Discovery of N-methyl-1-(1-phenylcyclohexyl)methanamine, a novel triple serotonin, norepinephrine, and dopamine reuptake inhibitor

Article abstract of DOI:10.1016/j.bmcl.2011.01.016

The current work discloses a novel cyclohexylarylamine chemotype with potent inhibition of the serotonin, norepinephrine, and dopamine transporters and potential for treatment of major depressive disorder. Optimized compounds 1 (SERT, NET, DAT, IC₅₀ = 169, 85, 21 nM) and 42 (SERT, NET, DAT IC₅₀ = 34, 295, 90 nM) were highly brain penetrant, active in vivo in the mouse tail suspension test at 30 mpk po and were not general motor stimulants.

Full text of DOI:10.1016/j.bmcl.2011.01.016

Bioorganic & Medicinal Chemistry Letters 21 (2011) 1438–1441
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Discovery of N-methyl-1-(1-phenylcyclohexyl)methanamine, a novel triple
serotonin, norepinephrine, and dopamine reuptake inhibitor
Liming Shao a, , Michael C. Hewitt b, , Fengjiang Wang a, Scott C. Malcolm a, Jianguo Ma a, John E. Campbell a,
⇑
Una C. Campbell a, Sharon R. Engel a, Nancy A. Spicer a, Larry W. Hardy a, Rudy Schreiber c, , Kerry L. Spear a,
Mark A. Varney d,
a Discovery and Early Clinical Research, Sunovion Pharmaceuticals Inc., 84 Waterford Drive, Marlborough, MA 01752, United States
b Constellation Pharmaceuticals, 215 First St., Suite 200, Cambridge, MA 02142, United States
c Evotec, Schnacokenburgallee 114, Hamburg 22525, Germany
d Cortex Pharmaceuticals, 15231 Barranca Parkway, Irvine, CA 92618, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
The current work discloses a novel cyclohexylarylamine chemotype with potent inhibition of the seroto-
nin, norepinephrine, and dopamine transporters and potential for treatment of major depressive disorder.
Optimized compounds 1 (SERT, NET, DAT, IC50 = 169, 85, 21 nM) and 42 (SERT, NET, DAT IC50 = 34, 295,
90 nM) were highly brain penetrant, active in vivo in the mouse tail suspension test at 30 mpk po and
were not general motor stimulants.
Received 13 October 2010
Revised 5 January 2011
Accepted 6 January 2011
Available online 12 January 2011
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Monoamines reuptake inhibitor
Depression
Understanding the impact of norepinephrine (NE) and dopa-
mine (DA) interactions on the treatment of major depressive disor-
der (MDD) is currently an area of active research.1 Dual dopamine
and norepinephrine reuptake inhibitors such as Bupropion in-
crease the concentrations of NE and DA in (depression) relevant
brain regions,2 and have been found to be effective at treating
MDD when used alone or in combination with SNRIs like mirtaze-
pine (Remeron) or duloxetine (Cymbalta).3 Dopaminergic agonists
such as pramipexole have demonstrated efficacy as antidepres-
sants.4 Additionally, D2 receptor partial agonists like aripiperazole,
typically employed as antipsychotics, when given at sub-therapeu-
tic doses for psychosis along with SNRIs like venlafaxine have dem-
onstrated efficacy at increasing remission rates in resistant patient
populations.1
As evidence continues to mount regarding the improved effi-
cacy resulting from increasing DA levels, one strategy is the addi-
tion of a dopamine component to a dual reuptake inhibitor to
create a ‘triple’ reuptake inhibitor.5 The ‘triple’ reuptake inhibition
theory was reduced to practice pre-clinically with DOV-219476
and DOV-216303,7 (Fig. 1) which both potently inhibit the three
monamine transporters (IC50 for hSERT, hNET, and hDAT for
DOV-21947 = 12, 23, 96 nM and for DOV-216303 = 14, 20, 78,
respectively). Both DOV compounds also dose-dependently reduce
the duration of immobility in the forced swim and tail suspension
tests in rats, two models that are highly predictive of antidepres-
sant efficacy in humans. More importantly, the triple reuptake
inhibition theory was validated in a Phase II efficacy trial in de-
pressed patients. According to press releases from DOV Pharma-
ceuticals, DOV-216303 was shown in a multicenter Phase II
study of patients with moderate to severe major depressive disor-
der (n = 67) to be safe and as effective as citalopram.8 Taken to-
gether, the body of preclinical and clinical evidence for triple
reuptake inhibitors such as the DOV compounds indicates that it
is a validated and promising approach for the treatment of depres-
sion. Herein we wish to disclose our own efforts to develop triple
reuptake inhibitors for MDD.
Screening of rationally designed compounds resulted in com-
pound 1 (Fig. 2), which had a desirable profile at the three trans-
porters and a long in vitro half life in human liver microsomes.
Cl
Cl
Cl
Cl
N
H
N
H
DOV-21,947
DOV-216,303
⇑
Corresponding author. Tel./fax: +1 508 357 7467.
E-mail addresses: liming.shao@sunovion.com, lshao@fas.harvard.edu (L. Shao).
(
+
)-(3,4-dichlorophenyl)-3-azabicyclo-[3.1.0]-hexane
Present address.
Figure 1. Structures of DOV-216303 and 21947.
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.01.016

