Heterocyclic cycloalkanol ethylamines as norepinephrine reuptake inhibitors

Article abstract of DOI:10.1016/j.bmcl.2010.03.059

A series of heterocyclic cycloalkanol ethylamines have been prepared to expand our norepinephrine reuptake inhibitor (NRI) program. Synthesis of a variety of heterocycles identified (+)-S-21, a potent NRI efficacious in an animal model for thermoregulatory dysfunction.

Full text of DOI:10.1016/j.bmcl.2010.03.059

Bioorganic & Medicinal Chemistry Letters 20 (2010) 2809–2812
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Heterocyclic cycloalkanol ethylamines as norepinephrine reuptake inhibitors
a
b
b
b
Joseph P. Sabatucci a, , Paige E. Mahaney , Jennifer Leiter , Grace Johnston , Kevin Burroughs ,
*
Scott Cosmi b, Yingru Zhang a, Douglas Ho c, Darlene C. Deecher b, Eugene Trybulski a
a Chemical Sciences, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA
b Department of Women’s Health and Musculoskeletal Biology, Wyeth Research, 500 Arcola Road, Collegeville, PA 19426, USA
c Department of Chemistry, Princeton University, Princeton, NJ 08544, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of heterocyclic cycloalkanol ethylamines have been prepared to expand our norepinephrine
reuptake inhibitor (NRI) program. Synthesis of a variety of heterocycles identified (+)-S-21, a potent
NRI efficacious in an animal model for thermoregulatory dysfunction.
Received 16 February 2010
Revised 10 March 2010
Accepted 11 March 2010
Available online 15 March 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Monoamine reuptake inhibitors
Selective norepinephrine reuptake inhibitor
Cycloalkano ethylamines
Table 1
The cycloalkanol ethylamine scaffold was successfully utilized in
the discovery and development of dual serotonin (5-HT)/norepi-
nephrine (NE) reuptake inhibitors (SNRIs).1 Drugs such as venlafax-
ine (1) and duloxetine (2) possessing norepinephrine reuptake
inhibition, either selectively or in combination with serotonin reup-
take inhibition were approved for major depressive disorder (MDD).
Recently, SNRIs have been evaluated clinically for the treatment of
stress urinary incontinence (SUI),2 and fibromyalgia.3 Further stud-
ies show that estrogen may stimulate the activity of both the norepi-
nephrine and/or serotonin neurotransmitter pathways.4,5
Inhibitory effect at human norepinephrine, serotonin, and dopamine transporters
HO
S
HN
O
N
O
1
2
Compounds containing an aryl propanamine pharmacophore
are known to have monoamine reuptake properties.6 Efforts to dis-
cover novel selective NRIs using the cycloalkanol ethylamine scaf-
fold as exemplified by venlafaxine (1) (Table 1) resulted in the
identification of piperazine analogue 3.7 A program to further ex-
pand the cycloalkanol ethylamine SAR by designing selective NRIs
was initiated. Consequently, we have structurally extended the
SAR of this template in a variety of ways to maintain potency
and achieve better norepinephrine transporter (NET) selectivity
over serotonin (SERT) and dopamine transporters (DAT).
HO
N
N
Cl
3
Compound 3 while having potent NRI activity with excellent
selectivity over SERT.7 also had affinity for DAT, which was outside
the therapeutic goals of the program. In addition, 3 had poor
microsomal stability in rats (t1/2 <1 min).
a
b
c
Compd
hNET IC50 (nM)
hSERT IC50 (nM)
hDAT IC50 (nM)
1
2
3
535
4
56
27
3
>2000
>10,000
>1000
247
Consequently, structural modifications to eliminate DAT bind-
ing while improving oral bioavailability were explored.
a
Inhibition of norepinephrine uptake in MDCK-Net6 cells, stably transfected
with human NET. Desipramine (IC50 = 3.4 1.6 nM) was used as a standard.
b
Inhibition of serotonin uptake in JAR cells, natively expressing human SERT.
Fluoxetine (IC50 = 9.4 3.1 nM) was used as a standard.
* Corresponding author. Tel.: +1 484 865 4410; fax: +1 484 865 9398.
E-mail addresses: sabatuj@wyeth.com, sabatuccij@comcast.net (J.P. Sabatucci).
c
Inhibition of [3H]WIN-35,428 binding to membranes from CHO cells expressing
recombinant hDAT. Mazindol (22.1 6.5 nM) was used as a standard.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.03.059

