Design, synthesis, and pharmacological evaluation of azetedine and pyrrolidine derivatives as dual norepinephrine reuptake inhibitors and 5-HT 1A partial agonists

Article abstract of DOI:10.1016/j.bmcl.2010.11.066

Compounds with combined norepinephrine reuptake inhibitor (NRI) and serotonin 1A (5-HT_1A) partial agonist pharmacology may offer a new therapeutic approach for treating symptoms of neuropsychiatric disorders including ADHD, depression, and anxiety. Herein we describe the design and optimization of novel chemical matter that exhibits favorable dual NRI and 5-HT_1A partial agonist activity. Lead compounds in this series were found to be devoid of activity at the dopamine transporter and were shown to be brain penetrant with high receptor occupancy.

Full text of DOI:10.1016/j.bmcl.2010.11.066

Bioorganic & Medicinal Chemistry Letters 21 (2011) 865–868
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis, and pharmacological evaluation of azetedine
and pyrrolidine derivatives as dual norepinephrine reuptake inhibitors
and 5-HT1A partial agonists
⇑
Martin Pettersson , Brian M. Campbell, Amy B. Dounay, David L. Gray, Longfei Xie, Christopher J. O’Donnell,
Nancy C. Stratman, Kim Zoski, Elena Drummond, Gary Bora, Al Probert, Tammy Whisman
Pfizer Global Research and Development, Eastern Point Road, Groton, CT 06340, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Compounds with combined norepinephrine reuptake inhibitor (NRI) and serotonin 1A (5-HT1A) partial
agonist pharmacology may offer a new therapeutic approach for treating symptoms of neuropsychiatric
disorders including ADHD, depression, and anxiety. Herein we describe the design and optimization of
novel chemical matter that exhibits favorable dual NRI and 5-HT1A partial agonist activity. Lead
compounds in this series were found to be devoid of activity at the dopamine transporter and were
shown to be brain penetrant with high receptor occupancy.
Received 17 August 2010
Revised 10 November 2010
Accepted 16 November 2010
Available online 21 November 2010
Keywords:
Norepinephrine reuptake inhibitor
Ó 2010 Elsevier Ltd. All rights reserved.
5-HT1A agonist
NRI
NET
DAT
SERT
ADHD
Depression
Pharmacological agents that increase synaptic levels of mono-
amine neurotransmitters are recognized as effective therapeutics
for some neuropsychiatric disorders.1 Attention Deficit Hyperactiv-
ity Disorder (ADHD) has been associated with low levels of dopa-
mine (DA) and norepinephrine (NE) at the synapse in cortical
brain regions.2,3 Treatment for ADHD includes the use of stimulant
medications such as amphetamine and methylphenidate, which in-
crease the synaptic concentration of NE and DA.4 Dopamine signal-
ing is a key component of the reward pathway, and some
compounds that rapidly and significantly enhance DA signaling in
areas like the nucleus accumbens and substantia nigra have been
associated with an increased potential for abuse.5 Atomoxetine is
a norepinephrine reuptake inhibitor that was approved in 2003 as
a non-stimulant treatment for ADHD. This compound acts to in-
crease NE signaling globally throughout the brain via blockade of
the norepinephrine reuptake transporter (NRI) responsible for the
synaptic clearance of released neurotransmitter. In the prefrontal
cortex there is negligible expression of the dopamine-specific reup-
take transporter (DAT) and released DA is instead cleared by the
norepinephrine reuptake transporter (NET), which performs a dou-
ble duty in this subregion. Thus, NRI inhibition is hypothesized to
increase DA signaling in the prefrontal cortex with less impact on
reward pathways. In additional to their demonstrated clinical effi-
cacy in ADHD, agents exhibiting NRI activity can be useful for man-
aging additional psychiatric disorders such as depression6,7 and
anxiety.8 Emerging studies suggest that the ability of NRI’s to ele-
vate prefrontal dopamine signaling can be significantly enhanced
with agonism or partial agonism at 5-HT1A autoreceptors.9,10 For
example, microdialysis measurement of rodent prefrontal neuro-
transmission showed a significant, synergistic increase in dopamine
levels after dosing a combination of atomoxetine and buspirone.11
Similarly, preclinical behavioral models of cognition and depression
indicate that the combination of NRI and 5-HT1A partial agonist
drugs afford greater efficacy than can be obtained with either mech-
anism dosed alone.12 On the basis of these theoretical and experi-
mental results, we hypothesized that compounds designed to
have appropriately balanced dual NRI and 5-HT1A partial agonist ac-
tion may offer a new and improved treatment strategy for address-
ing ADHD and other neuropsychiatric illness.
