Synthesis of N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamides as new selective ligands for sigma receptors

Article abstract of DOI:10.1016/j.bmc.2012.09.044

Novel benzofuran-2-carboxamide ligands, which are selective for sigma receptors, have been synthesized via a microwave-assisted Perkin rearrangement reaction and a modified Finkelstein halogen-exchange used to facilitate N-alkylation. The ligands synthesized are the 3-methyl-N-phenyl-N-(3-(piperidin- 1-yl)propyl)benzofuran-2-carboxamides (KSCM-1, KSCM-5 and KSCM-11). The benzofuran-2-carboxamide structure was N-arylated and N-alkylated to include both N-phenyl and N-(3-(piperidin-1-yl)propyl substituents, respectively. These new carboxamides exhibit high affinity at the sigma-1 receptor with K _i values ranging from 7.8 to 34 nM. Ligand KSCM-1 with two methoxy substituents at C-5 and C-6 of the benzofuran ring, and K_i = 27.5 nM at sigma-1 was found to be more selective for sigma-1 over sigma-2.

Full text of DOI:10.1016/j.bmc.2012.09.044

Bioorganic & Medicinal Chemistry 20 (2012) 6856–6861
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Synthesis of N-phenyl-N-(3-(piperidin-1-yl)propyl)benzofuran-2-carboxamides
as new selective ligands for sigma receptors
⇑
Karla-Sue C. Marriott , Andrew Z. Morrison, Misty Moore, Olarongbe Olubajo, Leonard E. Stewart
Department of Natural Sciences, Savannah State University, College of Sciences and Technology, PO Box 20600, 3219 College Street, Savannah 31404, Georgia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 July 2012
Revised 12 September 2012
Accepted 19 September 2012
Available online 29 September 2012
Novel benzofuran-2-carboxamide ligands, which are selective for sigma receptors, have been synthesized
via a microwave-assisted Perkin rearrangement reaction and a modified Finkelstein halogen-exchange
used to facilitate N-alkylation. The ligands synthesized are the 3-methyl-N-phenyl-N-(3-(piperidin-1-
yl)propyl)benzofuran-2-carboxamides (KSCM-1, KSCM-5 and KSCM-11). The benzofuran-2-carboxamide
structure was N-arylated and N-alkylated to include both N-phenyl and N-(3-(piperidin-1-yl)propyl
substituents, respectively. These new carboxamides exhibit high affinity at the sigma-1 receptor with
Ki values ranging from 7.8 to 34 nM. Ligand KSCM-1 with two methoxy substituents at C-5 and C-6 of
the benzofuran ring, and Ki = 27.5 nM at sigma-1 was found to be more selective for sigma-1 over
sigma-2.
Keywords:
Sigma
Receptor
Ligand
Ó 2012 Elsevier Ltd. All rights reserved.
Benzofuran
Carboxamide
Alzheimer’s
Neurodegenerative
1. Introduction
Various drugs, including antipsychotics (morphine analogs),
neuroleptics (haloperidol) and neuroactive steroids (progesterone,
In the mid-70s sigma receptors were mistakenly characterized
as a new subtype of opioid receptors.1 However, cloning of the
guinea pig sigma-1 binding site in 1996 revealed this protein to
be unique sharing no homology with any other mammalian pro-
tein including all types of molecular chaperones.2 Sigma receptors
are classified into two subtypes, sigma-1 and sigma-2. To date, the
sigma-2 receptor has not been cloned. Sigma-1 receptors are endo-
plasmic reticular (ER) proteins consisting of 223-amino acids with
a molecular mass of 24-kDa, and two-transmembrane-spanning
regions.3,4 Sigma-1 receptors are widely distributed throughout
the body, centrally and peripherally, primarily functioning in a
modulatory role on dopamine, acetylcholine, NMDA and opioid
receptors.5 They are known to translocate during signal transduc-
tion and have been linked to the modulation or production of var-
ious intracellular secondary messengers.3,6 Sigma-2 receptors are
understood to be slightly smaller in size than the sigma-1 receptor.
