striatal levels of both cAMP and cGMP.6 Due to its
localization in the striatum and dual substrate specificity, inhibi-
tion of PDE10A activity has recently been the subject of extensive
research efforts for the treatment of neurological disorders such as
schizophrenia, Parkinson’s disease and Huntington’s disease.7 Cur-
rent antipsychotic agents act as D2 dopamine receptor antagonists
that demonstrate effectiveness in treating positive symptoms of
schizophrenia (delusions, hallucinations, disorganized behavior
and speech) but alone are ineffective in treating negative
symptoms (apathy, anhedonia, avolition and social withdrawal)
⇑
Corresponding author.
E-mail address: rrzasa@amgen.com (R.M. Rzasa).
http://dx.doi.org/10.1016/j.bmc.2014.10.013
0968-0896/Ó 2014 Elsevier Ltd. All rights reserved.

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6571
HO
and cognition disorders. In addition, current treatments are associ-
ated with common side effects such as diabetes, weight gain, QT
prolongation and extrapyramidal syndrome.8 Preliminary investi-
gations also suggest that activation of the glutamatergic pathway
via modulation of NMDA receptor signaling may improve the
negative symptoms and cognitive deficits associated with schizo-
phrenia.9 PDE10A inhibition may treat both positive and negative
symptoms and improve cognition in schizophrenic patients by
modulating both the dopaminergic and glutamatergic pathways.10
Notably, selective PDE10A inhibitors have proven effective in
several preclinical rodent models of antipsychotic behavior (condi-
D
A
B
N
SAR
O
Z2
N
Strategy
O
X1
N
N
N
Z1
X2 X3
N
S
N
H
Y1
Y2
C
3
4
:
PDE10A IC50 0.2 nM
Solubility (PBS pH 7.4):
6 µM
Figure 2. PDE10A SAR strategy.
tioned avoidance response, phencyclidine- or
D-amphetamine-
induced hyperactivity), improvement in cognition (prepulse
inhibition) and extrapyramidal effects (catalepsy) suggesting
PDE10A inhibition as a novel mechanism for the treatment of
neurological disorders.6b
2. Results and discussion
Recently, we reported our on-going efforts to develop a PDE10A
inhibitor for the treatment of schizophrenia.11,12 Our initial efforts
focused on a series of novel cinnoline analogs 1 and 2 (Fig. 1).
Although this series showed excellent PDE10A potency and good
PDE3 selectivity (>300ꢀ) we hypothesized a greater selectivity
profile was required to avoid potential cardiovascular side
effects.13 X-ray crystallographic data revealed that compound 1
does not access the Q2 selectivity pocket as defined by residues
Met703 and Gly715 and the inability to occupy this pocket may,
in fact, be responsible for the modest selectivity profile. We also
disclosed the structure activity relationships of a biaryl ether
scaffold exemplified by compound 3 as a potent and selective
PDE10A inhibitor (>30,000ꢀ against PDE3, Fig. 2).14 Although
compound 3 exhibited excellent enzymatic inhibition of PDE10A
we hypothesized that its low aqueous solubility would make
further development difficult, and could be associated with its high
degree of aromaticity. It is well known in the literature that a high
degree of aromaticity of a molecule can lead to deleterious effects
on aqueous solubility.15 Given the importance and need to monitor
solubility in our SAR efforts, we included solubility assays into our
early screening paradigm. Thus, the goal of this investigation was
not only to identify a lead molecule with nanomolar PDE10A
potency and excellent PDE selectivity but also with improved
solubility in comparison to compound 3. Therefore, our strategy
to improve the solubility of our lead molecule 3 was to reduce
the degree of aromaticity by replacing an aromatic ring with a
saturated heterocycle. In particular, molecular modeling studies
suggested an azetidine ring was a viable alternative for the
phenyl B-ring by positioning the A- and C-rings in a similar
orientation within the PDE10A active site as compound 3. In this
report we describe our synthesis and preliminary biological
evaluation of 2-(3-alkoxy-1-azetidinyl) quinolines as novel
PDE10A inhibitors for the treatment of schizophrenia (generic
structure 4, Fig. 2).
The derivatives prepared in this study were evaluated for their
ability to inhibit purified recombinant human PDE10A. In addition,
compounds were preliminarily evaluated for aqueous solubility at
physiological pH using a phosphate buffered saline (PBS) solubility
assay and, for select compounds, in vitro selectivity against other
PDE isoforms.
The first compound examined in this study was compound 5
where the aromatic B-ring of compound 3 was replaced with an
azetidine moiety. Although compound 5 was 100-fold less potent
compared to compound 3, we were pleased to see it retained
significant PDE10A inhibition (Table 1). Our hypothesis of
replacing an aromatic ring with an azetidine to improve solubility
was realized as compound 5 displayed a 5-fold improvement in
solubility. Other analogs containing 6,6-bicyclic aromatic C-rings
also proved potent PDE10A inhibitors. Quinoxaline 6 and quinazo-
line 7 displayed equipotency as PDE10A inhibitors but showed
>5-fold improvement in solubility (6, 7 vs 5). The optimal C-ring
proved to be quinoline 8 with a 9-fold improvement in potency
and a 6-fold improvement in solubility compared to 5.
With a satisfactory C-ring identified, we continued our SAR
investigations with several B-ring modifications of compound 8.
The profiling data for these compounds are reported in Table 2.
Expansion of the B-ring to a pyrrolidine proved detrimental.
Table 1
PDE10A inhibitory activity of C-ring modified analogs
HO
N
O
N
N
N
R
Compound
R
PDE10Aa
0.2 0.1
PBSb
6
3
—
N
N
N
5
6
21
4
31
OH
S
N
OH
30 16
500
N
N
N
N
N
N
N
N
7
8
13 0.9
2.4 0.7
174
178
MeO
MeO
MeO
MeO
N
N
N
1
2
a
IC50 values (nM) are the means of at least three independent experiments.
Solubility data reported in lM.
b
Figure 1. Amgen PDE10A inhibitors.

6572
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
Table 2
of saturated, nitrogen-linked D-rings. Extension of the hydroxyl
PDE10A inhibitory activity of B-ring modified analogs
group by a single carbon atom resulted in an 8-fold loss in potency
(15 vs 8) whereas contracting the hydroxyl group by a single car-
bon atom decreased potency 23-fold (16 vs 8). Contraction of the
piperidine ring to the azetidine 17 resulted in a 15-fold loss in
potency and 4-fold loss in solubility. A decrease in D-ring size to
a five-membered ring resulted in a loss of potency but maintained
good solubility (18 vs 8). To examine the importance of the hydro-
xyl group had on potency we replaced the hydroxyl moiety with a
methoxy group. Compound 19 exhibited a >60-fold loss in potency
and a 3-fold decrease in solubility. Removal of the hydroxyl group
entirely resulted in a 13- and 43-fold loss in PDE10A potency and a
dramatic loss in solubility (20, 21 vs 8). Interestingly, morpholine
22 displayed equal potency in comparison to compound 20 but
the additional oxygen atom markedly improved solubility.
Although tertiary amine 23 displayed excellent solubility it was
not tolerated in the PDE10A assay exhibiting a >140-fold decrease
in potency. In comparison to compound 8, nitrile 24 and amide 25
showed good in vitro potencies but significantly reduced
solubilities.
We also examined the SAR of carbocyclic rings in the course of
our investigation (Table 5). We were pleased to find by converting
the piperidine ring to a phenyl ring resulted in only a modest loss in
potency (26 vs 8) although the reintroduction of aromaticity did
have a deleterious effect on solubility. Placement of the hydroxy-
methyl group to the meta position resulted in a 3-fold loss in
potency (27 vs 26). Similar to the piperidine SAR, the importance
of the hydroxyl group was observed as compounds devoid of the
hydrogen bond donor were less potent and significantly less soluble
(28, 29 vs 26). Other functional groups such as amides, esters and
nitriles were well tolerated but less potent (30, 31, and 32 vs 26).
Although the carbocyclic compounds in general showed modest
PDE10A potency they lacked satisfactory solubility. On the other
hand, compounds with heteroaromatic D-rings proved to have bet-
ter overall potency and solubility. In particular, a trend of improved
potency was observed in several analogs (3-pyridyl ꢁ 4-pyri-
dyl > 5-pyrimidyl > 2-pyridyl). For example, pyrimidine 36 was
3-fold more potent compared to compound 33 whereas pyridine
isomers 34 and 35 were 30-fold more potent. Unfortunately,
the reverse trend of decreasing solubility was also observed
(4-pyridyl < 3-pyridyl < 5-pyrimidyl < 2-pyridyl). Methyl substitu-
tion in the para and meta positions to the A–D ring junction was
well tolerated and resulted in excellent PDE10A potency (38 and
39). In contrast, methylation in the ortho position resulted in a
9-fold loss in potency (37 vs 34).16 Bicyclic heteroaromatic
D-rings were also investigated and were well tolerated. Quinolines
40 and 41 displayed modest enzyme potency whereas
benzothiazole 42 and amino-quinazoline 43 showed excellent
in vitro potency. In general, bicyclic aromatic D-rings showed good
to modest in vitro potencies but displayed considerably lower
solubility. Given our initial hypothesis that the total aromatic
ring count influenced aqueous solubility of a compound, we
designed inhibitors containing saturated, carbon-linked D-rings.
Gratifyingly, amide 44 exhibited good PDE10A inhibition and
excellent solubility. In comparison to compound 44, carbamate 45
and sulfonamide 46 maintained good aqueous solubility at the
detriment of potency. Amide 47, which contained a quinoxaline
A-ring, displayed excellent PDE10A potency (Fig. 3). In general,
the carbon-linked piperidine D-rings showed optimal PDE10
potency and solubility.
HO
N
Z2
N
O
N
N
N
Z1
Compound
Z1
Z2
CH2
(R)-CH2CH2
(S)-CH2CH2
CH2CH2
PDE10Aa
PBSb
8
9
10
11
CH2
CH2
CH2
2.4 0.7
30 0.4
46 3.0
6.5 0.2
178
339
315
81
CH2CH2
a
IC50 values (nM) are the means of at least three independent experiments.
Solubility data reported in lM.
b
Although compounds 9 and 10 displayed a 2-fold improvement in
solubility with respect to compound 8, the (R)- and (S)-enantio-
mers showed a dramatic 13-fold and 19-fold loss in potency (9,
10 vs 8). Further expansion of the B-ring to a six-membered piper-
idine ring recovered PDE10A potency at the expense of solubility
(11 vs 8).
As part of our SAR investigation we also studied the effect of the
heteroaryl A-ring on PDE10A inhibition and aqueous solubility
(Table 3). In our previous study, A-ring modifications had a pro-
nounced effect on PDE10A inhibition.14 Thus, we investigated the
most promising A-rings in this current SAR study. Replacement
of a nitrogen atom with a carbon atom gave pyridine 12 with sim-
ilar PDE10A potency and solubility compared to compound 8. In
contrast, pyridine isomer 13 showed similar PDE10A potency but
decreased solubility. Quinoxaline 14 exhibited single digit nano-
molar potency but unfortunately, with the larger bicyclic A-ring,
exhibited dramatically lower solubility.
A major focus of our SAR investigation was to examine the
effect of D-ring analogs and the results for these derivatives are
summarized in Tables 4 and 5. We initially examined the effect
Table 3
PDE10A inhibitory activity of A-ring modified analogs
HO
N
O
X1
X2 X3
N
N
R
Compound
R
PDE10Aa
2.4 0.7
PBSb
178
N
8
N
N
12
13
1.0 0.2
4.7 1.0
189
36
N
To evaluate PDE selectivity, potent PDE10A inhibitors in this
series were screened against other PDE isoforms (Table 6). With
the exception of compounds 11 and 43, compounds of this series
exhibited >1000-fold selective over the other PDEs.
Determination of the cocrystal structure of compound 8 bound
to human PDE10A provided insights into the potency and
N
14
6.8 0.7
<1
N
a
IC50 values (nM) are the means of at least three independent experiments.
Solubility data reported in lM.
b

