Studies on the structure-activity relationship of bicifadine analogs as monoamine transporter inhibitors

Article abstract of DOI:10.1016/j.bmcl.2008.05.077

Compounds with various activities and selectivities were discovered through structure-activity relationship studies of bicifadine analogs as monoamine transporter inhibitors. The norepinephrine-selective 2-thienyl compound S-6j was efficacious in a rodent

Full text of DOI:10.1016/j.bmcl.2008.05.077

Bioorganic & Medicinal Chemistry Letters 18 (2008) 3682–3686
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Studies on the structure–activity relationship of bicifadine analogs
as monoamine transporter inhibitors
Mingzhu Zhang a, Florence Jovic a, Troy Vickers a, Brian Dyck a, Junko Tamiya a, Jonathan Grey a,
Joe A. Tran a, Beth A. Fleck b, Rebecca Pick c, Alan C. Foster c, Chen Chen a,
*
a Department of Medicinal Chemistry, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
b Department of Pharmacology, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
c Department of Neuroscience, Neurocrine Biosciences, Inc., 12790 El Camino Real, San Diego, CA 92130, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Compounds with various activities and selectivities were discovered through structure–activity relation-
ship studies of bicifadine analogs as monoamine transporter inhibitors. The norepinephrine-selective
2-thienyl compound S-6j was efficacious in a rodent pain model.
Received 26 April 2008
Revised 16 May 2008
Accepted 19 May 2008
Available online 23 May 2008
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords:
Structure–activity relationship
Bicifadine
Monoamine transporters
Inhibitor
Potency
Selectivity
Pain
Bicifadine [1, ( )-1-(4-methylphenyl)-3-azabiocyclo[3.1.0]hex-
ane hydrochloride, DOV 220,075, Fig. 1],1 an inhibitor of norepi-
nephrine and serotonin reuptake transporters (NET and SERT), is
being developed for the treatment of acute and chronic pain. Bicif-
adine is active in models of neuropathic pain with no evidence of
abuse liability potential.2 Clinically, it has been shown to be effec-
tive in the treatment of acute dental pain3 and bunionectomy
pain.4,5 Bicifadine has also been reported to be as effective as the
standard of care in reducing chronic lower back pain.6
Bicifadine inhibits monoamine neurotransmitter uptake by re-
combinant human transporters in vitro with a relative potency of
NET (IC50 = 55 nM) > SERT (IC50 = 120 nM) > DAT (IC50 = 910 nM).7
This in vitro profile is supported by microdialysis studies in freely
moving rats, where bicifadine (20 mg/kg i.p.) increased extrasy-
naptic norepinephrine (NE) and serotonin (SER) levels in the pre-
frontal cortex, NE levels in the locus coeruleus, and dopamine
(DA) levels in the striatum.2 In comparison, DOV 216,303 (6b), a
close analog of bicifadine, is known as a triple inhibitor (NET
IC50 = 20.3 nM, SERT IC50 = 13.8 nM, DAT IC50 = 78 nM)8,9 and is
being studied for the treatment of major depression.10 Both of its
individual enantiomers, DOV 21,947 (S-6b)11–13 and DOV 102,677
(R-6b)14 (Fig. 1), are profiled as monoamine transporter inhibitors.
DOV 21,947 (S-6b) is also undergoing clinical evaluation for the
treatment of pain and other diseases related to these
neurotransporters.15
Recently, a dual NET/SERT inhibitor duloxetine (3) was ap-
proved by the FDA for the treatment of diabetic neuropathy.16 In
addition, experience with reboxetine (5) suggests that this norad-
renergic antidepressant may have efficacy in the treatment of
chronic pain in patients with depression.17 Like reboxetine, ato-
moxetine (4) is also a NET-selective inhibitor and is used for the
treatment of Attention Deficit Hyperactivity Disorder (ADHD),18
demonstrating the therapeutic potential of NET inhibitors.19
Bicifadine is a very small molecule (MW = 173) with moderate
lipophilicity (cLogP = 2.0). This feature is distinctly different from
the highly lipophilic atomoxetine (cLogP = 3.3) and duloxetine
(cLogP = 3.7) which have two lipophilic aromatic groups (Fig. 1).