Pharmacological evaluations reveal that sigma-2 receptors may be
lipid raft proteins that affect calcium signaling via sphingolipid
products and unlike sigma-1 receptors, sigma-2 receptors do not
translocate.7 Both sigma receptors are highly expressed on tumor
cell lines from human and rat cancer tissues. The overexpression
of sigma-2 receptors in human and murine tumors suggests that
these receptors may be a biomarker of tumor cell proliferation.7
DHEA), bind to sigma-1 receptors.8 Ligands that bind to and mod-
ulate the sigma-1 receptor have been proposed to exhibit effects in
several therapeutic areas such as neurodegenerative disorders,
pain, depression, schizophrenia, amnesia, Alzheimer’s disease,
Parkinson’s disease and stroke.8 Sigma-1 receptors have also been
documented as a target for cocaine and associated with the toxic
and stimulant actions of cocaine.7 In general sigma-1 antagonists
may have potential use in the treatment of addiction. The binding
site of sigma-1 receptors is reported to consist of an amine binding
site flanked on either side by hydrophobic binding pockets that
display bulk tolerance and as such, typical pharmacophoric
features of sigma-1 receptors include an alkylamine moiety within
the general molecular structure.9 Hence, a common pharmaco-
phoric feature of sigma-1 ligands is an N-alkyl, N,N-dialkyl or
N-arylalkyl amine moiety10 which poses a challenge in the synthe-
sis of these ligands. Interestingly, progesterone which lacks a basic
nitrogen, is considered one of the putative endogenous ligands for
the sigma-1 receptor.11 N,N-Dimethyltryptamine (DMT) has been
identified as a potential endogenous sigma-1 receptor ligand, but,
the role of DMT as a sigma-1 receptor modulator is unclear due
to low physiological concentrations in brain tissues.12 Our synthe-
sized ligands have a benzofuran-2-carboxamide structural moiety
which has been N-arylated and N-alkylated to include both N-phe-
nyl and N-(3-(piperidin-1-yl)propyl substituents, respectively, as
summarized structurally in Figure 1. These new carboxamide
ligands structurally consist of a basic alkylamine moiety the
⇑
Corresponding author. Tel.: +995 912 358 4454.
E-mail address: marriottk@savannahstate.edu (K.-S.C. Marriott).
0968-0896/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmc.2012.09.044

K.-S.C. Marriott et al. / Bioorg. Med. Chem. 20 (2012) 6856–6861
6857
reaction was employed to convert commercially available 1-(3-
chloropropyl)piperidine hydrogen chloride salt in the presence of
potassium iodide, tetrabutylammonium bromide (TBAB) and
potassium carbonate into the more reactive iodopropylpiperidine
in situ, which then reacted with anions obtained from treating car-
boxamides (2a and 2b) with sodium hydride producing KSCM-11
and KSCM-1. 3-Methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl)
benzofuran-2-carboxamide (KSCM-5) was similarly synthesized by
N-alkylation of carboxamide (2c) with 1-(3-iodopropyl)piperidine.
2.2. Binding assay
Compounds were screened by the National Institute of Mental
Health-Psychoactive Drug Screening Program (NIMH-PDSP)
against a panel of G-protein coupled receptors (GPCRs) and molec-
ular targets due to the fact that many ligands with high affinity at
sigma receptors have proven to also exhibit significant binding at
one or more other central nervous system (CNS) relevant receptor
sites. This evaluation has led to the discovery of three new sigma
receptor selective ligands. Primary binding assays were performed
at serotonin 5-HTs, adrenergic (Alpha1-A, -B, -D, Alpha2-A, -B,-C,
Beta-1, -2, -3), cannabinoid (CB1and CB2), Dopamine (D1–D5),
histamine (H1 and H2), opioid (KOR, MOR and DOR), Muscarinic
(M1–M5), N-methyl-D-aspartate (NMDA), Sigma-1, Sigma-2,
metabotropic glutamate (mGluR5 Rat Brain), and benzodiazepine
(BZP Rat Brain) receptor sites, as well as, dopamine transporter
Figure 1. General ligand structure.
N-(3-(piperidin-1-yl)propyl with a protonatable nitrogen and an
aromatic phenyl ring and benzofuran moiety as two hydrophobic
residues (Fig. 1). Additionally, we introduced structural variations
at the benzofuran moiety in the form of methyl ether substituents
(R1 and R2, Fig. 1) to investigate the effect these substituents have
on receptor binding affinity.
2. Results and discussion
2.1. Chemistry
(DAT), c-aminobutyric acid type A (GABAA), norepinephrine trans-
Our microwave-assisted expedited synthetic pathway is
straightforward, involving the preparation of 3-methylbenzofu-
ran-2-carboxylic acids (1a and 1b) in quantitative yields via a
Perkin rearrangement reaction of mono- and di-methoxy-3-bro-
mocoumarins as previously described.13 Mono- and di-hydrox-
ycoumarins were methylated and subsequently brominated at
position-3 via a microwave-assisted regioselective bromination
with N-bromosuccinimide (NBS) to yield mono- and di-methoxy-
3-bromocoumarins in 85–89% yields.13
3-Bromocoumarins traditionally undergo base-catalyzed Perkin
rearrangement, which requires 3 hours reflux quantitatively yield-
ing benzofuran-2-carboxylic acids.14 However under microwave
reaction conditions these reactions were completed in 5 min.13
Mono- and di-methoxy-3-methyl-N-phenylbenzofuran-2-carbox-
amides (2a and 2b) were produced by reacting aniline with the
corresponding 3-methylbenzofuran-2-carboxylic acids (1a and
1b) in the presence of DCC and DMAP at room temperature, as
outlined in Scheme 1. 3-Methyl-N-phenylbenzofuran-2-carboxam-
ide (2c) was produced by condensing commercially available
3-methylbenzofuran-2-carboxylic acid (1c) with aniline.
porter (NET) and serotonin transporter (SERT) molecular targets.
