Discovery of potent furan piperazine sodium channel blockers for treatment of neuropathic pain

Article abstract of DOI:10.1016/j.bmc.2008.05.003

The synthesis and pharmacological characterization of a novel furan-based class of voltage-gated sodium channel blockers is reported. Compounds were evaluated for their ability to block the tetrodotoxin-resistant sodium channel Na_v1.8 (PN3) as

Full text of DOI:10.1016/j.bmc.2008.05.003

Bioorganic & Medicinal Chemistry 16 (2008) 6379–6386
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Discovery of potent furan piperazine sodium channel blockers
for treatment of neuropathic pain
a
a
a
b
b
Irene Drizin a, , Robert J. Gregg , Marc J. C. Scanio , Lei Shi , Michael F. Gross , Robert N. Atkinson ,
James B. Thomas b, Matthew S. Johnson b, William A. Carroll a, Brian E. Marron b, Mark L. Chapman b,
Dong Liu b, Michael J. Krambis b, Char-Chang Shieh a, XuFeng Zhang a, Gricelda Hernandez a,
Donna M. Gauvin a, Joseph P. Mikusa a, Chang Z. Zhu a, Shailen Joshi a, Prisca Honore a, Kennan C. Marsh a,
Rosemarie Roeloffs b, Stephen Werness b, Douglas S. Krafte b, Michael F. Jarvis a, Connie R. Faltynek a,
Michael E. Kort a
*
a Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, IL 60064, USA
b Icagen, Inc., 4222 Emperor Boulevard, Durham, NC 27703, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis and pharmacological characterization of a novel furan-based class of voltage-gated sodium
channel blockers is reported. Compounds were evaluated for their ability to block the tetrodotoxin-resis-
tant sodium channel Nav1.8 (PN3) as well as the Nav1.2 and Nav1.5 subtypes. Benchmark compounds
from this series possessed enhanced potency, oral bioavailability, and robust efficacy in a rodent model
of neuropathic pain, together with improved CNS and cardiovascular safety profiles compared to the clin-
ically used sodium channel blockers mexiletine and lamotrigine.
Received 25 February 2008
Revised 30 April 2008
Accepted 2 May 2008
Available online 6 May 2008
Keywords:
Furan piperazine
Sodium channels
Voltage-gated
Blocker
Ó 2008 Elsevier Ltd. All rights reserved.
Nav1.8
PN3
Pain
1. Introduction
eral therapeutic classes of drugs, including antiarrhythmics (e.g.,
mexiletine), anticonvulsants (e.g., lamotrigine), and local anesthet-
Chronic pain comprises a breadth of heterogeneous symptoms
that can be characterized as inflammatory or neuropathic in nat-
ure. Neuropathic pain results from injury to the peripheral and/
or central sensory pathways where the painful state exists without
apparent noxious input, and is associated with hyperexcitability
and spontaneous action potential firing in sensory neurons.
Current treatment options do not provide adequate relief for many
patients and a significant number of the agents used have dose-
limiting side effects.1,2
ics (e.g., lidocaine), share the common mechanism of blocking
VGSCs and some have been used clinically to treat neuropathic
pain (Fig. 1).8 These non-selective agents provide effective analge-
sia despite their relatively weak in vitro potency against sodium
channel blockade, but possess a relatively narrow therapeutic in-
dex which limits their clinical utility.9
The VGSCs are a family of nine transmembrane proteins
that control the flow of sodium ions across cell membranes.10
Voltage-gated sodium channels (VGSCs) are critical modulators
for the transduction of action potentials in tissues such as nerve
and muscle.3 Considerable medical and experimental evidence
implicates abnormal sodium channel activity in the peripheral ner-
vous system in the pathophysiology of chronic pain,4 making them
attractive molecular targets for therapeutic intervention.5–7 Sev-
Cl
Cl
H
H
N
N
N
N
N
NH2
N
O
O
H2N
NH2
Mexiletine
Lamotrigine
Lidocaine
* Corresponding author. Tel: +1 847 937 7832; fax: +1 847 935 5466.
E-mail address: irene.drizin@abbott.com (I. Drizin).
Figure 1. Clinically used sodium channel blockers.
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.05.003

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I. Drizin et al. / Bioorg. Med. Chem. 16 (2008) 6379–6386
Susceptibility to blockade by natural toxins has been used to clas-
sify sodium channel currents in cells; the pufferfish toxin tetrodo-
toxin (TTx) is the most widely used of the toxins for
classification.11 Activation of tetrodotoxin-resistant sodium chan-
nels contributes to action potential electrogenesis in neurons.
Among the sodium channel subtypes expressed in primary sensory
neurons and dorsal root ganglia, Nav1.3,12 Nav1.7 (PN1),13 Nav1.8
(PN3),14,15 and Nav1.9 (NAN)16 present the best opportunities for
pain therapeutics. In particular, the tetrodotoxin-resistant (TTx-r)
subtype Nav1.8 carries a major portion of the TTx-r current in
peripheral nerves17 and has been strongly implicated in pain trans-
mission pathways.18
The objective of these efforts was to identify structurally novel,
orally bioavailable sodium channel blockers with enhanced po-
tency over existing agents such as lamotrigine and mexiletine.
The furfuryl glycinamide derivative 1 (Fig. 2)19,20 was identified
as a hit from a focused screening strategy using an Nav1.8 isotopic
flux assay.21 Herein we describe structure-activity relationships
observed with this chemotype as they pertain to piperazine-based
amides, and summarize the ability of representative analogs to
block VGSCs and dose-dependently reduce neuropathic pain in
an experimental rodent model.
O
O
O
a,b
CO2H
Br
Br
N
N
R2
14
c
15 R2 = cyclohexane
16 R2 = Me
17 R2 = H
R1
O
O
N
N
R2
18 R1 = 4-OCF3, R2 = cyclohexane
24 R1 =4- -phenoxy, R2 = Me
o
19 R1 = 4-t-butyl, R2 = cyclohexane
20 R1 = 4-NMe2, R2 = cyclohexane
21 R1 =3- Cl, R2 = cyclohexane
22 R1=2,4-Cl, R2 = cycloheaxane
25 R1 = 4-t-butyl, R2 = Me
26 R1 = 4-phenoxy, R2 =H,
27 R1 =4- -butyl, R2 = H
t
23 R1 = 4-phenoxy, R2 = cyclohexane
Scheme 2. Reagents and conditions: (a) (COCl)2, cat. DMF, CH2Cl2, 23 °C; (b) amine,
Et3N, CH2Cl2, 23 °C; (c) arylboronic acid, PdCl2(PPh3)2, aq Na2CO3, i-PrOH, reflux.
the 5-bromo-furoic acid 14 was converted to the amides (15–17)
for subsequent Suzuki coupling to provide 18–27 (Scheme 2).
