Design, synthesis, and biological evaluation of new monoamine reuptake inhibitors with potential therapeutic utility in depression and pain

Article abstract of DOI:10.1016/j.bmcl.2010.07.020

Two new series of monoamine triple reuptake inhibitors (TRIs) have been discovered through scaffold homologation of our recently reported series of 3,3-disubstituted pyrrolidine TRIs. The regioisomeric 2- and 3-ketopyrrolidines demonstrated high levels of

Full text of DOI:10.1016/j.bmcl.2010.07.020

Bioorganic & Medicinal Chemistry Letters 20 (2010) 5559–5566
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Design, synthesis, and biological evaluation of new monoamine reuptake
inhibitors with potential therapeutic utility in depression and pain
*
Matthew C. Lucas , Robert J. Weikert, David S. Carter, Hai-Ying Cai, Robert Greenhouse, Pravin S. Iyer,
Clara J. Lin, Eun Kyung Lee, Ann Marie Madera, Amy Moore, Kerem Ozboya, Ryan C. Schoenfeld,
*
Sandra Steiner, Yansheng Zhai, Stephen M. Lynch
Roche Palo Alto LLC, Department of Medicinal Chemistry, 3431 Hillview Avenue, Palo Alto, CA 94304, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 May 2010
Revised 2 July 2010
Accepted 7 July 2010
Available online 4 August 2010
Two new series of monoamine triple reuptake inhibitors (TRIs) have been discovered through scaffold
homologation of our recently reported series of 3,3-disubstituted pyrrolidine TRIs. The regioisomeric
2- and 3-ketopyrrolidines demonstrated high levels of potency against all three monoamine transporters
as well as good human in vitro stability, low drug–drug interaction potential and a decreased propensity
for hERG channel binding. Representative compounds from these series displayed good in vivo pharma-
cokinetics and high monoamine receptor occupancies which are indicators of good brain penetration.
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Monoamine reuptake inhibitors
Triple reuptake inhibitor
Serotonin
Norepinephrine
Noradrenalin
Dopamine
Major depressive disorder
Depression
Depression is an often disabling condition that will affect great-
er than 15% of the general population in their lifetime.1 The etiol-
ogy of the disease was widely considered to be due to sub-optimal
concentrations of the monoamine neurotransmitters serotonin
(5-HT) and norepinephrine (NE) in the central nervous system
(CNS). Although it is now apparent that depression is a conse-
quence of dysfunctional endocrine, immune and neurotransmitter
systems, the majority of antidepressants have been developed
based on the assumption that an imbalance in monoamine concen-
tration is the primary cause.2 Early therapeutics, which included
the monoamine oxidase inhibitors (MAOIs, e.g., NardilÒ, 1) and
the tricyclic antidepressants (TCAs, e.g., ElavilÒ, 2), treated a broad
array of symptoms commonly associated with depression (Fig. 1).
This broad activity was largely due to their ability to increase the
synaptic concentration of either two (5-HT and NE) or all three
(5-HT, NE and dopamine (DA)) neurotransmitters. These therapeu-
tics are far from ideal due to side effects caused by their ‘off-target’
introduction of the serotonin selective reuptake inhibitor (SSRI)
class of drugs (e.g., ProzacÒ, 3).3 The serotonin reuptake transporter
(SERT) is located on the pre-synaptic nerve terminals and is
H
N
NMe2
NH2
1, Phenelzine (Nardil), a MAOI
2, Amitriptyline (Elavil), a TCA
CF3
pharmacology (muscarinic,
potential to cause drug–drug interactions. One breakthrough in
modern antidepressant therapy came in the 1980’s with the
a-adrenergic, histaminergic) and a
O
O
NHMe
NHMe
S
* Corresponding authors. Tel.: +1 973 2357388 (M.C.L.); tel.: +1 973 2357315
3, Fluoxetine (Prozac), an SSRI
(S.M.L.).
4, Duloxetine (Cymbalta), an SNRI
E-mail addresses: matthew.lucas@roche.com (M.C. Lucas), stephen.lynch@ro-
che.com (S.M. Lynch).
Figure 1. Some marketed antidepressants.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.07.020

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M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
NH
O
HN
N
H
N
H
N
H
N
H
N
H
N
H
5
6
7
8a
Figure 2. Design of novel triple reuptake inhibitors.
responsible for signal termination and recycling of 5-HT that is re-
leased into the synaptic cleft during synapse firing. Inhibition of
this transporter results in the increased synaptic concentration of
5-HT and its duration of action, thus alleviating some of the symp-
toms of major depressive disorder (MDD) associated with low lev-
els of 5-HT (mood dysregulation, anxiety and sleep disorders).