L. Shao et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1438–1441
1439
Cl
norepinephrine,13 and dopamine14 transporters (Table 1). Inhibi-
tion of all three transporters was the assay used to develop SAR;
in vitro metabolic stability, liability SAR and brain penetration
were checked routinely on active analogs.
Profile of hit 1
SERT = 169 nM
NET= 85 nM
DAT = 21 nM
Cl
N
H
HLM t1/2 = 250 min
One of the first parameters that was optimized in the series was
the ring size of the cycloalkane. The cyclopentane (22) and cyclo-
hexane (14) dimethyl amine derivatives both inhibited all three
monoamines at sub-micromolar concentrations, while the cyclo-
heptane (21, primary amine, compare to 11) and cyclobutane
(23) derivatives showed diminished potency at the three trans-
porters to varying degrees. In the cyclohexane dichlorophenyl ser-
ies potency was best for the dimethyl derivative (14) compared to
the monomethyl (1) and primary amine (11) derivatives, a trend
which held up for other cyclohexane ring sizes and aryl substitu-
tions (data not shown). For amine variety in the cyclohexane
dichlorophenyl series, the NH-ethyl derivative 12 showed potent
DAT inhibition and reasonable inhibition of SERT and NET. The
cyclohexane cyclic amine derivatives were not potent SERT inhib-
itors, but pyrrolidine (17), piperidine (18), and N-methyl piperazi-
no (20) analogs showed excellent potency against NET and DAT.
Some other interesting cyclohexane analogs were 3-Cl-4-F-phenyl
dimethylamine 29 and 3,4-difluorophenyl 31 which inhibited all
three transporters with varying potency, but all less than
100 nM. In the data shown in Table 1, the most potent derivative
at the three transporters was dimethylamine cyclohexane dichlo-
rophenyl compound 14, while compound 1 showed a favorable
balance of reuptake potency across the three transporters and
in vitro metabolic stability. In general, we found the primary
(and some secondary) amine derivatives to be the most stable (lon-
gest microsomal t1/2) and the dimethylamine derivatives to be
least stable, presumably due to rapid N-demethylation.
CYP inhibition (µM): 1A, 2C19, 2C9, 3A4 > 25 µM;
µ
2D6 3.76 M
Brain exposure in mice after 10 mpk PO dosing
1
Figure 2. Profile of hit 1.
The compound was also brain penetrant in mice after oral dosing,
had a relatively simple architecture, and made an excellent starting
point for lead optimization efforts. Our goals for lead optimization
were to maintain the brain penetration of the scaffold, maintain
the low liability profile of the scaffold (CYP and hERG inhibition),
increase the functional potency for SERT, NET and DAT, and show
efficacy in multiple in vivo models.
Synthesis of analogs of amine 1 followed the general synthetic
route shown in Scheme 1, which was adapted from the literature.9
Briefly, alkylation of commercially available aryl acetonitriles
2 with dibromoalkanes (3) in DMSO gave intermediate phenyl
cycloalkanecarbonitriles (not shown), which were hydrolyzed with
base to give acid 4. Peptide coupling and subsequent reduction of
the resulting amides with borane in THF gave the target amine 5.
An alternative protocol was also used for the synthesis of
N-methyl and N,N-dimethyl amines from the primary amine pre-
cursors 7 (Scheme 2). Eschweiler–Clarke alkylation10 with formal-
dehyde and formic acid cleanly delivered the dimethyl amine
derivative 8, and a literature method11 provided access to methyl
amine derivatives via the N-formyl precursors.
In an effort to probe the size and electrostatic limitations of the
aromatic region of our pharmacophore, several alternative aromat-
ics were synthesized and tested for reuptake inhibition (Table 2),
A variety of analogs were prepared to probe the role that the
western aryl group, cycloalkane ring size and amine composition
had on potency at the human recombinant serotonin,12
R1
N
R2
O
R1
R1
OH
N
1. NaH, DMSO
1. amine, PyBOP, NMM, DMF
2. BH3-THF
R3
2
2. NaOH, 1,3-propanediol
( )n
( )n
Br
Br
( )n
4
5
3
Scheme 1. General synthetic scheme for synthesis of aryl cycloalkyl amines 5.
N
NH2
N
37% formaldehyde,
formic acid,
100°C
BH3, THF
( )n
( )n
( )n
8
7
6
O
N
O
Cl
formicacid,
DMAP
N
N
N-methyl morpholine, CH2Cl2
H
BH3, THF
H
N
NH
O
( )n
( )n
10
9
Scheme 2. Synthesis of monomethyl and dimethyl derivatives from primary amines.