2. Chemistry
In our previous paper,20 we disclosed potent and selective aryl-
furan amides with limited oral exposure. The relatively limited
synthetic complexity of this family of structures facilitated the
generation of a wide array of derivatives. The focus of the present
work was directed toward molecules containing piperazine or
piperazine-like moieties in efforts to improve the drug-like proper-
ties of this class of compounds. The commercially available 5-chlo-
rophenyl-furoic acid 2 was transformed to amides 4–13 via the
acid chloride intermediate 3 as shown in Scheme 1. Once a set of
preferential amides was established, aromatic substitution at the
5-position of the furan carboxamides was examined. To this end,
3. Results and discussion
Compounds were evaluated for their ability to block the recom-
binant mouse Nav1.8 sodium channel stably expressed in HEK293
cells, using an isotopic efflux assay.21 The activity of potent block-
ers was confirmed subsequently using conventional voltage-clamp
electrophysiology by measuring inhibition of TTx-r currents in dis-
sociated rat DRG neurons and inhibition of sodium currents in
HEK293 cells stably expressing recombinant human Nav1.8. Se-
lected analogs were also further examined for their selectivity ver-
sus Nav1.2 and Nav1.5 stably expressed in HEK293 cells. As sodium
channel blockers bind preferentially to the inactivated states of the
channel, electrophysiological protocols were designed to set the
membrane potential to the midpoint of voltage-dependent stea-
dy-state inactivation (i.e., the voltage at which 50% of channels
are inactivated) to allow a direct comparison of compound effects
across channel subtypes.19,20
O
As indicated in Table 1, preliminary studies of the truncated
analogs of 1 revealed that the piperazine moiety is an important
part of the pharmacophore. Replacement of the basic nitrogen
atom of 4 with oxygen (e.g., 7) led to significant loss of activity
in the mouse flux assay. Certain substituents at the terminus of
the piperazine, such as cyclohexane, provided analogs (e.g., 5) with
submicromolar potency as assessed by both the native rat (DRG
O
N
O
N
O
Cl
N
H
O
1 hNaV1.8 IC50 ~1 μM
Figure 2. Furan glycinamide screening hit.
O
O
Cl
Cl
Cl
b
a
O
O
O
CO2H
R
Cl
3
2
4-13
H
N
N
9 R =
4 R =
5 R =
6 R =
7 R =
8 R =
N
NH
H
N
10 R =
11 R =
12 R =
13 R =
N
N
N
N
N
N
O
N
N
H
N
N
H
N
N
CF3
N
N
Scheme 1. Reagents and conditions: (a) (COCl)2, cat. DMF, CH2Cl2, 23 °C; (b) amine, Et3N, CH2Cl2, 23 °C.

I. Drizin et al. / Bioorganic & Medicinal Chemistry 16 (2008) 6379–6386
6381
Table 1
SAR of amide variations
Cl
O
O
R
a
Compound
R
mNav1.8 IC50 (lM)
Rat DRG TTx-rb
% Inhibition V1/2
hNav1.8b
c
c
Conc (lM)
Conc (lM)
% Inhibition V1/2
4
5
2.9
1.0
9.9
32
0.3
41
2
0.3
55 11
N
N
N
NH
N
0.3
3
50
5
0.3
58
5
6
31
3
N
7
N
N
O
N
8
14
CF3
H
N
9
0.9
1.9
2.4
1.6
5.2
0.3
0.3
0.3
0.3
59
8
0.1
29
2
N
N
H
N
10
11
12
51 19
H
N
65
52
9
6
N
N
H
N
13
N
N
a
IC50 values were determined by least squares fitting of a logistic equation to data from full eight-point, half-log concentration response curves using an Nav1.8 isotopic
efflux assay as described in the experimental methods (mean of two to five separate determinations).
b
Data shown with standard error ( SEM) represent the mean of two to six separate determinations.
c
Inactivated state protocol: the pre-pulse voltage at which 50% of channels are inactivated (V1/2 = À40 mV).19
TTx-r current) and recombinant (hNav1.8) assays. In contrast, sub-
stitution with a methyl group as in 6 led to diminished Nav1.8 po-
tency, a somewhat surprising observation given the activity of the
unsubstituted piperazine 4. Attachment of a variety of functional-
ized aryl groups, such as in 8, also resulted in a dramatic loss in
activity, possibly due to the reduced basicity of the piperazine
nitrogen. To assess the effects of conformational rigidity and spac-
ing between the nitrogen atoms, compounds 9–13 were prepared.
Compounds 9, 11, and 12 displayed in vitro potency (DRG TTx-r
IC50 6300 nM) comparable to 5. These findings support the con-
clusion that a basic nitrogen enhances sodium channel activity
for this chemotype. The positioning of the amide linkage and prox-
imal basic nitrogen is not unimportant however as evidenced by
the moderate decrease in activity of 13 relative to piperidine 10,
5, and the open-chain analogs.
Continued examination of the pharmacophore was focused on
modifications of the C-5 substituent of the furan ring employing
three piperazinyl amides. The results of this effort are summarized
in Table 2. It was determined that the 4-Cl group could be replaced
effectively by 4-tert-butyl, 4-OCF3, and 4-phenoxy substituents,
thereby providing a boost in potency for sodium channel block
(hNav1.8 characterization) compared to 5. The increase in potency
was greater with cyclohexyl than with methyl or unsubstituted
(R2 = H) derivatives as exemplified by 19 and 23, which possessed
an estimated IC50 potency of <30 nM at human Nav1.8. Although
difficult to rationalize at the molecular level, we speculate that
the enhanced potency of these two derivatives arises from their in-
creased lipophilicity relative to other examples, a property which,
based on our work with a closely related series of molecules,20 we
believe to be important for interactions with hydrophobic regions
of the Nav1.8 channel. The compounds in Tables 1 and 2 demon-
strated voltage-dependent sodium channel blockade since they
did not have significant (>20%) current block (DRG TTx-r and
hNav1.8) at voltages that set all channels to a resting state (data
not shown).22
This new class of sodium channel blockers was surveyed for
cross-reactivity with other sodium channels and compared with
reference compounds as summarized in Table 3. Significantly, fur-
an piperazines 4, 5, and 19 were 100- to 1000-fold more potent in
blocking human Nav1.8 channels compared to mexiletine or lamo-
trigine. Their enhanced potency in blockade of native TTx-r cur-
rents in rat DRG neurons relative to the reference standards was
only slightly less profound. Compounds 4, 5, and 19 also were more
potent than lamotrigine and mexiletine versus Nav1.2 and Nav1.5,

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I. Drizin et al. / Bioorg. Med. Chem. 16 (2008) 6379–6386
Table 2
SAR of aromatic substitution for piperazine amides
O
R1
O
N
N
R2
Rat DRG TTx-ra
% Inhibition V1/2
Compound
R1
R2
hNav1.8a
% Inhibition V1/2
b
b
Concn (lM)
Concn (lM)
18
19
4-OCF3
Cyclohexyl
Cyclohexyl
0.3
0.1
0.1
0.03
1
89
42
81 10
57
65
80
22
12
93
5
3
4-tert-Butyl
0.1
0.03
58
20
2
3
6
4
5
2
4
1
20
21
4-NMe2
3-Cl
Cyclohexyl
Cyclohexyl
1
0.1
0.3
0.3
0.03
0.3
0.1
0.3
1
22
23
2,4-Cl
4-Phenoxy
Cyclohexyl
Cyclohexyl
1
67 11
90 10
55
55
56
68 10
24
4-Phenoxy
Me
1
0.1
1
87
35
32
93
39
85
44
2
1
6
1
3
5
6
8
5
9
25
26
4-tert-Butyl
4-Phenoxy
Me
H
1
0.1
1
0.1
27
4-tert-Butyl
H
10
86
3
a
Data shown with standard error ( SEM) represent the mean of two to six separate determinations.