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6573
Table 4
PDE10A inhibitory activity of nitrogen-linked D-ring analogs
R
O
N
N
N
N
Compound
R
PDE10Aa
2.4 0.7
PBSb
Compound
R
PDE10Aa
32 0.9
PBSb
HO
N
N
8
178
84
20
<1
<1
N
OH
15
18 0.7
21
103 2.8
N
OH
O
N
16
17
54 1.6
36 0.1
41 0.4
99
41
22
23
24
29 0.9
343 1.4
4.1 0.2
346
500
66
N
OH
N
N
N
OH
CN
18c
167
N
N
N
MeO
O
NH2
19
147 47
53
25
11 0.4
14
N
a
b
c
IC50 values (nM) are the means of at least three independent experiments.
Solubility data reported in
Racemic.
lM.
selectivity of this class of molecules (Fig. 4). Several important
ligand–protein interactions were observed. First, the hydroxyl moi-
ety of the piperidine D-ring displaces a water molecule in the lipo-
philic Q1 pocket of the catalytic site forming an H-bond with the
backbone carbonyl oxygen of Thr675. As a consequence, the hydro-
xyl group of Ser667 is oriented away from the ligand. This deep
penetration into the catalytic site may explain the high potency
for compound 8. Second, the quinoline moiety occupies the Q2
selectivity pocket adjacent to the sidechain of Met703 and the
nitrogen of the quinoline forms a hydrogen bond with Tyr683.
The occurrence of the small residue Gly715, present only in
PDE10A, allows these compounds to access this pocket, which
may explain the high selectivity over other PDEs. Lastly, the azeti-
dine–pyrazine rings form hydrophobic interactions with the
hydrophobic clamp as defined by residues Phe719, Phe686 and
Ile682.
toward the ligand forming Van der Waals contacts with the
quinoxaline ring. The C-ring quinoline occupies the Q2 selectivity
pocket engaging in a hydrogen bond with Tyr683. Lastly, the
D-ring piperidine is oriented toward the water coordinated metal
site.
The in vivo pharmacokinetic profiles for compounds 8, 44 and
47 are shown in Table 7. In comparison to the high in vivo rat
clearance (3.68 L/h/kg) and poor bioavailability (18%) of lead com-
pound 8, acetyl piperidines 44 and 47 displayed improved in vivo
rat plasma pharmacokinetic profiles. Compound 44 afforded lower
in vivo clearance (0.96 L/h/kg) and improved oral bioavailability
(62%). Compound 47 afforded the best improvement in in vivo
clearance (0.57 L/h/kg) while maintaining good oral bioavailability
(57%).
Recently, we demonstrated the use of a PDE10 receptor occupancy
(RO) assay to correlate in vivo target specificity in rat brain and effi-
cacy in a preclinical rodent model of schizophrenia.17 With potent
and selective PDE10A inhibitors in hand, we profiled our lead
molecules to assess whether compound covered the intended target
within the striatum as a predictor of in vivo efficacy. To this end, we
relied on an ex vivo RO assay using our recently reported PDE10A
tracer AMG-7980.18 The study was conducted in rats, administering
a10 mg/kgoraldoseafter60 min.Initialcompounds8 and 14showed
In contrast, the cocrystal structure of compound 47 bound to
PDE10A was obtained by X-ray crystallography revealing an alter-
native binding orientation compounds of this series can adopt
within the active site (Fig. 5). The A-ring quinoxaline ring occupies
the Q1 pocket forming a
due and a –edge interaction with Phe686 of the hydrophobic
clamp. As a consequence, the Ser667 hydroxy sidechain points
p-stacking interaction with Phe719 resi-
p

6574
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
Table 5
PDE10A inhibitory activity of carbon-linked D-ring analogs
R
O
N
N
N
N
Compound
R
PDE10Aa
10.3 0.4
PBSb
Compound
R
PDE10Aa
98 7.6
PBSb
253
HO
N
26
24
37
HO
N
27
28
29
32 0.8
39 0.6
29
<1
<1
38
39
40
8.5 1.2
5.7 0.4
43 0.4
21
73
47
N
N
107 2.1
O
NH
O
N
N
30
31
45 0.1
82
<1
41
42
38 0.6
<1
<1
O
S
38 2.0
7.8 0.02
CN
NH2
N
N
32
45 0.8
<1
43
6.8 1.4
<1
O
O
N
N
N
33
34
350 2.8
349
133
44
45
29 8.4
491
138
OMe
N
11 0.7
64 2.0
N
O
O
S
N
35
36
12 7.0
56
46
166 11
181
N
N
125 1.4
254
a
IC50 values (nM) are the means of at least two independent experiments.
Solubility data reported in lM.
b
modest 25% and 15% RO, respectively. The low RO result for
compound 14 was not surprising due its low solubility. Gratifyingly,
piperidine amides 44 and 47 exhibited good RO (46% and 57%,
respectively)anddemonstratedthatthisseriesofcompoundscrossed
the blood–brain barrier reaching the intended target in brain.
3. Chemistry
Compounds required for this investigation were synthesized as
described in Schemes 1–5. Pyrazine analogs 5–11 shown in Tables
1 and 2 were prepared in three steps from commercially available

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6575
O
N
materials (Scheme 1). Reaction of 2-chloroheterocycles 48–51 with
the appropriate cyclic amines under thermal conditions gave alco-
hols 52–58. Deprotonation of the secondary alcohols with sodium
hydride followed by treatment with 2,3-dichloropyrazine afforded
ethers 59–65. Nucleophilic displacement with 4-piperidinemethanol
under microwave conditions provided compounds 5–11. Likewise,
analogs 15–25 were prepared by treatment of compound 60 with
various secondary amines (Scheme 2). Analogs containing an aro-
matic D-ring 26–43, as shown in Table 5, were prepared under Suzuki
coupling conditions between compound 60 and the appropriate
boronic acid.
N
O
N
N
N
47
:
PDE10A IC50 2.6 0.6 nM
PBS (pH 7.4): 41 µM
Pyridine analogs 12 and 13 were prepared in two steps from
intermediate 53 as shown in Scheme 3. Treatment of intermedi-
ate 53 with either sodium hydride and 3-bromo-2-fluoropyri-
dine in DMSO or cesium carbonate and 3-bromo-4-
chloropyridine in DMF afforded azetidine ethers 66 and 67,
respectively. Palladium catalyzed coupling of 4-piperidinemetha-
nol with intermediates 66 and 67 provided compounds 12 and
13, respectively.
Figure 3. PDE10A enzyme inhibition and solubility data for compound 47.
Pyrazines containing
a
carbon-linked piperidine D-ring
were synthesized as described in Scheme 4. Suzuki coupling
between intermediate 60 and commercially available tert-butyl
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5,6-dihydropyri-
dine-1(2H)-carboxylate 68 afforded compound 69. Hydrogena-
tion of the trisubstituted double bond followed by acid
deprotection of the Boc group yielded intermediate 70. Acylation
or sulfonylation under basic conditions provided derivatives 44–
46.
Analogous to the conditions described previously, quinoxalines
14 and 47 were prepared according to Scheme 5. Reaction
between intermediate 53 and 2,3-dichloroquinoxaline in the pres-
ence of sodium hydride gave intermediate 71 and nucleophilic
displacement using 4-piperidinemethanol afforded quinoxaline
14. Cross-coupling of quinoxaline 72 and the organozinc derived
from benzyl 4-iodopiperidine carboxylate smoothly provided
compound 72. A one step deprotection and acylation procedure
provided compound 47.
Figure 4. 2.77 Å co-crystal of compound 8 (green) within the active site of human
PDE10A (PDB ID code 4TPM).
4. Conclusion
In conclusion, we have discovered a novel series of 3-alk-
oxy-azetidine inhibitors of PDE10A starting from lead com-
pound 3. Structure–activity relationship studies resulted in
improved aqueous solubility while maintaining high PDE selec-
tivity. X-ray crystallographic data suggested that compounds of
this series may adopt one of two different binding modes
depending on modifications of the D-ring. The bicyclic C-ring
in this series of inhibitors occupied the unique Q2 pocket
resulting in high selectivity among other PDEs. Using an
ex vivo receptor occupancy assay, it was demonstrated that
compounds 44 and 47 reached PDE10A in the striatum of rats.
In addition, compounds 44 and 47 exhibited acceptable phar-
macokinetic profiles.
Figure 5. 2.65 Å co-crystal of compound 47 (blue) within the active site of human
PDE10A (PDB ID code 4TPP).
Table 6
PDE potency for selected analogsa
Compound
PDE1B
8040
7920
>30,000
7610
503
>30,000
3680
PDE2A1
PDE3A
PDE4D2
PDE5A
PDE7A1
PDE8A1
PDE9A2
PDE10A2
PDE11A4
8
11
13
14
43
44
47
11,700
29,700
>30,000
12,900
>30,000
>30,000
3030
>30,000
>30,000
>30,000
>30,000
208
10,800
4690
>30,000
20,500
581
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
1170
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
2.4
6.5
4.7
6.8
6.8
29
>30,000
>30,000
>30,000
10,600
>30,000
>30,000
>30,000
>30,000
>30,000
>30,000
5050
>30,000
>30,000
2.6
a
IC50 values (nM) are the means of at least two independent experiments.

6576
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
Table 7
Pharmacokinetic profiles of selected compounds in male Sprague–Dawley rats
Compound
CL (L/h/kg)
IV (2 mg/kg)a
PO (10 mg/kg)b
AUC(0–1) (ng*h/mL)
1.30
17.4
27.9
Vdss (L/kg)
t1/2 (h)
F (%)
8
44
47
3.68
0.96
0.57
4.81
1.55
1.55
6.42
3.64
2.35
18
62
57
a
In DMSO.
b
Vehicles used: 1% Tween, 2% HPMC with methanesulfonic acid, pH 2.2.
HO
N
Cl
N
HO
2
O
O
2
Y
Y2
Y1 N
Y
Cl
N
a
b
N
c
Y1 N
Y
N
N
1 N
N
N
N
Z1
Z2
Z1
Z1
Z1
Z2
Z2
Z2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
48
52
59
5
Z , Z = S
Y = Y = CH2; Z , Z = S
Y = Y = CH2; Z , Z = S
Y = Y = CH2; Z , Z = S
49 Z1= Z2= CH
53 Y = Y2= CH2; Z1= Z2= CH
60 Y1= Y = CH2; Z1= Z2= CH
6 Y1= Y2= CH2; Z1= Z2= CH
7 Y1= Y2= CH2; Z1= N; Z2= CH
8 Y1= Y2= CH2; Z1= CH; Z2= N
1
2
50 Z1= N; Z2= CH
51 Z1= CH; Z2= N
54 Y = Y2= CH2; Z1= N; Z2= CH
61 Y1= Y = CH2; Z1= N; Z2= CH
1
2
1
2
55 Y = Y2= CH2; Z1= CH; Z2= N
62 Y1= Y = CH2; Z1= CH; Z2= N
56 (R)- Y1= CH2; Y = CH2CH2; Z1= Z2= CH
63 (R)- Y1= CH2; Y2= CH2CH2; Z1= Z2= CH
9 (R)- Y1= CH2; Y2= CH2CH2; Z1= Z2= CH
10 (S)- Y1= CH2; Y2= CH2CH2; Z1= Z2= CH
11 Y1= Y2= CH2CH2; Z1= Z2= CH
2
57 (S)- Y = CH2; Y2= CH2CH2; Z1= Z2= CH
64 (S)- Y = CH2; Y2= CH2CH2; Z1= Z2= CH
1
1
1
2
58 Y = Y2= CH2CH2; Z1= Z2= CH
65 Y1= Y = CH2CH2; Z1= Z2= CH
Scheme 1. Reagents and conditions: (a) 3-hydroxyazetidine, 3-hydroxypyrrolidine, or 4-hydroxypiperidine, Et3N, DMF, 90 °C; (b) 2,3-dichloropyrazine, NaH, DMF, 90 °C; (c)
4-piperidinemethanol, K2CO3, iPrOH/water,
l
W, 160 °C, 5 h.
NR2
Ar
Cl
O
O
O
a
b
N
N
N
N
N
N
N
N
N
N
N
N
15-25
60
26-43
Scheme 2. Reagents and conditions: (a) secondary amine, K2CO3, iPrOH/water,
Pd(PPh3)4, 2-tributylstannyl-pyridine, toluene, 110 °C.
lW, 160 °C, 5 h; (b) ArB(OH)2, Pd(PPh3)4, Na2CO3, dioxane/water, 110 °C or, for example 33,
HO
W
N
X2 X3
HO
a
O
O
b
N
N
N
N
N
N
=
X2 X3
53
=
=
=
CH
=
=
66 W=
67 W=
X2
X3
=
N
12 X2
13 X2
X3
N
Br;
Br;
CH;
N;
CH;
X2
X3
X3
CH
=
N;
Scheme 3. Reagents and conditions: (a), NaH, DMSO, then 3-bromo-2-fluoropyridine, 5 °C to rt or Cs2CO3, 3-bromo-4-chloropyridine, DMF, 90 °C; (b) 4-piperidinemethanol,
Pd2dba3, MePhos, LiHMDS, THF, 65 °C or 4-piperidinemethanol, Pd2dba3, t-ButylXphos, K3PO4, toluene, 100 °C.
Boc
N
R
N
H
N
Boc
N
c
a
b,
d
O
O
O
N
N
N
B
N
N
N
N
N
N
N
N
N
O
O
=
=
=
69
70
44 R Ac
68
45 R
46 R
Me
Me
CO2
SO2
Scheme 4. Reagents and conditions: (a) intermediate 60, Pd(dppf)Cl2, K3PO4, dioxane/H2O (b) Pd/carbon, H2, MeOH, rt; (c) HCl, MeOH, rt; (d) RCl, Et3N, DCM, 0 °C.