Although these therapeutics targeted a smaller range of symptoms,
their high level of selectivity led to improved safety and tolerability
through a much reduced side effect profile. Unfortunately, full
remission is only observed in approximately one third of treated
patients. To address the remaining clinical need, serotonin norepi-
nephrine selective reuptake inhibitors (SNRIs, e.g., CymbaltaÒ, 4)
have emerged that are able to treat a broader array of symptoms
compared to the SSRI class. SNRIs augment synaptic NE levels as
well as 5-HT while showing limited affinity for the receptors
responsible for many of the side effects observed with the tricyc-
lics.4 This results in a tolerability and safety profile comparable
to SSRIs while also addressing symptoms such as lack of energy,
concentration, and co-morbid pain.5 The SNRI class of antidepres-
sants are more likely to result in remission, and some (e.g., Cymb-
altaÒ, 4) are also approved to treat other diseases such as
fibromyalgia and neuropathic pain.6 Evidence also suggests that
the SNRIs reduce anxiety as well as depression (through noradren-
ergic (NA) pathways) and are therefore more likely to benefit a set
of patients that commonly suffer from anxiety in addition to
depression (approximately 60% of patients).
Elevating DA levels in addition to 5-HT and NE have generated a
class of therapeutics referred to as broad spectrum antidepressants
or triple reuptake inhibitors (TRIs) which are expected to show
superior efficacy to the SSRI and SNRI classes.7 Increasing brain
DA levels through dopamine transporter (DAT) inhibition should
address the anhedonia, lack of motivation, and lack of attention
components of MDD that the SSRIs and SNRIs do not, and may also
result in a faster onset of action.8 Recent clinical studies have sug-
gested that combination therapy using bupropion, a DAT inhibitor,
and an SSRI or SNRI offers improved efficacy in the treatment of
depression compared with monotherapy alone.9 Thus, TRIs may
provide the next major advancement in antidepressant and pain
therapy.
We recently reported on a series of 3,3-disubstituted pyrroli-
dine monoamine triple reuptake inhibitors (e.g., 7)10 that evolved
from indolyl phenyl propylamine SNRIs (e.g., 5)11 which were
developed into analogs with low nanomolar potency at all three
transporters. Examples from this series also demonstrated good
human in vitro microsomal and hepatocyte stability, high perme-
ability and low drug–drug interaction potential. To further im-
prove upon the pharmacological properties of this scaffold, we
sought to reduce the clog P.12 To this end, insertion of a carbonyl
linker between the indolyl moiety and the pyrrolidine ring to gen-
erate analogs such as 8a was investigated (Fig. 2). In addition to
reducing lipophilicity, we hypothesized that the reduction in pKa
of the cyclic amine imparted by the carbonyl moiety might offer
the additional benefit of reducing affinity at the hERG channel. Fur-
thermore, the modular chemistry required to access this type of
scaffold could facilitate the investigation of an expanded set of aryl
or heteroaryl moieties as potential indole replacements.
Table 1
Affinity at SERTa, NETa, DATa, human liver microsome clearance, hERG, and Caco-2
permeability measurements of 7 and 8a
Compound SERT NET DAT HLM (
l
L/
hERG
BA/AB (ER)
min/mg)
IC20
(l
M) (cm/s  10À6
)
7
8a
8.0
8.2
9.0
7.7
7.9
8.1
100
36
>1
6.1
14/17 (0.82)
19/17 (1.1)
Early results of this exercise were encouraging; 8a showed com-
parable potency to 7 and in vitro screening demonstrated a signif-
icant improvement in stability in human liver microsomes
a
Monoamine reuptake pKi values are the geometric mean of at least three
experiments.
O
O
O
OMe
OH
a
N
b
n
n
n
n
n
n
Me
N
N
N
N
Boc
Si(i-Pr)3
Boc
10
Boc
9
11
a. n = 1
b. n = 0
c. n = 2
d. n = 3
O
O
c
n
d, e
n
n
n
N
Si(i-Pr)3
N
N
N
H
H
Boc
12
8
Scheme 1. First generation synthesis of 3-substituted 3-keto cyclic amines. Reagents and conditions: (a) MeONHMeÁHCl, EDC, HOBt, DMF; (b) 5-bromo-1-(triisopropyl-
silyl)indole, t-BuLi, THF, À78 °C then 10; (c) LiHMDS, BnBr, THF, 0 °C; (d) TBAF, THF; (e) HCl, MeOH.