However, the metabolic and pharmacokinetic properties of bicifa-
dine20,21 and DOV 216,30322 are also significantly different from
the structurally related milnacipran (2),23 which is less lipophilic
(cLogP = 1.2). Although bicifadine and DOV 216,303 were initially
discovered in the early 1980s,1 the structure–activity relationship
of its analogs at the transporter levels has not been reported. Here,
we describe the synthesis and SAR studies of a series of bicifadine
analogs as monoamine transporter inhibitors in our efforts to
search for NET active compounds.
* Corresponding author. Tel.: +1 858 617 7600; fax: +1 858 617 7602.
E-mail address: cchen@neurocrine.com (C. Chen).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.05.077

M. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3682–3686
3683
X
6
1
5
O
NH2
O
4
2
3
N
N
NH
H
S
1 (bicifadine): X = 4-Me
6b (DOV 216,303): X = 3,4-Cl
2 (milnacipran)
3 (duloxetine)
O
O
Cl
Cl
Cl
5R
5S
O
Cl
N
H
NH
N
H
NH
O
5 (reboxetine: S,S-
and R,R-isomers)
R-6b (DOV 102,667)
S-6b (DOV 21,947)
4 (atomoxetine)
Figure 1. Chemical structures of bicifadine (1) and some other monoamine transporter inhibitors.
The target compounds 6–10 as pairs of enantiomers were syn-
thesized from arylacetic acids 14 as shown in Scheme 1. Alkyla-
tions of 14 with allyl bromides provided the ester intermediates
which were converted to the corresponding diazo compounds 15
using a sulfonylazide. Rhodium-catalyzed cyclizations of 15 gave
the lactones 16.24 Elaboration of 16 by ring opening with potas-
sium phthalimide, followed by activation of the carboxylic acid
and deprotection of the amine resulted in the lactams 17. Finally,
the reduction of 17 with lithium aluminumhydride provided the
bicifadine analogs 6–10.
Alternately, compounds 6 were prepared from 1-benzyl-3-oxo-
pyrrolidine 18 as shown in Scheme 2. Conversion of 18 to the tri-
flate 19 was achieved under basic conditions.25 Coupling
reactions of 19 with various arylboronic acids using a palladium
catalyst provided the corresponding arylolefins 20, which were
subjected to cyclopropanations26 to give the bicycles 6 as a mixture
of 5S- and 5R-isomers after debenzylation. N-Methylation of 6j
(Ar = 2-thienyl) by a reductive alkylation with formaldehyde gave
the tertiary amine 13.
Compounds S-6 and R-6 were synthesized from arylacetonitr-
iles 21 using a stereo-selective procedure12 as shown in Scheme
3. Cyclizations of 21 with S-(+)- or R-(À)-epichlorohydrin pro-
moted by NaHMDS provided the stereoisomers S-16 or R-16,
respectively. Elaboration of these intermediates using a procedure
described in Scheme 1 afforded the single isomers S-6 and R-6.