b
Inactivated state protocol: the pre-pulse voltage at which 50% of channels are inactivated (V1/2 = À40 mV).19
Table 3
nerve ligation (Chung) model of neuropathic pain,23 the potency
of compounds 4 and 5 for reversing mechanical allodynia was
somewhat greater than mexiletine and lamotrigine. It is notewor-
thy that increased in vitro sodium channel potency translated to
improved in vivo potency, as exemplified by 19. On the other hand,
lamotrigine is approximately 60-fold less active than 4 and 5 on
Nav1.8 (rat TTx-r), yet is only modestly (<2-fold) less active in
the Chung model despite an approximately 10-fold greater sys-
temic exposure (Cmax) relative to these two compounds. These re-
sults lead us to speculate that pharmacological activities other
than sodium channel blockade contribute to the analgesic activity
of lamotrigine and mexiletine. Treatment with 4, 5, or 19 resulted
in no impairment of locomotor activity at doses substantially
greater than required for analgesic efficacy, despite a large degree
of partitioning into the CNS (brain/plasma >8) in all three cases.
Similar findings were observed in the rotarod and edge tests.
Assessment of cardiovascular safety for 4 and 5 in anesthetized rats
indicated no sustained changes in mean arterial pressure or heart
rate at doses that yielded plasma levels 30- and 10-fold higher than
the therapeutic plasma level, respectively.
Na channel selectivity of the lead compounds: voltage clamp electrophysiological
characterization
4
5
19
Lamotrigine
Mexiletine
a
Rat TTx-r, IC50 (lM)
hNav1.8, IC50 (lM)
hNav1.2, IC50 (lM)
hNav1.5, IC50 (lM)
0.43
0.28
1.1
0.39
0.30
0.35
2.3
0.09
0.03
0.1
25
96
10
62
31
56
2.9
13
a
a
a
4.6
0.1
a
Data shown with standard error ( SEM) represent the mean of two to six
separate determinations. Data were collected using an inactivated state protocol
(the pre-pulse voltage at which 50% of channels are inactivated). V1/2 = À60 mV for
hNav1.2, hNav1.8, rat TTx-r; V1/2 = À90 mV for hNav1.5.19
and showed marginal selectivity for the hNav1.8 subtype. The volt-
age-dependent behavior noted above for Nav1.8 also was observed
with Nav1.2 and Nav1.5 for all compounds in Table 3 (data not
shown).
Assessment of pharmacokinetic properties revealed that com-
pounds 4, 5, and 19 afforded sufficient plasma levels upon oral
administration to enable evaluation in animal pain models. The re-
sults of these studies are summarized in Table 4. In the spinal
Table 4
Efficacy, safety profile, and PK properties of lead compounds
4
5
19
Lamotrigine
Mexiletineb
Chung, po ED50 (lmol/kg)
Locomotor, po ED50 (lmol/kg)
Edge test, po ED50 (lmol/kg)
Rotorod, p.o. ED50 (lmol/kg)
MAP effectc
24
37
>300
>300
>300
4.7
38% at 230
>300
>300
47
102
>300
>300
>300
None (30Â)
None (30Â)
50
21
0.13
24
42
>390
>390
>390
45 (lethal at 460)
lethal at 460
>140
None (10Â)
; 11% (3Â)
Heart rate effect
None (10Â)
; 27% (10Â)
Brain/Plasma
9
8
26
1.4
CLp (L/h kg)a
2.7
0.47
7.8
48
7.6
0.57
13.4
7
0.06
3.5
0.98
79
Cmax po (lg/mL)a
a
Vss (L/kg)
F (po)a
a
Administered at 10 mg/kg, 10% DMSO/PEG400.
Administered ip in all cases.
MAP (mean arterial pressure).
b
c

I. Drizin et al. / Bioorganic & Medicinal Chemistry 16 (2008) 6379–6386
6383
With the exception of weak binding to 5HT1A and 5HT1B recep-
tors (60% and 86% at 10 lM, respectively), 4 was found to be highly
selective for sodium channels compared to a diverse set of cell-sur-
face receptors, ion channels, and enzymes (CEREP, Poitiers, France;
70 receptor panel) and a number of other channels and receptors
expressed in peripheral sensory neurons.24
tion contained (mM): KCl 140, MgCl2 2, EGTA 5, HEPES 10, pH 7.2
(osmolarity, 285). The external solution contained (mM): NaCl 140,
KCl 5, CaCl2 2, MgCl2 2, HEPES 10, pH7.4 (osmolarity, 310). For voltage
clamp recordings, pipette solution contained (mM): CsF 135, NaCl 5,
CsCl 10, EGTA 5, HEPES 10, pH 7.2 (osmolarity, 285). The external
solution contained (mM): NaCl 22, cholineCl 110, CaCl2 1.8, MgCl2
0.8, HEPES 10, Glucose 5, pH 7.4 (osmolarity, 310).
4. Conclusions
5.3.2. Recombinant human sodium channels
Human embryonic kidney (HEK293) cells expressing recombi-
nant sodium channels were grown in DMEM/High Glucose Dul-
becco’s Mod, 10% Fetal Bovine Serum, 2 mM Sodium Pyruvate,
G418. For whole-cell voltage clamp recordings, patch pipettes were
pulled from borosilicate glass on a Flaming–Brown micropipette
puller (Sutter Instruments, Inc). Pipettes had a tip resistance of
0.8–2.5 MX using the internal solutions (mM): 135 CsF, 10 CsCl,
5 EGTA, 5 NaCl, 10 HEPES-free acid, pH to 7.3 with 5M CsOH and
voltage offset was zeroed prior to seal formation. The external buf-
fer consisted of (mM) 132 NaCl, 5.4 KCl, 0.8 MgCl2, 1.8 CaCl2, 5 Glu-
cose, 10 HEPES-free acid, pH to 7.3 with 6N NaOH. After
establishment of a whole-cell recording, cellular capacitance was
minimized using the analog compensation available on the record-
ing amplifier (Axopatch 200B). Series resistance was less than
5 MX and was compensated >85% in all experiments, resulting in
a final series resistance no greater than 0.75 MX . Signals were
low-pass filtered at 5–10 kHz, digitized at 20–50 kHz, and stored
on a computer for later analysis. Voltage protocols were generated
and data acquisition and analysis were performed using pCLAMP
software (Version 8.1, Axon Instruments, Inc.). All experiments
were performed at room temperature. Liquid junction potentials
were <10 mV and were not corrected.