Compounds showing >50% inhibition of radioligand specific bind-
ing at the stated GPCRs and molecular targets (Tables 1 and 2)
were forwarded for additional screening (secondary binding
assays) to determine Ki values at the respective GPCR binding sites
using radioligand binding assays. It was determined that com-
pounds KSCM-1, KSCM-5 and KSCM-11 have the desired selectivity
for sigma receptors (sigma-1 and sigma-2) over non-sigma
receptors.
Secondary binding assays of these compounds showed greater
affinity at sigma receptors over non-sigma receptors such as
5-HT2A, 5-HT2B, 5HT3, Alpha2A, Alpha2C, D3, and M4 (Tables 3
and 4). Consistent with documented sigma-1 receptor ligands,
the molecular structures of KSCM-1, KSCM-5 and KSCM-11 include
a basic alkyl amine group, flanked by two hydrophobic residues (an
aromatic phenyl and benzofuran ring).
Based upon the sigma-1 receptor selective ligand pharmaco-
phore profile [10], a sigma-1 selective ligand usually possesses a
primary and secondary hydrophobic site separated by an amine.
The sigma-1 receptor site displays some bulk tolerance and so this
prompted us to explore introducing a benzofuran moiety to pro-
duce the general molecular structure summarized in Figure 1. All
three compounds have an N-arylated benzofuran-2-carboxamide
scaffold which was then N-alkylated yielding N-(3-(piperidin-1-
Syntheses of mono- and di-methoxy-3-methyl-N-phenyl-N-(3-
(piperidin-1-yl)propyl)benzofuran-2-carboxamides (KSCM-11 and
KSCM-1) were achieved by treating carboxamides (2a and 2b) with
NaH followed by N-alkylation with 1-(3-iodopropyl)piperidine
outlined in Scheme 1. A modified halogen exchange Finkelstein
Scheme 1. Reagents: (a) DCC, DMAP, aniline, CH2Cl2; (b) NaH, 1-(3-chloropropyl)piperidineÁHCl, K2CO3, KI, TBAB, CH2Cl2.

6858
K.-S.C. Marriott et al. / Bioorg. Med. Chem. 20 (2012) 6856–6861
Table 1
over sigma-2, Table 3). KSCM-1 showed no significant affinity at
Primary binding assay at sigma receptors
non-sigma receptors selected for secondary binding assay, Ki deter-
mination (Table 4), with Ki values ranging from 945 nM at Alpha2A
to 7,612 nM at 5-HT3. The exclusion of a methoxy substituent at
C-5 of the benzofuran moiety to produce KSCM-11 resulted in a
slightly decreased affinity at sigma-1 (Ki = 34 nM, Table 3), how-
ever, a significant increase in affinity at sigma-2 (Ki = 41 nM, Table
3) in comparison to KSCM-1. The mono-methoxy compound
KSCM-11 has similar affinity at both sigma receptor binding sites
and thus no significant selectivity of sigma-1 over sigma-2 was
observed (Ki = 34 nM at sigma-1 and 41 nM at sigma-2, Table 3).
KSCM-11 showed no significant affinity at non-sigma receptors se-
lected for secondary binding assay, Ki determination (Table 4), with
Ki values ranging from 204 nM at 5-HT2B to >10,000 nM at M4. The
exclusion of both methoxy substituents at C-5 and C-6 of the
benzofuran moiety to produce KSCM-5 resulted in a significantly
increased affinity at both sigma-1 (Ki = 7.8 nM, Table 3) and sig-
ma-2 (Ki = 16 nM, Table 3) in comparison to KSCM-1 and KSCM-
11. However, selectivity of KSCM-5 for sigma-1 over the sigma-2
was only twofold. KSCM-5 showed no significant affinity at
non-sigma receptors selected for secondary binding assay, Ki deter-
mination (Table 4), with Ki values ranging from 249 nM at Alpha2C
to 6,739 nM at D3. The sigma-2 receptor secondary binding curves
for compounds KSCM-1, KSCM-5, KSCM-11, PDSP control, and hal-
operidol are shown in Figure 2. The sigma-2 receptor binding
curves illustrate the readily noticeable link between affinity at
the sigma-2 receptor and the loss of methoxy substituents at C-5
and C-6 of the benzofuran ring. Compound KSCM-5 without meth-
oxy substituents was found to be a potent sigma-2 ligand with
comparable potency to haloperidol at sigma-2 as is readily discern-
ible from the binding curve (Fig. 2).