The cis- and trans-4-methyl analogs of 6b were synthesized
from the lactone 16 (Scheme 4). Ring opening of 16 with diethyl-
amine gave an alcohol which was oxidized with TPAP to give the
aldehyde 22. The Grignard reaction of 22 with methylmagnesium
bromide was stereo-selective, and the secondary alcohol 23-I
15a: R1 = R2 = R3 = H
N2
R3
15b: R1 = R2 = H, R3 = F
a
O
R1
OH
15c: R1 = R2 = Me, R3 = H
E-15d: R1 = Ph, R2 = R3 = H
E-15e: R1 = Me, R2 = R3 = H
Z-15e: R1 = R3 = H, R2 = Me
Ar
Ar
O
R2
O
14
6 (+): R1 = R2 = R3 = H
R2
R3
R1 R2
R3
R1
R2
R1
7 (+): R1 = R2 = H, R3 = F
b
c
d
Ar
R3
Ar
Ar
O
8 (+): R1 = R2 = Me, R3 = H
cis-9 (+): R1 = Ph, R2 = R3 = H
cis-10 (+): R1 = Me, R2 = R3 = H
trans-10 (+): R1 = R3 = H, R2 = Me
O
N
H
N
H
17 (+)
O
16 (+)
Scheme 1. Reagents and conditions: (a) i—BrCH2C(R3)@CR1R2/CsCO3/acetone/rt, 10 h; ii—4-AcNHC6H4SO2N3/DBU/ACN/0 °C to rt, 3 h; (b) Rh(OAc)2/DCM/reflux, 3 h;
(c) i—potassium phthalimide/DMF/140 °C, 16 h; ii—(COCl)2/DMF (cat.)/DCM/0 °C to rt, 2 h; iii—MeONHMe Á HCl/Et3N/DCM/0 °C to rt, 2 h; iv—MeNHNH2/EtOH/rt, 20 h;
(d) LiAlH4/THF/reflux, 2 h.
Ar
TfO
O
Ar
5
c
d
Ar
a
b
N
H
N
Bn
N
N
Bn
18
N
Bn
19
13 (+)
6 (+)
20
Scheme 2. Reagents and conditions: (a) i—KHMDS/THF/À78 °C, 1 h; ii—PhN(Tf)2/THF/0 °C, 3 h; (b) ArB(OH)2/Pd(PPh3)4/CsF/THF/reflux, 8 h; (c) i—CH2I2/Et2Zn/DCM/0 °C,
0.5 h, then rt, 18 h; ii—CH3CH(Cl)OCOCl/DIEA/DCM/rt, 16 h; (d) For 6j: CH2O/B10H14/MeOH/H2O/rt, 1 h.

3684
M. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3682–3686
Ar
Ar
Ar
O
Ar
O
b
5R
5
R
5S
a
5S
or
or
Ar
CN
21
N
H
N
H
O
O
R
-16
S
-16
R-6
S-6
Scheme 3. Reagents and conditions: (a) i—NaHMDS/THF/0 °C; ii—(S)-(+)- or (R)-(À)-epichlorohydrin/0 °C to rt, 16 h; iii—KOH/EtOH/reflux, 8 h; iv—12 NHCl/0 °C to rt, 2.5 h;
(b) see Scheme 1.
S
S
N
S
N
S
b
a
d
R5
R4
R5
R4
O
O
O
O
N
H
O
HO
16a (+)
cis-11: R4 = Me, R5 = H
trans-11: R4 = H, R5 = Me
22
23-I: R4 = Me, R5 = H
23-II: R4 = H, R5 = Me
c
Scheme 4. Reagents and conditions: (a) i—Et2NH/Me3Al/toluene/reflux, 16 h; ii—TPAP/NMO/molecular sieves/DCM/0 °C to rt, 16 h; (b) MeMgBr/THF/À78 °C, 1 h, then rt,
16 h; (c) i—PDC/CH2Cl2/rt, 16 h; ii—Dibal-H/THF/À78 °C, 2 h; (d) i—NaN3/PPh3/CBr4/DMF/rt, 16 h; ii—H2/Pd-d/MeOH/rt, 16 h; iii—Et3N/toluene/reflux, 20 h; iv—LiAlH4/THF/
reflux, 2 h.
was purified to give a pair of diastereoisomers.27 23-I was con-
verted to the corresponding azide with the retention of configura-
tion.28 Hydrogenation of this azide intermediate gave an amine
which was cyclized to the corresponding lactam, followed by a
LiAlH4 reduction to give the methyl derivative cis-11. Alternatively,
oxidation of 23-I with PDC gave a ketone which was reduced with
Dibal-H to give 23-II, which was converted to the corresponding
trans-11.
The 2-methyl analog 12 was prepared from the lactam 17a as
shown in Scheme 5. Reaction of 17a with (Boc)2O, followed by a
MeLi addition afforded the ketone 24,29 which was reduced with
KBH4 to give the alcohol 25 as a pair of stereoisomers. Treatment
of 25 with methanesulfonyl chloride, followed by trifluoroacetic
acid, gave 12 as a pair of cis-isomers.