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6577
HO
Cl
O
HO
a
b
N
N
N
N
N
c
N
N
O
N
N
N
N
14
53
71
O
N
CBz
N
N
d
O
O
N
N
N
N
N
N
N
47
72
Scheme 5. Reagents and conditions: (a) 2,3-dichloroquinoxaline, NaH, DMF, 90 °C; (b) 4-piperidinemethanol, K2CO3, iPrOH/H2O,
carboxylate, zinc, TMSCl, 1,2-dibromoethane, PdCl2dppf CH2Cl2, CuI, DMA, 80 °C; (d) H2, Pd(OH)2, Ac2O, toluene, rt.
lW, 160 °C, 5 h; (c) benzyl 4-iodopiperidine
yazetidine hydrochloride (4.10 g, 37.4 mmol) followed by cesium
carbonate (24.20 g, 74.3 mmol). The reaction was heated at 85 °C
under nitrogen overnight. The reaction was cooled to room tem-
perature and partitioned between EtOAc/brine and the aqueous
layer was extracted with EtOAc (3ꢀ). The combined organic
layers were evaporated onto silica gel and purified by flash chro-
matography eluting with 2 M NH3 in MeOH/CH2Cl2 (0–5%) to
give 3.35 g (85%) of the title compound as a white crystalline
solid. 1H NMR (300 MHz, CD3OD) d 7.68 (dd, J = 7.89, 0.73 Hz,
1H), 7.51 (dd, J = 8.11, 0.51 Hz, 1H), 7.33 (td, J = 7.71, 1.24 Hz,
1H), 7.13 (td, J = 7.60, 1.17 Hz, 1H), 4.81 (tt, J = 6.65,
4.46 Hz, 1H), 4.37–4.51 (m, 2H), 3.97–4.08 (m, 2H). MS (ESI)
m/z: 207.1 [M+H].
5. Experimental section
5.1. Chemistry
Unless otherwise noted, all reagents were obtained from commer-
cial suppliers and used without further purification. Anhydrous sol-
vents such as dichloromethane (CH2Cl2), dimethylformamide
(DMF), dimethylsulfoxide (DMSO), dioxane, ethyl acetate (EtOAc),
tetrahydrofuran (THF), ethylene glycol dimethyl ether (DME),
dimethylacetamide (DMA) and toluene were obtained from Aldrich
Chemical Co. in Sure/Seal bottles. All reactions involving air- or mois-
ture-sensitive reagents were performed under a nitrogen or argon
atmosphere. MicrowaveassistedreactionswereperformedinBiotage
Initiator Sixty microwave reactor. Flash chromatography was per-
formed using EM Science silica gel 60 (230–400 mesh ASTM) or pre-
packed silica gel cartridges (Biotage or RediSep). All yields reported
are isolated yields. Reactions were monitored using Agilent 1100
series LC/MSD SL high performance liquid chromatography (HPLC)
systems with UV detection at 254 nm and a low resonance
electrospray positive ionization mode (ESI). All final compounds were
purified to >95% purity, as determined by high performance liquid
chromatography (HPLC). HPLC methods used the following: Agilent
1100 spectrometer, Zorbax SB-C18 column (50 mm ꢀ 3.0 mm,
5.1.2. 1-Quinolin-2-yl-azetidin-3-ol (53)
Triethylamine (4.5 g, 41.0 mmol), 2-chloroquinoline 49 (3.35 g,
20.5 mmol) and azetidin-3-ol (1.5 g, 20.5 mmol) were dissolved
in DMF (50 mL) and the resulting mixture was heated to 100 °C
overnight. The mixture was diluted with water (100 mL) and
extracted with EtOAc (2 ꢀ 70 mL). The combined organic extracts
were combined and washed with water (50 mL) and brine
(50 mL), dried over Na2SO4, and filtered. The filtrate was evapo-
rated in vacuo and the residue was purified by flash column chro-
matography eluting with 20–70% EtOAc/petroleum ether to give
3.20 g (78%) of the title compound as a white solid. 1H NMR
(300 MHz, CD3OD) d 8.00 (d, J = 8.92 Hz, 1H), 7.63–7.76 (m, 2H),
7.47–7.62 (m, 1H), 7.26 (ddd, J = 8.00, 6.98, 1.10 Hz, 1H), 6.72
(d, J = 8.92 Hz, 1H), 4.76 (tt, J = 6.58, 4.46 Hz, 1H), 4.34–4.53
(m, 2H), 3.91–4.07 (m, 2H). MS (ESI) m/z: 201 [M+H] calcd for
3.5 lm) at 40 °C with a 1.5 mL/min flow rate; solvent A of 0.1% TFA
in water, solvent B of 0.1% TFA in MeCN; 0.0–3.0 min, 5–95% B; 3.0–
3.5 min, 95% B; 3.5–3.51 min, 5% B. Flow from UV detector was split
(50:50) to the MS detector, which was configured with APIES as ion-
izable source. 1H NMR spectra were recorded on a Bruker DRX
300 MHz, Bruker DRX 400 MHz, Bruker AV 400 MHz, Varian
300 MHz, or a Varian 400 MHzspectrometer atambient temperature.
Chemical shifts are expressed in parts per million (ppm, d units). Sig-
nificant 1H NMR data are reported in the following order: multiplicity
(s, singlet; br s, broad singlet; d, doublet; t, triplet; q, quartet; m,
multiplet), number of protons, and coupling constants. All high
resolution mass spectrometry (HRMS) data were acquired on a
Synapt G2HDMS instrument (Waters Corporation, Manchester, UK)
operated in positive electrospray ionization mode.
C12H12N2O 200.
5.1.3. 1-(Quinazolin-2-yl)azetidin-3-ol (54)
The title compound was prepared in a similar manner as 52
using 3-hydroxyazetidine hydrochloride and 2-chloroquinazoline
50. (78%) white solid. 1H NMR (300 MHz, DMSO-d6) d 9.18
(d, J = 0.44 Hz, 1H), 7.84 (dd, J = 8.04, 0.88 Hz, 1H), 7.72
(ddd, J = 8.55, 6.94, 1.46 Hz, 1H), 7.52 (d, J = 8.48 Hz, 1H), 7.27
(td, J = 7.45, 1.02 Hz, 1H), 5.70 (d, J = 6.43 Hz, 1H), 4.60
(qt, J = 6.53, 4.53 Hz, 1H), 4.33 (dd, J = 9.57, 6.94 Hz, 2H), 3.87
(dd, J = 10.23, 4.53 Hz, 2H). MS (ESI) m/z: 202 [M+H].
5.1.1. 1-(Benzo[d]thiazol-2-yl)azetidin-3-ol (52)
To a room temperature solution of 2-chlorobenzothiazole 48
(2.50 mL, 19.20 mmol) in DMSO (30 mL) was added 3-hydrox-

6578
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
5.1.4. 1-(Quinoxalin-2-yl)azetidin-3-ol (55)
to 90 °C overnight and then diluted with water (60 mL) and
extracted with EtOAc (2 ꢀ 50 mL). The combined organic extracts
were washed with water (60 mL) and brine (60 mL), dried over
Na2SO4, and filtered. The filtrate was evaporated in vacuo and
the residue was purified by flash column chromatography eluting
with 5–30% EtOAc/petroleum ether to give 3.0 g (60%) of the title
compound as a white solid. 1H NMR (300 MHz, DMSO-d6) d 8.27
(d, J = 2.78 Hz, 1H), 8.15 (d, J = 2.78 Hz, 1H), 8.06 (d, J = 8.92 Hz,
1H), 7.73 (d, J = 7.31 Hz, 1H), 7.46–7.64 (m, 2H), 7.24 (ddd,
J = 7.97, 6.58, 1.39 Hz, 1H), 6.81 (d, J = 8.77 Hz, 1H), 5.49–5.69 (m,
1H), 4.45–4.69 (m, 2H), 4.17 (ddd, J = 9.90, 3.84, 0.88 Hz, 2H). MS
(ESI) m/z: MS (ESI) [M+H]: 313.0, 314.9. Calcd for C16H13ClN4O 312.
The title compound was prepared in a similar manner as 53
using azetidin-3-ol and 2-chloroquinoxaline 51. (80%) light-yellow
crystalline solid. 1H NMR (300 MHz, DMSO-d6) d 8.32 (s, 1H), 7.82
(d, J = 8.04 Hz, 1H), 7.50–7.69 (m, 2H), 7.38 (ddd, J = 8.22, 5.88,
2.41 Hz, 1H), 5.79 (d, J = 6.43 Hz, 1H), 4.66 (qt, J = 6.53, 4.53 Hz,
1H), 4.32–4.50 (m, 2H), 3.80–4.08 (m, 2H). MS (ESI) m/z: 202
[M+H].
5.1.5. (R)-1-(Quinolin-2-yl)pyrrolidin-3-ol (56)
The title compound was prepared in a similar manner as 53
using (R)-3-hydroxypyrrolidine and 2-chloroquinoline 49. (66%)
light-yellow crystalline solid. 1H NMR (300 MHz, DMSO-d6) d
7.98 (d, J = 9.06 Hz, 1H), 7.60–7.72 (m, 1H), 7.51–7.57 (m, 1H),
7.43–7.51 (m, 1H), 7.15 (ddd, J = 7.93, 6.54, 1.61 Hz, 1H), 6.86
(d, J = 9.06 Hz, 1H), 4.97 (d, J = 3.65 Hz, 1H), 4.35–4.53 (m, 1H),
3.40–3.73 (m, 4H), 1.98–2.14 (m, 1H), 1.85–1.98 (m, 1H). MS
(ESI) m/z: 215 [M+H].
5.1.10. 2-(3-((3-Chloropyrazin-2-yl)oxy)azetidin-1-
yl)quinazoline (61)
The title compound was prepared in a similar manner as 60
using 2,3-dichloropyrazine and compound 54. (63%) white crystal-
line solid. 1H NMR (300 MHz, DMSO-d6) d 9.24 (d, J = 0.44 Hz, 1H),
8.26 (d, J = 2.78 Hz, 1H), 8.15 (d, J = 2.78 Hz, 1H), 7.88 (dd, J = 8.04,
1.02 Hz, 1H), 7.76 (ddd, J = 8.55, 6.94, 1.46 Hz, 1H), 7.56 (d,
J = 8.33 Hz, 1H), 7.32 (ddd, J = 7.97, 6.94, 1.02 Hz, 1H), 5.59 (tt,
J = 6.47, 3.84 Hz, 1H), 4.62 (ddd, J = 10.30, 6.50, 1.02 Hz, 2H), 4.21
(ddd, J = 10.27, 3.84, 1.10 Hz, 2H). MS (ESI) m/z: 314.0, 316.0
[M+H].
5.1.6. (S)-1-(Quinolin-2-yl)pyrrolidin-3-ol (57)
The title compound was prepared in a similar manner as 53
using (S)-3-hydroxypyrrolidine and 2-chloroquinoline 49. (65%)
light-yellow crystalline solid. 1H NMR (300 MHz, CD3OD) d 7.94
(d, J = 9.06 Hz, 1H), 7.68 (d, J = 8.48 Hz, 1H), 7.62 (dd, J = 7.89,
1.32 Hz, 1H), 7.50 (ddd, J = 8.48, 6.94, 1.53 Hz, 1H), 7.17 (ddd,
J = 7.97, 6.94, 1.17 Hz, 1H), 6.86 (d, J = 9.06 Hz, 1H), 4.56
(tt, J = 4.59, 2.43 Hz, 1H), 3.66–3.81 (m, 3H), 3.54–3.66 (m, 1H),
1.97–2.30 (m, 2H). MS (ESI) m/z: 215 [M+H].
5.1.11. 2-(3-((3-Chloropyrazin-2-yl)oxy)azetidin-1-
yl)quinoxaline (62)
The title compound was prepared in a similar manner as 60
using 2,3-dichloropyrazine and compound 55. (62%) off-white
crystalline solid. 1H NMR (300 MHz, DMSO-d6) d 8.39 (s, 1H),
8.27 (d, J = 2.78 Hz, 1H), 8.16 (d, J = 2.63 Hz, 1H), 7.85 (d,
J = 7.89 Hz, 1H), 7.54–7.70 (m, 2H), 7.42 (ddd, J = 8.22, 6.18,
2.12 Hz, 1H), 5.54–5.71 (m, 1H), 4.71 (ddd, J = 10.16, 6.50,
0.88 Hz, 2H), 4.31 (ddd, J = 10.16, 3.80, 1.10 Hz, 2H). MS (ESI)
m/z: 327.0, 329.0 [M+H].
5.1.7. 1-(Quinolin-2-yl)piperidin-4-ol (58)
The title compound was prepared in a similar manner as 53
using 4-hydroxypiperidine and 2-chloroquinoline 49. (60%) white
amorphous solid. 1H NMR (300 MHz, CD3OD)
d 7.95 (d,
J = 9.21 Hz, 1H), 7.62 (d, J = 8.33 Hz, 2H), 7.43–7.55 (m, 1H), 7.21
(m, J = 7.45, 7.45, 1.02 Hz, 1H), 7.16 (d, J = 9.35 Hz, 1H), 4.20–4.37
(m, 2H), 3.88 (tt, J = 8.90, 4.26 Hz, 1H), 3.18–3.35 (m, 2H), 1.97
(dq, J = 12.81, 3.67 Hz, 2H), 1.56 (dtd, J = 13.03, 9.56, 9.56,
3.80 Hz, 2H). MS (ESI) [M+H]: 229.1 calcd for C14H16N2O 228.
5.1.12. (R)-2-(3-((3-Chloropyrazin-2-yl)oxy)pyrrolidin-1-
yl)quinoline (63)
The title compound was prepared in a similar manner as 60
using 2,3-dichloropyrazine and compound 56. (69%) light-yellow
glass. 1H NMR (300 MHz, DMSO-d6) d 8.29 (d, J = 2.78 Hz, 1H),
8.10 (d, J = 2.78 Hz, 1H), 8.02 (d, J = 9.06 Hz, 1H), 7.63–7.75 (m,
1H), 7.53–7.59 (m, 1H), 7.44–7.53 (m, 1H), 7.18 (ddd, J = 7.97,
6.58, 1.53 Hz, 1H), 6.93 (d, J = 9.06 Hz, 1H), 5.75 (m, 1H), 3.90–
4.02 (m, 1H), 3.75–3.90 (m, 2H), 3.67 (td, J = 9.87, 7.16 Hz, 1H),
2.21–2.48 (m, 2H). MS (ESI) m/z: 327 [M+H].
5.1.8. 2-(3-((3-Chloropyrazin-2-yl)oxy)azetidin-1-
yl)benzo[d]thiazole (59)
To a 100 mL 3-neck round bottom flask was charged 1-
(benzo[d]thiazol-2-yl)azetidin-3-ol 52 (1.96 g, 9.50 mmol) and
2,3-dichloropyrazine (1.55 g, 10.40 mmol). DMSO (24 mL) was
added and the mixture was cooled in an ice bath. Sodium hydride,
57% dispersion in mineral oil (0.460 g, 10.93 mmol) was added in
portions over 15 min. Upon complete addition, the reaction was
stirred at room temperature for 1 h. The reaction was recooled to
0 °C and quenched with water. The reaction mixture was extracted
with EtOAc (3ꢀ) and the combined organic layers were washed
with brine. The organic solution was evaporated onto silica gel
and purified by flash chromatography eluting with 0–50% EtOAc/
hexanes to give 2.45 g (81%) of an off-white crystalline solid. 1H
NMR (300 MHz, DMSO-d6) d 8.26 (d, J = 2.63 Hz, 1H), 8.16 (d,
J = 2.78 Hz, 1H), 7.80 (dd, J = 7.89, 0.88 Hz, 1H), 7.52 (d,
J = 7.45 Hz, 1H), 7.31 (td, J = 7.67, 1.17 Hz, 1H), 7.04–7.18 (m, 1H),
5.55–5.73 (m, 1H), 4.61 (ddd, J = 9.61, 6.47, 1.02 Hz, 2H), 4.25
(ddd, J = 9.65, 3.80, 1.02 Hz, 2H). MS (ESI) m/z: 319.0, 320.9 [M+H].
5.1.13. (S)-2-(3-((3-Chloropyrazin-2-yl)oxy)pyrrolidin-1-
yl)quinoline (64)
The title compound was prepared in a similar manner as 60
using 2,3-dichloropyrazine and compound 57. (79%) light-yellow
glass. 1H NMR (300 MHz, DMSO-d6) d 8.29 (d, J = 2.63 Hz, 1H),
8.10 (d, J = 2.78 Hz, 1H), 8.02 (d, J = 9.06 Hz, 1H), 7.63–7.75 (m,
1H), 7.53–7.60 (m, 1H), 7.45–7.53 (m, 1H), 7.18 (ddd, J = 7.93,
6.61, 1.53 Hz, 1H), 6.93 (d, J = 8.92 Hz, 1H), 5.75 (m, 1H), 3.90–
4.03 (m, 1H), 3.74–3.90 (m, 2H), 3.67 (td, J = 9.87, 7.16 Hz, 1H),
2.24–2.48 (m, 2H). MS (ESI) m/z: 327 [M+H].
5.1.14. 2-(4-((3-Chloropyrazin-2-yl)oxy)piperidin-1-
yl)quinoline (65)
5.1.9. 2-[3-(3-Chloro-pyrazin-2-yloxy)-azetidin-1-yl]-quinoline
(60)
The title compound was prepared in a similar manner as 60
using 2,3-dichloropyrazine and compound 58. (70%) white
solid. 1H NMR (400 MHz, CDCl3) d 8.02 (d, J = 2.74 Hz, 1H), 7.94
(d, J = 2.74 Hz, 1H), 7.91 (d, J = 9.19 Hz, 1H), 7.72 (d, J = 8.41 Hz,
1H), 7.61 (d, J = 7.82 Hz, 1H), 7.49–7.58 (m, 1H), 7.18–7.26
(m, 1H), 7.06 (d, J = 9.10 Hz, 1H), 5.31–5.50 (m, 1H), 4.03–4.23
To
a solution of 1-(quinolin-2-yl)azetidin-3-ol 53 (3.20 g,
16.0 mmol) in DMF (30 mL) at 0 °C was added sodium hydride
(60% wt in mineral oil) (1.28 g, 32 mmol). The mixture was stirred
at room temperature for 60 min and then 2,3-dichloropyrazine
(2.37 g, 16.0 mmol) was added. The reaction mixture was heated