We have discovered a novel series of voltage-dependent furan-
based sodium channel blockers with enhanced potency for blockade
of sodium channels relative to clinically used agents, mexiletine and
lamotrigine. Structure–activity relationship studies identified the
preferred amide substituents (e.g., cyclohexylpiperazine, methylpi-
perazine, and piperazine) and established the preferential aromatic
substitution for this class of compounds. Incorporation of a basic
nitrogen imparted enhanced solubility and a generally favorable
pharmacokinetic profile, but little selectivity among the sodium
channels subtypes. Analgesic efficacy in the spinal nerve ligation
model of neuropathic pain was observed for these analogs. For
example, the novel furan piperazine 19 exhibiteda >10-fold increase
in potency in the Chung model relative to lamotrigine and mexile-
tine. Interestingly, the activity at Nav1.2 and Nav1.5 exhibited by
these furan derivatives did not manifest itself appreciably in the
form of adverse CNS or cardiovascular effects, respectively. Furans
4 and 5 demonstrated favorable in vivo efficacy in the Chung model
of neuropathic pain compared to lamotrigine and mexiletine, along
with a benign CNS and cardiovascular safety profile.
5. Experimental
5.1. General procedures
5.4. In vivo evaluation
Nuclear magnetic resonance spectra were obtained on a General
Electric QE 300 MHz instrument with chemical shifts (d) reported
relative to tetramethylsilane as internal standard. Mass spectra
determinations were obtained using an electrospray (ESI) tech-
nique or by direct chemical ionization (DCI) methods employing
ammonia. Melting points were determined with capillary appara-
tus and are uncorrected. Elemental analyses were performed by
Robertson Microlit Laboratories, Inc., Madison, NJ. Analytical thin
layer chromatography was done on 2 Â 6 cm Kieselgel 60 F-254
plates pre-coated with 0.25 mm thick silica gel distributed by E.
Merck. LC-MS analyses were performed on ThermoQuest Navigator
systems using 10–100% acetonitrile: 10 mM ammonium acetate
gradient with MS data obtained using atmospheric pressure chem-
ical ionization (APCI) positive ionization over the range of m/z from
170 to 1200. Unless otherwise specified, column chromatography
was performed on silica gel (230–400 mesh). The term in vacuo re-
fers to solvent removal using a rotary evaporator at 30 mmHg.
Male Sprague–Dawley rats (Charles River, Wilmington, MA)
weighing 200–300 g were utilized. All animals were group-housed
in AAALAC approved facilities at Abbott Laboratories in a tempera-
ture-regulated environment with lights on between 0700 and
2000 h. Food and water was available ad libitum except during test-
ing. All animal handling and experimental protocols were approved
by an institutional animal care and use committee (IACUC). All
experiments were performed during the light cycle. Unless other-
wise noted, all experimental and control groups contained at least
six animals per group and data are expressed as mean SEM. Data
analysis was conducted using analysis of variance and appropriate
post-hoc comparisons (P < 0.05) as previously described.25 ED50 val-
ues were estimated using least squares linear regression.
5.4.1. Spinal nerve (L5/L6) ligation model of neuropathic pain
As previously described in detail by Kim and Chung,23 a 1.5-cm
incision was made dorsal to the lumbosacral plexus. In anesthe-
tized rats, the paraspinal muscles (left side) were separated from
the spinous processes, the L5 and L6 spinal nerves isolated, and
tightly ligated with 3–0 silk threads. Following hemostasis, the
wound was sutured and coated with antibiotic ointment. The rats
were allowed to recover and then placed in a cage with soft bed-
ding for 14 days before behavioral testing for mechanical allodynia.
5.2. High-throughput mouse Nav1.8 and hERG flux assays
HEK293 cells stably expressing mouse Nav1.8 or hERG were
loaded overnight with 86Rb+, followed by stimulation with delta-
methrin as previously described.21 The deltamethrin-stimulated
86Rb+ flux was measured for 30 min in the presence and absence
of test compounds.
5.4.2. Motor function
Locomotor activity was measured in an open field using photo-
beam activity monitors (AccuScan Instruments, Columbus, OH), and
rotorod performance was measured using an accelerating rotorod
apparatus (Omnitech Electronics, Inc. Columbus, OH). For the rotorod
assay, rats were allowed a 30-min acclimation period in the testing
room and then placed on a 9-cm diameter rod that increased in
speed from 0 to 20 rpm over a 60-s period. The time required for
5.3. Electrophysiology19
5.3.1. Rat Dorsal Root Ganglion (DRG) neurons
Whole-cell patch clamp recordings were performed at room tem-
perature on rat small diameter DRG neurons (18–25 lm) from the L4
and L5 lumbar region. For current clamp recordings, the pipette solu-

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I. Drizin et al. / Bioorg. Med. Chem. 16 (2008) 6379–6386
the rat to fall from the rod was recorded, with a maximum score of
60 s. Each rat was given three training sessions. To test for balance,
rats were also assessed for their ability to remain on top of a 0.5-cm-
thick edges of a 40 Â 40 Â 36 cm plexiglass box. The rats had to pull
themselves up on to the edge and avoid falling with a cut-off time of
2 min. The average (latency to fall) of two trials was recorded.
6.4. [5-(4-Chlorophenyl)furan-2-yl]-(4-methylpiperazin-1-yl)-
methanone hydrochloride (6)
A solution of 3 (0.100 g, 0.415 mmol) in dichloromethane was
reacted with 1-methylpiperazine (0.042 g, 0.415 mmol) by Method
A to yield 0.100 g (79%) of 6, mp 243–245 °C. MS (DCI/NH3) m/z
305 (M+H)+. 1H NMR (DMSO-d6) d 10.44 (br s, 1H), 7.82 (d, 1H,
J = 8.48 Hz), 7.23 (d, 2H, J = 8.48 Hz), 7.23 (d, 1H, J = 3.73 Hz),
7.21 (d, 1H, J = 3.39 Hz), 4.54 (d, 2H, J = 14.24 Hz), 3.58 (m, 4H),
3.13 (m, 2H), 2.80 (s, 3H). Anal. (C16H17ClN2O2ÁHClÁ0.25 H2O) C,
H, N.
5.4.3. Cardiovascular safety
Male Sprague–Dawley inaction-anesthesized rats were used to
measure mean arterial pressure and heart rate. Following a 30-min
control period, a sodium channel blocker or vehicle (PEG-400) was
administered intravenously over five, 30-min infusions at 1Â, 3Â,
10Â, 30Â, and 100Â of calculated therapeutic dose. A blood sample
and hematocrit were collected immediately after the infusion.
6.5. [5-(4-Chlorophenyl)furan-2-yl]-morpholin-4-yl-
methanone (7)
A solution of 3 (0.120 g, 0.500 mmol) in dichloromethane was
reacted with morpholine (0.044 g, 0.500 mmol) by Method A to
yield 0.070 g of 7, mp 152–153 °C. MS (DCI/NH3) m/z 292
(M+H)+. 1H NMR (DMSO-d6) d 7.79 (d, 2H, J = 8.81 Hz), 7.54 (d,
2H, J = 8.81 Hz), 7.17 (d, 1H, J = 3.73 Hz), 7.14 (d, 1H, J = 3.72 Hz),
3.67 (m, 8H). Anal (C15H14ClNO3) C, H, N.