M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
5561
(HLM),13 reduced hERG channel14 affinity, and excellent mem-
brane permeability15 (Table 1). Herein we describe the develop-
ment of several new scaffolds derived from the homologated
ketopyrrolidine 8a. We also highlight significant SAR and show se-
lected in vivo data.
halides. With the quaternary center in place, the nitriles were con-
verted to the corresponding aldehydes 18 via direct reduction
using diisobutylaluminum hydride (DIBAL). Alternatively, the es-
ters were subjected to a two step protocol involving initial lithium
aluminum hydride (LiAlH4) reduction to the alcohol followed by
oxidation with either manganese dioxide or Dess–Martin period-
inane. Subsequent treatment of 18 at low temperature with an aryl
lithiate or Grignard reagent afforded the secondary alcohols 19 as a
mixture of diastereomers. Finally, oxidation to the ketone and
deprotection of the tert-butyl carbamate afforded the desired pyr-
rolidinyl ketones 20. Scheme 3 outlines an analogous sequence
that was employed to synthesize a variety of aryl and heteroaryl
containing 2-pyrrolidinyl ketones (25) starting with commercially
available N-Boc proline methyl ester 21.
Our initial synthesis of 3-substituted 3-ketopyrrolidines is de-
scribed in Scheme 1. It commenced with the commercially avail-
able N-Boc-b-proline 9a which was converted to the Weinreb
amide 10 and added to the lithiate generated from 5-bromo-1-(tri-
isopropylsilyl)indole via halogen exchange. The resulting ketone
11 was alkylated by treatment with lithium hexamethyldisilazane
(LiHMDS) and benzyl bromide to install the quaternary center to
provide 12. Finally, the protecting groups were removed using tet-
rabutylammonium fluoride (TBAF) followed by hydrogen chloride
in methanol to provide 8a. This methodology was readily extended
to synthesize the analogous 3,3-disubstituted azetidines, piperi-
dines, and azepines (8b–d) beginning with the appropriate N-
Boc-amino acids. It should be noted that the 4,4-disubstituted
piperidines were also accessible using this synthetic sequence.
Although the ketone alkylation methodology was useful for the
synthesis of preliminary analogs, it became apparent that the
alkylation step was limited by the necessity for activated electro-
philes such as benzylic or allylic halides in order to achieve reason-
able yields of the hindered quaternary ketones. The alkylation
became far less efficient or failed entirely when less reactive ali-
phatic halides were employed. An alternative and more general
strategy toward 3-substituted 3-ketopyrrolidines was thus devel-
oped and is outlined in Scheme 2. The aliphatic side-chains a–f
were installed through alkylation of the 3-pyrrolidinyl nitriles 13
or esters 16 with LiHMDS in the presence of the appropriate alkyl
Seebach’s Self-Regeneration of Stereochemistry (SRS) methodol-
ogy was employed to access enantiopure 2-ketopyrrolidines
(Scheme 4).16 (2R,5S)-2-tert-Butyl-1-aza-3-oxabicyclo[3.3.0]octan-
4-one 26 (derived from L-proline) was allylated under kinetic con-
ditions with retention of stereochemistry to give 27. Mild silica
gel mediated hydrolysis provided 28 which was elaborated to the
desired product 31 through the usual sequence in reasonable over-
all yield and 90% ee (determined by chiral HPLC analysis of final
product, 31).
Encouraged by the initial results of 3-ketopyrrolidine 8a, we
proceeded to develop the SAR and identified the 7-fluoroindole
32 which had sufficiently good potency, stability, and permeability
for us to investigate its in vivo properties (Table 2). In the mouse
tail suspension assay, an assay used to evaluate antidepressant
agents,17 activity was observed at both 10 and 30 mg/kg, ip (data
not shown). With this data in hand, our optimization focused on
O
OH
R
R
R
CN
CN
a
b
g
H
Ar
N
N
N
N
Boc
Boc
Boc
Boc
19
a. R =
b. R =
13
14
18
c. R =
d. R =
e or h, i
d, e or f
O
O
O
O
O
R
R
OH
e. R =
f. R =
OMe
c
a
OMe
Ar
N
N
N
N
Boc
H
Boc
Boc
15
16
17
20
Scheme 2. General synthesis of 3-substituted 3-ketopyrrolidines. Reagents and conditions: (a) LiHMDS, THF, À78 °C then RI or RBr; (b) (i-Bu)2AlH; CH2Cl2, À40 °C; (c) Cs2CO3,
MeI, DMF; (d) LiAlH4, THF, 0 °C; (e) Dess–Martin periodinane, CH2Cl2; (f) oxalyl chloride, DMSO, Et3N; (g) ArLi or ArMgX, Et2O, À78 °C; (h) MnO2, toluene, 100 °C; (i) HCl,
MeOH.