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J. P. Sabatucci et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2809–2812
R
À78 °C in THF followed by addition of cyclohexanone provided
R
R
N
N
N
the alkanols 8a,b. The piperidine amides 9a,b were formed by stan-
dard peptide coupling with BOP reagent. The target products 10a,b
were generated by reduction of the amide with borane in THF.
Addition of HCl in ether removed the BOC group and in the case
of 10a, the protecting groups were removed by treatment with
HCl in ether.
N
N
N
OH
OH
OH
S
N
N
R2
4
5
6
In cases where the aryl acetic acid was unavailable or was diffi-
cult to handle, an alternative synthesis was employed. The quino-
line system 14 was made from the aryl aldehyde 11 by conversion
to the dibromo olefin 12.10 This intermediate was then converted
to the aryl acetyl amide 13 by treatment with Boc-piperazine
and water. This route avoids handling of amino acid intermediates
which may provide low if any yield while attempting to alkylate
with cyclohexanone. The desired cyclohexanol ring was then
added via alkylation with LDA. The target compound 14 was then
made via BH3ÁTHF reduction as before.
Figure 1. Selected heterocyclic targets for NRI.
Previous SAR in this series established the piperazine moiety to
impart hNET selectivity over hSERT.8,9 Moreover, DAT could be
manipulated by aromatic substitution, particularly in the 3-posi-
tion. We therefore concentrated our efforts on targets replacing
the 3-chloro phenyl group with indole (4), quinoline (5), and thio-
phene (6) cores that would further explore this topology (Fig. 1).
Scheme 1 illustrates the standard synthesis of the nitrogen
based analogues from commercially available or synthesized aryl
acetic acids. Treatment of the aryl acetic acids 7a,b with LDA at
Scheme 2 depicts the synthesis of key thiophene analogues. The
2-position of a 3-substituted thiophene is the more reactive posi-
tion therefore chlorination with 1 equiv of NCS gave exclusively
O
HO
OH
OH
HO2C
BocN
N
HN
N
CO2H
a
c
b
N
R
N
R
N
R
N
R
8a
8b
10a R=H
10b
7a R=t-BuSiMe3
7b R=Me
9a
9b
Boc
H
N
N
N
O
N
d
a,c
OH
e
CHO
Br
Br
N
N
N
N
11
12
13
14
Scheme 1. Synthesis of indole and isoquinoline analogues. Reagents and conditions: (a) LDA, THF, cyclohexanone, À78 °C (62–76%); (b) BOP reagent, Boc-piperazine, DMF
(68%); (c) (1) BH3, THF; (2) 2 N HCl, ether, methanol (65%); (d) CBr4, Ph3P, THF (69%); (e) KOH, H2O, Boc-piperazine (30%).
OH
H
N
N
X
OH
O
OH
O
2
OH
H
N
N
c
a
S
S
S
S
Cl
17a X= H
17b X= 4,5-benzo
15
16
17
Cl
OH
H
N
N
OH
3
OH
O
OH
N
N
OH
O
X
a
S
b
c,d
O
Cl
Cl
Cl
Cl
S
S
S
S
21a X=-2,5-Di-Cl
21b X=2-Cl
18
19
20
21
21c X=5-Cl
21d X= 4,5-benzo
Scheme 2. Synthesis of thiophene analogues. Reagents and conditions: (a) NCS, AcOH (72%); (b) Na (Hg), methanol (45%); (c) (1) LDA, THF, cyclohexanone, À78 °C (79%); (2)
BOP reagent, Boc-piperazine, DMF (69%); (3) BH3ÁTHF, (62%); (4) HCl; (d) (1) HCO2H, H2CO; (2) HCl(55%).