Toward this end, we recently disclosed the discovery of a series
of dual NRI/5-HT1A partial agonists as exemplified by 1.13 Encour-
aged by its excellent profile both in vitro and in vivo, efforts were
directed toward further optimization of this series. As depicted in
Figure 1, two approaches were pursued in parallel. The first in-
volved replacing one of the phenyl rings with a heterocycle. This
⇑
Corresponding author.
E-mail address: martin.pettersson@pfizer.com (M. Pettersson).
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.11.066

866
M. Pettersson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 865–868
H
N
H
O
O
H
R2
R2
R1
O
R4
R4
R1
F
HO
R3
a
b, c
Cl
+
H
N
R3
6
O
F
A
4
R1 = H, F
5
N
F
C
R
F
O
N
2, (Series 2)
B
OH
R1
R2
O
R2
NH
O
R4
R1
O
R4
d or e
1, (Series 1)
O
R2
R4
R1
R3
R3
O
8
: R = Boc
7
R3
f
9: R = H
g
g
3, (Series 3)
h
R
N
Figure 1
R
N
R
N
R2
O
R2
O
R2
culminated in the discovery of a phenoxy pyridyl series 2 as exem-
plified by 2, which exhibits superior NET/DAT-selectivity as com-
pared to 1.14 The second avenue, as exemplified by 3, focused on
replacing the piperidine A-ring with a less basic, less lipophilic
group, which may help improve safety margins in this series.15
The primary objective was to reduce potency at DAT while main-
taining or improving the 5-HT1A partial agonist activity and retain-
ing drug-like physicochemical properties.15 In the early part of
these optimization efforts, in-house PK/PD modeling suggested
that 5-HT1A partial agonist activity was important for elevating
maximal monoamine neurotransmission, and that reduced activity
at NET would be acceptable.16
An azetidine with a one-atom linker was envisioned as a suit-
able replacement for the piperidine moiety of 1 since it would con-
serve the distance between the secondary amine and the central
phenyl ring. Calculated pKa values indicated that the introduction
of an ether-linked azetedine would result in a 1.5 unit reduction
in pKa of the amine in Series 3 as compared to Series 1. The
ether-linkage would confer the additional advantage of enabling
the chemistry toward rapid evaluation of additional piperidine
replacements in parallel using Mitsunobu chemistry.
O
R1
O
R4 R1
O
R4 R1
O
R4
R3
R3
R3
10
: R = Boc
11
: R = Boc
12
: R = Boc
f
f
f
13: R = H
14: R = H
15: R = H
Scheme 1. Reagents and conditions: (a) K2CO3, DMA, reflux, 2.5 h (53–61%); (b)
mCPBA, CHCl3, 30 °C, 18 h; (c) KOH, MeOH/THF, 0 °C, (85–94% yield, two-steps); (d)
tert-butyl-3-(methylsulfonyloxy)azetidine-1-carboxylate, Cs2CO3, CH3CN, micro-
wave, 160 °C, 15 bar, 1.5 h, (42–86% yield); (e) tert-butyl-3-hydroxyazetidine-1-
carboxylate, DIAD, PPh3, THF, 50 °C, 16 h, (70–96%); (f) AcCl, MeOH, (67–89%); (g)
tert-butyl-4-hydroxypiperidine-1-carboxylate or tert-butyl-3-hydroxypyrrolidine-
1-carboxylate, DIAD (1.2 equiv), PPh3, THF, rt 16 h, (69–72%); (h) N-tert-butyl-3-
(methylsulfonyloxy)-piperidine-1-carboxylate, Cs2CO3, CH3CN, reflux, 5 h, (43%
yield).