1440
L. Shao et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1438–1441
Table 1
IC50 values for inhibition of human recombinant SERT, NET, and DAT transporters and human and rat liver microsome metabolic stability (t1/2, min) for analogs of lead 1
R3
R4
R1
N
R2
( )n
Compd
N
R1
R2
R3
R4
IC50 (nM)
NE
In vitro microsomal stability (t1/2, min)
Human Rat
32
5-HT
DA
21
150
4
2
1
1
<1
1
11
12
13
14
15
16
3
3
3
3
3
3
3
H
H
H
H
CH3
H
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
169
201
158
651
19
85
273
19
36
4
250
>300
121
32
120
22
12
10
17
21
CH2CH3
Cyclopropyl
CH3
CH2CH3
CH2CH3
CH3
CH3
CH2CH3
25
66
35
156
2240
9
6
N
17
18
3
3
Cl
Cl
Cl
Cl
8571
9674
232
114
2
N
12
N
O
19
3
Cl
Cl
7932
790
2
N
20
3
Cl
Cl
299
39
<1
N
H
CH3
CH3
CH3
H
CH3
H
CH3
CH3
H
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
4
2
1
3
3
3
3
3
3
3
3
3
3
3
3
3
3
H
Cl
Cl
Cl
H
H
Cl
Cl
F
Cl
Cl
F
F
F
Cl
Cl
Cl
Cl
Cl
H
H
Cl
F
F
F
F
H
F
637
278
898
102
1870
55
767
145
31
689
57
2723
224
33
2783
63
22
75
9
82
26
395
42
884
17
11
170
57
3639
546
125
384
625
268
66
19
19
18
14
10
8
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
51
28
326
9990
269
26
10
137
61
2188
146
206
346
28
>300
23
51
8
208
21
19
>300
25
211
40
16
13
>300
15
55
CH3
H
CH3
CH3
CH3
CH3
CH3
H
H
CF3
H
H
H
CF3
249
1530
96
529
Table 2
IC50 values for inhibition of human recombinant SERT, NET, and DAT transporters and human and rat liver microsome metabolic stability (t1/2, min) for aromatic analogs
R1
Ar
N
R2
Compd
R1
R2
Ar
IC50 (nM)
NE
In vitro microsomal stability (t1/2, min)
5-HT
DA
Human
Rat
38
39
40
41
42
43
44
45
46
H
H
CH3
H
H
CH3
H
H
H
1-Naphthyl
1-Naphthyl
1-Naphthyl
2-Naphthyl
2-Naphthyl
2-Naphthyl
4-Biphenyl
4-Biphenyl
2-Thiophene
1517
1079
<1
305
34
5761
3177
20
232
295
7
8733
9217
9987
6043
1777
1
83
90
Not tested
>300
25
>300
136
20
91
75
265
Not tested
5
22
2
4
CH3
CH3
H
CH3
CH3
H
3
3
5
855
286
>10K
996
739
>10K
29
21
215
CH3
H
H
including biphenyl, thiophene and 1- and 2-naphthyl systems. The
1-naphthyl analog 40 was among the most potent compounds at
the three transporters, although the potency declined dramatically
for 1-naphthyl N-methyl analog 39. The 2-naphthyl analogs
showed potent inhibition across all the analogs tested, with the
N-CH3 analog 42 showing the best combination of potency and
in vitro metabolic stability.
The relative in vitro potencies at the three transporters and
in vitro metabolic profile of dichlorophenyl N-Me amine 1 and 2-
naphthyl cyclohexane N-Me amine 42 prompted us to evaluate
them in the tail suspension test15 in mice, an in vivo model
predictive of antidepressant activity in humans. HCl salts of both
1 and 42 were prepared and dosed 3, 10, and 30 mg/kg po.
A 30-min pre-treatment time was used based on exposure work