Compound
% Inhibition
r
-1
r-2
KSCM-1
KSCM-5
KSCM-11
99.8
100.6
97.7
81.4
93.5
88.5
Primary binding assays performed in sigma binding buffer (50 mM Tris–HCl, pH
8.0). Sigma-1 receptors were labeled with [3H](+)-pentazocine and sigma-2
receptors were labeled with [3H]Ditolylguanidine (DTG) with haloperidol as the
reference compound in both cases. Data represent mean % inhibition (N = 4 deter-
minations) for compound tested at receptor subtypes. Significant inhibition is
considered >50%. In cases where negative inhibition (À) is seen, this represents a
stimulation of binding. Occasionally, compounds at high concentrations will non-
specifically increase binding. The default concentration for primary binding
experiments is 10 lM.
Table 2
Primary binding assay at nonsigma receptors
Compound
% Inhibition
5-HT2A 5-HT2B 5HT3 Alpha2A Alpha2C D3
M4
KSCM-1
KSCM-5
KSCM-11
76.6
18.1
61.2
43.8
69.2
93.9
64.2
2.9
7.3
55.2
77.7
81.1
78.9
61.9
49.0
38.8 54.4
60.6 43.1
40.6 68.4
Assays were performed using transiently or stably transfected cell lines (e.g.,
HEK293, COS, CHO, NIH3T3). Refer to Table 5 for radioligands and reference com-
pounds listing. Data represent mean % inhibition (N = 4 determinations) for com-
pound tested at receptor subtypes. Significant inhibition is considered >50%. In
cases where negative inhibition (À) is seen, this represents a stimulation of binding.
Occasionally, compounds at high concentrations will non-specifically increase
binding. The default concentration for primary binding experiments is 10 lM.
Table 3
3. Conclusion
Secondary binding assay, Ki determination at sigma receptors
Compound
r
-1 (Ki, nM)
r
-2 (Ki, nM)
r-2/r-1
In this study, we have identified three new sigma receptor
selective ligands based on features of the sigma-1 receptor binding
site which consists of an amine binding site flanked on either side
by hydrophobic binding pockets. All three ligands have high affin-
ity at sigma-1 with Ki values ranging from 7.8 to 34 nM. KSCM-1
was the most selective with Ki = 27.5nM at sigma-1 and a 19-fold
selectivity for sigma-1 over sigma-2. Ligands KSCM-1, KSCM-5
and KSCM-11 all possess basic nitrogen atoms and are structurally
composed of benzofuran-2-carboxamide moieties which have
been N-arylated and N-alkylated to include both N-phenyl and
N-(3-(piperidin-1-yl)propyl substituents. The expedited synthetic
procedures employed include regioselective microwave-assisted
NBS bromination as well as microwave-assisted Perkin rearrange-
ment reactions to prepare benzofuran-2-carboxylic acids (1a and
1b) from the corresponding 3-bromocoumarins in very high yields.
KSCM-1
KSCM-5
KSCM-11
Haloperidol
27.5
7.8
34
528
16
41
19
2
1.2
1.7
13
8
Affinities Ki (nM) were determined in rat brain homogenate (sigma-1), PC12 cells
(sigma-2), sigma binding buffer (50 mM Tris–HCl, pH 8.0). Sigma-1 receptors were
labeled with [3H](+)-pentazocine and sigma-2 receptors were labeled with [3H]DTG
with haloperidol as the reference compound in both cases.
yl)propyl introducing a basic protonatable nitrogen as well as a
three-carbon alkyl linker as summarized structurally in Figure 1.
Additionally, the benzofuran molecular structure was varied by
substitutions at C-5 and C-6 with methyl ether (R1 and R2, Fig. 1)
to explore the impact that introduction of additional hydrogen
bond acceptor (HBA) centers would have on receptor binding affin-
ity and selectivity. We observed that the inclusion of methoxy sub-
stituents at both C-5 and C-6 of the benzofuran moiety resulted in
both high affinity and selectivity at the sigma-1 receptor over the
sigma-2 receptor as observed for KSCM-1 with Ki = 27.5 nM at
sigma-1 and 528 nM at sigma-2 (19-fold selectivity for sigma-1
4. Experimental section
1H and 13C NMR spectra were recorded on a JEOL 300 MHz spec-
trometer. Chemical shifts for 1H and 13C NMR spectra are reported
in d values (parts per million, ppm) relative to an internal standard
Table 4
Secondary binding assay, Ki determination at nonsigma receptors
Ki (nM)
Compound
5-HT2A
5-HT2B
5HT3
Alpha2A
Alpha2C
D3
M4
KSCM-1
KSCM-5
KSCM-11
2564
NT
2766
NT
936
204
7612
NT
NT
945
1232
653
1542
249
NT
NT
6739
NT
2871
NT
>10,000
Assays were performed using transiently or stably transfected cell lines (e.g., HEK293, COS, CHO, NIH3T3). Refer to Table 5 for radioligands and reference compounds listing.
NT = not tested.