O
O
O
OH
R
N
R
R
a
b, c
d
OMe
Boc
OMe
H
Ar
N
N
N
Boc
Boc
Boc
21
22
23
24
O
R
c. R =
d. R =
a. R =
b. R =
O
c, e
Ar
NH
25
Scheme 3. General synthesis of 2-substituted 2-ketopyrrolidines. Reagents and conditions: (a) LiHMDS, THF, À78 °C, then RX; (b) LiAlH4, THF, 0 °C; (c) Dess–Martin
periodinane, CH2Cl2; (d) ArLi or ArMgX, Et2O, À78 °C; (e) HCl, MeOH.

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M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
H
H
a
b
c
O
O
O
N
N
N
H
N
CO2H
28
O
O
HO
H
L-proline
26
27
e, f
d
g, h
i
N
CO2Me
N
CO2Me
N
CHO
H
Boc
Boc
(-)-23a
29
(-)-22a
OH
O
Cl
Cl
Cl
Cl
j, k
N
NH
Boc
30
31
Scheme 4. Asymmetric synthesis of 31. Reagents and conditions: (a) see Ref.11; (b) (i) n-BuLi, iPr2NH, THF, À78 °C; (ii) CH2@CHCH2Br, À78 °C to À30 °C, 58%; (c) silica gel,
H2O, MeOH, rt, 85%; (d) TMS–CH2N2, MeOH, 27%; (e) Boc2O, DMAP, DCM, 93%; (f) H2, 20% Pd(OH)2/C, MeOH, 81%; (g) LiAlH4, THF, 0 °C, 76%; (h) Dess–Martin periodinane,
DCM, 0 °C, 75%; (i) 3,4-dichlorophenylMgBr, THF, 0 °C, 79%; (j) Dess–Martin periodinane, DCM, 0 °C, 78%; (k) HCl, MeOH, 100%.
Table 2
slightly, but at the expense of binding. During the course of this
side-chain exploration an interesting trend was discovered. We
Affinity at SERTa, NETa, DATa, CYP2D6, and human liver microsome clearance
found that by sequentially increasing the steric size of the hydro-
phobe, we were able to increase binding at all three transporters
and in particular at DAT. Disappointingly, this trend was also
accompanied by stronger CYP2D6 binding and increased clearance
likely due to increased lipophilicity (see 33, 34, 36 and 37). The
dimethylbutyl side-chain, however, proved to be an outlier; 38
was notable for its excellent binding properties, moderate clear-
ance, and somewhat weaker CYP2D6 affinity.
O
R2
N
N
H
H
R1
Compound R1 R2
SERT NET DAT CYP2D6
IC50
HLM
L/min/
mg)
(
l
(l
M)
While indole analogs have proved to provide potent mono-
amine reuptake inhibitors,10,19 there are potential safety issues re-
lated to certain indoles which could give rise to reactive
metabolites.20 We hypothesized that the indole itself, as opposed
to the side-chain, might be implicated in the persistent CYP2D6
inhibition. Our attempts to substitute either the 2- or 3-position
on the indole resulted in loss of potency at the transporters (data
not shown). As a consequence we designed, synthesized, and eval-
uated a series of isosteric indole replacements, many of which pos-
sessed significantly reduced CYP2D6 inhibition (Table 3). We were
successful in replacing the indole with a variety of simple monocy-
clic aryl and heteroaryl groups (e.g., 39–45) while maintaining po-
tent triple reuptake inhibitory profiles. Several heterobicyclic
analogs with interesting in vitro profiles were also identified
(e.g., 46–50); among them was quinoline 49, which proved partic-
ularly potent and balanced in its inhibition at all three transporters
but demonstrated high affinity for CYP2D6. Installation of a 5-
methyl group to generate 50 provided one of the our most potent
compounds and concurrently improved the CYP2D6 and HLM pro-
file relative to 49.