Table 1
Binding and selectivity of ether-linked azetidine analogs
NH
A
O
B
R2
C
R1
O
R4
As depicted in Scheme 1, the synthesis of compounds 9 and 13–
15 commenced with the formation of biaryl ether 6 via SNAr reac-
tion of various phenols 5 with commercially available 2-fluoroben-
zaldehydes 4 bearing either a hydrogen or a fluoro-substituent in
the R1-position. Dakin oxidation of the aldehyde function of 6
afforded the corresponding formate ester, which, in turn was
hydrolyzed to phenol 7 in excellent yield (85–94% over two steps).
We next explored introducing the azetidine moiety via alkylation
of phenol 7. The azetedine ether-linkages of 9a, 9b, and 9c (Table 1)
were forged by heating a mixture of requisite phenols 7, the mes-
ylate derived from N-Boc-3-hydroxyazetedine, and Cs2CO3 in ace-
tonitrile at 160 °C, in a microwave reactor for 1.5 h. Using these
rather forcing reaction conditions, the ether-linkage of 9a was
formed in excellent yield (87%), whereas, the corresponding carbon
oxygen bonds of 9b and 9c were formed only in lower yield (42%).
To incorporate additional substituents that may not be compat-
ible with the harsh reaction conditions used in this alkylation pro-
tocol, we explored the use of Mitsunobu chemistry to carry out the
etherification. The coupling of phenol 7 with N-Boc-3-hydroxyaze-
tedine proceeded slowly at room temperature and required an ex-
cess (3 equiv) of PPh3 and DIAD to go to completion.17
Alternatively, warming the reaction to 50 °C significantly increased
the reaction rate while only requiring 1.1–1.2 equiv of both DIAD
and PPh3 to afford the desired products in excellent yield (70–
96%).18 These conditions were successfully run on 25 g scale. The
Boc-protected pyrrolidine and piperidine rings were also intro-
duced using the Mitsunobu chemistry to afford 10, and 12, but in
contrast to the azetidines, these reactions did not require heating.
9
R3
CP
R1
R2
R3
R4
5-HT1A
Kia
(nM)
NET
DAT
SERT
Kib
(nM)
c log P
Kib
Kib
(nM)
(nM)
1
2
—
—
H
H
F
F
F
F
F
—
—
H
F
F
Cl
F
F
F
Cl
Cl
Cl
—
—
H
H
H
—
—
H
H
H
H
H
H
H
H
H
Cl
4.6
11
57
22
12
14
1
3
<3
6
32
33
278
>6180
2090
2040
>4860
4700
>6460
>6460
>6410
>5940
>6410
312
1260
194
4.1
3.0
3.4
3.3
3.4
4.0
3.9
3.9
3.4
4.5
4.5
4.6
9a
9b
9c
9d
9e
9f
9g
9h
9i
1640
528
507
198
138
116
482
164
433
374
2670
>4710
>4710
1710
>4900
1160
>4620
>4620
>4610
94
H
Cl
Me
F
Cl
Me
H
F
F
F
16
16
9j
a
5-HT1A RBSHA binding assay; Ki values are the mean of at least two experiments
carried out in duplicate.20
b
Monoamine transporter binding scintillation proximity assay (SPA); Ki values
are the mean of at least two experiments carried out in duplicate.21
Initial attempts to install the 3-hydroxypiperidine group of 11
using Mitsunobu chemistry resulted in low yields. This problem
was circumvented by using the corresponding mesylate and form-
ing the ether-linkage by alkylation of phenol 7. The final step in the
syntheses involved removal of the Boc-group by treating 8, 10, 11
and 12 with methanolic HCl19 at room temperature to deliver the
target secondary amines in good yield.