6. Chemistry
6.1. Representative procedure for conversion of carboxylic
acid derivatives to amides via acid chlorides (Method A)
5-(4-Chlorophenyl)-2-furoyl chloride (3)
5-(4-Chlorophenyl)-2-furoic acid (1.10 g, 5.00 mmol) in dichlo-
romethane (50 mL) was treated with oxalyl chloride (0.650 mL,
7.50 mmol) and a catalytic amount of N,N-dimethylformamide
(100 lL). The mixture was stirred at ambient temperature for 2 h
and the solvent and excess oxalyl chloride were removed under re-
duced pressure to provide 1.11 g of 3 which was used without fur-
ther purification.
6.6. [5-(4-Chlorophenyl)-furan-2-yl]-[4-(3-
trifluoromethylphenyl)-piperazin-1-yl]-methanone (8)
A solution of 3 (0.100 g, 0.415 mmol) in dichloromethane was
reacted with 1-(3-trifluoromethylphenyl) piperazine (0.096 g,
0.415 mmol) by Method A to yield 0.125 g of 8, mp 150–151 °C.
MS (DCI/NH3) m/z 435 (M+H)+. 1H NMR (DMSO-d6) d 7.82 (d, 2H,
J = 8.48 Hz), 7.55 (d, 2H, J = 8.48 Hz), 7.46 (t, 1H, J = 7.97 Hz),
7.27–7.18 (m, 4H), 7.10 (d, 1H, J = 7.46 Hz), 3.90 (m, 2H), 3.38 (m,
6H). Anal. (C22H18ClF3N2O2Á0.5 H2O) C, H, N.
6.2. 1-[5-(4-Chlorophenyl)-2-furoyl]piperazine hydrochloride
(4)
A solution of 3 (0.55 g, 2.50 mmol) in dichloromethane (10 mL)
was treated with tert-butyl-1-piperazine carboxylate (0.46 g,
2.50 mmol) and triethylamine (0.3 mL). The mixture was stirred
at ambient temperature for 16 h. The mixture was diluted with
dichloromethane (25 mL) and washed with 5% NaHCO3 solution
(25 mL). The organic phase was dried over MgSO4, filtered, and
concentrated in vacuo. The obtained residue was purified by silica
gel chromatography (elution with 5% ethanol/dichloromethane).
The purified material was redissolved in dichloromethane
(50 mL) and treated with trifluoroacetic acid (15 mL). The mixture
was stirred at room temperature for 1 h after which the solvent
was removed in vacuo and the residue was partitioned in dichloro-
methane/1 M NaOH solution (25 mL). The organic phase was dried
over MgSO4, filtered, and concentrated in vacuo. The obtained res-
idue was converted to HCl salt by treatment of the ethanolic solu-
tion of the residue with ethereal HCl to provide 0.550 g (68%) of 4,
mp 251 °C. MS (DCI/NH3) m/z 291 (M+H)+. 1H NMR (DMSO-d6) d
9.04 (br s, 1H), 7.82 (d, 2H, J = 8.81 Hz), 7.55 (d, 2H, J = 8.81 Hz),
7.22 (d, 2H, J = 3.73 Hz), 7.21 (d, 2H, J = 3.73 Hz), 3.93 (br s, 4H),
3.21 (br s, 4H). Anal. (C15H15N2O2ClÁHCl) C, H, N.
6.7. 5-(4-Chlorophenyl)furan-2-carboxylic acid-(2-piperidin-1-
yl-ethyl)amide hydrochloride (9)
A solution of 3 (0.240 g, 1.00 mmol) in dichloromethane was re-
acted with 1-(2-aminoethyl)piperidine (0.130 g, 1.00 mmol) by
Method A to yield 0.160 g of free base of 9 as an oil that was con-
verted to its hydrochloride salt, mp 225–227 °C. MS (ESI) m/z 333
(M+H)+. 1H NMR (DMSO-d6) d 9.50 (br s, 1H), 8.84 (t, 1H,
J = 5.93 Hz), 7.96 (d, 2H, J = 8.48 Hz), 7.58 (d, 2H, J = 8.48 Hz), 7.24
(d, 1H, J = 3.73 Hz), 7.17 (d, 1H, J = 3.73 Hz), 3.66 (q, 2H,
J = 5.88 Hz), 3.55 (d, 2H, J = 11.19 Hz), 3.23 (q, 2H, J = 5.65 Hz),
2.93 (m, 2H), 1.83 (m, 2H), 1.70 (m, 3H), 1.40 (m, 1H). Anal.
(C18H21ClN2O2ÁHCl) C, H, N.
6.8. 5-(4-Chlorophenyl)furan-2-carboxylic acid (1-methylpiperi-
dine-4-yl)amide hydrochloride (10)
A solution of 3 (0.100 g, 0.400 mmol) in dichloromethane was
reacted with 1-methylpiperidine-4-ylamine (0.050 g, 0.440 mmol)
by Method A to yield 0.100 g of free base of 10 as an oil that was
converted to hydrochloride salt, MS (ESI) m/z 319 (M+H)+. 1H
NMR (DMSO-d6) d 9.97 (br s, 1H), 8.53 (d, 1H, J = 7.8 Hz), 7.93 (d,
2H, J = 8.82 Hz), 7.55 (d, 2H, J = 8.82 Hz), 7.21 (d, 1H, J = 3.39 Hz),
7.17 (d, 1H, J = 3.73 Hz), 4.0 (m, 1H), 3.47 (m, 2H), 3.10 (m, 2H),
2.74 (s, 3H), 1.75–2.05 (m, 4H), mp 220–222 °C. Anal.
(C17H19ClN2O2ÁHClÁ0.75 H2O) C, H, N.
6.3. [5-(4-Chlorophenyl)furan-2-yl]-(4-cyclohexylpiperazin-1-
yl)-methanone hydrochloride (5)
A solution of 3 (0.3 g, 1.2 mmol) in dichloromethane was re-
acted with 1-cyclohexylpiperazine (0.20 g, 1.2 mmol) as described
in Method A to yield 0.28 g (63%) of 5 as a white powder, mp
256 °C. MS (DCI/NH3) m/z 373 (M+H)+. 1H NMR (DMSO-d6) d
10.49 (s (HCl), 1H), 7.83 (d, 2H, J = 8.82 Hz), 7.55 (d, 2H,
J = 8.82 Hz), 7.24 (d, 1H, J = 3.39 Hz), 7.21 (d, 1H, J = 3.39 Hz), 4.58
(d, 2H, J = 13.56 Hz), 3.52 (m, 4H), 3.22 (m, 2H) 2.11 (d, 2H,
J = 10.85 Hz), 1.83 (d, 2H, J = 11.87 Hz), 1.62 (d, 1H, J = 12.21 Hz),
1.49–1.03 (m, 5H). Anal. (C21H25N2O2ClÁHCl) C, H, N.