8a
H
F
8.2
7.7
8.1
—
36
32
(+)-32
(À)-32
33
8.2
8.4
6.7
8.0
8.1
7.7
7.9
8.1
6.7
0.08
0.07
0.34
35
25
—
8.5
8.8
8.2
8.6
7.8
7.8
2.3
0.8
6
6
F
F
(+)-33
34
(+)-34
9.0
9.4
8.6
8.9
8.1
8.3
1.0
1.3
3
8
35
F
F
8.5
7.7
7.1
4.1
10
O
36
(+)-36
8.9
9.2
8.6
9.0
8.2
8.4
0.75
0.04
27
12
37
(+)-37
9.1
9.4
9.1
9.3
8.8
9.0
0.05
—
43
32
F
F
38
(+)-38
9.1
9.3
8.9
8.9
9.1
9.2
1.8
0.6
15
18
a
Monoamine reuptake pKi values are the geometric mean of at least three
experiments.
improving the stability in HLM and reducing the potent CYP2D6
inhibition18 observed for this compound. Separation of the enanti-
omers by chiral HPLC revealed that one enantiomer (+)-32 not only
retained most of the potency for binding to the monoamine trans-
porters, but also for CYP2D6. Replacing the benzyl side-chain with
a propyl group offered a significant advantage with respect to sta-
bility in HLM, providing molecules that were equipotent at the
transporters and predicted to be of high stability. While there
was a 10-fold improvement with respect to the CYP2D6 inhibition,
it still remained at an undesirable level (see (+)-32 and (+)-33).
Insertion of a polarizing heteroatom (35) reduced CYP2D6 affinity
While the 3-ketopyrrolidine compounds described in Tables 2
and 3 had excellent binding affinities for the monoamine reuptake
transporters and acceptable hERG safety windows, the develop-
ment of an asymmetric synthesis proved challenging. We had been
simultaneously investigating modifications to the basic heterocy-
cle and discovered several plausible alternatives that might either
provide achiral molecules or, alternatively, offer established enan-
tioselective syntheses. Some of these modifications relative to the
3-ketopyrrolidine 8a are summarized in Table 4. Ring contraction
to the azetidine 8b met our desire for an achiral scaffold but also
caused significant loss of potency. On the other hand, ring expan-

M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
5563
Table 3
Affinity at SERTa, NETa, DATa, CYP2D6, and human liver microsomal clearance
R
N
H
Compound
R
SERT
9.0
NET
DAT
7.9
CYP2D6 IC50
13
(lM)
HLM (
lL/min/mg)
O
O
Cl
39
8.4
29
40
(+)-40
8.6
9.0
8.2
8.5
8.2
8.4
7.5
10
7
27
Cl
Cl
Cl
Cl
O
O
41
42
8.5
8.3
8.0
8.1
8.0
8.7
13
15
15
17
F
S
Cl
Cl
O
O
N
Cl
43
44
7.9
9.0
8.0
8.3
8.0
8.5
3
4
9
Cl
Cl
12
NH2
O
O
Cl
45
46
47
7.5
9.2
9.0
7.3
8.2
8.6
7.2
8.1
8.9
36
14
12
26
18
22
N
NH2
N
N
H
O
O
S
48
49
8.2
8.7
8.6
8.5
8.6
8.4
23
8
N
H
O
O
N
N
0.6
35
50
9.7
9.2
9.0
9
25
a
Monoamine reuptake pKi values are the geometric mean of at least three experiments
sion to the 3- or 4-ketopiperidines 8c and 52 was very encourag-
be reported in due course. Further ring expansion provided the
ing. These compounds were selected for additional SAR studies to
azepine 8d which maintained some affinity at the transporters,

5564
M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
Table 4
but its inferior in vitro profile compared to the pyrrolidine and
Affinity at SERTa, NETa, DATa
piperidine series led to its deprioritization. Perhaps the most excit-
ing modification was the transposition of the basic nitrogen alpha
to the carbonyl to generate the 2-ketopyrrolidine regioisomer (À)-
51 with a significantly reduced pKa. While the SERT affinity of (À)-
51 was poor, the NET and DAT potency remained respectable. Data
generated for other asymmetric scaffolds suggested that (+)-51
should offer a more balanced profile. While (+)-51 was not synthe-
sized, the (+)-enantiomers of other members of this scaffold did
provide more potent and balanced triple reuptake inhibitors than
their antipodes (e.g., (+)-55 vs 31, Table 5).