J. P. Sabatucci et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2809–2812
2811
Table 2
Inhibitory activity of heterocyclic cycloalkanol ethylamines at hNET, hSERT, and hDAT
R
N
N
OH
Ar
hNET %I @1a
(l
M)
hNET IC50 (nM)
hSERT %I @1b
(lM)
hDAT IC50 (nM)
a
c
Compd
Ar
R
10a
10b
14
21a
21b
21c
21d
17b
17a
17
21
(+)-S-21
(À)-R-21
(+)-S-3
(À)-R-3
Indol-3-yl
N-Methyl indol-3-yl
Quinolin-3-yl
H
H
H
H
H
H
H
H
21
32
19
94
55
86
82
73
54
50.8
88
91
0
ND
ND
ND
225 65
720 190
100 35
255 85
550 97
ND
90
ND
ND
ND
ND
ND
ND
12.2
34
2,5-Cl-thien-3-yl
2-Cl-thien-3-yl
2-Cl-thien-4-yl
Benzothiophen-3-yl
Benzothiophen-2-yl
Thien-2-yl
5-Cl-thien-2-yl
2-Cl-thien-4-yl
2-Cl-thien-4-yl
2-Cl-thien-4-yl
3-Cl-phenyl
ND
À1
(43)d
(51)d
(61)d
ND
48
89
H
H
ND
ND
À3
À1
À1
À3
32
ND
ND
Me
Me
Me
Me
Me
95 22
57 10
18,000
30 3.2
576 46
389 46
212 46
>6000
175 45
30 3.2
92
ND
3-Cl-phenyl
a
b
c
Inhibition of norepinephrine uptake in MDCK-Net6 cells, stably transfected with human NET. Desipramine (IC50 = 3.4 1.6 nM) was used as a standard.
Inhibition of serotonin uptake in JAR cells, natively expressing human SERT. Fluoxetine (IC50 = 9.4 3.1 nM) was used as a standard.
Inhibition of [3H]WIN-35,428 binding to membranes from CHO cells expressing recombinant hDAT. Mazindol (22.1 6.5 nM) was used as a standard.
%Inhibition measured at a concentration of 1000 nM. ND = not determined.
d
the 2-chlorothiophen-3-acetic acid. Treatment with 2 equiv of NCS
ultimately gave chlorination at the 2- and 5-positions (19). The
higher reactivity of the 2-position was then exploited by treatment
with sodium amalgam to reduce the chlorine at position 2 as the
major product 20. The 3-benzothiophene target 21d was made
from 3-benzothiophene acetic acid in an analogous manner to
10b. The 2-benzothiophene target 17b was made from 2-benzo-
thiophene carboxaldehyde analogous to 14. Enantiomers of the
most interesting compounds were separated by chiral HPLC.
In vitro data for hNET, hSERT, and hDAT for the heterocyclic
propanol amine series is depicted in Table 2. The nitrogen based
analogues (10a, 10b, 14) were weak inhibitors (<35% inh @
1 lM) and their IC50s not determined. The benzothiophene ana-
logues 21d, 17b had moderate NRI potency, however the most po-
tent NRIs were the chloro substituted thiophene based analogues
21, 21a, 21c. As expected, compound 21, a thiophene core contain-
ing similar topology as compound 3, had comparable activity in
hNET and selectivity over hSERT. Disappointingly, there was no in-
creased selectivity over hDAT with compound 21. The enantiomers
of these two compounds were separated by chiral HPLC and the
eutomer (+)-S-21 determined by X-ray crystallography. In both
cases, the S-enantiomer was the preferred isomer for NRI potency
(compound (+)-S-21 (IC50 value of 57 nM) and compound (+)-S-3
(IC50 value of 30 nM)) with both compounds possessing very sim-
ilar potency. The R-enantiomer was significantly less active in both
cases (compound (+)-R-21 and compound (+)-R-3). Figure 2 shows
Figure 2. X-ray structure of (+)-S-21.
the X-ray structure of compound (+)-S-21 confirming the
configuration.
S
Table 3
Summary of selected compounds in Telemetric Rat Model of OVX-Induced Thermo-
regulatory Dysfunction dosed 30 mg/kg
The release of norepinephrine in the hypothalamus is involved
in temperature regulation and sleep.11 Rodent models of estrogen
deficiency associated thermoregulatory dysfunction are based on
measuring changes in tail–skin temperature (TST) in ovariecto-
mized (OVX) rats.12 Intact cycling rats exhibit a diurnal TST pattern
with lower TST during the active (dark) phase and higher TST dur-
ing the inactive (light) phase over a 24 h period. In OVX rats, the
TST decrease during the active phase is reduced. Estrogen restores
the TST pattern in OVX rats, that is, transition to the active phase
coincides with a decrease in TST. An implanted chip was used to
Compd
Route of
Duration Mean reduction in Max reduction
administrationa of action TST from baseline
in TST from
(h)
(°C)
baseline (°C)
21
ip
6
À2.75
À3.3
À2.6
À3.1
À4.2
À4.6
À3.5
À3.8
(+)-S-21 ip
3
3
5.5
6.5
3
sc
po
a
ip and po dosing in 2% Tween 80/0.5% methylcellulose in water as the vehicle, sc
dosing in sterile water as the vehicle.