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6579
(m, 2H), 3.64–3.85 (m, 2H), 2.10–2.24 (m, 2H), 1.92–2.05
(m, 2H). MS (ESI) [M+H]: 341 calcd for C18H17ClN4O 340.
iPrOH (3 mL) and water (1.0 ml). The solution was heated to 160 °C
in the microwave for 5 h. The mixture was concentrated and
extracted with EtOAc (2 ꢀ 30 mL). The combined organic extracts
were washed with water (10 mL) and brine (10 mL), dried over
Na2SO4, and filtered. The filtrate was evaporated in vacuo and
the residue was purified by flash column chromatography eluting
with 20–60% EtOAc/petroleum ether to give 67 mg (18%) of
the title product as a white solid. 1H NMR (400 MHz, CD3OD) d
7.86–7.72 (m, 3H), 7.58–7.47 (m, 3H), 7.30–7.20 (m, 1H), 6.56
(d, J = 8.8 Hz, 1H), 5.51 (s, 1H), 4.63–4.59 (m, 2H), 4.23–4.19 (m,
1H), 3.97–3.94 (m, 2H), 3.86–3.84 (m, 1H), 3.12–3.09 (m, 2H),
2.20–1.93 (m, 3H), 1.66–1.60 (m, 2H). HRMS (ESI): calcd for
5.1.15. 2-(3-((3-Bromopyridin-2-yl)oxy)azetidin-1-yl)quinoline
(66)
The title compound was prepared in a similar manner as
59 using 3-bromo-2-fluoropyridine and compound 53. (91%)
light-tan glass. 1H NMR (300 MHz, CD3OD) d 8.12 (dd, J = 4.90,
1.68 Hz, 1H), 7.90–8.04 (m, 2H), 7.61–7.77 (m, 2H), 7.47–7.60
(m, 1H), 7.24 (ddd, J = 7.97, 6.87, 1.10 Hz, 1H), 6.93 (dd, J = 7.67,
4.90 Hz, 1H), 6.73 (d, J = 9.06 Hz, 1H), 5.59 (tt, J = 6.50, 4.17 Hz,
1H), 4.56–4.72 (m, 2H), 4.11–4.30 (m, 2H). MS (ESI) m/z: 356.0,
358.0 [M+H].
C21H23N5O2 [M+H] 378.1925. Found: 378.1931.
5.1.16. 2-Chloro-3-((1-(quinolin-2-yl)azetidin-3-
yl)oxy)quinoxaline (71)
5.1.20. (1-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)piperidin-4-yl)methanol (6)
The title compound was prepared in a similar manner as 60
using 2,3-dichloroquinoxaline and compound 53. (60%) white crys-
talline solid. 1H NMR (300 MHz, DMSO-d6) d 8.07 (d, J = 8.92 Hz,
1H), 8.00 (dd, J = 8.33, 1.02 Hz, 1H), 7.88–7.95 (m, 1H), 7.83 (td,
J = 7.60, 1.46 Hz, 1H), 7.68–7.78 (m, 2H), 7.58–7.65 (m, 1H), 7.49–
7.58 (m, 1H), 7.20–7.32 (m, 1H), 6.84 (d, J = 8.77 Hz, 1H), 5.59–
5.83 (m, 1H), 4.67 (dd, J = 9.65, 6.58 Hz, 2H), 4.26 (dd, J = 10.16,
3.73 Hz, 2H). MS (ESI) m/z: 363.0, 365.0 [M+H].
The title compound was prepared in a similar manner as 16 using
4-piperidinemethanol and compound 60. (50%) amorphous solid. 1H
NMR (400 MHz, CD3OD) d 7.96 (d, J = 9.2 Hz, 1H), 7.70–7.31 (m, 3H),
7.54–7.49 (m, 2H), 7.25–7.23 (m, 1H), 6.66 (d, J = 9.2 Hz, 1H), 5.52
(s, 2H), 4.62–4.58 (s, 2H), 4.22–4.17(m, 4H), 3.41–3.39 (m, 2H),
2.79–2.78 (m, 2H), 1.79–1.75 (m, 3H); 1.34–1.30 (m, 2H). HRMS
(ESI): calcd for [M+H] 392.2081. Found: 392.2087.
5.1.21. (1-(3-((1-(Quinazolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)piperidin-4-yl)methanol (7)
5.1.17. 2-(3-((3-Bromopyridin-4-yl)oxy)azetidin-1-yl)quinoline
(67)
The title compound was prepared in a similar manner as 16
using 4-piperidinemethanol and compound 61. (59%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 9.02 (s, 1H), 7.74–7.67 (m,
3H), 7.53 (d, J = 8.4 Hz, 1H), 7.47 (d, J = 2.8 Hz, 1H), 7.27–7.23 (m,
1H), 5.51–5.54 (m, 1H), 4.64–4.59 (m, 2H), 4.22–4.18 (m, 4H),
3.49–3.40 (m, 2H), 2.81–2.75 (m, 2H), 1.78–1.75 (m, 2H), 1.66–
1.64 (m, 2H), 1.37–1.27 (m, 2H). HRMS (ESI): calcd for
To a solution of 1-(quinolin-2-yl)azetidin-3-ol 53 (320 mg,
1.60 mmol) in DMF (10 mL) was added cesium carbonate
(1.04 g, 3.2 mmol) and 3-bromo-4-chloropyridine (307 mg,
1.60 mmol). The mixture was stirred at 90 °C overnight and then
diluted with water (20 mL) and extracted with EtOAc
(2 ꢀ 30 mL). The combined organic extracts were washed with
water (30 mL) and brine (30 mL), dried over Na2SO4, and
filtered. The filtrate was evaporated in vacuo and the residue
was purified by flash column chromatography eluting with
5–30% EtOAc/petroleum ether to give 350 mg (61%) of the
title product as white solid. MS (ESI) [M+H]: 356 calcd for
C21H25N6O2 [M+H] 393.2034. Found: 393.2040.
5.1.22. (1-(3-((1-(Quinoxalin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)piperidin-4-yl)methanol (8)
The title compound was prepared in a similar manner as 16
using 4-piperidinemethanol and compound 62. (50%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 8.23 (s, 1H), 7.82–7.79 (m,
1H), 7.69 (d, J = 2.8 Hz, 1H), 7.64–7.62 (m, 2H), 7.59 (d, J = 1.2 Hz,
1H), 7.40–7.36 (m, 1H), 5.56–5.55 (m, 1H), 4.72–4.68 (m, 2H),
4.31–4.20 (m, 4H), 3.40–3.39 (m, 2H), 2.84–2.77 (m, 2H), 1.79–
1.76 (m, 3H), 1.34–1.30 (m, 2H). HRMS (ESI): calcd for
C17H14BrN3O 355. MS (ESI) m/z: 355 [M+H].
5.1.18. (1-(3-((1-(Benzo[d]thiazol-2-yl)azetidin-3-
yl)oxy)pyrazin-2-yl)piperidin-4-yl)methanol (5)
A glass microwave reaction vessel was charged with 2-(3-((3-
chloropyrazin-2-yl)oxy)azetidin-1-yl)benzo[d]thiazole 59 (0.153 g,
0.480 mmol) and 4-piperidinemethanol (0.171 g, 1.485 mmol).
DMSO (1 mL) was added and the reaction mixture was sealed under
argon and heated at 120 °C overnight. The reaction was cooled to
room temperature and diluted with water. The slurry was extracted
with EtOAc (3ꢀ) and the combined organic layers were evaporated
onto silica gel and purified by flash chromatography eluting with
0–100% EtOAc/hexanes to give 116 mg (61%) of a white crystalline
solid. 1H NMR (300 MHz, CD3OD) d 7.77 (d, J = 2.92 Hz, 1H), 7.71 (d,
J = 7.60 Hz, 1H), 7.47–7.60 (m, 2H), 7.28–7.41 (m, 1H), 7.07–7.23
(m, 1H), 5.66 (tt, J = 6.50, 4.09 Hz, 1H), 4.68 (dd, J = 9.50, 7.31 Hz,
2H), 4.28 (dd, J = 10.01, 3.58 Hz, 4H), 3.47 (d, J = 6.28 Hz, 2H), 2.89
(td, J = 12.53, 2.12 Hz, 2H), 1.85 (dd, J = 13.01, 1.75 Hz, 2H),
1.64–1.80 (m, 1H), 1.39 (qd, J = 12.20, 3.87 Hz, 1H). HRMS (ESI): calcd
for C20H24N5O2S [M+H] 398.1650. Found: 398.1650.
C
21H25N6O2 [M+H] 393.2034. Found: 393.2037.
5.1.23. (R)-(1-(3-((1-(Quinolin-2-yl)pyrrolidin-3-yl)oxy)pyrazin-
2-yl)piperidin-4-yl)methanol (9)
The title compound was prepared in a similar manner as 16
using 4-piperidinemethanol and compound 63. (17%) amorphous
solid. 1H NMR (400 MHz, CDCl3) d 8.16 (s, 1H), 8.03–7.98 (m,
1H), 7.72–7.67 (m, 2H), 7.54–7.52 (m, 1H), 7.46–7.41 (m, 2H),
6.88–6.86 (m, 1H), 5.83 (s, 1H), 4.27–3.98 (m, 7H), 3.59–3.40 (m,
1H), 2.99–2.83 (m, 2H), 2.54–2.53 (m, 2H), 2.01–1.72 (m, 3H),
1.41–1.32 (m, 2H). HRMS (ESI): calcd for C23H28N5O2 [M+H]
406.2237. Found: 406.2237.
5.1.24. (S)-(1-(3-((1-(Quinolin-2-yl)pyrrolidin-3-yl)oxy)pyrazin-
2-yl)piperidin-4-yl)methanol (10)
The title compound was prepared in a similar manner as 16
using 4-piperidinemethanol and compound 64. (23%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 8.37 (s, 1H), 7.91–7.88 (m,
2H), 7.68–7.67 (m, 1H), 7.60–7.59 (m, 1H), 7.54–7.50 (m, 1H),
7.30–7.20 (m, 2H), 5.90–5.89 (m, 1H), 4.23–4.09 (m, 7H), 4.01–
3.99 (m, 1H), 2.93–2.86 (m, 2H), 2.61–2.59 (m, 2H), 1.78–1.75
5.1.19. 1-[3-(1-Quinolin-2-yl-azetidin-3-yloxy)-pyrazin-2-yl]-
piperidin-4-ol (16)
To a mixture of 2-[3-(3-chloro-pyrazin-2-yloxy)-azetidin-1-yl]-
quinoline (312 mg, 1.0 mmol) and piperidin-4-ol (0.101 g,
1.0 mmol) and potassium carbonate (0.276 g, 2.0 mmol) was added