The activity of bicifadine 1 at the cloned human monoamine
transporters was recently reported.2,7 Inhibition of rat brain synap-
tosomal uptake of norepinephrine and serotonin was reported by
Beer et al. in a patent application and the IC50 values of 1 were
215 and 96 nM at NET and SERT, respectively.30 In comparison,
the unsubstituted phenyl compound 6a displayed IC50 values of
401 and 470 nM, respectively, indicating the additional methyl
group of 1 improves SERT activity by 5-fold but only 2-fold at
NET. In our assays using cloned human transporters,31 6a was
To explore the influence of a small substituent at the core struc-
ture, compounds 7–10 were prepared, and their activities were
compared with 6a and 6b. In human subjects, bicifadine is oxidized
to the corresponding 4-oxo metabolite, and both had similar plas-
ma concentrations.21 Compound 7 with a fluorine at the 5-position
was designed to potentially reduce the rate of this oxidation. How-
ever, 7 was substantially less potent than 6a, despite the fact that
the fluorine atom is only about 40% larger in size than hydrogen.
Incorporation of two methyl groups at the 6-position of 6a almost
abolished its activity at NET (8, IC50 = 7200 nM). However, a 6-phe-
nyl group at the same side of the 1-phenyl of 6a improved its po-
tency, especially at SERT (cis-9a, IC50 = 240 nM). These results
indicate that a 6-methyl group at the opposite side of the 1-phenyl
of 6a is detrimental to its inhibitory activity at NET. This hypothe-
sis is supported by a pair of 6-methyl analogs of 6b. Thus, cis-10
was almost 20-fold more potent than trans-10 at NET, although
these two stereoisomers showed similar potencies at SERT and
DAT. The cis-phenyl analog cis-9b displayed a slightly higher activ-
ity at NET than 6b but was less potent at SERT. It is worth noting
that bicifadine has polymorphism in crystalline forms, which is
mainly caused by the different orientation of its aryl group.32 The
fact that trans-10 is much less potent than cis-10 suggests that a
small steric effect of the trans-methyl of 10 reduces its interaction
with both NET and SERT, while the cis-methyl group might affect
the orientation of the phenyl ring that is required by SERT.
somewhat
NET-selective
(NET = 350 nM,
SERT = 5200 nM,
DAT = 2700 nM, Table 1) at the cloned human monoamine trans-
porters. The lipophilic 3,4-dichloro analog 6b (DOV 216,303) was
much more potent at all three transporters compared to 6a, partic-
ularly at SERT (IC50 = 27 nM). Between the individual stereoiso-
mers, the 1R,5S-compound S-6b (DOV 21,947) was about 8-fold
more potent than the 1S,5R-isomer R-6b (DOV 102,667) at both
NET and SERT. Although these compounds are known as triple
inhibitors,22 S-6b was somewhat more potent at SERT
(IC50 = 8.6 nM) than at the other two transporters (NET
IC50 = 51 nM, DAT IC50 = 260 nM) in our assays.
SAR of different phenyl substitutions showed that the ethylen-
edioxyphenyl derivative 6c was much less potent than 6a at NET.
This aryl group displays a 6-fold improvement at milnacipran
2,33 indicating different pharmacophores between these two tem-
plates despite some similarity in chemical structure. Compared to
the biphenyl compound 6d, the naphthyl analog 6e was much
more potent at all three transporters. Among the bicyclic heterocy-
cles 6f–6i, the hydrophilic 6-quinolinyl 6f showed a weak potency,
while the lipophilic 2-benzothienyl 6h had IC50 values around
S
S
S
S
c
b
a
NHBoc
NHBoc
O
N
H
N
H
O
OH
25
17a (+)
24
12
Scheme 5. Reagents and conditions: (a) i—(Boc)2O/DMAP/CAN/rt, 16 h; ii—MeLi/THF/À78 °C to rt, 1 h; (b) KBH4/MeOH, rt, 1 h; (c) i—MsCl/Et3N/DCM/rt, 1 h; ii—TFA/DCM/rt,
2 h.

M. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3682–3686
3685
Table 1
SAR of bicifadine analogs at monoamine transportersa
6
R
1
Ar
5
4
2
3
N
6-13
H
Compound
Ar
R
NET IC50 (nM)
SERT IC50 (nM)
DAT IC50 (nM)
cLogP
6ab
7
8
cis-9a
6bb,c
R-6bd
S-6bd
trans-10
cis-10
cis-9b
6c
6d
6e
6f
6g
6h
6i
6j
R-6j
S-6j
trans-11
cis-11
cis-12
13
17a
6k
R-6k
S-6k
6l
6m
6n
6o
R-6l
R-6p
R-6q
R-6r
S-6s
S-6t
S,S-5
Phenyl
Phenyl
Phenyl
Phenyl
Phenyl, 3,4-dichloro
Phenyl, 3,4-dichloro
Phenyl, 3,4-dichloro
Phenyl, 3,4-dichloro
Phenyl, 3,4-dichloro
Phenyl, 3,4-dichloro
Phenyl, 3,4-ethylenedioxy
Phenyl, 4-phenyl
2-Naphthyl
H
350
1800
7200
120
88
430
51
500
29
5200
2900
1800
240
27
66
8.6
200
190
350
1500
160
50
640
140
2700
>10,000
>10,000
8,700
380
330
260
500
400
1.5
1.3
2.5
3.1
2.6
2.6
2.6
3.1
3.1
4.2
1.2
3.3
2.7
1.4
2.0
3.7
3.7
1.2
1.2
1.2
1.7
1.7
1.7
1.6
À0.3
1.8
2.6
1.8
2
5-F
6,6-Me
6-Ph
H
H
H
6-Me
6-Me
6-Ph
H
H
H
H
H
H
H
H
H
H
4-Me
4-Me
2-Me
3-Me
2-Oxo
H
H
H
H
H
H
H
H
H
H
H
H
H
34
360
3500
360
36
1400
48
>10,000
2300
190
3900
330
6-Quinolinyl
2-Benzofuranyl
2-Benzothienyl
3-Benzothienyl
2-Thienyl
2-Thienyl
2-Thienyl
2-Thienyl
2-Thienyl
2-Thienyl
2-Thienyl
53
71
73
180
780
220
130
150
92
320
560
150
1600
>10,000
130
590
77
190
5300
6800
3100
340
300
4800
2000
470
67
4500
4900
1900
7600
6000
5800
6300
>10,000
190
1300
81
140
4200
>10,000
190
7500
6200
2400
3400
9500
8900
>10,000
>10,000
3300
2500
1500
2400
>10,000
>10,000
>10,000
1700
8200
9100
>10,000
>10,000
420
2-Thienyl
2-Thienyl, 5-chloro
2-Thienyl, 5-chloro
2-Thienyl, 5-chloro
2-Thienyl, 5-bromo
2-Thienyl, 3,5-dichloro
2-Thienyl, 4-methyl
2-Thienyl, 5-trifluoromethyl
2-Thienyl, 5-bromo
3-Thienyl
5-Benzofuranyl, 2,3-dihydro
5-Indenyl, 1,2-dihydro
2-Thienyl, 5-fluoro
2-Benzothienyl, 5-fluoro
2.4
1.6
2.2
2
1.2
1.4
2.6
1.5
3.7
2.8
380
6800
610
97
8100
33
3.1
5200
>10,000
a
Data are average of two or more independent measurements.
b
The following IC50 values at rat synaptosomal preparations were reported by Beer and Epstein.30 For 6a: NET = 401 nM, SERT = 470 nM; for 1: NET = 215 nM,
SERT = 96 nM; for 6b: NET = 145 nM, SERT = 26 nM; DAT = 232 nM.
c
The following data for 6b at the cloned human monoamine transporters were reported by Skolnick et al.9 NET = 20.3 nM, SERT = 13.8 nM, DAT = 78 nM.
d
The following data at the cloned human monoamine transporters were reported by Skolnick et al., for S-6b:11 NET = 22.8 nM, SERT = 12.3 nM, DAT = 96 nM; for R-6b:14
NET = 103 nM, SERT = 133 nM, DAT = 129 nM.