M. Pettersson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 865–868
867
Table 2
Biological characterization of this series began by assessing the
Binding and selectivity of ether-linked pyrrolidine and piperidine analogs
unsubstituted azetidine analog 9a (Table 1). As observed in our
previously described series (e.g., 1 and 2, Fig. 1) only moderate
5-HT1A activity and weak NET activity could be attained with
unsubstituted B- and C-rings (9a).13,14 Introduction of a fluoro-sub-
stituent on the C-ring R2 position (9b) increased both 5-HT1A and
NET activity (two- and three-fold increase, respectively). This re-
sult was further improved by installing a fluoro-substituent on
the B-ring (9c) which afforded an additional two-fold increase in
5-HT1A binding affinity. While the 5-HT1A activity of 9c is compa-
rable to that of 2, potency at NET was approximately 20-fold weak-
er. Previous SAR studies in series 2 demonstrated that larger
substituents such as a chloro-, methyl-substituent in the R2 posi-
tion of the C-ring afforded improved activity at NET while being
well tolerated by 5-HT1A. Accordingly, 9d was prepared which
demonstrated that this SAR trend holds true for the ether-linked
azetedine series as well, providing a 2.5-fold increase in NET po-
tency over 9c.
R
O
B
R2
C
R1
O
13-15
R3
R
R1
R2
R3
5-HT1A
Kia
NET
Kib
DAT
Kib
SERT
Kib
(nM)
(nM)
(nM)
(nM)
NH
13a
H
F
H
693
1000
4510
>4710
13b
13c
13d
F
F
F
F
F
F
H
Cl
Me
30
8
4
489
218
323
2190
>6370
>6460
>4650
2040
3250
14a
F
F
F
H
H
90
1950
>5590
>4710
NH
NH
Among the analogs prepared, the best C-ring substitution pat-
terns were 2-fluoro-6-chloro (9e) and 2-fluoro-6-methyl (9f).
These compounds were selected for further evaluation in vivo (vide
infra). It is noteworthy that careful selection of the substitution
pattern on the B- and C-ring resulted in significant gains in 5-
HT1A and NET activity, while the potency at DAT and SERT gener-
ally did not increase. In particular, key analog 9e is devoid of
DAT and SERT activity while 9f exhibited weak potency at SERT.
This stands in contrast to 1, which displays a DAT Ki of 278 nM.
Furthermore, DAT and SERT selectivities are particularly sensitive
to substitution on the C-ring R4 position as exemplified by 9j in
which selectivity for NET over DAT and SERT is completely lost.
We next turned our attention to examining the effect of chang-
ing the size of the A-ring heterocycles (Table 2). While piperidine
analogs 13b–d displayed similar binding affinity at 5-HT1A as the
corresponding azetidines 9c, 9e, 9f, their functional 5-HT1A activity
was considerably lower (data not shown). Moving the piperidine
nitrogen from the 4-position to the 3-position (e.g., 14a) resulted
in significantly less in potency at both NET and 5-HT1A as com-
pared to the corresponding 4-piperidine 13b and 3-azetidine 9c.
The pyrrolidine derivatives 15a–g on the other hand appeared
more promising (Table 2). In particular, racemic pyrrolidine 15e,
which incorporates a 2-chloro-6-fluoro substitution pattern on
the C-ring exhibited Ki of 3 nM at 5-HT1A and 226 nM at NET.
The pure enantiomers of 15e were then prepared starting from
commercially available (R)- and (S)-N-Boc-3-hydroxypyrrolidine
using Mitsunobu chemistry as in Scheme 1. Interestingly, the S-
enantiomer 15g was approximately 10-fold more potent than the
R-enantiomer 15f at both 5-HT1A and NET while maintaining excel-
lent selectivity against DAT and SERT.