L. Shao et al. / Bioorg. Med. Chem. Lett. 21 (2011) 1438–1441
1441
Figure 3. (a) Compound 1 in the mouse TST at 3, 10, and 30 mpk po. DES = desipramine 100 mpk po. (b) Compound 1 in mouse locomotor activity assay at 5-min time point,
at 3, 10, and 30 min.
Figure 4. (a) Compound 42 in the mouse TST at 3, 10, and 30 mpk po. DES = desipramine 100 mpk po. (b) Compound 42 in mouse locomotor activity assay at 5 min time
point, at 3, 10, and 30 min.
predictive of antidepressant activity in humans. Our future efforts
will be targeted at fine tuning the potency and metabolic stability
of the scaffold, with an emphasis on increasing potency at SERT
Table 3
Whole brain and plasma levels of compounds 1 and 42 from TST animals
Compd
Dose (mg/kg), po
Plasma levels (ng/ml)
Brain levels (ng/g)
and NET and finding the optimal potency at DAT.
1
3
10
30
3
11
50
227
8
546
2166
7464
123
References and notes
42
1. El Mansari, M.; Guiard, B. P.; Chernoloz, O.; Ghanbari, R.; Katz, N.; Blier, P. CNS
Neuorosci. Ther. 2010, 16, (epub ahead of print).
2. Millan, M. Pharmacol. Ther. 2006, 110, 135.
10
30
21
120
306
2175
3. Blier, P.; Ward, H. E.; Trembley, P.; Laberge, L.; Herbert, C.; Bergeron, H. Am. J.
Psychiatry 2010, 167, 281.
4. Kapur, S.; Mann, J. J. Biol. Psychiatry 1992, 32, 1.
prior to the assay which showed maximal brain levels 30 min after
po dosing. Compound 1 (Fig. 3a) and 42 (Fig. 4a) showed a dose-
dependent reduction in immobility, which was statistically signif-
icant at the 30 mpk dose; the positive control desipramine also
showed a reduction in immobility. Both compounds showed brain
concentrations at the 30 mpk dose that were significantly higher
than their IC50’s (Table 3). The effect of compound 1 (Fig. 3b) and
42 (Fig. 4b) in the TST were also not due to a general locomotor
activation effect; the compounds did not significantly increase
spontaneous locomotor activity in vivo in the first 5 min at the
30 mpk dose—the 5-min time point was significant because that
is the amount of time the compounds were evaluated in the TST.
Our initial lead optimization efforts directed toward a novel tri-
ple reuptake inhibitor for depression achieved the goal of develop-
ing a novel cyclohexane alkyl amine chemotype. Exemplified by
dichlorophenyl methylamine 1 and 2-naphthyl methylamine 42,
we developed compounds with good potency for all three mono-
amine transporters, excellent in vitro metabolic stability, brain
penetration and, most importantly, efficacy in an in vivo model
5. (a) Lucas, M. C.; Weikert, R. J.; Carter, D. S.; Cai, H.-Y.; Greenhouse, R.; Iyer, P. S.;
Lin, C. J.; Lee, E. K.; Madera, A. M.; Moore, A.; Ozboya, K.; Schoenfeld, R. C.;
Steiner, S.; Zhai, Y.; Lynch, S. M. Bioorg. Med. Chem. Lett. 2010, 20, 5559; (b) Lee,
K.-H.; Park, C.-E.; Min, K.-H.; Shin, Y.-J.; Chung, C.-M.; Kim, H.-H.; Yoon, H.-J.;
Kim, W.; Ryu, E.-J.; Shin, Y.-J.; Nam, H.-S.; Cho, J.-W.; Lee, H.-Y. Bioorg. Med.
Chem. Lett. 2010, 20, 5567.
6. Skolnick, P.; Popik, P.; Janowsky, A.; Beer, B.; Lippa, A. S. Eur. J. Pharmacol. 2003,
461, 99.
7. (a) Beer, B.; Stark, J.; Krieter, P.; Czobor, P.; Beer, G.; Lippa, A.; Skolnick, P. J. Clin.
Pharmacol. 2004, 44, 1360; (b) Skolnick, P.; Popik, P.; Janowsky, A.; Beer, B.;
Lippa, A. S. Life Sci. 2003, 73, 3175.
8. DOV Pharmaceutical Press Release September 27, 2005.
9. Calderon, S. N.; Izenwasser, S.; Heller, B.; Gutkind, J. S.; Mattson, M. V.; Su, T.-P.;
Newman, A. H. J. Med. Chem. 1994, 37, 2285.
10. Eschweiler–Clarke reductive alkylation of amines. In Name Reactions for
Functional Group Transformations, John Wiley & Sons, Inc.: Hoboken, N. J.,
2007; pp 86–111.
11. De Luca, S.; Giacomelli, G.; Porcheddu, A.; Salaris, M. Synlett 2004, 2570.
12. Gu, H.; Wall, S.; Rudnick, G. J. Biol. Chem. 1994, 269, 7124.
13. Galli, A.; DeFelice, L. J.; Duke, B. J.; Moore, K. R.; Blakely, R. D. J. Exp. Biol. 1995,
198, 2197.
14. Pristupa, Z. B.; Wilson, J. M.; Hoffman, B. J.; Kish, S. J.; Niznik, H. B. Mol.
Pharmacol. 1994, 45, 125.
15. Steru, L.; Chermat, R.; Thierry, B.; Simon, P. Psychopharmacology 1985, 85, 367.