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J. P. Sabatucci et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2809–2812
measure TST and thus the method was defined as the Telemetric
Rat Model.
Petucci, Rebecca Dooley, Scott Brecker, Diane Andraka and Oliver
McConnell.
Compounds 21 and (+)-S-21 were tested in the Telemetric Mod-
el at 30 mg/kg ip and compared to compound 3 according to our
previously published procedure.13 The summarized results (Table
3) depict significant reduction of TST for the compounds regardless
of the route of administration dosed at 30 mg/kg. The compound
21 and its active enantiomer (+)-S-21 showed significant maxi-
mum reduction in TST when dosed ip.
References and notes
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2004, 50, 2974.
In conclusion, we have expanded our cyclohexanol ethylamine
program by synthesizing a variety of heterocyclic core derivatives.
As in the case of the phenyl derivatives, ring substitution was crit-
ical to maintaining NRI activity and the thiophene cores produced
the most active compounds. The novel thiophene core with match-
ing topology to the previous lead compound produced the most ac-
tive compound of the series. The compounds had excellent activity
in vivo as well, however we did not achieve the desired selectivity
over DAT with the thiophene core.
4. Panuk, D. U.; Dixon, W. R. J. Pharmacol. Exp. Ther. 1986, 236, 646.
5. McEwen, B. Recent Prog. Horm. Res. 2002, 57, 357.
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7. Husbands, G. E.; Stack, G. U.S. 4826,844.
8. Gavrin, L. K.; Jenkins, D. J.; Mahaney, P. E.; Belardi, J. K.; Trybulski, E. J.; Bray, J.
A.; Johnston, G. H.; Leiter, J.; Koury, E.; Deecher, D. C. Abstracts of Papers, 234th
National Meeting of the American Chemical Society, Boston, MA; American
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9. Mahaney, P. E.; Gavrin, L. K.; Trybulski, E. J.; Stack, G. P.; Vu, A. T.; Cohn, S. T.;
Ye, F.; Belardi, J. K.; Santilli, A. A.; Sabatucci, J. P.; Leiter, J.; Johnston, G. H.; Bray,
J. A.; Burroughs, K. D.; Leventhal, L.; Zhang, Y.; Mugford, C. A.; Ho, D. M.;
Rosenweig-Lipson, S.; Smith, V. A.; Deecher, D. C. J. Med. Chem. 2008, 51, 4038.
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Acknowledgments
The authors wish to acknowledge the expertise of the Discovery
Analytical Chemistry group at Wyeth, in particular Christopher
13. Pawlyk, A. C.; Cosmi, S.; Alfinto, P.; Maswood, N.; Deecher, D. C. Brain Res. 2006,
1123, 135.