100 nM for all three transporters. These results suggest that a lipo-
philic aromatic group generally increases potency but not
selectivity.
log of 6j was inactive (17a), confirming the importance of the basic
amine. Chlorine substitution at the 5-position of the 2-thienyl ring
of 6j resulted in an about 20-fold improvement in SERT activity
(6k, IC50 = 190 nM), further demonstrating that a lipophilic aro-
matic ring is preferred for SERT activity. For the two individual
stereoisomers, the 1S,5S-compound S-6k was more potent than
the 1R,5R-isomer R-6k at all three transporters. Compound S-6k
had an equal potency at NET and SERT and was about 20-fold
selective over DAT. The bromo compound 6l displayed a similar
profile to its chloro analog 6k. Unexpectedly, the 3,5-dichloro-2-
thienyl compound 6m had very low activities at all three trans-
porters, suggesting that a steric effect of the 3-chlorine limits its
rotation to a favored orientation. The 4-methyl 6n and the 5-tri-
fluoromethyl-2-thienyl compound 6o were also weakly active at
NET.
The 2-thienyl compound 6j displayed an IC50 of 130 nM at NET
and was over 30-fold selective over SERT and DAT. The two indi-
vidual enantiomers R-6j and S-6j were separated using chiral HPLC
and were found to possess NET selectivity. Thus 1S,5S-isomer S-6j,
its stereochemistry was confirmed by a chiral synthesis using the
procedure described in Scheme 3, was slightly more potent than
the 1R,5R-isomer R-6j. Since 6j possessed the NET-selectivity and
a good physicochemical property (cLogP = 1.2), we further ex-
plored the effect of a methyl substitution on its transporter activ-
ity. A conformational analysis of 6j showed that the aromatic
thienyl group was freely rotatable despite its compact structure,
and a small methyl group might slow down the rotation. Both
cis-11 and trans-11 had reduced potencies compared to 6j, while
cis-12 had a comparable potency. N-Methylation of 6j also reduced
its potency at NET (13, NET IC50 = 1600 nM), while the 2-oxo ana-
For the chiral compounds synthesized, the 5R-compounds R-6l,
and R-6p–6r were not very active at NET, including the 3-thienyl R-
6p (NET IC50 = 300 nM). The 5-fluoro-2-thienyl S-6s (NET

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M. Zhang et al. / Bioorg. Med. Chem. Lett. 18 (2008) 3682–3686
120
100
80
60
40
20
0
Acknowledgments
Vehicle
The authors are indebted to Mr. Michael Johns and Ms. Hua
Wang for their technical assistance.
References and notes
*
*
1. Epstein, J. W.; Brabander, H. J.; Fanshawe, W. J.; Hofmann, C. M.; McKenzie, T.
C.; Safir, S. R.; Osterberg, A. C.; Cosulich, D. B.; Lovell, F. M. J. Med. Chem. 1981,
24, 481.
*
2. Basile, A. S.; Janowsky, A.; Golembiowska, K.; Kowalska, M.; Tam, E.;
Benveniste, M.; Popik, P.; Nikiforuk, A.; Krawczyk, M.; Nowak, G.; Krieter, P.
A.; Lippa, A. S.; Skolnick, P.; Koustova, E. J. Pharmacol. Exp. Ther. 2007, 321, 1208.
3. Stern, W.; Czobor, P.; Stark, J.; Krieter, P. 11th World Congress International
Association for the Study of Pain, Sydney, Australia, 2005, Abstracts, p. 111.
4. Riff, D.; Huang, N.; Czobor, P.; Stern, W. J. Pain 2006, 7, S40.
5. Wang, R. I.; Johnson, R. P.; Lee, L. C.; Wang, E. M. J. Clin. Pharmacol. 1982, 22,
160.