6580
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
(m, 3H), 1.33–1.27 (m, 2H). HRMS (ESI): calcd for C23H28N5O2
[M+H] 406.2237. Found: 406.2243.
amorphous solid. 1H NMR (400 MHz, CD3OD) d 7.87–7.73 (m,
3H), 7.59–7.47 (m, 3H), 7.22–7.21 (m, 1H), 6.58–6.56 (m, 1H),
5.51 (s, 1H), 4.62–4.61 (m, 2H), 4.20–4.16 (m, 4H), 3.31–3.22 (m,
5H), 2.81–2.75 (m, 2H), 1.80–1.77 (m, 3H), 1.36–1.27 (m, 2H).
HRMS (ESI): calcd for [M+H] 406.2243. Found: 406.2250.
5.1.25. (1-(3-((1-(Quinolin-2-yl)piperidin-4-yl)oxy)pyrazin-2-
yl)piperidin-4-yl)methanol (11)
The title compound was prepared in a similar manner as 16
using 4-piperidinemethanol and compound 65. (48%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 8.40 (d, J = 9.6 Hz, 1H), 7.91
(s, 2H), 7.67–7.66 (m, 1H), 7.57–7.53 (m, 4H), 5.56–5.54 (m, 1H),
4.23–4.20 (m, 2H), 4.09–4.06 (m, 5H), 3.47–3.40 (m, 2H), 2.94–
2.87 (m, 2H), 2.35–2.69 (m, 2H), 2.17–2.12 (m, 2H), 2.00 (s, 2H),
1.85–1.81 (m, 1H), 1.37–1.35 (m, 2H). HRMS (ESI): calcd for
5.1.31. 2-(3-((3-(Piperidin-1-yl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline (20)
The title compound was prepared in a similar manner as 16
using piperidine and compound 60. (60%) amorphous solid. 1H
NMR (400 MHz, CDCl3) d 7.88 (d, J = 8.8 Hz, 1H), 7.76–7.75 (m,
2H), 7.61 (d, J = 8.4 Hz, 1H), 7.60–7.55 (m, 1H), 7.48 (d, J = 2.8 Hz,
1H), 7.25–7.21 (m, 1H), 6.61 (d, J = 8.8 Hz, 1H), 5.56–5.52 (m,
1H), 4.66–4.62 (m, 2H), 4.26–4.23 (m, 2H), 3.48–3.45 (m, 4H),
C24H30N5O2 [M+H] 420.2393. Found: 420.2400.
1.68–1.66 (m, 6H). HRMS (ESI): calcd for
362.1976. Found: 362.1980.
C21H24N5O [M+H]
5.1.26. (1-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)quinoxalin-2-
yl)piperidin-4-yl)methanol (14)
The title compound was prepared in a similar manner as 16
using 4-piperidinemethanol and compound 71. (60%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 8.35 (d, J = 9.2 Hz, 1H), 7.90 (d,
J = 8.0 Hz, 1H), 7.82–7.78 (m, 2H), 7.71–7.66 (m, 2H), 7.54–7.40
(m, 3H), 7.00 (d, J = 9.2 Hz, 1H), 5.79–5.83 (m, 1H), 5.07–5.03 (m,
2H), 4.68–4.65 (m, 2H), 4.52–4.49 (m, 2H), 3.47–3.45 (m, 2H),
3.07–3.01 (m, 2H), 1.92–1.76 (m, 3H), 1.49–1.39 (m, 2H). HRMS
(ESI): calcd for C26H28N5O2 [M+H] 442.2237. Found: 442.2240.
5.1.32. 2-(3-((3-(4-Methylpiperidin-1-yl)pyrazin-2-
yl)oxy)azetidin-1-yl)quinoline (21)
The title compound was prepared in a similar manner as 16
using 4-methylpiperidine and compound 60. (60%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 8.32 (d, J = 9.6 Hz, 1H), 7.87
(d, J = 8.0 Hz, 1H), 7.78–7.76 (m, 3H), 7.52–7.50 (m, 2H), 6.96 (d,
J = 9.6 Hz, 1H), 5.66–5.61 (m, 1H), 4.97 (s, 2H), 4.55–4.59 (m, 2H),
4.22–4.19 (m, 2H), 2.94–2.87 (m, 2H), 1.98–1.72 (m, 2H), 1.65–
1.60 (m, 1H), 1.35–1.26 (m, 2H), 1.27–1.26 (s, 3H). HRMS (ESI):
calcd for C22H26N5O [M+H] 376.2132. Found: 376.2128.
5.1.27. 2-(1-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)piperidin-4-yl)ethanol (15)
The title compound was prepared in a similar manner as 16
using 4-piperidineethanol and compound 60. (100%) light-yellow
oil. 1H NMR (400 MHz, DMSO-d6) d 8.12 (d, J = 9.68 Hz, 1H),
7.71–7.84 (m, 2H), 7.50–7.68 (m, 3H), 7.29 (t, J = 8.36 Hz, 1H),
6.85 (d, J = 9.24 Hz, 1H), 5.43–5.57 (m, 1H), 4.62 (dd, J = 10.56,
7.04 Hz, 2H), 4.05–4.25 (m, 6H), 2.76 (t, J = 13.86 Hz, 2H), 1.71 (d,
J = 14.96 Hz, 3H), 1.09–1.44 (m, 4H). HRMS (ESI): calcd for
5.1.33. 4-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)morpholine (22)
The title compound was prepared in a similar manner as 16
using morpholine and compound 60. (60%) amorphous solid. 1H
NMR (400 MHz, CDCl3) d 8.35 (d, J = 9.2 Hz, 1H), 7.90 (d, J = 8.0 Hz,
1H), 7.81–7.78 (m, 3H), 7.59 (d, J = 3.2 Hz, 1H), 7.54–7.52 (m, 1H),
6.98 (d, J = 9.2 Hz, 1H), 5.67–5.64 (m, 1H), 4.98–4.93 (m, 2H),
4.61–4.55 (m, 2H), 3.81–3.79 (m, 4H), 3.56–3.53 (m, 4H). HRMS
(ESI): calcd for C20H22N5O2 [M+H] 364.1769. Found: 364.1766.
C23H28N5O2 [M+H] 406.2237. Found: 406.2241.
5.1.28. 1-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)azetidin-3-ol (17)
5.1.34. N,N-Dimethyl-1-(3-((1-(quinolin-2-yl)azetidin-3-
yl)oxy)pyrazin-2-yl)piperidin-4-amine (23)
The title compound was prepared in a similar manner as 16
using 3-hydroxyazetidine and compound 60. (43%) off-white
amorphous solid. 1H NMR (400 MHz, DMSO-d6)
d 8.04 (d,
The title compound was prepared in a similar manner as 16
using 4-dimethylaminopiperidine and compound 60. (77%) light-
yellow oil. 1H NMR (400 MHz, DMSO-d6) d 8.04 (d, J = 9.68 Hz,
1H), 7.67–7.83 (m, 2H), 7.48–7.62 (m, 3H), 7.18–7.29 (m, 1H),
6.79 (d, J = 8.80 Hz, 1H), 5.45–5.57 (m, 1H), 4.55 (dd, J = 10.12,
7.04 Hz, 2H), 4.04–4.24 (m, 5 H), 2.78 (t, J = 14.08 Hz, 2H), 2.15
(s, 6H), 1.74–1.88 (m, 2H), 1.33–1.51 (m, 2H). HRMS (ESI): calcd
for C23H29N6O [M+H] 405.2397. Found: 405.2399.
J = 9.24 Hz, 1H), 7.49–7.75 (m, 4H), 7.38 (d, J = 3.08 Hz, 1H), 7.19–
7.28 (m, 1H), 6.79 (d, J = 9.24 Hz, 1H), 5.66 (d, J = 6.16 Hz, 1H),
5.44–5.53 (m, 1H), 4.52 (dd, J = 10.56, 6.60 Hz, 3H), 4.27–4.38 (m,
2H), 4.02–4.14 (m, 2H), 3.84–3.88 (m, 1H). MS (ESI) [M+H]:
350.1617. Calcd for C19H20N5O2 [M+H] 350.1617.
5.1.29. rac-{1-[3-(1-Quinolin-2-yl-azetidin-3-yloxy)-pyrazin-2-
yl]-pyrrolidin-3-yl}-methanol (18)
5.1.35. 1-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)piperidine-4-carbonitrile (24)
The title compound was prepared in a similar manner as 16
using pyrrolidin-3-yl-methanol and compound 60. (43%) off-white
amorphous solid. (61%), tan amorphous solid. 1H NMR (400 MHz,
CD3OD) d 1H NMR (300 MHz, CD3OD) d 8.37 (d, J = 9.35 Hz, 1H),
7.92 (d, J = 7.45 Hz, 1H), 7.73–7.86 (m, 2H), 7.62 (d, J = 3.22 Hz,
1H), 7.53 (ddd, J = 8.00, 6.61, 1.61 Hz, 1H), 7.30 (d, J = 3.07 Hz,
1H), 7.00 (d, J = 9.35 Hz, 1H), 5.62 (tt, J = 6.72, 4.09 Hz, 1H), 4.90–
5.04 (m, 2H), 4.53–4.66 (m, 2H), 3.80–3.98 (m, 2H), 3.68–3.80
(m, 1H), 3.48–3.68 (m, 3H), 2.49 (m, 1H), 2.00–2.20 (m, 1H), 1.77
(dq, J = 12.42, 7.94 Hz, 1H). HRMS (ESI): calcd for C21H24N5O2
[M+H] 378.1930. Found: 378.1929.
The title compound was prepared in a similar manner as 16
using 4-cyanopiperidine and compound 60. (15%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 7.94–7.92 (m, 1H), 7.73 (d,
J = 2.8 Hz, 1H), 7.65–7.64 (m, 2H), 7.55–7.51 (m, 2H), 7.20–7.18
(m, 1H), 6.65 (d, J = 9.2 Hz, 1H), 5.51 (s, 1H), 4.60–4.55 (m, 2H),
4.18–4.14 (s, 2H), 3.79–3.73 (m, 2H), 3.35–3.29 (m, 2H), 2.95–
2.93 (m, 1H), 2.01–1.96 (m, 2H), 1.94–1.89 (m, 2H). HRMS (ESI):
calcd for C22H23N6O [M+H] 387.1929. Found: 387.1928.
5.1.36. 1-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)piperidine-4-carboxamide (25)
The title compound was prepared in a similar manner as 16
using isonipecotamide and compound 60. (50%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 7.97–7.96 (m, 1H), 7.89
(d, J = 9.2 Hz, 1H), 7.70–7.69 (m, 2H), 7.57–7.52 (m, 1H),
5.1.30. 2-(3-((3-(4-(Methoxymethyl)piperidin-1-yl)pyrazin-2-
yl)oxy)azetidin-1-yl)quinoline (19)
The title compound was prepared in a similar manner as 16
using 4-(methoxymethyl)piperidine and compound 60. (78%)