Applying the SAR knowledge already developed (Table 2) to fur-
ther improve this sub-series, we replaced the benzyl group with a
propyl to generate 53 and were pleased with the high potency at
SERT, NET, and DAT (Table 5). We next introduced a 7-F substituent
to the indole (54), which improved HLM stability but showed
strong CYP2D6 inhibition and increased affinity for the hERG chan-
nel (Tables 5 and 6). It has been proposed that the hERG channel
prefers binding with lipophilic, basic substrates.21 We had ex-
pected the reduction in calculated pKa of the 2-ketopyrrolidines
(cpKa ꢀ8) compared to the 3-ketopyrrolidines (cpKa ꢀ10) to reduce
the relative hERG channel affinity, but this was not apparent. It ap-
pears that within this chemical series any positive effect gained by
reducing pKa was negated by the deleterious effect of the increased
lipophilicity as measured by log D (Table 6). The increase in log D
was also manifest in excellent permeability but sharp loss of stabil-
ity towards HLMs. Replacing the indole with dichlorophenyl (53 vs
55) provided a further boost in lipophilicity which resulted in even
stronger hERG channel binding and drastically reduced stability to-
ward HLM. Ultimately a solution for this problem was found by
introducing polarizing heteroatoms remote to the cyclic amine
which reduced the overall log D of the molecule while maintaining
the desired low pKa. Thus, replacing the para-chloro moiety of 55
O
A
N
HN
H
Compound
Ring A
SERT
6.1
NET
6.8
DAT
6.1
8b
N
H
8a
8.2
5.9
7.9
7.7
8.1
7.6
8.1
7.4
7.2
N
H
(À)-51b
8c
NH
N
H
52
8d
8.1
7.1
7.0
6.6
8.0
6.6
HN
N
H
a
Monoamine reuptake pKi values are the geometric mean of at least three
experiments
b
Racemate nor opposite enantiomer were synthesized.
Table 5
Affinity at SERTa, NETa, DATa, and CYP2D6, and human liver microsomal clearance
R2
R1
NH
Compound
R1
R2
SERT
NET
8.5
DAT
8.6
CYP2D6 IC50
0.3
(lM)
HLM (
lL/min/mg)
O
53
8.7
8.2
109
N
H
O
54
8.7
8.4
0.03
21
N
H
F
55
(+)-55
31
8.6
9.3
8.1
7.7
7.9
6.8
7.8
8.2
7.3
4
2
12
220
362
384
O
Cl
Cl
O
O
Cl
56
8.7
9.4
8.1
8.6
8.2
8.5
7
0
NH2
Cl
(+)-57
12
13
NH2

M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
5565
Table 5 (continued)
Compound
R1
R2
SERT
8.9
NET
8.6
DAT
8.5
CYP2D6 IC50
(lM)
HLM (
lL/min/mg)
O
Cl
O
(+)-58
(+)-59
14
14
NH2
O
7.8
8.6
8.3
7.9
8.1
8.1
7.9
8.2
8.5
15
6
27
25
54
N
N
H
O
O
(+)-60
N
N
H
61
8
N
N
H
a
Monoamine reuptake pKi values are the geometric mean of at least three experiments.
Table 6
Table 8
Receptor occupancy data for selected compounds in rats
hERG, log Da, Caco-2 permeability, and plasma protein binding for selected
compounds
Compound
SERTOcc80 (mg/kg ip)
SERT:DAT Balance at SERTOcc80
Compound
hERG IC50/IC20
(
l
M)
Log D
BA/AB (ER)
PPB h, r (%)
(+)-33
(+)-38
(+)-40
56
(+)-57
(+)-60
4
3.9
1.15
3.16
0.11
3.8
80:31
80:35
80:20
80:85
80:6
(cm/s  10À6
)
53
54
55
56
(+)-58
(+)-59
(+)-60
61
>10/7.3
5.9/1.5
3.1/1.2
>10/6.1
>10/3.1
>10/7.9
>10/4.2
>10/4.0
1.45
1.56
2.77
0.86
0.84
1.0
10/41 (0.25)
18/43 (0.41)
8/19 (0.42)
19/37 (0.5)
18/30 (0.6)
16/29 (0.55)
20/32 (0.62)
12/20 (0.60)
63, 66
64, 65
86, 95
42, 45
61, 51
2, 15
80:67
tional in vivo assessment (data not shown). We were delighted
when the improved in vitro profile obtained by replacing the in-
dole of (+)-38 with dichlorophenyl ((+)-40) translated into superior
bioavailability, comparable to duloxetine (4). PK in higher species
was also very good.
1.0
2.03
20, 13
50, 48
a
Log D was measured using the shake flask method.