S-6j (30mg/kg)
S-6j (60 mg/kg)
5 (30 mg/kg)
6. Stern, W.; Pontecorvo, M.; Czobor, P.; Waldron, D.; Apfel, S. J. Pain 2006, 7, S40.
7. Koustova, E.; Basile, A. S.; Lippa, A.; Skolnick, P. The 25th Annual Scientific
Meeting of the American Pain Society, San Antonio, May 3–6, 2006. Poster #
666.
8. Skolnick, P.; Krieter, P.; Tizzano, J.; Basile, A.; Popik, P.; Czobor, P.; Lippa, A. CNS
Drug Rev. 2006, 12, 123.
Figure 2. Compound S-6j in comparison with S,S-5 in phase 2 of the formalin test in
rats. One hour after administration of S-6j or S,S-5, mice received a mid-plantar
injection of 5% formalin solution. Hindpaw flinching number was recorded between
10 and 40 min after formalin injection.
9. Skolnick, P.; Popik, P.; Janowsky, A.; Beer, B.; Lippa, A. S. Life Sci. 2003, 73, 3175.
10. Chen, Z.; Skolnick, P. Expert Opin. Investig. Drugs 2007, 16, 1365.
11. Skolnick, P.; Popik, P.; Janowsky, A.; Beer, B.; Lippa, A. S. Eur. J. Pharmacol. 2003,
461, 99.
12. Xu, F.; Murry, J. A.; Simmons, B.; Corley, E.; Fitch, K.; Karady, S.; Tschaen, D. Org.
Lett. 2006, 8, 3885.
13. Tizzano, J. P.; Stribling, D. S.; Perez-Tilve, D.; Strack, A.; Frassetto, A.; Chen, R. Z.;
Fong, T. M.; Shearman, L.; Krieter, P. A.; Tschöp, M. H.; Skolnick, P.; Basile, A. S.
J. Pharmacol. Exp. Ther. 2008, 324, 1111.
14. Popik, P.; Krawczyk, M.; Golembiowska, K.; Nowak, G.; Janowsky, A.; Skolnick,
P.; Lippa, A.; Basile, A. S. Cell Mol. Neurobiol. 2006, 26, 857.
15. Skolnick, P.; Basile, A. S. CNS Neurol. Disord. Drug Targets 2007, 6, 141.
16. Smith, T. R. Expert Opin. Pharmacother. 2006, 7, 215.
IC50 = 470 nM) were significantly less potent than S-6j, indicative
of an electronic requirement of the aromatic ring. The 5-fluoro-2-
benzothienyl S-6t was quite potent as a dual NET/SERT inhibitor.
However, its selectivity over DAT was slightly lower than the 5-
chloro-2-thienyl S-6k. In general, 5S-isomers were more active
than the 5R-counterparts.
The moderately lipophilic S-6j was further profiled because its
NET activity matched with DOV 216,303 (6b, NET IC50 = 88 nM).
In an in vitro human liver microsomal assay, S-6j displayed moder-
ate metabolic stability with a CLsys of 12.7 mL/min.kg. In a Caco-2
monolayer assay, S-6j showed high permeability (Papp = 17.6 Â
10À6 cm/s) and low efflux ratio (0.7).
17. Krell, H. V.; Leuchter, A. F.; Cook, I. A.; Abrams, M. Psychosomatics 2005, 46, 379.
18. Hah, M.; Chang, K. J. Child. Adolesc. Psychopharmacol. 2005, 15, 996.
19. Zhou, J. Drugs Future 2004, 29, 1235.
20. Erickson, D. A.; Hollfelder, S.; Tenge, J.; Gohdes, M.; Burkhardt, J. J.; Krieter, P. A.
Drug Metab. Dispos. 2007, 35, 2232.
21. (a) Buice, R.; Krieter, P. The 25th Annual Scientific Meeting of the American
Pain Society, San Antonio, May 3–6, 2006. Poster # 753.; (b) Musick, T. J.;
Gohdes, M.; Duffy, A.; Erickson, D. A.; Krieter, P. A. Drug Metab. Dispos.