K.-S.C. Marriott et al. / Bioorg. Med. Chem. 20 (2012) 6856–6861
6859
Figure 2. Secondary binding curves for Ki determinations of new ligands at sigma-2. Ligand binding of KSCM-1 (A), KSCM-5 (B) and KSCM-11 (C) at sigma-2 receptors. Sigma-
2 receptors were labeled with [3H]DTG and haloperidol as the reference ligand.
of tetramethylsilane (TMS) in CDCl3. Multiplicities are presented as
follows: s = singlet, d = doublet, t = triplet, q = quartet, qt = quintu-
plet, m = multiplet. Microwave syntheses were carried out on a
CEM MarsXpress. HRMS data were obtained in the Mass Spectrom-
etry Laboratory, School of Chemical Sciences, University of Illinois.
Solvents were purified using standard procedures. TLC analyses
taining 100 ll of Standard Binding Buffer. Then, duplicate 50-ll ali-
quots of the test and reference compound dilutions were added.
Finally, either crude membrane fractions prepared from rat brain
homogenate for sigma-1 receptors or PC12 cell homogenates for
sigma-2 receptors were added to the wells, and the plates shielded
from light to prevent photolysis of light sensitive ligands. For sig-
ma-1 receptors, the reactions were incubated at 37 °C for 2.5 h,
and for sigma-2 receptors, the reactions were incubated at room
temperature for 2 h. Labeled receptors were harvested by rapid
filtration on to Whatman GF/B glass filters pre-soaked with 0.3%
polyethyleneimine using 96-well Brandel harvester. Four rapid
were performed on Fluka 200 lm Silica Gel particle size 25 lm
F254 plates and visualized by quenching of UV fluorescence
(kmax = 254 nm). All new compounds were purified on a Biotage
Isolera-4 flash purification system using the indicated SNAP
cartridges and solvents as eluents.
500 ll washes are performed with chilled Standard Binding buffer
to reduce non-specific binding. Filters were placed in 6-ml scintil-
lation tubes and allowed to dry overnight. EcoScint scintiallation
cocktail (National Diagnostics) was added to each tube prior to
counting. For higher throughput assays, bound radioactivity was
harvested onto 0.3% polyethyleneimine-treated, 96-well filter mats
using a 96 well Filtermate harvester. The filter mats were dried, the
scintillate melted onto the filters and the radioactivity counted in a
Microbeta scintillation counter. Raw data (dpm) representing total
radioligand binding (i.e., specific + nonspecific binding) were plot-
ted as a function of the logarithm of the molar concentration of the
competitor (i.e., test or reference compound). Non-linear regres-
sion of the normalized (i.e., percent radioligand binding compared
to that observed in the absence of test or reference compound) raw
data was performed in Prism 4.0 (GraphPad Software) using built-
in three parameter logistic model describing ligand competition
binding to radioligand-labeled sites: y = bottom + [(topÀbottom)/
(1 + 10 Â Àlog IC50)] where bottom equals the residual radioligand
binding measured in the presence of 10 mM reference (i.e., non-
specific binding) and top equals the total radioligand binding ob-
served in the absence of competitor. The log IC50 (i.e., the log of
the ligand concentration that reduces radioligand binding by
50%) was thus estimated from the data and used to obtain the Ki
by applying the Cheng-Prusoff approximation.
5. In vitro characterization, primary and secondary binding
experiments
Radioligand binding assays using cloned G-protein coupled
receptors (GPCRs), ion channels, and transporters were performed
by the National Institute of Mental Health-Psychoactive Drug
Screening Program (NIMH-PDSP) using membranes from
transiently transfected or stable cell lines. Detailed protocols
(including cell handling, buffer composition, assay conditions,
etc.) for all assays are available online (http://pdsp.med.unc.edu/).