Severalcompoundswere characterized in vivo to determineSERT
and DAT receptor occupancies in rats.22 High receptor occupancies
are indicators of high brain penetration, and also allowed us to select
compounds with diversified profiles for additional pharmacological
testing to challenge the hypothesis that a TRI compound will have
improved efficacy and faster onset of action than either an SSRI or
SNRI. We established the dose that would provide 80% SERT occu-
pancy and from this determined the corresponding DAT occupancy
at the same dose as summarized in Table 8. We were pleased to find
that we could obtain high occupancies at low ip doses for many of
the preferred representatives, and that we could also cover a wide
range of DAT occupancies. These compounds provide additional
tools to help determine the optimal contribution of the dopamine
transporter to best address the unmet clinical need for the treatment
of major depressive disorder.
In summary, we have discovered several new series of novel
and potent inhibitors of serotonin, norepinephrine and dopamine
reuptake. The regioisomeric 2- and 3-ketopyrrolidinyl scaffolds
have provided molecules with excellent in vitro properties as well
as in vivo transporter occupancies at low doses. Molecules within
these series possess therapeutic indices that permitted progression
further towards the clinic. Further pharmacological studies for
these compounds will be reported elsewhere.
with an anilino-group (56) dramatically improved stability toward
HLMs with a somewhat lessened affinity for hERG. Increasing the
steric bulk of the side-chain (e.g., (+)-57) and inserting a second
polarizing heteroatom (e.g., (+)-58) also provided molecules with
good in vitro profiles. Likewise, replacing the indole in 53 with
an indazole afforded additional drug-like molecules (see (+)-59,
(+)-60 and 61). It should be noted that as the side-chain was ex-
tended and the log D approached 2 the HLM stability of the mole-
cules again began to decrease ((+)-60 vs 61, Table 6). Compounds
with lower measured log D also showed reduced plasma protein
binding. These in vitro profiles translated into potent in vivo occu-
pancies of the SERT and DAT transporters (Table 8) as well as
behavioral paradigms (data not shown).
Pharmacokinetic properties were determined for representa-
tives of several sub-series in the rat. As exemplified in Table 7,
clearances in rat were generally high (a common characteristic of
many marketed antidepressants) and oral bioavailability was
low, however, microsomal and hepatocyte stability in human,
dog and cynomolgus monkey was generally much better and this
did not necessarily preclude compounds from undergoing addi-
Table 7
Rat pharmacokinetic data for 4, (+)-38 and (+)-40
Compound
Species
T1/2 (h)
CL (mL/min/kg)
F (%)
Vss (L/kg)
Acknowledgments
4
Rat
Rat
Rat
1.5
1.6
1.2
178
153
125
22
5
57
20.9
14
14.3
(+)-38
(+)-40
We thank Francisco Talamas for his interest in this work, Xing-
rong Liu and Olga Vilenski for DMPK support, Linda Bristow, Joyce

5566
M. C. Lucas et al. / Bioorg. Med. Chem. Lett. 20 (2010) 5559–5566
Jamie-Figueroa, S.; Lynch, S. M.; Raptova, L.; Stein, K. A.; Weikert, R. J.
US2007123535(A1), 2007.
12. (a) Gleeson, M. P. J. Med. Chem. 2008, 51, 817; (b) Waring, M. J.; Johnstone, C.
Bioorg. Med. Chem. Lett. 2007, 17, 1759.
Kwan, and Subbu Apparsundaram for occupancy studies, and Mar-
quis Cummings for HPLC analytical purification and enantiomeric
separation.
13. CLint measured in HT format: total incubation volume 250
microsomal protein, reaction started by adding NADPH and performed at 37 °C
with no shaking. 40 L aliquots at four time-points (0.1, 10, 20 and 30 min)
lL, 0.5 mg/mL
References and notes
l
were taken then the samples transferred to 384 well plates for LC/MS analysis.
14. hERG IC50/IC20 values calculated using the PatchXpress 7000A (MDS, Inc.
Toronto, Canada) to carry out electrical recording of K+ currents in CHO cells
expressing the human ERG channel. Recordings were made at 30 °C with test
compounds at two concentrations (1 lM, 10 lM) or more.
15. Permeability was measured using Caco-2 cells at 21 days of culture. Efflux
ratios are measured using the bi-directional (Papp A to B and B to A) values.
1. Baldessarini, R. J. In The Pharmacological Basis of Therapeutics; Hardman, J. G.,
Limbird, L. E., Gilman, A. G., Eds., 10th ed.; McGraw-Hill, 2001; pp 451–483.
2. (a) Nemeroff, C. B. J. Psychiatry Res. 2007, 41, 189; (b) Walter, M. W. Drug Dev.
Res. 2005, 65, 97; (c) Liu, S.; Molino, B. F. Annu. Rep. Med. Chem. 2007, 42, 13.