2008, 36, 241; (c) Krieter, P. A.; Gohdes, M.; Musick, T. J.; Duncanson, F. P.;
Bridson, W. E. Drug Metab. Dispos. 2008, 36, 252.
22. Beer, B.; Stark, J.; Krieter, P.; Czobor, P.; Beer, G.; Lippa, A.; Skolnick, P. J. Clin.
Pharmacol. 2004, 44, 1360.
23. Puozzo, C.; Panconi, E.; Deprez, D. Int. Clin. Psychopharmacol. 2002, 17, S25.
24. (a) Doyle, M. P.; Davies, S. B.; Hu, W. Org. Lett. 2000, 2, 1145; (b) Doyle, M. P.;
Wu, W. Adv. Synth. Catal. 2001, 343, 299.
25. Fraley, M. E.; Garbaccio, R. M.; Arrington, K. L.; Hoffman, W. F.; Tasber, E. S.;
Coleman, P. J.; Buser, C. A.; Walsh, E. S.; Hamilton, K.; Fernandes, C.; Schaber, M.
D.; Lobell, R. B.; Tao, W.; South, V. J.; Yan, Y.; Kuo, L. C.; Prueksaritanont, T.; Shu,
C.; Torrent, M.; Heimbrook, D. C.; Kohl, N. E.; Huber, H. E.; Hartman, G. D.
Bioorg. Med. Chem. Lett. 2006, 16, 1775.
26. Miura, T.; Murakami, Y.; Imai, N. Tetrahedron Asymmetry 2006, 17, 3067.
27. Shuto, S.; Ono, S.; Hase, Y.; Kamiyama, N.; Takada, H.; Yamashita, K.; Matsuda,
A. J. Org. Chem. 1996, 61, 915.
28. Kazuta, Y.; Tsujita, R.; Ogawa, K.; Hokonohara, T.; Yamashita, K.; Morino, K.;
Matsuda, A.; Shuto, S. Bioorg. Med. Chem. 2002, 10, 1777.
29. Bonnaud, B.; Bigg, D. C. H. J. Heterocycl. Chem. 1993, 30, 505.
30. Beer, B.; Epstein, J. W. US 6,204,284 B1, 2001.
The antinociceptive efficacy of bicifadine has been examined
by Basile et al. in the formalin model of persistent pain processes,
and their results show that the antinociceptive actions of bicifa-
dine in formalin-treated mice are more pronounced in Phase 2
than in Phase 1, with all doses of bicifadine (5–60 mg/kg) signif-
icantly reducing the time spent licking by as much as 89% at
60 mg/kg.2 We studied S-6j in the formalin model to compare
its effects with the NET-selective S,S-reboxetine (S,S-5). Oral
administration of S-6j at 30 mg/kg reduced the number of hind-
paw flinches as much as 40% compared to vehicles, which was
only slightly less effective than S,S-reboxetine at the same dose.
Increase of S-6j dose to 60 mg/kg had no significant additional ef-
fect (Fig. 2).
In conclusion, a series of bicifadine analogs were synthesized
and profiled as monoamine transporter inhibitors. Lipophilic
aromatic compounds such as 2-naphthyl and 2-benzothienyl
derivatives possessed high activity at NET and SERT and low
selectivity over DAT. The 1S,5S-isomer S-6j displayed a good po-
tency at NET and selectivity over SERT and DAT. S-6j also dem-
onstrated efficacy in a rat formalin model with comparable
activity to S,S-reboxetine.
31. For experimental detail, see WO 07098356.
32. McArdle, P.; Gilligan, K.; Cunningham, D.; Ryder, A. Appl. Spectrosc. 2005, 59,
1365.
33. Tamiya, J.; Dyck, B.; Zhang, M.; Jovic, F.; Grey, J.; Vickers, T.; Fleck, B. A.;
Aparicio, A.; Foster, A. C.; Chen, C. Bioorg. Med. Chem. Lett., 2008, 18, 3328.