Having established that ether-linked azetidines and pyrrol-
idines are suitable A-ring piperidine replacements with improved
5-HT1A/DAT selectivity, we next sought to further improve physi-
cochemical properties by incorporating a pyridyl nitrogen in the
B-ring, as this was a successful strategy in Series 2. Heating a mix-
ture of 3-bromo-2-chloropyridine (16) and phenol 17 in the pres-
ence of cesium carbonate delivered pyridyl ether 18 in 80% yield
(Scheme 2). Halogen-metal exchange followed by addition of tri-
isopropyl borate gave 19 (40% yield),22 which upon oxidation with
30% hydrogen peroxide furnished the requisite phenol 20 in 86%
yield. The remainder of the syntheses was carried out as described
in Scheme 1, the only difference being that the Mitsunobu reaction
of phenol 20 with N-Boc-azetedinol required heating to 70 °C to
reach completion. Introduction of a pyridyl nitrogen into the B-ring
provides improved physicochemical properties (e.g., c log P). Pyr-
rolidine 22 exhibited weaker affinity for both 5-HT1A and NET
whereas azetedine 24 showed an improvement in potency at
NET as compared to the corresponding biaryl ethers 9a–j (Table 3).
15a
H
193
1350
>6220
>4710
15b
15c
15d
15e
F
F
F
F
F
Cl
F
H
H
Me
Cl
8
19
4
1020
192
328
226
3880
2030
>6460
>6460
>4710
2230
>4690
>4900
F
3
NH
NH
15f
F
F
F
F
Cl
Cl
13
1
1010
110
>5870
>5870
>4530
>4530
15g
a
5-HT1A RBSHA binding assay; Ki values are the mean of at least two experiments
carried out in duplicate.20
b
Monoamine transporter binding scintillation proximity assay (SPA); Ki values
are the mean of at least two experiments carried out in duplicate.21
Br
F
Br
F
Cl
HO
Cl
O
a
b
+
N
N
Cl
16
17
18
R
N
HO
OMe
O
B
F
OH
F
f
O
c
d
O
F
O
N
N
Cl
Cl
N
Cl
19
20
21:
R = Boc
e
e
R
22: R = H
N
O
F
O
23:
R = Boc
24: R = H
N
Cl
Scheme 2. Reagents and conditions: (a) Cs2CO3, DMSO, 140 °C, 80%; (b) nBuLi
À78 °C; then B(OiPr)3, À78 °C to rt; MeOH, 40%; (c) 30% H2O2, CH2Cl2, 86%;
(d) tert-butyl-3-(methylsulfonyloxy)pyrrolidine-1-carboxylate, Cs2CO3, CH3CN,
reflux, 56%; (e) AcCl, MeOH, (89–94%); (f) tert-butyl-3-azetidine-1-carboxylate,
DIAD, PPh3, THF, 70 °C, 83%.
Without the B-ring fluoro-substituent, however, only moderate
affinity for 5-HT1A was observed. Introduction of the B-ring flu-
oro-substituent para to the pyridyl nitrogen was therefore at-
tempted, but these efforts were hampered by chemical instability.
A subset of these compounds with promising activity and selec-
tivity in the monoamine and 5-HT1A in vitro binding and functional
assays were selected for further profiling using ex vivo receptor

868
M. Pettersson et al. / Bioorg. Med. Chem. Lett. 21 (2011) 865–868
Table 3
uated in vivo and were shown to be brain penetrant and to display
excellent receptor occupancy at 5-HT1A and NET.
Binding and selectivity of pyridyl analogs 22 and 24
NH
( )n
A
Acknowledgments
O
B
F
O
C
We are grateful to Roberta L. Dorow and Michael W. Fichtner for
scale-up of select compounds, and to Douglas S. Johnson, Cory M.
Stiff, Subas M. Sakya, and John A. Lowe for helpful discussions.
N
Cl
n
5-HT1A
Kia
NET
Kib
(nM)
DAT
SERT
Kib
(nM)
c log P
Kib
(nM)
References and notes
(nM)
22
24
2
1
203
64
1140
73
>4620
>4260
>6130
>6280
2.84
2.83
1. Baldessarini, R. J. In The Pharmacological Basis of Therapeutics; Bruton, L. L., Lazo,
J. S., Parker, K. L., Eds., 11th ed.; McGraw-Hill, 2006; p 429.
2. Volkow, D.; Wang, G.; Fowler, J.; Logan, J.; Gerasimov, M.; Maynard, L.; Ding, Y.;
Gatley, S.; Gifford, A.; Franceschi, D. J. Neurosci. 2001, 21. RC121/1-RC121/5.