Initial primary binding screening assays were performed using a
50
lM (initial) À10
lM (final) assay concentration of reference
and test compounds. The percent inhibition of specific binding by
the test compound was determined and if the test compound
inhibited >50% of radioligand specific binding, then secondary
binding assays Ki determinations were performed. Secondary bind-
ing assays, Ki determinations were performed by measuring the
inhibition of radioligand binding by various concentrations of test
and reference compound. In summary, compounds/ligands were
prepared as a 1.0 mg/ml stock in Standard Binding Buffer (50 mM
Tris HCl pH 8.0) or DMSO according to the solubility of the com-
pound. A similar stock of Haloperidol was also prepared as a refer-
ence for a positive control. Dilutions of the test and reference
compounds were then prepared in Standard Binding Buffer:
5.1. Ligand synthesis
0.05 nM, 0.5 nM, 1.5 nM, 5 nM, 50 nM, 150 nM, 500 nM, 1.5
M and 50
M. [3H]Pentazocine (3 nM) was used as the radioli-
gand for sigma-1 receptors and [3H]Ditolyglguanidine (DTG)
(1 nM) as the radioligand for sigma-2 receptors. Aliquots (50 l)
of radioligand were dispensed into the wells of a 96-well plate con-
lM,
5
l
l
5.1.1. 6-Methoxy-3-methyl-N-phenylbenzofuran-2-carboxamide
(2a)
To a mixture of aniline (0.689 g, 7.4 mmol) in dichloromethane
(25 mL), 3-methyl-6-methoxybenzofuran-2-carboxylic acid (1a)
l

6860
K.-S.C. Marriott et al. / Bioorg. Med. Chem. 20 (2012) 6856–6861
(1.501 g, 7.3 mmol) was added with stirring. Then DMAP (0.094 g,
0.77 mmol) was added, followed by DCC (1.583 g, 7.7 mmol). The
reaction was left to stir at room temperature for 23 h. The reaction
mixture was then filtered and the filtrate washed with water
(20 mL Â 2), then 5% acetic acid (20 mL Â 2) and again with water
(20 mL Â 2). The crude product was recrystallized from methanol
to yield 2a as white crystals (1.37 g, 67%), mp 176–178 °C. 1H
NMR (300 MHz, CDCl3) d 2.64 (s, 3H), 3.88 (s, 3H), 6.93–7.00 (m,
2H), 7.12–7.16 (t, J = 7.41 Hz, 1H) 7.35–7.40 (t, J = 7.65 Hz, 2H),
7.48–7.50 (d, J = 8.6 Hz, 1H), 7.68–7.71 (d, J = 8.5 Hz, 2H), 8.26 (s,
1H). 13C NMR (300 MHz, CDCl3) d 9.2, 55.8, 95.6, 112.9, 119.9,
121.4, 123.3, 124.4, 129.1, 137.7, 141.8, 154.5, 158.1, 160.5. MS(E-
SI)+ calcd for C17H16NO3 [M+H]+: 282.1130, found: 282.1124.
1H NMR (300 MHz, CDCl3) d 1.38–1.56 (m, 6H), 1.81–1.91 (qt,
J = 7.58 Hz, 2H), 2.31–2.36 (m, 6H), 2.34 (s, 3H), 3.80 (s, 3H), 3.87
(s, 3H), 3.86-3.93 (m, 2H), 6.52 (s, 1H), 6.81 (s, 1H), 7.10–7.30 (m,
5H).13C NMR (300 MHz, CDCl3) d 9.9, 10.1, 24.5, 25.3, 26.0, 29.7,
49.0, 54.6, 56.2, 56.3, 56.6 94.7, 100.8, 120.8, 122.4, 126.5, 126.9,
128.9, 143.2, 143.6, 146.7, 148.4, 149.9, 161.4. MS(ESI)+ calcd for
C
26H33N2O4 [M+H]+: 437.2440, found: 437.2440.
5.1.5. 3-Methyl-N-phenyl-N-(3-(piperidin-1-yl)propyl) benzo
furan-2-carboxamide (KSCM-5)
Compound 2c (0.200 g, 0.80 mmol) was added to dry dichloro-
methane (25 ml) with stirring under nitrogen atmosphere. To this
solution NaH (290 mg, 7.25 mmol) 60% dispersion in mineral oil
was added and at reflux for 1 h. The reaction mixture was cooled
in an ice-bath and 1-(3-chloropropyl)piperidine hydrogen chloride
salt (0.238 g, 1.2 mmol), potassium carbonate (0.660 g, 4.8 mmol),
tetrabutylammoniumbromide (0.100 g, 0.310 mmol) and potas-
sium iodide (0.299 g, 1.8 mmol) added with stirring. The reaction
mixture was reflux for 24 h. The reaction mixture was then cooled
and slowly quenched with ethanol. The reaction mixture was
washed with water (10 ml  2) and the organic layer dried over
magnesium sulfate. The crude product was purified by high perfor-
mance flash purification using a Biotage Isolera 4 system, SNAP
(SiO2) KP-NH column, solvent dichloromethane/methanol (9:1) as
eluent to give 0.189 g (63%) of KSCM-5 as a light brown paste. 1H
NMR (300 MHz, CDCl3) d 1.36–1.56 (m, 6H), 1.82–1.92 (qt,
J = 7.58 Hz, 2H), 2.31–2.36 (m, 6H), 2.34 (s, 3H), 3.90–3.95 (t,
J = 7.64 Hz, 2H), 7.03–7.05 (d, J = 8.03 Hz, 1H), 7.11–7.26 (m, 7H),
7.43–7.45 (d, J = 6.85 Hz, 1H).13C NMR (300 MHz, CDCl3) d 9.1,
24.5, 25.3, 26.0, 49.0, 54.6, 56.6, 111.4, 120.3, 121.2, 122.6, 126.2,
126.7, 127.0, 128.9, 129.0, 142.8, 144.4, 153.4, 161.5. MS(ESI)+ cal-
culated for C24H29N2O2 [M+H]+: 377.2229, found: 377.2227.