6.9. 5-(4-Chlorophenyl)furan-2-carboxylic acid (3-dimethylamino-
2,2-dimethylpropyl)amide hydrochloride (11)
A solution of 3 (0.100 g, 0.400 mmol) in dichloromethane was
reacted with N,N-2-tetramethyl-1,3-propanediamine (0.570 g,
0.440 mmol) by Method A to yield 0.120 g of free base of 11 as

I. Drizin et al. / Bioorganic & Medicinal Chemistry 16 (2008) 6379–6386
6385
an oil that was converted to hydrochloride salt. MS (ESI) m/z
6.14. (5-bromofuran-2-yl)(piperazine-1-yl)methanone. (17)
335 (M+H)+. 1H NMR (DMSO-d6) d 8.61 (t, 1H, J = 5.76 Hz), 7.88
(d, 2H, J = 8.48 Hz), 7.55 (d, 2H, J = 8.48 Hz), 7.16 (d, 1H,
J = 3.39 Hz), 7.13 (d, 1H, J = 3.73 Hz), 3.18 (d, 2H, J = 6.1 Hz), 2.28
(s, 6H), 2.20 (s, 2H), 0.89 (s, 6H). Anal. (C18H23ClN2O2ÁHClÁ0.5
H2O) C, H, N.
5-Bromo-2-furoic acid (1.0 g, 5.0 mmol) was treated with
oxalyl chloride (0.650 mL, 7.50 mmol) and the resulting product
was treated with t-butyl-1-piperazine carboxylate (0.930 g,
5.00 mmol) as described in 15 to yield 1.40 g of 4-(5-Bromofu-
ran-2-carbonyl)-piperazine-1-carboxylic acid tert-butyl ester,
mp 83–84 °C. 1H NMR (DMSO-d6) d 7.05 (d, 1H, J = 3.39 Hz),
6.78 (d, 1H, J = 3.39 Hz), 3.62 (br s, 4H), 3.41 (m, 4H), 1.38
(s, 9H). 4-(5-Bromofuran-2-carbonyl)-piperazine-1-carboxylic
acid tert-butyl ester (1.4 g, 3.9 mmol) was dissolved in methy-
lene chloride (10 mL) and reacted with trifluroacetic acid
(2 mL) at ambient temperature for 1h. The reaction mixture
was concentrated and partitioned in NaHCO3 sol./dichlorometh-
ane. The organic layer was separated, dried over MgSO4 and
concentrated to yield 0.85 of 17. MS (DCI/NH3) m/z 260
(M+H)+.1H NMR (CDCl3) d ppm 6.96 (d, J = 3.57 Hz, 1 H), 6.42
6.10. 5-(4-Chlorophenyl)furan-2-carboxylic acid (3-piperidin-
1-yl-propyl)amide hydrochloride (12)
A solution of 5-(4-Chlorophenyl)-2-furoyl chloride (0.100 g,
0.400 mmol) in dichloromethane was reacted with 1-(3-aminopro-
pyl)piperidine (0.063 g, 0.440 mmol) by Method A to yield 0.100 g
of free base of 12 as an oil that was converted to hydrochloride salt,
mp 160–162 °C MS (ESI) m/z 347(M+H)+. 1H NMR (DMSO-d6) d 9.94
(br s, 1H), 8.75 (t, 1H, J = 6.1 Hz), 7.94 (d, 2H, J = 8.48 Hz), 7.56 (d, 2H,
J = 8.48 Hz), 7.17 (d, 1H, J = 3.39 Hz), 7.15 (d, 1H, J = 3.73 Hz), 3.39 (m,
2H), 3.05 (m, 2H), 2.87 (m, 2H), 1.95 (m, 2H), 1.65–1.82 (m, 5H), 1.35
(m, 1H). Anal. (C19H23ClN2O2ÁHClÁ0.5 H2O) C, H, N.
(d, J = 3.57 Hz,
1 H), 3.75 (m, 4 H), 2.93 (m, 4 H). Anal
(C9H11BrN2O2) C, H, N.
6.11. [5-(4-Chlorophenyl)furan-2-yl-(4-dimethylamino-
piperidin-1-yl)-methanone (13)
6.15. Representative procedure for Suzuki coupling (MethodB):
(4-Cyclohexylpiperazin-1-yl)-{[5-(4-trifluoromethoxy)phenyl]furan-
2-yl}-methanone (18)
A solution of 3 (0.240 g, 1.00 mmol) in dichloromethane was re-
acted with 4-dimethylamino-piperidine-1-yl-amine (0.140 g,
1.10 mmol) by method A to yield 0.140 g of 13 as an oil that, upon
trituration with 30% ethylacetate/hexane, was converted to white
crystalline powder, mp 81–82 °C. MS (ESI) m/z 333(M+H)+. 1H
A solution of 15 (100 mg, 0.300 mmol) in 2:1 toluene–water
(5 mL) was reacted with 4-(trifluoromethoxy)phenylboronic acid
(80 mg, 0.39 mmol) in the presence of Na2CO3 (80 mg, 0.80 mmol)
and PdCl2(PPh3)2 (10 mg) at 80 °C for 16 h. The reaction mixture
was concentrated and purified by chromatography on silica gel,
eluting with ethylacetate to yield 85 mg (66%) of 18, mp 108–
109 °C. MS (DCI/NH3) m/z 423 (M+H)+. 1H NMR (DMSO-d6) d 7.90
(d, 2H, J = 8.82 Hz), 7.48 (d, 2H, J = 8.82 Hz), 7.18 (d, 1H, J = 3.39
Hz), 7.10 (d, 1H, J = 3.39 Hz), 3.69 (m, 4H), 2.60 (m, 4H), 2.25 (m,
1H), 1.75 (m, 4H), 1.60 (m, 1H), 1.20 (m, 4H), 1.11 (m, 1H). Anal.
(C22H25F3N2O3) C, H, N.
NMR (DMSO-d6)
d 7.78 (d, 2H, J = 8.82 Hz), 7.54 (d, 2H,
J = 8.82 Hz), 7.15 (d, 1H, J = 3.39 Hz), 7.08 (d, 1H, J = 3.73 Hz), 3.01
(m, 2H), 2.21 (s, 6H), 1.85 (d, 2H, J = 10.51 Hz), 1.38 (m, 2H). Anal.
(C19H23ClN2O2ÁHClÁ0.6H2O) C, H, N.
6.12. (5-Bromofuran-2-yl)-(4-cyclohexylpiperazine-1-yl)metha-
none (15)
Asolutionof5-bromo-2-furoic acid(1.00 g, 5.00 mmol)indichlo-
romethane (50 mL) was treated with oxalyl chloride (0.650 mL,
7.50 mmol) and a catalytic amount of N,N-dimethylformamide
(100 lL). The mixture was stirred at ambient temperature for 2 h
and the solvent and excess oxalyl chloride were removed under re-
duced pressureto provide the intermediate 5-bromo-furoyl chloride
which was used without further purification.