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6581
7.44–7.43 (m, 1H), 6.53 (d, J = 9.2 Hz, 1H), 5.54–5.47 (m, 2H),
5.39 (s, 1H), 4.73 (s, 1H), 4.32 (s, 1H), 4.19–4.18 (m, 2H),
2.84–2.77 (m, 2H), 2.54–2.51 (m, 1H), 2.37–2.29 (m, 1H);
1.96–1.73 (m, 4H). HRMS (ESI): calcd for C22H25N6O2 [M+H]
405.2034. Found: 405.2035.
5.36–5.46 (m, 1H), 4.29–4.43 (m, 4H), 3.92–4.01 (m, 2H). HRMS
(ESI): calcd for C23H21N4O2 [M+H] 385.1660. Found: 385.1658.
5.1.40. (3-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)phenyl)methanol (27)
The title compound was prepared in a similar manner as 26
using 3-(hydroxymethyl)phenylboronic acid and compound 60.
(79%) amorphous solid. 1H NMR (400 MHz, DMSO-d6) d 8.39
(d, J = 2.64 Hz, 1H), 8.22 (d, J = 2.64 Hz, 1H), 7.91–8.08 (m, 3H),
7.71 (d, J = 8.80 Hz, 1H), 7.35–7.63 (m, 4H), 7.23 (t, J = 8.14 Hz,
1H), 6.79 (d, J = 9.24 Hz, 1H), 5.58–5.68 (m, 1H), 5.34 (d,
J = 5.72 Hz, 1H) 4.51–4.63 (m, 4H), 4.16 (dd, J = 10.56, 4.40 Hz,
2H). HRMS (ESI): calcd for C23H21N4O2 [M+H] 385.1660. Found:
385.1651.
5.1.37. (1-(2-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyridin-3-
yl)piperidin-4-yl)methanol (12)
A
glass microwave reaction vessel was charged with 2-
(3-((3-bromopyridin-2-yl)oxy)azetidin-1-yl)quinoline 66 (0.176 g,
0.494 mmol), 4-piperidinemethanol (0.076 g, 0.660 mmol), 2-
(dicyclohexylphosphino)-20-methylbiphenyl (0.015 g, 0.041 mmol)
and Pd2(dba)3 (0.020 g, 0.022 mmol). The vessel was capped and
evacuated/purged with argon (3ꢀ). A 1.0 M solution of lithium
bis(trimethylsilyl)amide in THF (1.1 ml, 1.10 mmol) was added
and the reaction mixture was heated at 65 °C overnight. The reac-
tion was cooled to room temperature, diluted with EtOAc, evapo-
rated onto silica gel and purified by flash chromatography
eluting with 2 M NH3 in MeOH/CH2Cl2 (0–5%) to give 81 mg
(42%) of a tan crystalline solid. 1H NMR (300 MHz, CD3OD) d 8.00
(d, J = 8.92 Hz, 1H), 7.75 (dd, J = 4.97, 1.61 Hz, 1H), 7.61–7.71 (m,
2H), 7.54 (ddd, J = 8.44, 6.98, 1.39 Hz, 1H), 7.29 (dd, J = 7.75,
1.61 Hz, 1H), 7.19–7.27 (m, 1H), 6.94 (dd, J = 7.60, 4.97 Hz, 1H),
6.74 (d, J = 8.92 Hz, 1H), 5.59 (tt, J = 6.45, 4.15 Hz, 1H), 4.59–4.71
(m, 2H), 4.20 (dd, J = 10.38, 4.09 Hz, 2H), 3.55 (d, J = 11.84 Hz,
2H), 3.45 (d, J = 6.14 Hz, 2H), 2.51–2.71 (m, 2H), 1.74–1.93 (m,
2H), 1.52–1.70 (m, 1H), 1.34–1.52 (m, 2H). HRMS (ESI): calcd for
5.1.41. 2-(3-((3-Phenylpyrazin-2-yl)oxy)azetidin-1-yl)quinoline
(28)
The title compound was prepared in a similar manner as 26
using phenylboronic acid and compound 60. (64%) amorphous
solid. 1H NMR (400 MHz, CD3OD) d 8.28–8.25 (m, 1H), 8.10–8.08
(m, 1H), 7.98–7.95 (m, 2H), 7.84 (d, J = 8.8 Hz, 1H), 7.61–7.55 (m,
2H), 7.47–7.30 (m, 4H), 7.19–7.16 (m, 1H), 6.55 (d, J = 8.8 Hz,
1H), 5.52–5.49 (m, 1H), 4.54–4.49 (m, 2H), 4.13–4.09 (m, 2H).
HRMS (ESI): calcd for
355.1561.
C22H19N4O [M+H] 355.1555. Found:
5.1.42. 2-(3-((3-(p-Tolyl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline (29)
C23H27N4O2 [M+H] 391.2128. Found: 391.2134.
The title compound was prepared in a similar manner as 26
using p-tolyl boronic acid and compound 60. (53%), amorphous
solid. 1H NMR (400 MHz, CDCl3) d 8.27 (d, J = 2.8 Hz, 1H), 8.00–
7.97 (m, 3H), 7.86 (d, J = 9.2 Hz, 1H), 7.74 (d, J = 8.4 Hz, 1H),
7.60–7.51 (m, 2H), 7.26–7.20 (m, 3H), 6.58 (d, J = 9.2 Hz, 1H),
5.63–5.59 (m, 1H), 4.06–4.62 (m, 2H), 4.29–4.25 (m, 2H); 2.38 (s,
3H). HRMS (ESI): calcd for C23H21N4O [M+H] 369.1711. Found:
369.1718.
5.1.38. (1-(4-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyridin-3-
yl)piperidin-4-yl)methanol (13)
A
mixture of (3-((3-Bromopyridin-4-yl)oxy)azetidin-1-yl)
quinoline 67 (0.30 mmol), 4-piperidinemethanol (0.30 mmol),
Pd2(dba)3 (0.03 mmol), t-ButylXphos (0.03 mmol) and K3PO4
(0.6 mmol) in toluene (10 mL) was stirred at 100 °C for 10 h.
The mixture was left to reach room temperature and filtered
through a pad of Celite™ and the filter cake was washed with
CH2Cl2 (20 mL). The combine filtrate was evaporated in vacuo
and the residue was purified by flash column chromatography
eluting with 30–50% EtOAc/petroleum ether. Further purification
by reverse phase HPLC eluting with 10–80% water/MeCN afforded
40 mg (40%) of the title compound as an amorphous solid. 1H
NMR (CD3OD, 400 MHz): d 8.16–8.14 (m, 2H), 7.89 (d, J = 8.8 Hz,
1H), 7.73 (d, J = 8.2 Hz, 1H), 7.61–7.59 (m, 2H), 7.25–7.23 (m,
1H), 6.59 (d, J = 9.2 Hz, 1H), 6.46 (d, J = 4.2 Hz, 1H), 5.14–5.12
(m, 1H), 4.62–4.58 (m, 2H), 4.26–4.23 (m, 2H) 3.52–3.50 (m,
4H), 2.83–2.62 (m, 3H), 1.83–1.80 (m, 2H), 1.63–1.62 (m, 1H),
1.48–1.41 (m, 2H). MS (ESI) [M+H]: 391.2132. Calcd for
5.1.43. N-Methyl-4-(3-((1-(quinolin-2-yl)azetidin-3-
yl)oxy)pyrazin-2-yl)benzamide (30)
The title compound was prepared in a similar manner as 26
using 4-(N-methylaminocarbonyl)phenylboronic acid and com-
pound 60. (72%) amorphous solid. 1H NMR (400 MHz, CD3OD) d
8.31–8.25 (m, 2H), 8.09–8.08 (m, 2H), 8.07–7.79 (m, 3H), 7.70–
7.69 (m, 2H), 7.43–7.39 (m, 1H), 6.90–6.87 (m, 1H), 5.69–5.65
(m, 1H), 4.92–4.88 (m, 4H), 4.55–4.51 (m, 2H), 2.84 (s, 3H). HRMS
(ESI): calcd for C24H22N5O2 [M+H] 412.1769. Found: 412.1773.
5.1.44. Methyl 4-(3-((1-(quinolin-2-yl)azetidin-3-
yl)oxy)pyrazin-2-yl)benzoate (31)
C23H26N4O2 [M+H] 391.2128.
The title compound was prepared in a similar manner as 26
using 4-methoxycarbonylphenylboronic acid and compound 60.
(43%) amorphous solid. 1H NMR (400 MHz, DMSO-d6) d 8.44
(d, J = 2.64 Hz, 1H), 8.17–8.31 (m, 3H), 8.00–8.11 (m, 3H), 7.72
(d, J = 9.24 Hz, 1H), 7.49–7.64 (m, 2H), 7.18–7.29 (m, 1H), 6.80
(d, J = 9.24 Hz, 1H), 5.59–5.70 (m, 1H), 4.59 (dd, J = 10.34,
6.82 Hz, 2H), 4.20 (dd, J = 10.34, 4.18 Hz, 2H), 3.87 (s, 3H).
5.1.39. (4-(3-(1-(Quinolin-2-yl)azetidin-3-yloxy)pyrazin-2-
yl)phenyl)methanol (26)
A glass microwave vessel was charged with compound 60 (40 mg,
0.128 mmol), 4-(hydroxymethyl)phenylboronic acid (29 mg,
0.192 mmol), sodium carbonate (41 mg, 0.384 mmol), and dioxane/
water (1.0 mL:0.18 mL). The solution was purged with nitrogen for
5 min, then Pd(PPh3)4 (15 mg, 0.013 mmol) was added. The reaction
mixture was stirred and heated at 120 °C for 64 h. The reaction mix-
ture was filtered and washed with EtOAc/MeOH. The was concen-
trated and purified by reverse phase HPLC to give 21 mg (43%) of
the title compound as an amorphous solid. 1H NMR (400 MHz,
DMSO-d6) d 8.16 (d, J = 2.64 Hz, 1H), 7.99 (d, J = 2.64 Hz, 1H), 7.82
(d, J = 8.36 Hz, 3H), 7.51 (d, J = 8.80 Hz, 1H), 7.28–7.43 (m, 2H)ß 7.22
(d, J = 8.36 Hz, 2H), 7.03 (t, J = 7.70 Hz, 1H), 6.59 (d, J = 9.24 Hz, 1H),
HRMS (ESI): calcd for
413.1612.
C24H21N4O3 [M+H] 413.1609. Found:
5.1.45. 4-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)benzonitrile (32)
The title compound was prepared in a similar manner as 26
using 4-cyanophenylboronic acid and compound 60. (53%) amor-
phous solid. 1H NMR (400 MHz, CDCl3) d 8.25 (d, J = 1.6 Hz, 1H),
8.21 (d, J = 2.8 Hz, 1H), 7.87–7.82 (m, 3H), 7.80–7.55 (m, 5H),