3. Moltzen, E. K.; Bang-Andersen, B. Curr. Top. Med. Chem. 2006, 6, 1801.
4. Zajecka, J. M.; Albano, D. J. Clin. Psychiatry 2004, 65, 11.
Substrate concentration 10 lM.
5. Nemeroff, C. B.; Entsuah, R.; Benattiab, I.; Demitrack, M.; Sloan, D. M.; Thase, M.
E. Biol. Psychiatry 2008, 63, 424.
16. Seebach, D.; Sting, A. R.; Hoffmann, M. Angew. Chem., Int. Ed. 1996, 35, 2708.
17. Steru, L.; Chermat, R.; Thierry, B.; Simon, P. Psychopharmacology 1985, 85, 67.
18. CYP2D6 inhibition was measured in a fluorescence based assay where CYP
marker substrates become fluorescent upon CYP metabolism.
19. (a) Mahaney, P. E.; Kim, C. Y.; Coghlan, R. D.; Cohn, S. T.; Heffernan, G. D.;
Huselton, C. A.; Terefenko, E. A.; Vu, A. T.; Zhang, P.; Burroughs, K. D.; Cosmi, S.
A.; Bray, J. A.; Johnston, G. H.; Deecher, D. C.; Trybulski, E. J. Bioorg. Med. Chem.
Lett. 2009, 19, 5807; (b) Kim, C. Y.; Mahaney, P. E.; McConnell, O.; Zhang, Y.;
Manas, E.; Ho, D. M.; Deecher, D. C.; Trybulski, E. J. Bioorg. Med. Chem. Lett.
2009, 19, 5029.
20. (a) Kalgutkar, A. S.. In Biotechnology: Pharmaceutical Aspects (Advances in
Bioactivation Research); Elfarra, A. A., Ed.; Springer, 2008; Vol. 9, pp 27–55; (b)
Levesque, J.-F.; Day, S. H.; Chauret, N.; Seto, C.; Trimble, L.; Bateman, K. P.; Silva,
J. M.; Berthelette, C.; Lachance, N.; Boyd, M.; Li, L.; Sturino, C. F.; Wang, Z.;
Zamboni, R.; Young, R. N.; Nicoll-Griffith, D. A. Bioorg. Med. Chem. Lett. 2007, 17,
3038.
6. Pedersen, L. H.; Nielsen, A. N.; Blackburn-Munro, G. Psychopharmacology 2005,
182, 551.
7. (a) Guiard, B. P.; El Mansari, M.; Blier, P. Curr. Drug Targets 2009, 10, 1069; (b)
Marks, D. M.; Pae, C.-U.; Patkar, A. A. Curr. Neuropharmacol. 2008, 6, 338; (c)
Skolnick, P.; Chen, Z. Expert. Opin. Invest. Drugs 2007, 16, 1365.
8. Lemke, M. R.; Brecht, H. M.; Koester, J.; Reichmann, H. J. Neuro. Sci. 2006, 248,
266.
9. Trivedi, M. H.; Fava, M.; Wisniewski, S. R.; Thase, M. E.; Quitkin, F.; Warden, D.;
Ritz, L.; Nierenberg, A. A.; Lebowitz, B. D.; Biggs, M. M.; Luther, J. F.; Shores-
Wilson, K.; Rush, A. J. N. Eng. J. Med. 2006, 354, 1243.
10. Bannwart, L. M.; Carter, D. S.; Cai, H.-Y.; Choy, J. C.; Greenhouse, R.; Jaime-
Figueroa, S.; Iyer, P. S.; Lin, C. J.; Lee, E. K.; Lucas, M. C.; Lynch, S. M.; Madera, A.
M.; Moore, A.; Ozboya, K.; Raptova, L.; Roetz, R.; Schoenfeld, R. C.; Stein, K. A.;
Steiner, S.; Villa, M.; Weikert, R. J.; Zhai, Y. Bioorg. Med. Chem. Lett. 2008, 18,
6062.
21. Aronov, A. M. Curr. Top. Med. Chem. 2008, 8, 1113.
22. Liu, X.; Vilenski, O.; Kwan, J.; Apparsundaram, S.; Weikert, R. Drug Metab.
Dispos. 2009, 37, 1548.
11. (a) Greenhouse, R.; Jaime-Figueroa, S.; Raptova, L.; Reuter, D. C.; Stein, K. A.;
Weikert, R. J. WO2005118539A1, 2005.; (b) Iyer, P.; Lucas, M. C.; Schoenfeld, R.
C.; Villa, M.; Weikert, R. J. US20070123527(A1), 2007.; (c) Greenhouse, R.;