3. Volkow, D.; Wang, G.; Fowler, J.; Gatley, S.; Logan, J.; Ding, Y.; Pappas, N. J.
Psychiatry 1998, 155, 1325.
4. Gray, D. L. In The Art of Drug Synthesis; Li, J., Johnson, D., Eds.; Wiley, 2007; p
241.
a
5-HT1A RBSHA binding assay; Ki values were determined in a single experiment
carried out in duplicate.20
b
Monoamine transporter binding scintillation proximity assay (SPA); Ki values
were determined in a single experiment carried out in duplicate.21
5. Volkow, N. D.; Swanson, J. M. Am. J. Psychiatry 2003, 160, 1909.
6. Chuluunkhuu, G.; Nakahara, N.; Yanagisawa, S.; Kamae, I. Kobe J. Med. Sci. 2008,
54, E147.
Table 4
7. Schatzberg, A. F. J. Clin. Psychiatry 2000, 61, 31.
Functional activity and in vivo occupancy at 5-HT1A receptor and NET
8. Dannon, P. N.; Iancu, I.; Grunhaus, L. Hum. Psychopharmacol. 2002, 17, 329.
9. Weikop, P.; Kehr, J.; Scheel-Krüger, J. J. Psychopharmacol. 2007, 21, 795.
10. Bourin, M.; Chenu, F.; Prica, C.; Hascoet, M. Psychopharmacology 2009, 206, 97.
11. Personal communication, Brian Campbell, Pfizer Global Research and
Development, Groton, CT, USA (manuscript in preparation).
5-HT1A
EC50
(nM)
5-HT1A
% IAa
NET
Receptor occupancy
(% at 10 mg/kg s.c.)27
a
EC50
(nM)b
5-HT1A
NET
12. Jensen, N. H.; Rodriguiz, R. M.; Caron, M. G.; Wetsel, W. C.; Rothman, R. B.;
Roth, B. L. Neuropsychopharmacology 2008, 33, 2303.
1
9e
9f
15e/g
341
197
225
77c
84
88
28
40
62
81
76
3
1
2
80
87
84
2
2
1
13. Gray, D. L.; Xu, W.; Campbell, B. M.; Dounay, A. B.; Barta, N.; Boroski, S.; Denny,
L.; Evans, L.; Stratman, N.; Probert, A. Bioorg. Med. Chem. Lett. 2009, 19, 6604.
14. Dounay, A. B.; Barta, N. S.; Campbell, B. M.; Coleman, C.; Collantes, E. M.;
Denny, L.; Dutta, S.; Gray, D. L.; Hou, D.; Iyer, R.; Maiti, S. N.; Ortwine, D. F.;
Probert, A.; Stratman, N. C.; Subedi, R.; Whisman, T.; Xu, W.; Zoski, K. Bioorg.
Med. Chem. Lett. 2010, 20, 1114.
15. Hughes, J. D.; Blagg, J.; Price, D. A.; Bailey, S.; DeCrescenzo, G. A.; Devraj, R. V.;
Ellsworth, E.; Fobian, Y. M.; Gibbs, M. E.; Gilles, R. W.; Greene, N.; Huang, E.;
Krieger-Burke, T.; Loesel, J.; Wager, T.; Whiteley, L.; Zhang, Y. Bioorg. Med.
Chem. Lett. 2008, 18, 4872.
84
239
79c
97d
73 2d
54 1d
a
5-HT1A GTPcS functional assay; EC50 and intrinsic activity (IA) values are the
mean of at least two experiments carried out in duplicate.28
b
NET functional assay; EC50 values are the mean of at least two experiments
carried out in duplicate.29
c
Determined for single enantiomer 15g.
Determined for racemate 15e.
d
16. Li, C. S.-w.; Zhang, L.; Brudfuehrer, J.; Lepsy, C.; Haske, T.; Campbell, B.M.
A.A.P.S. abs 2008, Atlanta, GA.