The acid chloride (840 mg, 4.00 mmol) was dissolved in dichlo-
romethane (10 mL) and treated with 1-cyclohexylpiperazine
(740 mg, 4.40 mmol) and triethylamine (0.750 mL, 5.40 mmol) at
ambient temperature. The mixture was stirred for 16 lh at ambient
temperature and was then was diluted with dichloromethane
(20 mL) and washed with saturated NaHCO3 solution (10 mL).
The organic phase was dried over MgSO4, filtered and concentrated
in vacuo. The obtained residue was crystallized from hexane/ethyl
acetate to provide 1.15 g (84%) of 15, mp 128–130 °C. MS (DCI/
NH3) m/z 343 (M+H)+. 1H NMR (DMSO-d6) 7.0 (d, 1H, J = 3.73 Hz),
6.75 (d, 1H, J = 3.73 Hz), 3.59 (m, 4H), 2.55 (m, 4H), 2.25 (m, 1H),
1.73 (m, 4H), 1.57 (m, 1H), 1.18 (m, 4H), 1.07 (m, 1H).
6.16. [5-(4-tert-Butylphenyl)furan-2-yl]-(4-cyclohexylpiperazin-
1-yl)-methanone hydrochloride (19)
Compound 15 (1.10 g, 3.20 mmol) was treated with 4-tert-buty-
lphenylboronic acid (0.800 g, 5.00 mmol) by Method B. The ob-
tained free base of 19 (0.700 g, 55%) was converted to HCl salt,
mp >250 °C. MS (DCI/NH3) m/z 395(M+H)+. 1H NMR (DMSO-d6) d
10.02 (br s, 1H), 7.72 (d, 2H, J = 8.48 Hz), 7.50 (d, 2H, J = 8.48 Hz),
7.21 (d, 1H, J = 3.73 Hz), 7.08 (d, 1H, J = 3.39 Hz), 4.61 (d, 2H,
J = 13.56 Hz), 3.55 (m, 4H), 3.22 (m, 2H,), 2.58 (m, 1H), 2.09 (d,
2H, J = 13.56 Hz), 1.82 (d, 2H, J = 10.85 Hz), 1.62 (m, 1H), 1.45–
1.22 (m, 4H), 1.20 (m, 1H), 1.15 (s, 9H). Anal. Calcd. for
(C25H34N2O2ÁHCl) C, H, N.
6.17. (4-Cyclohexylpiperazin-1-yl)-{[5-(4-dimethylamino)-
phenyl]-furan-2-yl}-methanone (20)
Compound 15 (0.100 g, 0.300 mmol) was treated with 4-dim-
ethylaminophenylboronic acid (0.060 g, 0.360 mmol) by Method
B to provide 20, mp 124–125 °C. MS (DCI/NH3) m/z 382 (M+H)+.
1H NMR (DMSO-d6) d 7.56 (d, 2H, J = 9.15 Hz), 7.02 (d, 1H,
J = 3.73 Hz), 6.78 (m, 3H), 3.68 (m, 4H), 2.96 (s, 6H), 2.55 (m, 4H),
2.28 (m, 1H), 1.76 (m, 4H), 1.56 (m, 1H), 1.20 (m, 5H). Anal.
(C23H31N3O2) C, H, N.
6.13. (5-Bromofuran-2-yl)-(4-methylpiperazine-1-yl)methanone
(16)
5-Bromo-2-furoic acid (0.450 g, 2.00 mmol) was reacted with
oxalyl chloride and the resulting product was treated with 1-meth-
ylpiperazine (0.218 g, 2.20 mmol) as described in 15 to provide
0.460 g of 16, mp 93–94 °C. MS (DCI/NH3) m/z 273 (M+H)+.1H
NMR (DMSO-d6) 7.02 (d, 1H, J = 3.39 Hz), 6.75 (d, 1H, J = 3.39 Hz),
3.63 (m, 4H), 2.34 (m, 4H), 2.16 (s, 3H). Anal (C10H13BrN2O2) C,
H, N.
6.18. (4-Cyclohexylpiperazin-1-yl)-{[5-(3-chloro)phenyl]furan-
2-yl}-methanone hydrochloride (21)
Compound 15 (0.100 g, 0.300 mmol) was reacted with 3-chloro-
phenylboronic acid (0.056 g, 0.360 mmol) by Method B to provide

6386
I. Drizin et al. / Bioorg. Med. Chem. 16 (2008) 6379–6386
21, mp 236–238 °C. MS (DCI/NH3) m/z 373 (M+H)+. 1H NMR
(DMSO-d6) (free base) d 7.85 (t, 1H, J = 1.87 Hz), 7.72 (dt, 1H,
J = 7.71, 1.4 Hz), 7.51 (t, 1H, J = 7.97 Hz), 7.43 (ddd, 1H, J = 7.97,
2.03, 1.19 Hz), 7.28 (d, 1H, J = 3.66 Hz), 7.22 (d, 1H, J = 3.66 Hz),
3.68 (m, 4H), 2.58 (m, 4H), 2.27 (m, 1H), 1.75 (m, 4H), 1.58 (m,
1H), 1.22 (m, 4H), 1.12 (m, 1H).). Anal. (C21H26ClN2O2. HClÁ0.5H2O)
C, H, N.
6.24. [5-(4-tert-Butylphenyl)-furan-2-yl]-piperazin-1-yl-
methanone (27)
A solution of 17 (0.120 g, 0.300 mmol) was reacted by method B
with 4-tert-butylphenylboronic acid (0.064 g, 0.36 mmol) to pro-
vide 27. MS (DCI/NH3) m/z 313 (M+H)+. 1H NMR (DMSO-d6) d
7.68 (d, 2H, J = 8.33 Hz), 7.49 (d, 2H, J = 8.74 Hz), 7.08 (d, 2H,
J = 3.57 Hz), 7.02 (d, 1H, J = 3.57 Hz), 3.63 (br s, 4H), 2.75 (t, 4H,
J = 5.15 Hz), 1.30 (s, 9H). Anal (C19H24N2O2ÁHClÁ0.25H2O) C, H, N.
6.19. (4-Cyclohexylpiperazin-1-yl)-{[5-(2,4-dichloro)phenyl]-
furan-2-yl}-methanone hydrochloride (22)
Supplementary data
Compound 15 (0.100 g, 0.300 mmol) was reacted with 2,4-dic-
hlorophenylboronic acid (0.068 g, 0.036 mmol) by Method B to
provide 22, mp 238–240 °C. MS (DCI/NH3) m/z 407 (M+H)+. 1H
NMR (DMSO-d6) (free base) d 7.87 (d, 1H, J = 8.48 Hz), 7.78 (d,
1H, J = 2.03 Hz), 7.55 (d, 1H, J = 2.03 Hz), 7.24 (d, 1H, J = 3.73 Hz),
7.13 (d, 1H, J = 3.39 Hz), 3.68 (m, 4H), 2.58 (m, 4H), 2.27 (m, 1H),
1.75 (m, 4H), 1.58 (m, 1H), 1.22 (m, 4H), 1.12 (m, 1H). Anal.
(C21H24Cl2N2O2ÁHCl) C, H, N.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmc.2008.05.003.