5.1.2. 5,6-Dimethoxy-3-methyl-N-phenylbenzofuran-2-carboxa
mide (2b)
To a mixture of aniline (0.398 g, 4.27 mmol) in dichloromethane
(15 mL), 3-methyl-5,6-dimethoxybenzofuran-2-carboxylic acid
(1b) (1.005 g, 4.25 mmol) was added with stirring. Then DMAP
(0.090 g, 0.44 mmol) was added, followed by DCC (0.934 g,
4.53 mmol). The reaction was left to stir at room temperature for
23 h. The reaction mixture was then filtered and the filtrate
washed with water (20 mL Â 2), then 5% acetic acid (20 mL Â 2)
and again with water (20 mL Â 2). The crude product was recrys-
tallized from methanol to yield 2b as white crystals (0.94 g, 71%),
mp 183–185 °C. 1H NMR (300 MHz, CDCl3) d 2.64 (s, 3H), 3.95 (s,
6H), 6.97 (s, 1H), 6.99 (s, 1H) 7.12–7.72 (m, 5H), 8.26 (s, 1H). 13C
NMR (300 MHz, CDCl3) d 9.2, 56.3, 56.4, 94.9, 101.2, 119.8, 121.7,
124.3, 129.1, 137.7, 141.8, 147.2, 148.3, 150.8, 158.0. MS(ESI)+
calcd for C18H18NO4 [M+H]+: 312.1236, found: 312.1235.
5.1.3. 3-Methyl-N-phenylbenzofuran-2-carboxamide (2c)
To a mixture of aniline (0.690 g, 7.41 mmol) in dichloromethane
(25 mL), 3-methylbenzofuran-2-carboxylic acid (1c) (1.00 g,
5.7 mmol) was added with stirring. Then DMAP (0.116 g,
0.57 mmol) was added, followed by DCC (1.220 g, 5.9 mmol). The
reaction was left to stir at room temperature for 23 h. The reaction
mixture was then filtered and the filtrate washed with water
(20 mL Â 2), then 5% acetic acid (20 mL Â 2) and again with water
(20 mL Â 2). The crude product was recrystallized from methanol
to yield 2c as off-white crystals (0.896 g, 63%), mp 118–120 °C.
1H NMR (300 MHz, CDCl3) d 2.68 (s, 3H), 7.13–7.18 (t, J = 7.4 Hz,
1H), 7.30–7.52 (m, 5H), 7.62–7.65 (d, J = 7.57 Hz, 1H) 7.72–7.73
(d, J = 8.57 Hz, 2H), 8.35 (s, 1H). 13C NMR (300 MHz, CDCl3) d 9.1,
111.6, 120.0, 121.1, 123.4, 123.9, 124.6, 127.5, 129.2, 129.9,
137.5, 142.4, 153.3, 158.1. MS(ESI)+ calcd for C16H14NO2 [M+H]+:
252.1025, found: 252.1027.
5.1.6. 6-Methoxy-3-methyl-N-phenyl-N-(3-(piperidin-1-yl)
propyl)benzofuran-2-carboxamide (KSCM-11)
Compound 2a (0.200 g, 0.71 mmol) was added to dry dichloro-
methane (25 mL) with stirring under nitrogen atmosphere. To this
solution NaH (0.290 g, 7.25 mmol) 60% dispersion in mineral oil
was added and the reaction heated at reflux for 1 h. The reaction
mixture was then cooled in an ice-bath and 1-(3-chloropro-
pyl)piperidine hydrogen chloride salt (0.238 g, 1.2 mmol),
potassium carbonate (0.660 g, 4.8 mmol), tetrabutylammoniumbr-
omide (0.090 g, 0.279 mmol) and potassium iodide (0.357 g,
2.15 mmol) added with stirring. The reaction mixture was then
heated at reflux for 24 h. The reaction mixture was then cooled
and slowly quenched with ethanol. The reaction mixture was
washed with water (10 ml  2) and the organic layer dried over
magnesium sulfate. The crude product was purified by high perfor-
mance flash purification using a Biotage Isolera 4 system, SNAP
(SiO2) KP-NH column, solvent dichloromethane/methanol (9:1) as
eluent to give 0.168 g (58%) of KSCM-11 as a brown paste. 1H
NMR (300 MHz, CDCl3) d 1.39–1.57 (m, 6H), 1.82–1.92 (qt,
J = 7.14 Hz, 2H), 2.33–2.37 (m, 6H), 2.35 (s, 3H), 3.74 (s, 3H), 3.90–
3.95 (t, J = 7.57 Hz, 2H), 6.52 (s, 1H), 6.78–6.80 (d, J = 8.61 Hz, 1H),
7.12–7.33 (m, 6H). 13C NMR (300 MHz, CDCl3) d 9.2, 24.5, 25.3,
26.0, 49.0, 54.6, 55.6, 56.6, 95.3, 112.3, 120.6, 122.1, 122.4, 126.6,
127.0, 129.0, 143.1, 143.6, 154.6, 159.6, 161.4. MS(ESI)+ calcd for
5.1.4. 5,6-Dimethoxy-3-methyl-N-phenyl-N-(3-(piperidin-1-yl)
propyl)benzofuran-2-carboxamide (KSCM-1)
Compound 2b (0.100 g, 0.321 mmol) was added to dry dichloro-
methane (15 mL) with stirring under nitrogen atmosphere. To this
solution NaH (0.130 g, 3.25 mmol) 60% dispersion in mineral oil
was added and the reaction heated at reflux for 1 h. The reaction
mixture was then cooled in an ice-bath and 1-(3-chloropro-
pyl)piperidine hydrogen chloride salt (0.110 g, 0.555 mmol), potas-
sium carbonate (0.380 g, 2.75 mmol), tetrabutylammoniumbr-
omide (0.046 g, 0.143 mmol) and potassium iodide (0.292 g,
1.76 mmol) added with stirring. The reaction mixture was then
heated at reflux for 24 h. The reaction mixture was then cooled
and slowly quenched with ethanol. The reaction mixture was
washed with water (5 ml  2) and the organic layer dried over
magnesium sulfate. The crude product was purified by high perfor-
mance flash purification using a Biotage Isolera 4 system, SNAP
(SiO2) KP-NH column, solvent dichloromethane/methanol (9:1) as
eluent to give 0.0841 g (60%) of KSCM-1 as a light brown paste.