17. 1.5 equiv of each reagent were initially added, and an additional 1.5 equiv of
each reagent were added at the 8 h time point.
occupancy.23 Table 4 highlights functional and receptor occupancy
data for azetidines 9e and 9f and pyrrolidine 15e/g. High 5-HT1A
intrinsic activity was observed for all three compounds with 88%,
84%, and 79% agonism, respectively, which compares well to 1. Fol-
lowing 10 mg/kg subcutaneous dosing, the three lead compounds
were shown to be brain penetrant and exhibiting excellent binding
18. The reactions were complete after stirring at 50 °C overnight (ca. 16 h).
19. Anhydrous HCl was generated by the addition of AcCl to MeOH at 0 °C.
20. Assay conducted as described in Graham, J. M.; Coughenour, L. L.; Barr, B. M.;
Rock, D. L.; Nikam, S. S. Bioorg. Med. Chem. Lett. 2008, 18, 489.
21. The affinity of test compounds for binding to human NET, DAT, and SERT were
assessed by measuring inhibition of binding to [3H]nisoxetine, [3H]WIN
35,428, and [3H]citalopram, respectively, using
assay. Assay protocol is described in Ref. 14
a scintillation proximity
to the target receptors in vivo. A dose–response was generated for
24
azetidine 9e indicating a NET ID50
,
of 1.2 mg/kg and a 5-HT1A
22. While the boronic acid was isolated upon aqueous work-up, following
purification by column chromatography on silica eluting with 20–45% ethyl
acetate in heptane, concentration of the solvents under reduced pressure, and
co-evaporation from methanol, the mixed boronate ester 19 was obtained as
the sole product.
25
ID10
,
of less than 1 mg/kg. Additionally, compounds 9e, 9f, and
15g were shown to have good oral exposure as determined in a
dog pharmacokinetic study.26
In summary, we have developed a novel biaryl-ether series dis-
playing dual NRI and 5-HT1A partial agonist pharmacology. Our
main design objective was to identify a replacement for the A-ring
piperidine of 1 that would drive reduced potency at the dopamine
transporter while maintaining or improving 5-HT1A partial agonist
pharmacology. This goal was achieved through the identification of
an oxygen-linked azetidine or pyrrolidine moiety as a suitable
piperidine A-ring replacement. It is noteworthy that in the case
of azetedine lead compound 9e, optimization of the pharmacolog-
ical profile relative to 1 was achieved without an increase c log P
while also affording a reduction in the pKa. As observed in Series
1 and 2, selectivity for NET over DAT and SERT was found to be
highly dependent on the sterics and electronics associated with
the C-ring substitution pattern. Finally, key compounds were eval-
23. Grimwood, S.; Hartig, P. R. Pharmacol. Ther. 2009, 122, 281.
24. Dose at which 50% receptor occupancy was observed.
25. Dose at which 10% receptor occupancy was observed. The minimal
pharmacologically active dose is typically observed at 5–10% 5-HT1A receptor
occupancy using competitive agonist binding assays.
26. Dog plasma exposures (Cmax) for 9e, 9f, 15g at the 1 h time point (Tmax
)
following 5 mg/kg p.o. dosing were 919, 525, and 146 ng/ml (n = 2),
=
respectively. The corresponding AUC exposures (extrapolated from 0–24 h)
for 9e, 9f, 15g were = 3480, 2800, and 560 ng h/ml, and the half-life in dog
plasma was 2.35, 3.01, and 1.85 h (n = 2), respectively.
27. Ex vivo receptor occupancy data were collected at 1 h post-dose for 1, 9e, 9f,
15e following subcutaneous administration. Total brain drug concentration for
1, 9e, 9f, 15e were = 2230 179, 5900 585, 5690 370, 5620 555 ng/ml
(mean SEM, n = 4), respectively.
28. Assay conducted as described in published protocol: Newman-Tancredi, A.;
Assie, M.-B.; Martel, J.-C.; Cosi, C.; Slot, L. B.; Palmier, C.; Rauly-Lestienne, I.;
Colpaert, F.; Vacher, B.; Cussac, D. Br. J. Pharmacol. 2007, 151, 237.
29. Monoamine functional assay conducted as described in Ref. 13