References and notes
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6.20. (4-Cyclohexylpiperazine-1-yl)(5-(4-phenoxyphenyl)furan-
2-yl)methanone (23)
Compound 15 (0.100 g, 0.300 mmol) was reacted with 4-pheno-
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d 7.77 (d, 2H, J = 8.81 Hz), 7.43 (t,
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2H,J = 8.47 Hz), 7.20 (t, 1H,J = 7.46 Hz), 7.09 (m, 5H), 7.02 (d, 1H,
J = 3.39 Hz ), 3.68 (m, 4H), 2.57 (t, 4H, J = 5.09 Hz), 2.27 (m, 1H),
1.75 (m, 4H), 1.55 (d, 1H, J = 11.53 Hz), 1.20 (m, 4H), 1.15 (m,
1H). Anal (C27H30N2O3Á HCl), C, H, N.
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16. Priest, B. T.; Murphy, B. A.; Lindia, J. A.; Diaz, C.; Abbadie, C.; Ritter, A. M.;
Liberatore, P.; Iyer, L. M.; Kash, S. F.; Kohler, M. G.; Kaczorowski, G. J.;
MacIntyre, D. E.; Martin, W. J. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 9382–9387.
17. Renganathan, M.; Cummins, T. R.; Waxman, S. G. J. Neurophysiol. 2001, 86, 629–
640.
Compound 16 (0.430 g, 1.60 mmol) was treated with (4-phen-
oxy)phenylboronic acid (0.420 g, 2.00 mmol) by Method B to pro-
vide 0.390 g of free base of 24, that was converted to HCl salt,
mp 181–182 °C. MS (DCI/NH3) m/z 363 (M+H)+. 1H NMR (DMSO-
d6) (free base) d 7.71 (d, 2H, J = 8.48 Hz), 7.44 (t, 2H, J = 7.46 Hz),
7.19 (t, 1H, J = 8.48 Hz), 7.09 (m, 5H), 7.02 (d, 1H, J = 3.73 Hz),
3.70 (br s, 4H), 2.36 (t, 4H, J = 5.08 Hz), 2.21 (s, 3H). Ana-
l.(C22H22N2O2ÁHClÁH2O) C, H, N.
18. Lai, J.; Gold, M. S.; Kim, C.-S.; Bian, D.; Ossipov, M. H.; Hunter, J. C.; Porreca, F.
Pain 2002, 95, 143–152.
6.22. (4-Methylpiperazin-1-yl)-[5-(4-t-butylphenyl)furan-2-yl]-
methanone hydrochloride (25)
19. Jarvis, M. F.; Honore, P.; Shieh, C. C.; Chapman, M.; Joshi, S.; Zhang, X.; Kort, M.;
Carroll, W. A.; Marron, B.; Atkinson, R.; Thomas, J.; Liu, D.; Krambis, M.; Liu, Y.;
McGaraughty, S.; Chu, K.; Roeloffs, R.; Zhong, C.; Mikusa, J. P.; Hernandez, G.;
Gauvin, D.; Wade, C.; Zhu, C.; Pai, M.; Scanio, M.; Shi, L.; Drizin, I.; Gregg, R.;
Matulenko, M.; Hakeem, A.; Gross, M.; Johnson, M.; Marsh, K.; Wagoner, P. K.;
Sullivan, J.; Faltynek, C.; Krafte, D. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 8520–
8525.
20. Kort, M. E.; Drizin, I.; Gregg, R. J.; Scanio, M. J.; Shi, L.; Gross, M. F.; Atkinson, R.
N.; Johnson, M. S.; Pacofsky, G. J.; Thomas, J. B.; Carroll, W. A.; Krambis, M. J.;
Liu, D.; Shieh, C. C.; Zhang, X.; Hernandez, G.; Mikusa, J. P.; Zhong, C.; Joshi, S.;
Honore, P.; Roeloffs, R.; Marsh, K. C.; Murray, B. P.; Liu, J.; Werness, S.; Faltynek,
C. R.; Krafte, D. S.; Jarvis, M. F.; Chapman, M. L.; Marron, B. E. J. Med. Chem. 2008,
1, 407–416.
Compound 16 (0.100 g, 0.360 mmol) was treated with (4-phen-
oxy)phenylboronic acid (0.078 g, 0.430 mmol) by Method B to pro-
vide 0.100 g of free base of 25, that was converted to HCl salt, mp
250–251 °C. MS (DCI/NH3) m/z 327 (M+H)+. 1H NMR (DMSO-d6)
(free base) d 7.68 (d, 2H, J = 8.74 Hz), 7.49 (d, 2H, J = 8.74 Hz),
7.08 (d, 2H, J = 3.57 Hz), 7.02 (d, 1H, J = 3.57 Hz), 3.70 (br s, 4H),
2.38 (t, 4H, J = 5.15 Hz), 2.21 (s, 3H), 1.3 (s, 9H). Ana-
l.(C20H26N2O2ÁHClÁ0.25H2O) C, H, N.
21. Daniel, S.; Malkowitz, L.; Wang, H.-C.; Beer, B.; Blume, A. J.; Ziai, M. R.
J. Pharmacol. Methods 1991, 25, 185–193.
6.23. [5-(4-Phenoxyphenyl)-furan-2-yl]-piperazin-1-yl-
methanone hydrochloride (26)
22. For the inactivated state protocol, a pre-pulse voltage at which 50% of channels
are inactivated (V1/2 = À40 mV) was employed. For the resting state protocol, a
pre-pulse voltage at which 100% of channels are available to be activated
(V0 = À100 mV) was employed. Additional details are provided in Ref. 19.
23. Kim, S. H.; Chung, J. M. Pain 1992, 50, 355–363.
24. Jarvis, M. F.; Burgard, E. C.; McGaraughty, S.; Honore, P.; Lynch, K.;
Brennan, T. J.; Subieta, A.; van Biesen, T.; Cartmell, J.; Bianchi, B.;
Niforatos, W.; Kage, K.; Yu, H.; Mikusa, J.; Wismer, C. T.; Zhu, C. Z.;
Chu, K.; Lee, C. H.; Stewart, A. O.; Polakowski, J.; Cox, B. F.; Kowaluk, E.;
Williams, M.; Sullivan, J.; Faltynek, C. Proc. Natl. Acad. Sci. U.S.A. 2002, 99,
17179–17184.
Compound 17 (0.120 g, 0.300 mmol) and 4-phenoxyphenylbo-
ronic acid (0.077 g, 0.36 mmol) were processed by Method B to
yield 26, mp 195–196 °C. MS (DCI/NH3) m/z 349 (M+H)+. 1H NMR
(DMSO-d6)(free base) d 7.76 (d, 2H J = 8.82 Hz), 7.42 (t, 2H,
J = 7.46 Hz), 7.18 (t, 1H, J = 8.48 Hz), 7.09 (m, 5H), 7.02 (d, 1H,
J = 3.39 Hz), 3.65 (br s, 4H), 2.80 (m, 4H). Anal (C21H20N2O3ÁHClÁ0.5
H2O) C, H, N.
25. Joshi, S. K.; Honore, P. Expert Opin. Drug Discov. 2006, 1, 323–334.