6582
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
7.50–7.46 (m, 1H), 6.95 (d, J = 9.6 Hz, 1H), 5.77–5.73 (m, 1H), 5.00–
4.91 (m, 2H), 4.64–4.60 (m, 2H). HRMS (ESI): calcd for C23H18N5O
[M+H] 380.1508. Found: 380.1505.
1H), 8.45 (d, J = 2.64 Hz, 1H), 8.33 (d, J = 2.64 Hz, 1H), 8.05 (d,
J = 9.24 Hz, 1H), 7.83–7.92 (m, 2H), 7.72 (d, J = 9.24 Hz, 1H), 7.49–
7.63 (m, 2H), 7.19–7.29 (m, 1H), 6.80 (d, J = 9.24 Hz, 1H), 5.60–
5.69 (m, 1H), 4.60 (dd, J = 10.34, 7.26 Hz, 2H), 4.21 (dd, J = 10.56,
4.40 Hz, 2H), 2.54 (s, 3H). HRMS (ESI): calcd for C22H20N5O
[M+H] 370.1664. Found: 370.1667.
5.1.46. 2-(3-((3-(Pyridin-3-yl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline (34)
The title compound was prepared in a similar manner as 26
using pyridine-3-boronic acid and compound 60. (95%) amorphous
solid. 1H NMR (400 MHz, DMSO-d6) d 9.22 (s, 1H), 8.63 (d,
J = 5.28 Hz, 1H), 8.39–8.49 (m, 2H), 8.29 (d, J = 2.64 Hz, 1H), 8.05
(d, J = 9.24 Hz, 1H), 7.72 (d, J = 9.24 Hz, 1H), 7.48–7.64 (m, 3H),
7.19–7.30 (m, 1H), 6.80 (d, J = 9.24 Hz, 1H), 5.57–5.73 (m, 1H),
4.59 (dd, J = 10.56, 7.04 Hz, 2H), 4.19 (dd, J = 10.56, 3.96 Hz, 2H).
5.1.52. 5-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)quinoline (40)
The title compound was prepared in a similar manner as 26
using quinolin-5-boronic acid and compound 60. (87%) amorphous
solid. 1H NMR (400 MHz, DMSO-d6) d 8.88 (dd, J = 4.18, 1.54 Hz,
1H), 8.49 (d, J = 3.08 Hz, 1H), 8.38 (d, J = 2.64 Hz, 1H), 8.13
(d, J = 8.80 Hz, 2H), 8.01 (d, J = 9.68 Hz, 1H), 7.77–7.92 (m, 2H),
7.36–7.75 (m, 4H), 7.17–7.27 (m, 1H), 6.71 (d, J = 9.24 Hz, 1H),
5.51–5.65 (m, 1H), 4.49 (dd, J = 9.90, 7.26 Hz, 2H), 3.92 (dd,
J = 10.56, 4.40 Hz, 2H). HRMS (ESI): calcd for C25H20N5O [M+H]
406.1664. Found: 406.1671.
HRMS (ESI): calcd for
356.1507.
C21H18N5O [M+H] 356.1508. Found:
5.1.47. 2-(3-((3-(Pyridin-4-yl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline (35)
The title compound was prepared in a similar manner as 26
using pyridine-4-boronic acid and compound 60. (53%) amorphous
solid. 1H NMR (400 MHz, CDCl3) d 8.71–8.60 (m, 2H), 8.30–8.29 (s,
1H), 8.07 (d, J = 2.8 Hz, 1H), 7.95–7.97 (m, 2H), 7.81 (d, J = 8.4 Hz,
1H), 7.54–7.52 (m, 1H), 7.49–7.45 (m, 2H), 7.18–7.15 (m, 1H),
6.53 (d, J = 8.8 Hz, 1H), 5.60–5.57 (m, 1H), 4.62–4.58 (m, 2H),
5.1.53. 3-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)quinoline (41)
The title compound was prepared in a similar manner as 26
using quinoline-3-boronic acid and compound 60. (39%) amor-
phous solid. 1H NMR (400 MHz, DMSO-d6) d 9.55 (d, J = 2.20 Hz,
1H), 9.07 (s, 1H), 8.51 (d, J = 2.64 Hz, 1H), 8.33 (d, J = 2.64 Hz,
1H), 8.03–8.20 (m, 3H), 7.50–7.90 (m, 5 H), 7.27 (d, J = 7.92 Hz,
1H), 6.84 (d, J = 9.24 Hz, 1H), 5.64–5.75 (m, 1H), 4.60–4.70
(m, 2H), 4.23–4.36 (m, 2H). HRMS (ESI): calcd for C25H20N5O
[M+H] 406.1664. Found: 406.1671.
4.23–4.20 (m, 2H). HRMS (ESI): calcd for
356.1508. Found: 356.1512.
C21H18N5O [M+H]
5.1.48. 2-(3-((3-(Pyrimidin-5-yl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline (36)
The title compound was prepared in a similar manner as 26
using 5-pyrimidylboronic acid and compound 60. (34%) amor-
phous solid. 1H NMR (400 MHz, DMSO-d6) d 8.35 (d, J = 2.64 Hz,
1H), 8.05 (d, J = 9.68 Hz, 1H), 7.49–7.76 (m, 5 H), 7.18–7.29 (m,
1H), 6.81 (d, J = 9.24 Hz, 1H), 5.62–5.71 (m, 1H), 4.59 (dd,
J = 10.34, 7.26 Hz, 2H), 4.22 (dd, J = 10.34, 4.18 Hz, 2H). HRMS
(ESI): calcd for C20H71N6O [M+H] 357.1461. Found: 357.1461.
5.1.54. 5-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)benzo[d]thiazole (42)
The title compound was prepared in a similar manner as 26
using 1,3-benzthiazol-6-ylboronic acid and compound 60. (38%)
amorphous solid. 1H NMR (400 MHz, DMSO-d6) d 8.80 (s, 1H),
8.45 (d, J = 2.64 Hz, 1H), 8.17–8.32 (m, 3H), 8.08 (d, J = 9.68 Hz,
1H), 7.73 (d, J = 8.36 Hz, 1H), 7.51–7.66 (m, 3H), 7.21–7.31 (m,
1H), 6.83 (d, J = 9.24 Hz, 1H), 5.68 (s, 1H), 4.59–4.68 (m, 2H), 4.24
(d, J = 14.96 Hz, 2H). HRMS (ESI): calcd for C23H18N5OS [M+H]
412.1229. Found: 412.1239.
5.1.49. 2-(3-((3-(2-Methylpyridin-3-yl)pyrazin-2-
yl)oxy)azetidin-1-yl)quinoline (37)
The title compound was prepared in a similar manner as 26
using 2-methylpyridine-3-boronic acid, pinacol ester and com-
pound 60. (60%) amorphous solid. 1H NMR (400 MHz, CDCl3) d
8.78 (s, 1H), 8.51–8.38 (m, 2H), 8.27 (s, 1H), 8.13–8.10 (m, 1H),
7.86–7.84 (m, 2H), 7.69–7.62 (m, 2H), 7.42–7.38 (m, 1H), 6.68 (d,
J = 8.4 Hz, 1H), 5.68 (s, 1H), 5.01–4.90 (m, 2H), 4.57–4.52 (m,
5.1.55. 6-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
yl)quinazolin-2-amine (43)
The title compound was prepared in a similar manner as 26
using 2-aminoquinazolin-6-ylboronic acid and compound 60.
(27%) amorphous solid. 1H NMR (400 MHz, DMSO-d6) d 9.11 (s,
1H), 8.49–8.60 (m, 2H), 8.35 (d, J = 2.54 Hz, 1H), 8.09 (d,
J = 2.54 Hz, 1H), 7.92 (d, J = 9.00 Hz, 1H), 7.77 (d, J = 7.63 Hz, 1H),
7.52–7.70 (m, 4H), 6.64 (d, J = 8.80 Hz, 1H), 5.64–5.75 (m, 1H),
5.35 (br s, 2H), 4.73 (t, J = 7.82 Hz, 2H), 4.35 (d, J = 5.67 Hz, 2H).
MS (ESI) [M+H]: 422.1726. Calcd for C24H20N7O [M+H] 422.1729.
2H); 2.75 (s, 3H). HRMS (ESI): calcd for
370.1664. Found: 370.1668.
C22H20N5O [M+H]
5.1.50. 2-(3-((3-(6-Methylpyridin-3-yl)pyrazin-2-
yl)oxy)azetidin-1-yl)quinoline (38)
The title compound was prepared in a similar manner as 26
using 2-methylpyridine-5-boronic acid and compound 60. (45%)
amorphous solid. 1H NMR (400 MHz, DMSO-d6) d 9.10 (s, 1H),
8.22–8.46 (m, 3H), 8.06 (d, J = 9.24 Hz, 1H), 7.72 (d, J = 8.36 Hz,
1H), 7.49–7.64 (m, 2H), 7.39 (d, J = 9.24 Hz, 1H), 7.19–7.30 (m,
1H), 6.80 (d, J = 9.24 Hz, 1H), 5.65 (d, J = 6.60 Hz, 1H), 4.60 (dd,
J = 10.34, 7.26 Hz, 2H), 4.19 (dd, J = 10.12, 3.96 Hz, 2H), 2.52 (s,
3H). HRMS (ESI): calcd for C22H20N5O [M+H] 370.1664. Found:
370.1661.
5.1.56. 2-(3-((3-(Pyridin-2-yl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline (33)
A solution of compound 60 (312 mg, 1.0 mmol), 2-tributylstan-
nyl-pyridine (369 mg, 1.0 mmol) and Pd(PPh3)4 (50 mg,
0.04 mmol) in toluene (10 mL) was stirred at 110 °C under N2
atmosphere overnight. The reaction mixture was filtered through
Celite™ and washed with CH2Cl2 (30 mL). The filtrate was
concentrated and the crude product was purified by flash column
chromatography eluting with 30–50% EtOAc/petroleum ether to
give 80 mg (23%) as an amorphous solid. 1H NMR (400 MHz,
5.1.51. 2-(3-((3-(2-Methylpyridin-4-yl)pyrazin-2-
yl)oxy)azetidin-1-yl)quinoline (39)
The title compound was prepared in a similar manner as 26
using 2-picoline-4-boronic acid and compound 60. (46%) amor-
phous solid. 1H NMR (400 MHz, DMSO-d6) d 8.56 (d, J = 5.28 Hz,
CD3OD)
d 9.09–8.97 (m, 2H), 8.74–8.70 (m, 2H), 8.70–8.60
(m, 1H), 8.51 (d, J = 2.4 Hz, 1H), 8.33 (d, J = 9.6 Hz, 1H), 8.12–8.09
(m, 1H), 7.86 (d, J = 8.4 Hz, 1H), 7.78–7.76 (m, 2H), 7.47–7.50
(m, 1H), 6.98 (d, J = 9.2 Hz, 1H), 5.91–5.88 (m, 1H), 5.15–5.03 (m,

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6583
4H). HRMS (ESI): calcd for C21H18N5O [M+H] 356.1508. Found:
5.1.60. 1-(4-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-
356.1514.
yl)piperidin-1-yl)ethanone (44)
The title compound was prepared in a similar manner as 45
using acetyl chloride and compound 70. 33% colorless solid. 1H
NMR (300 MHz, CD3OD) d 8.13 (d, J = 2.78 Hz, 1H), 7.98–8.07 (m,
2H), 7.68 (d, J = 8.33 Hz, 2H), 7.55 (ddd, J = 8.40, 6.94, 1.46 Hz,
1H), 7.18–7.32 (m, 1H), 6.76 (d, J = 8.92 Hz, 1H), 5.63 (tt, J = 6.43,
4.09 Hz, 1H), 4.54–4.72 (m, 3H), 4.23 (ddd, J = 6.83, 5.88, 3.07 Hz,
2H), 4.02 (m, J = 13.74 Hz, 1H), 3.41 (tt, J = 11.47, 3.87 Hz, 1H),
3.26 (dd, J = 13.45, 3.22 Hz, 1H), 2.80 (td, J = 12.83, 2.70 Hz, 1H),
2.11 (s, 3H), 1.62–2.03 (m, 4H). HRMS (ESI): calcd for C23H26N5O2
[M+H] 404.2081. Found: 404.2087.
5.1.57. tert-Butyl 4-(3-((1-(quinolin-2-yl)azetidin-3-
yl)oxy)pyrazin-2-yl)-5,6-dihydropyridine-1(2H)-carboxylate
(69)
To a solution of compound 60 (624 mg, 2.0 mmol), tert-butyl
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-5,6-dihydropyri-
dine-1(2H)-carboxylate 68 (618 mg, 2.0 mmol) and K3PO4 (848 mg,
4.0 mmol) in 1,4-dioxane (20 mL) and H2O (4 mL) was added
Pd(dppf)Cl2 (146 mg, 0.2 mmol) then the reaction mixture was
stirred at 110 °C under N2 atmosphere overnight. The reaction mix-
ture was filtered through Celite™ and washed with CH2Cl2 (50 mL).
The filtrate was concentrated and the crude product was purified
by silica gel column to give 600 mg (65%) of the title compound
as an off-white solid. 1H NMR (400 MHz, CDCl3) d 8.18 (d,
J = 2.35 Hz, 1H), 7.94 (d, J = 2.35 Hz, 1H), 7.91 (d, J = 8.80 Hz, 1H),
7.77 (br s, 1H), 7.62 (d, J = 8.02 Hz, 1H), 7.57 (t, J = 7.53 Hz, 1H),
7.19–7.32 (m, 2H), 6.88 (br s, 1H), 6.62 (d, J = 8.80 Hz, 1H), 5.53–
5.67 (m, 1H), 4.67 (br s, 2H), 4.27 (br s, 2H), 4.14 (br s, 2H), 3.61
(t, J = 5.38 Hz, 2H), 2.70 (br s, 2H), 1.48 (s, 9H). MS (ESI) [M+H]:
460 calcd for C26H29N5O3 459.
5.1.61. 2-(3-((3-(1-(Methylsulfonyl)piperidin-4-yl)pyrazin-2-
yl)oxy)azetidin-1-yl)quinoline (46)
The title compound was prepared in a similar manner as 45
using methanesulfonyl chloride and compound 70. (77%) amor-
phous solid. 1H NMR (400 MHz, CDCl3) d 8.19 (d, J = 2.8 Hz, 1H),
8.13 (d, J 9.2 Hz, 1H), 7.99–7.93 (m, 2H), 7.76–7.70 (m, 2H), 7.48–
7.44 (m, 1H), 6.62 (d, J = 9.2 Hz, 1H), 5.58 (s, 1H), 5.14–4.39 (m,
4H), 3.23–3.10 (m, 1H), 3.92–3.93 (m, 2H), 2.90–2.81 (m, 2H),
2.81 (s, 3H), 1.97–1.96 (m, 4H). HRMS (ESI): Calcd for C22H26N5O3S
[M+H] 440.1751. Found: 440.1758.
5.1.58. 2-(3-((3-(Piperidin-4-yl)pyrazin-2-yl)oxy)azetidin-1-
yl)quinoline hydrochloride (70)
5.1.62. Benzyl 4-(3-((1-(quinolin-2-yl)azetidin-3-
A mixture of compound 69 (459 mg, 1.0 mmol) and 10% Pd–C
(50% wet, 300 mg) in MeOH (20 mL) was stirred under H2
(30 psi) at room temperature overnight then the reaction mixture
was filtered through Celite™ and washed with MeOH. The filtrate
was concentrated in vacuo to give 400 mg (86%) of tert-butyl
4-(3-((1-(quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-2-yl)piperidine-
1-carboxylate. 1H NMR (300 MHz, DMSO-d6) d 8.20 (d, J = 2.78 Hz,
1H), 8.08 (d, J = 2.78 Hz, 1H), 8.05 (d, J = 8.77 Hz, 1H), 7.72 (d,
J = 7.45 Hz, 1H), 7.48–7.63 (m, 2H), 7.23 (ddd, J = 7.97, 6.50,
1.46 Hz, 1H), 6.80 (d, J = 8.77 Hz, 1H), 5.57 (tt, J = 6.36, 4.02 Hz,
1H), 4.56 (dd, J = 9.65, 6.58 Hz, 2H), 4.12 (dd, J = 9.87, 4.17 Hz,
2H), 4.03 (d, J = 12.72 Hz, 2H), 3.23 (tt, J = 11.60, 3.45 Hz, 1H),
2.86 (br s, 2H), 1.80 (d, J = 10.82 Hz, 2H), 1.49–1.69 (m, 2H),
1.31–1.48 (m, 9 H). MS (ESI) [M+H]: 463 calcd for C26H31N5O3 462.
To tert-butyl 4-(3-((1-(quinolin-2-yl)azetidin-3-yl)oxy)pyrazin-
2-yl)piperidine-1-carboxylate (400 mg, 0.86 mmol) was added 4 M
HCl in MeOH (20 mL). The reaction mixture was stirred at room
temperature for 30 min and concentrated. The residue was dried
under high vacuum to give 310 mg (100%) of the title compound
as a white solid. MS (ESI) [M+H]: 362 calcd for C21H23N5O 361.
yl)oxy)quinoxalin-2-yl)piperidine-1-carboxylate (72)
A premixed mixture of TMSCl and 1,2-dibromoethane (7:5, v/v,
0.80 mL total volume added) was added dropwise over 5 min to a
suspension of zinc (1.622 g, 24.8 mmol) in DMA (12 mL) under
argon atmosphere. The mixture was stirred for 15 min before ben-
zyl 4-iodopiperidine-1-carboxylate19 (7.13 g, 20.7 mmol) was
added dropwise over 15 min as a solution in DMA (6 mL). This mix-
ture was stirred for an additional 15 min before adding to quinox-
aline 71 below.
The
above
(1-((benzyloxy)carbonyl)piperidin-4-yl)zinc(II)
iodide (8.49 g, 20.7 mmol) solution was added slowly to a sus-
pension of 2-chloro-3-((1-(quinolin-2-yl)azetidin-3-yl)oxy)quin-
oxaline 71 (5.0 g, 13.8 mmol), copper(I) iodide (0.262 g,
1.378 mmol), and Pd(dppf)Cl2 dichloromethane adduct (0.56 g,
0.69 mmol) in DMA (15 mL) under argon. This mixture was stir-
red at 80 °C for 2 h, then cooled to room temperature. EtOAc
was added and the suspension was filtered through Celite™ to
remove insoluble material. The filtrate was then diluted with
more EtOAc and then washed with water (3ꢀ), brine (1ꢀ), dried
(MgSO4), filtered, and concentrated in vacuo to give an oil. This
oil was purified by silica gel chromatography eluting with
0–100% EtOAc/hexane to give 6.93 g (92%) of the title compound
an off-white solid. 1H NMR (400 MHz, DMSO-d6) d 1.72 (qd,
J = 12.32, 3.91 Hz, 2H), 1.91–2.02 (m, 2H), 3.03 (br s, 2H), 3.45
(tt, J = 11.47, 3.40 Hz, 1H), 4.15 (d, J = 13.11 Hz, 2H), 4.22 (dd,
J = 9.88, 4.01 Hz, 2H), 4.65 (dd, J = 9.68, 6.55 Hz, 2H), 5.10 (s,
2H), 5.72 (tt, J = 6.41, 4.16 Hz, 1H), 6.82 (d, J = 8.80 Hz, 1H),
7.23 (td, J = 7.34, 1.37 Hz, 1H), 7.28–7.34 (m, 1H), 7.35–7.40
(m, 4H), 7.51–7.56 (m, 1H), 7.57–7.61 (m, 1H), 7.61–7.67 (m,
1H), 7.69–7.75 (m, 2H), 7.83 (dd, J = 8.22, 1.17 Hz, 1H), 7.96
(dd, J = 8.22, 1.17 Hz, 1H), 8.06 (d, J = 8.80 Hz, 1H). MS (ESI) m/
z: 546.2 [M+H]. Calcd for C33H31N5O3: 545.2.
5.1.59. Methyl 4-(3-((1-(quinolin-2-yl)azetidin-3-
yl)oxy)pyrazin-2-yl)piperidine-1-carboxylate (45)
To a solution of compound 70 (100 mg, 0.29 mmol) in dry
CH2Cl2 (10 mL) was added Et3N (1 mL). The reaction mixture was
cooled to 0 °C with an ice bath, and methyl chloroformate
(54 mg, 0.58 mmol) was added dropped to the reaction mixture.
After 1 h, the reaction mixture was warmed to room temperature,
and stirred overnight. Then the reaction mixture was washed with
brine, dried over Na2SO4, filtered, and concentrated under vacuum
to give the crude product. The crude product was purified via flash
chromatography eluting with 20–45% EtOAc/petroleum ether to
give 93 mg (79%) of the title compound as a white solid. 1H NMR
(CD3OD, 400 MHz) d 8.38–8.35 (m, 1H), 8.18–8.17 (m, 1H), 8.17–
8.02 (m, 1H), 7.92–7.90 (m, 1H), 7.83–7.76 (m, 2H), 7.55–7.51
(m, 1H), 7.01–6.99 (m, 1H), 5.70–5.67 (m, 1H), 5.00–4.95 (m, 1H),
4.63–4.59 (m, 2H), 4.58–4.24 (m, 2H), 4.21–3.69 (m, 2H), 3.35 (s,
3H), 3.35–3.34 (m, 2H), 3.02–3.01 (m, 2H), 1.81–1.75 (m, 2H).
5.1.63. 1-(4-(3-((1-(Quinolin-2-yl)azetidin-3-yl)oxy)quinoxalin-
2-yl)piperidin-1-yl)ethanone (47)
Palladium hydroxide, 20 wt % Pd (dry basis) on carbon, wet,
Degussa type e101 ne/w (1.15 g, 1.63 mmol) was added to a
mixture of benzyl 4-(3-((1-(quinolin-2-yl)azetidin-3-yl)oxy)
quinoxalin-2-yl)piperidine-1-carboxylate 72 (5.93 g, 10.9 mmol)
HRMS (ESI): calcd for
420.2039.
C23H26N5O3 [M+H] 420.2030. Found:

6584
R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
and acetic anhydride (3.08 mL, 32.6 mmol) in THF (50 mL) under
argon atmosphere. The mixture was placed under 1 atm hydrogen
and the mixture was heated to 50 °C for 6 h. The filtrate was
diluted with EtOAc, transferred to a separatory funnel, and washed
with satd NaHCO3 (2ꢀ), dried over MgSO4, filtered, and concen-
trated in vacuo to give an oil. This oil was purified by silica gel
chromatography eluting with 0–100% acetone/hexane to give
3.34 g (68%) of the title compound as a white solid. 1H NMR
(400 MHz, DMSO-d6) d 1.71 (qd, J = 12.39, 4.30 Hz, 1H), 1.90 (qd,
J = 12.42, 4.01 Hz, 1H), 2.03–2.12 (m, 2H), 2.13 (s, 3H), 2.83 (td,
J = 12.76, 2.25 Hz, 1H), 3.28–3.38 (m, 1H), 3.59 (tt, J = 11.49,
3.47 Hz, 1H), 4.05 (d, J = 13.69 Hz, 1H), 4.30–4.37 (m, 2H), 4.61
(d, J = 13.30 Hz, 1H), 4.77 (dd, J = 9.29, 6.75 Hz, 2H), 5.84 (ddd,
J = 6.41, 4.06, 2.25 Hz, 1H), 6.94 (d, J = 9.00 Hz, 1H), 7.34 (td,
J = 7.34, 1.17 Hz, 1H), 7.61–7.67 (m, 1H), 7.68–7.72 (m, 1H),
7.72–7.77 (m, 1H), 7.80–7.86 (m, 2H), 7.94 (dd, J = 8.22, 1.17 Hz,
1H), 8.07 (dd, J = 8.12, 1.08 Hz, 1H), 8.17 (d, J = 8.80 Hz, 1H). HRMS
(ESI): calcd for C27H28N5O3 [M+H] 454.2243. Found: 454.2247.
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 used for dose response data analysis in Gene-
data Screener is a custom implementation of a robust curve-fitting
algorithm called ROUT (Robust regression with outlier detection)
and uses a four-parameter logistical (4PL) Hill model.
5.3.2. Ex vivo RO
Adult male Sprague Dawley ratsÒ weighing 180–225 g (Harlan,
San Diego) were cared for in accordance to the Guide for the Care
and Use of Laboratory Animals, 8th Edition. Animals were
group-housed at an Association for Assessment and Accreditation
of Laboratory Animal Committee, internationally-accredited
facility in nonsterile ventilated micro-isolator housing on corn
cob bedding. All research protocols were approved by the Amgen,
Thousand Oaks Institutional Animal Care and Use Committee.
Animals had ad libitum access to pelleted feed (Harlan Teklad
2020X, Indianapolis, IN) and water (on-site generated reverse
osmosis) via automatic watering system. Animals were maintained
on a 12:12 h light/ark cycle in rooms at (70 5 °F, 50 20% RH) and
had access to enrichment opportunities (nesting materials and
plastic domes). All animals were sourced from approved vendors
who meet or exceed animal health specifications for the exclusion
of specific pathogens (i.e., mouse parvovirus, Helicobacter).
Rats were allowed at least 3 days of acclimation prior to any
procedures.
5.2. Solubility assay
Compounds as 10 mM DMSO stock solutions were dispensed
into 96 deep well plates at a volume of 10 lL per well. Four copies
of identical plates were created. The DMSO was removed in a Gen-
evac Evaporator for 2.5 h, 40 °C, under full vacuum. After dry down
was complete, a Tecan Evo Liquid Handler was used to transfer
200 lL of the buffer to the corresponding plate copy. The buffer
used was phosphate-buffered saline (PBS, pH 7.4) and the solvent
DMSO was used to create the standard plate for comparison. The
plates were sealed and centrifuged at 1000 rpm for 1 min to push
all liquid from walls to the bottom of the wells. The plates were
shaken at 1500 rpm on a 3 mm radius orbital shaker for 1 h. The
samples were equilibrated at room temperature for 72 h. The
plates were centrifuged at 4000 rpm for 30 min. The supernatant
PDE10 inhibitors were dissolved in 2% hydroxypropylmethyl-
cellulose (HPMC), 1% Tween-80, pH 2.2 with methanesulfonic acid.
4 rats per group were dosed orally with either vehicle or 3 mg/kg
PDE10 inhibitors and then returned to their home cage to allow
for absorption of the compounds. After 4 h rats were sacrificed
by CO2 inhalation. Blood was obtained by heart puncture and
plasma was frozen and stored at ꢂ80 °C for exposure analysis.
Brains were removed and immediately frozen in chilled methylbu-
tane, and stored at ꢂ80 °C until cutting. Three coronal brain slices
was analyzed by LC/MS, at 215 nm, 2
lL injection volume. Peak
area in PBS was compared to DMSO standard to determine solubil-
ity, accurate within the range of 5–500
5.3. Biology
l
M.
per brain containing the striatum were cut at 20 lm using a cryo-
stat and placed onto microscope slides, air-dried and stored at
ꢂ20 °C. For radioligand binding experiments, slides were thawed
at room temperature and then incubated with 1 nM 3H-5-(6,7-
bis(methyloxy)-4-cinnolinyl)-3-methyl-N-(1-methylethyl)-2-pyri-
dinamine18 in binding buffer (150 mM Phosphate-buffered saline
containing 2 mM MgCl2 and 100 mM DTT, pH 7.4) for 1 min at
4 °C. To assess nonspecific binding, slides containing adjacent
brain sections were incubated in the same solution with addition
of 10 mM 2-(((4-(4-(4-pyridinyl)-1H-pyrazol-5-yl)phenyl)oxy)
methyl)quinoline20, an unlabelled, structurally unrelated PDE10
antagonist. Afterwards slides were washed 3 times in ice-cold
binding buffer, dipped into distilled water to remove buffer salts,
and dried under a stream of cold air. Emission of beta particles
from the sections was counted for 8 h in a Beta Imager 2000
(Biospace, Paris, France) and digitized and analyzed using M3
Vision software (Biospace, Paris, France). Total binding radioactiv-
ity in the striatum was measured as cpm/mm2 in hand-drawn
regions of interest and averaged across the three sections per brain.
Nonspecific binding was subtracted to obtain specific binding
values and percent occupancy was calculated by setting vehicle
specific binding as 0% occupancy.
5.3.1. Enzyme assay
The purified human PDE enzymes were obtained from BPS Biosci-
ence (San Diego, CA). IMAP™ TR-FRET progressive binding system,
FAM-cAMP or FAM-cGMP substrates were obtained from Molecular
Devices (Sunnyvale, CA). The PDE IMAP assay was conducted in a
384-well black Greiner polypropylene plate (Sigma, St. Louis, MO).
PDE inhibitors were serial diluted in 100% DMSO and dispensed into
assay plate at 200 nL per well (65 nL per well in case of PDE 10) using
EchoÒ Liquid Handling System from LABCYTE. Ten
lL of PDE enzyme
inIMAPreaction buffer (10 mMTris–HCl, pH7.2, 10 mMMgCl2, 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 condi-
tion. Enzyme was pre-incubated with inhibitors for 60 min at room
temperature before addition of 10 lL of substrate, which results in
100 nM of FAM-cAMP or FAM-cGMP in the reaction. In the PDE
assays, FAM-cAMP was used as substrate for PDE isoforms 1B, 2A1,
3A, 4D2, 7A1, 8A1, 10A2, 11A4 and FAM-cGMP was used as substrate
for isoforms 5A, 9A2. Enzyme reaction was allowed to proceed at
room temperature for 90 min, and the reaction is stopped by 55
lL
Acknowledgments
addition of binding reagent according to manufacturer’s recommen-
dation. The mixture is further incubated at room temperature for
additional 4 h, and signal was read on an Envision multimode reader
(PerkinElmer). Fluorescence signals were measured at 520 nm and
485 nm. The signal ratio at 520/485 nm corresponded to the genera-
tion of reaction product of AMP/GMP, and it was used in all data
The authors would like to thank Iain Campuzano for the acqui-
sition of high resolution mass spectral data and the Advanced Light
Source staff at beamline 5.0.1 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.

R.M. Rzasa et al. / Bioorg. Med. Chem. 22 (2014) 6570–6585
6585
12. Hu, E.; Kunz, R. K.; Rumfelt, S.; Andrews, K. L.; Li, C.; Hitchcock, S. A.; Lindstrom,
M.; Treanor, J. Bioorg. Med. Chem. Lett. 2012, 22, 6938.
Department of Energy under Contract DE-AC03-76SF00098 at Law-
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13. Inhibition of PDE3 has been associated with undesirable cardiovascular effects.
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