C
25H31N2O3 [M+H]+: 407.2335, found: 407.2339.
Acknowledgments
Special thanks and appreciation are extended to the NIMH Psy-
choactive Drug Screening Program (PDSP). [Ki determinations,
receptor binding profiles, agonist and/or antagonist functional
data, HERG data, MDR1 data, etc. as appropriate] was generously

K.-S.C. Marriott et al. / Bioorg. Med. Chem. 20 (2012) 6856–6861
6861
provided by the National Institute of Mental Health’s Psychoactive
References and notes
Drug Screening Program, Contract # HHSN-271-2008-00025-C
(NIMH PDSP). The NIMH PDSP is Directed by Bryan L. Roth MD,
PhD at the University of North Carolina at Chapel Hill and Project
Officer Jamie Driscol at NIMH, Bethesda MD, USA. For experimental
details please refer to the PDSP web site http://pdsp.med.unc.edu/
and click on ‘Binding Assay’ or ‘Functional Assay’ on the menu bar
(experimental details have been updated!).
Thanks also extended to John C. Watts Jr. (external advisor),
Savannah, GA.
Karla-Sue C. Marriott received support for this work from the
National Institute of Health/National Institute on Drug Abuse
(NIH/NIDA) (DA027086).
1. Martin, W. R.; Eades, C. G.; Thompson, J. A.; Huppler, R. E.; Gilbert, P. E. J.
Pharmacol. Exp. Ther. 1976, 197, 517.
2. Hanner, M.; Moebius, F. F.; Flandorfer, A.; Knaus, H.-G.; Striessnig, J.; Kempner,
E.; Glossmann, H. Proc. Natl. Acad. Sci. U.S.A. 1996, 93, 8072.
3. Aydar, E.; Palmer, C. P.; Klyachko, V. A.; Jackson, M. B. Neuron 2002, 34, 399.
4. Jbilo, O.; Vidal, H.; Paul, R., et al J. Biol. Chem. 1997, 272, 27107.
5. Bowen, W. D. Pharm. Acta Helv. 2000, 74, 211.
6. Hayashi, T.; Su, T. P. Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 491.
7. Narayanan, S.; Mesangeau, C.; Poupaert, J.; McCurdy, C. Curr. Top. Med. Chem.
2011, 9, 1128.
8. Valade, A.; Cross, S. B.; Brown, C.; Detrait, E.; Ene, D.; Gillard, M.; Guyaux, M.;
Lamberty, Y.; Maguire, M.; Namdev, N.; Provins, L.; Schwartz, E.; Vermeiren, C.
Med. Chem. Commun. 2011, 2, 655.
9. Glennon, R. A. Mini-Rev. Med. Chem. 2005, 5, 927.
10. Ablordeppey, S. Y.; Fischer, J. B.; Glennon, R. A. Bioorg. Med. Chem. 2000, 8, 2105.
11. Hayashi, T.; Su, T. P. CNS Drugs 2004, 18, 269.
12. Fontanilla, D.; Johannessen, M.; Hajipour, A. R.; Cozzi, N. V.; Jackson, M. B.;
Ruoho, A. E. Science 2009, 323, 934.
Supplementary data
13. Marriott, K.-S. C.; Bartee, R.; Morrison, A. Z.; Stewart, L.; Wesby, J. Tetrahedron
Lett. 2012, 53, 3319. http://dx.doi.org/10.1016/j.tetlet.2012.04.075.
14. Jackson, Y. A.; Marriott, K.-S. C. Molecules 2002, 7, 353.
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmc.2012.09.044.